Cpci Manual 4 Full

CONTENTS

CHAPTER 1 METHODS AND MATERIALS

CHAPTER 2 ANALYSIS AND DESIGN OF STRUCTURES

CHAPTER 3 DESIGN OF ELEMENTS

CHAPTER 4 DESIGN OF CONNECTIONS

CHAPTER 5 ARCHITECTURAL PRECAST CONCRETE

CHAPTER 6 RELATED CONSIDERATIONS

CHAPTER 7 PRODUCT INFORMATION AND CAPACITY

CHAPTER 8 GENERAL DESIGN INFORMATION

INDEX

Copyright 2007

by

Canadian Precast/Prestressed Concrete Institute

www.cpci.ca

All rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the

Canadian Precast/Prestressed Concrete Institute.

First Edition 1982 Second Edition 1987 Third Edition 1996

Fourth Edition 2007

ISBN 978-0-9691816-8-2

Printed in Canada

DESIGN MANUAL 4th Edition

Precast and Prestressed Concrete

Canadian Precast/Prestressed Concrete Institute

100 196 Bronson Avenue Ottawa, ON, K1R 6H4

Tel: (613) 232-2619 Fax: (613) 232-5139 Email: [email protected] Web: www.cpci.ca

STRUCTURAL / ARCHITECTURAL

FOREWARD The Canadian Precast/Prestressed Concrete Institute (CPCI) is a non-profit corporation founded in 1961 for the purpose of advancing the design, manufacture and use of architectural and structural precast and prestressed concrete throughout Canada.

CPCI represents a fast growing segment of the Canadian construction industry. The first prestressed concrete structure in Canada was a precast, prestressed concrete bridge erected in 1952 in North Vancouver. Since then, precast prestressed concrete has been used in buildings and all types of engineered structures. Structural and architectural, reinforced, pretensioned and post-tensioned, precast concrete has been successfully and economically utilized in an ever expanding variety of applications.

CPCI developed into a unique trade and professional association, with a representative mix of companies and individuals. CPCI members include producers (Active Members), suppliers (Associate and Supporting Members), engineers and architects (Professional Members), plus Affiliate and Student Members.

From the beginning, CPCI established a close working arrangement with the Precast/Pre-stressed Concrete Institute (PCI). CPCI continues to enjoy a mutually beneficial relationship with PCI sharing state of the art information about the industry, its products and services, that results in combined knowledge, developments and experience.

The focus of CPCIs current activities includes the design and construction community in Canada in the areas of specifications, codes and standards, liaison with technical schools and universities, awards programs, seminars, trade shows and conventions of owner/user groups.

CPCI continues a liaison with the federal government on behalf of the industry in two principal areas. The Institute assists CPCI members in marketing their products and services to government. Secondly, an important dialogue has been established to provide the government with information about the industry.

CPCI participates with the Cement Association of Canada (CAC) and allied concrete industry members to promote concrete as a safe, fire resistant, sustainable construction material.

The Active Membership in the Institute represents over 75% of the industry's capacity in Canada. CPCI continually disseminates information on design, production practices, field techniques and environmental issues, via national and regional chapter programs and technical publications, all directed towards advancing the state of the art for Canadian owners and designers.

Architects, engineers, owners, developers and contractors are invited to contact CPCI for additional information on the design and construction of precast and prestressed concrete and on membership in CPCI. Please visit: www.cpci.ca

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PREFACE In 1964, the Canadian Precast/Prestressed Concrete Institute (CPCI) published the first design manual in North America on precast, prestressed concrete. This was a major undertaking for a fledgling industry. This handbook consisted of 4 parts: Part 1 contained the CSA Standard CSA-A135-1962 and a commentary, Part 2 contained design theory and practice, Part 3 dealt extensively with connection design and Part 4 contained sections on specifications and plant standards. The handbook was well received with orders received from around the world.

During the 1970's, the standard design references for precast, prestressed concrete in North America were published by the Prestressed/Prestressed Concrete Institute (PCI) in Chicago. The first edition of the PCI Design Handbook was published in 1971, followed by the second edition in 1978 and a series of new editions including a comprehensive updated sixth edition published in 2004.

The Canadian Government's decision in the mid 70's to adopt Sl metric units and the adoption of limit-states design codes reduced the relevance of PCI publications in Canada. CPCI undertook what was to become the single largest undertaking in its history; the publishing in 1978 of the First Edition of the CPCI Metric Design Manual. This publication, four years in the making, was based on the PCI Design Handbook and the PCI Structural Design of Architectural Precast Concrete Handbook. The manual was written entirely in Sl units with extensive references to Canadian design codes.

In 1984, CPCI published a Second Edition of the CPCI Metric Design Manual. This decision was based upon extensive revisions to CSA Standard A23.3.

The Third Edition of the CPCI Design Manual introduced significant changes in the state of the art for precast, prestressed concrete, plus important changes in A23.3 that recognized the benefits of quality control in certified precast concrete plants.

See page iv for important updates contained in this Fourth Edition.

DISCLAIMER Substantial effort has been made to ensure that the Fourth Edition of the CPCI Design Manual is accurate. However, the Canadian Precast/Prestressed Concrete Institute (CPCI) cannot accept responsibility for any errors or oversights in the use of material or in the preparation of engineering plans. The designer

must recognize that no manual or code can substitute for experience and engineering judgment. This publication is intended for use by professional personnel competent to evaluate the significance and limitations of its contents and able to accept responsibility for the application of the material it contains.

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EDITORIAL COMMITTEE

CPCI DESIGN MANUAL 4 Editor in Chief David Rogowsky, UMA Engineering, Edmonton, AB


Editor John Fowler, CPCI, Ottawa, ON

CHAPTER 2 ANALYSIS AND DESIGN OF STRUCTURES Editor Wayne Kassian, Kassian Dyck & Associates, Calgary, AB

CHAPTER 3 DESIGN OF ELEMENTS

Editor Medhat Ghabrial, HGS Consultants, Windsor, ON

CHAPTER 4 DESIGN OF CONNECTIONS Editor Don Simms, Pre-Con Inc., Belleville, ON

CHAPTER 5 ARCHITECTURAL PRECAST CONCRETE

Editor Malcolm Hachborn RES Precast, Innisfil, ON

CHAPTER 6 RELATED CONSIDERATIONS Editor John Fowler, CPCI, Ottawa, ON

CHAPTER 7 PRODUCT INFORMATION AND CAPACITY

Editor Bill LeBlanc, Con-Force Structures, Calgary, AB

CHAPTER 8 GENERAL DESIGN INFORMATION Editor Shahid Shaikh, Coreslab Structures, Dundas, ON

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FOURTH EDITION - IMPORTANT UPDATES

CHAPTER 1 METHODS AND MATERIALS The chapter on methods and materials has been updated to reflect current applications of precast prestressed concrete. New applications such as ultra high performance concretes are presented. Previous applications have become more sophisticated and have kept pace with modern architectural trends.

CHAPTER 2 ANALYSIS AND DESIGN OF STRUCTURES The chapter on the design of structures has been modified to reflect changes in the National Building Code of Canada. The changes in NBCC 2005 have had a major impact on the design examples in this chapter, including the introduction of principal and companion load factors and major changes in seismic design.

CHAPTER 3 DESIGN OF ELEMENTS The chapter on element design has required revisions due to changes in A23.3 and NBCC 2005. The concrete resistance factor for precast concrete produced in a precast plant certified in accordance with A23.4 has increased from 0.65 to 0.70. The method for design of elements for shear and torsion has been modified to suit the new requirements of A23.3.

CHAPTER 4 DESIGN OF CONNECTIONS Alternate design methods for corbels and dapped ended beams, other than strut and tie, have been included. The chapter now includes design methods and tables for the design of headed studs. Connection details have been selected to reflect current practice.

CHAPTER 5 ARCHITECTURAL PRECAST CONCRETE The design of architectural precast concrete has been extensively updated to reflect current industry practices.

CHAPTER 6 RELATED CONSIDERATIONS In addition to updating the technical content throughout the chapter, extensive revisions to the vibration and fire resistance sections have been included. A new section on sustainable design has been added.

CHAPTER 7 PRODUCT INFORMATION AND CAPACITY This chapter has undergone revisions to have the load capacity tables conform to A23.3. More information is provided on 3660 mm wide double tee sections. Tables for hollow box section beams have been added. The span and depth ranges for I-girders have been increased.

CHAPTER 8 GENERAL DESIGN INFORMATION New information has been added on the design of beams with overhangs and torsion diagrams, reactions and rotations. Development lengths for bars in tension and heavier confined reinforcing bars are given. Plastic modulus and shape factors are provides for common steel shapes.

CPCI CERTIFICATION How Precast Certification is a Requirement of the National Building Code

CSA A23.3 Design of concrete structures:

CSA A23.3-04 Clause 16.1.3 For elements produced in manufacturing plants certified in accordance with Clause 16.2, the concrete material resistance factor, c, specified in Clause 8.4.2 may be taken as 0.70.

A23.3 allows an increased material resistance factor, c = 0.70 for precast concrete members that are certified in accordance with A23.4 in recognition of the quality control and accurate placement of forms and reinforcement. The material resistance factor, c = 0.65 applies to cast-in-place and non-certified precast concrete members.

CSA A23.3-04 - Clause 16.2.1 All precast concrete elements covered by this standard shall be manufactured and erected in accordance with CSA A23.4.

CSA A23.4 Precast concrete Materials and construction:

CSA A23.4-05 - Clause 4.2.1 Precast concrete elements produced and erected in accordance with this standard shall be produced by certified manufacturers, with certification demonstrating the capability of a manufacturer to fabricate precast concrete elements to the requirements of this Standard.

CPCI Precast Concrete Certification Program for Architectural and Structural Precast Concrete Products and Systems

The CPCI Certification Program qualifies precast concrete manufacturers who fabricate architectural and structural precast concrete and meet CPCI certification requirements.

Manufacturers are evaluated on their quality system, documentation, production and erection procedures, management, engineering, personnel, equipment, finished products and assemblies. Independent professional engineers conduct audits twice annually.

Certification confirms a manufacturer's capability to produce quality products and systems.

The CPCI Certification Program assures project specifiers and owners of a manufacturers comprehensive in-house quality assurance program and acceptable production methods.

Manufacturers are required to: Establish and maintain the highest standard of

integrity, skill and practice in the design and fabrication of their products and systems;

Undertake the performance of only those services and produce only those products for which they are qualified;

Be in compliance with current governing codes and regulations; and

Supply products only from a manufacturer that is certified under the CPCI Certification Program.

Audits are performed to: Determine the conformity or nonconformity of the

manufacturers quality system and finished products with the specified requirements;

Determine the effectiveness of the implemented quality system in meeting specified quality objectives;

Provide the manufacturer with an opportunity to improve their quality system; and

Confirm that the manufacturer meets the regulatory requirements.

Program Requirements The manufacturing of precast concrete must be in accordance with the requirements of the latest editions of CSA Standard A23.4 and the PCI Quality Control Manuals MNL-116 and 117 (US equivalent), with the more stringent requirements being the governing criteria.

CSA Standard CSA A23.4 - Precast Concrete Materials and

Construction, including Appendices A and B

Canadian Precast/Prestressed Concrete Institute CPCI Quality Audit Manual CPCI Design Manual Architectural Precast Concrete - Colour and

Texture Selection Guide

Precast/Prestressed Concrete Institute (US) Manual for Quality Control for Plants and

Production of Precast and Prestressed Concrete Products MNL-116

Manual for Quality Control for Plants and Production of Architectural Precast Concrete Products MNL-117

PCI Design Handbook PCI Architectural Precast Concrete Manual

v

CANADIAN CODES AND STANDARDS National Building Code of Canada 2005 Major changes to NBCC 2005 include an objective based format, revised companion load factors and major revisions to seismic forces that may govern designs in locations formerly governed by wind. Provincial building codes are largely based on NBCC 2005.

Design CSA A23.3-04, Design of concrete structures, Canadian Standards Association This standard governs the design of buildings and most other concrete structures (except bridges). The major change affecting precast design is a change to the design for shear and the elimination of the simplified method currently used by most engineers and the introduction of new seismic provisions.

CSA S413-07, Design of parking structures, Canadian Standards Association

CSA S6-06, Canadian highway bridge design code, Canadian Standards Association

CSA S806-02, Design and Construction of Building Components with Fibre-Reinforced Polymers, Canadian Standards Association This standard was developed to provide material selection and design criteria for concrete members reinforced with non-metallic reinforcement. The ISIS Canada Research Network, headquartered at the University of Manitoba, is developing new applications for FRP materials in concrete.

CSA S16-01, Limit states design of steel structures, Canadian Standards Association This standard is used to design steel connections and other structural steel supports used in precast concrete construction.

CSA A371-04, Masonry Construction for Buildings, Canadian Standards Association

Materials and Construction CSA A23.1-04/A23.2-04, Concrete materials and methods of concrete construction / Methods of test and standard practices for concrete, Canadian Standards Association The A23.1 standard governs cast-in-place construction and is the basis for much of the material in A23.4. Major changes are the addition of C-1 and C-XL concretes and new performance requirements for different classes of concrete in Table 2.

CSA 23.4-05, Precast concrete materials and construction, Canadian Standards Association The content of A23.4 has been updated to conform to A23.1-04. A thorough review and updating of all sections has been completed. A251 has been withdrawn.

CSA A3000-Series-03, Cementitious materials compendium, Canadian Standards Association This national standard contains the testing, inspection, chemical, physical and uniformity requirements of various cements, blended cements and supplementary cementing materials such as fly ash, blast-furnace slag and silica fume.

CSA A370-04, Connectors for Masonry, Canadian Standards Association

Welding CSA W186-M1990 (R2002), Welding of reinforcing bars in reinforced concrete construction, Canadian Standards Association

CSA W47.1-03, Certification of companies for fusion welding of steel, Canadian Standards Association These standards are referenced in A23.4 and govern welding materials and practices in precast plants.

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ACKNOWLEDGMENTS We gratefully acknowledge the people responsible for developing the First, Second and Third Editions of the CPCI design manuals. Readers should refer to these editions for the names of the more than 100 contributors. They laid the foundation for the Fourth Edition.

A wide range of consultants, university professors and industry professionals gave generously of their time to prepare material and review draft copies and final proofs of this Fourth Edition Design Manual.

CPCI members express their sincere appreciation for the effort contributed by the following persons: Perry Adebar, University of British Columbia, Vancouver, BC Grant Ormberg, Univ. of Alberta, Edmonton, AB Robert Loov, University of Calgary, Calgary, AB Paul Breeze, CH2M Hill, Calgary, AB Richard McGrath, Cement Association of Canada, Ottawa, ON William Brown, Morrison Hershfield Inc., Ottawa, ON David Scott, Morrison Hershfield Inc., Ottawa, ON Dave Allen, Consultant, Ottawa, ON Donald Morse, Consultant, Calgary, AB Bruce Taylor, RES Precast, Innisfil, ON Rasvan Petanca, Con-Force Structures, Calgary, AB Darlene Deare, Pre-Con Inc., Brampton, ON Geoff Sarazin, Kassian Dyck &Associates, Calgary, AB Ken Kapusniak, HGS Consultants, Windsor, ON Eric Leme, Kassian Dyck & Associates, Calgary, AB Rick Dozzi, Harris P/T, Stoney Creek, ON Richard Golec, Pre-Con Inc., Brampton, ON Eugene Shelestynsky, Procon Engineering Inspections Inc., Inglewood, ON Peter Kluchert, Kluchert & Assoc., Toronto, ON Mike Lau, Manitoba Highways and Transportation, Winnipeg, MB Don Zakariasen, Lafarge Precast Division, Calgary, AB Doug Harman, Coreslab Structures, Dundas, ON Jason Kroeker, University of Waterloo, ON Tibor Kokai, Halcrow Yolles, Toronto, ON Peter Cicuto, Global Precast, Maple, ON Ghani Razakpur, McMaster University, Hamilton, ON Gary Fillmore, Strescon Ltd., Saint John, NB

Venkatesh Kodur, Michigan State University, East Lansing, MI Saeed Mirza, McGill University, Montreal, QC O. Burkan Isgor, Carleton University, Ottawa, ON Karl Truderung, Lafarge Precast Division, Winnipeg, MB Ifan Lim, Lafarge Precast Division, Winnipeg, MB Zhu Liu, Btons Prfabriqu du Lac, Alma, QC Stephan Martel, Groupe Tremca Prfabriqu Inc., Iberville, QC

CPCI acknowledges the outstanding contributions of David Rogowsky, editor-in-chief, and T. Ivan Campbell, Queens University, for their careful and thoughtful review of the entire contents of the CPCI Design Manual prior to publication.

CPCI acknowledges David Marshall, BlackMint Software (www.BlackMint.com) for his application of the CONCISE Beam software to check the Chapter 3 examples.

CPCI gratefully acknowledges the generosity of the Precast/Prestressed Concrete Institute (PCI) for permission to use sections of their PCI Design Handbook, Sixth Edition, as a basis for this manual.

CPCI members thank the Cement Association of Canada (CAC) for their financial contribution and permission to use material from their Concrete Design Handbook.

CPCI is indebted to the National Research Council of Canada for permission to reproduce certain tables and figures from the National Building Code of Canada, 2005 and the supplement to the National Building Code of Canada, 2005.

The Canadian Standards Association is ack-nowledged for their permission to reproduce material from CSA Standards A23.1 and A23.4.

The CPCI Design Manual, Fourth Edition page layout and drafting was done by Christopher J. Perry and Quentin C. Plock.

CPCI Design Manual 4 11


1.1 PRECAST CONCRETE METHODS ........................................................................... 1-2 1.1.1 Introduction......................................................................................................... 1-2 1.1.2 Total Precast Concrete Structures ..................................................................... 1-2 1.1.3 Product Manufacturing ....................................................................................... 1-7 1.1.4 Warehouses and Industrial Buildings ................................................................. 1-8 1.1.5 Schools, Universities, Colleges .......................................................................... 1-9 1.1.6 Shopping Centres............................................................................................. 1-10 1.1.7 Residential Buildings ........................................................................................ 1-11 1.1.8 Parking Structures ............................................................................................ 1-12 1.1.9 Office Buildings................................................................................................. 1-14 1.1.10 Public Buildings ................................................................................................ 1-15 1.1.11 Stadiums and Arenas ....................................................................................... 1-16 1.1.12 Storage and Treatment Tanks.......................................................................... 1-17 1.1.13 Bridges.............................................................................................................. 1-18 1.1.14 Special Structures ............................................................................................ 1-19 1.1.15 Architectural Wall Panels.................................................................................. 1-20 1.1.16 Veneer Faced Wall Panels ............................................................................... 1-21 1.1.17 Modular Sandwich Wall Panels........................................................................ 1-22 1.1.18 Ultra High Performance Concrete .................................................................... 1-23

1.2 PRECAST CONCRETE MATERIALS........................................................................... 1-24 1.2.1 Concrete .......................................................................................................... 1-24 1.2.2 Grout, Mortar, and Drypack...........................................................................1-28 1.2.3 Reinforcement .................................................................................................. 1-29 1.2.4 Protection of Connections ................................................................................ 1-32 1.2.5 Ultra High Performance Concrete .................................................................... 1-34

1.3 POST-TENSIONED CONCRETE ................................................................................. 1-37 1.3.1 Post-Tensioning Materials ................................................................................ 1-37 1.3.2 Segmental Construction ................................................................................... 1-38

1.4 REFERENCES ............................................................................................................. 1-40

12 CPCI Design Manual 4

1.1 PRECAST CONCRETE METHODS

1.1.1 Introduction

Plant-cast precast concrete is more durable than site-cast concrete because it can be cast with lower water-to-cementing materials ratios and with greater accuracy under controlled conditions. This natural durability is enhanced by the use of admixtures making the concrete matrix less permeable and more resistant to steel corrosion. The past decade has seen the development of more efficient structural sections and more complex architectural shapes. The strict demands of owners and architects for quality finishes have led to the development of new surface textures and surface treatments.

Precast concrete manufactured by CPCI members in certified plants ensures the production of high quality architectural and structural members and systems. Precasting facilitates the production of a wide variety of shapes and sizes. The use of prestressing substantially extends the span capability of the structural members, and enables architects and engineers to achieve highly innovative and competitive building products and systems for a variety of buildings and structures.

Important benefits of precast and prestressed concrete include:

1. Construction speed

2. Plant-fabrication quality control

3. Fire resistance and durability

4. Prestressing: greater span-to-depth ratios, more controllable performance, less material usage

5. Architectural precast concrete: wide variety of highly attractive surfaces, shapes, finishes and colors

6. Thermal and acoustical control

7. All weather construction

8. Plant prefabrication allows inspection and quality control prior to installation of precast in a finished structure

The following general principles are offered to achieve the most economical and effective use of precast concrete:

1. Precast concrete is basically a "simple-span" material. However, continuity can be effectively achieved with properly detailed connections.

2. Sizes and shapes of members are often limited by production, hauling and erection consider-ations.

3. Concrete is a heavy material. This is an advantage for stability under wind loads, thermal changes, acoustical vibration and fire resistance. The high dead-to-live load ratio provides a greater safety factor against gravity overloads.

4. Maximum economy is achieved with maximum repetition. Standard shapes or repetition of similar sections (master molds) should be used whenever possible.

5. Successful use is largely dependent on an effective structural layout and carefully detailed connections.

6. The effects of restraint due to volume changes caused by creep, shrinkage and temperature changes must be considered in every structure.

7. Architectural precast panels can be used as cladding as well as for load bearing members. Panels can be used to resist loads in both the vertical and lateral directions.

8. Prestressing improves the economy and per-formance of precast members.

1.1.2 Total Precast Concrete Structures

The use of precast concrete often extends beyond an architectural enclosure to include structural elements and stair systems. Integration of the structure, building envelope and vertical circulation is often referred to as a Total Precast System. Precast buildings can be framed in different configurations depending on overall geometry, floor spans, interior and exterior layout and cladding arrangements. Engineering total precast concrete structures also requires the analysis of the manufacturing, handling, transportation and erection of the precast system in addition to the analysis and design for the relevant loads.

Total precast building designs can be optimized by following these general principles:

1. Maximize repetition

2. Use modular dimensions for plan layouts and member dimensions

3. Use simple spans when possible

4. Standardize the size and locations of openings in precast members

5. Use standard, locally available member sizes


Fig 1.1.1 Multi-storey beam-column construction

Beam-column framing is suitable for both low and high-rise buildings. Multi-storey columns with simple-span beams are the preferred method.

6. Minimize the number of different member types and sizes

7. Consider the size and weight of products to avoid costs associated with producing, shipping and erecting oversize and/or overweight pieces

8. Use prestressing reinforcement in precast members for long spans and to minimize member depth

9. Use precast exterior wall panels as load bearing members and/or shear walls whenever possible

10. Maximize form use on architectural products

11. Contact your local CPCI member as early as possible during the design development stages of a project for assistance in answering the above questions

The load tables in Chapter 7 can be used for preliminary design.

Preliminary analysis Considerations in developing a preliminary layout are:

1. Framing dimensions

2. Span-to-depth ratios

3. Connection concepts

4. Gravity and lateral load resisting systems

5. Mechanisms for the control of volume changes

Framing dimensions Bay sizes should be a multiple of the widths of the double tee or hollow core floor and roof slabs. Double tee and hollow core floor and roof slabs should be used at spans close to their maximum capacity to reduce the number of slabs to be installed. Planning modules are useful to ensure client needs are met at minimum cost. Economies will be realized when a buildings wall/floor area ratio is kept to a minimum. Notches and setbacks can be framed on upper floors with additional framing supports.

Optimum framing dimensions will result when the total number of precast components is minimized. The maximum shipping size and weight, and the plant and erection crane capacity must be considered when establishing maximum component sizes.

Span-to-depth ratios During preliminary analysis, it is helpful to determine beam and slab depths, and the space required for other construction elements, including suspended ceilings and mechanical duct work, to establish the


Fig 1.1.2 Single-storey load bearing wall construction

This system provides economy by eliminating the need for a perimeter structural frame. The wall panels can be selected from a variety of standard sections, flat panels or specially formed architectural precast shapes. Long-span double tee or hollow core slabs can be used for the roof.

floor-to-floor dimensions of a building. See Chapter 2 for typical span-to-depth ratios of precast, pre-stressed concrete members.

Gravity and lateral load resisting systems The building system should be selected during preliminary analysis. Gravity and lateral load resisting systems may function separately or may be

combined. Bearing wall construction and beam-column framing have been successfully used for low, medium and high rise buildings. Lateral forces can be resisted by interior shear walls, exterior shear walls, moment frames, or a combination of these.

Diaphragm action will dictate placement of lateral force resisting elements. Refer to Chapter 2 for lateral force resisting system analysis and design.


Fig 1.1.3 Interior shear wall framing system

Lateral loads are transmitted by floor and roof diaphragms to a structural core built using precast shear walls.

Fig 1.1.4 Exterior shear wall framing system

The exterior shear wall system permits greater design flexibility because it eliminates the need for a structural core. The exterior shear wall system may be more economical because gravity loads and lateral forces are resisted by the same panels.


Fig 1.1.5 Single-storey beam-column construction

The standard precast beam and column sections shown in Chapter 7 can be used for single-storey structures. The type of beam used depends on span length, superimposed loads, depth of ceiling construction and desired architectural expression.

Fig 1.1.6 Multi-storey bearing wall construction

Precast bearing walls can be cast in one-storey or multi-storey configurations. Some walls can be started at the second floor level with the first floor framing consisting of beams and columns to obtain more open space on the first level.

1.1.3 Product Manufacturing

A steel form is used to manufacture precast prestressed panels end to end. Similar long-line forms are used to manufacture pretensioned beams, hollow core and double tee slabs.

Long-stroke hydraulic jacks are used to pretension individual prestressing strands.

Most precast architectural panels are manufactured using wood molds. Molds are coated with resin that is often reinforced with fibreglass cloth. A well designed and maintained wood mold can be used to cast 20 to 40 similar panels.

Heavily reinforced Bulb-Tee bridge girder Strands in the bottom flange are pretensioned. Strand is post-tensioned in three ducts after girder installation to provide continuous prestressing. The shear steel is prefabricated to allow for casting on a daily cycle.

Precast prestressed pile manufacturing These square piles are prestressed on long-line beds with four corner strands. Transverse reinforcement is a spiral wire tie closely spaced at the ends where the stresses are higher. Piles are made in standard lengths and stock-piled at the plant until required at the jobsite.

Tunnel liner manufacturing Precast tunnel liners are manufactured and cured in accurate steel or concrete molds. Liners are segments of a complete tunnel ring installed behind a tunnel-boring machine.


1.1.4 Warehouse and Industrial Buildings

Fiera Foods manufacturing plant, Toronto, ON

The ability of precast, prestressed concrete to span long distances (hollow core 9 m to 15 m, double tees 20 m to 30 m, single tees 25 m to 40 m, girder sections 50 m and up) and carry heavy loads with minimum span/depth rations is particularly useful in the construction of warehouses and industrial buildings. Longer spans can be obtained using custom solutions (segmental construction).

Precast floor and roof framing can be designed to accommodate a variety of mechanical systems and support hanging loads and bridge cranes for heavy industrial uses.

Solid precast concrete panels or insulated sandwich panels can be readily used for load bearing or non-load bearing walls. Roof and floor elements can bear directly in pockets or on haunches provided on the inside faces of wall panels or directly on the top of the wall panels. Roof slabs can be cantilevered beyond the walls to form a decorative or protective overhang.

Attractive, durable exterior walls can be formed or machine cast using standard shapes that are efficiently prestressed in long line production facilities. Custom shapes are produced in architectural molds with smooth, textured, sandblasted, acid etched or exposed aggregate surfaces. Insulation can be incorporated in sandwich wall panels to provide the required RSI-values.

STORA Paper Mill, Port Hawksbury, NS High strength precast concrete resists the effects of fire, damp conditions and a variety of chemical substances. The clean, smooth surfaces obtainable with factory produced precast concrete are ideal for food processing, wet operations or computer component manufacturing where cleanliness is required.

Cargill Meat Processing Plant, High River, AB


Foothills Industrial Park, Calgary, AB

1.1.5 Schools, Universities, Colleges

SITE Building, University of Ottawa, Ottawa, ON

The superior finishes achievable in a precast plant have enabled many designers to expose the structure in many types of buildings.

Education Building, University of Regina, Regina, SK Precast, prestressed concrete is a favoured material for school, college and university building structures, providing design flexibility and reduced construction time.

Durable, pleasing exterior finishes using architectural precast panels provide years of maintenance free use.

Olympic Speed Skating Oval, University of Calgary, Calgary, AB

This portable classroom, constructed using 12 precast panels, was assembled in one day.

In addition to classroom and office facil it ies, student residences, auditoriums, gymnasiums and aquatic faci l i t ies have been constructed using precast framing and walls, together with long span precast concrete floor and roof members.


CTC Sheppard, Toronto, ON

1.1.6 Shopping Centres

Precast, prestressed concrete components can be quickly fabricated and erected to provide early occupancy of retail stores and shopping centres.

The long spans possible using precast, prestressed floor and roof slabs provide column free retail areas. Precast concrete construction minimizes floor vibrations and provides built-in fire resistance.

Cineplex Theatre

The use of architectural precast concrete provides a quality appearance and offers years of maintenance free operation. Warehouse retailers use prestressed sandwich panels for fast all-weather construction, economy, low maintenance and a superior corporate image.


Co-op Mall, Airdrie, AB

1.1.7 Residential Buildings

Villas of Normandy Condominiums, LaSalle, ON Only by using a precast solution could this six storey, 47 unit residential condominium building's structure be completely installed and turned over to the client in less than six weeks. The structure used precast, prestressed concrete hollow core slabs, balcony slabs, precast load bearing walls, stairs and landings. Hollow core bearing supports can be precast concrete, masonry, steel or cast-in-place construction. Construction rates of 1 floor per week and better are often achieved. Precast walls and frames speed the erection process. Architectural precast insulated exterior wall panels provide a durable, attractive, energy efficient building envelope. Ancillary recreation, parking and convention facilities are commonly constructed using precast concrete framing with long span roof and floor members.

Hollow core slabs combined with precast walls are the standard components used in this type of construction. The most common floor and roof elements employed are 203 mm deep hollow core units. These slabs can span up to 10 m or more without intermediate supports. Longer spans can be achieved by using 254 mm or 305 mm deep hollow core units.

Hollow core slabs usually span between load bearing shear walls or from the central corridor to an exterior wall for hotels, motels and apartments. Slabs can be cantilevered to form exterior balconies. Slab soffits form a finished ceiling in the rooms below.

Precast and prestressed concrete enjoys broad acceptance by builders of low and mid-rise apartment buildings, hotels, motels, and nursing homes, where the repetitive use of standard components manufactured in a precast factory can be fully utilized. Owners and developers recognize the superior fire resistance and sound control features.

Concrete and masonry are not a nutrient source, and therefore, will not support the growth of mold and mildew that need food, moisture, oxygen and suitable temperature to survive.

Willow Park Retirement Home

The non-combustibility of precast concrete construction inherently provides the required fire ratings for fire containment within living units. This ensures the safety of adjacent units, that can reduce fire insurance rates. Precast concrete significantly reduces the risk of fire during construction. Precast concrete housing offers a safe, soundproof, high quality environment.


1.1.8 Parking Structures

Chapman Parkade, Kelowna, BC The City of Kelowna chose precast concrete for a fast-tracked parking garage. Double tee parking garage floor slabs were cast using Self Consolidating Concrete (SCC) to speed the casting production, with the added benefits of low permeability concrete and highest quality surface finish. Erection of the five storey 480 car parking structure was completed in 6 weeks.

Speed of construction, versatility of design, attractive exterior finishes, durability and economy make precast prestressed concrete parking garages a popular choice with commercial, municipal and institutional clients. Long spans and open walls improve user safety.

Loads and forces Allowances must be made in the design to accommodate volume changes resulting from creep, shrinkage and extreme temperature differences. Lateral design loads due to wind, earthquake or earth pressures (in the case of in-ground or partially buried structures) can be resisted in a precast concrete structure by transferring loads through the floor diaphragm to either shear walls or to beam and column moment frames. The joints in precast construction increase flexibility to accommodate movements.


Chapman Parkade, Kelowna, BC Express ramp framing.

Eccentrically loaded beams and spandrel panels must be designed for torsion effects. Connections should be designed to prevent beam rotation and absorb bumper loads without undue restraint against volume change. Uplift loads on shear walls can be minimized by loading the walls with beams or floor members.

Bay sizes Bay sizes should be as large as possible and modular with the width of the standard precast concrete floor elements selected. For clear span parking, the bay size selected need not be a multiple of the width of parking stalls. Stall width can also be changed after construction.

Drainage Providing slope in a structure to achieve positive drainage is essential for rapid removal of salt laden water. The drainage pattern selected should repeat for all floors to allow for repetition in the manufacturing of the precast elements. Locate isolation (expansion) joints at high points to minimize possible leakage. Slope floors away from columns, walls and spandrels where standing water and leakage can corrode connections.

Durability High strength factory produced precast reinforced and pretensioned concrete components have been found to be highly resistant to chloride ion attack. Wire mesh reinforcement should be incorporated in the topping when a cast-in-place composite topping is used over precast floor members. Good results have been achieved by providing a high strength concrete topping having a water-to-cementitious materials ratio of 0.40 or less. Wet cured, air entrained concrete will produce the best results.

CSA Standard S413 specifies requirements for low-permeability concrete, acceptable protection systems and concrete cover to reinforcement and prestressing tendons.

Saw cut joints should not be used. A series of control joints should be tooled into the topping above all joints in the precast members below. Later this joint is prepared by grinding and filled with a traffic grade sealant.

The application of a penetrating sealer to the concrete surfaces may be a good investment to help inhibit water and chloride ion penetration. A regular maintenance program is essential to maximize the life of a parking structure.

Canada Post Headquarters Garage, Ottawa, ON Lattice bearing walls support double tee slabs on both sides of the wall. These walls reduce shipping weight and create a more open and safe environment.

Metro Park Garage, Halifax, NS The lower two floors were clad with earth colored pigmented precast concrete panels to blend in with the older brick and stone in downtown Halifax. The column free interior of this parking garage provides parking for 575 cars in 15,500 sq. m of floor area. A two level commercial, leased, space of 800 sq. m, offers a beautiful view of Halifax Harbour.


1.1.9 Office Buildings

High quality architectural load bearing exterior walls, precast concrete framing and mass produced structural precast floor and roof members provide open, attractive, fire resistant and economical office buildings.

Load bearing architectural spandrel panels can support double tee floor and roof slabs.

Total precast concrete construction is very suitable for office buildings. The quality finishes result in tenant satisfaction. Shortened schedules provide early occupancy and reduced financing costs.

Total precast concrete structures can achieve significant time savings. The superstructure is manufactured while the on-site foundations are being built. Potential delays are reduced with the complete building system supplied under one contract.

Erection of large precast concrete components can proceed during adverse weather conditions to quickly enclose the structure. Architectural precast panels provide a finished exterior.

Prestressed floors provide an immediate working platform allowing other trades an early start to install the mechanical, electrical and interior finishing work. Long span double tee or hollow core floors reduce interior framing, providing large column free areas.

Architectural finishes can be used in the interior of an office building for columns, atrium framing, entrance and elevator shaft walls. Interior or exterior shear wall systems and rigid frame beam-column systems can be used to resist lateral forces.

High-rise office building This eight storey tower is built entirely using structural and architectural load bearing precast concrete components.


Burlington Water Treatment Plant Expansion, Burlington, ON The double tee roof was designed to support 5 monorail systems in different locations attached to the underside the roof double tees. The design and layout minimized differential cambers and accommodated the heavy equipment loads.

1.1.10 Public Buildings

The use of precast and/or prestressed concrete will contribute in a number of ways:

Exposing precast concrete in the interior of public buildings can produce dramatic facades.

Rugged exterior and interior surface treatments look good and are long lasting.

Integral insulation in exterior walls will conserve energy and lower operating costs.

Calgary Remand Centre, Calgary, AB The secure perimeter of this 17,190 sq.m, 350 cell prison building was constructed using load bearing precast concrete insulated sandwich wall panels as the exterior building envelope.

Designers strive to create public buildings that are open, functional and inviting. Precast concrete construction is ideal for airports, theatres, museums, galleries, libraries, convention centres, bus and train stations.

Precast concrete construction permits the plastic nature of concrete to be realized in unique ways. A controlled factory environment facilitates achievement of the highest quality.


1.1.11 Stadiums and Arenas

Large stadiums and arenas are impressive structures. These projects are often built on tight schedules to accommodate important sporting events. Precast concrete is the overwhelming choice, providing fast construction and a long service life for these projects.

The technique of post-tensioning precast segments together has allowed complex cantilever arm and ring beam construction to support the roofs of these structures. Post-tensioning is commonly employed to reinforce precast concrete cantilevered raker beams that carry seating elements past columns to provide unobstructed viewing of the playing surface.

Seahawks Stadium, Seattle, WA Most of the bleachers were prestressed triple riser units. The vertical riser height increases progressively as you go up the stadium to allow for clear site lines. Only minor damage occurred to the precast components when a major earthquake struck the Seattle area during construction. The precast components were manufactured in Canada.

Molson Centre, Montreal, QC Stadium risers can be quickly erected on sloping raker beams. Single, double or triple risers can be provided in accordance with manufacturers preferences and design criteria.

Many arenas are built using hollow core bleachers.

Long-spans and the ability to eliminate costly on-site formwork make precast prestressed concrete the best choice for stadium construction. Precast seating units can be standardized to take advantage of repeated form utilization. Mass produced seating units are manufactured in a variety of configurations and spans to provide for quick installation. Consult CPCI members for available riser sections. Pedestrian ramps, concession areas, washrooms, and dressing rooms can all be framed and constructed using precast concrete elements.


Tanks are prestressed both vertically and horizontally allowing the design to be crack-free. Joint closures can be accomplished on-site with field-placed concrete after the panels are installed. This method of sealing the tank joints allows a tank to perform in a monolithic manner (acting as a single unit). Horizontal in-field post-tensioning introduces com-pression forces that resist the pressure from the stored material.

1.1.12 Storage and Treatment Tanks

Precast construction offers fast, economical and efficient storage solutions for materials from potable water to hazardous waste. Sizes can range from 400,000 to 120 million litres. Seismic design features can be easily and economically accommodated. Precast concrete tank systems are adaptable to a wide range of site and environmental conditions.

High performance precast concrete is superior for corrosion, impact and fire resistance, lowering maintenance costs and increasing longevity.

Precast concrete accelerates construction schedules. Fabrication in precast plants under quality controlled conditions will result in reduced on-site construction and labour.

Problems with remote sites and access are easily overcome with precast prestressed concrete tank construction.

Precast tank wall with built-in launder trough.

Effluent Treatment Tanks, Prince Rupert, BC


1.1.13 Bridges

The use of voided slab and box girder sections are economical for short spans and shallow depths, up to 40 m.

I-girders are the most common product used for short to medium-spans. Spans of 20 to 60 m are common using l-girders, bulb tees or NU girders. Spliced girders can accommodate spans up to 100 m. [35]

Spans over 100 m can be achieved using full width precast box segments that are post-tensioned together in the field. Cable stayed bridges can span over 300 m using precast and prestressed concrete decks.

Maximum girder length, height and weight are determined by available equipment and transportation regulations.

64 m long, 2800 mm deep girders weighing over 130 t have been successfully transported by road in Alberta.

Precast deck panels can save considerable time and cost by eliminating formwork and reducing the field placement of reinforcing steel and concrete. Partial depth panels become composite with field-placed concrete. Full depth precast deck panels, used for both new and retrofit construction, can be connected to the support beams to achieve composite action. [38]

Other bridge components such as precast footings, piers, abutments, wing walls, diaphragms, pile caps, traffic barriers and retaining walls are used to speed construction and enhance durability.

Oldman River Bridge, Taber, AB Twenty eight 2800 mm deep NU girders formed the superstructure for this 301 m long 5 span bridge - 3 main spans of 62 m and 2 end spans of 57.5 m. The composite deck roadway is supported by 4 lines of girders spaced at 2500 mm c/c. Spliced girders were erected on temporary scaffolding and post-tensioned together after the joints were completed.

Bridge construction gave the precast, prestressed concrete industry its start in North America. Precast is now the dominant structural material for short and medium-span bridges. Precast, prestressed concrete bridge construction offers speed of construction in all weather conditions, reduced traffic disruption, assured quality, inherent durability, low maintenance and economy.

Highway bridges are designed and constructed in accordance with CSA Standard S6 Canadian Highway Bridge Design Code (CHBDC). Railway bridges are designed and constructed in accordance with AREMA specifications.


Highway Overpass, Edmonton, AB

1.1.14 Special Structures

A high degree of design flexibility makes prestressed concrete ideal for a wide variety of special structures.

Precast properties, such as corrosion resistance (piling), durability (railway ties), sound attenuation (sound walls), fire resistance (pipe racks), tight tolerances (tunnel liners), architectural finishes (chimney stacks), strength (silos) and fast installation and economy, have all been used to good advantage.

Where repetition and standardization exist, precast components can provide economical and quality solutions. Plant manufactured products can eliminate expensive and risky field procedures.

Innovative applications rely on the skill and imagination of creative designers.

Canadian Plaza Improvements Toll Booth Canopy Stage 1 Fort Erie, ON The curved canopy was constructed using 15 tapered segmental precast canopy units, erected on 14 permanent columns and temporary scaffolding. Segments were post-tensioned together. Units were 11.5 m long and tapered from 3.024 m wide at the front to 2.794 m at the rear. Exposed faces were precast using a board pattern form liner. Interior units weighed 34 t. End units weighed 40 t.

Syncrude Arch Conveyor Crossing, Fort McMurray, AB. Custom steel forms were used to manufacture twenty 2.4 m wide x 14 m long x 4.6 m high, 68 t, precast arch segments. The arch sections were positioned together and covered by 1.5 m of earth at the crown to allow haul trucks to cross over the conveyor.

Pipe Racks Custom precast concrete framing is often used to prevent collapse in a fire.


1.1.15 Architectural Wall Panels

Architectural precast cladding combines the maximum freedom of architectural expression with the economies of mass production of repetitive precast elements.

Understanding how architectural precast concrete can be used as an integral part of a building envelope will enable designers to make appropriate design choices. It is important to consider the overall requirements of the building envelope during design and construction.

Architectural precast concrete systems can vary from conventional cladding systems to composite sandwich assemblies that function as the entire environmental separator.

Architectural precast concrete can be cast in almost any colour, form, or texture to meet aesthetic and practical requirements. Sculptured effects can provide

Vancouver Public Library

Insulated architectural wall panels contribute substantially to the overall thermal efficiency of a building. Precast cladding may simply enclose a structure, or be designed to support gravity loads and contribute to the resistance of lateral loads.

Melchoir Office Building, Barrie, ON Panels Incorporate reflective mica and green-coloured gravel aggregates.

such visual expressions as strength and massiveness or grace and openness.

Aesthetic appearance can be achieved by varying aggregates and matrix colour. Combining colour with texture accents the natural beauty of aggregates.

Panel geometry (shape details) has a major influence on fabrication economy and engineering requirements, with overall size and configuration being the most important elements.


1.1.16 Veneer Faced Wall Panels

Sparrow Hospital Parking Garage, Lansing, MI

Historic Toronto City Hall and Civic Square (completed 1965) The curving towers feature arch-itectural precast panels faced with Italian marble. These panels acted as stay-in-place exterior formwork for the cast-in-place reinforced concrete frame.

To supplement the variety of colours and textures available with conventional precast finishes, additional aesthetic expression can be achieved by casting other materials, such as veneers on the face of precast concrete panels. Natural stone, such as polished and thermal-finished granite, limestone, marble, and clay products such as brick, tile and terra-cotta, are frequently used as veneer materials.

Bankers Hall, Calgary, AB Granite-faced precast concrete window panels were used on both high rise towers, built 12 years apart.

Worker installs brick inserts in a plastic form liner. Dovetail slots on the back help to anchor the brick tiles into the precast panels.

Complex brick faced panels have been precast in plants to produce results virtually impossible to achieve using field-set masonry.


1.1.17 Modular Sandwich Wall Panels

Precast concrete sandwich wall panels are available across Canada in varying lengths, thicknesses and exterior finishes. Panels are mass-produced in standard widths on long-line casting beds.

With attractive sculptured exterior surfaces and smooth interior faces, these panels provide strong, durable, energy efficient, economical and fire resistant wall systems.

Leons Retail Store, Edmonton, AB

Insulated wall panels consist of two concrete wythes with a continuous layer of rigid insulation sandwiched between them. The type and thickness of insulation contained in sandwich panels can vary to meet the specified RSI requirements. Insulation is installed under controlled factory conditions and is well protected by the concrete.

Panels can be erected at rates of up to 120 lineal meters per day on concrete or steel frame buildings. Panels can be used for both load bearing and non-load bearing applications.

Airdrie Co-op, Calgary, AB


The advanced properties of Ultra High Performance Concrete (UHPC) enable designers to create thin sections and long spans that are light, graceful and innovative in geometry and form. UHPC provides improved durability and impermeability against corrosion, abrasion and impact.

UHPC materials with their high ultimate compressive and flexural-tensile strengths offer additional opportunities when prestressed. UHPC can be designed to carry shear loads without auxiliary shear reinforcement. Very thin sections are possible for a wide variety of innovative and efficient cross sections. Current structural precast shapes used for prestressed beams in buildings and bridges were developed for concretes with much lower strength properties. UHPC provides the opportunity to create new prestressed beam shapes and to reduce beam structural depth and dead loads.

UHPC suits applications requiring: High compressive and tensile strength Durability - long service life Complex structural and architectural shapes

1.1.18 Ultra High Performance Concrete

Footbridge, Sherbrooke, QC, 1997 This pedestrian bridge, built in 1997, is the first industrial use of UHPC. Ten factory precast match-cast segments, 3.3 m wide, 3.0 m deep, 6.0 m long, were delivered and post-tensioned together at the site to form the 60 m main bridge span. [67]

Shawnessy LRT Transit Station Canopies, Calgary, AB, 2003 Twenty-four unique, thin-shelled canopies, 5.1 m x 6.0 m and just 20 mm thick, are supported on single columns to protect commuters from the elements. [70]

123

Footbridge Cross Section

CPCI Design Manual 4


1.2 PRECAST CONCRETE MATERIALS

This section of the manual provides a brief review of the materials used in precast and prestressed concrete. Refer to Chapter 8 for design information on concrete and concrete reinforcing materials.

1.2.1 Concrete

Types of hydraulic cement*: A23.1 classifies the types of hydraulic cement as:

Type GU: General use hydraulic cement, for use in general concrete construction when the special properties of the other types are not required.

Type HE: High-early-strength hydraulic cement, for use when high-early-strength is required.

Type MS: Moderate sulphate-resistant hydraulic cement, for use in general concrete construction exposed to moderate sulphate action.

Type HS: High sulphate-resistant hydraulic cement, for use when high sulphate resistance is required.

Type MH: Moderate heat of hydration hydraulic cement, for use in general concrete construction when moderate heat of hydration is required.

Type LH: Low heat of hydration hydraulic cement, for use when low heat of hydration is required.

Types of supplementary cementing materials*: A23.1 classifies the types of supplementary cementing materials as:

Natural pozzolan is Type N.

Fly ash is Type F: low calcium content (< 8), Type Cl: intermediate calcium content or Type CH: high calcium content (> 20).

Ground granulated blast-furnace slag is Type S.

Silica fume is Type SF.

A3001 allows blending of up to three individual supplementary cementing materials to produce a blended supplementary cementing material. For additional information, see A3001, Clause 5. *Material is reproduced with the permission of Canadian Standards Association from the CSA Standard A23.1-04/A23.2-04, Concrete Materials and Methods of Concrete Construction/Methods of Test and Standard Practices for Concrete that are copyrighted by Canadian Standards Association, 178 Rexdale Blvd., Toronto, Ontario, M9W 1R3. While use of this material has been authorized, CSA shall not be responsible for the manner in which the information is presented, nor for any interpretations thereof. For more information on CSA or to purchase standards, please visit www.shopcsa.ca or call 1-800-463-6727.

Aggregates: Aggregates for structural precast products are usually the same as those used for other high-quality concrete in the local area. Where lightweight aggregates are available, semi-low

density structural concrete can also be used for precast products. Appropriate mix designs should be obtained from local CPCI members. Aggregates commonly selected for exposed concrete facings are limestone, quartz, granite or marble. These offer a wide variety of colour and texture. Lower cost sand and gravel aggregates can also be used to produce architectural concrete. Special attention should be paid to sand and gravel aggregates to ensure they do not rust or stain when exposed to the environment.

Concrete strength: The 28-day design strength of concrete used in precast and prestressed products is usually in the 35 MPa to 50 MPa range. The transfer strength (when the prestress force is transferred to the concrete) is usually about 25 MPa and can be more or less as required by the design. However, a practical limit is the strength that can be attained in about 16 hours to allow for the removal of a product from the forms on a daily basis.

Curing: During production, architectural precast concrete panels generally do not receive accelerated heat curing as do precast, prestressed concrete structural members. Architectural precast panels are removed from forms at an age of about 16 hours after the concrete has reached a strength adequate to withstand stripping and handling.

Self-consolidating concrete (SCC):

Self-consolidating concrete is an advanced approach to the production of highly flowable, self-leveling concrete that can be placed with minimal or no vibration and without segregation. SCC requires a high performance superplasticizer to achieve and maintain the desired workability. SCC can be made with standard available raw materials. However, to achieve the unique rheological properties of SCC, special attention must be paid to the mix design process. [21]

High Performance Concrete (HPC):

High Performance Concrete offers more than just high strength. HPC is predominately specified for its durability. A23.1 requires high performance structural concretes exposure class A-1, C-1, or exposure class C-XL for higher protection.

Ultra High Performance Concrete (UHPC):

Ultra High Performance Concrete (UHPC) covers concretes with compressive strengths from 120 MPa to 200 MPa with flexural strengths of up to 40 MPa.

Note: Practices that apply to the manufacturing and testing of regular concrete may not be applicable to UHPC.


Concrete exposure classes* A23.1 defines the following exposure classes:

C-XL Structurally reinforced concrete exposed to chlorides or other severe environments with or without freezing and thawing conditions, with higher durability performance expectations than the C-1, A-1 or S-1 classes.

C-1 Structurally reinforced concrete exposed to chlorides with or without freezing and thawing conditions. Examples: bridge decks, parking decks and ramps, portions of marine structures located within the tidal and splash zones, concrete exposed to seawater spray, and salt water pools.

C-2 Non-structurally reinforced (i.e., plain) concrete exposed to chlorides and freezing and thawing. Examples: garage floors, porches, steps, pavements, sidewalks, curbs, and gutters.

C-3 Continuously submerged concrete exposed to chlorides but not to freezing and thawing. Examples: underwater portions of marine structures.

C-4 Non-structurally reinforced concrete exposed to chlorides but not to freezing and thawing. Examples: underground parking slabs on grade.

F-1 Concrete exposed to freezing and thawing in a saturated condition but not to chlorides. Examples: pool decks, patios, tennis courts, freshwater pools, and freshwater control structures.

F-2 Concrete in an unsaturated condition exposed to freezing and thawing but not to chlorides. Examples: exterior walls and columns.

N Concrete not exposed to chlorides or to freezing and thawing. Examples: footings and interior slabs, walls and columns.

A-1 Structurally reinforced concrete exposed to severe manure and/or silage gases, with or without freeze-thaw exposure. Concrete exposed to the vapour above municipal sewage or industrial effluent, where hydrogen sulphide gas may be generated. Examples: reinforced beams, slabs and columns over manure pits and silos, canals, pig slats, access holes, enclosed chambers, and pipes that are partially filled with effluents.

A-2 Structurally reinforced concrete exposed to moderate to severe manure and/or silage

gases and liquids, with or without freeze-thaw exposure. Examples: reinforced walls in exterior manure tanks, silos and feed bunkers, exterior slabs.

A-3 Structurally reinforced concrete exposed to moderate to severe manure and/or silage gases and liquids, with or without freeze-thaw exposure in a continuously submerged condition. Concrete continuously submerged in municipal or industrial effluents. Examples: interior gutter walls, beams, slabs and columns, sewage pipes that are continuously full (e.g., force mains), submerged portions of sewage treatment structures.

A-4 Non-structurally-reinforced concrete exposed to moderate manure and/or silage gases and liquids, without freeze-thaw exposure. Examples: interior slabs on grade.

S-1 Concrete subjected to very severe sulphate exposure (A23.1 Tables 2 and 3).

S-2 Concrete subjected to severe sulphate exposure (A23.1 Tables 2 and 3).

S-3 Concrete subjected to moderate sulphate exposure (A23.1 Tables 2 and 3).

Table 2 of A23.1 gives the requirements for C, F, N, R, S, and A classes of exposure.

Low-permeability concrete*

Low-permeability concrete is obtained by using exposure class C-1 concrete, or for added protection, exposure class C-XL concrete.

Class of exposure C-1 C-XL Maximum water-to-cementing materials ratio 0.40 0.37

Minimum specified compressive strength (MPa) and age (d) at test

35 at 28 d 50 within 56 d

Air content category:

(a) concrete exposed to freezing and thawing 1 1

(b) concrete not exposed to freezing and thawing 2 2

Chloride ion penetrability test requirements and age at test in accordance with ASTM 1202

< 1500 coulombs within 56 d

< 1000 coulombs within 56 d


Requirements for the air content categories*

Range in air content for concretes with indicated nominal maximum sizes of

coarse aggregate, % Air content

category 10mm 14-20 mm 28-40 mm

1 6-9 5-8 4-7

2 5-8 4-7 3-6 Note: See A23.1 Clause 4.3.3.2 for determining the air content

in hardened concrete.

The curing procedures specified in A23.1 are not required to be followed if alternate curing procedures specific to a particular plant are used, and provided these procedures are shown to produce a finished concrete that meets or exceeds all of the performance requirements for C-1 or C-XL concrete. *Material is reproduced with the permission of Canadian Standards Association from the CSA Standard A23.1-04/A23.2-04, Concrete Materials and Methods of Concrete Construction/Methods of Test and Standard Practices for Concrete that are copyrighted by Canadian Standards Association, 178 Rexdale Blvd., Toronto, Ontario, M9W 1R3. While use of this material has been authorized, CSA shall not be responsible for the manner in which the information is presented, nor for any interpretations thereof. For more information on CSA or to purchase standards, please visit www.shopcsa.ca or call 1-800-463-6727.

Compressive strength The compressive strength of concrete made with aggregate of adequate strength is governed by either the strength of the cement paste or the bond between the paste and the aggregate particles. At early ages, the bond strength is lower than the paste strength. At later ages, the reverse can be the case.

For a given cement and acceptable aggregates, the strength that can be developed by a workable, properly placed mixture of cement, aggregate, and water (under the same mixing, curing, and testing conditions) is influenced by:

1. The ratio of water to cementing materials

2. The ratio of cementing materials to aggregate

3. Grading, surface texture, shape, strength, and siffness of aggregate particles

4. Maximum size of the aggregate

Mix factors, partially or totally independent of water-to-cementing materials ratio, that affect the strength are: 1. Type and brand of cement 2. Amount and type of admixture or pozzolan 3. Mineral composition of the aggregate

Compressive strength is measured by testing 100 200 mm cylinders in accordance with A23.2 procedures. Grout materials are tested using 50 or 100 mm cubes.

Testing of no-slump concrete is covered in A23.4.

Because of the need for early strength gain, HE cement is often used by precasters so that molds can be reused daily. Structural precast concrete and much architectural concrete is made with gray cement that meets A3001. HE and GU white hydraulic cements are frequently used in architectural products and are usually assumed to have the same characteristics (other than colour) as gray cement. Pigments are also available to colour concrete, and, at the recommended dosages, have little or no effect on strength. Cement type and colour should be chosen with the help of local producers who may have experience with the proposed mix.

Concrete mixes with strengths up to 50 MPa or more are available in most areas. CPCI member precast manufacturers may be contacted for concrete design information.

Initial curing of precast concrete takes place in the form, usually by covering to prevent loss of moisture and, in many instances (particularly for structural products), with the application of radiant heat or live steam. Additional curing is rarely necessary to attain the specified strength. [23]

Concrete subjected to freezing and thawing should be air-entrained. For some precast concrete mixes it is sometimes difficult to obtain air contents as large as those normally specified for the leaner mixes most often used in cast-in-place flatwork. Admixtures are added to the concrete during the mixing cycle to entrain the air. A slight reduction of strength should be anticipated when concrete is air entrained.

Tensile strength A critical measure of the performance of architectural precast concrete is its resistance to cracking that is a function of the tensile strength. Reinforcement does not prevent cracking, but controls crack widths after cracking has occurred. Tensile stresses that would theoretically result in cracking are permitted by A23.3 in prestressed concrete.

The flexural tensile strength is called the modulus of rupture. It can be determined by test, but for structural design the modulus of rupture is generally assumed to be a function of compressive strength as given by:

fr = c0.6 f fr = modulus of rupture (MPa)

cf = compressive strength (MPa) = 1.0 for normal density concrete = 0.85 for structural semi-low density concrete = 0.75 for structural low density concrete


Shear strength The shear (or diagonal tension) strength of concrete is also a function of compressive strength. The equations for shear strength specified in A23.3 are given in Chapter 3. The shear strength of semi-low density and low-density concrete is determined using the factor, , as described on the preceding page. Modulus of elasticity The modulus of elasticity, E, is the ratio of normal stress to corresponding strain. It is the material property that determines the immediate deformation under load. E is used to calculate deflections, axial shortening and elongation, buckling and relative distribution of applied forces in composite and non-homogeneous structural elements.

The modulus of elasticity of concrete and other masonry materials is not as well defined as for materials such as steel. E is therefore defined by an approximate slope, such as the secant modulus. Calculations that involve E have an inherent imprecision, but this seldom affects practical performance. While it can be desirable in rare instances to determine the modulus of elasticity by test, particularly with some low density concretes, the equation given in A23.3 is usually adequate for design:

Ec =1.5

cc(3300 f 6900) 2300

+

Ec = modulus of elasticity (MPa) c = density of concrete (kg/m3)

Poisson's ratio

Poisson's ratio is the ratio of transverse strain to axial strain. Values generally range between 0.11 and 0.27, and are usually assumed to be 0.20 for both normal and low density concrete.

Volume changes Volume changes in precast concrete members are caused by changes in temperature, shrinkage and by creep caused by sustained stress. If precast concrete members are free to deform, volume changes are of little consequence. If elements are restrained by foundations, connections, steel reinforcement, or connecting elements, significant stresses can develop over time.

The volume changes due to temperature variations and creep can be positive (expansion) or negative (contraction), while volume changes from shrinkage are only negative.

Much of the creep and shrinkage in precast members takes place during yard storage. Connection details and joints must be designed to accommodate the volume changes that occur after the precast elements have been erected and connected to the structure. Hollow core slabs are often shipped at an early age, but are not normally rigidly connected to the supporting structure.

Typical creep, shrinkage, and temperature strains and design examples are given in Chapter 2.

Temperature effects:

The coefficient of thermal expansion of concrete varies with the aggregate used as shown in Fig. 1.2.1. Ranges for normal density concrete are 9 to 13 106/ C when made with siliceous aggregates and 6 to 9 x 106/ C when made with calcareous aggregates. The approximate values for structural low density concretes are 6.5 to 11 106/ C, depending on the type of aggregate and amount of natural sand. Coefficients of 11 106/ C for normal density and 9 106/ oC for semi-low density concrete are frequently used. If greater accuracy is needed, tests should be conducted on the specific concrete.

Since the thermal coefficient for steel is also about 11 x 106/ C, the steel reinforcement does not produce significant stresses in the concrete due to temperature changes.

Shrinkage and creep:

Precast concrete elements are subject to air-drying as soon as they are removed from the forms. As a result of this drying, the concrete slowly loses some of its original water causing shrinkage to occur.

When concrete is subjected to a sustained load, the deformation can be divided into two parts:

1. elastic deformation that occurs immediately, and

2. time-dependent deformation, called creep, beginning immediately and continuing over time.

Creep and shrinkage strains vary with relative humidity, volume-surface ratio (see Fig.1.2.2), level of sustained load including prestress, concrete age and strength at the time of load application, amount and location of steel reinforcement, and other characteristics of the material and design. Different values of shrinkage and creep may be needed when high strength concretes are used. Typically, the joints between precast members are detailed to relieve such strains.


Fig. 1.2.1 Average coefficients of linear thermal expansion of rock (aggregate) and concrete

Type of Rock (Aggregate)

Average Coefficient Of Thermal Expansion

(106 / C) Aggregate Concrete*

Quartzite, Cherts 11.0 - 12.6 11.9 - 12.8

Sandstones 10.0 - 12.0 10.0 - 11.7

Quartz Sands & Gravels 9.9 - 12.8 11.0 - 15.7

Granites & Gneisses 5.8 - 9.5 6.8 - 9.5

Syenites, Diorites, Andesite, Gabbros, Diabas, Basalt

5.4 - 8.1 8.0 - 9.5

Limestones 3.6 - 6.5 6.1 - 9.2

Marbles 4.0 - 7.0 4.1

Dolomites 7.0 - 9.9

Expanded Shale, Clay & Slate

6.5 - 7.7

Expanded Slag 7.0 - 11.2

Blast-Furnace Slag 9.2 - 10.6

Pumice 9.4 - 11.0

Perlite 7.6 - 11.7

Vermiculite 8.3 - 14.2

Barite 18.0

Limonite, Magnetite 8.3 - 11.0

None (Neat Cement) 18.5

Cellular Concrete 9.0 - 12.6

1 : 1 (Cement : Sand) 13.5

1 : 3 11.2

1 : 6 10.0 * Coefficients for concretes made with aggregates from

different sources vary from these values, especially those for gravels, granites, and limestones. Fine aggregates are generally the same material as coarse aggregates.

Tests made on 2-year old samples.

Freeze-thaw and chemical resistance

Cycles of freezing and thawing can cause damage to concrete ranging from minor surface scaling to severe disintegration. Corrosion of reinforcement, prestressing strand or connection hardware can also result, affecting the integrity of the structure.

The effects of freezing and thawing can be resisted by high quality concrete and air entrainment. Adequate concrete cover over reinforcement and surface drainage is essential in structures exposed to weather.

Fig.1.2.2 Volume-surface ratios for precast structural concrete elements

Freeze-thaw damage is accelerated by deicing chemicals. Deicers can be applied indirectly in various ways such as salt water dripping from the undersides of vehicles and splash water. Some proprietary treatments such as sealers, membranes and corrosion inhibiters have been found to provide additional protection to freeze-thaw, deicing and other chemical damage. (See S413 Parking Structures.)

Other foreign materials, such as sulphates in soils or ground water and industrial acids, can damage concrete. The former can be resisted by specifying cements with a low C3A content. The presence of acids generally requires a membrane or a topping of concrete or other material. When aggregates or cement with high alkali content are used in a moist environment, the danger of alkali-aggregate reactivity (AAR) should be considered. [5]

1.2.2 Grout, Mortar and Drypack

When water, sand and cementing materials are mixed together without coarse aggregate, the result is called mortar, grout, or drypack, depending on the consistency. These materials have numerous applications in precast concrete construction: sometimes for fire or corrosion protection, for cosmetic treatment, or to transfer loads in horizontal and vertical joints.

Different materials are used: 1. Cement 2. Shrinkage-compensating cement 3. Expansive cement made with special additives 4. Gypsum or gypsum cements 5. Epoxy resins 6. Proprietary grouts and repair mortars


Sand-cement mixtures

Most grout is a simple mixture of cement, sand, and water. Proportions are usually one part cement to 2.25 to 3 parts sand. The amount of water depends on the method of placement.

Flowable grouts are high-slump mixes used to fill voids that are either formed in the field or cast into the precast element such as the shear keys between hollow core slabs. Grouts are used at joints that may be heavily congested but not confined, requiring some formwork. These grouts usually have a high water-cement ratio, resulting in low strength and high shrinkage. There is a tendency for the solids to settle, leaving a layer of water on the top. Admixtures can improve the characteristics of flowable grouts.

For very small spaces in confined areas, grouts can be pumped or pressure injected. Confinement must be sufficiently strong to resist the hydraulic pressure. Less water can be used than for flowable grouts, hence less shrinkage and higher strengths can be obtained.

A stiffer grout, or mortar, is used when the joint is not totally confined, for example in vertical joints between wall panels. This material will usually develop strengths of 20 MPa to 45 MPa, and have much less shrinkage than flowable grout.

Drypack is the name used for very stiff sand-cement mixes. Drypack is used if a relatively high strength is desired, for example, under bearing walls and column base plates. Compaction is by hand tamping, using a rod or stick.

When freeze-thaw durability is a factor, grout should be air-entrained. An air content of 9 or 10% may be required for adequate protection.

Typical cement mortars have very slow early strength gain when placed in cold weather. Heating is usually not effective because the heat is rapidly dissipated into the surrounding concrete. Special proprietary mixes may be required unless a heated enclosure can be provided.

Non-shrink grout Shrinkage of sand-cement grout can be reduced by using proprietary non-shrink mixes, or by adding aluminum powder to the mix. Non-shrink grouts can be classified by the method of expansion: 1. Gas-liberating 2. Metal-oxidizing 3. Gypsum-forming 4. Expansive cement

Manufacturers' recommendations should be followed as some expansive ingredients may cause undesirable effects in some applications.

Aluminum powder added to ordinary sand-cement grout forms a gas-liberating mixture. Extremely small amounts of powder are required (about a teaspoonful per bag of cement) making these mixes very sensitive to variations in the ingredients. Trial mixes should be tested.

Epoxy grouts Epoxy grouts are used when very high strength is desired, or when positive bonding to the concrete is necessary. They are mixtures of epoxy resins and a filler material, usually sand.

The physical properties of epoxy compounds vary widely. The compound to be used should be determined either through experience or by test. [41] The thermal expansion of epoxy grouts can be up to 7 times that of concrete, and the modulus of elasticity of epoxy grouts are considerably different than concrete.

Low viscosity epoxy resins without fillers can be pressure-injected or gravity fed into cracked concrete as a repair measure.

Post-tensioning grout Post-tensioning grouts are a mixture of cement and water with or without admixtures. [48]

1.2.3 Reinforcement

Reinforcement used in structural and architectural precast concrete includes prestressing tendons, deformed steel bars, and welded wire reinforcement.

Metallic and non-metallic fibre reinforcing can also be used. Specifications for non-metallic reinforcing materials are covered in S806.

Prestressing tendons

Tendons for prestressing concrete can be wires, strands, or bars. In precast, prestressed structural concrete, nearly all tendons are 7-wire strands conforming to ASTM A416/A416M. The strands are usually pretensioned (tensioned prior to concrete placement). After the concrete has reached a predetermined strength, the strands are cut and the prestress force is transferred to the concrete through bond.

Until the late 1970s, most prestressing strand was stress-relieved. Today, low-relaxation strand is almost universally used. Low-relaxation strand as specified in ASTM A416/A416M differs from stress-


relieved strand in two respects: first, it meets more restrictive relaxation loss requirements, and second, the minimum yield strength at an extension of 1% is 90% of the specified minimum tensile strength, compared to 85% for stress-relieved strand. The load tables in Chapter 7 are based on low-relaxation strand.

Architectural precast concrete is sometimes prestressed. Prestressing tendons can be either pretensioned or post-tensioned depending on the facilities available at the plant.

Prestressing wire or bars are occasionally used as primary reinforcement in precast elements. The properties of prestressing strand, wire and bars are given in Chapter 8.

Deformed reinforcing bars and wires Hot-rolled deformed reinforcing bars are required to meet one or more of the following standards: CSA G30.18 or ASTM A82, A184, A185, A496, A497, A704 or A775. These specifications cover both weldable steel and regular steel. Bars are usually specified to have a minimum yield strength of 400 MPa (Grade 400R and 400W). Grade 300R bars may be available only in sizes 10M and 15M. Grade 500R and 500W steel are also available. The maximum yield strength of 400W and 500W bars is limited to 525 MPa and 625 MPa, respectively, to ensure ductile behaviour. The W in the grade designation indicates a weldable bar with controlled chemistry and a maximum carbon equivalent of 0.55%.

Some precast plants use weldable steel (400W) for all reinforcement. Advantages are a reduction in inventory and the possibility of errors. Another advantage is that bar ends can be used for welded connections instead of being scrapped. See W186 for the welding of reinforcing bars.

For a reinforcing bar to develop its full strength in concrete, a minimum length of embedment or a hook is required. Information on bar sizes, bend and hook dimensions and development lengths are given in reference [13] and Figs. 8.2.6 to 8.2.10.

Deformed wire can be used in small, thin members when reinforcement smaller than 10 M bars is used to meet concrete cover and/or small bend radii requirements. Deformed wires should conform to ASTM A497 see Figs 8.2.11 and 8.2.14.

Welded wire reinforcement Welded wire reinforcement is prefabricated reinforcement consisting of parallel cold-drawn wires welded together in square or rectangular grids. Each wire intersection is electrically resistance-welded by a

continuous automatic welder. Pressure and heat fuse the intersecting wires together and fix all wires in their proper position.

Smooth wires, deformed wires or a combination of both can be used in welded wire reinforcement. Wire sizes are denoted by their area in mm2 prefixed with the letters MW for smooth wire or MD for deformed wire. Welded wire reinforcement styles are de

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