CHAPTER 1:DESIGN CONCEPTS

By:

Ir. MOHAMMAD SOFFI MD NOH

Introduction to Structural System• Building is an assemblage of various

systems such as Infrastructure System,Structural System, M&E System, Security System and etc.

• Structural system – a system that holding the components of a certain system and transfer the load through the members of a structure to provide stability and durability.

Types of Buildings Structural System

Beam and column structural system

The load of the slab is transferred to the columns orwalls through the beams, down to the foundation,and then to the supporting soil beneath

Reinforced Concrete

Steel

Timber

Reinforced Concrete

• Reinforced concrete is one of the principal materials use in many civilengineering applications.

• Such applications are in construction of buildings and infrastructures,retaining walls, foundations, water retaining structures, highway andbridges.

• Around 70% buildings around the world were constructed using reinforcedconcrete due to reliability and low cost.

• It is a composite material, consisting of steel reinforcing bars embedded in a hardened concrete matrix that have complementary properties.

Concrete

Steel reinforcement

Highly in compressive strength but weak in tensile strength

Highly in tensile strength but weak in compressive strength

Reinforced Concrete

Tensile strength test Cube test

Reinforced Concrete

• By providing steel bars in thezones within a concrete memberwhich will subjected to tensilestresses, an economical structuralmaterial can be produced throughits composite action.

• In addition, the concrete providescorrosion protection and fireresistance to the embedded steelreinforcing bars.

Main RC elements for building

Reinforced Concrete

• Failure mechanisms of reinforced concrete structure (flexural member):

• Types of cracks:

1)Flexure tension cracks, 2) Flexure compression cracks,

3) Flexure – shear cracks, 4) Diagonal tension cracks,

5) Shear compression cracks, 6) Dowel cracks and

7) Diagonal tension crack from flexure – shear crack.

Reinforced Concrete

• Failure mechanisms of reinforced concrete structure (compression member)

Buckling Crushing Shear

Failure mechanisms of foundation

Reinforced Concrete

Steel

• Steel is one of the most important and efficient material forstructural purposes.

• There are a number of inherent characteristics that make steelan ideal construction material; these include its high strength toweight ratio, the weight of steel structure is relatively small.

• This property makes steel a very attractive structural materialfor high rise building and long span girder. Speed of erection isoften one of the main criteria for selecting steel.

• Steel sections used for construction are available in a variety ofshapes and sizes that make it a remarkably versatile and anaesthetically pleasing material.

Steel

Hot rolled steel Cold formed steel

Steel

Universal Beam (UB) Universal Column (UC) Hollow Section Angle Section

Hot rolled steel Section

Steel

Mechanical Properties of Steel

Steel

Column

Main beam

RC Slab

Base

Secondary beam

Steel Structural Elements

Steel Connection

Steel Truss

Steel

Steel Structural Failure

Squashing Overall Flexural Buckling

Torsional Buckling

Local Buckling

STEEL COLUMN:

Timber

• The wood which is suitable or fit for engineering construction orstructural purpose is called timber.

• The use of timber as a structural material is not new, in fact datingback many centuries.

Typical Malaysian Timber House

Timber

Manufacturing process

Saw

n t

imb

er

Structural timber elements

Timber log

Timber

Truss / Rafter

Joist

Beam / Girder

Column

Purlin / Battern

Structural elements

• Structural timber design in Malaysia is according to MS 544 –Permissible stress design.

• Design consideration:• Density

• Strength group (SG1 – SG7)

• Moisture content • > 19 % - Wet

• < 19 % - Dry

• Timber defect • Seasoning defect

• Natural defect

Timber

Structural design

Structural Design

The basic requirements of structural design:

A process of determination of reliable structural system, selection of suitable materials and obtaining theoptimum member sizes for the structure to be built. The aim of structural design is to ensure that the structureperforms satisfactorily during its design life.

1) Function and aesthetic

• The arrangement of space, span, ceiling height, access ability, and traffic flow must complement the intended use.

2) Safety and reliability

• A structure must be strong enough to support all anticipated loadings safely and it must not deflect, overturn, tilt,vibrate or crack in any manner that impairs its usefulness.

3) Economy and cost effective

• The overall cost of the structure should not exceed the client’s budget. The designer should take into account not onlythe cost of materials, but also the buildability, construction time, cost of temporary structures required and cost ofmaintenance.

4) Maintainability and sustainability

• A structure should be designed to require minimum maintenance and be able to be maintained with ease.

Code of Practice

• Developed started from 1975.

• Effectively replaced the currentBritish Standard since 2010.

• Claimed to be the most technicallyadvanced structural codes in theworld.

• Resulted in more economicstructures, Logical and organizedto avoid repetition.

• Less restrictive and moreextensive than existing codes.

• There are ten (10) Eurocodescovering all the main structuralmaterials.

Eurocode Standard

Code of Practice

MS EN 1990 : EUROCODE 0 Basis of Structural DesignContents

Section 1 General

Section 2 Requirements

Section 3 Principles of Limit State Design

Section 4 Basic Variables

Section 5 Structural analysis and design assisted by testing

Section 6 Verification by the partial factor method

Annex A1 Application for buildings

Annex A2 Application for bridges

Annex B Management of structural reliability for construction works

Annex C Basis for partial factor design and reliability analysis

Annex D Design assisted by testing

EUROCODE 1: ACTIONS ON STRUCTURES

EN 1991-1-1 Densities, self weight and imposed loads

EN 1991-1-2 Actions on structures exposed to fire

EN 1991-1-3 Snow loads

EN 1991-1-4 Wind loads

EN 1991-1-5 Thermal loads

EN 1991-1-6 Actions during execution

EN 1991-1-7 Accidental actions

EN 1991-2 Traffic loads on bridges

EN 1991-3 Actions induced by cranes and machinery

EN 1991-4 Silos and tanks

Code of Practice

MS EN 1991 : EUROCODE 1 (EC1)

Actions on Structures

EUROCODE 2: DESIGN OF CONCRETE STRUCTURES

EN 1992-1 General rules and rules for buildings

EN 1992-1-2 General rules –Structural fire design

EN 1992-2 Concrete bridges –design and detailing rules

EN 1992-3 Liquid retaining and containment structures

Code of Practice

MS EN 1992 : EUROCODE 2 (EC2)

EUROCODE 3: DESIGN OF STEEL STRUCTURES

EN 1993-1-1 General rules and rules for buildings

EN 1993-1-2 General rules – Structural fire design

EN 1993-1-3 General rules – Supplementary rules for cold-formed members and sheeting

EN 1993-1-4 General rules – Supplementary rules for stainless steels

EN 1993-1-5 General rules – Platted structural elements

EN 1993-1-6 Strength and stability of shell structures

EN 1993-1-7 Strength and stability of planar platted structures subjected to out of plane loading

EN 1993-1-8 Design of joints

EN 1993-1-9 Fatique

EN 1993-1-10 Material toughness and through-thickness properties

EN 1993-1-11 General structures with tension components

EN 1993-1-12 General – High strength steels

EN 1993-2 Steel bridges

EN 1993-3 Tower, masts and chimneys

EN 1993-4 Silos

Code of Practice

MS EN 1993 : EUROCODE 3 (EC3)

Code of Practice

BS EN 1995 : EUROCODE 5 (EC5)

MS 544 – Part 1 & 2 : 2001

• Principles - Clauses that are general statements, definitions, requirements andanalytical models. They are identified by (P) after the clause number.

• Characteristic value – The characteristic values are denoted by subscript ‘k’ (e.g.Qk etc).

• Design values - These refer to representative values modified by partial factors.They are denoted by subscript ‘d’ (e.g. fcd = fck/γc ; Qd = γ Q Qk).

• Action (F) - Set of forces, deformations or accelerations acting on the structure.

• Permanent actions (G) – Permanent load (Dead load).

• Variable actions (Q) - Actions whose magnitude will vary with time (e.g. windloads, imposed load).

Code of Practice

EUROCODE Terminology

• The design method of EC is based on limit state principles which thestructure should not become unfit for use as well as should not reach alimit state during its intended life.

Limit State Design

Deals with the strength and stability of the structureunder the maximum design load it is expected to carry.

Ultimate Limit State (ULS)

Deals with the conditions beyond service requirementare no longer met such as excessive deflection andcracking.

Serviceability Limit State (SLS)

• Given in MS EN 1990: Cl. 2.3. The values for design life as presented in the Malaysian National Annex to EC are shown below.

Design Working Life

• There are 4 basic design situations that can be considered.

Design Situation

Design situations Definition

Persistent These situations refer to the condition of normal use, which generally

relate to the design working life.

Transient These situations refer to temporary conditions, such as during

execution or repair.

Accidental These situations refer to exceptional condition such as during fire,

explosion or impact.

Seismic These situations refer to exceptional conditions applicable to the

structure when subjected to seismic events.

▪ Exposure classes related to environmental condition

Exposure Condition

Actions

• EC terminology for loads and imposed deformations.

• The characteristic actions are the actual loads that the structure isdesigned to carry.

• The characteristic actions used in design and defined in EC2 are asfollows;

▪ Characteristic permanent action, Gk

▪ Characteristic variable action, Qk

▪ Characteristic wind action, Wk

Actions

• Is the selfweight of the structure, weight of finishes, ceiling andservices. Examples of weight of materials as given in EC1 are shownin table below.

Characteristic permanent action, Gk

Materials Density (kN/m3)

Lightweight concrete 9.0 – 20.0

Normal weight concrete 24.0 – 25.0

Cement mortar 19.0 – 23.0

Wood 3.5 – 10.8

Plywood 4.5 – 7.0

Particle boards 7.0 – 12.0

Steel 77.0 – 78.5

Water 10.0

▪ Cause by people, furniture, equipment etc. Which variation inmagnitude with time is considered.

▪ Example of variable action as given in EC1 are shown in table below:

Actions

Characteristic variable action, Qk

▪ In order to account for variation in loads due to:

• Errors in the analysis and design

• Constructional inaccuracies

• Possible load increases

▪ The characteristic loads Fk (Gk,Qk,Wk) are multiplied by the appropriate partialsafety factor for loads γf to give the design action acting on the structure.

▪ Value of γf are given in

EN 1990: Annex A1

Actions

Design action

fkd FF Design situation

Permanent actions (Gk) Variable actions (Qk)

Unfavourable Favourable Unfavourable Favourable

Ultimate limit state

Persistent & Transient

1.35 1.0 1.50 0

Serviceability limit state

All 1.0 1.0

• In the EC the term ‘combination of actions’ is specifically used for the definitionof the magnitude of actions to be used when a limit state is under the influenceof different actions.

• It should not be confused with ‘load cases’, which are concerned with thearrangement of the variable actions to give the most unfavourable conditions.

• The following process can be used to determine the value of actions used foranalysis:• Identify the design situation (e.g. persistent, transient, accidental).

• Identify all realistic (characteristic) actions.

• Determine the partial factors for each applicable combination of actions.

Maximum action = 1.35Gk + 1.50Qk Minimum action = 1.35Gk

• Arrange the combined actions to produce the most critical conditions.

Actions

Combination of action

End of Chapter 1………

THANK YOU !