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5. STRUCTURE

5.1 IntroductionThe structural section of the report lists the criteria, methodology and systems that are adopted in the design of the towers structural components and external works. It includes; the codes of practice utilized, loading criteria, and material selections; and gives a brief description of the proposed structural systems to be used together with the envisaged structural monitoring system.The structural design concepts and structural systems are typically integrated with the architectural features of the project to serve the space usage, while maintaining structural integrity, serviceability and durability, and addressing four elements of major importance, namely:

- Safety of the buildings occupants and systems together with human comfort in terms of sway and acceleration.

- Durability of the structural elements reducing the need for future maintenance- Aesthetical values paying special attention to adopt structural concepts in harmony with the

architectural requirements, and- Rationalization of the structural design leading to the optimization of the initial construction

costs.

Design is based on the use of Saudi Arabia Building codes in addition to international standards, mainly American standards. The following paragraphs describe in details the different design aspects and parameters that will be utilized for designing and detailing of this project.

5.2 Project componentsThe development aims to build a large exclusive Residential, Commercial Complex, including 5-star Building Towers with all related services and external works for the visitors of the Holy Kaaba.

5.3 Design criteriaIn addition to Saudi Building Codes, the design is based on the following codes of practice:

5.3.1 Concrete Design

- ACI 318-08 “Building Code requirements for Structural Concrete”. - ACI report 423.3R-96 for pre-stressed concrete. - SBC 301-2007: “Saudi Building Code, Loads and Forces Requirements, 2007”. - IBC International Building Code, 2006. - ACI 350 for water retaining structures.- ACI 315 for detailing

5.3.2 Steel Design

- AISC 143th Edition “Steel Construction Manual”. - ANSI-AWS-D1.1 –Latest Edition “Structural Welding Code”. - SSPC – 2000latest edition “Steel Structures Painting Council”. - ANSI/ASCE 7-05 “Minimum Design Loads for Buildings and other Structures”.

5.4 Loading criteria

5.4.1 Dead Loads

5.4.1.1 General Buildings

-Self-Weight of Structure- Floor finishes-Electro mechanical installations- Partitions:

o Light weight in Typical and VIP floorso Masonry in other floors mainly podium levels

- Landscape loads

5.4.1.2 General Bridges

-Self-Weight of Structure- Superimposed loads including the weight of non-structural fixtures attached to the

bridge namely, deck wearing course, pre-cast parapets, handrails, lighting fixtures and the like.

5.4.2 Live Loads

5.4.2.1 General Buildings

Live loads are based on ASCE 7-05- Stairs 500 Kg/m2

- Roof According to MEP requirements: 500 Kg/m2(minimum)

- Traffic loads as per the below are taken into consideration:o Passenger cars for 3rd to 7th floor inclusive

o Truck loads for basement 2, basement 1, ground floor, upper ground floor, and

first floor.

5.4.2.2 General Bridges

The highway loading will based on AASHTO Standards 17th Edition 2002 requirements magnified by two and will consist of a 60 Ton truck on 3 axles, and its corresponding lane loading (uniform load and concentrated load) and a 32 ton hypothetical single axle load as shown below (figure 5.1).

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fig. 5.1 Highway Loading

5.4.3 Wind LoadsBased on the ANSI/ASCE 7-05 Section 6.0:

- Basic wind speed 95mph

- Exposure type C

- Importance factor 1.15

Wind tunnel test will be conducted in order to assess:- The dynamic behavior of the tower

- Acceleration for human comfort

- The exact wind pressure applied on the towers facades.

5.4.4 Seismic Loadings

- Based on the Saudi Building Code SBC 301- Seismic Design Category: A

5.4.5 Temperature VariationsThe seasonal change in temperature is evaluated at ± 30°C.

5.5 Deflection criteria

Overall building movements and individual member designs are set with the following deflection limits:

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5.6 Expansion Joints and Shrinkage stripsExpansion joints are used to reduce temperature and shrinkage stresses. The Complex podium is divided through expansion joints into 5 parts of maximum width reaching 150 meters above the first floor level.Shrinkage strips are envisaged from top of foundation at B2 level till first floor level inclusive (within basement walls, slabs and beams).In the upper towers, expansion joints are envisaged at connecting bridges between all towers except the bridges between towers 6A and 6B which are connecting the towers rigidly.

5.7 WaterproofingAdequate waterproofing systems are applied depending on site conditions:

- Suitable tanking membrane will be applied to all external surfaces of reinforced concrete structures in contact with soil up to certain specified level close to the design ground water level.

- Coatings as specified to be applied to all external and internal surfaces of reinforced concrete structures in direct contact with soil in the other areas.

- Coatings as specified to be applied to all interior surfaces of water retaining structures and sewage structures.

5.8 Fire Protection5.8.1 Concrete structures

Walls, columns and main beams : 4 Hours

Floor construction / slabs : 2 Hours

5.8.2 Structural Steel

Towers 2,3,4,5 Roof Structures: - Main columns and beams up till the pitched roof: 4 Hours fire rated.

- Secondary structure (including pitched roofs):         2 Hours fire rated.

Tower 6 Roof Dome Structure: - Columns and beam girders up till the curved roof:       4 Hours fire rated.

- Secondary floor beams (including curved dome):   2 Hours fire rated.

Linking bridges between Towers:

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Lateral drift(at service due to wind including P-Delta effect)

-Total drift: limited to H/500 for the diaphragm and H/400 for the maximum point displacement.

-Inter-story drift: limited h/350

Vertical deflection of concrete beams and slabs:

Immediate deflection due to live load L/360

Deflection occurring after attachment of non-structural elements likely to be damaged by large deflections L/480

Deflection occurring after attachment of non-structural elements not likely to be damaged by large deflections

L/240

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- Structural elements:                                                   2 Hours fire rated.

Miscellaneous Structures: - Canopies, Secondary stairs …                                  2 Hours fire rated.

Arch bri d ge in the podium: 2 Hours fire rated.

5.9 Structural Materials

5.9.1 ConcreteReinforced concrete is the main construction material in the project due to its availability and the ease of application in the project’s region.

The classes of concrete indicated below reflect the 28-day cylindrical compressive strength:

5.9.1.1 Main building (podium and towers)

[5.9.1.2] External worksClass fc’ (MPA) Location

A 50 Bridge Foundation, piles, piers

B 5550 Superstructure

C 30Retaining walls foundations, retaining walls, abutments foundations, abutments, pedestals

D 21 Blinding

5.9.2

ReinforcementReinforcing steel are deformed reinforcing bars with minimum yield stress of 420 MPa conforming to ASTM A615 (grade 60).

5.9.3 CementOrdinary Portland cement shall conform to “Specifications for Portland Cement”, ASTM C150 Type I would be used for all structural elements based on chemical properties of the soil. Cement

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Class fc’ (MPA) Location

A 70

All Reinforced concrete vertical elements except basement walls for levels up till 5th floor in the towers inclusive for vertical elements and 6th floor slab in the towers inclusive for coupling beams.

B 60All Reinforced concrete vertical elements for remaining tower floors (columns, walls and coupling beams).

C 50

Raft, piles, and basement walls (except areas of attached columns) and all other reinforced concrete elements (except as shown below) including transfer slabs, namely: slabs, beams, ribs and panels for levels up till 5th floor slab in the towers inclusive.

CD 505 Prestressed concrete elements

DE 45All other reinforced concrete elements namely slabs, beams, ribs and panels for remaining tower floors.

EF 254Slab on compacted fill / grade, and concrete topping of the structural steel slabs, and external works except otherwise shown..

FG 21 Blinding

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additives, microsilica, fly ash, GGBE, may be needed to ensure the required “Low” permeable concrete, satisfying the specifications.

5.9.4 Structural SteelRoofs, bridges and other light-weight structural components will be made of structural steel to meet the architectural requirements. The structural steel items will be either one of the following:

- Mild grade steel, to conform to ASTM A36, having a yield stress of 2480 Kg/cm2 .

- High grade steel, to conform to ASTM A572, having a yield stress of 3450 Kg/cm2 (Grade 50).

- Mild grade steel, to conform to ASTM A36, having a yield stress of 2480 Kg/cm2.

- Steel pipes shall conform to ASTM A53 Type E grade B, having a yield stress of 2450 Kg/cm2Structural steel HSS round and rectangular: ASTM A618 grade III with maximum yield stress 345 N/mm2 .

5.9.5 Prestressing StrandsPre-stressing strands shall be low relaxation seven-wire super Stabilized strands with nominal diameter of 15.7mm and minimum granted breaking load of 279 KN and shall conform to the requirements of BS5896.

5.10 Structural Systems-Main Building (Podium and Towers)The structural design covers all the structural components of the project as mainly summarized below:

- Foundations

- Gravity and lateral loads resisting systems

- Floor slabs and beams

5.10.1 FoundationsThe foundation consists mainly of a thick raft foundation with piling mainly under tower 1A according to the geotechnical recommendations. Design is based on ultimate flexure, shear capacities, and serviceability criteria.

5.10.2 Gravity and lateral loads resisting systems5.10.2.1 General for all towers

The gravity system consists of reinforced cast in situ concrete columns, walls and core walls. These elements are transferring the vertical loads to the foundation.

The main lateral load resisting system consists of cast in situ reinforced concrete walls and core walls coupled with interior and exterior frames as needed.

The vertical and lateral load systems are not fully continuous to the foundations. The upper and lower systems will be linked through transfer slab/beam systems as applicable at top of podium (piazza floor slab). The first floor includes localized transfer slab system for some podium columns/walls.

5.10.2.2 Additional elements for towers 6A and 6BThe two half circular shape towers are linked together through linking bridges at various floors and a complete transfer post tensioned slab at top which acts as a foundation for the upper structural steel floors and domes.

5.10.3 Floor slabs and beams

- Towers: Mainly solid slab and drop beams of variable depth/thickness

- Podium: Several slab systems are envisaged, mainly:

o Solid slab on drop beams

o Ribbed slab on banded beams

o Post tensioned slab on drop beams

5.10.4 Structural steel: - Linking bridges between the towers

- Arch bridge in the podium

- Roof top of all towers except towers 1A/1B

- The top common combined block of towers 6A-6B (Ball room, convention center and dome above towers 6A and 6B)

- Structural steel mezzanine slabs

- Structural steel staircases

- Miscellaneous steel structures such as canopies

5.11 Structural Systems- BridgesThe project comprises three vehicular bridges, forming part of the project internal road network. Their widths and spans will vary depending on the corresponding road.

Bridges 1 and 3: These structures consist of a prestressed concrete box girder deck (multi spans: 7 spans with a maximum span length of around 30m for bridge 1 and a maximum span length of around 32m for bridge 3) supported on reinforced concrete piers and abutments using pot bearings. All main piers and abutments are supported on reinforced concrete shallow foundations. However, piling shall be used if deemed necessary.

Bridge 2: This bridge's total length is around 450m, and it consists of a double cellular prestressed box girder. It's a 14 span bridge deck having a maximum span length of 40m. The multi-cellular box girder is supported on reinforced concrete piers and abutments via pot bearings from abutment A1 to pier 7 and is cast monolithically with piers 8 to 13. Piers and abutments are supported on reinforced concrete shallow foundations. However, piling shall be used if deemed necessary.

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5.12 Analysis software- The computer program ETABS: Three Dimensional Static and Dynamic Analysis of Building

Systems,- The computer program SAP2000: Integrated finite elements Analysis and design of the

structures,- The computer program SAFE: for analysis and design of slabs and foundations,

- PCACOL Reinforced Concrete Column Section Design Software, Portland Cement Association PCA.

5.13 Structural Monitoring System for Main Building (Podium and Towers)Structural Monitoring system is envisaged in this project as part of the structural works to measure, in selected/limited critical locations, loads and settlements under the foundation, strains in selected members (mainly transfer slab and some main columns/walls and core walls) and monitor movements at the top of the tallest towers. for acceleration and tilting. These measurements are essentially needed mainly to verify the design assumptions, parameters, and considerations.

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