Building Structural System

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Building Structural Systems


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Functions of Building Structural System

Building Structure system (BSS) refers to a system ofconnected parts, the primary function of which is to

support loads acting on the building during its service

life.

A structural system consists only of the members

designed to carry the loads, all other members are

referred to as non-structural.

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Functions of BSS

Basically, the BSS has to support loads for strength and

serviceability under:

normal use (service) conditions

maximum considered use conditions various environmental conditions such as wind and

earthquake



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Loads on BSS

Types of loading to be resisted by a building structural

system:

Gravity Load Lateral Load Others

Dead Wind TemperatureLive Earthquake Blast

Snow Lateral soil Impact

Rain / Flood pressure Centrifugal

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Design Requirements

Safety

Serviceability

Aesthetics

Economy Environmental conditions

Several possibilities should be considered for a structure

before selecting a final design based on severalperformance criteria.

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Design Requirements

Design are aimed to be creativeand technical

Design Process requires:

a fundamental knowledge of material properties andmechanics

knowledge of various types of structural forms and

configurations

calculation of loads and load effects acting on thestructure



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Design Requirements

knowledge of structural analysis to calculate design

forces

knowledge to design structural members and

connections

ability to evaluate designs and consider various

options



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Subsystems or Components ofBuilding Structural System

Building Structural Systems Compose of:

Floor systems

Vertical load resisting systems

Lateral load resisting systems Connections

Energy dissipation (vibration damping) systems



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Floor Systems

The floor system carries the gravity loads during and

after construction. It should be able to accommodate the

heating, ventilating and air conditioning systems, and

have built in fire resistance properties.

Floor systems can usually be classified as one-way

systemsand two-way systems.



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Floor Systems

One-way systems include:

Slabs of constant thickness

Slabs supported by closely spaced joists - lattice

floor joists and girders are convenient for theinstallation of ductworks.

Beam and slab systems



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Floor Systems

Flat plate (slab) system

Advantages:

Simple in construction

Flat ceiling (lower finishing costs)

Lower story heights due to shallower floors

Applications:

Short-to-medium spans with light loading Maximum span ranges from 5m to 10m depending on

loading



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Floor Systems

Flat plate with spandrel beam floor system



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Floor Systems

Flat plate with spandrel beam floor system

Advantages:

Same as flat plate system, plus

Increased gravity and lateral load resistance

Increased torsional resistance

Decreased slab edge displacements

Typical Applications:Same as flat plate systems



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Floor Systems

Flat plate with beams floor system

Advantages:

Increased gravity and lateral load resistance

Simple constructionTypical Applications:

Medium spans with light loading

Maximum span ranges from 6m to 10m depending on

loading



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Floor Systems

Flat slab floor system



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Floor Systems

Flat slab floor system

Advantages:

Reduced slab displacements

Increased slab shear resistance

Relatively flat ceiling (reduced finishing costs)

Low story heights due to shallow floors

Typical Applications:

Medium spans with moderate to heavy loading

Maximum span ranges from 8m to 12m depending onloading



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Floor Systems

One-Way joist floor system



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Floor Systems

One-Way joist floor system

Advantages:

Longer spans with heavy loads

Reduced dead load due to voids Electrical, mechanical etc. can be placed betweenvoids

Good vibration resistance

Typical Applications:

Medium-to-long spans with heavy loading Maximum span can be up to 15m



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Floor Systems

Two-way Waffle Floor System



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High-rise Building Structural Systems

Structural members in a high-rise building structural system

are usually designed to resist both gravity (vertical) and

lateral (horizontal) loads simultaneously.

There are many types of building structural systems.The commonly used systems are:

Braced Frame (Vertical Truss) Systems

Moment Resisting Frame Systems

Shear Wall Systems

Shear Wall and Frame (Dual) Systems



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The Lateral Force Resisting System is used to resist

forces resulting from wind or seismic activity.

Buildings are basically big cantilever beams. They are

supported on one end only and the loads areperpendicular to the beam.

As in a beam, buildings are designed for strength

(shear and flexure) and serviceability (deflection).

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Braced Frame (Vertical Truss) System

Braced Frames are basically vertical

truss systems.

Almost exclusively steel or timber.

Highly efficient use of material since

forces are primarily axial. Creates alaterally stiff building with relatively

little additional material.

Has little or no effect on the design of

the horizontal floor system.

Good for buildings of any height.

Bracing may intrude on the spatial

constraints.

Frame may be internal or external.



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Types of Bracing

Different types of bracing

Single Diagonal

Double Diagonal

Chevron Bracing

Story height knee bracing

(eccentricity braced frames)

May be single story and/or bay

or may span over multiple

stories and/or bays

Braced Frame (Vertical Truss) System



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Moment Resisting Frame System



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Moment resisting frames are column and girder (beam)

plane frames with fixed or semi-rigid connections.

The strength and stiffness are proportional to the story

height and column spacing.Concrete moment resisting frames, steel moment resisting

frames and composite moment resisting frames are the

commonly used types.



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Moment resisting frames could also be built with:

composite beams and composite columns

concrete encased steel columns

steel beams encased in concrete steel beams connected to slabs by shear connections

columns connected to flat plates in concrete



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Advantages:

Relatively low in construction cost

Allow large windows to be installed

More sunlight and natural ventilation to living area Greater flexibility in partitioning



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Disadvantages:

Sizes of beams and columns at lower stories increase

rapidly with building height.

Larger sizes of beams and columns reduce ceilingheight and usable space.

Uneconomical and low performance efficiency when

building height is more than 30 storeys.



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Shear Wall System

Typical shear wall building



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Shear Wall System

Typical shear wall building



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Shear Wall System

A shear wall is a rigid vertical diaphragm capable of

transferring lateral forces from exterior walls, floors, and

roofs to the ground foundation in a direction parallel to their

planes.

Shear walls are the main vertical structural elements with a

dual role of resisting both the gravity and lateral loads. A

shear wall system in a high-rise building usually consists of

reinforced concrete walls and reinforced concrete slabs.



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Shear Wall System

Shear wall buildings are usually regular in plan and in

elevation.

However, in some buildings, lower floors are used for

commercial purposes and the buildings are characterizedwith larger plan dimensions at those floors. In other cases,

there are setbacks at higher floor levels.

Shear wall buildings are commonly used for residential

purposes.



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Shear Wall System

Lateral forces caused by wind and earthquake produceslarge shear forces in structural members.

These lateral forces when combined with uneven

settlement at the foundation, and the unbalanced weight of

the structure and occupants, might create powerful twisting

(torsional) forces and hence further intensify the shear

forces.

Reinforcing a frame by attaching or placing a rigid wall

inside it could maintain the shape of the frame and prevent

rotation at the joints.



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Shear Wall System

Shear walls are especially important in high-rise buildings

subject to lateral wind and seismic forces.

Shear walls for earthquake resistance are designed to be

ductile.Coupling beams between shear walls should have diagonal

reinforcement to provide adequate shear resistance.



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Shear Wall System

Advantages:

Very efficient in resisting lateral load due to wind and

earthquake

Low construction cost Can provide fire separation for elevators (lifts) and exit

staircases



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Shear Wall System

Disadvantages:

Restriction on window opening sizes.

Low flexibility in partitioning.

Reduce interior open space on floor.



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Shear Wall and Frame (Dual) System

This is the most commonly used structural system in Hong

Kong to build high-rise residential buildings between 20 to

50 storeys high.

The combined shear wall and frame system has the

advantages of both the frame system and the shear wall

system.

However, for buildings more than 50 storeys, the

performance efficiency of the system decreases. Other

building structural systems have to be used.



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Other High-Rise BuildingStructural Systems

Shear Truss-Outrigger Braced Systems

Framed-Tubes Systems

Tube-in-Tube Systems with Interior Columns

Bundled Tubes Systems

Truss Tubes without Interior Columns Systems



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Under Lateral Loads:

Columns on one side are

in tension

Columns on other side are

in compression



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Structural depth is increased (i.e. the moment of

inertia of the structure is increased)

Shear strength is unchanged.

Utilizes a braced core with stiff outriggers to mobilizedouter columns in tension and compression.

4 to 5 outriggers appear to be the economical limit.



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Building Structural System

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