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Lateral Load Resisting Systems.
Presented By : Chirag Shah
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1 Frame Action Of Column and Two-Way
Slab Systems
Concrete floors in tall buildings oftenconsist of a two-way floor system such as aflat slab, or a waffle system.
Advantages1. Optimum use of floor space
2. Relatively simple construction process
Disadvantages1. Generally flexible structure and lateral
deflection govern the design process.
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Effective Width of flat Slab.
The effective width offlat slab can be usedto determine theequivalent width of
slab. The effective width
depends on
1. Column aspect ratios
2. Distance betweencolumns
3. Thickness of flat slab.
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2 Rigid Frame
Cast in Place Concrete Building has inherentadvantages of continuity at joints.
Beams framing directly into columns, can be
considered rigid with the columns. Beams carry shear and bending moments
due to lateral loads often require additionalconstruction depth.
The design and detailing of joints wherebeams and columns meet the specialattention is required.
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Behaviour of Rigid Frame
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Advantages
1. Rigid Frame systems for resisting lateral
and vertical loads have long been acceptedas a standard means of designing buildings.
because they make use of the stiffness inthe beams and columns that are required in
any case to carry the gravity loads. Limitation
1. Rigid Frames are not Stiff as compared to
shear wall.2. Excessive depth of girder required to make
the rigid frame economical.
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Disadvantages
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3 Rigid Frame with Haunch Girder
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Uses
When the Structure is of tube type and the adjacentdistance between two columns are 40ft then thebeam depth required is much more and this beam iscalled haunch beams.
If the depth of haunch beam is more then 3 ft thenthe posttensioning is used.
A haunch girder with more depth give the requiredstiffness for lateral loads without having to increase
the floor to floor height. This is achieved by making the mid section of the
girder flush with the floor system.
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4 Shear Walls
The elevator shafts, stairwells necessary for
access in a high rise must be protected by
fire walls, as demanded by fire safety
regulation. It makes sense to exploit them in improving
the building rigidity.
With their highly resistance to shear stress,are highly suitable for assuming the shear
forces that arise through lateral loads.
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Classification of Shear Walls
Classification of Shear wall should be based
on following criteria.
1. Based On Shape
2. Based on dimension
3. Based on Opening
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Based On Shape
1. Rectangular
2. Dumbled
3. Intersection of Two Shear Walls
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Based on Dimension
h/ l < 1 Square shear wall
H / l > = 1 Slender Shear Wall
l
h
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Based on Opening
Solid
With Opening
Coupled Shear Walls
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Failures in Shear Walls
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Coupled Shear Walls
When two or more shear walls are interconnectedby a system of beams or slabs, the total stiffness ofthe system exceeds the summation of the individualwall stiffnesses because, the connecting slab or
beam restrains the individual cantilever action byforcing the system to work as composite unit.
used economically to resist lateral loads in buildingupto about 40 stories.
However planer shear walls are only efficient lateralcarieers only in that planes hence it is necessary toprovide wals in two orthogonal directions.
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Behaviour Of Couple shear wall.
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5 Shear Wall Frame Interaction
Most Popular System
Broad Range of Application and has been used for
10 stories to as high as 50 stories or even taller
building.
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Rigid Frame Shear Wall Interaction.
Using only shear walls torespond to lateral loads isimpractival above about500ft.
The lateral rigidity is gratly
improved by using not onlythe shear wall system butalso the rigid frame to resistlateral forces.
The total deflection of theinteracting shear wall and
rigid frame systems isobtained by superimposingthe individual models ofdeformation as shown in fig.
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Thank You