seismic analysis of rc building

8/12/2019 Seismic Analysis of RC Building

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Seismic Analysis of

Multi-storied RC Building

Presented by .

Rahul Leslie

Part - I


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Topics Covered:

Aspects of computer modelling Static analysis as per IS:1893(Part 1)-2002

Dynamic analysis as per IS:1893(Part 1)-

2002

Directional combinations

Miscellaneous points

Seismic Analysis of Multi-storied RC Building Presented by Rahul Leslie


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Topics Covered:

Aspects of computer modelling Static analysis as per IS:1893(Part 1)-2002

Dynamic analysis as per IS:1893(Part 1)-

2002

Directional combinations

Miscellaneous points



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Aspects of Computer Model:

Modelling is done using analysis packages likeSTAAD.Pro, STRAP, NISA/Civil, ETABS, etc.

Model contains Beams

Columns

Shear walls

But not usually Slabs (except in Flat slab - Shear wall construction)

Masonry wall infills

Stair slabs

Foundation is represented by support points only


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Aspects of Computer Model (Cont)

A model must ideally represent the complete three

dimensional (3D) characteristics of the building,including

geometry

stiffness of various members

supports

load distribution

mass distribution



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Beams and columns Beams and columns are modelled by frame elements

Plinth beams should also be modelled as beams Slabs are not usually modelled



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Supports: The type of support to be provided is decided by

considering the degree of fixity provided by thefoundation.

Fixed Supports: Raft foundation:Support to be provided at the column

ends (located at top of the raft) Pile cap for multiple piles: Support to be provided at the

column ends (located at top of the pile cap)

I solated footing: When it is founded on hard rock, thecolumn end may be modelled as fixed (located at the top of

the footing) Single pile: Fixed support of the column is recommended

at a depth of five to ten times the diameter of pile,depending upon the type of soil, from the top of pile cap.



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Supports (cont): Pinned supports:

I solated footing: Support to be provided at the columnends, (located at the bottom of the foundation).

Combination of Fixed & Pinned support: Combined footing: When the footings are adequately

restrained by tie beams, the column ends can be modelledas fixed in the direction of the beam, but pinned in adirection perpendicular to it, provided the tie beam is alsomodelled.

In General Engineering judgement must be exercised in modelling the

support



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Slabs and Masonry walls The weight of slabs are distributed, as 2-way load, on

the supporting beams. The weight of masonry wall is applied as uniform

load on the supporting beam



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Slabs and Masonry walls Since the slabs are not modelled by plate elements, the

structural effect due to their in-plane stiffness (7.7.2.1,IS:1893(Part 1)-2002)can be taken into account by using Master/Slave option (STAAD.Pro)

assigning Diaphragm action (ETABS)



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Slabs and masonry walls (cont) Masonry walls have in-plane stiffness that can

influence the behaviour of the building under lateralload (7.10.2, IS:1893(Part 1)-2002):


Masonry infills are modelled by equivalent diagonalstruts (7.10.2, IS:1893(Part 1)- Proposed Draft)


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Slabs and masonry walls (cont) A dual model approach can be taken

1. one model with equivalent struts

2. other without equivalent struts.

(or use Inactivate Members option in STAAD.Pro)

Maximum forces from either of the case taken for design

However, the weight of the infill walls on the supporting

beams should be considered in both the models.



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Shear walls

Structural shear walls and Shear core which are

integrally connected to the frame and floor slabs, canbe modelled by plate elements

Surface elements (STAAD.Pro)

Wall element (ETABS)



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Masses to be included: For dynamic analysis, the effective masses to be

included for analysis are : Full dead load 0.25 times Imposed Loads having intensity 3 kN/m2

0.5 times Imposed Loads having intensity > 3 kN/m2

Imposed Load on roof need not be considered

(7.3.1 & 7.3.2, IS:1893(Part 1)-2002)

Live load reduction for upper floors (as per 3.2,IS:875(Part 2) - 1987) shall not be applied further for

mass calculation (7.3.3, IS:1893(Part 1) - 2002)



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End of Part - I

seismic analysis of rc building

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