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Seismic Analysis of Janabikash Secondary School

The seismic analysis of the two story masonry building is done using SAP2000V14.

A. Salient features of the building Shape of Building - Rectangular Plinth Area - 143 Sqmt No. of Story - 2 Building Type - Brick Masonry Wall Thicness - External- 380 mm, Internal- 250 mm Binding Material - Cement Mortar Floor Type - RCC Floor thickness - 100 mm (assumed) Plaster - Both internally and externally

The Original dimensions of some windows are reduced to limit the openings to 0.42 to 0.5 times the

room dimension.

Figure below shows the plan of the building with modified doors and windows openings

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B. DesignParameter Unit weight of brick masonry - 19.6 KN/m3 Masonry Compressive strength (fm) -2 Mpa (as mentioned in the provided report) Concrete compressive strength (fc) - 10 Mpa (assumed) Rebar Grade -Fe 415 Live load - 3 KN/m2 Roof live load - 1.5 KN/m2

C. LoadingIS 1893:2002 is follow for equivalent static method. Following load combinations are uses as per NBC

105

DL + LL

0.7DL+ EqX

0.7DL- EqX

0.7DL+ EqY0.7DL- EqY

DL+LL+EqX

DL+LL-EqX

DL+LL+EqY

DL+LL-EqY

D. Analysis ModelThe masonry building is modeled in SAP2000 V14.2.4. The seismic analysis of the building is performed

by Equivalent Static Method as per IS 1893 :2002. Masonry walls and slab are modeled by using thick-

shell element with pinned support.

Figure below shows the 3-D diagram of the building as modeled in SAP.

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E. ResultsResults are presented in form of maximum base shear and wall stresses for each load

combination

1) Maximum Base shearThe total weight of the building, Wt., (DL+ LL) is 2976 KN

Seismic weight of the building, Ws., (DL+0.25LL) is 2544 KN

The maximum base shear of the building is 763.353 KN which is equal to 0.3Ws

(In the report provided, the total seismic weight is 2018 KN and the maximum base shear

is 817.67 KN which is .405 times the total seismic weight.

2) Wall stressesStress in all the walls for load combinations EqX and 0.7DL+EqX are noted for

comparison.

The walls are denoted by their grid name as shown below.

Wall -3X, Load case EqX

Stress- S22

Maximum Tension near openings = 0.19 Mpa

Maximum Compression near openings = 0.21 Mpa

From Report

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Maximum Tension near openings = 0.308 Mpa

Maximum Compression near openings = 0.187 Mpa

Wall -3X, Load case EqX

Stress- SMax

Maximum Tension near openings = 0.25 Mpa

Maximum Compression near openings = 0.08 Mpa

From Report

Maximum Tension near openings = 0.389 MpaMaximum Compression near openings = 0.24Mpa

Wall -3X, Load Combination0.7DL+EqX

Stress- SMax

Maximum Tension near openings = 0.18 Mpa

Maximum Compression near openings = 0.1 Mpa

From Report

Maximum Tension near openings = 0.236 Mpa

Maximum Compression near openings = 0.148 Mpa

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Wall -2X, Load case EqX

Stress- S22

Maximum Tension near openings = 0.29 Mpa

Maximum Compression near openings = 28 Mpa

From Report

Maximum Tension near openings = 0.306 Mpa

Maximum Compression near openings = 0.63 Mpa

Wall -2X, Load combination 0.7DL- EqX

Stress- SMax

Maximum Tension near openings = 0.21 Mpa

Maximum Compression near openings = 0.1 Mpa

From Report

Maximum Tension near openings = 0.305 Mpa

Maximum Compression near openings = 0.143Mpa

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Stress distribution of walls in Y direction

Wall -AY, Load combination EqY

Stress- SMax

Maximum Tension near openings = 0.36 Mpa

Maximum Compression near openings = 0.1 Mpa

Stress distribution of walls in Y direction

Wall -BY, Load combination EqY

Stress- SMax

Maximum Tension near openings = 0.25 Mpa

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Remarks

1) The stresses are maximum at the openings of the walls.2) The middle portion of the wall does not need any strengthening.3) Stress is maximum for the load combination DL+LL+EqX but for retrofit design purpose, the

stress is checked for load combination DL+EqX only4) The minimum allowable stress in masonry unit is 0.3 Mpa, which looks too conservative.5) The maximum principal stress level for load combination DL+LL+EqX is 5.74 Mpa.