Projefct 1_Comparative study of different storey buildings for Seismic forces

• First open the ETABS software.
• Next click on the file option at the left side top corner and select the new model,as shown below.
• After selecting the new model the new tab opens in that tab w have to select 'Use Built-in settings with' option as shown below.
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• Ater seting the model intialization the templates tab will opens and select the Grid only and press ok.
• Next we need to do the settings in grid sysytem data,as shown below.
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• Number of bays along the X and Y direction are 4 and 3.
• Column size is 400x400,beam size is 300x400mm and slab thickness is 150mm and Dead load on beams from infill wall:10kn/m and live load on floor:3kn/m.
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• MODELING BUILDING:-
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• RESULT:-
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BUILDING(B):-

• Number of storys are 5.
• Number of bays along the X and Y direction are 4 and 3.
• Column size is 400x400,beam size is 300x400mm and slab thickness is 150mm and Dead load on beams from infill wall:10kn/m and live load on floor:3kn/m.

MODELING BUILDING:

RESULT:-

BUILDING(C):-

• Building with rectangular columns oriented along X-direction.
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RESULT:-

BUILDING(D):

• Building with rectangular columns oriented along Y-direction.
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• RESULT:-
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BUILDING(E):

• Building with 10 storys and sizes of column according to storey hiehts are
• Upper 5 storeys 400x400mm.
• Bottom 5 storeys 600x600mm.
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RESULT:

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BUILDING(F):

• 10 story building with colunm size 600x600mm.
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RESULT:

BUILDING(G):

• Building with 25 storys and columns sizes according to story heights are
• Upper 5 storys 400x400mm.
• Middle 10 storys 600x600mm.
• Bottom 10 storys 800x800mm.
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RESULT:

BUILDING(H):

• Building with 25 storys and column size of 800x800mm and beam size 300x400mm.
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RESULT:

BUILDING(J):

• In this model the imposed load has been increased by 10% so the live load increased from 3kn/m to 3.3kn/m.
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RESULT:

BUILDING(K):

• In this model the imposed load has been increased by 20% so the live load increased from 3kn/m to 3.6kn/m.
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RESULT:

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1. A) Comparing fundamental natural period for buildings E and F as well as G and H.

For building E:-

Tx1=1.161sec

Ty1=1.124sec

For building F:

Tx1=1.231sec

Ty1=1.19sec

Fr building G:

Tx1=2.896sec

Ty1=2.602sec

For building H:

Tx1=3.581sec

Ty1=3.3sec

• When compared the building E,F and G,H .The time period is marginally increasing for building F and H,This is because the column sizes have been maitained uniform.So this arrangement will have negligible impact on the stiffness but mass of structure will get slightly increase.
• As we know time period is directly proportional to mass of the system.so while increasing the mass of the story ,it relatively increaes the time period of the structure.

1. B) Comparing fundamental natural period of building H,j and K and the justifications regarding its flexibilty:

For building H:

Tx1=3.581sec

Ty1=3.3sec

For building J:

Tx1=4.548sec

Ty1=4.273sec

For building K:

Tx1=4.881 sec

Ty1=4.577 sec

• The difference between buildings H,J and K is the increment in their imposed mass . Buiiding J has 10% more imposed mass and building K 20% more imposed mass.So we know that mass is directly proportional to the time period so that is why period of buildings J and K is higher.
• The imposed mass is not a part of stiffnes component of the structure .The imposed mass are from the wall loads. so increasing the mass in the building does not mean the stiffness increment .simply it means more the time period of a building ,the more it is flexible .So that is why building J and K are more flexible.

1. C) Comparing fundamental natural period for buldings A,B and F,H and justification regarding its height impac:

For building A:

Tx1=0.368 sec

Ty1=0.361 sec

For building B :

Tx1=0.755 sec

Ty1=0.746 sec

For building F:

Tx1=1.231sec

Ty1=1.19sec

For building H:

Tx1=3.581sec

Ty1=3.3sec

• If we compare the building A (2 story) and B (5 story), The time period of B is higher and if we compare the building F (10 story) and H(25 story). The time period of H is higher ,as we know stiffness of a building is inversly proportional to the height ,So that means stiffness of a building decreases with increase in height .If the stiffness of building decrease it eventually decreases the time period.

1. D) Comparing the fundamental natural period for buildings B,C and D and the justifications regarding column orientation:

For building B :

Tx1=0.755 sec

Ty1=0.746 sec

For building C : X direction stiffness is higher so its time period will be lesser in X direction than the Y direction.

Tx1=1.684 sec

Ty1=1.448 sec

Fopr building D: Y-direction stiffness is higher . So its time period will be lesser in Y direction than the X-direction.

Tx1=1.642 sec

Ty1=1.492 sec

1. E) Comparing the two different configurations of building B with changes in beam flexural stiffness:

case1: When the size of beam is 300x400mm (oiginal condition).

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Case2: When the size of beam is very small 100x100mm modified condition.

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• Since we neglected the stiffness of beams ,The building became more flexible and thus led to much higher time period.
• Effect of relative flexural stiffness of structural elemants ,The fundamental traslational mode shape changes from flexural type to shear type with increases in beam flexural stiffness relative to that of column.

1. F) Comparing the two different configurations of building H with changes in axial property of column:

Case1:When the size of the column is 800x800mm (original condition).

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Case2: When the size of column is small 300x300mm (modified condition).

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• Since we neglected the stiffness of beams ,The building became more flexible and thus led to much higher time period.
• Effect of relative flexural stiffness of vertical elemants ,The fundamental traslational mode shape changes from flexural type to shear type with increases in beam axial stiffness of vertical members.

1. G) Comparing the two different configurations of building B with changes in base support condition:

• Original condition with pinned support.
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Tx1=0.755 sec

Ty1=0.746 sec

• Modified condition with fixed support:
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Tx1=0.696 sec

Ty1=0.692 sec

• Fixed support assinged:
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CONCLUSION:-

• All the building models with different configurations are analysed and compared the impacts in their time period with changes in selection parameters.