Projefct 1_Comparative study of different storey buildings for Seismic forces

AIM: To have a comparative study on –

Factors influencing the dynamic characteristics of a building

Factors influencing the Natural Period of a building

Factors influencing the Mode shape of oscillations

Procedure:

Create the models of buildings A, B, C, D, E, F, G, H, J & K which are given below.

Assume the details for modeling the building.

Model the buildings as per the details given in the question and do an analysis and compare the things as asked. Here I am furnishing the results that are obtained after the modeling and analysis.

Building A:

Building B :

Building C :

Building D :

Building E :

Building F :

Building G :

Building H:

Building J:

Building K:

• Effect of stiffness on T: Compare fundamental natural periods of buildings E & F as well as G & H. Why is there a marginal or significant difference in the fundamental natural periods?

The time period of E and F are 1.73 and 1.74, we can see the time period is the same even though column size varies.

The time period of G & H are 4.57 and 4.78, here H> G. The column Size decreases as the floor increases which leads to less flexibility compared to the same column size.

• Effect of mass on T: Compare fundamental natural periods of buildings H, J and K. Have the buildings become more flexible or stiff due to change in mass?

T of H= 4.783

T of J = 4.79

T of K = 4.8

Here there is a very slight increase in T when imposed load are increased then the building becomes more flexible.

• Effect of Building Height on T: How do the fundamental natural periods of Buildings A, B, F, and H change with change in building height?

T of A= 0.5

T of B= 0.36

T of F= 1.735

T of H= 4.78

Increase in height of building there is an increase in the time period of building increases.

• Effect of Column Orientation on T: How do the fundamental natural periods of Buildings B, C, and D change with change in column orientation?

T of B = 1.036

T of C = 1.127

T of D = 1.153

Here we can see an increase in the time period then we can see the change in orientation towards Y. So, the columns are to be placed in a longer direction.

• Effect of Flexural Stiffness of Structural Elements on mode shapes: Compare fundamental mode shape of Building B in two situations when flexural stiffness of beams relative to that of adjoining columns is very small versus when it is large.

When flexural stiffness of beams relative to the adjoining columns is large T is 1.036 and if it is small 1.967. Each story is leading to the shear type deformation.

• Effect of Axial Stiffness of Vertical Members on mode shapes: Compare fundamental mode shape of Building H in two situations when the axial cross-sectional area of columns is very small versus when it is large.

Here axial stiffness depends on the vertical member that is the column. Change in axial stiffness cause deformation in columns.

Here decreasing in the axial area of the member there is an increase in the fundamental natural period from 4.78 to 6.9.

• Effect of Degree of Fixity at column bases on mode shape: Compare fundamental mode shape of Building B in two situations when the base of columns is pinned versus when it is fixed.

The T when hinged and pinned are 1.036 and 0.9

When a building is fixed at the base the rotational moment is restricted and also restricts the sway of the building at the base.

When the building is hinged, it allows the rotational moment. This will make building sway when subjected to Seismic force.

Result:

Thus, the models with different structural detailing are analyzed and compared according to the comparison given in the question.