Projefct 1_Comparative study of different storey buildings for Seismic forces

Aim: To have a comparative study on;
Factors influencing the dynamic characteristics of different storey building for seismic force
Factors influencing the Natural Period of different storey building for seismic force
Factors influencing the Mode shape of oscillations of different storey building for seismic force
Introduction: Every building offers a minimum resistance to the forces induced by the external effects like Earthquake. The important dynamic characteristics of a building are the modes of oscillation and damping.Thus it has effect of :

                   Flexural Stiffness of Structural Elements on mode shapes
                   Axial Stiffness of Vertical Members on mode shapes
                   Degree of Fixity at column bases on mode shape
Data assumed:
Structural Element Sizes
Beams : 300 × 400 mm
Columns : 400 × 400 mm
Slab : 150 mm thick
Material Properties
Grade of Concrete : M30
Grade of Steel Reinforcement Bars : Fe 415
Loading
Dead Load on beams from infill wall : 10 kN/m
Live load on floor : 3 kN/m2
Buildings are assumed to be pinned at base
Buildings considered to illustrate concept of natural period

General procedure
Open the ETabs Software, Select New model
Use the Built in settings with:
Now add the grids, number of storeys
Now to add the material, select Define, then select Material properties and add new material.
Now to add the Beam property, select Define, select the section properties and select the frame sections. Select Add new property and insert concrete
Now select the Modify/Show rebar
Now to add the column property, select Define menu, select section properties, select Frame sections, Add new property
Select Modify Rebar and edit
Now to add the Slab property, again select the Define menu, Select Slab section and add new slab
Now using the Quick draw beams/columns option draw the beams and columns to the whole structure
Now we need to add the slabs Using Quick draw floor/wall option
Now select the base plan and select all the base points
Now from the Assign menu, select the Restraints from the Joint option. Thus, the pin joints are added to the base of the structure.
Now from the Define option select the Load patterns and add the Dead load, live load, Brickwall load and earthquake load.
Now select Eqx and click the Modify lateral load, and in the new tab appeared, seismic zone factor as per code is given and selected Site type as III.
Similarily done for all the seismic loads
Now we need to add the Live load, for that, select the Assign menu and select the shell loads , and select Uniform option
Here, we consider a live load of 3KN/m^2 upto the 2nd top most floor and 1.5KN/m^2 to the top most floor
Now from the Select Manu, select the Object Type option, now a new tab appears, and select the beams and click on the select option and close
Now from Assign Menu, select frame loads and select Distributed
Select Load pattern ad Brickwall in the new tab and click apply
Now from the Define Menu, select Mass source, select Modify/show mass source option and add the load patterns
Again from the Define menu, select the load combination and add Default design combination
Now from the Select menu, select select option and select Object type, Now select the floors and select and close
Now from the Assign Menu, select shell, and select Diaphragms
Now when the new tab appears, select D1 and click on apply and then close
Now from the Analyze menu, click Check Model option
When the new tab appears, select all the options and click ok
Now after checking, a warning tab appears, and then select Run analysis
Select Show tables from the Display menu, and select Analysis result, select the required tables and now the selected tables will be visible.

BUILDING A:

BUILDING B:

BUILDING C:

BUILDING D: 

BUILDING E:

BUILDING F:

BUILDING G:

BUILDING H :

BUILDING J:

BUILDING K:

RESULT :

From Comparing the fundamental natural periods of buildings E & F as well as G & H
a. The fundamental natural period of building E is 1.459 sec
b. The fundamental natural period of building F is 1.527 sec
c. The fundamental natural period of building G is 3.738 sec
d. The fundamental natural period of building H is 4.22 sec
e. Since we used two different column size in E building and used only one type of column for F building, caused the significant change in the time period.
The same has happened with the case of G and H

From Comparing the fundamental natural periods of buildings H, J and K.
a. When comparing the Natural period of Buildings H,J and K, the time period remains constant, which means, a small increment in the live load causes no change in thw stiffness and flexibility of the structure.
b. While a significant change in the structural flexibility can be expected with greater increament in live load.
c. Thw weight of the building is directly proportional to the flexibility of the structure.

From Comparing the fundamental natural periods of Buildings A, B, F and H change with change in building height
a. When observing the height and the natural period of building A,B, F and H, it can be observed that, whith the increase in height of the structure, the natural period of the building also increases.

From  Comparing the fundamental natural periods of Buildings B, C and D change with change in column orientation
b. With the change in the orientation of the buildings B,C and D, a significant change in the fundamental natural period is observed