Project 1_Comparative study of different storey buildings for Seismic forces

1. Aim and Introduction

1.1 Aim of the Project-

To study the dynamic characteristics, mode shape of oscillation and factors that influences the natural periods of different buildings having different size of columns, varying columns sizes with respect to storey and for different base support by using ETAB software.

1.2 Introduction

All the specification and size of columns and support condition of different buildings having different storey have been given below,

Data related to structural elements, materials properties and loading has been given below,

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

2. Procedure

2.1 Procedure in modelling and analysis of Building A as per the given data,

Step 1- after the opening of the ETAB , the new model has been created by using built up setting which is given below,

Step 2- Grids has been created by using the custom spacing with edit grid data as per the given data i.e. x coordinate data and y coordinate data with spacing of 4m has been created which is given below,

Step 3- After grid formation, story data has been inserted as per the given data i.e. plinth level at 1.5m from the ground level and at 3m the height of story 1 to story 2 has been created by making the story 1 as master story and other story is similar to storey 1 except plinth.

Step 4- After creating grids and story, then the material properties has been defined by clicking on the define option and then define material and then new properties and then a pop-up box will be opened where the concrete and steel has been specified as per the required data.

For this project, concrete of M30 grade and steel as reinforcement i.e. rebar of fe415 which is given below,

Step 5-After defining the material properties, frame properties of the model has been defined by clicking on the define option and then section properties and then frame properties then a pop-up will be opened.

After a pop up box is opened, then by clicking on the add new properties and then specify the concrete rectangular and then rectangular section and then another pop up box frame section propertied data will be opened where properties name, material, section dimension, property modifier and reinforcement details has been assigned.

For this project, the data for column as well as beam also has been added that is given below,

Step 6- Same procedure has been followed for adding of beam sectional properties and data that has been used in this project is given below,

Step 7- For defining of the section properties of slab, go to the define and then clicking on section properties and then click on the slab definition, and then as per the given data which has been shown below,

Step 8- Now the load pattern has been defined I.e. wall load, live load, dead load and seismic load i.e. EQX (in x direction) and EQY (in y direction) with supporting of IS code of 1893:2016.

Step 9- After defining the load pattern, mass sources data has been added by clicking on the define option and then mass source where % mass has been defined for dead load, live load or imposed load and for wall i.e. super dead load which is given below,

Step 10- check for the load cases which will be found on the define option and then the load combination is added from define option and by clicking on add default design combo for concrete frame structure which is given below,

Step 11- after defining the material properties, section properties and loads, now all the section has been assigned to the required places.

For column, by accessing the quick draw column and the required column size has been chose and the selected column has been assigned to the required places and all the storey must be selected.

Same procedure has been followed for beam and slab: for beam, quick draw beam and for slab, quick draw slab/ floor has been chosen.

But, for slab only similar storey has been selected as the slab has not been assigned to plinth level.

Step 12-After assigning the frame properties, now the load i.e. dead load, live load or imposed load and wall load has been added to the frame structure.

Here in this project, live load for 3kn/sq-m is applied on the slab and wall load of 10 Kn/m is applied on the beam frame.

Step 13- Assigning of diaphragms on the slab of all assigning slab for making mass of all the slab should be concentered on the CG of the slab.

First of all the slab has been selected and then by clicking on the assign option and then shell and then diaphragms has been selected which is given below,

Step 14- Then this model has been saved as name Building_A before the model being analyzed.

Step 15- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step 16- After model is analyzed, the model properties and frequency has been found which steps has been shown below,

2.1.1 All the step wise screen shots in modeling and analyzing the Building_A has been given below chronologically,

2.2 Procedure in modelling and analysis of Building B as per the given data,

Step-1- After analyzing of the Building_A, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_B.

Step-2- By using the edit storey option in Edit, the new model has been edited as the given data i.e. addition three more stories as Building_B having 5 storey building. Plinth level of 1.5m and storey height of 3m from base level have been created. Storey 1 is the master storey and other stories is similar to the storey 1 except.

Step-3- Building_B has been checked the load that has been assigned in Building_A i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.2.1 All the step wise screen shots in modeling and analyzing the Building_B has been given below chronologically,

2.3 Procedure in modelling and analysis of Building C as per the given data,

Step-1- After analyzing of the Building_B, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_C.

Step-2- As the Building_C having the same material and grid pattern but the size of the Building_C is different so the size of column has been changed as per the given data which is 550×300 and named as C 550×300 in the define section by adding new property and beam size and slab size is same as that of Building_B.

After defining and assigning of new column, as per the given data, the column has been oriented to x axis by using frame assignment-local axis and then the angle has been changed to 90 degrees.

Step-3- Building_C has been checked the load that has been assigned in Building_B i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.3.1 All the step wise screen shots in modeling and analyzing the Building_C has been given below chronologically,

2.4 Procedure in modelling and analysis of Building D as per the given data,

Step-1- After analyzing of the Building_C, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_D.

Step-2- As the Building_D having the same material and grid pattern but the size of the Building_D is different so the size of column has been changed as per the given data which is 550×300 and named as C 550×300 in the define section by adding new property and beam size and slab size is same as that of Building_B.

After defining and assigning of new column, as per the given data, the column has been oriented to Y axis by using frame assignment-local axis and then the angle has been changed to 0 degrees.

Step-3- Building_D has been checked the load that has been assigned in Building_C i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.4.1 All the step wise screen shots in modeling and analyzing the Building_D has been given below chronologically,

2.5 Procedure in modelling and analysis of Building E as per the given data,

Step-1- After analyzing of the Building_D, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_E.

Step-2- By using the edit storey option in Edit, the new model has been edited as the given data i.e. addition five more stories as Building_B having 10 storey building. Plinth level of 1.5m and storey height of 3m from base level have been created. Storey 1 is the master storey and other stories is similar to the storey 1 except.

Step-3- Building_E has been checked the load that has been assigned in Building_D i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

As per the given data for Building_E i.e. two new column size has been asked to assign that is column size of 600×600 has been assigned to lower 5 storey whereas column size of 400×400 has been assigned to upper 5 stories using set storey limit and hiding all other elements except column which is then simply selected using mouse and then size has been assigned. Before these columns is assigned, these columns has been defined from define in frame section.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.5.1 All the step wise screen shots in modeling and analyzing the Building_E has been given below chronologically,

2.6 Procedure in modelling and analysis of Building F as per the given data,

Step-1- After analyzing of the Building_E, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_F.

Step-2- As per the given data for Building_F, the column size is 600×600 which has been define by selecting the existing column size and then it is modified to size of 600×600 which is directly to reflected in the model and changed to 600×600 irrespective of numbers of storey.

Step-3- Building_F has been checked the load that has been assigned in Building_E i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.6.1 All the step wise screen shots in modeling and analyzing the Building_F has been given below chronologically,

2.7 Procedure in modelling and analysis of Building G as per the given data,

Step-1- After analyzing of the Building_F, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_G.

Step-2- By using the edit storey option in Edit, the new model has been edited as the given data i.e. addition fifteen more stories as Building_B having 15 storey building. Plinth level of 1.5m and storey height of 3m from base level have been created. Storey 1 is the master storey and other stories is similar to the storey 1 except.

Step-3- Building_G has been checked the load that has been assigned in Building_F i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

As per the given data for Building_G i.e. three new column size has been asked to assign that is column size of 800×800 has been assigned to lower 10 storey, column size of 600×600 has been assigned to middle 10 storey whereas column size of 400×400 has been assigned to upper 5 stories using set storey limit and hiding all other elements except column which is then simply selected using mouse and then size has been assigned. Before these columns is assigned, these columns has been defined from define in frame section.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.7.1 All the step wise screen shots in modeling and analyzing the Building_G has been given below chronologically,

2.8 Procedure in modelling and analysis of Building H as per the given data,

Step-1- After analyzing of the Building_G, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_ H.

Step-2- As per the given data for Building_ H, the column size is 800×800 which has been define by selecting the existing column size and then it is modified to size of 800×800 which is directly to reflected in the model and changed to 800×800 irrespective of numbers of storey.

Step-3- Building_ H has been checked the load that has been assigned in Building_G i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.8.1 All the step wise screen shots in modeling and analyzing the Building_H has been given below chronologically,

2.9 Procedure in modelling and analysis of Building J as per the given data,

Step-1- After analyzing of the Building_ H, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_J.

Step-2- Here in the Building_J, it is same as the Building_ H in aspect of structural size and loads, but the imposed mass has been increased of 10% which has been assigned by selecting the slab and then by going to the load cases and then impose load i.e. live load has been changed to 3.3 Kn/sq-m which is directly reflected on the model.

Step-3- Building_J has been checked the load that has been assigned in Building_ H i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.9.1 All the step wise screen shots in modeling and analyzing the Building_J has been given below chronologically,

2.10 Procedure in modelling and analysis of Building K as per the given data,

Step-1- After analyzing of the Building_J, a new model has been created by using the save as option because the new building having the same material and grid properties and saved name as Building_K.

Step-2- Here in the Building_K, it is same as the Building_ H in aspect of structural size and loads, but the imposed mass has been increased of 20% which has been assigned by selecting the slab and then by going to the load cases and then impose load i.e. live load has been changed to 3.6 Kn/sq-m which is directly reflected on the model.

Step-3- Building_K has been checked the load that has been assigned in Building_J i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.10.1 All the step wise screen shots in modeling and analyzing the Building_K has been given below chronologically,

2.11 Procedure in modelling and analysis of Building_B_zero_inertia as per the given data

Step-1- In making the Building_B_zero_inertia, firstly the Building_B has been opened as all the building properties like size and material properties of frame is same as Building_B and the grids and number of storey is also same and this building has been saved as Building_B_zero_inertia.

Step-2- By going to the frame section properties from define option where moment of inertia about 2 axis and moment of inertia about 3 axis has been changed to 10% i.e. 0.10 (equal to negligible) by clicking on the modify option.

Step-3- Building_B_zero_inertia has been checked the loads i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.11.1 All the step wise screen shots in modeling and analyzing the Building_B_zero_inertia has been given below chronologically,

2.12 Procedure in modelling and analysis of Building_H_zero_axial_area as per the given data

Step-1- In making the Building_H_zero_axial_area, firstly the Building_H has been opened as all the building properties like size and material properties of frame is same as Building_H and the grids and number of storey is also same and this building has been saved as Building_H_zero_axial_area.

Step-2- By going to the frame section properties from define option where cross section (axial) area has been changed to 10% i.e. 0.10 (equal to negligible) by clicking on the modify option.

Step-3- Building_H_zero_axial_area has been checked the loads i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.12.1 All the step wise screen shots in modeling and analyzing the Building_H_zero_axial_area has been given below chronologically,

2.13 Procedure in modelling and analysis of Building_B_fixed_support as per the given data

Step-1- In making the Building_B_fixed_support, firstly the Building_B has been opened as all the building properties like size and material properties of frame is same as Building_B and the grids and number of storey is also same and this building has been saved as Building_B_fixed_support.

Step-2- To make the support to fixed support, firstly the nodes on the base has been selected which is then assigned to fixed support from assign option and joint assignment restraints.

Step-3- Building_B_fixed_support has been checked the loads i.e. dead load, live load and wall load and also definition of all the define section as well as load properties.

Step-4- As the diaphragms has not been assigned, so the diaphragms has been assigned to all the floors. First of all, the slab has been selected and then diaphragms option from assign tool to ensure the mass of floor or slab must be in the CG.

Step-5- Now using the F5 bottom or by directly by clicking on the run option; this model is analyzed.

Step-6- After model is analyzed, the model properties and frequency has been found from display result option.

2.13.1 All the step wise screen shots in modeling and analyzing the Building_B_fixed_support has been given below chronologically,

3. Results and discussion-

3.1 Results-

After the buildings are analyzed, the modal periods and frequencies and storey drift in X and Y direction for seismic load has been found for respective building has been given below,

3.1.1 Results for Building_A

3.1.2 Results for Building_B

3.1.3 Results for Building_C

3.1.4 Results for Building_D

3.1.5 Results for Building_E

3.1.6 Results for Building_F

3.1.7 Results for Building_G

3.1.8 Results for Building_H

3.1.9 Results for Building_J

3.1.10 Results for Building_K

3.1.11 Results for Building_B_zero_inertia

3.1.12 Results for Building_H_zero_axial_area

3.1.13 Results for Building_B_fixed_support

3.2 Discussion-

Criteria	Model	Analysis results	Conclusion
Effect of stiffness on time periods	Building_E (10 storey with varying column size)	1.731 sec (time period due to mode 1)	Time period of uniform column of 10 storey building is slightly greater than varying column which is because of slightly lesser mass and less stiffness in varying column.
	Building_F (10 storey with Uniform column size)	1.735 sec (time period due to mode 1)
Effect of stiffness on time periods	Building_G (25 storey with varying column size)	4.17 sec (time period due to mode 1)	Time period of uniform column of 25 storey building is greater than varying column which is because of lesser mass and less stiffness in varying column. As the height increases, the mass and stiffness as compared to 10 storey building increases which increases the difference of time period in comparison to 10 storey building. Height of the building is directly proportional to time period.
	Building_H (25 storey with Uniform column size)	4.416 sec (time period due to mode 1)
Effect of stiffness on time periods	Building_H (25 storey with 3 Kn/sq-m of imposed load)	4.416 sec (time period due to mode 1)	Mass is directly proportional to the lateral loads. Increase in imposed load causes in increase in mass which results increasing in time periods. In 10% increase in imposed load causes slightly increase in time period which is linear.
	Building_J (25 storey with 3.3 Kn/sq-m of imposed load	4.425 sec (time period due to mode 1)
	Building_K (25 storey with 3.6 Kn/sq-m of imposed load	4.435 sec (time period due to mode 1)
Effect of building height on time period	Building_A (2 storey)	0.5 sec (time period due to mode 1)	As the height of building is directly proportional to the time period which is also shown in IS 1893.
	Building_B (5 storey)	1.036 sec (time period due to mode 1)
	Building_F (10 storey)	1.735 sec(time period due to mode 1)
	Building_H (25 storey)	4.416 sec(time period due to mode 1)
Effect of column orientation on time period	Building_B (all floor column size is 400×400)	1.036 sec (time period due to mode 1)	Building_B is not comparable with Building_C and Building_D because number storey in building_b is not same. Moment of inertia of Building_C having lesser value than Building_D which reflects that the time periods for Building_C is higher than Building_D as MOI is inversely proportional to Time periods.
	Building_C (all floor column size is 550×300, oriented in X direction)	1.145 sec (time period in Y direction)
	Building_D (all floor column size is 300×550, oriented in Y direction)	0.953 sec (time period in y direction)
Effect of flexural stiffness of structural elements on mode shapes	Building_B_zero_inertia (flexural stiffness of the beam close to nil i.e. zero inertia)	2.627 sec (time period due to mode 1)	As Moment of inertia is inversely proportional to time periods.
	Building_B (Full flexural stiffness of beam i.e. regular)	1.036 sec (time period due to mode 1)
Effect of axial stiffness of vertical elements on mode shapes	Building_H_zero_axial_area (axial cross section for columns is close to nil i.e. zero axial area)	5.991 sec (time period due to mode 1)	For zero axial area of column, the stiffness of the building is negligible in comparable to regular type of column sized building which increases the time period.
	Building_H (Full axial cross section for columns i.e. regular)	4.416 sec (time period due to mode 1)
Effect of degree of fixity at column base on mode shape	Building_B (column support is pinned)	1.036 sec (time period due to mode 1)	Fixed support increase the stiffness of the building in comparison to the pinned supports which results in decrease in time periods.
	Building_B_fixed_support (column support is fixed)	0.941 sec (time period due to mode 1)

3.2.1 NOTE-

The results in modelling and analysing of the buildings as per the given data by using ETAB i.e. the .edb file named as “Building_A”, “Building_B”, “Building_C”, “Building_D”, “Building_E”, “Building_F”, “Building_G”, “Building_H”, “Building_J”, “Building_K”, “Building_B_zero_inertia”, “Building_H_zero_axial_area”, “Building_B_fixed_support” have been uploaded below.