Project 1_Comparative study of different storey buildings for Seismic forces

 Project :- 1 Comparative study of different storey buildings for Seismic forces 

Aim :-

• The model and analyse multiple building with different floor levels and design parameters using ETabs software and compare the results to understand their overall siesmic behaviour. 

Introduction of ETABS:

• ETABS is one of the most powerful software tools for structural analysis.
• 3D modeling, visualization, and automatic code-based learning are some of the unique features of this software.
• ETABS also supports several analytical models like response spectrum analysis, time-history analysis, and line direct integration time-history analysis. 

Advantages :-

• Built-in drawing utilities: To aid the engineers in modeling, ETABS comes with a built-in feature for drawing and drafting. Some other packages also have this feature, but the quality is much better in ETABS.
• Extensive reports: ETABS generates detailed and comprehensive reports for every project or task you perform, be it calculation of stresses, deformation or failure analysis, and design summary.
• Design of concrete and steel frames: Among all the materials available to build structures, concrete and steel are by far utilized the most in terms of volume. ETABS has specialized modules that deal with concrete and steel frames to optimize your calculations and offer capacity checks for frame elements.

Procedure :-

1. Building A (G+2):

• Open the ETabs software.
• Click the file menu and choose to create a new model option.
• After choosing a new model a dialogue box will appear as Model Initialization.

              

• Choose the built-in settings option and select the display units and codes.
• New dialogue box will appear named New Model Quick Templates.
• Select Custom Grid spacing and custom story data.

             

• After models initialization, select grid and storey inputs from new model quick templates dialogue box.
• In the dialogue box choose grid spacing and custom story data which is used to provide the input specified above.
• Enter X Grid data at a distance of 4 m and Y Grid data as 4 at a distance of 4m.

              

• Now edit stories by using the user-defined story input, 2 stories are incorporated (plinth at 1.5m and 2 story with 3m height each).
• Storey 1 has been labelled as a master storey and all above levels are labelled similar to that.

• So, 2 storeys are successfully added in the peoject.
• Create alll the storeys as similar to storey 1.

• Select Material properties under define tab.
• New dialogue box will appear named Define Materials.
• Select Add new Material from the window.
• Define the materials of concrete M30 Grade and steel of reinforcement as 415 Grade and longitudinal reinforcement as 500 Grade.

• Now select Section Properties under Define Tab.
• Select Frame Sections.
• Select Add new properties in Frame Properties.
• Create a new Property as a beam and input values as 300X400.
• Select Modify/Show Rebar in Reinforcement option.
• Select M3 Design only (Beam).
• Select Reabar as HYSD415.

• Create a new Property as a column and input values as 400X400.

• Now select Section Properties under Define Tab.
• Select Slab Sections.
• Select Add new properties in Slab Properties.

• Using the membrane properties, slab size 150 mm has been added to the list.
• Membrane property will help to consider only slab weights and Floor weights in analysis of structure while no stiffness component of flange advantage are considered during calculation.

• Now draw columns of size 400X400mm at the intersection of the horizontal and vertical grids and beams with quick draw Column keeping all the stories on.

• Now Go to Replicate tool in Edit Menu.
• In Linear Option, Select dx as 4 and dy as 0.
• Insert the Number as 4.

 

• Columns are Successfully added to the structure.
• Now draw the Beams.
• Draw beams of size 300X400mm at the intersection of the horizontal and vertical grids and beams with quick draw beam keeping all the stories on.
• Beams are Successfully added to the structure.
• Draw slab of size 150mm thickness, Draw slabs with quick draw floor/wall keeping all the stories on.
• Slabs are Successfully added to the structure.

• Now define the load patterns.
• Click on the define tab and click on load patterns.
• Define the loads like dead load, live load, brick load, earthquake load in X direction and same loads in Y direction also.
• Mention IS codes of respective loads.

• Click on modified lateral load.
• Set range from base to 25th story and siesmic Zone factor as 0.36, important factor 1.25 and time perod 0.5 S.
• Now go to Mars Source from define tab.
• Modify the mars source and tick mark the required loads.
• Add load patterns and assign the model.
• Insert the dead load as multiplier to 1, live load as multiplier to 0.25 and wall load as multiplier to 1.
• Now go to Load combinations in define Tab.

 

• Mars source is been added successfully.

• Now go to Load cases in define Tab.

 

• Select add default design combos.
• Select concrete frame Design.

  

• Now go to Select option in select Menu.
• Slect Properties.
• Select Frame Sections.
• Select B400X300 option.
• Now assign the loads.
• Frame loads -> Distributed.

• Now go to Select option in select Menu.
• Slect Properties.
• Select slab Sections.
• Select All the Slab150.

 

• Do the same process for all the earthquake load.
• Assign the loads and select in similar stories.
• Click on shell load under the assigne tab.
• Click on live load and give value as 3 kn/m^2.
• Click on apply.

• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 2. Building B (G+5):

• Here we have to create 5 storey model having same column dimension 400x400 mm.
• Now go edit tab and than click on edit storey and grid system.
• Then click on modify or show storey data. Then change the storey right click and Add three storeys and make them similar to storey 1.
• Check all Shell Load in load pattern for Live load and Frame load in load pattern for Wall.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 

 3. Building C (G+5 with Column orientation in X direction):

• Here we have to change the column size to 550x300 and rotate the column along X direction.
• Select the column and click on the modify option. Then change the column property and column size to 550x300.

• Now go to the assign tab-frame-local axis and than change the angle to 90 degree.

• Check all Shell Load in load pattern for Live load and Frame load in load pattern for Wall.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 4. Building D (G+5 with Column orientation in Y direction):

• Here we have to just orient the column along Y axis.
• Now go to the assign tab-frame-local axis and than change the angle to 0 degree.
• Check all Shell Load in load pattern for Live load and Frame load in load pattern for Wall.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 

 5. Building E (G+10):

• Here we have to create 10 storey and column size should be 600x600 at bottom 5 Storeys and 400x400 at upper 5 storeys.
• Go to the edit option and click on edit storey and grid system than click on the modify/show storey data.
• Create storey right click and add storey. Create more five storeys and make them similar to storey 1.

• Now go to define tab-frame-frame section. Then Click on modify/show property. There make the previous column to 600 x 600mm.
• Create another column by add new property option and make the column as 400x400mm.

• Now go to the set display option there untick the beam and floor option.
• Now go to the view option tab and click on the set building view limits, than change the value from base to storey 5.
• Select all the columns and assign the section property as column 600x600.

• Similarly for column 400x400mm from storey 6 to storey 10 go to again view option tab and click on the set building view limits.
• Change the value from storey 6 to storey 10. Than assign the frame properties as column 400x400mm as done in steps 8.
• Now in the set display option tick the beam and floor option.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 6. Building F (G+10):

• Here we have to make the columns 600x600 for all 10 storeys.
• Now again click on the set display options untick the beam and floor option.
• Select all the columns and assign the frame - property and than select the column 600x600mm.
• All the columns will be assigned to 600x600mm. Now again tick the beam floor option from the set display option.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 

 

 7. Building G (G+25):

• Here we have to create 25 storeys and varying column sizes such as column 400x400 for upper 5 storeys, column 600x600 middle 10 storeys and column 800x800 for bottom 10 storeys.

• Create another column by add new property option and make the column as 800x800mm.

 

• Now click on the set display options untick the beam and floor option.
• Set Building View Limit from 21-25 storeys and 
• Assign the Column sizes of 400X400

 

• Set Building View Limit from 20-11 storeys and 
• Assign the Column sizes of 600x600

• Set Building View Limit from 10-1 storeys and 
• Assign the Column sizes of 800x800

• Check all Shell Load in load pattern for Live load and Frame load in load pattern for Wall.
• Now again tick the beam floor option from the set display option.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 8. Building H (G+25):

• Here we have to make the columns 800x800 for all 25 storeys.
• Now again click on the set display options untick the beam and floor option.
• Select all the columns and assign the frame - property and than select the column 800x800mm.
• All the columns will be assigned to 600x600mm. Now again tick the beam floor option from the set display option.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 

 

 

 9. Building J (G+25):

• Here we have to create imposed mass 10% larger than building H.
• Select the slab and than Go to the assign tab- shell loads- uniform. Than select the live load and enter the value as 3.3kn/m sq. i.e 10%.
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 10. Building K (G+25):

• Here we have to create imposed mass 10% larger than building H.
• Select the slab and than Go to the assign tab- shell loads- uniform. Than select the live load and enter the value as 3.6kn/m sq. i.e 20%
• To assign the diaphragam select the slab from the select tab option and than assign shell-diaphragam and run the analysis.

 

 Comparison the analysis result between the time period in various condition:

 

Criteria	Model	Analysis Result
Effective stiffness on Time Period	Building-E (10 storey with varying column size) Building-F (10 storey with uniform column size)	1.73sec         1.73sec
Effect of stiffness on time period	Building-G (25 storey with varying column size) Building-H (25 storey with uniform column size)	4.17sec         4.41sec

Conclusion: It can be concluded that higher the storey and varrying column sizes i.e reducing column sizes at top storeys it is more stable and time period is greater for higher storeys.

 

Criteria	Model	Analysis Result
Effect of mass on time period	Building-H (25 storey with 3 kN/m2 imposed load) Building-J (25 storey with 3.3 kN/m2 imposed load) Building-K (25 storey with 3.6 kN/m2 imposed load)	4.41sec       4.42sec       4.43sec

Conclusion: There is no differences in the time period as the load is uniformly distributed at all floors. Time period varies factor of 0.01s.

 

Criteria	Model	Analysis Result
Effect of building height on time period	Building-A (2 storey) Building-B (5 storey) Building-F (10 storey) Building-H (25 storey)	0.5 sec 1.03 sec 1.73 sec 4.41 sec

Conclusion:  As the building height increases time period also increases i.e time period is directly proportional to the building height.

 

Criteria	Model	Analysis Result
Effect of column orientation on time period	Building-B (all floors column size 400X400) Building-C (all floors column size 550X300) X-direction Building-D (all floors column size 300X550) Y-direction	1.03 sec   1.145 sec   1.12 sec

Conclusion:  For same column sizes defelction is same in both x & Y direction. But for varying column sizes the defelction will be higher in X direction for Model D than Model C.

 

Criteria	Model	Case	Analysis Result
Effect of flexural stiffness of structural elements on mode of shapes	Building-B	Flexural stiffness of beams close to nil (zero inertia) Full flexural stiffness of beams (regular)	2.62 sec   1.03 sec

Conclusion: It is almost double in time period if consider the flexural stiffness almost close to zero than regular.

 

Criteria	Model	Case	Analysis Result
Effect of axial stiffness of vertical members on mode shapes	Building-H	Axial cross section for columns is closed nil (Zero axial area) Full axial cross section for columns (regular)	5.99 sec   4.41 sec

 Conclusion: Making the axial cross section as 10% the time period increases by 1.5 secs.

 

Criteria	Model	Case	Analysis Result
Effect of degree of fixity at column base on mode shapes	Building-B	Column support pinned (regular) Column support fixed	1.03 sec   0.941 sec

 Conclusion: When the column support are fixed lesser the time period hence lesser deflected as compared to pinned.