Project 1_Comparative study of different storey buildings for Seismic forces

AIM :

• KNOW HOW TO EXTRACT DIFFERENT SEISMIC RESPONSES FOR STRUCTURE
• KNOW HOW TO ALTER POROPERTIESIN ETABS MODEL
• KNOW THE FACTORS INFLUENCING THE DYNAMIC CHARACTERISTICS OF BUILDINGS
• KNOW THE FACTORS INFLUENCING TIME PERIOD OF BUILDING
• KNOW THE FACTORS INFLUENCING MODE SHAPE OF BUILDING

PROCEDURE :

• MODELING OF BUILDINGIS DONE JUST LIKE CHALLENGE 6, STEPS AR SHOWN BELOW

STEP-1

1. Open ETABS.
2. Go to file menu and select new model, a pop up window of model initialization will be opening.
3. Select use built in settings.
4. Select display units as Metric SI, Steel section data base as Indian, Steel design code as IS 800:2007, concrete design code as IS 456:2000.
5. Select OK.

STEP-2 DRAWING GRIDS

1. A new window of new model quick templates will be appearing.
2. Select the grids and customise grids.
3. Set X grid data at spacing of 4m, and number of grids is 5.
4. Set Y grid data at spacing of 4m, and number of grids is 4.
5. Click OK

STEP-3 EDITING STOREY DATA

1. Now select the option custom story data and select edit storey data.
2. Select plinth height as 1.5m, and height of storey as 3m.
3. Add storey and make total number of story as 2.
4. Keep master storey 1 as yes.
5. Click OK.

STEP-4 DEFINING MATERIAL PROPERTIRES

1. Defining the properties of elements.
2. Go to define and select material properties.
3. Select grade of concrete as M30.
4. Select steel as HYSD 500and HYSD 415 steel.

STEP-5 DEFINING COLUMN AND BEAMS

1. Defining beam column properties.
2. Go to define tab, section properties and frame sections.

STEP-6 DEFINING SLAB PROPERTIES

1. Defining slab properties.
2. Go to define tab, section properties and slab sections.

STEP-7 PLACING THE COLUMNS AND BEAMS

1. Drawing of beams and columns.
2. In the left side of the draw panel select the option quick draw column.
3. Place columns on the grids
4. For drawing of beams select the option quick draw beams in the draw panel and place the beams.

STEP-8 PLACING THE SLABS

1. Drawing of slab.
2. In the left side of the draw panel select the option quick draw floor.
3. Place slabs between the grids.

STEP-9 MODELING THE BASE CONNECTIONS

1. Change the base connections.
2. Go to the base view in the plan.
3. Select the base view.
4. Select assign tab, joints, restraints and select pinned connection.

STEP-10 ASSIGNING LOADS

1. Assigning loads on the structure.
2. Select define, load patterns and enter the load patterns as shown in the image.

STEP-11 ASSIGNING LIVE LOAD ON SLAB

1. Assigning live loads.
2. Go to assign tab and select shell loads , uniform and assign load of 3KN/M

STEP-12 ASSIGNING WALL LOAD ON BEAMS

1. Assigning load on beam as brick wall load.
2. Apply load of 10KN/M^2.

STEP-13 ASSIGNING MASS SOURCE

1. Assigning mass source to model.
2. Go to define tab select mass source and enter the details as shown in the image.

STEP-14 ASSIGNING LOAD COMBINATIONS

1. Generating load combinations.
2. Select define tab- load combinations- add default- concrete frame- convert to editable.
3. Enter data as shown in the image.

STEP-15 ASSIGNING DIAPHRAGMS

1. Assigning diaphragms to the model.
2. Go to assign tab select shell, select diaphragms and select D1.
3. Apply the diaphragms

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• FOR MODELLING THE STRUCTURE ALL THE STEPS ARE SIMILAR FOR EVERY STRUCTURE IN THIS PROJECT
• THE PROPERTIES AND CHARRACTERISTICS IN ALL STRUCTURE ARE LISTED IN IMAGE BELOW

1. BUILDING 'A'

1. Column sizes are 400 X 400
2. Building 'A' is of 2 storey

2. BUILDING 'B'

1. Column sizes of building A & B are same 400 x 400
2. Building 'B' is a 5 storey building
3. Storey of Building A are increased and saved as building 'B'
4. Stories were increased by going to EDIT section > Edit storey and grid data > stories were added

3. BUILDING 'C'

1. Building C has same storeys as building B
2. The difference in Building 'B' & 'C' is change in column size i.e. 550 X 300
3. The existing column properties are edited/modified
4. The orientatation of column is done by selecting all columns > define > frame section > local axes > assigning to 90 degree

4. BUILDING 'D'

1. Every properties in Building 'C' and 'D' are similar except the column size
2. The orientation of column is changed in Building D

5. BUILDING 'E'

1. Building 'E' is 10 story building
2. The column size of, bottom 5 storey is 600X600 and top 5 storey are 400x400

• FIRST STORIES ARE ADDED TO BUILDING

• COLUMN SIZE UPTO STORY 5 ARE 600x600

• COLUMN SIZES FROM STOREY 6 TO STOREY 10 ARE 400X400

• BUILDING 'E'

6. BUILDING 'F'

1. Building 'F' is a 10 story structure
2. Column sizes from base to story 10 is same 600X600

7. BUILDING 'G'

1. Building F is 25 story structure
2. Building F have 3 different sizes for column
3. Such that upper 5 storeys column size are 400X400, Middle 10 storeys have column size 600X600, Bottom 10 storeys have column sie 800X800.
4. While Modelling first the new column properties and sizes were defined
5. the storeys are added to structure
6. Then required column sizes were assign to the storeys

STOREYS ADDED

BUILDING 'G'

8. BUILDING 'H'

1. Building H is a 25 storeys structure
2. Column sizes of building H from base to 25 storeys is 800x800 mm

BUILDING H

9. BUILDING 'J'

Building H & J are similar only difference is the live load is increased by 10%

10. BUILDING K

Building K is also similar to buulding H only difference the live mass is increased by 20%

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ANALYSIS RESULT TABLE :

BUILDING 'A'

BUILDING 'B'

BUILDING 'C'

BUILDING 'D'

BUILDING 'E'

BUILDING 'F'

BUILDING 'G'

BUILDING 'H'

BUILDING 'J'

BUILDING 'K'

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RESULT AND CONCLUSION:

CRITERIA	MODEL	ANALYSIS RESULT
Effect of STIFFNESS on period time	Building - E (10 storey with varying column size)	1.73 s
	Building - F (10 storey with uniform column size)	1.73 s
Effect of STIFFNESS on period time	Building - G (25 storey with varying column size)	4.17 s
	Building - H (25 storey with uniform column size)	4.41 s

CONCLUSION :

• The natural periods of building E and F are almost same as the buildings have same height. The only difference in them is the size of columns.
• The buildings G and H have more time period because the height of the building is more. Due to the height of building it has sufficient ductility and the time period is more for G and H buildings. The size of Columns in G and H building is more than E and F hence there is more flexibility in the building.

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CRITERIA	MODEL	ANALYSIS RESULT
Effect of MASS on time period	Building - H (25 storey with 3 KN/sq.m imposed load)	4.41 s
	Building - J (25 storey with 3.3 KN/sq.m imposed load)	4.42 s
	Building - K (25 storey with 3.6 KN/sq.m imposed load)	4.43 s

CONCLUSION :

• Their is no significant change in variation
• The reason can also be that the imposed load is provided uniformly the floors

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CRITERIA	MODEL	ANALYSIS RESULT
Effect of BUILDING HEIGHT on Time period	Building - A(2 storey)	0.5 s
	Building - B (5 storey)	1.03 s
	Building - F (10 storey)	1.73 s
	Building - H (25 storey)	4.41 s

CONCLUSION :

• Taller buildings are more flexible and have larger mass, and therefore have a longer T. On the contrary, low- to medium-rise buildings generally have shorter T (less than 0.5s). As the building A and B has 2 and 5 number of floors its time period is less, where as F and H buildings are 10 and 25 storey their time period T is more.

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CRITERIA	MODEL	ANALYSIS RESULT
Effect of COLUMN ORIENTATION on Time period	Building - B (All floors column size 400X400)	1.03 s
	Building - C (All floors column size 550X300) Oriented in X-direction	1.14 s
	Building - D (All floors column size 300X550) Oriented in Y-direction	1.12 s

CONCLUSION :

• The change in column orientation increases the time period of buildings. Columns should be oriented in longer direction to increase the time period.

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Effect of Flexural stiffness of structural elements on mode shapes -

• The overall lateral translational mode shapes depend on the flexural stiffness of beams relative to that of adjoining columns. The fundamental mode shape of buildings changes from flexural-type to shear-type as beam flexural stiffness increases relative to that of column.

Effect of Axial Stiffness of Vertical members on mode shapes -

• Mode shapes depend on axial stiffness of vertical members in a building (i.e., of columns or structural walls).
• Small Axial Stiffness causes significant axial compressive and tensile deformation in columns in addition to single or double curvature flexural deformations.
• Additional Axial Deformation changes the fundamental mode shape from shear-type to flexural type, particularly in tall buildings.
• Pure Flexural Response is not desirable because of large lateral sway, particularly at higher floors.

Effect of Degree of Fixity at column bases on mode shapes -

• Highly Flexible soils make column bases as good as hinged, and rocky layers below as good as fixed.
• Lack of Rotational Fixity at the Column Base (hinged condition) increases the lateral sway in the lower storey than in the higher storey, and the overall response of the building is more of shear-type.
• On the other hand, full rotational fixity at the column base restricts the lateral sway at the first storey and thus, induces initial flexural behaviour near the base.
• The overall response of the building is still of shear-type due to flexural stiffness of beams.

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