Project 2_Design & Analysis of a Hostel building at Guwahati, Assam

In this project, participants will get to experience the entire design process from modelling, analysis, design, and preparation of construction drawings. The architectural drawings of a G+3 RCC building is provided. The following information on the building is to be used:

• Location – Guwahati, Assam
• Function – Hostel block in an academic institute

The walls will be made of AAC blocks. Other loadings are to be calculated as per the architectural drawings. 

The buildings rest on type 3 soil. Piles of length 10 meters and 500 mm diameter with a load-carrying capacity of 280 KN are to be used. 

The ground floor level will be at a height of 2 meters above the existing site level to avoid floodwater entering the building.

M25 grade of concrete with Fe500 for longitudinal reinforcement and Fe 415 for shear reinforcement is to be used. 

The following design IS codes will be required for reference:

• IS 875 part 1
• IS 875 part 2
• IS 13920
• IS 1893
• IS 2911 part 2
• IS 456
• SP 34

Students will have to produce the following:

• Etabs model for the two blocks on either side of the expansion gap
• Foundation details illustrating the pile & pile cap reinforcement
• Tie beam details connecting the pile caps
• Column reinforcement
• Framing plan for typical floor
• Beam reinforcements for ground floor

Aim: To design and analyze G+3 (RCC) Hostel building in ETABS and Foundation in CSI SAFE.

Introduction: - 

The procedure for analysis and design of a given building will depend on the type of building, its complexity, the number of stories, etc.

First, the architectural drawings of the building are studied, the structural system is finalized sizes of structural members are decided and brought to the knowledge of the concerned architect

The procedure for Structural Design will involve some steps which will depend on the type of building and also its complexity and the time available for structural design.

Often, the work is required to start soon, so the steps in design are to be arranged in such a way the foundation drawings can be taken up in hand within a reasonable period of time.

Further, before starting the structural design, the following information of data are required,

a. A set of architectural drawings;

b. Soil Investigation Report (SIR);

c. Location of the place or city in order to decide on wind and seismic loadings;

d. Data for lifts, water tank capacities on top, special roof features or loadings

PROCEDURE: -

• In the first step open the Etabs software, go to file and click on new model.
• A model initialization window will appear.
• Click on the use built in setting and select the Indian codes and click ok.
• Click on the custom grid data and click ok.
• Now the values as per the given plans are inserted and our model will be ready.
• In the next step material has to be defined. Go to define and click on material properties and add the concrete and rebar material specification.
• In the next step section properties have to be defined. Go to define and click on section properties and add the beam and column specification.
• A 400mm x 500 mm beam size is provided for all the beams.
• 400 mm x 500 mm beams are provided for the beams at periphery so as to increase the torsional resistance of the building
• Moment of inertia for beams and columns should be reduced by 0.35% and 0.7% respectively.
• In the next step define the slab properties by going in to define and slab sections. Add the slab property as While defining the slab for Stair case it should be One way.
• Define the stair case slab and provide its thickness as 175mm 
• Draw all the beams using beam command.
• Draw all the columns using column command
• In the next step slabs are drawn using slabs command
• Now go to define and define the loads.
• Next select the beams and floors and add the loads.
• AAC load of 3.5 kN/m since the AAC blocks are used.
• The live loads values are got from Is 1875 part 2 for residential buildings.
• As per table 1 of IS 875 part 2
• For hostel buildings
• As per clause number IS875 part2 a reduction factor should be applied on the imposed loads.
• Live load at the roof floor needs to be reduced hence 2 kN/m is applied.
• Floor finish on all the floors 1.5kN/m is applied.
• Parapet wall load as 1 KN/M
• Seismic loads should be defined so as per IS 1893 Table no. 8 importance factors should be 1.2
• Time period is calculated as per clause number 7.6.2 of IS 1893

T=0.09h/sqrtd

Tx=(0.09*16.85)/(67.7)^0.5=0.184 Seconds. Or Ty=0.09*16.85/(13.3)^0.5=0.415 sec

• Now define the load combinations
• In the next step we have to define the mass source, for that go to define and click on mass source and add on the new, click on specified load data, in the mass options click on include lateral mass and lump lateral mass at story levels, in the load pattern add multiplier 0.25 for LL and 1 for all the dead and super dead loads.
• And select all the floors and apply diaphragm D1
• In the next step we have to define for the modal cases for that go to define and click on modal cases click add new model cases select eigen and put the number of modes shape required.
• Now go to define function and click on response spectrum and add a new function in accordance with IS 1893-2016 check all the values click ok.
• Name the function as IS function, Response spectrum IS function IS 1893-2016 tab will appear check all the values Seismic zone factor soil type, importance factor click on linear x linear y click ok.
• Now go to define Load cases and click on Add new case and Add RSX and RSY.
• select the response spectrum click on Add select the function as IS function and U1 for Rx, and U 2 for RSX and IS function
• Go to define click on load combinations and click on default design combo, click on create frame design and click on convert to design combo click ok.
• Now check the model if there are any warning correct it and run the model.

Results and discussion

• Go to display then click show tables and then structural data click ok.
• Click on show tables, select the Analysis results structure output click ok.
• Select the base reaction and check the eqx eqy values, Rx and Ry value see which values are larger if the Rx RY values are lesser than the Eqx Eqy   unlock the model and then go to define load case and delete the Rx RY cases and again select the load combinations and define that again.
• Go to modal mass participation ration and check the values for U1 U2 U3 values sum of these UX Uy UZ for the first 3 modes it should be greater than 65%.
• Go to concrete frame design and select the start design or check. and note down the values of reinforcement details.
• 2.select modal participating ratios we have got that at mode 7 we have got above 90% so its ok.
• 3.now select the base reactions check that Eqx Eqy   values should be same and Rsx and Rsy values also should be at least equal to Eqx and Eqy respectively. If not then just take the rsx values and divide them by Eq values whatever the values will get that values need to be multiplied in the load cases rsx tab.
• Check for the share of shear walls, go to base level and click on reaction Ex and ey values will be available take these values and divide it be Total base shear which should be greater than 90%. If now add the shear walls in appropriate directions

• Assign the support (fixed supported) to the base level

• Go to Analyze and check model

• Run the analysis

• Run the check that all members are passed.

• Beam- longitudinal reinforcement for Ground Floor

• Beam-Shear reinforcement for ground floor

• All beams are passed
• Column - Longitudinal reinforcement

• Column - Shear reinforcement

• Hence the design is completed. Now, we need to export these Base reactions and load conditions in f2k format for footing design using SAFE software.
• Importing the software Safe
• Go to the file click on export and select the safe v12.fk.
• A tab will appear then click on the story as base and select the loads and loads from above click on the combination click ok,
• Goto SAFE and to file click import and select the file and save the file as FDB.
• Go to display click on the show loads select dead above and love above the values will be appeared.

Given data: -

• Column of size: - 650 x 650mm
• pile has a load carrying capacity of 280kN
• Pile length-16 m and dia of pile -500 mm
• SBC-150kN/m^2

1. Number of piles=Total Axial load/pile capacity=(1.5DL+1.5LL)/280= numbers
2. Piles in the springs are defined as spring so for that the spring constant is 

• K=EA/L
• E=5000(fck)^0.5=5000(25) ^0.5=25000 N/mm^2
• Area of pile =22/7*d^2=3.142*(500) ^2/4=196375m^2
• L-10000m
• K=25000*0.7855/16=306835.9N/mm==419.
• Spacing of the piles as per clause number 6.6.2 of IS  2911 the spacing between the piles =2.5dia of the piles =2.5*500=1250mm

4. Now in the next step we have to define the material properties for go to define and define the material properties of Concrete and Reinforcement properties Fe500 & Fe 415.
5. Select the values.
6. Go to define section properties and define pile caps, pile Dia , and column
7. Add new, defined pile cap pile 500 as Mat, and Column as Stiff.
8. Click on the quick draw around the plots a window will open there insert the columns sizes and these columns to their specified positions. Columns should be stated as stiff material.
9. In the next step pile caps needs to be drawn for that go to Quick draw slab command select pile caps and add it. Piles and pile caps should be described as stiff material.
10. Select the pile caps and change the rebar material to Fe 500.
11. Next go to draw and draw point and a window will open up there draw the points where piles are to be drawn.
12. Now again select the quick draw around the points there select the property circular slab add piles dia  in this case 0.5m and add to the points. Select these piles and again check for the rebar materials.
13. Now we have to define all the piles as spring for that go to define
14. select soil spring properties add new property there click on compression only and add the calculation value of K=EA/L.
15. Select all the piles and go to assign and select support data and select spring properties and assign it.
16. Go to define and select the define beam and define the tie beams whose thickness should be as of pile caps.
17. Check whether the rebar material is Fe 500 under design preferences
18. Go to define and define the load combinations sls and uls
19. Go to design and design preferences
20. Save the model and run the Analysis
21. Deformed shapes showed that deformations are negligible
22. Assign add the design strips
23. Run the analysis
24. Deformed shape all the values are less than 25 mm hence ok.
25. Now go to display and click on the punching shear the values we have got are less than 1 hence ok.
26. Now go to display and select slab design.
27. All the reinforcement details will be available
28. For X DIRECTION MIDDLE STRIP

maximum Reinforcement was

• For Top: - 29834 mm^2/m=29834/3.3=9041 mm^2=28 nos. 20 mm dia are provided
• For Bottom-13326mm^2/m=4038 mm^2=13 nos. 20 mm dia are provided

29. For layer Y direction

maximum Reinforcement was

• For Top: - 19926= 3831mm^2/m=12 nos of 20 mm dia are provided
• For Bottom-22784mm^2/m=4398 mm^2=14 nos 20 mm dia are provided