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

Project:2_Design and Analysis of a Hostel Building at Guwahati, Assam.

Aim:

To Create and Analyse the given building in ETABS, the structural model has to be prepared in accordance with IS: 1893 & as per IS: 13920. To design the pile cap & pile reinforcement details, Tie beam connecting the pile caps, to sketch the column reinforcements, to produce the framing plan and beam detailing for ground floor.

Introduction:

• ETABS is an engineering software product that caters to multi-storey building analysis and design.
• Modelling tools and templates, code-based load prescriptions, analysis methods and solution techniques, all coordinate with the grid-like geometry unique to this class of structure.
• Creating the structural model and run the model.
• Analyze the result and note down the result values from ETABS.
• Next is to export the model to Safe software in order to design the foundations.

Objective:

• To model a Female Hostel building with all seismic considerations, based on given architectural inputs.
• Foundation details illustrating the pile & pile cap reinforcement.
• Tie beam details connecting the pile caps.
• Column reinforcement.
• Beam reinforcement for ground floor.

Given Hostel Building Ground Floor plan, First floor plan & Elevation.

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

Procedure:

Open ETABS & setup the model.

• Once the software is up & running, click on the new model option.
• Once you click on the new model, a dialogue box will pop up where you can set up the codes and units to be used in your project.

Setting up the Grid data.

• To setup the grid data, you need to click on the custom grid option.
• Once you do that, a menu with all the grid settings will open up.
• In the same menu, you can fix the length, numbers of grids in both the orthogonal directions, spacing b/w all the vertical & horizontal grids etc,
• So, by following the same approach, we have setup a display grid data as spacing, as shown below

Fixing the storey data.

• Similarly, to what we did while setting up the grids, click on the custom storey data option.
• Then, specify the base level, plinth level, height of each floor, & the no:of floors to be included in the model.
• We have arranged for a G+3 building with a 1.9m plinth ht. from bae.
• Also, you need to fix a master storey and all the similar storeys in the same menu.
• First Floor is master & all other remaining floors are similar storeys.
• Once, you do this, model is set to be executed in ETABS with the grid & storeys as specified.

3D view of Grids G+3 Residential building

Defining the Material Properties.

• It is important to set details of the materials you are going to use for the project in ETABS.
• We have to use M25 grade concrete and Fe500 HYSD steel as per the specifications.
• So, in order to define the same, go to define > material properties > add new > concrete/steel > grade > ok.
• However, since we have already specified the Indian standard codes of practices, the M25 concrete and 500 steel is added by default into the project.

M25 Concrete grade:

HYSD500 Rebar:

Defining section properties.

• We are using the rectangular concrete sections for all the structural elements like beams, columns, and slabs.
• So, we need to define that in ETABS software so that it allows us to use these sections repeatedly throughout the project.
• Go to define > section properties > frame sections > concrete rectangular.
• Then, a dialogue box will appear on your ETABS screen where you can specify the column/beam dimensions and the type of reinforcement (HYSD 500) to be used in the model.
• So, you can define both columns and beams from the same menu.
• Now, to define the slab section, again go to define > section > slab.
• Again, a menu will open up where you need to set the slab specifications required for the project.
• Here, you need to specify the slab thickness as 150mm & the section as a membrane.

BEAM 400 x 500 mm

COLUMN 450 x 650 mm.

SLAB 150 mm

STAIR SLAB 200 mm.

Execute the Modeling.

• Now that we have defined everything from materials to beams, columns & slabs to be needed for our structure, we can go ahead and draw each structural element as per the specifications.
• We can use the commands in ETABS named quick draw tool.
• As the name suggests, you can draw all the beams, floors & columns with the help of this tool.
• Select the relative tool that is quick draw columns for drawing columns and vice versa, then choose the section from the dropdown list.
• Then, simply go to the grid system in plan view and start clicking on the grid locations where you want to build these structural elements.
• So, the same approach was followed and the following beams, floors & slabs were drawn in our ETABS model.

Quick draw columns.

Quick draw beams.

Quick draw slab floors

Quick draw stair slab.

Define the load patterns.

• After completing the model, now we need to list down the types of loads that are expected on the structure during its service period.
• Go to define > load patterns > add loads.
• Here, you can add all the loads and for our project, we are having the dead load, super dead load (AAC wall load), live load & the earthquake load in x & y directions.
• Also, you need to define the mass source by adding 100% of dead & super dead load as well as 25% of the imposed or live load.

Check load cases:

Mass Source Data:

Generate load combinations.

• Go to define > load combinations > check the convertible option.
• A list of load combinations will appear which you can look at and modify anytime during the project if needed.

Assign loads to the structural members.

• You can select a particular structural member from the model and assign it the load that is imposed on it.
• For example, select the beam and assign a UDL of super dead load due to the brick wall resting upon it.
• Go to define > load combinations > check the convertible option.
• A list of load combinations will appear which you can look at and modify anytime during the project if needed.

3.5 KN/m brick wall load on beams

• Wall made of AAC blocks.

3 KN/m² Live load on Corridor,Toilet & Stair case area.

• Live loads as per IS 875 part 2

2 KN/m² Live load on Floor slabs.

• Live loads as per IS 875 part 2

1.5 KN/m² Finishes on First to Third Floor slabs.

1 KN/m² Finishes on Terrace Floor slabs.

Live load Reduction 10%.

• Now we add the reduction factor by decreasing 10% from first floor to seventh floor, as shown below.as per IS 875 part 2

Check the Model.

Function of Response Spectrum.

• Now, we select the response spectrum from define > function > response spectrum.
• After selecting the RS, the new tab is visible, in that we choose IS 1893-2016, ''choose function type'' & click on modify/show spectrum option, as shown below.

Load case data in Response Spectrum.

In x-direction RSx, as shown below

In Y-direction RSx, as shown below.

Assign the floor diaphragm

• Select the Slab150 slab section from the select option.
• Go to assign > shell > diaphragm.
• Select the default D1 diaphragm already incorporated in ETABS and press ok.
• It is now done, and you can see the center of mass for our model has been automatically calculated as we assigned the floor diaphragm.

Save the Model and Run Analysis.

• Now that everything with regards to our first model is complete, we can proceed to run the analysis for this building.
• But we’ll have to first save our project before running the analysis so do it at the preferred location within your system.
• Then, you can simply press F5 on your keyboard or click on the arrowhead available on the ETABS screen to run the analysis for the current model.

Modal Response for G+3 Building.

• Base reactions table as shown above.
• Here we have to check that EQ should be closer to RS to get the closer to each other, we should calculate that, (EQ / RS)x scale factor of RS.
• Now substituting the values from the table, as x-direction (3819 / 37205)x(9806.65), at y-direction (3819 / 37300)x (9806.65) from the above table..
• At x-direction we get, 1006.0
• At y-direction we get, 1004.0
• we put the above values as scale factor for RS at x & y-directions in the load case data, as shown below.

Load case data in Response Spectrum.

In x-direction RSx, as shown below

In Y-direction RSx, as shown below.

Modal Response for G+3 Hostel Building. We get.

• After we enter these for response spectrum as scale factors at x & y-directions in load case data, then the EQ is closer to the RS from the base reaction table, as shown below.

• The shown Principal modes to be greater than torsional mode
• Therefore, modal 1 & 2 is greater than modal 3, Hence Achieved.

• Modal mass ratio in x-direction 0.013 + 0.86 = 0.813.
• Hence 65% is achieved in x-direction.

Maximum storey drift ratio EQx & EQy.

• Display > storey response plots.
• In display type > check max storey drifts
• In case/combo> check EQx & EQy, as shown below.

• As we can check in EQx, maximum storey drifts is 0.004.
• As we can check in EQy, maximum storey drifts is 0.004.
• Hence inter storey drifts ratio is limited wthin 0.004.

Concrete Frame Design:

BEAM DESIGN:

Longitudinal Reinforcement of Beam at Grid-N.

Shear Reinforcement of Beam at Grid-N.

1). For Sway Shear Force Right 2). For Sway Shear Force Left

Design moment values from Etabs.

Shear Force values for selected beam from Etabs,

As per IS 13920 1.2 loading applied for (DL+LL).

SF value at point A SF value at point B

As per IS 13920-2016 clause 6.3.3 (b)

Mas = 368.18 KN-m Mah = 374.15 KN-m

Mbh =374.82 KN-m Mbs =367.78 KN-m

L ab = 2.20 m Lab = 2.20 m

Vu,a(d+l) = 6.32 Vu,b(d+l) =6.87

Vu,a = 331.4 KN Vu,a = 465.81 KN

Vu,b = 344.6 KN Vu,b = 479 KN

Grid N_At TOP

• Maximum Ast at support = 2398
• Maximum Ast at middle = 1104
  • 3 # of 25 mm = 1473
  • 3 # of 20 mm = 942

• Therefore, to satisfy the support we need to provide 3# of 25 mm bar and additionally in the middle need to provide 3# of 20 mm.

Grid N_At BOTTOM

• Maximum Ast at support = 2349
• Maximum Ast at middle = 1124
  • 3# of 25 mm = 1473
  • 3 # of 20 mm = 942

• Therefore, to satisfy the support we need to provide 3# of 25 mm bar and additionally in the middle need to provide 3# of 20 mm.

• As per clause 6.3.3 the design force of equivalent Ve = 507.9 KN.
• Shear force under the linear analysis as per the load combination of UD cons23 = 351.07 KN.

Beam Reinforcement details.

Beam-@ Grid-N.

Beam c/s.

Shear capacity in beam as per drawing:

(As per IS 456-2002 clause 40.4)

Fy = 415 N/mm2

Asv = 151 mm2

d = 650 mm

Sv = 100 mm

Vus =354.37 KN-m.

COLUMN DESIGN:

Longitudinal Reinforcement of Column at Grid-3N.

from Etabs (450x650):

Shear Reinforcement of Column at Grid-3N.

GRID 3N:

Calculation for Longitudinal Reinforcement:

• From base to first floor the maximum Ast is = 7983 mm²

= 7983 / 10 = 793 mm²

= Considering 32 mm dia = Ast = 804 mm²

• So, we can provide 10# of 32 mm dia Longitudinal bar= 10 x 804 = 8040 mm²

Calculation for Shear Reinforcement:

• From base to first floor the maximum shear value is = 720 mm²

=(1000/Sv) X L x Ast

= 1000/200 x 2 x 78.55

=785.5 mm²

• So, we can provide 10mm dia @200 mm spacing shear.
• Therefore, it can be satisfied the entire span.

Elevation & Cross sectional details of Column using AutoCAD:

Foundation Design using Importing from Etabs file.

Procedure:

Given.

Column size = 450 x 650 mm

Unfactored load = 450 KN

Pile length = 10m

Pile diameter = 500 mm

Load carrying capacity = 280 KN.

Calculations.

Number of pilers = 450 / 280 = 1.60 = 2Nos.

Spring constant = ExA / L

Where, E = 25000 N/mm²

A = `(pi/4)`(500)² = 196375 mm²

L = 10000 mm

Spring constant =25000 x 196375 / 10000=490937.5 N/mm or 490937.5 KN/m

Edge spacing is taken as 300 mm.

• Material property data:

Click define > material properties >M25 grade of concrete.

Modulus of elasticity

E = 25x5000 = 25000 N/mm²

Fe 500 rebar was added next as shown below.

• Define Slab properties.
• Define pile cap/Footing.

• Define Column.

• Define pile_500 dia details.

• Define spring property data, as shown below.

• Add piles at the point
• Modify the edge distance to 0.2m
• Create a column of 450 x 650 mm, as shown below.
• Draw the column in center using quick draw tool

• Select pile > assign > support data > point springs.

• Springs constant is taken from above calculation.

• Load case combination was define, as shown below.

• After defining the load combination Run the analysis.

• Max displacement was found as shown, So its Safe.
• Reinforcement details are added next as shown in both X & Y-direction.

• Reinforcement Slab Design.

• Reinforcement shown in cab.

• Pile beam Reinforcement.

RESULT.

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