Analysis & Design of RCC shear walls in the model using ETABS

QUESTION:

The tabs file for a G+6 building is provided. Run the analysis and design the RCC shear walls (shown in the tabs model). The following challenge deals specifically with the shear wall of size 300x1500 at grid A-11 in the structural model.

• Extract values of longitudinal steel ratio, boundary element length, and shear reinforcing ratio from the design results.
• Provide cross-sectional steel arrangement of the shear wall from its base up to the terrace, in compliance with provisions of IS 13920 – 2016. AutoCAD application can be used for this exercise. Alternatively, it can be drawn by hand as well.
• Provide elevation drawings of the reinforcement details of the shear wall from the base up to the terrace.

ANS:

AIM:

• To Extract values of longitudinal steel ratio, boundary element length, and shear reinforcing ratio from the design results.
• To provide a cross-sectional steel arrangement of the shear wall from its base to the terrace.
• Use the AutoCAD application for this exercise, which can also be drawn by hand.
• To provide elevation drawings of the reinforcement details of the shear wall from the base up to the terrace.

INTRODUCTION:

• Shear walls are vertical elements of the horizontal force-resisting system.
• They are constructed to counter the effects of lateral load acting on a structure.
• When shear walls are designed and constructed correctly, they will have the strength and stiffness to resist horizontal forces.
• Shear walls are essential in high-rise buildings subjected to lateral wind and seismic forces.

PROCEDURE:

STEP: 1

• Open Challenge and download the attached file
• open it in the tabs 2018.
• Go to the tool ribbon and select analyze < run analysis.
  
  

• The 3D view is as shown below:

Extract values of longitudinal steel ratio, boundary element length, and shear reinforcing ratio from the design results of a shear wall at grid A11

• Fig A shows the plan of the given G+6 structure having located the grid A11 shear wall.

Fig A: Plan of G+6 structure in Etabs locating shearwall of grid A11.

• Now check for Piers, and go to Display options icon > Other assignments> check the Labels under Pier as shown in fig A1. We can see that Piers are assigned, and the piers labeled for Grid A11 shear wall are P1.

Fig A1: Check for Piers.

• First, as usual, let's run the analysis to achieve different results. Once the studies are done, click on the design shear wall icon, as shown in Fig B, to complete all the shear wall designs.

Fig B: Shear wall design

• To extract values of longitudinal steel ratio, click on the dropdown box of shear wall design> Display design info. As shown in Fig C.

Fig C: Display design info.

• Now select Pier reinforcement ratio for data output and click on apply, and we can see the reinforcement ratio value is extracted on the shear wall of grid A11.
  • As per the etabs design, the shear wall's reinforcement ratio is as follows.

• For the shear wall from the base - the Ground floor is 2.92%

  For shear wall from the Ground - 1st floor is 1.84%

  For shear wall from the 1st floor-2nd floor is 1.09%

  For shear wall from the 2nd floor - 3rd floor is 0.57%

  For shear wall from the 4th floor - 5th floor is 0.48%

  For shear wall from the 5th floor - 6th floor is 0.47%

  For the shear wall from the 6th floor - Terrace is 0.48%

From the above result, we must provide the highest reinforcement ratio throughout the structure for better efficiency. Here we will provide 2.92% of longitudinal support, which reinforcement area would be Ast = 300x1500x2.92%= 13140 mm2

Check for the safety of longitudinal reinforcement designed in Etabs as per IS 13920 -2016 Table 1, page no 15

As per the code, the wall is identified as thin walls since the hw/Lw >2 (21/1.5= 14).

Hence the net minimum vertical reinforcement is shown in Fig D1.

Fig D1: Slender wall min vertical reinforcement formula.

The minimum required longitudinal reinforcement is 0.0025+0.01375(300/1500)=0.00525, i.e., around 0.525%, which would be Astreq = 300X1500X0.525%=2362.5mm2.

Since Etab designed Ast is more significant than min required Ast. Hence it is safe.

And as per clause 10.4.2.1, the vertical reinforcement shall not be less than 0.8% and more than 6%.

Min vertical reinforcement for the left boundary element is 600X300X0.8% = 1440 mm2

Min vertical reinforcement for the right boundary element is 450X300X0.8% = 1080 mm2

Hence safe.

• Now, to extract the length of boundary elements of the shear wall, select the design output as Pier Edge/ Boundary zones widths in Display shear wall design results and click on apply as shown in fig E.

As per Etab's design, Shear reinforcement of 750 mm2 / m will be provided throughout.

As shown in Fig G, could you check for shear reinforcing according to IS 13920 - 2016?

Fig G: Min horizontal reinforcement

Min horizontal reinforcement = 0.0025 + 0.5 ((21000/1500)-2) ((750/300X1000)-0.0025) = 0

Hence provided reinforcement design is as same as min shear reinforcement. Hence it is satisfied.

• Max dia of the bar to be provided per IS 13920 2016 clause 10.1.8 is shown in Fig H.

Fig H: IS 13920 2016 clause 10.1.8.

Largest diameter = 300/10 = 30

We can provide a full 25 mm dia bar as per commercial provision.

• With all the details above, Fig I shows the Cross-section details of the shear wall with detailed reinforcement, and Fig J shows the elevation of the support of the shear wall.