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

Aim

• To run the anlaysis and design the RCC Shear walls for the given ETABS model.
• To extract the values of longitudinal steel ratio, boundary element length and shear reinforcing ratio from the design results.
• To provide the cross sectional steel arrangement of shear wall from its case up to terrace, in compliance with provisions of IS13920-2016
• To provide elevation drawings of reinforcement details of the shear wall from base to terrace.

Introduction

This model is crated using etabs and the deatils are explained in detail.

Shear wall

A shear wall consist of a web and boundary elements at either sides.This boundary elements in shear walls are subjected to alternate compression and tension when it is subjected to lateral force(EQ), hence it is neccessary to provide special reinforcement for the boundary elements.

Procedure

• open the given etabs model in attachement
• in analysis tab and check the model.
• After that run the analysis.

• the analysis is completed we need to carry out the design of the shear wall, for this go to shear wall design.
• again we need to start the design.
• the design is completed go to display design option.
• Then we have checked for any failures in the design.
• Now, we need to extract certain values from the design.
• Go to display design info --> pier longitudinal reinforcing.

• Go to display design info and click pier reinforcing ratios.

• Go to display design info and click pier edge/boundary zone width.

• Go to display design info and click pier shear reinforcing .

• we need to draft the details of a RC wall in AutoCAD for the wall for A11.

Shear wall detailing calculations:

Here, the total height of the wall is 21000mm and the width of the wall is 1500mm.

Hence, the ratio is obtained as `21000/1500=14`which is greater than 2 hence, it can be considered as a slender wall.

Maximum diameter of the bar that can be used from IS code = 1/10th of thickness of that part = 30mm

Hence, we take the dia of bar as 25mm.

Maximum spacing between the bars should not exceed the minimum of the following:

a) 1/5 x 1500 = 300mm

b) 3x300 = 900mm

c) 450mm

Hence, the maximum spacing is limited to 300mm.

Shear Wall Calculations:

IS 13920-2016 provides guidelines on several aspects of shear wall detailing.

• Thickness of wall (clause 10.1.2)
• Minimum ratio of wall length to thickness (clause 10.1.3)
• Largest diameter of longitudinal steel bar (clause 10.1.8)
• Maximum spacing of horizontal and vertical reinforcement (clause 10.1.9)
• Conditions for base of shear wall (clause 10.1.10)
• Minimum reinforcement in RC shear wall (clause 10.1.6)

From clause 10.1.4, walls can be categorised as squat walls, intermediate walls andf slender walls as given below:

Now the minimum shear reinforcement in boundary element of RC shear wall can be determined from the formula;

• Base floor to First floor:

Lets assume a Slender wall since height/length ratio is greater than 2.

That is, we have , height of the wall,H = 2100mm and Length of the wall,L =1500mm. Thickness , T = 300mm

P_{h = 0.0297*1500*300 =13365}

Now, Minimum Horizontal Reinforcement ,(P_h)_min = 0.0025 + 0.5 ( H/L- 2) (P_h- 0.0025) = 0.76

Minimum Vertical Reinforcement ,(PV)_{min = 0.0025 + 0.01375 (T/L) = 0.0052}

Longitudinal reinforcement

in ETABS, the required Rebar Area = 13128 mm²

Minimum Vertical reinforcement , P_v = 13128/ (1500*300) = 0.0297 > 0.0080

From IS 13920:2016,

Assuming minimum number of bars as 8, thus A_sh = 50.24mm²

50.24 = 0.05*100*H * (25/100)

Therefore, H= 200.98

Considering 25mm dia bars, Number of bar = 13128/ area of 25mm dia bars = 13128/490.87 = 28 bars

Therefore, 28 number of 25mm dia bars are provided

Shear Reinforcement

Assuming 2 legged 8 mm dia bars at 100 mm c/c

A_sh= 2* 8mm dia bar/ 0.100 = 1005.3 > 750mm²

Hence the shear reinforcement is okFirst floor to Second floor:

Longitudinal reinforcement

Using ETABS, the required Rebar Area = 8273mm²

Minimum Vertical reinforcement , P_v = 8273/ (1500*300) = 0.018 > 0.0080

From IS 13920:2016,

Assuming minimum number of bars as 8, thus A_sh = 50.24mm²

50.24 = 0.05*100*H * (25/100)

Therefore, H= 200.98

Considering 20mm dia bars, Number of bar = 8273/ area of 20mm dia bars = 26 bars

Therefore, 26 number of 20mm dia bars are provided

Shear Reinforcement

Assuming 2 legged 8 mm dia bars at 100 mm c/c

A_sh= 2* Area of 8mm dia bar/ 0.100 = 1005.3 > 750mm²

Hence the shear reinforcement is ok

Second floor to Terrace:

Longitudinal reinforcement

Using ETABS, the required Rebar Area = 4896 mm²

Minimum Vertical reinforcement , P_v = 4896/ (1500*300) = 0.01 > 0.0080

From IS 13920:2016,

Assuming minimum number of bars as 8, thus A_sh = 50.24mm²

50.24 = 0.05*100*H * (25/100)

Therefore, H= 200.98

Considering 16mm dia bars, Number of bar = 8273/ area of 16mm dia bars = 26 bars

Therefore, 26 number of 16mm dia bars are provided

Shear Reinforcement

Assuming 2 legged 8 mm dia bars at 100 mm c/c

A_sh= 2* Area of 8mm dia bar/ 0.100 = 1005.3 > 750mm²

Hence the shear reinforcement is ok

Result:

• Hence the values of longitudinal steel ratio and shear reinforcing ratio from the design results is done.
• The cross sectional steel arrangement of shear wall from its base up to terrace, in compliance with provisions of IS13920-2016 has been drafted after appropriate calculations.
• The elevation drawings of reinforcement details of the shear wall from base to terrace has also been drafted in autocad.