Reinforcement detailing of Columns from ETABS output

Reinforcement detailing of columns in Etabs 2018.

The ETABS file for a G+4 building is provided. Run the analysis and design the RCC Moment Resisting Frame. The following challenge deals specifically with two columns at the following grid intersections.

1. 3A
2. 3B

• Provide details of longitudinal reinforcement for the two columns, from foundation to terrace level. Sketch the column cross sectional & elevation details or draft it using autocad software.
• Show shear reinforcement & lapping details as per special confining reinforcement provision of clause 8.1 of IS 13920 - 2016.

Aim: to provide details of longitudnal reinforcement for the two columns from foundation to terrace level.Also calculate the special confining reinforcement based on clause 8.1 of IS 13920-2016.

Procedure:

• After downloading the model given on the question,open the ETABS software and open the downloaded model.
• Click on view and revise preferences.Check all the design codes are correct or not.
• Analyze and check the model.

• Analyse and run analysis,
• Using the above toolpath,the given model is checked for its error and warnings.The model found to be ok.
• Analysis is complete.
• Now click on design preferences and click on ok.

• Click on design combinations and click on ok.

• Now click on desgin and verify all members as passed.
• Design>display design info>flexural reinforcement
• Design>display design info>shear reinforcement

• With view selected objects only toll the two columns Grid 3A and 3B are views.

• Longitudinal Reinforcement

• Using the above toolpath the model is verified for all members satisfy design criteria.The design flexural reinforcement and shear reinforcement are noted from design output for requested RC columns.

a) Longitudnal reinforcement for the two columns from foundation to terrace:

Grid A

• From base to ground Ast=7027 sq.mm
• Area of 34mm dia bar=907
• Ast/area of reinforcement
• 7027/907=7.74 Appprox-8
• So we can provide 8 bars of 35mm=8 x 907 = 7256 sq.mm which is ok

• From ground to first Ast=6926 sq.mm
• Area 34mm dia bar=907
• Ast/area of reinforcement
• 6926/907=7.6 Approx-8
• So we can provide 8 bars of 32mm=8 x 907 = 7256 sq.mm

• From first to Second Ast=4800 sq.mm
• Area 32mm dia bar=804
• Ast/area of reinforcement
• 4800/804 =5.97 Approx-6
• So we can provide 6 bars of 32mm=6 x 804 = 4824 sq.mm

• From Second to Third Ast=4213 sq.mm
• Area 32mm dia bar=804
• Ast/area of reinforcement
• 4213/804 =5.24 Approx-6
• So we can provide 6 bars of 32mm=6 x 804 = 4824 sq.mm

• From Third to fourth Ast=3525 sq.mm
• Area 32mm dia bar=804
• Ast/area of reinforcement
• 3525/490 =7.12 Approx-8
• So we can provide 8 bars of 32mm=8 x 490 = 3920 sq.mm

Grid B

• From base to ground Ast=4218 sq.mm
• Area 32mm dia bar=804
• Ast/area of reinforcement
• 4218/804 =5.24 Approx-6
• So we can provide 6 bars of 32mm=6 x 804 = 4824 sq.mm

• From base to ground Ast=4942 sq.mm
• Area of 34mm dia bar=907
• Ast/area of reinforcement
• 4942/907=5.44 Appprox-6
• So we can provide 8 bars of 34mm=6 x 907 = 5442 sq.mm which is ok

• From ground to first Ast=5046 sq.mm
• Area of 34mm dia bar=907
• Ast/area of reinforcement
• 4942/907=5.44 Appprox-6
• So we can provide 8 bars of 34mm=6 x 907 = 5442 sq.mm which is ok

• From Second to Third Ast=4858 sq.mm
• Area of 34mm dia bar=907
• Ast/area of reinforcement
• 4942/907=5.44 Appprox-6
• So we can provide 8 bars of 34mm=6 x 907 = 5442 sq.mm which is ok

• From Third to fourth Ast=4902 sq.mm
• Area of 34mm dia bar=907
• Ast/area of reinforcement
• 4942/907=5.44 Appprox-6
• So we can provide 8 bars of 34mm=6 x 907 = 5442 sq.mm which is ok

b) Calculation of special confining reinforcement:

As per clause 8.1 of IS 13920-2016,the special confining reinforcement is calculated:

As per the clause 8.1 section a,the confing reinforcement length lo should be least of

i) larger dimension of frame member(650mm)

ii) 1/6th of clear span(591mm)

iii) 450mm

So maximum of three is 650mm so Lo=650mm.

Now for the maximum spacing of confining reinforcement:

As per clause 8.1 section b the maximum spacing of confining reinforcement shall be:

i) 1/4th of minimum member dimension(112.5mm).

ii) 6 times of smallest longitudnal bar ( 108mm).

iii) 100mm

So maximum shear link spacing maintained=100mm

So minimum special confining reinforcement should be maximum of

Ash= 631 sq.mm/m

Ash= 337 sq.mm/m

Required minimum special confining reinforcement at joint Ash=631 sq.mm

Now provide shear reinforcement at joint = (1000/100)X4 legs Xarea of 8mm dia rebar(50.3 sq.mm)=2010 sq.mm

Conclusion: Detailing of two RC columns were done using AutoCAD and special reinforcement is verified with respect to IS13920 clause 8.1.