Challenge

Reinforcement detailing of Columns from ETABS output

DDijin V8 Oct 2022

AIM

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.

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.

INTRODUCTION

ETABS is an engineering software that is used for multi-story building analysis and design. Modeling 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.

Here we are analysing a given structure and detailed drawing of the column is drawn using AutoCAD.

We provide longitudinal and shear reinforcement according to the results from the ETABs analysing

PROCEDURE

Step 1:Open the given file

Step 2:Select the column

Right click-Show selected objects only

Step 3:Select 3D view

Click on the Run analyse

Step 4:Click on Concrete Frame Design button

Select elevation -select elevation 3

Step 3:Select Concrete Frame Design button

Select Display Design Info

Select shear reinforcement.

Elevation info

Step 4:Reinforcement details of column on grid 3A

Longitudinal Reinforcement

Ast max =7027 mm^2

Provide 10 number of 32 mm diameter bars

Ast=(10x 804)

=8040 mm^2

Which is greater than the Ast required

Hence ok

Anchorage length=Ld+10db

Ld = φ σst/4τ bd

τ bd value from the IS 456:2000 ,we know=2.24

So, Ld for T-32 rebar,

Ld=((32x415)/(4x2.24))

Ld=1482 mm

Anchorage length=1482+10*32

=1802mm

Shear Reinforcement

Special confinement from IS13296-2016 Clause 8.1

1)Lo should not less than

a)Larger column dimension 650

b)⅙ of clear span of column

c)450 mm

Lo is taken as 650 mm

2)Confinement spacing should not more than

a)¼ of smaller column dimension -450mm

b)6 times diameter of column main bar -6*32=192mm

c)100 mm

Taken the lower value

The values are similar for all floors ,There is no shear requirement due to loading

The minimum shear reinforcement is required as per ductility standards

Provide 8 mm lateral ties at 200 mm c/c spacing

Provide 8 mm lateral ties at 100 mm c/c spacing in confinement zones

Step 4:Reinforcement details of column on grid 3B

Longitudinal Reinforcement

Ast max =5046 mm^2

Provide 10 number of 28 mm diameter bars

Ast=(10x 616)

=6160 mm^2

Which is greater than the Ast required

Hence ok

Anchorage length=Ld+10db

Ld = φ σst/4τ bd

τ bd value from the IS 456:2000 ,we know=2.24

So, Ld for T-28 rebar,

Ld=((28x415)/(4x2.24))

Ld=1296 mm

Anchorage length=1296+10*28

=1576mm