| Applies To | |||
| Product(s): | STAAD Advanced Concrete Design | ||
| Version(s): | Connect Edition | ||
| Environment: | |||
| Area: | Concrete Design | ||
| Subarea: | Beam Design | ||
| Original Author: | Aaradhya Rahate, Bentley Technical Support Group | ||
RCDC is providing steel for beams in several layers of 12mm dia. for some beams. Instead of using greater diameter of bar and less number of layers, software is providing all layers with T12 bars.
This scenario happens when we select ductile design for beams. As per IS13920:2016 clause 7.1.1 (a) the minimum dimension of column shall not be less than 20Db where Db is the largest diameter of longitudinal bar in the beam passing through or anchoring at the column.
In RCDC as we design every element type in different module, this check was not available earlier. In recent updates we have provided this check in beam module. So, now the highest reinforcement dia permissible in beam is not greater than column dimension in the direction of beam spanning /20. So, if the dimension of column is 300mm, maximum allowable bar dia is 300 /20 = 15mm. But as 12mm and 16mm are the diameter available practically, we will use 12mm dia. If you want to use higher diameter rebar then you need to increase the size of column.
This point has been discussed with the professor who is on panel of IS code committee. They have confirmed that the this clause is applicable to reinforcement passing through or anchorage in to column and wall at the joint. Refer commentary available in clause 18.18.2.3 of ACI 318M-2019 for the same requirement.
As per the logic, this clause should be applicable to all ductile beams resting on column or wall.
Wall is also part of lateral load resisting frame. If beam is ductile and resting on wall, it will participate in the lateral load resisting frames thus clause 7.1.1 is applicable. the requirement of this clause is to make sure that the during earthquake straight longitudinal beam bars should not slip within beam column / wall joint during a series of large moment reversals. For beam resting on shorter direction of the wall generally doesn't participate as lateral force resisting frames due to less wall stiffness along that direction. If you are expecting that the beam resting on shorter direction should participate as lateral frame along that direction then clause 7.1.1 should be applicable. It is suggested that the beam resting on shorter direction of wall shall be treated as Non-ductile / Gravity type so that clause 7.1.1 is not applicable.
This is not clearly mentioned in the code however it is confirmed by code committee members several times during presentation on IS 13920-2016. This might update in the Amendment 2 of IS 13920-2016.
Regarding the other codes, the relevant clause numbers are shown below for your ready reference.
You may refer the below video as well to understand it.