R.C Column with Two layers of Reinforcement

[Ahmed A. Alamin]

Hi, i came across R.C column which is reinfirced in two layers. Is this allowed? How the inner layer contriibutes? and if it's allowed could someone recommend some references or resources that discuss this. #See attached pic

 

[bugbus]

You could have two or more layers, same as for a beam. Column from the (collapsed) Hanshin Expressway in Kobe below with 3 concentric rings of reinforcement. (I'm not suggesting that this was the reason for the collapse, by the way).

 

[BridgeSmith]

The second layer is not as effective for bending as the outer layer. It was most likely done to provide the necessary bending strength, while maintaining the required clearance between bars for consolidation of the concrete.

Rod Smith, P.E., The artist formerly known as HotRod10