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Re: Box Culvert Design

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        The reason for the minimum steel requirement is to prevent a fracture failure at the formation of the initial crack.  You can develop this analytically using a triangular stress distribution and the tensile strength of unreinforced concrete as follows:

                b*d*F(tc)/4 < As*Fy.

Of course you will want to add reliability and safety factors to this to get your final answer.

        But tell me, considering the small cost of a little extra rebar compared to either the large cost of the project as a whole or the very large cost of a failure do you really want to design the secondary reinforcing that tight?


H. Daryl Richardson

À̼º¸é wrote:

I am working on the design of box culvert passing under the railway and vehicle road. The box culvert is used for the channel irrigating the cooling water for power plant. In analysis of the box culvert, the culvert is simplified into frame structure with 1 foot strip in breadth of member. Of course, the structural analysis of the frame was done by SAP 2000 software. The roof, base slab, and walls of the frame undergoes both the axial and flexural loads based on the result of the structural analysis. In the reinforcement of the culvert, the ACI 318 code has many different minimum steel ratios for the specific structural members. For example, the minimum reinforcement for the flexural member is about 0.0035. For the slab, that is 0.0018. For the wall, the minimum reinforcement is 0.0015 in the vertical bars.  And that in the horizontal bars of the wall is 0.0025. Actually, the roof, walls, and base slab fo the culvert can be reinforced following the above three ways. I think that it is important to decide how the members behave under the design loading condition. If the members of the culvert under the design loads behave like beams, the minimum reinforcement for the member should comply the beam requirements of the ACI 318. Please help me make a choice the one among three cases on the basis of the member behavior. According to the AASHTO, they recommends that the minimum steel raito for the elements of the culvert is 0.0025. I am really looking forward to your reply. Thanks in advance.