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Top bars vs other bars splice length

Top bars vs other bars splice length

Top bars vs other bars splice length

Hey all,

According to ACI 318 - Section 3 Method of splicing, top bars are horizontal bars with more than 12 inch of concrete underneath.
As per the chart, the top bars have a greater splice length then the bottom bars (other bars?). Can anyone explain why that is? Why do the bottom bars (other bars ) have a shorter splice ? If they're primarily going to be in tension shouldn't it be as conservative as the top bars?
Am i reading the chart wrong?

Thanks in advance !

RE: Top bars vs other bars splice length

Concrete below the beam top reinforcement is prone to issues such as settlement and bleeding of the fresh concrete mix which eventually results into a weaker bond. Therefore, as per ACI, any reinforcement with more than 12 in of concrete below it required more development length to transfer the same stresses.

RE: Top bars vs other bars splice length

It's also due to the air entrained in fresh concrete migrating upwards when there is more than 300mm of fresh concrete cast below the bars. This air effects the bond available for bar development, hence the longer splice lengths.

RE: Top bars vs other bars splice length

thank you for the responses !

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