I am currently working on a project with a prestressing / precasting fabricator to design roof beams for a large warehouse type building. The conceptual detail shown on the contract plans was for 48"wide x 33" deep voided rectangular adjacent box beams similar to many bridge structures. Majority of my experience is in bridge design and the design program I'm most familiar with is PennDOT/AASHTO based (PSLRFD).
Reviewing the design generated with that program, I found that the AASHTO cracking moment requirement (1.2*Mcr) was satisfied, but when back-checking against the ACI / PCI codes (both cited in the contract docs), I calculated an Mcr that was approximately 40% higher than what AASHTO calculates. This has BIG implications on the design and the amount of P/S steel in the beams. Any insight as to why the Mcr value prescribed by ACI and PCI (not identical but similar) is so much higher than that required by AASHTO? Or maybe my calculations / interpretation of the codes are incorrect?
Thanks!
Reviewing the design generated with that program, I found that the AASHTO cracking moment requirement (1.2*Mcr) was satisfied, but when back-checking against the ACI / PCI codes (both cited in the contract docs), I calculated an Mcr that was approximately 40% higher than what AASHTO calculates. This has BIG implications on the design and the amount of P/S steel in the beams. Any insight as to why the Mcr value prescribed by ACI and PCI (not identical but similar) is so much higher than that required by AASHTO? Or maybe my calculations / interpretation of the codes are incorrect?
Thanks!
