07-04-2010, 09:38 AM
The reduction of I is not a code matter. No code can force you to use I for cracked or I for uncracked section (I don't refer to seismic codes). If we make the assumption that the section is uncracked (I is 100%) then the reinforcement stress will be a lot smaller than the yielding stress of the reinforcement. As an example: for a section 300x700mm, with 4x20mm bars as bottom reinforcement the cracking moment (the maximum moment for stage I behavior of the section-uncracked concrete is 60 kNm; the yielding moment of the section is 299 kNm, while the ultimate moment is 306 kNm).
So if somebody wants to use I for the uncracked section for ULS design, then the reinforcement computation must be taking into account the fact that the reinfrocement stress is a lot smaller than the yielding stress. Otherwise the section capacity should be computed using I for the cracked section.
So if somebody wants to use I for the uncracked section for ULS design, then the reinforcement computation must be taking into account the fact that the reinfrocement stress is a lot smaller than the yielding stress. Otherwise the section capacity should be computed using I for the cracked section.