Concentrated Load on Existing Composite Slab
Concentrated Load on Existing Composite Slab
(OP)
I have come across many threads on this site regarding concentrated loads on composite slabs. But I have a slightly different twist on things on which I am hoping to get opinions. I have reviewed the concentrated load example in various deck catalogs as well as reviewed the information in SDI’s Standard for Composite Steel Floor Deck Slabs. For my particular case, much is known about the existing composite slab because I have existing drawings. The one thing that I am not confident about is the concrete cover dimension over the welded wire reinforcement.
When analyzing the slab for a known concentrated load over a known contact surface area, the slab has enough capacity for strong axis moment, one-way shear, and punching shear. The only limit state in which capacity is exceeded is weak axis moment. I am hesitant to proceed with a slab strengthening remediation to the existing slab solely for this lone limit state not meeting the required demand.
If I were to assume zero welded wire fabric in the slab and analyzing the weak axis direction as plain concrete also does not provide sufficient capacity. The equations and notes in the deck catalog example and SDI Standard do not state that the distribution of the concentrated load in the directions parallel (W) and perpendicular (be) to the flutes vary with or without WWF. Although I agree that distribution steel helps.
So even if the weak axis moment demand exceeds capacity, how will this really impact the slab? If this causes the slab to crack parallel with the flutes, the slab will act even more like a one-way slab. Anyway, I’ve spent significant time pondering this issue and would appreciate any opinions/advice from others. Thanks in advance!
When analyzing the slab for a known concentrated load over a known contact surface area, the slab has enough capacity for strong axis moment, one-way shear, and punching shear. The only limit state in which capacity is exceeded is weak axis moment. I am hesitant to proceed with a slab strengthening remediation to the existing slab solely for this lone limit state not meeting the required demand.
If I were to assume zero welded wire fabric in the slab and analyzing the weak axis direction as plain concrete also does not provide sufficient capacity. The equations and notes in the deck catalog example and SDI Standard do not state that the distribution of the concentrated load in the directions parallel (W) and perpendicular (be) to the flutes vary with or without WWF. Although I agree that distribution steel helps.
So even if the weak axis moment demand exceeds capacity, how will this really impact the slab? If this causes the slab to crack parallel with the flutes, the slab will act even more like a one-way slab. Anyway, I’ve spent significant time pondering this issue and would appreciate any opinions/advice from others. Thanks in advance!






RE: Concentrated Load on Existing Composite Slab
RE: Concentrated Load on Existing Composite Slab
I agree that composite deck slabs are only considered in one direction. But following the concentrated load example in the deck catalog and the requirements of SDI (2017 version currently on their site), one of the design checks is for the weak axis moment of the slab (perpendicular to the ribs). This is the check that I am struggling with. I haven't been able to find a basis for this equation. Neither the catalog example nor the SDI Standard are going to state that this design check can be overlooked, but in reality, can it?
RE: Concentrated Load on Existing Composite Slab
RE: Concentrated Load on Existing Composite Slab
Dik
RE: Concentrated Load on Existing Composite Slab
Concentrated Load example - https://www.canam-construction.com/wp-content/uplo...
SDI Composite Slab Standard - http://www.sdi.org/publications-2/standards/, (you enter your email address and they send you a link to download); section 2.4.B.11.b, page 15.