How to determine if a slab is restrained for fire cover requirements
How to determine if a slab is restrained for fire cover requirements
(OP)
2006 IBC, Tables 721.2.3(1)-(5) deal with the increased cover requirements for fire protection. The tables provide separate requirements depending if your slab is restrained or unrestrained.
My case is a 7 span, two-way flat plate analysis. The end span is 30'-10" but is supported by a full length (equal to tributary width or slab analysis) 12" c.i.p. concrete shear wall. The joint will be detailed to make the slab/wall act monolithic.
Q1: Would you all consider the shear wall as restraining the slab for cover requirements?
Q2: How do you determine whether something is a restraint? Is it a thrust force applied to the top of the wall and the wall can't deflect a certain amount? If so, how is the thrust force determined and how much deflection is too much?
Thanks in advance.
My case is a 7 span, two-way flat plate analysis. The end span is 30'-10" but is supported by a full length (equal to tributary width or slab analysis) 12" c.i.p. concrete shear wall. The joint will be detailed to make the slab/wall act monolithic.
Q1: Would you all consider the shear wall as restraining the slab for cover requirements?
Q2: How do you determine whether something is a restraint? Is it a thrust force applied to the top of the wall and the wall can't deflect a certain amount? If so, how is the thrust force determined and how much deflection is too much?
Thanks in advance.






RE: How to determine if a slab is restrained for fire cover requirements
RE: How to determine if a slab is restrained for fire cover requirements
RE: How to determine if a slab is restrained for fire cover requirements
For fire protection, a "restrained" condition is one that is prevented from expanding. An "unrestrained" condition is one that is free to expand. Generally, interior bays are restrained and exterior bays are unrestrained.
The UL book has clear definitions. Also ASTM E-119.
RE: How to determine if a slab is restrained for fire cover requirements
We can apprecciate the stabilization given by just small variation of the lengths between columns, this would had more to do with linear expansion and is still a true factor in general stability. It is scarcely affected by cover, except a mechanism forms. So, I still see, for a RC framed structure, this is of lesser impact on stability than hinge formation (and subsequent to it).
RE: How to determine if a slab is restrained for fire cover requirements
I believe this has a lot to do with the floors above and below as well. If it is a lower floor in a 10 story building, there is going to be a lot of compression in the wall that will help with the restraining capacity but may result in a snap-through bifurcation if the thrust force is large enough. If the restraint is at the roof, the wall will act as a cantilever and not be as stiff even though the wall thickness may not change.
ishvaaag, jike is correct. Restrained/unrestrained has to do with the ability to limit the expansion, not with the rotation of the ends.
Thanks guys. Judging by the answers, this apparently is another area the Code needs improvement/direction/clarification.
RE: How to determine if a slab is restrained for fire cover requirements
In your case, your cover requirements for an unrestrained end span may control.
I have heard many recommendations from PTI suggesting that end spans in concrete construction is unrestrained.
AISC's research has suggested that all steel construction can be considered to be restrained, including end spans with simple connections.