Fire fighters have wondered if the roof support system in tilt-up buildings burned down, would the walls collapse? They didn't in March 1986 when a severe fire in a Phoenix tilt-up building consumed the entire wood roof system. The building, a U.S. postal annex built around 1970 was constructed of 5.5-inch-thick tilt-up concrete walls with a wood roof system. The plywood roof deck was connected to a ledger consisting of a 6 by 8.2 steel channel with a wood nailer attached. After the fire, all that remained of the roof system was the middle one-third cross section of the laminated girders. The walls deflected out 6 to 8 inches on the north, west, and south sides of the building. Aggregate popouts and large panel deflections suggested a very hot fire.
Too many times I have been called to look at some problem only to find that the specifications virtually guaranteed the poor result.
