DCEngr1
Structural
- Feb 14, 2008
- 40
Engineers . . .
I have a load-bearing concrete-block industrial building built in 1935 that I have examined. The roof is framed with open-web steel bar joists; 50 foot span, 5-foot on-center spacings. A fire occurred in a machine inside the building. The direct-destructive fire damage is limited to the machine and the roof framing - joists, roof deck and roofing materials.
Three bar joists were directly over the fire origin. I measured the elevations of 6 joists at the distance from bearings to the center of the fire origin from the ends of each joist; comparing the elevations to the bottom chord at the fire origin to the elevations at the bearing points. At the two joists closest to the fire origin, the trusses were flat. Measurements away from the fire origin - extending from the closest joist to joists farther away, the joists extending from one side of the origin appeared to have a rise of the bottom chord of 0.125, 0.3125, and 0.4 inches. Visually, the joists and their components do not appear to have sustained any deformation; though supported ribbed metal roof deck had deformed between 4 of the joists.
Is it typical that steel bar joists for roof framing were, or are now, cambered as part of the design/mfgr.? If you are aware of good information on this question, and/or can direct me to current pertinent information regarding analysis of steel bar joists for reuse/replacement following a fire event, please assist me with links, etc. Again, this structure was built in 1935.
Thank you for your help.
Dana
I have a load-bearing concrete-block industrial building built in 1935 that I have examined. The roof is framed with open-web steel bar joists; 50 foot span, 5-foot on-center spacings. A fire occurred in a machine inside the building. The direct-destructive fire damage is limited to the machine and the roof framing - joists, roof deck and roofing materials.
Three bar joists were directly over the fire origin. I measured the elevations of 6 joists at the distance from bearings to the center of the fire origin from the ends of each joist; comparing the elevations to the bottom chord at the fire origin to the elevations at the bearing points. At the two joists closest to the fire origin, the trusses were flat. Measurements away from the fire origin - extending from the closest joist to joists farther away, the joists extending from one side of the origin appeared to have a rise of the bottom chord of 0.125, 0.3125, and 0.4 inches. Visually, the joists and their components do not appear to have sustained any deformation; though supported ribbed metal roof deck had deformed between 4 of the joists.
Is it typical that steel bar joists for roof framing were, or are now, cambered as part of the design/mfgr.? If you are aware of good information on this question, and/or can direct me to current pertinent information regarding analysis of steel bar joists for reuse/replacement following a fire event, please assist me with links, etc. Again, this structure was built in 1935.
Thank you for your help.
Dana