3 wide double tee capacity

huangyhg

3' wide double tee capacity
wdm (structural) sep 18, 2003
i am inspecting an old road bridge made from (6) 36" wide double tees.  the double tees are 19" overall depth, 5" flange thickness, webs at 24" on center, with (2) 0.5" strands in the bottom of the webs.  the bridge was abandoned and moved to a residence for crossing a small stream.  the original span (28')has been halved by adding a steel support beam at mid-span.  the local fire department has asked for a letter from a structural engineer stating the bridge is safe for a fire truck to cross.  this is a very infrequent load, hopefully.
does anyone know where i can get load tables for this old section?
i plan to use h20 loading.
thanks in advance.
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sounds interesting.
i assume you know there are two strands based on the original shop drawings?  or is that from looking at the ends of the double tees?
without shop drawings it is difficult to determine the capacity since the strands could be draped or straight, they may be stress-relieved strands(older style of strand) instead of low-relaxation strands, you also wouldn't know the jacking stress of the strands which determines if the double tees would crack under service loads.
another thing which is concerning is that there has now been an additional support added at the midspan.  it is likely difficult to get three point bearing unless you're very careful about the detail.  not only that, the double tee would now act as a continuous member, which could lead to cracking at the top due to moment at midspan and the strand eccentricity at the support.
sorry, that's not a lot of help but maybe consider trying to find out the original manufacturer of the double tees and see if they could give you guidance on the design..