AASHTO LRFD Concrete Stresses at Service :
AASHTO -LRFD Concrete Stresses at Service for superstructure tutorial checks ;
- stresses on concrete,
- girder top fiber stresses ,
- girder bottom fiber stresses and,
- deck stresses.
Concrete Stresses ;
First of all, designers need to check the service limit state. Because, exceedance of stress limits will result in cracking or crushing of concrete. Furthermore, the excessive compressive stresses can initiate creep induce cracks in longitudinal direction. Additionally, the excessive concrete tensile cracks can reduce the durability of the girder due to water intrusion thru cracks. Under those circumstances, it can speed up the corrosion of the strands.
Girder Top and Bottom Fiber Stresses ;
Secondly, service condition usually represents the force effects due to unfactored loads that can be observed very often in daily use of a bridge. The girder top fiber stresses can be determined using classical stress computations. Girder bottom fiber stresses can be determined in a similar way. In use of given equation in tutorial, AASHTO recommends a reduction of 20 percent on live load effects while checking tension limit state, which show itself in combination factors as 0.8.
Deck Stresses ;
Lastly, deck stresses do not include prestressing since prestressing is only given to girders. That is the reason only stresses developed on the deck will be due to superimposed dead loads and live loads plus impact.