The new AASHTO code for the load and resistance factor design of bridges introduced a so-called empirical method for designing deck slabs of reinforced concrete. The reinforcement ratio is constant, and it does not depend on the girder spacing. The objective is to verify whether the empirical method is adequate for wider girder spacing [~3 m (~10 ft)]. Bridge behavior is analyzed by an advanced finite element method. The developed procedures are applied to two structures: a steel girder bridge and a prestressed concrete girder bridge. Strains and corresponding stresses due to dead load, live load, and shrinkage effect are determined. The analytical model is calibrated with the use of field test data. Stress distribution is then investigated. Field test results indicate a considerable difference in live load distribution factors between steel and prestressed concrete girders, primarily because of stiffness differences between the girders and the slab. Prestressed concrete girders are considerably more rigid than steel girders and therefore have very limited load sharing. For bridges designed by the empirical method, expected extreme values of the stress caused by live load (heavy trucks) were observed to be lower than the critical (cracking) values. However, dead and live loads combined with shrinkage (particularly restrained shrinkage) can lead to cracking and eventually even failure of the deck and the bridge.
Abstract