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Multi-span Pre-tensioned Pre-stressed Concrete Beam (PPCB) bridges made continuous usually experience a negative live load moment region over the intermediate support. Conventional thinking dictates that sufficient reinforcement must be provided in this region to satisfy the strength and serviceability requirements associated with the tensile stresses in the deck. The AASHTO LRFD bridge design manual recommends negative moment reinforcement be extended beyond the inflection point. Based upon satisfactory previous performance and judgment, the Iowa DOT OBS currently terminates b2 reinforcement at 1/8 of the span length. Although the Iowa DOT policy results in approximately 50% shorter b2 reinforcement than the AASHTO LRFD specifications, the Iowa DOT has not experienced any significant deck cracking over the intermediate supports. The primary objective of this project is to investigate the Iowa DOT OBS policy regarding the required amount of b2 reinforcement to provide the continuity over bridge deck. Other parameters, such as termination length, termination pattern and effects of the secondary moments were also studied. Live load tests on five bridges were carried out. The data were used to calibrate three-dimensional finite element models of two bridges. A parametric study was conducted on the bridges with uncracked deck, a cracked deck, and a cracked deck with cracked diaphragm. The general conclusions were as follows.  The parametric study results show an increased area of the b2 reinforcement slightly reduces the strain over the pier. Whereas, increased length and staggered reinforcement pattern slightly reduce the strains of the deck at 1/8 of the span length.  Secondary moments affect the behavior in the negative moment region. The impact may be significant enough that the deck over piers may never experience a tensile stress.  Finite element results suggested that the transverse field cracks over the pier and at 1/8 of the span length, are mainly due to the deck shrinkage.  Bridges with higher skew angles have lower strains over the intermediate supports.

Investigation of negative moment reinforcing steel in pre-cast pre-stressed concrete beam bridge decks