Bridges constructed with adjacent precast prestressed concrete box beams have been in service for many years and provide an economical solution for short and medium span bridges. A recurring problem is cracking in the longitudinal grouted joints between adjacent beams, resulting in reflective cracks forming in the asphalt wearing surface or concrete deck. The cracking appears to be initiated by, but not limited, to stresses caused by temperature gradients, live loads, transverse post-tensioning, or grout shrinkage. Once the cracking has occurred, chloride-laden water can penetrate the cracks and cause corrosion of the reinforcement and prestressing strand.
NCHRP Synthesis 393: Adjacent Precast Concrete Box Beam Bridges: Connection Details reported a wide variety of practices used by state highway agencies for the connection details between adjacent box beams. These practices include partial depth or full depth grouted keyways, keyways grouted before or after transverse post-tensioning, prepackaged or non-prepackaged grout materials, post-tensioned or non-tensioned transverse ties, a wide range of applied transverse post-tensioning forces, and cast-in-place concrete decks or no decks. A few states reported that their practices had reduced the longitudinal cracking, whereas others had not been successful using similar practices.
In 2014, FHWA conducted extensive evaluation of the use of the ultra-high performance concrete (UHPC) connections for adjacent box beam bridges to address the connection performance. In fact, the FHWA-developed UHPC connections have been used by some states.
Since the previous research focused on the connections’ performance as an individual component, there is a need to evaluate their performance as part of an overall adjacent precast box beam bridge system. In addition, new adjacent precast box beam bridge systems could be developed by integrating both proven and innovative connections.
The objectives of this research were to (1) develop guidelines for the design and construction of various adjacent precast box beam bridge systems to enhance performance of connections and bridge service life and (2) propose design and construction specifications with commentary in the format of the AASHTO LRFD Bridge Design Specifications.
STATUS: The final deliverable has been published as NCHRP Research Report 1026. The research report can be downloaded here.