Funded by the California Department of Transportation. Investigators – Y. H. Chai & Carlos Zuritz (UC Davis), Li-Hong Sheng and Ganapathy Murugesh (Caltrans), Hans Strandgaard (CH2M Hill) and Karen Cormier (TY Lin International).
This project examines the short and long-term service performance of the long-span box-girder bridges constructed of lightweight aggregate concrete. While many bridge structures constructed of lightweight aggregate concrete have performed satisfactory in California, there have been instances where unexpected deformation was observed during the service life of the structure. Most notably, the Parrotts Ferry Bridge near Vallecito in California, which was completed in 1979, experienced a large mid-span deflection after about 12 years of service. The large mid-span deflection affected the general appearance of the bridge as well as the sight distance of vehicles traveling on the bridge and raised concerns regarding its structural integrity. The unexpected time-dependent deformation of the bridge also hampered the general acceptance of lightweight aggregate concrete as a suitable structural material for long-span bridge construction in California for many years that follow.
The new Benicia-Martinez Bridge, currently under construction in Northern California, is the first major lightweight aggregate concrete bridge since the completion of the Parrotts Ferry Bridge. The new bridge, which is over 2.5 km (1.6 miles) long, will provide five 3.6 m (12 ft) wide traffic lanes plus two 3 m (9.8 ft) wide shoulders and carry the northbound traffic on Interstate 680 over the Carquinez Strait. The alignment of the new bridge will be east of the existing Benicia-Martinez Bridge and Union Pacific Railroad Bridge.
A key feature of the new Benicia-Martinez bridge is the use of sand-lightweight concrete for the superstructure, which will be constructed of a large single-cell box-girder with rib-supported deck overhangs. Prompted by the concern over the time-dependent behaviors of the Parrotts Ferry Bridge and the general lack of field data for the behavior of box-girder bridges constructed of high strength lightweight aggregate concrete, a health monitoring plan is put in place to monitor the short and long-term behavior of the new bridge. The health monitoring program is a part of a larger instrumentation program which includes the monitoring of the bridge for extreme seismic events. Short and long-term service performance of the new bridge is monitored through time-dependent deformation of the superstructure, corrosion of the pile casings, temperature distribution in the superstructure box-girder, and acoustic sensing for possible fracture of prestressing tendons. Vertical deflection and shortening of superstructure will be measured in the longest span of the bridge, which is 200.8 m (659 ft) over the shipping channel. Local deformation in the box-girder, as characterized in terms of section curvature and axial strain at the centroid of the section, will be measured using strain gages at four sections of bridge. In addition to correlation with strains and deformations, measured temperature gradient will also be compared with current code recommended temperature gradients, and may serve as the basis for future temperature distribution for design of high strength lightweight aggregate concrete box-girder bridges. Measured deformation of the bridge will also be compared with deformations predicted by current analytical tools and creep and shrinkage models. These data, once collected and reduced, will also serve to advance the useful knowledge base for design and analysis of future high strength lightweight concrete structures in California and elsewhere.
For construction photos of the new Benicia-Martinez Bridge, click here