Developing Extended Strands in Girder-Cap Beam Connections for Positive Moment Resistance

2017PDFTech ReportWA-RD 867.1Agreement T1461, Task 23Girder bridgesPrecast concretePrestressed concrete bridgesConcrete bridgesGirdersBentsEarthquake resistant structuresLongitudinal Seismic ResistancePositive MomentExtended GirderStrandsGirder-Cap Beam ConnectionPrecast Prestressed ConcreteGirdersStrand Anchorage Bearing CapacityWashingtonUnited StatesWashington (State). Dept. of Transportation. Research OfficeTsvetanova, KristinaStanton, John F.Eberhard, Marc O.Washington State Transportation CenterWashington (State). Dept. of Transportation. Research OfficeUnited States. Federal Highway AdministrationUS Transportation CollectionIn bridges constructed with precast prestressed concrete girders, resistance to seismic effects is achieved by the interaction between the columns, the cap beam and the girders. These components must be connected to provide flexural resistance. Under the impact of longitudinal seismic motion, the bottom flanges of the two girders that meet end-to-end at the cap beam will be under tension and compression, respectively. The tension connection between bottom girder flange and cap beam is presently made by extending some of the bottom strands into the cast-in-place diaphragm. At this location, the space available is too small for development by bond in the straight strands alone, so some form of mechanical anchorage is needed. Since concrete in the diaphragm is highly confined, it can probably carry high bearing stress and an anchor with a small bearing area may be possible. Thus, the goal of this project is to create a reliable, effective, as well as practically applicable, way of anchoring strands extended from the girder into the cap beam. The first stage in the development of the girder-diaphragm seismic connection consists of establishing the adequacy of the smallest possible strand anchor that still leads to a strand ductile failure due to yielding rather than strand anchor failure by crushing of the concrete. As a second stage, the impact of the possible failure mechanisms of the strands, embedded in the diaphragm, on the development of the girder-cap beam positive moment connection was investigated. Finally, the distribution of girder bending moments across the bridge deck was evaluated, while investigating the influence on that distribution of the most important bridge parameters, such as cracking of bridge components, as well as varying cross sectional dimensions