Field Measured Dynamic Effects and Load Distribution in a Prestressed Concrete Light Rail Bridge

Live load performance of a recently constructed, prestressed concrete bridge was investigated to determine the Impact Factors (IMs), the Girder Distribution Factors (GDFs). The bridge was subjected to controlled static and dynamic loading using two Denver Transit Partners (DTP) electric-multiple-unit rail cars prior to a commuter rail line being placed into service. The rail cars travelled along northbound and southbound tracks of the four span, horizontally curved, bridge at various speeds. A total 24 tests were conducted and response was measured using a combination of strain sensors and accelerometers installed at critical sections on the supporting girders. Results for IMs and GDFs obtained from the field tests are presented. These results are also compared against relevant code provisions and these preliminary results indicated that IMs are insensitive to train speed and are smaller than investigated code provisions and that measured GDFs were different than those provided by these code provisions.