Repair and Rehabilitation of a Pony Truss Span Bridge during Service Time

A pony truss span bridge of 110 feet long, built by the Bureau of Public Roads (BPR) in 1944, is analyzed and a rehabilitation process is designed in order to keep the bridge in service during the construction time. No fresh concrete could be used to rebuild the slab because the vibration due to transit load would avoid the concrete hardening process, then a post-tensioned slab was designed in order to assembly each lane by parts and bond all the parts by a compression force. It was necessary to add stringers to the floor structure in order to support the parts of one lane before the post-tensioning process was accomplished. The analysis of stress was performed using actual transit loads and the post-tension compression forces. A longitudinal compression stress was generated in order to avoid tension stresses during transit and earthquake loading. The trusses were transformed in statically indeterminate trusses to reduce deformation and reduce the vibration periods. Temperature stresses were generated in the trusses during temperature changes, however they were evaluated and considered as minor stresses. The number and amplitude of load and unload cycles in the old structure and in the repaired structure were added to confirm that fatigue is far to be attained.