STRUCTURAL TESTS OF 27-YEAR-OLD PRESTRESSED CONCRETE BRIDGE BEAMS

Two 27-year-old precast, prestressed concrete box beams (36 in. wide x 27 in. deep (914 x 686 mm) were removed from a deteriorated 54 ft (16.5 m) span multi-beam bridge and were subjected to structural load tests. One beam, from the center of the bridge, showed no visual signs of deterioration. Another beam, located next to a badly deteriorated beam, showed some signs of minor concrete cracking and spalling. Both beams proved to be structurally strong and ductile. Behavior at service load and at factored ultimate load was excellent. Flexural cracking occurred at about two times the 1989 AASHTO service load, and the measured ultimate flexural strength exceeded the required strength at factored loads. Load-deflection response closely followed the predicted response. Measured prestress losses were much less than predicted. Maximum measured strand stresses were very close to the values predicted by the ACI Code and by the strain compatibility procedure.