Structural Assessment, Jack-Based Realignment, and Load-Test Verification of a Fire-Damaged Six-Cell RC Box Girder Bridge During Construction

Abstract

Abstract

Construction-stage bridge fires are seldom documented in detail, although they can change the behavior of an incomplete structural system. This paper records a 35 m span of a six-cell RC box girder at the Al-Sadreen intersection in Samawa, Iraq, damaged after the bottom slab and webs had been cast and before the top slab was completed. Burning timber formwork locally removed the temporary soffit support. The open-top section, therefore, shifted from the intended fixed–pin construction-stage response toward a pin–pin-like response, with sagging and vertical web cracks near the intended fixed support. A closed-form check showed that the required negative-restraint moment was about 5.3–5.9 times the cracking moment of the incomplete section. Visual inspection, Schmidt hammer, UPV, cores, and steel tests showed localized damage; 28 MPa was used as a representative residual concrete strength for the affected cast components. CSiBridge was used only for completed rehabilitated-state verification. The strengthened model gave maximum shear D/C ≈ 0.529 and flexural D/C < 1.0. Spreadsheet-guided jacking, top-slab reinforcement upgrading, sensitivity checks, and a 350-ton five-lane load test confirmed satisfactory service behavior and negligible residual response.