Static Performance of a Scaled Continuous Rigid-Frame Bridge Model Under Progressive Multi-Location Strengthening: Deflection, Strain, and Response-Line Evaluation

Abstract

Continuous rigid-frame bridges experience web, bottom-slab, and deck-slab deterioration in service, yet strengthening locations are rarely compared within a single structure. A 3.68-m acrylic (polymethyl methacrylate, PMMA) model of a three-span rigid-frame bridge was tested at four static load levels with a three-axle vehicle. The web void was patched, and the bottom and deck slabs were then stiffened, forming cumulative Stages 0–3; a beam model matched the measurements within 3.6–9.7%. At the mid-span section, full strengthening reduced the 20-kg deflection by 39.8% and raised equivalent flexural stiffness by 51.5%. The bottom-slab stage gave the largest incremental gain, raising bottom-flange strain improvement at the mid-span and side-span one-third control sections from 2–4% to 28–31%; the deck-slab stage added a comparable stiffness gain. Web patching acted locally (21.9% strain reduction beside the defect and 0.5% at the mirror gauge) but left the control-section flexural indices unresolved; as a web void mainly affects shear, which is unmeasured here, it is reported as localized restoration. Response-line shapes were preserved while Stage-3 envelope areas contracted by 30–40%. The specimen was not replicated, and the mid-span improvement spans 37.4–48.0% across three data treatments. The results support mechanism-based screening of strengthening locations in similar box girders under service loading.