A case study on the impact of fiber distribution on X-connections of complex-shaped UHPFRC footbridges cast with recyclable formwork

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is increasingly recognized worldwide for its potential in constructing innovative architectural footbridges. This study examines the influence of fiber distribution on the mechanical behavior of the X-connection, a critical structural detail in a novel latticework concept for UHPFRC footbridges, while also introducing an innovative approach using recycled wax formwork for shaping complex geometries. Following the architectural design process for the latticework UHPFRC footbridge, the methodology involves: (i) fabrication of fully recyclable wax formwork using CNC milling for two X-connection configurations with distinct crossing angles (i.e., the angle formed at the intersection of the X shape); (ii) gravity casting of UHPFRC, incorporating 1% steel microfibers; (iii) application of the magnetic inductance method (MIM) for non-destructive testing to evaluate fiber distribution, supplemented by fiber counting and image analysis of cracked sections post-testing; (iv) mechanical testing of the X-connection under bending to assess structural performance; and (v) a nonlinear Finite Element Analysis (NLFEA) to comprehensively examine the impact of fiber distribution. The findings underscore the pivotal role of fiber distribution in determining the ductility and strength of X-connections within the latticework UHPFRC footbridge, elucidating both the strengths and constraints of contemporary magnetic methods integrated with the Finite Element Method for accurately predicting the effects of fiber distribution.