Polyurethane Flexible Joints as an Advanced Adhesive Layer in Sustainable Prefabricated Small Bridge Structures

This study presents an analysis of adhesively bonded reinforced concrete composite beams. Experimental results are compared with two computational approaches-an iterative algorithm based on an analytical solution and finite element analysis (FEA)-for simply supported composite beams subjected to four-point bending. The cross-section of the beam consists of two reinforced concrete beams bonded together with different adhesive layers: either flexible polyurethane or a stiff epoxy resin layer. This article begins by outlining the process used to determine the parameters for the flexible materials. The linear analytical model, based on the hypothesis of planar cross-sections for bent components and approximating the behavior of the adhesive layer by the pure shear state, leads to closed-form formulas for deflections and stresses in individual components of the system. These formulas are employed in an iterative procedure to evaluate the post-cracking behavior of composite beams. Conversely, the FEA model accounts for material non-linearity in both the adhesive and concrete, as well as the possibility of decohesion of the adhesive layer, providing a more detailed and accurate representation of the structure. The allowable loads, deflections, and stresses derived from both methods are evaluated and compared across various stages of structural performance: prior to cracking, and two serviceability limit states. The obtained results are validated through comparison with experimental data. The aim of this study is to evaluate the effectiveness of the analytical method for rapid assessment of the capacity of composite concrete structures in different work phases. The iterative procedure based on the analytical solution is found to provide reasonable approximations in terms of the deflection, stress distribution, and crack depth.