Development of lightweight emergency bridge using GFRP-metal composite plate-truss girder

Design of a lightweight emergency vehicular bridge comprising a GFRP-metal composite plate-truss girder and measuring 24 m in span is reported. The said bridge was designed based on optimization of an original 12-m bridge specimen. The bridge, so developed, is intended to be lightweight, structurally sound with modular feasibility, and representative of a construction that is less time consuming overall and fully exploits advantages offered by the use of inherent and complementary pultruded GFRP materials. Conceptual design and considerations of the large-scale structure were first described in detail. Subsequently, full-scale nondestructive tests were performed under on- and off-axis static loadings to evaluate the actual linearly elastic mechanical behavior of the prototype. Experimental results demonstrated that the bridge satisfactorily met the requirements of strength, overall bending stiffness, and torsional rigidity with regards to emergency-bridge applications. Being recognized as the most critical loading case for emergency bridges with major influence on load distribution among truss girders, the lateral live-loading distribution was assigned great importance during design of the unique bridge. Extrusion-type unidirectional GFRP profiles with high-longitudinal but low shear strengths are predominantly suitable for structures subjected to large axial forces, and are, therefore, appropriate for application in the proposed hybrid structural system. Favorable testing results demonstrated that the proposed improved version of the original conceptual design can appropriately be used as a truss girder for a new lightweight emergency bridge with a longer measured span. It is suggested that such a hybrid bridge, which demonstrates reasonably good linearly elastic behavior under service live loads, must also be designed in accordance with a stiffness criterion. Corresponding finite element and analytical analyses were performed and compared against experimental results whilst demonstrating good agreement. The elicited comparisons indicated that the established simplified analytical models and the finite element model (FEM) were both equally applicable for use in preliminary structural calculations and design of the improved bridge under states within its serviceability limit. Results reported herein are expected to make a valuable initial contribution, which in turn, could further lead to development of similar lightweight structural systems.