Form-finding of funicular geometries in spatial arch bridges through simplified Force Density Method

Abstract

In a "classical" vertical planar arch bridge subjected only to in-plane loads, its funicular geometry (which is the geometry that results in an equilibrium state free from bending stresses, i.e., simply under axial forces) is contained within a vertical plane. In the so-called "spatial arch bridges," their structural behavior extends from the essentially vertical in-plane behavior of the "classical" arch bridges to a three-dimensional behavior. The paper presents how the Force Density Method, which is a form-finding method originally developed for cable meshes, can be simplified to easily obtain three-dimensional funicular arches. The formulation and flow chart of the method is presented and discussed in detail within this paper. Additionally, some case studies illustrate its scope. This paper intends to be useful at the conceptual stage of bridge design when the three-dimensional geometry for the spatial arch bridge typology is considered either because of functional requirements, structural efficiency, or for aesthetical purposes.