Investigation into the Stability Behavior of Single-Layer Barrel Vault Space Structures

Space structures are economical and aesthetic in appearance. They provide a unique solution to cover large column free areas. Sports stadia, industrial buildings, exhibition halls, cinema theatres, swimming pools, airport hangars, conference halls, etc, can be economically covered with the use of space structures. Space grids are characterized as two-way or three-way, depending on whether the members intersecting at a node run in two or three directions. Three-way grids are very extremely strong and lead to a very uniform stress distribution. Barrel vault is one of the oldest architectural forms, used since antiquity. The popularity of barrel vaults derived partly from the economy of these structures, as all arches could be constructed as identical members. Braced barrel vaults are developable surfaces of zero Gauss curvature generated by the movement of a curve, known as the. directrix., over a generator straight line. The directrix may be a circular arc, an ellipse, a catenary, a parabola or a cycloid. Single-layer barrel vaults show a range of different instability modes, namely, member instability, node instability, line instability and overall instability, normally each occurring under different loading and boundary conditions. There are two important types of instability, namely: limit point instability and bifurcation point instability. In limit point instability, a structure with nonlinear un-stiffening characteristics loses its stability by a sudden buckling into a mode of deformation which is in accordance with the initial mode of deformation. However, in the bifurcation point instability, a structure with nonlinear softening characteristics may lose its stability by a sudden buckling into a mode of deformation which is quite distinct from the initial unstiffening mode. There are three types of bifurcation point instability, namely: asymmetric bifurcation, stablesymmetric bifurcation and unstable-symmetric bifurcation. However, in most cases, space structures show limit point instability and unstable-symmetric bifurcation point instability. In single-layer braced barrel vaults, the effect of geometric nonlinearity is very important. In fact, due to small angles between the members, deflections and member forces are large and thus significant changes in structural geometry occur. Also, in these structures the possibility of plasticity occurring in the members causes a reduction in their load carrying capacity. Plasticity can occur before the first limit point load in single-layer braced barrel vaults, so despite the fact that the main source of nonlinearity in these structures is geometric, the inclusion of plasticity in the analysis is necessary to safely predict their true collapse load and post-collapse behavior. Therefore, geometric and material nonlinearities should be considered in the analysis of these structures. In the present study, the stability of singlelayer barrel vaults with three-way triangular configuration is investigated by carrying out nonlinear collapse analysis using finite element method. The effects of different parameters, such as initial geometric imperfections, load on a single node, loads on some nodes, unsymmetrical load distribution with different intensities, length to span ratio, height to span ratio, boundary conditions and material yield stress are considered on the stability behavior of single-layer barrel vaults. According to static collapse analyses of studied models, three collapse mechanisms were determined as overall collapse, local collapse with snap-through and localcollapse without snap-through. In the case of local collapse with snap-through, it has been indicated that to evaluate realistic response of the structure, the static collapse analysis is not adequate by itself, and a dynamic snap-through analysis must be performed, as well.