Structural Aspects of an Arched Glass Masonry Bridge

Abstract

The glass group of the TU Delft plans to realize a 14m span glass arched masonry bridge, yet no prescriptions are available on how to assess the structural safety of such a structure. Regulations and guidelines for structural glass relate to float glass elements and do not refer to structures of cast glass elements. In addition, to display the aesthetic glass masonry structure, the arch directly serves as deck limiting the slope of the arch. Therefore its rise is relatively low compared to traditional stone masonry structures. It is unknown how this will affect the stability. In this report the stability and strength of arched glass masonry bridges is investigated. In addition TU Delft’s design is elaborated upon in more detail. In order to establish which aspects are important when designing in glass, references of both glass bridges as well as glass brick structures are discussed. Subsequently a theoretical background is formed for both arched masonry, as well as for structural glass. In analytical investigations, the effect of the geometry on the stability is assessed. Both an analytical as well as a numerical analysis of the stability have been executed for the boundary conditions of TU Delft’s design. Resilient interlayers may be applied to limit the tensile stresses introduced by imperfect conditions, i.e. an imperfect surface flatness of the glass and a discontinuous stress distribution due to an eccentric line of thrust. These imperfect condition were analytically respectively numerically investigated, in order to enable the formulation of a maximum interlayer-stiffness. This maximum interlayer stiffness will assure that the maximum tensile stress remains sufficiently low. This was followed by an experimental assessment of three interlayer materials in four thicknesses, to establish their suitability for application as interlayer in TU Delft’s design. Finally, the failure behavior with respect to the strength was established, resulting from experimental research in which a 1m span glass arch was loaded. Several design diagrams were composed that can be used to define the geometry of a circular segmented arch, taking into account the stability of the structure. A glass element in the arch is loaded in compression, but will only fail if too high tensile stresses are introduced as a result of imperfect conditions. If sufficiently large, the eccentricity of the line of thrust will cause tensile stresses. An imperfect glass surface may also introduce tensile stresses. An interlayer may be used to resolve these problems, if its stiffness is not too large. If fracture in a glass brick occurs, this will likely not lead to global failure, which means that the failure behavior of an arched glass masonry bridge is ductile. The stability of TU Delft’s glass masonry bridge is sufficient under the expected support settlements, as well as under an asymmetrical crowd load scenario. The load scenario concerning a service vehicle, significantly reduces the stability. It is therefore recommended to prevent entrance for service vehicles. Resilient interlayers with a stiffness between 3 3 26N/mm and 40N/mm should be applied between the bricks to assure adequate stress transfer, without compromising the stability. From the experimental research it followed that a 1mm-PVC or a 4mm-PU70 interlayer will be suitable. The design is deemed feasible, but before construction additional investigations on the time and temperature-dependent behavior of the interlayer should be executed. Additionally the strength of the full scale bricks must be assessed, too guarantee it is sufficient to resist the design loads.