Numerical Solutions to Unilateral Frictional Contact Problems in Glass Façade Systems

Glass is a brittle material. Its use in constructing structural elements of civil engineering can still be considered as an innovative technique. In order to take a full advantage of its principal qualities (transparency, aestheticism, durability, etc.), architects are pushing the conception of glass structural elements towards the adoption of more and more slender elements, entailing necessarily appropriated assembling techniques. One of the most widely used techniques for glass plates is the bolted connection that ensures the transmission of shear stresses by friction. Soft aluminum pads are used as inserts between metallic splice plates and glass plates. A precise characterization of the friction between an aluminum pad and a glass plate is then the key both to the design and the safety of such assembling systems. This can be done only through an experimental approach. At the same time, the bolted connection of two glass plates gives rise to a unilateral frictional contact problem. This strongly nonlinear problem can be solved only numerically. The objective of this work is to provide numerical solutions for practical problems arising from the friction-gripped bolted connections of glass stiffeners, using a precise experimental characterisation of the frictional properties of an aluminium pad rubbed against a glass plate. To achieve the experimental objective, an original tribometer was designed and constructed. Experiments were performed to determine the influence of the constant normal loading’s duration on the static friction between glass and aluminum. The obtained experimental results show that the Coulomb friction law is not sufficient and an internal variable needs being introduced to describe the state of two surfaces in contact. The evolution law of this variable is then identified by the experiments and implemented in a finite-elements commercial code. To obtain numerical solutions, the MSC MARC finite element code has been used. Threedimensional frictional unilateral contact analyses have then been carried out for several bolted connections of glass plates. In these analyses, the friction law resulting from the experimental investigation has been used. The numerical simulations give the stress distribution induced by the bolt’s tightening and the maximal tangential load that a glass bolted assemblage can support. The coexistence of slip and adhesion zones inside the contact area has been shown by the appearance of discontinuities in the contact shear stresses. An important local tensile stress concentration, probably responsible for a tensile mode of failure of the joint, has been identified in good agreement with experimental results.