Structural behaviour of laminated glass beams reinforced and post-tensioned with adhesively bonded iron-based shape memory alloy tendons

Laminated glass beams are used as supporting structural elements for glass roofs or glass facades to maximize their transparency. Their failure is rather brittle, with a residual load-carrying capacity ensured by the interlayers significantly lower than the initial glass fracture resistance. By adding ductile tendons as reinforcement elements along the glass edges subjected to tensile stresses, both the initial glass fracture resistance and especially the residual load-carrying capacity can be improved. An additional post-tensioning of the beams by pre-stressing the tendons can increase the initial glass fracture resistance even further. In most previous research, mechanically pre-stressing the tendons and subsequently fixing them to steel parts at the ends of the beams was used for obtaining post-tensioned laminated glass beams. This paper presents investigations on a novel approach for post-tensioning laminated glass beams with adhesively bonded iron-based shape memory alloy tendons along both longitudinal glass beam edges. This allows a relatively easy post-tensioning process by, first, adhesively bonding pre-strained tendons to the glass beam edges and, second, triggering the shape memory effect of the tendons through electrical resistive heating. Experimental and simulation results are presented for laminated glass beams without reinforcement, reinforced laminated glass beams and post-tensioned laminated glass beams subjected to four-point bending. Two different adhesives, an epoxy and a methacrylate, are investigated for bonding the tendons to the glass beam edges. The results show that a post-tensioning of laminated glass beams is feasible by electrical resistive heating of the iron-based shape memory alloy tendons, but also indicate an optimization potential of the applied process. Moreover, the contribution of the tendons, with and without post-tensioning, to improving the initial glass fracture resistance and the residual load-carrying behaviour are evaluated and advantages and disadvantages of the two different adhesives are highlighted. The applied simulation approach, covering both the post-tensioning and the four-point bending, allows a relatively good prediction of the initial and residual force versus displacement behaviour, and of the glass crack patterns for the different types of beams.