Application of adhesively bonded Fe-SMA for post-tensioning glass beams

Laminated glass beams and glass fins are structural elements increasingly used to support transparent roofs and facades. Constraining aspects for the design with such elements are the brittleness of the material glass and the rather low residual load-bearing capacity after initial glass failure. To obtain a ductile failure, reinforced and post-tensioned glass beams are suitable solutions. While by adding a ductile reinforcement on the tension side of a glass beam, its post-cracking behaviour and its redundancy are improved, an additional pre-stressing of this reinforcement helps to increase as well the initial cracking resistance. Because of the rather complex mechanical pre-stressing procedures, real applications of such beams are extremely rare, although promising research results were obtained with stainless steel and fibre-reinforced plastic tendons in the past.

A more efficient pre-stressing procedure is considered possible with the iron-based shape memory alloy (Fe-SMA) developed by external page re-fer AG. This material can be delivered as pre-strained strips and easily be fixed by adhesive bonding to a parent structure. After fixing the strips, a compressive stress can be induced into the parent structure by heating the Fe-SMA strip with electricity or infrared transmitter to a certain temperature. In a collaboration with external page re-fer AG and the department for external page Structural Engineering at Empa and with the support of an external page Innosuisse innovation check (application number 51447.1 INNO-ENG), the feasibility of this novel concept is studied. Preliminary lap-shear tests, release (activation) tests and related simulations are carried out in a first step to assess the suitability and limitations of selected adhesives. In a second step, medium-scale post-tensioned glass beams with adhesively bonded Fe-SMA strips are tested in four-point-bending to analyse the assembly sequence and the structural capacity.