Strength analysis and failure prediction of glass adhesive joints

Abstract

This research study seeks to evaluate the load response and failure prediction of glass/steel adhesive joints. The need for sustainable construction materials along with recent architectural trends and technological developments have made glass more accessible than ever before in the construction industry. Limited attempts have been made to compare the performance of bolted and adhesive connections for glass/steel structures, while interface characterisation studies are also lacking. Damage initiation and propagation in the adhesive layer is rarely modelled numerically, and the development of cohesive zone models has been restricted to reference values as hybrid coupon tests are difficult to test successfully. Lastly, while the degradation of glass/steel adhesive joints has been examined experimentally, a numerical tool for the prediction of the performance of the joints after exposure is currently lacking.

Benchmark designs of glass/steel bolted and adhesive joints were introduced and tested experimentally in four different load cases. Adhesive joints were found to be stronger and stiffer for all load cases examined. It was also observed that lower strength ductile adhesive (in terms of bulk properties) produced joints with higher failure loads. Numerical analyses showed that ductile adhesives developed a large plastic zone and redistributed the stress concentrations more effectively from the corners of the joints. Therefore, a larger adhesive area was resisting the loading. This understanding of the synergistic property combinations of strength and ductility of the adhesives led to the development of a numerical tool for the optimum selection of adhesives based on the joint design. The identified adhesive led to a significant strength increase for every load case examined.

The long term performance of glass/steel adhesive joints was evaluated by exposing the joints to conditions of high temperatures and humidity, and the degradation of the bulk properties and the interfaces was recorded. It was shown that the bulk properties and the interface properties degrade at different rates. The glass/adhesive interface degradation was shown to be more significant and controlled the failure performance of the joints.

Numerically, a continuum mechanics and a cohesive zone modelling (CZM) approach were evaluated for their suitability in predicting the failure load of glass/steel adhesive joints before and after environmental exposure. Input parameters for continuum mechanics approaches are based on bulk properties only and are easier to evaluate than CZM interface parameters. An in-house heat strengthening methodology development was necessary to increase the strength of small coupon sized glass substrates for accurate interface characterisation. It was shown in this work that both numerical methods were accurate in predicting the performance of the unaged joints. After environmental exposure, the CZM approach, which allows to account for the more severe interface degradation, performed significantly better. This finding highlights the need for reliable enhanced experimental testing procedures for interface characterization for hybrid glass/steel joints.

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