Experimental and Numerical Study of Glass Façades Breakage Behavior under Fire Conditions


Student thesis: Doctoral Thesis

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  • Yu WANG


Awarding Institution
Award date20 Jun 2016


As the weakest part of a building, glass is more prone to breakage when subjected to fire. The opening resulting from the breakage and fallout of glass panels may easily form a corridor through which fresh air can enter the compartment and promote fire spread, accelerating the fire development. Therefore, glass breakage plays an important role for fire development in compartment fire. In this thesis, experimental, numerical and theoretical analysis is performed to investigate the thermal breakage and breakage mechanism of glasss façades. The aim of investigation on glass curtain wall is to propose an optimized design method in fire safety of glass curtain wall, which provides references for fire extinguishing and evacuation.

A total of 16 full scale tests were firstly performed to investigate the breakage behavior of fully exposed, horizontal-hidden, vertical-hidden and fully hidden framing coated glass curtain walls. Several critical parameters, such as the time of breakage occurrence, crack initiation and propagation, heat release rate, incident heat flux, central gas temperatures, glass surface temperatures and loss of integrity of the glazing assembly, were recorded. Semi-exposed framing glass curtain walls demonstrate greater fire resistance than fully exposed framing façades. Meanwhile, the fire resistance of hidden framing glass façades defers markedly when fire location changes. Radiation from the fire source dominates the heat exchange form to heat glazing. An in-house software was developed for glazing behavior prediction. The temperature measured in experiments is used as thermal loading. The time of first breaking, stress field, crack initiation and propagation are calculated through the simulation assuming the thermal loading is the same as the experiment data. The numerical results agree well with experimental results. Temperature gradient in glazing is considered the predominant cause of glass breakage occurrence. All the cracks are initiated from the glass edges, but the crack initiation is located only at the frame covered edges. The stress distribution simulated using the finite element method revealed the breakage mechanism of four different glass curtain walls.

A set of 24 experiments were conducted to investigate thermal performance of point-supported glass breaking behavior. The results indicate that changes in fixing location have a considerable effect on point-supported glass curtain walls: The closer to the horizontal or vertical center line the fixing points are located, the shorter the time a pane will take to fall out. Horizontal changes are much more sensitive than vertical changes. The glass panes studied exhibited three kinds of breaking pattern, and normally occurred during the steady state of fuel combustion. It is found that the mechanism of breaking is the combined effect of thermal stress and mechanical stress. Almost all cracks initiated at the supporting points. Point-supported glass panes may fall out much more easily than edge-covered glass panes. Finite element method was employed to simulate the glazing stress distribution under fire conditions. Uniform and non-uniform thermal loading were applied. The simulation results agree well with our previous experiments in terms of variation trend of breaking times, position of crack initiation, crack propagations. The mechanism of point supported glass was revealed.

The effect of the fire location change on thermal performance of glass was investigated. With increasingly diversity in the form of glass installation, the combined effect of fire location and installation form is complicated and thus studied. Through changing fire location in thickness direction, the fire resistance of tempered glass was analysed and the critical breakage conditions of single and double glazing were determined. Theoretical models for single glazing and double glazing were developed to predict the breakage time and temperature increasing. The model can well work and has a good agreement with experimental results. Fire location was also changed in surface direction. It was found that framing glass is more prone breakage when fire positioned at the center of pane, while point supported glass will likely break only when the fire is at fixing point. To investigate the micro-mechanism of breakage, small scale experiments and theoretical analysis was conducted. The breaking stress and micro flaws in clear, coated and ground glasses at different temperatures are studied. The heat transfer and micro-dynamic mechanism of important parameters, such as breaking strength, coefficient of linear expansion, critical temperature difference, were revealed.

The results in this thesis reveal the breakage mechanism of glass façade in fire and are intended to provide significant reference for fire safety design in building envelop.

    Research areas

  • breakage behavior, fire resistance, glass façade, installation form, fire location, critical condition, micromechanism