| Glass curtain walls have been widely used as building exterior walls in recent years because of their good transparency and aesthetics.However,the fire resistance of glass materials is low,and curtain wall glass is usually the most fragile part of the exterior wall structure.The application presents a potential fire risk.In a fire,the glass pane is prone to break and form multiple cracks crisscrossing.When the cracks form an"island",the glass pane usually falls off the frame under the coupling action of the external environment such as wind load and fire to form new vents.The new vents accelerate the development of ventilation-controlled indoor fires,causing catastrophic flashbacks and even flashovers.Fire overflows from indoor fires can also spread the fire to the superstructure through the new vents.Therefore,the breakageof glass will greatly accelerate the development of fire,resulting in three-dimensional interactive fire spread inside and outside the building.In this study,the breakagebehavior of different types of glass curtain walls and glass panels under external wind loads in fire scenarios was revealed experimentally.The temperature field,stress field,first breaking time and dynamic crack propagation of the glass pane are accurately predicted by numerical calculation,which provides a certain theoretical support for the fire resistance design of glass curtain wall.The temperature field distribution,first breaking time,stress distribution and dynamic propagation of single crack of Low-E and clear glass pane in the closed chamber under the action of radiant heat source are predicted by numerical calculation and analysis.The calculation results show that the temperature of the Low-E glass pane is lower than that of the ordinary clear glass pane without coating,and the Low-E glass has better fire resistance during the same time of receiving heat radiation.The established thermodynamics-solid mechanics coupled glass curtain wall first breaking timeprediction model based on the finite element method can fill the theoretical support lacking in the fire resistance evaluation of Low-E glass curtain wall.The breakagemechanism of the midpoint-supported glass curtain wall in the presence of different external wind speeds was explored.The experimental results show that with the increase of wind speed,the time required for the first breakageof the glass pane to occur decreases,and the drop-off rate increases accordingly.The established thermodynamic-solid mechanics coupled numerical calculation model reveals the stress field distribution of the point-supported glass curtain wall when there is an external wind load in the fire.Based on this numerical model,the Levenberg-Marquardt solver was used to solve the least squares method to obtain the convective heat transfer coefficient of the glass pane surface on the backfire side.The effects of different installation forms on the breakagebehavior of point-supported glass curtain walls were studied by experimental and numerical methods.The results show that the first breaking time of different types of point-supported glass curtain walls is distributed in the range of 68-421 s,in which the single-point-supported glass curtain wall has the longest first breaking time,but the glass fragments eventually fall out of the frame completely,while the six-point-supported glass curtain wall has the longest first breaking time.The supported glass curtain wall had the shortest first breaking time,but did not fall off after rupture.Numerical calculation obtained four different types of point-supported glass curtain wall with two-point,four-point,six-point(supporting points arranged vertically)and six-point(supporting points arranged horizontally).s and 97 s,which are in good agreement with the results of the actual first breaking time for cases 4(259 s),7(278 s),11(117 s)and 13(83 s)in the experiment,indicating that the thermodynamic-Accuracy of solid mechanics coupled numerical models.Based on the numerical calculation model verified by experiments,the boundary optimization method of quadratic approximation is used to optimize the distance L from the center of the hole to the glass edge.The calculation results show that the optimized L value makes the glass pane have better fire resistance.The optimization calculation tool can provide reference for engineering practice.Through the experimental study of the point-supported glass curtain wall with three different shielding areas around the support point in the fire scene,it is concluded that the glass curtain wall with a relatively small shielding area around the support point has a longer first breaking time,but eventually falls off the frame.The higher the ratio.In the four repeated experiments of condition 1 with the largest shielding area,the final drop-off rate of the glass pane is 0%.This is because although the glass pane is cracked from the edge of the hole,the larger shielding area provides a certain support and restraint effect.Make the glass pane break but not fall off from the frame.The numerically calculated first breaking times of No.2 in case 1,No.2 in case 2,and No.1 in case 3 are 131 s,155 s,and 200 s,respectively,which is consistent with the experimental result,that is,130 s,150 s and 185 s,which are very similar,and the accuracy of the numerical calculation model is verified by comparing with the experimental results. |
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