Validation of a numerical model for curtain walls with MVHS during free burning

Abstract

Glass breakage of curtain wall coverings during a fire can promote the spread of a fire in high-rise buildings. Prior to the development of sprinklers to prevent and delay glass breakage, it is necessary to identify the breakage mechanism of curtain wall glass panes and to establish a numerical model to simulate various fire situations using sprinklers to design effective sprinkler systems. The present study was conducted to establish a numerical model and analysis procedures to simulate fire situations. First, curtain wall was installed on one side of a testing chamber that was 3 m (L) x 3.2 m (W) x 2.4 m (H), and a free burning experiment was conducted using heptane. The same experimental conditions were simulated using a numerical model employing the modified volume heat source (MVHS) model. To analyze the validity of the numerical model, the air temperature inside the room and the surface temperatures of the curtain wall Al frame and glass panes calculated by numerical analysis were compared with experimental values, and the location and timing of the initial crack were compared. Thermocouples were installed on the Al frame and the glass surface to measure the surface temperature of the curtain wall during the fire for approximately 100 s after the onset of the fire. Additional thermocouples were installed to measure the air temperature inside the room to verify the results of the numerical analysis. A numerical model using the MVHS model was established to analyze the overall temperature distribution and the behavior of thermal stress on the curtain wall caused by the fire. MVHS calculations were based on measured fuel consumption, and the numerical analysis results were compared with the experimental values. We confirmed that the temperature calculated using computational fluid dynamics (CFD) was in good agreement with the temperature measured in the experiment. The temperature distribution and thermal stress of the curtain wall up to the point of glass breakage were reviewed using a thermal stress structural analysis that employed the results of the CFD analysis with MVHS. The time required to reach the temperature required for glass to break in the numerical analysis and the time required for the first crack to occur in the experiment were identical. The crack positions obtained from the numerical model and experiments were also the same. Overall, our results showed that the numerical model using the MVHS model is suitable for predicting curtain wall breakage and temperature distributions inside a space during the fire.