OpenSees is an open-source, object-oriented software framework developed at UC Berekeley. The OpenSees framework has been recently extended to deal with structural behaviour under fire conditions. This paper summarizes the key work done for this extension and focuses on the application of the developed OpenSees to study the influence of fire scenarios and bracing system on the resistance of steel frames against fire-induced progressive collapse. Single- and multi-compartment fire scenarios are applied. Additional horizontal and vertical restraints are applied to the frame to simulate the braced steel frame. A parametric study is carried out to find the fire-induced progressive collapse mechanisms of steel frames under various fire scenarios and restraining conditions. The collapse mode of frames is in the form of lateral drift and downward collapse of frames. It is proved that these two collapse nodes can be resisted by applying lateral and vertical restraint on the frame, respectively. The combination of two restraints has a better resistance effect.
Prestressed stayed columns are vulnerable to the stiffness loss in fire. This study aims to reveal the fire resistance and failure behavior of this system. Based on the theoretical optimum prestress, the fire behavior of prestressed stayed columns is investigated using transient state analysis within ABAQUS version 6.14.4 with both the uniform and nonuniform temperature distributions considered. Results show that the stayed columns' approximate failure is above 600°C, and the system usually fails with stay slackening and sometimes with stay retension. If the reflective symmetric buckling mode is dominant and the linear buckling loads of reflective and rotational symmetric modes are numerically close, unstable behavior such as 'mid-span reverse' and 'mode transition' can be observed in conjunction with stay slackening at the heating stage. For the nonuniform temperature distribution, 'mode transition' occurs in most cases, but this transition only reduces the critical temperature significantly in the preceding special cases. Prestress is recommended to be higher than the theoretical optimum prestressing level to avoid premature stay slackening and 'mode transition', but for the preceding special cases with nonuniform temperature distribution, raising prestressing levels may reduce the critical temperature owing to the different failure modes from obvious 'mode transition'. This study would provide basis to establish the design guidance for stayed columns in fire in the future.
The blast resistance of point-supported laminated glass curtain wall has been investigated by means of field blast tests and numerical simulation. Nine site blast tests were carried out, considering two types of glass thickness and six TNT charges ranging from 0.4 to 30 kg. The overpressure and displacement time histories were measured and the failure modes were observed. The overpressure obtained from the measurement panel exhibited a typical pattern of near-field blast with a steep increase followed by a rapid decay within a few milliseconds. The displacement response of the laminated glass panels increased with the increase in the TNT charge almost linearly in the smaller tests (scaled distance ranging 4.5–7 m/kg 1/3 ), which was in line with the increase in the blast impulse in these tests. The failure mode of the point-supported laminated glass panels was featured by tearing off of the polyvinyl butyral layer around the support area, while the glass shards still adhered to the polyvinyl butyral interlayer. Nonlinear dynamic finite element simulation agrees reasonably well with the results from the blast tests. Severe stress concentration has been predicted to occur at the rim of the support holes, leading to initiation of failure at these supports, and this also agrees with the failure mode observed from the blast test. Finally, parametric studies are carried out to investigate the influence of TNT charge weight and the geometric parameters of the panel on the blast response of the glass curtain wall.
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