爆燃火灾全程下多梁式PCT型梁桥剪力滞效应

Shear-lag effect of multi-beam prestressed concrete t-shaped girder bridge exposed to explosion fire

针对火灾下预应力混凝土T(PCT)型梁桥顶板的开裂,利用热力耦合方法分析了爆燃火灾下4片预应力混凝土T梁桥的温度场和剪力滞时程演变规律。研究结果表明:火温全程T型梁翼缘板连接部位温度值高于翼缘板根部,呈现出以腹板与顶板交合部位为中心逐渐向翼缘板边缘部位呈稀疏温度带间隔梯度过渡的'V'状分布云;火温初时,恒载作用下顶板最大压应力位于两边肋顶部,最小压应力位于两边梁外侧悬臂板端部,单片梁体顶板呈负剪力滞状态,4片梁体顶板剪力滞呈'W'状,其峰值之比接近1.0;随火温时间延增,两中肋的应力峰值点出现在半悬臂板宽度处,应力变化幅值大于两边肋与四肋同时受火的顶板应力变化幅值,顶板部分出现拉应力;随火温时间延增,各片T梁顶板处于负剪力滞状态;研究可为预应力桥梁实用抗火设计提供依据。

Aimed at the crack of upper floor for multi-beam prestressed concrete（PCT） T-shaped girder bridge, thermo-mechanics coupled method was adopted to analyze time-dependent law for temperature dis- tribution of sections and space shear lag of girder. The results indicate that in the whole process of fire time, temperature in brim of the cantilever plate is higher than that in root of the cantilever plate, which has a sparse and interval temperature cloud presenting a V-shaped distribution from the combination location of web floor and upper floor to the rim of cantilever plate; at initial time of fire temperature, in the condition of bridge acted by dead load, the maximum compression stress is located in upper part of bias girder, the mini- mum compression stress is located in the end of outer cantilever plate, upper floor of each girder has an even negative shear lags condition, shear lags of 4 piece of girders presents a W shape, and the ratio of the peak stress is close to 1.07 with increment of fire time, the peak value of stress is located in a half part of cantile- ver width, the variation amplitude of stress is more obvious than that in the condition that two bias girder and two middle girder are both exposed to fire, and a tensile stress appears in part of upper floor; with in-crement of fire time, each T-shaped girder presents a negative shear lags condition. The research can pro- vide basis for fire-resistant design of prestressed bridge. 2 tabs, 3 figs, 17 refs.