混凝土梁桥过火后预应力损失

火灾中产生的高温对预应力结构有较大影响,因降低结构的有效预应力,导致过火后受拉外缘压应力储备降低,结构提前开裂,影响结构使用性能和耐久性。为快速确定预应力混凝土梁过火后的有效预应力,以某省过火后拆除的32片梁为样本,通过实测过火后混凝土梁桥钢绞线永存应力,获得剥落深度比与预应力损失比的回归公式,选用极限承载能力试验及有限元数值分析验证该公式的适用性。结果表明,火灾后梁板预应力钢束出现应力损失,当混凝土剥落深度超过1/3钢绞线净保护层时,预应力损失不可忽略;先张法预应力混凝土结构,抗火设计应适当提高钢绞线保护层厚度;当混凝土剥落深度超过2/3钢绞线净保护层时,预应力损失率达10%,严重影响结构刚度。

The prestressing loss of concrete beams after exposed to fire

The high temperature produced in fire has a great influence on the pretensioned pre-stressed concrete beams. Due to the decrease of the effective prestressing force in the structure, the compressive stress spread over edge girth in tension is reduced, and structural cracks appear early, resulting in the decrease of service performance and durability. To detect the effective prestressing force of the pre-stressed concrete beams exposed to fire quickly, thirty-two pieces of beams exposed to fire were taken as samples. The regression formula of spalling depth ratio and prestress loss ratio was obtained by measuring the permanent stress of steel strand of concrete girder bridge after exposed to fire, and the applicability of the formula was verified by an experimental and finite element analysis on ultimate bearing capacity. The results show that the phenomenon of prestress loss of beam prestressed steel bundle exists. When the spalling depth of concrete exceeds 1/3 of the net protective layer of steel strand, the prestress loss cannot be ignored. The thickness of the steel strand protective layer should be increased appropriately for pretensioned prestressed concrete structures in fire resistance design. When the spalling depth of concrete exceeds 2/3 of the net protective layer of steel strand, the rate of prestressing loss due to high-temperature creep exceeds 10%, resulting in severe decrease of the girder stiffness.