两跨无粘结预应力混凝土连续板抗火性能试验与分析

完成了9块两跨无粘结预应力混凝土连续单向板抗火试验。通过布置于试验板内的热电偶,获得了试验板截面的温度场分布。通过布置于无粘结筋锚固端的力传感器和试验板上的位移传感器,获得了试验板中无粘结筋应力和试验板新增变形在火灾下的变化过程。通过布置于各试验板边支座上的压力传感器,获得了两跨连续板支座反力在火灾下的变化过程。受火过程中试验板背火面经历了水分溢出、水蒸气形成和发展、溢出水干涸及水蒸气消失的过程。基于不同试件不同时刻的无粘结钢丝应力实测值、边支座反力实测值、跨中新增变形实测值,拟合出了考虑各关键参数影响的火灾下两跨连续板中无粘结钢丝应力计算公式、边支座反力计算公式和跨中新增变形计算公式。针对在抗火试验中有4块试验板板顶负弯矩的钢筋截断处出现了贯穿裂缝的现象,提出了火灾下两跨连续板中支座两侧负弯矩钢筋的截断建议。

Experiment and analysis on fire resistance of two-span unbonded prestressed concrete continuous slabs

Experiment on fire resistance of nine two-span unbonded prestressed concrete(PC) continuous one-way slabs is completed.Temperature distribution along section of the slabs was obtained by embedded thermocouples in the slabs.Variation of new deflection of the slabs and stress of the unbonded prestressing steel wires in the slabs subjected to fire were obtained by load cells at the anchorage end and displacement transducers on the slabs.Variation of side supports reaction of the slabs subjected to fire was obtained by load cells at the side supports.The fire witnessed the whole process of water overflowing,vapor appearing and developing,and water drying,vapor disappearing on the unexposed surface.Calculation formula of side supports reaction,stress of unbonded prestressing steel wires and new deflection in the mid-span of slabs subjected to fire were obtained by fitting curve of experimental data considering every key factor.For in 4 slabs cracks penetrate the slab close to the cut-off point of negative flexural reinforcements at the top of intermediate support,proposition for cutting off of negative flexural reinforcements at the top of intermediate support of two-span continuous slabs is proposed.