预应力混凝土简支板抗火性能试验与分析  

Experimental analysis of anti-fire capacity of simply supported prestressed concrete slabs

作　　者：郑文忠[1] 许名鑫[1] 杨杰[1] 胡琼[1] 侯晓萌[1] 石东升[1] 

机构地区：[1]哈尔滨工业大学土木工程学院,黑龙江哈尔滨150090

出　　处：《建筑结构学报》2006年第6期48-59,共12页Journal of Building Structures

基　　金：黑龙江省杰出青年科学基金资助项目(2001-8)

摘　　要：完成了9块无粘结和1块有粘结预应力混凝土单向简支板的抗火试验。各试验板内的热电偶在火灾下的实测结果表明,温度由迎火面至背火面逐渐递减,由迎火面至背火面的温度变化梯度随离迎火面距离的增大而减小。布置于无粘结预应力筋锚固端的力传感器和试验板上的位移传感器的测试结果表明,受火初期试验板挠曲变形增长较快,无粘结预应力筋应力呈增长趋势;受火一段时间之后试验板变形增长速度有所减缓,无粘结预应力筋应力呈减小趋势,且这种趋势一直延续到停火后一段时间;停火一段时间之后,试验板有变形恢复趋势,无粘结预应力筋应力水平又有所恢复。在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。在试验炉两侧壁的观察孔观测到有6块试验板发生了爆裂,爆裂发生在预应力度较高、荷载作用水平较低的试验板的邻近支座区域。基于试验结果,试算确定了对流换热系数、辐射换热相当发射率系数、混凝土导热系数和比热的取值,应用ANSYS软件实现了对预应力混凝土单向简支板的非线性全过程分析。提出合理考虑温度膨胀、高温蠕变影响的荷载项对应的火灾下无粘结预应力筋应变及应力计算方法。沿板厚将截面分成若干条带,将各条带的板宽乘以所考察条带混凝土与迎火面所在条带混凝土的模量比即可得到火灾下预应力混凝土简支板的等效截面,利用常温下刚度计算公式便可计算出火灾下荷载作用所引起的变形值。Experiment on anti-fire capacity of nine unbonded and one bonded prestressed concrete simple slabs were carried out. Test results measured by thermocouples in slabs indicate that temperature decreases gradually from the surface to the opposite side, and thermal gradient decreases with the increase of distance from the surface. Test result measured by force sensors at the anchorage end and displacement sensors on the slabs indicate that the deflection of the slabs increases rapidly and stress of the unbond tendons increases in the early stage in fire; when exposed to fire for some time, the increase of deflection slows down and the stress decreases, and these decrease lasts till fire is ceased for some time; after that the deflection of the slabs and the stress of the unbond tendons begin to recover slightly. During the fire, the whole process of water overflowing, vapor appearing and developing, and water drying, vapor disappearing occurs on unexposed surface. Observing through holes at two sides of the furnace shows that spalling of concrete occurs near supports regions in six slab specimens with greater prestress and smaller load level. Based on test result, the values of convection heat transfer coefficient, radiation emissivity coefficient, thermal conductivity and specific heat of concrete are determinated by a trial and error procedure. Nonlinear time-history analysis of prestressed concrete simple slab subjected to fire is carried out by using of ANSYS software. Calculating method for strain and stress of unbonded tendon for load is presented with the influence of expansion and creep due to high temperature is taken into account. Dividing section of slab into strips along the depth,equivalent section of slab subjected to fire can be obtained by multiplying width of each strip with elasticity modulus ratio of concrete in each strip to that in the strip including exposed surface. Therefore, the deflection of slab due to load could be calculated by using stiffness formula at normal temperature.

关 键 词：预应力混凝土 简支板 抗火性能 试验 分析 

分 类 号：TU378.5[建筑科学—结构工程] TU317.1