无黏结预应力束切割崩弹分析

Analysis on Unbonded Prestressing Tendon Cutting and Burst

预应力技术在混凝土桥梁建设及加固中应用广泛,在桥梁拆除施工中,需要对体内及体外预应力进行释放。由于预应力处于弹性张拉状态,切割过程中体内弹性势能瞬间释放,可能造成钢束崩弹,产生安全风险,需要对其进行分析。首先从理论层面建立单股预应力束切割崩弹的能量传递模型,解释钢束张拉切割全过程受力变化与能量传递关系;进而依据理论分析结果,采用精细化数值模拟方法,定量计算断裂瞬间钢束崩弹速度及各能量之间转化定量关系;通过与已有试验结果以及能量传递模型结果对比,验证数值模型的准确性;计算不同切割位置和初始预应力情况下的能量传递过程和切割崩弹速度。结果表明:受应力波传播过程影响,钢束对称位置切割时崩弹速度最大,且初始预应力越大,钢束断裂释放的弹性应变能越多,崩弹风险越大;控制张拉应力为1395 MPa的螺旋预应力束对称切割时,崩弹速度最高达到24.9 m/s,对施工人员和机具造成极大安全风险,施工时应严格遵守施工规范,保障生命财产安全。

Prestressing technology is widely used in the construction and reinforcement of concrete bridges,and it is necessary to release the internal and external prestressing in the bridge demolition construction.As the prestressing force is in elastic tension state,the instantaneous release of elastic potential energy in the body during cutting process may cause the steel to collapse and produce safety risk,which needs to be analyzed.The energy transfers model of single-strand prestressing tendon cutting and burst was firstly established at the theoretical level to explain the relation between force variation and energy transfer during the whole process of beam tensioning and cutting.The refined numerical simulation method was used to quantify the beam burst speed at the moment of fracture,and to calculate the quantitative relation among the transformations of energy.Firstly,the accuracy of numerical model was verified by comparing with existing test results and energy transfer model results.The energy transfer process and the cutting burst velocity were calculated for different cutting positions and initial pre-stress conditions.The results show that the burst velocity is the highest when the tendon is cut at symmetric position due to the stress wave propagation process.The higher the initial prestress,the more the elastic strain energy released by the beam fracture,and the higher the risk of burst.When the spiral prestressing beam with 1395 MPa tensioning stress is cut symmetrically,the maximum burst velocity reaches 24.9 m/s,which poses great safety risk to the construction personnel and machinery,and the construction specifications should be strictly observed to ensure the safety of life and property.