超声波测量混凝土密实度在桥梁承载力评价中的应用

针对桥梁中箱梁腹板、顶底板预应力筋间尺寸小且配筋密集的部位混凝土不密实现象，依据超声回弹综合法的测强原理，提出混凝土密实度系数的概念。基于概率思想提出了2种桥梁整体密实度的计算方法，通过4片后张法变截面预应力工字梁的超声回弹试验，计算了混凝土梁的密实度，分析了混凝土密实度的分布规律。通过弯曲静载试验，分析了混凝土密实度对桥梁开裂荷载与极限承载能力的影响，给出了考虑密实度的预应力工字梁开裂荷载和极限荷载的计算公式。结果表明，尺寸及配筋会影响混凝土的密实度，混凝土密实度近似正态分布，以均值为中心95％保证率的密实度上下限的表征方法能更好地表征混凝土的密实度，考虑混凝土密实度计算桥梁承载力更加符合实际。

Application of Measuring Concrete Compactness Using Supersonic in Bridge Bearing Capacity Appraisal

Aiming at the phenomenon of small size and concrete incompacmess in the densely packed reinforcement in the web plate, the top plate and between the prestressed reinforcement, the concrete compactness coefficient is put forward based on the strength measurement principle using ultrasonic-rebound method. On the basis of probability theory, two kinds of methods are proposed to calculate the compactness of the whole bridge.The compactness is calculated and its distribution regularity is analyzed through the ultrasonic-rebound test of four pieces of post tensioned prestressed beams with variable section. In addition, the influence of concrete compactness on cracking load and ultimate capacity is analyzed through the bending static test.The formulas are given to calculate cracking load and ultimate capacity of prestressed beam with I type section taking compactness into consideration. The results show that size and distributed reinforcing bar can influence the concrete compactness which presents normal distribution approximately. And the attribute method of compactness super limit and low limit which takes equalizing value as the center with 95 % guaranteed rate can show concrete compactness better. It is more practical to consider concrete compactness in calculating the bearing capacity.