预应力混凝土连续梁桥动力特性及影响因素分析

Dynamic Characteristics and Influence Factors of Pre-stressed Concrete Continuous Beam Bridge

为了探明新建桥梁动载试验实测一阶频率与理论计算结果产生偏差的原因,以某预应力混凝土变截面连续梁成桥动载试验为背景,实测了在脉动荷载下桥梁的一阶频率和振型,建立了有限元模型,同时计算了桥梁一阶频率的理论值,并对二者进行了对比;分析了纵向普通钢筋、预应力钢筋、护栏、混凝土动弹性模量等4个因素对桥梁动力特性的影响。结果表明:一阶频率实测值为1.760 Hz,理论计算值为1.395 Hz,二者偏差约21%;在有限元模型中计入纵向普通钢筋、预应力钢筋、护栏和混凝土动弹性模量后,结构的一阶频率分别为1.416、1.413、1.384和1.634 Hz,综合考虑4个因素的一阶频率为1.684 Hz;4个因素中,混凝土动弹性模量对结构一阶频率影响最为显著,其它因素影响较小可不考虑。建议利用桥梁基频进行结构刚度评定时,应在有限元模型中计入混凝土动弹性模量,使其更为接近实际状态。

In order to find out the causes of deviation between first-order frequency of dynamic load test of some new bridges and the theoretical calculation results,based on the dynamic load test of a pre-stressed concrete cross-section continuous beam bridge,the first-order frequency and vibration mode of the bridge under fluctuating load were measured;meanwhile,the finite element model was established.The theoretical value of the first-order frequency of bridge was calculated,and the two were compared.The influence of 4 factors such as common longitudinal steel bar,pre-stressed steel bar,guardrail and dynamic elastic modulus of concrete on the dynamic characteristics of bridge was analyzed.The results show that the measured value and theoretical value of the first-order frequency are 1.760 Hz and 1.395 Hz respectively,whose deviation is about 21%.Taking the factors such as common longitudinal steel bar,pre-stressed steel bar,guardrail and dynamic elastic modulus of concrete into the finite element model respectively,the first-order frequency of the structure are 1.416Hz,1.413 Hz,1.384 Hz and 1.634 Hz respectively;and the first-order frequency is 1.684 Hz when the above four factors are considered comprehensively.Based on the above analysis results,among 4 influence factors,the dynamic elastic modulus of concrete has the most significant influence on the first-order frequency of the structure;and other factors have less influence,which may not be considered.It is suggested that when the bridge fundamental frequency is used to evaluate structure stiffness,the dynamic elastic modulus of concrete should be calculated in the finite element model,which makes the results closer to the actual state.