Study Of The Vibration Characteristics For Bridge Structures Under The Influence Of Prestress Effect

With the existence of prestress, the static and dynamic characteristics of concretestructures will be changed. There were lots of depth researches and reasonableconclusions in the static effect of structure.For example, prestress can make full use ofthe tensile and compressive strength of the material and save effectively, which aslostrengthen the capacity, stability and weaken the deflection of the structure.The impact of dynamic characteristics of the structure is worth to be studidedin-depth. As one kind of compression-flexure members, the free vibration frequency ofthe prestressed beam responses the vibration characteristic of the bridge, bridgeearthquake resistance and shock absorption design and bridge structure dynamiccalculation must be responsed by structural dynamic, however, the most basic and mostcritical is to analysis and calculate for the natural frequency and vibration mode of thebridge structure. Bridges under prestressed (axial force) caused second-order effect willchange the stiffness and sectional properties and quality characteristics of the bridge,and leading the structural vibration characteristics to change.This paper select common simply supported beam and continuous beam structure,through the reasonable simplification of the figure of prestress tendons,the equivalentforce of prestressed could be calculated.Through FEM and principle of virtual work, theplane beam element stiffness matrix was deduced, especially focus on derivinggeometric stiffness matrix under prestress.Based on MATLAB, a program which is usedto calculate the natural vibration characteristics under the influence of prestress is to bewrote,and through it the natural vibration feature of a couple of simply beam andcontinuous beam bridges which have different spans are calculated.This study shows that prestress reduce the natural frequencies of the simplysupported beam and continuous beam,and the prestress to bridge low-orderself-vibration frequency is greater than the high-order natural frequency.