Study On The Methods Of Widening Superstructure Based On Stiffness Difference

With the rapid development of economy,the number of highway reconstructions and expansion projects in China has been increasing.The bridge expansion projects became a controlling project due to the problems involving concrete shrinkage and creep and foundation settlement.The existing researches are based on the stiffness of new and old beams,and there is little involvement in the unequal stiffness of the old and new girders.This article was based on the Shanxi Provincial Traffic Construction Science and Technology Project “Research on the Safety Assessment and Key Techniques of Cracked Damaged Assembled Box Girder Bridges”,taking the typical simple beam with a span of 30 m in Changhan highway reconstruction project as the research object.In view of the related problems such as the stiffness and the unequal stiffness of the old and new beams,a literature review and numerical analysis methods were conducted.The main work and achievements as follows:(1)The force of the mixed structure after being widened with equal stiffness beams was studied.The results show that: with two kinds of widening methods,the stress of old bridges has been declined to varying degrees.The improvement effect of the two sides' widening methods is better than that of the single side widening.The distribution of non-uniform internal forces in the two patch widths is uniform,and there is no significant difference in the effect of non-uniform internal forces.(2)The force of the mixed structure was studied with unequal stiffness beams.The results show that the strength of the old bridge is improved to different extents by using two kinds of methods for inequality stiffness beams.The improvement effect of the two-sided widening on the old beam is better than that of the single-sided;From the perspective of additional internal forces,the stiffness of the new and old beams is not equal,so the combined rules of different beams have their own characteristics in the distribution of additional internal forces caused by axial force of contraction,creep effect,and foundation settlement effect.(3)The force characteristics of the hybrid structure after using a stiffened beam and an inequality beam for a hollow slab bridge are compared.In the case of single-sided widening,for the lateral distribution coefficient and live load effect,a stiffer hollow plate should be used to improve the force of the old beam;while,for other additional internal forces,using the T beam has less effect than other beams.In the case of double-side widening,the use of hollow slab beams can reduce the lateral distribution coefficient of the old beams.For live-load effects,the use of small box beams can reduce the live load effect of the old beams;and for other additional internal forces,the use of hollow slabs has greater effect than other beams(4)The force characteristics of hybrid structures after using equal stiffness beams and unequal stiffness beams for small box bridges are compared.For small box girder bridges,the two kinds of spelling widths are the same for live load and additional internal forces.After the use of small box beams,the live beam effect and the most unfavorable lateral distribution coefficient of the old beam are smaller than those of the T beam.For the additional internal forces other than the contraction axial force,the old beam is less stressed than the small box beam after using the T beam.