However,crack and excess deflection of rigid frame bridges became a serious problems.

In recent years, there are many long span prestressed concrete continuous rigid-frame bridges constructed in our country, at the same time, some problems have been exposed which are quite markable, especially the crack, the deflection and so on.

In addition, the cause of cracks in box girder and long-term deflection of bridge is summarized from aspects of design, construction, material and using conditions, and then the measures which are used to prevent the disease of the bridge are also put forward.

This paper describes in details the principle, the operation and the experience for modifying the down deflection of a fixed-girder for bucket wheel stacker/reclaimer and keeping its pre-designed up deflection by means of firing and pre-tension method.

Which is used to correct the down deflection on the gir der of 20 t bridge crane under longitudinal shear.

The main reason of the main beam down deflection was that the most complex stress exceeded the admissible value and achieved the yield limit value.

On the causes of beam bridge continuous down-warping and its control measures;

Research purposes:The post down-warping is a common disaster for large span concrete beam bridge,which can cause serious danger to bridge,so it is urgent to find out the main cause for down-warping for the purposes of prevention of it and finally control of down-warping.

Genetic analysis of large span beam bridges long downwarping and controlling downwarping;

Research on the safety of pre-stress T beam down warping of one railway bridge;

Discussion on the prevention of reinforced concrete beam in down warping in engineering practice;

According to theoretic analysis, computing the bending deflection of every roller is enabled to ignore the effect of the web and only allow to the rectangular section made up of flange plates.