【正文】 trong wind , heavy snow , earthquake happen , explode etc.. Stress crack once means the stress of secondary caused by loading outside produces the crack. The reason why the crack produces is as follows, 1, In design outside load function , because actual working state and routine , structure of thing calculate have discrepancy or is it consider to calculate, thus cause stress once to cause the structure to fracture in some position. Two is it join bridge arch foot is it is it assign X shape reinforcing bar , cut down this place way , section of size design and cut with scissors at the same time to adopt often to design to cut with scissors, theory calculate place this can store curved square in , but reality should is it can resist curved still to cut with scissors, so that present the crack and cause the reinforcing bar corrosion. 2, Bridge structure is it dig trough , turn on hole , set up ox leg ,etc. to need often, difficult to use a accurate one diagrammatic to is it is it calculate to imitate to go on in calculating in routine, set up and receive the strength reinforcing bar in general foundation experience. Studies have shown , after being dug the hole by the strength ponent , it will produce the diffraction phenomenon that strength flows, intensive near the hole in a utensil, produced the enormous stress to concentrate. In long to step prestressing force of the continuous roof beam , often block the steel bunch according to the needs of section internal force in stepping, set up the anchor head, but can often see the crack in the anchor firm section adjacent place. So if deal with improper, in corner or ponent form sudden change office , block place to be easy to appear crack strength reinforcing bar of structure the. In the actual project, stress crack once produced the most mon reason which loads the crack. Stress crack once belong to one more piece of nature of drawing , splitting off , shearing. Stress crack once is loaded and caused, only seldom calculate according to the routine too, but with modern to calculate constant perfection of means, times of stress crack to can acplish reasonable checking putations too. For example to such stresses 2 times of producing as prestressing force , creeping ,etc., department39。 Do not do the tired intensity checking putations under machine vibration and wait to the structure . 3, Using stage, the heavyduty vehicle which goes beyond the design load passes the bridge。 Is it prefabricate structure structure receive strength characteristic , stand up , is it hang , transport , install to get up at will to understand。 Construct and deal with improperly。 It is simply little and assigning the mistake for reinforcing bar to set up。 Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design。 Load and calculate or leak and calculate few。 Calculate the model is unreasonable。The bridge crack produced the reason to simply analyse In recent years, the traffic capital construction of our province gets swift and violent development, all parts have built a large number of concrete bridges. In the course of building and using in the bridge, relevant to influence project quality lead of mon occurrence report that bridge collapse even because the crack appears The concrete can be said to often have illness ing on while fracturing and frequentlyoccurring disease , often perplex bridge engineers and technicians. In fact , if take certain design and construction measure, a lot of cracks can be overe and controlled. For strengthen understanding of concrete bridge crack further, is it prevent project from endanger larger crack to try one39。s best, this text make an more overall analysis , summary to concrete kind and reason of production , bridge of crack as much as possible, in order to design , construct and find out the feasible method which control the crack , get the result of taking precautions against Yu WeiRan. Concrete bridge crack kind, origin cause of formation In fact, the origin cause of formation of the concrete structure crack is plicated and various, even many kinds of factors influence each other , but every crack has its one or several kinds of main reasons produced . The kind of the concrete bridge crack, on its reason to produce, can roughly divide several kinds as follows : (1) load the crack caused Concrete in routine quiet . Is it load to move and crack that produce claim to load the crack under the times of stress bridge, summing up has direct stress cracks , two kinds stress crack onces mainly. Direct stress crack refer to outside load direct crack that stress produce that cause. The reason why the crack produces is as follows, 1, Design the stage of calculating , does not calculate or leaks and calculates partly while calculating in structure。 The structure is supposed and accorded with by strength actually by strength 。 Internal force and matching the mistake in putation of muscle。 It is insufficient to design the section。 Structure rigidity is insufficient。 The design drawing can not be explained clearly etc.. 2, Construction stage, does not pile up and construct the machines , material limiting 。 Construct not according to the design drawing, alter the construction order of the structure without authorization , change the structure and receive the strength mode。 Receive the contact , striking of the vehicle , shipping。s finite element procedure calculates levels pole correctly now, but more difficult 40 years ago. In the design, should pay attention to avoiding structure sudden change (or section sudden change), when it is unable to avoid , should do part deal with , corner for instance, make round horn , sudden change office make into the gradation zone transition, is it is it mix muscle to construct to strength