【正文】 ut heat, cause inside very much high temperature, the internal and external difference in temperature is too large, cause the surface to appear in the crack. Should according to actual conditions in constructing, is it choose heat of hydration low cement variety to try one39。 Strong 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 of ponent form sudden change office, block place to be easy to appear crack strength reinforcing bar of the structure. 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 本 科畢業(yè)設(shè)計 英文文獻 8 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 本 科畢業(yè)設(shè)計 英文文獻 7 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。 this may affect the structural form selected, i. e. whether or not a tie should be introduced, or the stiffness of the deck relative to the arch. In recent years, the traffic capital construction of our country 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。 it did not apply to steel or reinforced concrete (or timber for that matter) as these materials were capable of resisting tensile stresses. Twentieth century arch bridges have bee increasingly sophisticated structures bining modern materials to create exciting functional urban sculptures. Types of arch bridge The relevant terms that are used to describe the various parts of an arch bridge are shown in Figure 1. Arches may be grouped according to the following parameters: 1. the materials of construction 2. the structural articulation 3. the shape of the arch Historically, arch bridges are associated with stone masonry. This gave way to brickwork in the nieenth century. Because these were proportioned to minimise the possibility of 本 科畢業(yè)設(shè)計 英文文獻 3 tensile stress, they tend to be fairly massive structures. By parison the use of reinforced concrete and modern structural steel gives the opportunity for slender, elegant arches. Nowadays, timber is restricted to small bridges occasionally in a truss form but more usually as laminated curved arches. Although timber has a high strength to density ratio parallel to the grain, it is anisotropic and strength properties perpendicular to the grain are relatively weak. This requires careful detailing of connections to ensure economic use of the material. With regard to structural articulation the arch can be fixed or hinged. In the latter case either one, two or three hinges can be incorporated into the arch rib. Whilst the fixed arch has three redundancies, the introduction of each hinge reduc