1、 附录 外文翻译 A primary analysis on the causes of bridge cracks Recent years, the transportation infrustracture construction of our province has got a swift and violent development, and a large number of concrete bridges were built. However, in the courses of building and using these bridges, there are a
2、 lot of reports about the collapse of the bridges which are caused by the bridge cracks coming from time to time. Thus the concrete cracks can be called an often-occurring disease or an frequently-occuring disease which troubled a lot of the bridge engineering and technical personnel. However, if so
3、me measures can be taken during the design and construction of the bridge, many of the cracks can be controlled or even overcome. In order to enhance our understanding of the concrete bridge cracks and avoid the huge damage caused by the bridge cracks, this essay is thus writen to make a relatively
4、detailed analysis and summary of the classification and causes of the concrete bridge cracks and will try to find some feasible ways to control the bridge cracks in the courses of design and building. There are various causes of the bridge cracks. Sometimes a bridge crack may influence each other. B
5、ut the appearance of each crack has its own reason or reasons. In terms of the causes, the bridge cracks can be divided into the following types: First,cracks caused byload The cracks that are caused by the regular dynamic, static load or secondary stress are called load crack, which can be divided
6、into direct stress cracks and secondary stress cracks. Direct stress crack refers to the cracks that are directly caused by the outside load stress. The causes of this kind of crack are as follows: 1, When calculating during the design stage, it does not calculate or calculates partly； The model is
7、unreasonable； The structure supposed is not accorded with the actual strength ； Load is less or leak calculated； Internal forces and reinforcement calculation discounts； Safety coefficient of structure is not enough. Do not consider the possibility of construction at the time of the structural desig
8、n； It is insufficient to design the section； It is simply little and assigning the mistake for reinforcing bars to set up； The structure rigidity is insufficient； Construct and deal with improperly； The design drawing can not be explained clearly etc. 2,At the construction stage, does not pile up th
9、e machines , materials restrictively； Dont understand precast structure mechanical characteristics. Does it stand up , hang , transport , install are at will to understand； Construct not according to the design drawing. Alter the construction order of the structure without authorization. Change the
10、structure strength mode； Do not do the tired intensity checking computations under machine of vibration condition etc. 3, At the using stage, the heavy-duty vehicle which is beyond the design load passes the bridge； Receive the contact, striking of the vehicle, shipping； Strong wind, heavy snow, ear
11、thquake happen, explode etc. Times stress cracks once means the stress of secondary caused by load outside produces the cracks. The reason why the cracks produce is as follows: 1, In designing outside load function, actual working condition and routine , structure of calculating have discrepancy or
12、is are considered to calculate, thus cause stress once to make the structure to fracture in some position. For example, the arch feet design of two hinge arch bridge is often in decorate X form reinforced, while cutting down this section of design size. By means of the theoretical calculation, the d
13、epartment never exist bending moment , but actually should is it can resist curved still to the hinge, so it 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 an accurate diagram to ana
14、log computation. It is general according to experience to set mechanical reinforced. Studies have shown that after mechanical components are dug hole, diffraction flow will produce. It gathers near the hole and produces the enormous stress concentration. In long span prestressed continuous beams, it
15、 is often to block the steel beam according to the needs of section internal force in the span, and set up the anchor head, but in near anchorage section can often see a crack. So if dealing with improperly, in the corner of the structure or components shape mutations, stress reinforced truncation p
16、lace easily crack. In the actual project, times stress cracks can be the most common reason which lead to load crack. Times stress cracks are tension, splitting, shear properties. Stress crack once is loaded and caused, only seldom calculates according to the routine too, but along with the continuo
17、us improvement of the modern computing method, times stress cracks can accomplish reasonable checking computations. For example, on the secondary stress produced by prestressing force, creep etc., many plane stem department finite element program all can calculate correctly, but it is more difficult
18、 40 years ago. In the design, should pay attention to avoid structural break (or section mutation). When it is unable to avoid , should do local processing, such as corners do rounded corners, mutations make gradual transition, and strengthen constructional reinforcement at the same time. Corners in
19、crease oblique reinforced. For larger holes, if conditional, can install edge angles in the surrounding Settings. In accordance with the load characteristics, load cracks present different characteristics. This kind of cracks appear in more tensile crack, shear zone or severe vibration parts. But it
20、 must be pointed out, if pressure areas appear peeling or have short cracks along the compressive direction, it is often the symbol of structure can limit bearing capacity, it is an omen that the structure is destroyed. The reason is often that sectional size is partial and small. According to the d
21、ifferent structure stress modes, the resulting crack characteristics are as follows: 1, Center tensile. Cross-section throughout component cracks. The spacings are approximately the same. The direction perpendicular to the force. When using thread steels, times cracks appear near reinforced between
22、Cracks. 2, Center compression. Along the components of parallel to the stress direction appears short and secret parallel crack. 3, Bending terminal. Near bending moment maximum section, from the tensile crack edges appear tensile direction with vertical cracks. And gradually to neutralize axis dire
23、ction. When using thread reinforced, between gaps appear shorter times crack. When constructional reinforcement is fewer, cracks are few and wide, the structure may happen brittle fracture. 4, Large eccentric compression. Large eccentric compression and small eccentric compression of lower tensile r
24、einforcement, are similar to the flexural members. 5, Small eccentric compression. Small eccentric compression and large eccentric compression of more tensile reinforcement, are similar to the central compression members. 6, Shear. When the stirrup are too dense, baroclinic destruction happens. Along the girder ends 45 direction belly appear the diagonal crack； When stirrups are appropriate, shear compression failure occurs. Along the girder ends about 45 direction in the mid-lower appear parallel inclined cracks. 7, Torsion. Component side more than 45 comes first abdomen direction diagonal
