【正文】 he deck may be used to ?tie‘ the arch. Tied arches are particularly appropriate when deck construction depths are limited and large clear spans are needed (particularly if ground conditions are also difficult and would require extensive piling to resist the horizontal thrusts). Returning to Hooke‘s anagram, the perfect shape for an arch would be an inverted catenary – this would only be the case for carrying its own selfweight. Vehicle loading and varying superincumbent dead load both induce bending moments. Consequently the arch has to have sufficient thickness to acmodate the ?wandering‘ thrust line. For ease of setting out and construction simpler shapes are adopted nowadays segmental or parabolic shapes are used. Although in situations where maximum widths of headroom have to be provided (say over a railway, road or canal) an elliptical shape may be required or its nearest ?easy‘ equivalent the threecentred arch. It is worth menting at this stage regarding the idealization of arch structures. 本 科畢業(yè)設(shè)計(jì) 英文文獻(xiàn) 5 Traditionally arches are perceived as being twodimensional structures。 Calculate the model is unreasonable。 Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design。 Construct and deal with improperly。 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 is it is it destroy to press to cut to happen when the hoop muscle is proper, underpart is it invite 45 degrees direction parallel oblique crack each other to appear along roof beam end. (7) Sprained. Component one side belly appear many direction oblique crack, 45 degrees of treaty, first, and to launch with spiral direction being adjoint. (8) Washed and cut. 4 side is it invite 45 degrees direction inclined plane draw and split to take place along column cap board, form the tangent plane of washing. (9) Some and is pressed. Some to appear person who press direction roughly parallel large short cracks with pressure. Second, crack caused in temperature change. The concrete has nature of expanding with heat and contract with cold, look on as the external environment condition or the structure temperature changes, concrete take place out of shape, if out of shape to restrain from, produce the stress in the structure, produce the temperature crack promptly when exceeding concrete tensile strength in stress. In some being heavy to step footpath among the bridge, temperature stress can is it go beyond living year stress even to reach. The temperature crack distinguishes the main characteristic of other cracks will be varied with temperature and expanded or closed up. The main factor is as follows, to cause temperature and change. (1) Annual difference in temperature. Temperature is changing constantly in four seasons in one year, but change relatively slowly, the impact on structure of the bridge is mainly the vertical displacement which causes the bridge, can prop up seat move or set up flexible mound, etc. not to construct measure coordinate, through bridge floor expansion joint generally, can cause temperature crack only when the displacement of the structure is limited, for example arched bridge, just bridge etc. The annual difference in temperature of our country generally changes the range with the conduct of the average temperature in the moon of January and July. Considering the creep characteristic of the concrete, the elastic mould amount of concrete should be considered rolling over and reducing when the internal force of the annual difference in temperature is calculated. (2) Rizhao. After being tanned by the sun by the sun to the side of bridge panel, the girder or the pier, temperature is obviously higher than other position, the temperature gradient is presented and distributed by the line shape. Because of restrain oneself function, cause part draw stress to be relatively heavy, the crack appears. Rizhao and following to is it cause structure mon reason most, temperature of crack to lower the temperature suddenly. (3) Lower the 本 科畢業(yè)設(shè)計(jì) 英文文獻(xiàn) 10 temperature suddenly. Fall heavy rain, cold air attack, sunset, etc. can cause structure surface temperature suddenly dropped suddenly, but because inside temperature change relatively slow producing temperature gradient. Rizhao and lower the temperature internal force can adopt design specification or consult real bridge materials go on when calculating suddenly, concrete elastic mould amount does not consider converting into and reducing. (4) Heat of hydration. Appear in the course of constructing, the large volume concrete (thickness exceeds 2. 0), after building because cement water send out 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。 And such absorbing water rates as the sandstone, slate, angle amphibolite, etc. are greater, contractivity is relatively high. Aggregate grains of footpath heavy to shrink light in addition, water content big to shrink the larger. (3) Water gray than. The heavier water consumption is, the higher water and dust are, the concrete shrinks the more greatly. (4) Mix the pharmaceutical outside. It is the better to mix pharmaceutical waterretaining property outside, then the concrete shrinks the smaller. (5) Maintain the method. Water that good maintenance can accelerate the concrete reacts, obtain the intensity of higher concrete. Keep