【正文】 55s / time. It is too short, shake and can not smash closely knit , it is insufficient or not even in intensity to form the concrete。 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。 Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design。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。 Structure rigidity is insufficient。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 strengthen at the same time, corner mix again oblique to reinforcing bar , as to large hole in a utensil can set up protecting in the perimeter at the terms of having angle steel. Load the crack characteristic in accordance with loading differently and presenting different characteristics differently. The crack appear person who draw more, the cutting area or the serious position of vibration. Must point out , is it get up cover or have along keep into short crack of direction to appear person who press, often the structure reaches the sign of bearing the weight of strength limit, it is an omen that the structure is destroyed, its reason is often that sectional size is partial and small. Receive the strength way differently according to the structure, the crack characteristic produced is as follows: 1, The centre is drawn. The crack runs through the ponent cross section , the interval is equal on the whole , and is perpendicular to receiving the strength direction. While adopting the whorl reinforcing bar , lie in the secondclass crack near the reinforcing bar between the cracks. 2, The centre is pressed. It is parallel on the short and dense parallel crack which receive the strength direction to appear along the ponent. 3, Receive curved. Most near the large section from border is it appear and draw into direction vertical crack to begin person who draw curved square, and develop toward neutralization axle gradually. While adopting the whorl reinforcing bar , can see shorter secondclass crack among the cracks. When the structure matches muscles less, there are few but wide cracks, fragility destruction may take place in the structure 4, Pressed big and partial. Heavy to press and mix person who draw muscle a less 西南交通大學(xué)本科 畢業(yè)設(shè)計(jì) 外文翻譯 第 4 頁 one light to pigeonhole into the ponent while being partial while being partial, similar to receiving the curved ponent. 5, Pressed small and partial. Small to press and mix person who draw muscle a more one heavy to pigeonhole into the ponent while being partial while being partial, similar to the centre and pressed the ponent. 6, Cut. Press obliquly when the hoop muscle is too dense and destroy, the oblique crack which is greater than 45?? direction appears along the belly of roof beam end。 Once temperature goes up , the frozen soil is melted, the setting of ground. So the ground is icy or melts causes and does not subside evenly . 7, Bridge foundation put on body, cave with stalactites and stalagmites, activity fault,etc. of ing down at the bad geology, may cause and does not subside evenly . 8, After the bridge is built up , the condition change of original ground . After most natural grounds and artificial grounds are soaked with water, especially usually fill out such soil of special ground as the soil , loess , expanding in the land ,etc., soil body intensity meet water drop, press out of shape to strengthen. In the soft soil ground , season causes the water table to drop to draw water or arid artificially, the ground soil layer consolidates and sinks again, reduce the buoyancy on the foundation at the same time , shouldering the obstruction of 西南交通大學(xué)本科 畢業(yè)設(shè)計(jì) 外文翻譯 第 10 頁 rubing to increase, the foundation is carried on one39。直接應(yīng)力裂縫是指外荷載引起的直接應(yīng)力產(chǎn)生的裂縫。 橋梁結(jié)構(gòu)中經(jīng)常需要鑿槽、開洞、設(shè)置牛腿等，在常規(guī)計(jì)算中難以用準(zhǔn)確的圖式進(jìn)行模擬計(jì)算，一般根據(jù)經(jīng)驗(yàn)設(shè)置受力鋼筋。在設(shè)計(jì)上，應(yīng)注意避免結(jié)構(gòu)突變（或斷面突變），當(dāng)不能回避時(shí)，應(yīng)做局部處理，如轉(zhuǎn)角處做圓角，突變處做成漸變過渡，同時(shí)加強(qiáng)構(gòu)造配筋，轉(zhuǎn)角處增配斜向鋼筋，對(duì)于較大孔洞有條件時(shí)可在周邊設(shè)置護(hù)邊角鋼。沿構(gòu)件出現(xiàn)平行于受力方向的短而密的平行裂縫。小偏心受壓和受拉區(qū)配筋較多的大偏心受壓構(gòu)件，類似于中心受壓構(gòu)件。 受沖切。引起溫度變化主要因素有： 年溫差。 驟然降溫。采用電熱張拉法張拉預(yù)應(yīng)力構(gòu)件時(shí)，預(yù)應(yīng)力鋼材溫度可升高至 350℃，混凝土構(gòu)件也容易開裂。在構(gòu)件豎向變截面處如 T梁、箱梁 腹板與頂?shù)装褰唤犹?，因硬化前沉?shí)不均勻?qū)l(fā)生表面的順腹板方向裂縫。自生收縮是混凝土在硬化過程中，水泥與水發(fā)生水化反應(yīng)，這種收縮與外界濕度無關(guān)，且可以是正的（即收縮，如普通硅酸鹽水泥混凝土），也可以是負(fù)的（即膨脹，如礦渣水泥混凝土與粉煤灰水泥混凝土）。另外水泥標(biāo)號(hào)越低、單位體積用量越大、磨細(xì)度越大，則混凝土收縮越大，且發(fā)生收縮時(shí)間越長(zhǎng)。外摻劑保水性越好，則混凝土收縮越小。機(jī)械振搗方式比手工搗固方式混凝土收縮性要小。比如丘陵