Research On Selection Of Design Parameters Of Short-Medium Span Bridges Based On The Analysis Of Cracks

In recent years, a lot of short-medium span bridges have been damaged by all kinds of diseases frequently, which is a reflection of many shortages of design and maintenance, as well as the negligence of short-medium span bridges-construction. Among the bridge diseases, crack must be the most common phenomenon, which is better in reflecting the health situation of bridges. So, we can choose crack as a key to find out the relationship between the design parameters and cracks. In this way, we can control the diseases such as crack effectively, and increase the rationality of bridge design fundamentally. Especially, short-medium span bridges are huge in quantities and are designed by using standard styles mostly, so they must have same or similar frames, sections and so on. Therefore, those bridges which have same or similar styles also must have crack problems in a similar way. In a word, it is practicable that finding out the relationship between design-parameters and cracks by analyzing cracks of such kind of bridges.The research is based on many studies of scholars at home and abroad. And it analyzes the selection of design parameters by investigating the diseases of short-medium span bridges. The concrete contents are as follows:First of all, the mechanism and control-standards of cracks are introduced by analyzing the causes of cracks, and then the danger of cracking is discussed thoroughly.Secondly, this article summarizes the cracking characteristics of conventional bridges such as T section bridges and slab bridges. Using Data Mining method to find out the elements which have a close relationship with stress crack, and puts forward that the elements such as rebar, side-mid span ratio, depth-span ratio are sensitive to cracking.Thirdly, after manipulating raw dates, and doing the regression analysis by using least squares techniques, what can be proved is that the cracking condition of side-span is tend to become worse, with the side-mid span ratio increases. The whole crack parameter of bridges decreases, going along with the increase of depth-span ratio. The sugession in design is that side-mid span ratio between 0.5-0.75, depth-span ratio between 1/12-1/14 is better.Finally, by using MIDAS to analyze T section and hollow slab bridges ,comparing different size of T section and hollow slab bridges ,we can find out that the thickness of roof and sternum remarkably influence the section stresses, especially the shear stress. Therefore, bridge designers should handle the detail of section with great care.