Study On The Vault Off-limits Of Stone Arch Bridge In Three-gorge Reservoir

With the advantages of easily obtained structure and strong durability, stone arch bridges are widely used. However, there are generally various of diseases in stone arch bridge ,which were brought from frequent loads, the worse overloading, rock weathering, old and without repair. Those stone arch bridges are facing the situation of lack of carrying capacity and security. Therefore the practical safety identifying and treatment techniques urgently need to be developed, which are Safe, economical, easy to promote the application, suitable for mountain Characteristics, and which don't to do the load test and guide scientifically in safety evaluation and reinforcement Treatment. At present the Specifications and documents on the Stone Arch Bridge limits Index are lacking. Therefore in the paper some research on off-limits in the apex of arch was done and the main contents and conclusions of this thesis are as follows:1. According to the field survey data and national office-related documents, the causes of offing in the apex of arch are summarized in many ways, such as rock weathering, construction and management, and so on.2. To study the internal force affecting in the main arch caused by rock offing in the apex of arch, some conclusions are draw as follows by finite element analysis: With the vault off depth from 0 cm to 20 cm, the changes rate of axial force is less than 1%; the changes rate of the moment in vault section is up to 7 times the original, or even 10 times, the changes rate of the moment in quarter section and side-wall section is less than 5%. The conclusion that the vault section is the worst section which affects the offing limits in the apex of arch has been arrived.3. Offing-limits in the apex of arch are influencing by several parameters, this paper analysis the sensitivity of some parameters, such as span ratios, height of the main arch and span, the result indicates: Offing-limits in the apex of arch increases with depth-to-span ratio increasing, decreases with span increasing. Comparing with depth-to-span ratio and height of the main arch, span is easier to influence the off-limits in the apex of arch. With the span form 30 meters to 50meters, the decreased rate of off-limits in the apex of arch is up to 49.4%. The conclusion that span is one of the most important factors which affects the off-limits in the apex of arch has been arrived.4. In this paper, at the first the off-limits in the apex of arch were calculated, which is with span in 30 meters, 40meters, 50meters, deferent depth-to-span ratio, the height of the main arch and span, then the calculated result was fitted on the principle of least squares surface fitting, at last the formula expressions of off-limits in the apex of arch with three deferent spans were proposed.