Preliminary Design And Analysis Of Mechanical Behavior Of Partial Cable-stayed Bridge Under Static/dynamic Load

As a new bridge type, the design of partial cable-stayed bridge is more flexible. The economic span of such bridge ranges from 100m to 280m. And such type of bridge is very applicable in bridge construction of China.Firstly, the development of partial cable-stayed bridge is introduced and structural parameters and constructional details of the established partial cable-stayed bridges are collected and generalized in this thesis, which offers a reference for design of such type of bridge. Based on the references generalization, the static mechanical behavior of Kangqiaolu bridge over the canal in Hangzhou is studied using a beam structure model and a three dimensional finite element model.The anchoring fixing in the saddle of cable directly affects the safety and construction of the tower. For the partial cable-stayed bridge, fiber tubes are widely used in the anchorages of cables due to its feasibility in construction. However, using this anchoring method will introduces the reduction of the section area and the enlargement of the local stress of the tower. Hence, the local stress of the tower needs to be analyzed with a more precise method. In this thesis, the tower of Kangqiaolu bridge over the canal in Hangzhou is simulated with a three dimensional finiteelement model, and the mechanical behavior of the tower is investigated.Dynamic analysis is the last topic of this thesis. The present references about thedynamic analysis of partial cable-stayed bridge are mainly focused on the topics about free vibration, earthquake responses, and fatigue problem of cables. The vehicle-bridge interaction of such bridge has not been investigated. The dynamic effect of vehicles on bridges in reflected by impact factor in design code in China, thus the impact factors of different structure component of the bridge are studied in this thesis. The Kangqiaolu bridge over the canal in Hangzhou is studied as the case, and the dynamic characteristics and responses due to vehicles are obtained considering the bridge-cable coupling vibration. Different road surface roughness, lanes, and vehicle velocities are considered to investigate the displacement impact factors of the girder and tower and tension impacts of cables.Conclusions are presented as:1) The height-to-span ratio of the tower of such bridge is generally below 1/5; the ratio between the side-span and mid-span ranges in 0.45-0.7; the height-to-span ratio of the girder ranges in 1/24-1/45; the the anchorages of the cables locate in the side span and the one-third region of the mid-span; the tolerable stress ranges in 0.4-0.6σ_u2) For partial cable-stayed bridge, the stress distribution of the girder is relatively uniform in the no-cable-region and non-uniform in the region with cable located. The stress increases from the side to the middle in the neighborhood of the cable anchorage.3) Fiber tubes are adopted in the saddle of the tower, and the reduction of section area does not affect the local stress of the tower and the mechanical behavior of the whole bridge.4) The effect of road surface roughness on the dynamic responses of partial cable-stayed bridge is very significant, thus smoothing the road surface is an effective method to reduce the influence of vehicles; the vibration of partial cable-stayed bridge is complicated due to vehicles, and impact factors of different structural components are quit different; the variations of impact factors of girders and cables are slight due to vehicles located in different lanes.