Research On Key Technologies For Construction Control Of Multi-Tower Suspension Bridge

Compared with the two-tower suspension bridge,the three-tower suspension bridge can reduce the span,greatly reduce the cable tension and the scale of anchorage,which is favored by bridge engineers.Because of the effect of middle tower,its construction control is more difficult than that of two-tower suspension bridge,so it is necessary to further study the construction monitoring of three-tower suspension bridge.Based on the background of a three-tower suspension bridge under construction,this dissertation studies and analyzes the main construction control problems in the construction process of the superstructure of the suspension bridge.Mainly completed work is as followed:1.The finite element model of the whole bridge is established by Midas civil.The influences of the elastic modulus deviation of the cable,the dead load deviation of the stiffening beam on the unstressed length of the cable,the pre deviation of the saddle and the midspan elevation at cable finished stage are discussed.At the same time,the influence of temperature,span and cable length on the sag at cable finished stage is analyzed.The results show that the elastic modulus deviation of cable and the dead load deviation of stiffening beam have great influence on the unstressed cable length,the pre deviation of saddle and the cable shape at cable finished stage.The cable elastic modulus and the static load of processed stiffening beam should be measured to ensure that the unstressed length of cable and the pre deviation of saddle are under control;for the midspan,the influence coefficient of span change and cable length change on midspan sag is close,but the direction is opposite;the smaller the rise span ratio is,the faster the midspan sag changes with cable length and span;when the rise span ratio is fixed,the larger the height difference span ratio is,the more obvious the influence of cable length and span change on midspan sag is;the alignment adjustment of the two midspan should be synchronized as much as possible;the influence coefficients of the two midspan sags with the deviation of the main tower are equal in size and opposite in direction;2.Based on the rotating stiffness of the saddle,the influence of temperature change and the side span sag deviation on the saddle deflection angle is discussed,and the calculation formula of the splay saddle angle is derived.On this basis,a simplified adjustment method of the anchor span tension considering the rotating effect of the saddle is proposed.The results show that the temperature change is the main cause of the saddle deflection,and the proposed adjustment method has the advantages of significantly reducing the adjustment times,effectively avoiding the slippage of the cable strands,saving the construction period and high accuracy of the cable adjustment,which has been successfully applied in practice;3.This dissertation discusses the proper hoisting and closure scheme of stiffening beam,the reason and essence of saddle pushing,the timing and calculation method of pushing amount,studies the variation law of the related control parameters such as tower bottom stress,horizontal displacement of tower,unbalanced horizontal force of saddle,and analyzes the longitudinal deviation of the tower and the anti sliding problem of the cable at the middle tower caused by asymmetric lifting.The results show that for the three-tower suspension bridge,the control standard of the pushing amount and timing of the side tower saddle is that the stress at the bottom of the tower is not over the limit,and the pushing amount and timing of the middle saddle should be determined by considering the actual construction convenience and structural safety,generally in several times;in the late stage of the saddle pushing,the absolute coordinates of the side saddle did not change much,while for the middle saddle,the absolute coordinate of the saddle does not change much The movement of saddle is about 6-8 times of the movement of tower;the anti sliding safety factor of main cable is gradually increasing towards the hoisting of beam section;when asymmetric hoisting occurs,the most unfavorable condition for the cable of middle tower to slip is the hoisting of the first beam section,so it is necessary to ensure that the hoisting of beam section of two middle spans should be carried out synchronously.