Study On Cable Forces Optimization And Mechanical Behavior Of Deck Type Arch Bridges With Diagonalcables

The deck type arch bridge with diagonal cables is a new kind of bridge typewhich is the development and improvement of trussed combination arch bridge.Flexible diagonal stayed-cables are introduced into the deck type arch bridge withdiagonal cables, just as rigid prestressed concrete diagonals are adopted to trussedcombination arch bridge. Flexible diagonal stayed-cables act as both temporarysupporting cables during construction process, but permanent structural members ofthe completed status of the deck type arch bridge with diagonal cables. Taking thedeck type arch bridge with diagonal cables as the research object, this thesis studies itscable tensions optimization, construction process, static performance, dynamiccharacteristics and seismic responses systematically. The main research contents andachievements cover the following aspects:1, Introduction of the structural system and features of this birdge type andresearch on impact of cable force variation on moment of arch ribsTaking the comparison design layout of Xianshenhe bridge as engineeringbackground, the structural system of the deck type arch bridge with diagonal cablesare introduced firstly. The structural features of the bridge type was obtained bycontrast with other deck type bridges and cable-supported lattice shells. The mostprominent feature of those is that the internal force may be adjusted by adjusting thecable force after closure of arch ribs. The impact of cable force variation on momentof arch ribs is studied.2, Research on control method of cable tensions adjustment on the constructionprocess of the deck type arch bridge with diagonal cablesSeveral cable forces should be adjusted on the same construction stage in order tomake cable forces meet the optimal values during construction."Adjusted cableforces method" is put forward to calculate pull-out length of every stayed-cable incase of batch adjustment of cable, taking into consideration the interaction betweenthe cable forces. The formula of pull-out length and adjusted value of cable forces isdeduced out in this thesis. Without iterative calculation,the exact pull-out length ofevery stayed-cable could be obtained by using this method immediately, on theassumption that sag effect of stayed-cable can be neglected. So the formula isconvenient to use. Taking the longest cantilever construction stage as example, thecomparison study of control method of cable tensions adjustment is carried out.3, Research on determination of the cable forces and mechanical behaviorduring construction of the deck type arch bridge with diagonal cablesThe construction method of cantilevered segment assembling is adopted to build the deck type arch bridge with diagonal cables. Cable forces must be made adjustmentto control the internal force and lineshape of arch rib during construction, so the keycontruction technologies are determination of the cable forces and control of cabletensions adjustment. Construction process of the deck type arch bridge with diagonalcables is divided into thirty stages in this thesis. Construction simulation is carried outfor cantilevered segment assembling process of steel structure and pouring process ofarch rib concrete. The extensive studies have been conducted on mechanical behaviorduring construction of the deck type arch bridge with diagonal cables. Optimal cableforces are sought out by both "zero moment method" and "zero deflection method" atevery construction stage. Variation law of cable forces is gained on the constructionprocess.4, Research on optimization of cable tensions of the finished deck type archbridge with diagonal cablesMathematical model is usually established for optimization of cable tension by"influence matrix method" or "unit load method" now, without regard to mutual effectbetween adjusted cable forces. Aimed at their shortcomings,"double influencematrixes method" for optimization of cable tensions is put forward and theoreticalderivation is made in this thesis. The optimization calculation of cable forces isperformed by means of two influence matrixes method, taking minimum bendingstrain energy and appointed stress states of arch ribs as optimum object separately.Without iterative calculation, exact cable forces could be obtained using this methodimmediately. Taking the deck type arch bridge with diagonal cables as an example,optimization calculation of cable tension is conducted using three different kinds ofmethod in this thesis separately. The research result shows that "double influencematrixes method" has the characteristic of fast operating speed and high precision.5, Research on static performance of the deck type arch bridge with diagonalcables subjected to dead loadOn the base of optimization of cable tensions of finished deck type arch bridgeswith diagonal cables, its mechanical behavior is studied subjected to dead load,vehicle live load and uniform change in temperature。Since the cable forces actuallyare just optimal cable forces of the deck type arch bridge with diagonal cables, themechanical behavior of arch ribs of the deck type arch bridge with diagonal cables isbetter than ordinary deck type arch bridge. Applied the same grade of vehicle live load,bending moments in arch ribs of the deck type arch bridge with diagonal cables is lessthan the ordinary deck type arch bridge. The results show that it is effective to reducebending moment of arch rib subjected to vehicle live load that the stayed-cable isadopted to the ordinary deck type arch bridge When the deck type arch bridges withdiagonal cables is subjected to uniform change in temperature., the deformation of girder is restrained by ground anchors, so the girders have great temperature stresses.6, Research on dynamic characteristics and seismic response of the deck typearch bridge with diagonal cablesThe natural vibration frequencies and modes of the bridge are calculated by thesubspace iteration method, and then its seismic response is also analyzed by means ofmode-shape decomposition response spectrum method. The comparative analysis ofdynamic performance and earthquake response is also carried out between the decktype arch bridge with diagonal cables and the ordinary deck type arch bridge with thesame structural parameters. This two kinds of deck type arch bridge have the samebasic frequency, whereas the first vertical vibration frequency of the deck type archbridge with diagonal cables is about twice as much as that of the ordinary deck typearch bridge. The results of the studies indicate that stayed cables have little influenceon horizontal stiffness of the deck type arch bridge with diagonal cables, but increasevertical rigidity obviously. Some seismic responses to vertical ground motioncomponent are greater than to horizontal ground motion component, so it is concludedthat vertical ground motion component play an important role in the composition ofseismic responses, and can not be ignored.