Leaning Arch Bridge Construction Mechanical Properties

Double X-arch bridge, derived from X-arch bridge, is one of the new arch bridge types. This type of bridge is of novelty style with complex constitution and distinct spatial mechanics effect, its construction is difficult; To ensure that the internal force and the line font of completed construction answer for designment demand, it is required that we carry out the static mechanics function analysis on its process being under construction. In this dissertation, the main bridge of Zhanhe bridge over Chengdong River in Pingdingshan City, a double X-arch bridge is discretized by Finite element software MIDAS/Civil according to its structural characteristics with the spatial beam element simulating the longitudinal tied beams, end floor beams, middle floor beams, arch ribs and the like, and with the plate element simulating the bridge deck, and with the spatial pole element of bearing pull force simulating the suspenders, and with the spatial pole element of bearing pressure simulating the holders to erect the bridge's spatial mechanical computational finite element model. Suspenders' initial force of bridge structure is calculated with influence matrix method, and Suspenders' initial force of bridge structure of drawing simultaneously inside and outside suspenders, drawing inside suspenders firstly is calculated with backward method, thus build two construction phase analysis models of responding to drawing order and calculate,analyse the static state and stability of this double X-arch bridge's construction on the initial equilibrium configuration. Summarizing above work, we can get the following conclusions:1,Suspenders' initial force of two kinds of construction order is calculated, Suspenders' internal force in answer to drawing inside suspenders firstly is nearly designing value in comparison with drawing simultaneously inside and outside suspenders.2,Most of arch ribs and longitudinal tied beams resemble like that of continuous beams with the full cross-section compressing in two kinds of construction order, except the under brim of span center cross-section with tension stress, the maximal pressure strain is -11.2 MPa, being smaller than 50 concrete material resists compression -21.64 MPa; The maximal pull strain is 0.898 MPa, being smaller than 50 concrete material resists strength 1.794 MPa. The strain of dominate cross section of drawing inside suspenders firstly is comparatively homogeneous between upper and down border, and smaller tension stress in span center cross-section of longitudinal tied beams in comparison with drawing simultaneously inside and outside suspenders. To make sure the construction process safe, drawing inside suspenders firstly is better than drawing simultaneously inside and outside suspenders.3,Because of holders effect under construction, this bridge basically have no vertical displacement, the maximal vertical displacement of tied beams is -0.03m after dismantling holders, the maximal transverse displacement of arch ribs in span centre is 0.102m, the vertical displacement of drawing simultaneously inside and outside suspenders is little greater in comparison with drawing inside suspenders firstly, but the transverse displacement of former is 0.02 m bigger than latter, because transverse direction of arch ribs may possibly lead to change the inner , the outside arch dip angle, then affect entire structure, so drawing inside suspenders firstly is better than drawing simultaneously inside and outside suspenders.4,The bridge's 1st order stability factors under considered cases and construction process are greater than 6.9, which meet the require of larger than 4～5 and indicate the bridge has highly stability; The bridge's 1st order buckling modes are all out-plane torsional buckling modes of composite arches which indicates the arches' stiffness out of plane is relatively smaller than that in plane and controls the stability of the bridge. The order stability factors under construction process of drawing inside suspenders firstly is larger in comparison with drawing simultaneously inside and outside suspenders, it is good for the bridge construction stability.5,Under construction process of drawing inside suspenders firstly, in compared with the construction of not bending inside and outside ribs firstly ,in the construction of bending inside and outside ribs firstly, the strain of longitudinal tied beams and arch ribs is well equabler, which is also lower than material resists compression; The vertical displacement of longitudinal tied beams is less; The stability factors is greater; So the construction of bending inside and outside ribs first benefits to bridge line font and stability.Synthesizing all above conclusion we know that the construction of drawing inside suspenders firstly benefits to control the bridge structure line font and ensure the process structure safety and stability under construction; Under construction process of drawing inside suspenders firstly, the construction of bending inside and outside ribs firstly is better than the construction of not bending inside and outside ribs firstly.