Equivalent Static Wind Load Study Of Construction State For Large Span Cantilever Arch Bridge

Arch bridges are an important part of the modern bridge system.The development of bridge technology has led to an increase in the number and span of newly constructed arch bridges,and the cable-stayed suspension method is being adopted widely.However,excessively large spans make the arch bridge less stiff during construction,and vibration is easily generated under wind load,which seriously affects construction safety.Therefore,this article carries out research on buffeting for large span cable-stayed construction arch bridges,discusses the calculation method of equivalent static wind load(ESWL),and analyzes the relevant influence parameters,which has important practical engineering significance.This article takes a cable-stayed construction arch bridge as the engineering background,and carries out a study on the buffeting response in the "maximum cantilever state" where its stiffness is weakest,and derives the equations for calculating the ESWL of arch circle.The main research results were obtained as follows:(1)The in-plane and out-of-plane vibration control equations of the arch bridge constructed by the cable-stayed suspension method are derived from Hamilton’s principle,and the Galerkin method is used to truncate the first-order mode,and the approximate equations for calculating the in-plane and out-of-plane fundamental frequencies of the arch circle are discussed.By comparing different ESWL calculation theories,an approximate calculation formula for the buffeting response of an arch bridge with engineering practicality is proposed,and an ANSYS finite element model of an arch bridge constructed is established to verifying it.It shows that: the calculation accuracy of the formulae for calculating the in-plane and out-plane fundamental frequencies of arch bridges derived in this paper is relatively accurate,and the solved in-plane and out-plane frequencies are within 5% error of the finite element solution.The validity of the buffeting response solution formula derived in this paper is excellent,and the calculated vault displacement is in agreement with the finite element results,which can be applied to the subsequent derivation of the ESWL.(2)Based on the correct solution of the buffeting response,a simplified formula for the ESWL inside and outside the arch bridge deck is proposed by drawing on the principle of the three-component method,and its validity is verified by comparing the FEM results.Research shows that: in the displacement within the arch circle in-plane,the relative error between the results of the equations in this paper and the FEM results near the foot of the arch is large,but due to the small value of displacement in this region,the absolute value of the error between the two is not large;And the relative error between the two near the vault is less than 20%,which is a better match.In the out-of-plane displacement of the arch circle,the formulas in this paper all overestimate the transverse displacement and torsional displacement of the arch circle;the relative error of the transverse displacement of the arch circle is between 7%-20%,and the relative error of the torsional displacement of the arch circle is between 12%-30%.(3)In order to study the buffeting response mechanism of the arch circle,the influence law of different wind spectrum types,background and resonance load components,damping ratio,buckling cable and walked bar specification parameters on the ESWL of the buffeting is explored respectively.Research shows that: the calculation of the ESWL in the arch circle in-plane can only consider the vertical pulsating wind w(t),and out-of-plane’s can only consider the downward pulsating wind u(t);background and resonance response are accounted for a considerable proportion,the calculation of ESWL should jointly consider the background,resonance wind load.In different damping ratio intervals,the sensitivity of damping ratio-displacement of arch circle vibration is different,specifically,the smaller the damping ratio interval,the more drastic the buffeting displacement change when changing the damping ratio.In the outof-plane displacement response of the arch circle,the torsional displacement is more influenced by the characteristics of the cable,so the vibration suppression effect is better by adjusting the cable specification.(4)To facilitate the engineering application,I(s)is taken as 1 in the ESWL calculation,and the analysis is verified by three cable-stayed suspension method construction arch bridges.Research shows that: when the ESWL calculated using the above formula acts on the structure,the tangential displacement of the arch circle along the full arch axis is larger than the results of FEM,but the relative error between the two gradually decreases from the foot to the top of the arch,and the relative error at the top of the arch is about 10%;The vertical displacement of the arch circle is smaller near the foot of the arch than the FEM results,but larger near the top of the arch,and the relative error at the top of the arch is within 10%;the transverse displacement of the arch circle along the whole arch axis is larger than the FEM results,but the relative error is within 20%;the torsional displacement of the arch circle is larger near the foot of the arch than the FEM results by about 10%,and smaller near the top of the arch by about 10%.Overall,it can meet the requirements of engineering practicality.