| Composite box girder bridge with corrugated steel webs is a new type of structural system girder bridge,which stress system and construction technology are different from the traditional prestressed concrete continuous girder bridge.Based on the Zhanhe Bridge on Shenma Road,Pingdingshan City,the mechanical properties in the construction process are analyzed,the shear force distribution of key sections of main girder under lane load is studied.Meanwhile,the variation and transverse distribution of roof and floor stress in the construction process is also analyzed,and compared with concrete web box girder bridge.Main content is as follows:(1)The beam element model and shell&solid model are established by the finite element software Midas/Civil and Midas/FEA respectively.In the beam element model,three corrugated steel webs are simplified into two webs,the thickness of webs is changed into 1.5 times of design drawing,and full concrete webs are used in the lining concrete area.Meanwhile,the haunch concrete of middle web shall be added in the side webs according to the principle of area equivalence,so that the section stiffness can be compensated.Finally,the results of beam element model are basically consistent with those of shell&solid model.At the same time,the influence of shear deformation on the deflection of main girder is also analyzed.The results show that under the self-weight and prestress action respectively,the deflection of the main girder in the shell&solid model is between that of the beam element model with or without shear deformation,and the results of beam element model considering shear deformation are closer to those of shell&solid model.(2)The linear monitoring scheme is formulated according to the characteristics of cantilever pouring construction.And based on the beam element model and preloading data,the construction and completion pre-camber of Zhanhe Bridge are analyzed,then calculate the theoretical formwork elevation which is applied to the construction process of Zhanhe Bridge.By comparing the deviation between the measured elevation and the theoretical elevation of the bridge deck measuring points after prestressed tensioning,the deviation of each piece was basically no more than 20mm,which indicates that the formwork elevation provided is more accurate and the linear is controlled well.(3)Based on beam element model,six key sections of main girder are selected to analyze the variation of internal force and stress in construction stage under the dead load,primary effect of tendons and secondary effect of tendons.The results show that the influence of creep and shrinkage on the internal force of girder can be ignored.In the process of cantilever construction,under the action of dead load and primary effect of tendons,the internal force and stress amplitude of each section increase with the increase of cantilever length.In the subsequent construction stage,under the action of dead load,the system conversion has greatest influence on bending moment and shear force of each section,and under the action of primary effect of tendons,the tensioning of side-span closure tendons,mid-span closure tendons and external tendons have significant influence on the internal force and stress of each section.The secondary effect of tendons only exists in the statically indeterminate structure after the closure of side-span,and the bending moment and stress of each section change significantly when the closure tendons of mid-span and external tendons are tensioned.The analysis results provide a reference for the monitoring of structural stress.(4)In order to clarify the shear transfer path of single-box double-chamber composite box girder bridge with corrugated steel webs,based on shell&solid model,five key sections of main girder(side span section II and middle span section III)are selected to analyze the shear-bearing ratio of concrete roof and floor and steel webs of each key section under lane load.The results show that the influence of section shear mutation can be eliminated by shifting the concentrated load one element to the loading area when the lane load is added to the shell&solid model.Meanwhile,the deviation of results between line load+concentrated load and area load+line load is less than 2%,therefore,any loading mode can be used in shear analysis.Whether under central load or eccentric load,the shear force produced by concentrated load is more borne by the roof and floor than by the webs.The middle web(web 2)and especially the east web(web 3)of each section have a larger shear bearing ratio when three lanes work together,and the web in each section that single-lane load acts directly has the largest shear-bearing ratio.The web shear-bearing ratio of section II and section Ⅲ has the largest non-uniformity when lane 1(near web 1)acts alone,and their web 1 and web 3 have the deviation of shear-bearing ratio more than 70%,while the deviation between web 1 and web 3 of the other three sections is covering from 30%to 65%.(5)The stress variation and transverse distribution of the roof and floor of the root section of corrugated steel web box girder bridge and concrete web box girder bridge are studied during construction.The transverse distribution of stress will be affected by the selection of key sections.There is an obvious stress concentration due to the existence of prestressed steel anchor end in the roof of beam block interface.Although the stress difference before and after concrete pouring and before and after prestressed tension is given in this paper,the stress at the interface of beam block and its adjacent section is not representative due to the existing stress concentration phenomenon.Stress distortion occurs when the critical section is close to the concrete placement.The transverse distribution of floor stress caused by the tensile prestress near the cantilever root is larger near the web and smaller at other positions,while the transverse distribution of floor stress caused by the tensile prestress far from the cantilever root is smaller near the web and larger at other positions.For the simulation of concrete wet weight and hanging basket load,when the loading position is close to the key section,the top and bottom plate loading form should be adopted to reduce the influence of stress concentration on the results.For corrugated steel web box girder bridge,tensile stress occurs in the roof section of cantilever root section and compressive stress occurs in the floor section when concrete is poured in the construction process.The stress amplitude increases with concrete pouring position away from,and the transverse unevenness of stress becomes significant.Except for the complex stress at the joint between the bottom plate and the corrugated steel web,the transverse stress distribution of the roof and floor is smaller near the web and larger at other positions.After the corrugated steel webs were replaced with concrete webs,although the dead load of the structure is larger,the stress amplitude of the roof and floor decreased slightly due to the participation of the concrete webs in the longitudinal stress,but the reduction is generally less than 0.2MPa.moreover,the transverse fluctuation of the floor stress is smaller,and basically only the stress wave peak appeared near the middle web.For box girder Bridges with corrugated steel webs,the tensile prestress in cantilever casting stage produces compressive stress on the cantilever root roof section and tensile stress on the floor.Because the prestressed steel bundle is in the top plate and close to the web,the roof stress amplitude is large,but not more than 3MPa,the transverse distribution of stress is small in the middle of the box and increases sharply near the web;the amplitude of floor stress is small,all of which are less than 0.35MPa.At section 1,which is close to the root of the cantilever,the transverse distribution of floor stress is large near the web and small at other positions;at section 2,which is a little far from the root of the cantilever,the transverse distribution of floor stress is small near the web and large at other positions.Due to the large number of external prestressed steel strands distributed uniformly in the box chamber,the compressive stress on the roof and floor of the cantilever root section is generated when the external prestressed steel strands are tensioned,and the stress amplitude increases significantly,the transverse distribution of stress is smaller near the web and larger in other positions.Due to the difference of shear lag effect between the bottom of the two sections,the stress at the bottom of section 1 decreases sharply near the web,while the stress amplitude at the bottom of section 2 decreases sharply at the joint of the most outer edge of the floor and the corrugated steel web,but decreases greatly near the middle web.After the corrugated steel webs are replaced by concrete webs,the roof stress changes in the whole tensioning process is basically the same,only the amplitude decreases,and the decrease of section 2 is more significant.The transverse distribution of floor stress is basically the same as that of section 2 in the cantilever casting stage,the floor stress amplitude is basically unchanged,but when the external prestressed steel strands are tensioned,the floor stress amplitude decreases,and the decrease is more significant with section 2.(6)The transverse distribution of stress on roof and floor of key sections of main girders between corrugated steel box girder bridge and concrete box girder bridge with web is compared under the maximum cantilever state and bridge closure。Under the maximum cantilever state and bridge closure,the stress on the roof and floor of the cantilever root section(section 1 and 2)and the mid-span 1/4 section(section 6)of the two web box girder bridges is the accumulation of the stress obtained in each construction stage,except for the complex stress at the joint between the corrugated steel web and the floor,the transverse distribution of roof stress in each section is small in the center of the chamber and the position of the wing plate,while the compressive stress near the web increases sharply,the transverse distribution of floor stress is basically small near the middle web and large in other positions,and the stress amplitude and transverse fluctuation of section 1 and section 2 are large.In the mid-span mid-span section(section 7),the compressive stress of roof is small,and the compressive stress of floor is large.The transverse distribution is basically uniform,except that the stress amplitude near the most outer edge of the floor of corrugated steel web box girder bridge is small,and the stress amplitude near the most outer edge of the floor of concrete web box girder bridge is large. |
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