| The prestressed composite girder with corrugated steel webs is a new type of composite steel-concrete structure.This structure is widely used in recent years with the characteristics of clear mechanical behavior,light self-weight,beautiful shape and so on.The fatigue problem of composite girder with corrugated steel webs is always the focus of attention.However,fatigue design of this structure is not referred in the existing design regulation of the bridge.Therefore,the study of anti-fatigue design of composite girder with corrugated steel webs is very urgent.In order to study the anti-fatigue design and evaluation methods of this structure,the constant amplitude fatigue load tests of 7 girders were performed and the fatigue properties of external prestressed composite girder with corrugated steel webs were studied in detail.On the basis of test data,the fatigue problems of the typical structural details of this structure were studied by means of nominal stress method,hot spot stress method,notch stress method and fracture mechanics theory respectively.The main research contents and achievements are as follows:(1)The anti-fatigue design criteria and the classification of the fatigue details etc in the related provision of British,United States,Euro,Japan and Chinese steel design specification,railway steel bridge specification and highway steel bridge specification were introduced and summarized.The comparative study in aspects of the anti-fatigue design criteria and the classification of the fatigue details in each specification was carried out.Points for attention in anti-fatigue design were put forward in this paper.Typical welding details associated with fatigue of composite girder with corrugated steel webs were summarized to provide theoretical basis on the traditional fatigue S-N curve analysis of composite girder with corrugated steel webs.(2)8 test girders were built and constant amplitude fatigue load tests of 7 girders were performed.The fatigue failure characteristics and typical fatigue details(weak link)of this structure were obtained from the test.The fatigue damage cumulative rule of concrete strain,steel strain,deflection development and crack distribution,etc,was researched.The fatigue failure mode in the fatigue failure process was discussed.The fatigue fracture sequence of components,location of fatigue fracture and the stress state of different shear joints were analyzed.(3)Using nominal stress method,the fatigue performance of girder with corrugated steel webs was studied.Based on test results data fitting,considering theinfluence of the thickness effect and the comparative analysis of other test results data at home and abroad,the nominal stress fatigue curves of typical fatigue details in composite girder with corrugated steel webs and steel girder with corrugated steel webs were obtained,respectively.Through the comparative analysis of fatigue fitting curve,it was revealed that the fatigue resistance performance of steel girder with corrugated steel webs is better than composite girder with corrugated steel webs and the fatigue resistance performance of composite girder with corrugated steel webs with PBL shear connectors is better than composite girder with corrugated steel webs with stud shear connectors,but there's not much difference in the whole.By referring to the design fatigue detail classification curve at home and abroad,comparing and analyzing the test data,the classification of the fatigue details was recommended for finite life fatigue design calculations of girder with corrugated steel webs.(4)The hot spot stress method was adopted to study the fatigue performance of girder with corrugated steel webs.By comparative analysis of the finite element modeling methods for the typical welded joint of girder with corrugated steel webs,it was revealed that the sub model method can reflect the model boundary conditions more accurately.Through finite element modeling and the hot spot stress concentration factor method,the hot spot stress at the typical fatigue details of the test girders was derived.The fatigue performance of test girders was estimated by the hot spot stress method.The results showed that the hot spot stress method was safe in evaluating the fatigue test results of the girders with corrugated steel webs.It was showed that the web bending angle and the flange thickness have great influence on the hot spot stress by parameter analysis.(5)The notch stress method was adopted to study the fatigue performance of girder with corrugated steel webs.Using the parameters of the welded details recommended by the notch stress method of IIW,three FEM girders were established.The notch stress and its concentration factor of the welded details of model girders were calculated by the sub model method.The fatigue performance of test girders was estimated by the notch stress method.The results showed that the notch stress method was feasible in evaluating the fatigue test result of the girders with corrugated steel webs.It was showed that the corner radius and bending angle of web have great influence on the notch stress by parameter analysis.(6)The fracture mechanics method was adopted to study the fatigue performance of girder with corrugated steel webs.Based on the basic principle of fracture mechanics,weight function formula of stress intensity factors for Glinka G andrecommended parameter of IIW,the fatigue crack propagation mode of typical fatigue detail in girder with corrugated steel webs was established.On the base of this model,the S-N curve of typical fatigue detail in girder with corrugated steel webs was deduced.By the comparative analysis of fatigue test results,the optimization of model parameter was proposed.(7)Based on the fatigue test data of deformed bars in this article,the fatigue properties and degenerate rule of deformed bars in composite girder with corrugated steel webs were explored.Through the comparison and analysis of several groups' data from the fatigue test in this article and other 9 fatigue tests,the main influence factors of the fatigue strength for deformed bars were studied,the importance of stress ratio was confirmed,and the influence rule of stress concentration factor of deformed bars in concrete girder was investigated.Based on the fatigue test data of deformed bars in prestressed girders,the fatigue properties and degenerate rule of deformed bars in prestressed structures were explored.It provided reference to the fatigue design of deformed bars for prestressed composite girder with corrugated steel webs. |
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