Research On Mechanical Properties Of Steel Octagon-web Beam

In recent years,people pay more and more attention to environmental protection,and the concept of"Lucid waters and lush mountains are invaluable assets"has also been widely recognized by people.Due to the recyclability of steel,the use of steel bridge plays an important role in environmental protection.With the aggravation of China's population aging problem,the problem of insufficient effective labor force and rising labor cost has become increasingly prominent.Therefore,lightweight,industrialized and assembled bridge construction will occupy the main position of bridge construction in the future.Therefore,a new type of open web steel structure girder based on the appearance of honeycomb beam,steel octagon-web beam(SOWB),was proposed.In the dissertation,based on the 12^thbatch of high level talents selection and funding scheme of“six talent peaks”in Jiangsu Province,theoretical and experimental studies on the bending behavior,ultimate bearing capacity,failure modes,circumferential stress at web opening,web buckling capacity and pure shear buckling capacity of web were carried out.The design points of SOWB were summarized.A simple supported bridge of SOWB and an emergency bridge were designed,respectively,which show the feasibility of applying the structure to the field of bridge engineering.The work mainly includes the following aspects:1.Referring to the relevant codes and the design drawings of a steel truss-web and concrete composite box-girder bridge,a reduced scale model of SOWB was designed and manufactured.The bending behaviour of test specimen was studied by four-point loading.From the load-deflection curve of specimen,the working state of SOWB mainly can be divided into three stages:elastic deformation stage,elastic-plastic deformation stage and yield stage.According to the failure mode of the specimen,it can be found that the top slab has obvious compression buckling deformation,and the web also has compression buckling phenomenon.2.The nonlinear finite element analysis model of the specimen was realized by using general finite element software ABAQUS 2017.The deflection deformation characteristics,the stress and strain distribution characteristics of the slabs and the failure modes of the structure under bending load were studied through the test and finite element analysis method.In order to avoid the web buckling under compression,the web stiffness should be increased.3.Based on the theory of Vierendeel truss in deflection calculation of castellated steel beam,the deflection calculation formula of SOWB was derived.The corresponding calculation methods of the deflection of SOWB were also proposed for different load types.On the basis,a simple method of deflection calculation of SOWB based on parameter analysis was proposed.The deflection calculation methods of SOWB were used to evaluate the deflection of the specimen,which were compared with these obtained by finite element analysis and test.4.Three parameters that may affect the deflection of SOWB were analyzed,including opening type,expansion ratio and height span ratio.By analyzing the influence of various parameters on deflection,a reasonable range of parameters was obtained.The stress characteristics of the structure under bending load was analyzed.The stress calculation method and the bearing capacity of the structure under three failure modes of web buckling,deck edge instability and strength failure were studied.Based on the assumptions of ultimate bearing capacity of castellated steel beam,the calculation methods of bending and shear ultimate bearing capacity of SOWB were deduced.5.By introducing the theory of Vierendeel truss and combining the characteristics of the web,the web can be divided into five calculation sections and the calculation methods of the web stress for each calculation section which were verified by comparing with test were discussed,respectively.A modified strut model for calculating the web-post shear buckling capacity of steel octagon-web beam was proposed,which was obtained based on the calculation method of web-post shear buckling capacity of castellated beams in European code.In order to verify the accuracy and reliability of the proposed strut model,a web-post shear buckling model of steel octagon-web beam was realized by ABAQUS 2017.The influences of two parameters,expansion ratio and thickness ratio of flange plate to web,on the web-post shear buckling capacity were considered.On the basis,the proposed strut model was improved by introducing the effect of flange plate restraint.6.The pure shear buckling behavior of octagonal perforated thin plate with four sides simply supported,four sides fixed,two sides simply supported and two sides fixed were analyzed.By comparing with the calculation formula of the buckling capacity of rectangular thin plate,the reasonable boundary conditions of finite element method were determined.Through finite element method,the influences of the width height ratio,side height ratio and expansion ratio on the buckling coefficient of the octagonal perforated thin plate were studied.The calculation formula of the buckling characteristic coefficient of the rectangular thin plate was modified to obtain the shear buckling calculation formula of the octagonal perforated thin plate.