Research On Mechanical Properties Of Rectangular Hole Castellated Beams

Castellated beam is a new type of steel component that emerged in the last century.It can save steel,reduce the weight and make the shape beautiful by opening holes in the web.In recent years,it has been widely used at home and abroad.In this paper,the mechanical properties of rectangular castellated beams are studied from three aspects: experimental analysis,numerical simulation and theoretical derivation.Two kinds of tests are carried out,which are used as the standard to create finite element models.On this basis,reasonable theoretical derivation is carried out to summarize the stress and deflection distribution of castellated beams with rectangular holes,providing theoretical support for engineering design.20 kinds of castellated beam models with rectangular holes are designed considering the span-depth ratio,constraint conditions and load conditions.The normal stress distribution of castellated beams with different span-depth ratios under different loads is studied through electrical measuring experiment,and the normal stress of piers and beam bridges of different castellated beams is analyzed and compared with that of solid beams.It is found that the normal stress of castellated beam cross section is no longer consistent with plane cross-section assumption but in the shape of a curve.The normal stress of castellated beam with small spandepth ratio under uniform load of full span appears point of inflection.In the test process,it is found that the electrical measuring experiment is complicated and can only focus on the condition of one point.The optical 2D-DIC and 3D-DIC measuring methods are introduced to obtain the stress and deflection fields of the castellated beam.The error analysis of the results of the two types of the optical experiment is carried out based on the results of the electrical measuring experiment.It is found that the displacement in the Z direction of the castellated beam is large,which results in the inaccuracy of the 2D-DIC measuring method.The 3D-DIC measuring is spatial,which has higher accuracy and is more suitable to be used in this experiment.The application scope of electrical measuring method,2D-DIC measurement method and 3D-DIC measurement method are summarized.The distribution of normal stress,shear stress and vertical displacement in the web area of castellated beam measured by 3D-DIC is analyzed.It is found that the normal stress of simply supported castellated beam decreases gradually from the support to the middle of the span under the action of uniform load.The deflection in the Y direction of castellated beam shows an uneven curve distribution.The stronger the restraint of castellated beam is,the smaller the midspan deflection is;the more obvious the wavy deflection curve is;and the more accurate the3D-DIC measuring method is.The finite element analysis software ABAQUS is used to carry out numerical simulation of castellated beams.The accuracy of the model is verified by comparing with the results of electrical measuring experiment and optical experiment.By means of the control variable method,the influences of span-depth ratio,width-depth ratio,length-depth ratio and space-depth ratio are studied.It is found that the mechanical properties of castellated beams are greatly affected by the span-depth ratio and width-depth ratio,but less affected by the length-depth ratio and space-depth ratio.When the length-depth ratio and space-depth ratio are reasonable(about 4/7),the influence of them can be ignored.The stress and deflection of castellated beams increase with the increase of the span-depth ratio and width-depth ratio.On the basis of Altfillisch’s vierendeel truss method and considering the effect of the width-depth ratio,the formula of normal stress and shear stress distribution in the cross section of castellated beam under uniform load is improved.On the basis of this,the deflection formula of Altfillisch’s vierendeel truss method is improved,and the mid-span deflection calculation formula of castellated beam under uniform distribution load is proposed.It is found that the accuracy of the formula is higher when the span-depth ratio of honeycomb beam is relatively small and the width-depth ratio is relatively large,which is a supplement to the deflection formula of Altfillisch’s vierendeel truss method.