Local Stability Of Web Of Castellated Beams Under Pure Shear

Due to limitations on maximum allowable deflections, the high strengthproperties of structural steel cannot always be utilized to best advantage. As a result,several new methods have been aimed at increasing the stiffness of steel memberswithout any increase in weight of the steel required. Castellated beams are one ofthese solutions. Castellated beams are varieties of girders with generally circular orhexagonal web openings, distributed along the beams with regular intervals. Theprocess of manufacturing castellated beams by cutting the web in zigzag pattern alongits centerline and then rejoining the two halves by welding, or by cutting openings infabricated steel sections, leads into a reduction of the weight of the beam allowingthis type of beams to be used for medium to long spans constructions.The presence of the holes in the web will change the structural behaviour of thebeam from that of plain webbed beams. Experimental tests on castellated beams haveshown that web slenderness, castellation parameters, geometry and size of openings,lateral supports provision and the loading type are the main parameters, which dictatethe strength and modes of failure of these beams. The openings change the boundaryconditions of the plate, which makes solving the theoretical derivation equation ofbuckling bearing capacity complex. Due to the complexity of the behaviour ofcastellated beams, there is not a generally accepted theoretical solution or analyticalsolution of web local buckling of castellated beams at present. Currently availablemethods for the web local stability of castellated beam are complicated and quitedifferent with China’s code for design of steel structure.Some previous studies of web-post buckling on the interaction of shear andmoment forces on the behaviour of castellated beams have been carried out. Thisthesis takes the web saperately and does the analysis of local stability that based onthe stability theory of thin plate and drawing on the analysis of local stability of theweb of plain webbed beams. In this thesis, use of finite element software package isextended to the analysis of plates which have hexagon holes under uniform shear. Thenumerical model takes into account both material and geometric nonlinearities. Andthe eigenvalue buckling analysis is also included. Thin webs in practice are notperfectly flat. In addition, there is extensive distortion due to manufacturing and it is,therefore, essential to represent appropriately these imperfections in the finite element modeling. The accuracy of the model established is verified by a comparison withmore refined finite element analysis results and experimental data.The plates are considered to be simply supported along four edges and keptstraight. In the analysis process of the local stability of castellated beams, thebuckling mode shapes of plate with openings that under uniform shear are observedand the stress of elastic buckling is calculated. The effects of web openingspacing/web depth and web opening depth/web depth are studied to investigate thelocal stability of the perforated plates. By the regression analysis of the finite elementanalyses results obtained, a closed-form empirical formula for calculating the shearbuckling coefficient of palte with hexagon holes is derived. The accuracy of theformula developed is verified by a comparison with more refined finite elementanalyses results. Based on the above formula, the limit ratio of web height tothickness when subjected to pure shear has derived. Finally, the embedded solid factoris considered to measure the actual elastic restraint of the flange.