The Design And Performance Of The Welded Stiffened Ribs Of The Welded Webs

With the booming development of large-span space system and light steel structure in China, overall or local buckling problems caused by increasing span and reducing plate thickness were increasingly prominent. The welding combined steel I-beams which were composed by superior height-thickness ratio of web in practical engineering should be guaranteed local buckling of web by setting stiffener frequently. Compared with common transverse or longitudinal stiffener, it was a relatively novel design concept to set the diagonal stiffener in steel I-beams. The current limited research agreed that diagonal stiffener which was better than other forms not only had advantages in promoting the local buckling of web, but also could delay post-buckling deformation development of web and meanwhile increase available space of post-buckling strength. However, performance study of diagonal stiffener was still in the preliminary experiment phase of conceptual design. There were few literatures put forward applicable conditions, arrangement forms, design procedures and checking computation methods of diagonal stiffener. It was difficult to deal with the complex situations of practical engineering. Therefore, this article will comprehensively analyze the importance of various geometric parameters which influenced local buckling of web and performance of diagonal stiffener. Combined with structural requirements of steel structure, the steel beam diagonal stiffener design scheme which could be applied to practical engineering will be proposed and perfected after researching the quantitative relationship among parameters.Based on the introduction of basic steel structure stability concept and its computational method, this article summarized the key points involved in stability theory of thin plate. Combined with buckling analysis of stiffening plate and theoretical exposition of web local buckling, the performance of steel beam diagonal stiffener and its stiffening effect has been studied. Depending on finite element analysis software ABAQUS, Multi-group steel I-beam models with setting different stiffeners were analyzed by elastic eigenvalue buckling. The local critical buckling loads of web and buckling modes which were influenced by a variety of geometric parameters have been researched. The main parameters used in analysis above including inclination, spacing, additional position, section width of diagonal stiffener, span of steel I-beam, height-thickness ratio of web and width-thickness ratio of flange. The extent of diagonal stiffener performance impact of the various factors and the web local buckling sensitivity of these variations was compared with each other in importance analysis. Based on the research above and combined with detailing requirements and calculation formula of stiffener in existing specification, the reasonable methods, design recommendations and checking computation methods of setting diagonal stiffener in steel I-beam were been put forward. The simplified computing model and design flow conducive to engineering application was proposed at the same time. The research results of this paper can be summarized as the following conclusions:(1) The importance analysis of geometric parameters demonstrated that height-thickness ratio of web, additional position of diagonal stiffener, spacing of stiffener, inclination of diagonal stiffener are direct factors, while the span of steel I-beam, section width of diagonal stiffener, width-thickness ratio of flange are indirect factors.(2) The practical value of diagonal stiffener in engineering is mainly reflected in two aspects, including reinforcement measure of steel beams and economic benefits of members. To the steel I-beam with higher web, the advantage of diagonal stiffener in strengthening works is embedded more significantly if the additional position of diagonal stiffener is reasonable; after setting diagonal stiffener in the design of steel I-beam, the thickness of web can be further reduced. And the manufacturing costs are reduced dramatically.(3) The strengthening of the diagonal stiffener on web can achieve optimum effect when web of welding combined steel I-beam relatively high with the height-thickness ratio between 130 and 140.(4) Due to different additional positions of diagonal stiffener, the discrepancy of web local buckling can reach 40%. No matter for the design of diagonal stiffener or the reinforcement of existing steel I-beam, the diagonal stiffener should be preferentially set near the area of steel I-beam's support which primarily bears shear stress.(5) Alternative arrangement of transverse and diagonal stiffener or the pattern of additional diagonal stiffener in transverse stiffener area is recommended. And it is proposed to give priority to prefer even region. When diagonal stiffeners are used alone, the bearing stiffener and middle transverse stiffener should be respectively and symmetrically set at support and middle of beam span.(6) When the alternative arrangement of transverse and diagonal stiffener is adopted, it is suggested that the aspect ratio of transverse stiffener area should stay above 1. When diagonal stiffeners are used alone, the aspect ratio of diagonal stiffener area ought to be more than 0.75.(7) It's better to choose lesser inclination of diagonal stiffener. The suitable angle is between arctan (IWa) and 45 degrees. It is advised to close to 45 degrees.(8) The structural design procedure of diagonal stiffener is:applicability judgment, additional position option of diagonal stiffener, determination of stiffener spacing, inclination adjustment of diagonal stiffener and sectional dimension determination of diagonal stiffener.(9) It's recommended that the relevant welding detailing requirements of diagonal stiffener and the requirements of transverse stiffener in "Code for Design of Steel Structures" GB50017-2003 should be unified. Diagonal stiffener and transverse stiffener should not be welded in the same place.(10) It's proposed that the steel beam with diagonal stiffener should be converted to truss system. The diagonal stiffeners should be regarded as diagonal web member of truss. The axial pressure of diagonal stiffeners can be estimated.