Thin Web Plates Research Articles

Effectiveness of stiffeners on steel plate shear buckling at ambient and elevated temperatures

There are a growing number of bridge fire events and the National Fire Protection Association (NFPA) requires that critical structural elements of the bridge be protected from elevated temperatures due to fire. However, no guidance is given on how to protect these critical elements, nor how to identify them. Further, slender steel web plates have been shown to be vulnerable to shear buckling in fire events and recent research that indicates that the load path of shear forces in thin web plates is not well understood. The overall objective of this paper is to examine the effectiveness of stiffeners for enhancing the shear capacity of slender plates at ambient and elevated temperatures. Specifically, evaluations are made regarding the effectiveness of stiffeners for increasing the shear buckling capacity through various stiffener orientations, providing lateral restraint, and providing a load path for shear forces. In particular, the elastic shear buckling load, Vcr, and the ultimate shear postbuckling load, Vu, of the steel plate are examined. Finite element analyses, which have been validated with experimental data, are used as a basis for the study. The temperatures studied range from ambient to 1100 °C. This study provides some important insights on the behavior of plates under shear loads. For example, results indicate that the stiffener’s role is not that of a load path for the shear forces, but one of lateral restraint, regardless of its geometric orientation. Further, it is shown that for lower temperatures a stiffener oriented along the compression diagonal (opposite to a tension field) provides the most improvement in postbuckling strength.

Forming defect control and optimization of multi-step spinning thickening process considering the variation of spinning gap

Spinning thickening is a novel metal-bulk forming technology for sheet metal, which gains successful applications in the net-shape manufacture of the structural parts with thin web plates and thick rims in automobile industry. However, through-process design of the forming scheme considering the possible variation of relative position of the plate is still lacking. To this end, the instantaneous stress-strain distribution of the plate, the bending force of the plate, and the order of the metal filling into roller groove were analyzed. Additionally, forming quality of the Eigen-structure with different spinning gaps was studied and quantitatively evaluated by experiments and FE simulation. It is found that pit, flash, hump, and depression are the dominant forming defects that influence the surface quality and performance of the parts. With the increase of positive spinning gaps, the area of the pit increases firstly and then decreases. With the increase of the absolute value of negative spinning gaps, the area of the pit increases continuously. By employing weighting method, a new index is proposed to evaluate the combined forming quality of the Eigen-structure. In addition, a phenomenological model was established for characterizing the correlation between the spinning gap and the quality index. Finally, taking the variation of spinning gap into consideration, process optimization of a two-step spinning thickening process was carried out under the constraint of multiple defects. The optimized range of spinning gap was obtained and experimentally validated. Results show that the quality of thick rim is improved by utilizing the optimized scheme and the target parts were formed with high quality under the reasonable range of spinning gap.

Push-out behavior of headed shear studs welded on thin plates and embedded in UHPC

A novel repair method has been developed for steel bridge girders with corrosion damage at the ends. The concept involves welding headed studs to the intact portion of the web plate and encasing them in Ultra-High Performance Concrete (UHPC). This creates a bearing force transfer mechanism to bypass the corroded web plate. Since the headed studs play a crucial role in transferring the shear forces to the UHPC, a careful study is needed to validate their shear capacity when welded to thin web plates typical of steel girders. This paper presents the experimental results from a series of push-out specimens with studs welded to a 9.5-mm thick plate extracted from an old steel bridge. The objective of the study is to understand the influence of design parameters including diameter, spacing and layout on the capacity and failure mechanism of headed studs in UHPC. The experimental results indicate that the capacity was consistently higher than that predicted by design codes such as AASHTO or Eurocode-4. The results show that studs with significantly smaller spacing than what is typically used in practice reach their full capacity. This enables placement of many studs in small regions of the web as may be required in this repair design. The consistent mode of failure was shear rupture at the stud shank. Based on these results, an existing capacity formulation was refined for headed studs embedded in UHPC.

Strip Model Analysis for Steel Plate Shear Walls in Earthquake Resistant Structures

Unstiffened Steel Plate Shear Walls (SPSWs) are very effective structural systems designed to resist lateral forces. SPSW systems consist of thin web plates infilled within frames of steel horizontal and vertical boundary elements. The thin unstiffened web plates are expected to buckle in shear and to develop diagonal tension field after buckling under the action of horizontal loads. For unstiffened steel plates, buckling in shear occurs in the elastic range at low stress levels. This behaviour provides strength, stiffness and ductility and allows to have an appropriate level of energy dissipation through tension yielding of the web plates. This paper assesses the inelastic structural response and behaviour of Steel Plate Shear Wall systems using both a modified strip model approach and a new simplified strip model for only beam connected SPSWs. Both models are developed with plasticity concentrated elements and the performed analyses include the nonlinear behaviour of strips, also considering the compressive forces effects over the strip model elements. This research indicates fundamental aspects of the seismic performance of Steel Plate Shear Wall systems, such as energy dissipation capacity, panel ductility demand, seismic inter-story drift and design load demands in Vertical Boundary Elements (VBE) and Horizontal Boundary Elements (HBE) of the frame. The results obtained from the use of these models are compared with selected experimental and numerical results to enrich the research conclusions.

11.40: Cyclic bending of multi‐stiffened plate girders: Numerical model development and analysis

ABSTRACTDuctile design of steel structures subjected to seismic effects requires creation of dissipative zones. In case of moment resisting frames and eccentrically braced frames, in order to achieve high ductility this requirement often yields to the application of compact sections in the dissipative zone, otherwise premature local plate buckling will govern the design and high ductility cannot be obtained.Buckling resistance of thin web plates of I girder can be significantly increased by application of stiffeners in the web. Vertical stiffeners are often required in seismic links of eccentrically braced frames, but rarely used in moment resisting frames. Application of longitudinal stiffeners is common in bridge structures only. Such stiffeners are typically designed as relatively stiff and strong stiffener, that is characterized by column‐type buckling behaviour, resulting in relatively low ductility.This paper introduces an innovative structural solution: using flexible (i.e. with low rigidity relative to the plate rigidity) multiple longitudinal stiffeners enables plate‐like overall buckling behaviour, which is beneficial with respect to ductility. Although the behaviour of such stiffened plates subjected to monotonic loading is studied in several researches, there is no data available on the cyclic ductility.To study the cyclic behaviour and ductility of such girders, numerical and experimental programme is worked out. This paper primarily focuses on the numerical model development. Shell element numerical model is developed for non‐linear static analysis of the monotonic and cyclic loading. The model is validated by the test results. The developed and verified model is being applied for parametric analysis to study the cyclic performance of various configurations.

Innovative Structural Solution for Dissipative Zone Stiffened by Longitudinal Stiffeners

This paper introduces an innovative structural solution for dissipative seismic resistant structures. A steel seismic link is created using multiple longitudinal stiffeners enabling the web plate for overall plate buckling behaviour, which is beneficial with respects to ductility. Although the behaviour of such stiffened plates subjected to monotonic loading is studied in several researches, there is no data available on the cyclic ductility.Buckling resistance of thin web plates of I girder can be significantly increased by application of stiffeners in the web. Vertical stiffeners are often required in seismic links of eccentrically braced frames, but rarely used in moment resisting frames. Application of longitudinal stiffeners is common in bridge structures only. Such stiffeners are typically designed as relatively stiff and strong stiffener, that is resulting in relatively low ductility.To study the cyclic behaviour and ductility of such girders, numerical and experimental programme is worked out. Cyclic ductility is studied and compared at different stiffened geometries. The obtained results confirm the practical applicability of the conceived configurations of flexible multiple stiffeners. The results also provide as basis for further design provision development.

A sheet blank rotary forging process for disk-like parts with thickened rims

Disk-like parts with both thin web plates and thick rims are widely applied in automotive and aviation industries. These parts are usually made via welding and machining, which often lead to low material utilization, high energy consumption and low product performance. Therefore, a new sheet blank rotary forging process for thickening the rims of disc-like sheet blanks with uniform thicknesses was proposed in this paper. Based on FEA and experiments, both the effects of main defects and process parameters on forming were investigated. Besides, by considering the flow line distribution in formed parts, the material deformation feature in the forming process was analyzed. The results showed that the deformation process can be divided into four stages, and there are mainly four kinds of defects occurring during forming. Materials in the outer side of rim flows not only in the radial direction but also in the tangential direction.

Effect of forming parameters on sheet metal stability during a rotary forming process for rim thickening

A new rotary forming process for rim thickening was proposed in this paper, which can be applied on sheet metals to produce parts with thin web plates and thick rims integrally. Via FE simulation, an orthogonal test was conducted to investigate the effects of forming parameters on γmax, which is the ratio of maximum blank size to thickness and indexes the stability of sheet metals while during forming. It is found that the incline angle of the upper roller groove surface, and the friction condition between the sheet metal and roller groove are the dominant factors affecting the process, while the influence of the feeding velocity and the groove arc radius are relatively slight. It is also proved that interactions exist among these factors. Furthermore, an optimized parameters group is obtained, and a process window plot showing the limits of the forming process is achieved. The facticity of FE simulation is verified by technological experiments.

Seismic behavior of code designed steel plate shear walls

The AISC Seismic Design Provisions now include capacity design requirements for steel plate shear walls, which consist of thin web plates that infill frames of steel beams, denoted horizontal boundary elements (HBEs), and columns, denoted vertical boundary elements (VBEs). The thin unstiffened web plates are expected to buckle in shear at low load levels and develop tension field action, providing ductility and energy dissipation through tension yielding of the web plate. HBEs are designed for stiffness and strength requirements and are expected to anchor the tension field formation in the web plates. VBEs are designed for yielding of web plates and plastic hinge formation at the ends of the HBEs. This paper assesses the behavior of code designed SPSWs. A series of walls are designed and their behavior is evaluated using nonlinear response history analysis for ground motions representing different hazard levels. It is found that designs meeting current code requirements satisfy maximum interstory drift requirements considering design level earthquakes and have maximum interstory drifts of less than 5% for maximum considered earthquakes. Web plate ductility demands are found to be significantly larger for low rise walls than for high rise walls where higher modes of vibrations impact the response. The percentage of story shear resisted by the web plate relative to the boundary frame is found to be between 60% and 80% and is relatively independent of panel aspect ratio, wall height, or hazard level, but is affected by transitions in plate thickness. Maximum demands in VBEs in design level shaking are found to be considerably less than those found from capacity design for SPSWs with 9 or more stories.

Bridge Girders with Corrugated Webs

In plate girders, the use of corrugated webs permits the use of thin web plates without stiffeners, which reduces the cost of beam fabrication and improves fatigue life. Experimental and analytical studies on the behavior of girders with corrugated webs were conducted that have led to design recommendations. For girders with corrugated webs subjected to shear, it was noted from the experimental as well as the analytical results that failure of the web occurs because of local or global shear buckling, which depends on the corrugation configuration. For girders with corrugated webs subjected to uniform bending, the failure was due to yielding and vertical buckling of the compression flange into the web. The test and analytical results indicate that the web offered negligible contribution to the moment-carrying capacity of the beam, and the ultimate moment capacity may be calculated on the basis of the flange yielding, ignoring any contribution from the web. The behavior of girders with corrugated webs under in-plane compressive edge loads applied directly on the top flange was investigated, and design recommendations are made. Tests to examine the behavior of girders with corrugated webs under repeated loads are few. The results from the available tests are reported and compared with the results from test on conventionally stiffened girders with flat webs.