Establishing and Developing the Weak-Axis Strength of Plates Subjected to Applied Loads

Special concentrically braced frames (SCBFs) are economical and provide substantial lateral resistance and stiffness. They are frequently used in seismic design, since recent issues with steel moment resisting frames have increased their cost and raised doubts about their performance. Unfortunately SCBFs are not as well understood as many other structural system, because they rely on inelastic post-buckling of the brace during extreme seismic events. As a result, several research studies have been undertaken to better understand and improve SCBF seismic behavior. A research study has been in progress at the University of Washington (UW) to improve the seismic performance of SCBF gusset plate connections. To date more than 20 large-scale SCBF frames with gusset plate connections have been tested, and extensive analysis has been performed. This work is summarized, and the broad general conclusions from the experimental work are noted and demonstrated. The importance of connection stiffness and gusset plate welding and the relative performance of bolted vs. welded and tapered vs. rectangular gusset plates are shown. The results lead to recommended changes in the current design methods. In particular, a modified method for assuring end rotational capacity for brace buckling is proposed. This method provides lighter more compact gusset plates, which develop greater inelastic deformation capacity from the frame and less secondary damage to framing members.

Investigation of the seismic response of three-story special concentrically braced frames

SummaryThe design and detailing of gusset plate connections greatly influence the seismic performance of a special concentrically braced frame (SCBF). Recently, a balanced design approach has been proposed in order to develop significant inelastic deformation from multiple yield mechanisms and to delay the failure of connections of SCBF system. Although extensive studies have been conducted on the corner gusset plate connections of SCBFs, research on the detailing of mid‐span beam gusset plates is rather limited. This study aims at investigating the required free length for the detailing of the mid‐span gusset plates with different brace slenderness ratios. A nonlinear finite element analysis has been conducted for a braced frame with 4 different values of linear clearance in the mid‐span gusset plates and 2 values of brace slenderness ratios. In all simulation models, the corner gusset plates have been designed using balanced design approach and detailed using an elliptical clearance of 8 times the gusset plate thickness. An experimental study has also been conducted on 2 gusset plate sub‐assemblages having similar brace slenderness ratio but with 2 different values of linear clearance in the middle gusset plates. The lateral drift capacity corresponding to the brace fracture and the level of damage are found to be dependent on the detailing of the gusset plates. Based on the results of numerical and experimental studies, the required free length has been recommended for the detailing of middle gusset plates of SCBFs of different brace slenderness ratios.

Seismic performance of all-steel buckling-controlled braces with various cross-sections

Investigation led by the National Transportation Safety Board (NTSB) suggests that inadequate design of gusset plates played a key role in the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plate connection was at a panel point designated as U10. Further understanding of the behavior of the U10 gusset plates is essential. In the present study, the U10 gusset plates were analyzed using detailed nonlinear finite element models. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were, in turn, used to calculate possible stress and strain states of the U10 gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse. Weight increase due to deck reconstruction, staged construction materials, and thermal effects, along with insufficient strength of the gusset plate, seem to be the main contributing factors to the substantial yielding. The results also suggest that the interaction of large compression and large shear should be addressed. This interaction is not well understood.

The external geometry of the fillet weld plays an important role in the strength of the weld. Two factors that influence the external geometry of the fillet weld are weld size and profile. The fillet weld must be made to the weld size and profile as specified in the welding code. Unacceptable profile not only is a defect of the weld but also produces stress risers that reduce the fatigue strength. Insufficient weld that reduces the cross sectional area of weld throat may cause premature failure. Visual inspection and weld gages are two most widely used simple tools to provide a rapid assessment of the external geometry of the fillet weld. In this study, the reverse engineering technique, which a laser scanning system integrates with CAD software, is used to provide a more accurate measurement of the weld contour. The weld samples were made of low-carbon steel plates with T-joint using CO2 welding. The weld volume, weld size and convexity were determined from CAD model to evaluate the weld quality. The reverse engineering technique provides a more accurate and efficient method to inspect the external geometry of fillet weld.

Concentrically braced frames exhibit adequate stiffness against lateral loads. However, a critical issue with these frames lies in the connection between the brace and beam/column. The compressive and tensile forces in the braces induce significant shear at the end of the beam, leading to yielding of the beam and failure of the connection to the column. Additionally, in many cases, welds at the edge of the gusset plate to the beam experience premature failure due to stress concentration before brace yielding or buckling. In this study, it is proposed to replace the I-shaped beam with a double channel beam (2-UNP) and to allow the gusset plate to pass continuously through the beam. Consequently, in consecutive stories, there will be a continuous connection plate passing through. The research results demonstrate that in this configuration, the stress level in the beam web, connection of the beam to the column, and weld at the edge of the connection plate are significantly reduced. In frames with through gusset plates, as a portion of the brace force is transferred through the connection plate passing through the U-shaped beam, less force is absorbed by the weld, preventing premature brace yielding or buckling before weld failure. Furthermore, due to increased allowable drift in frames with through gusset plate, the ductility of the frame enhances compared to frames with a conventional gusset plate.

Framework.—Aircraft wings, fuselages, and other light structures comprising tubular members built up from two or more metal strips with out‐turned flanges and continuous from end to end of the member, have gusset plates secured to adjoining flanges on the tubular members, and bracing members are secured to the gusset plates so that the line of action of each member of the structure passes through the centroid of that member. The tubular members are formed from two, three, or four metal strips extending the whole length of the member, as described in Specification 264,626. Figs. 7 and 8 show a joint for a fuselage wherein a gusset plate 34 is secured between the flanges of a tubular boom 33 and also between the flanges of two tubular bracing members 37, 42. A bracing member 41 is similarly secured to the boom 33. A plate 44, having bent flanges 45, 46 is secured to the flanges of the members 37, 41, and the flanges of a diagonal member 43 are secured thereto on opposite sides. Alternatively, the flanges of the boom may be embraced by pairs of gusset plates secured between the flanges of the bracing members. Fig. 15 shows a modification in which two bracing members 81, 82 are secured to a single gusset plate having a bent portion 84 resting against the boom 83. The ends of the bracing members may be reinforced internally or externally by sleeves, or by flat plates butted against the edges of the gusset plates and riveted between the flanges. For building up irregular outlines, the gusset plates or the flanges of the boom may be bent into the plane of the bracing member. Specification 24948/96 is referred to.

In this paper the outline and test results of the experimental study about fillet welded joints using vertical connecting plates. 5 kinds of specimens concerning of this type joint were designed (see Fig.2, Fig.3) to investigate the statical characteristics of the joints. The parameters are width and thickness of vertical connecting plates, length and size of fillet weld and existence of boxing welds. It becomes clear that the maximum strength and plastic deformation ability of fillet welded joints using vertical connecting plates is little smaller than that of usual fillet welded lap joints using splice plates in case fracture mode 4 (see Fig.5) occurred. The height to thickness ratio of the connecting plate has a major influence on the maximum strength of this type of the fillet welded joints.

To facilitate the disassembly and recycling of structural components, this study proposes a novel demountable reinforced-concrete column–steel beam (RCS) joint. Numerical simulations were conducted to analyze the performance of this new RCS joint using finite element software ABAQUS 2021. Simultaneously, to expand the parametric analysis of the finite element model, further validating aspects such as concrete strength, the flange strength of the steel beam, the strength of the gusset plates, and the longitudinal reinforcement ratio were studied. The finite element analysis results demonstrate that the proposed demountable RCS joint exhibits superior bearing capacity and ductility compared to conventional cast-in-place joints. To further investigate the seismic behavior and influencing rules of this joint, analyses were carried out focusing on aspects such as hysteresis curves, skeleton curves, ductility, energy dissipation, residual deformations, and strength degradation. The findings reveal that gusset plate strengths, steel beam strength, beam-end connecting plate strength, longitudinal reinforcement ratio, and concrete strength have significant impacts on the strength and failure modes of the RCS joints. In addition, the life cycle analysis of four different material structures shows that the demountable RCS joints have the smallest carbon emission during the life cycle, which is conducive to the reuse of resources. Finally, the development of demountable RCS joints is proposed for China’s construction industry.

Gas metal arc (GMA) fillet welding is one of the most important processes for metal joining because of its high productivity and amiability to automation. This welding process is characterized by the complicated V-shaped joint geometry, a deformable weld pool surface, and the additions of hot metal droplets. In the present work, a three-dimensional numerical heat transfer and fluid flow model was developed to examine the temperature profiles, velocity fields, weld pool shape and size, and the nature of the solidified weld bead geometry during GMA fillet welding. The model solved the equations of conservation of mass, momentum, and energy using a boundary fitted curvilinear coordinate system. Apart from the direct transport of heat from the welding arc, additional heat from the metal droplets was modeled considering a volumetric heat source. The deformation of the weld pool surface was calculated by minimizing the total surface energy. Part I of this article is focused on the details of the numerical model such as coordinate transformation and calculation of volumetric heat source and free surface profile. An application of the model to GMA fillet welding of mild steel is described in an accompanying article (W. Zhang, C.-H. Kim and T. DebRoy, J. Appl Phys. 95, 5220 (2004)).

The harsh marine environment causes the corrosion of gusset plates on offshore platforms, which seriously threatens their safety and lifespan. This study investigates the corrosion behavior of 16Mn steel gusset plates in a marine environment, focusing on the effects of chloride ion concentration, dry-wet ratio, and applied stress. The mathematical model, developed using Response Surface Methodology (RSM) and COMSOL Multiphysics simulations, reveals that chloride ion concentration exerts the greatest influence on the corrosion rate, followed by the dry-wet ratio and applied stress. A significant interaction between chloride ion concentration and dry-wet ratio was observed. The model’s R² value is 0.9961, confirming its accuracy. Corrosion mainly occurs at the right-angled edges and curved edges of the gusset plates. These research findings provide a scientific basis for the anti-corrosion design of marine materials, contributing to ensuring the safety of offshore platforms and extending their service life.

Numerical & experimental investigation of slotted-hidden-gap connection for square HSS brace members

In previous studies, many fatigue tests have been performed to investigate the fatigue behaviour of out-of-plane gusset welded joints. However, fatigue behaviour of out-of-plane gusset joints with a one-side fillet weld has not yet been clarified sufficiently. In this research, in order to quantitatively clarify the behaviour, welding residual stress at the weld toes of the joint was measured by a cutting method. In addition to this, fatigue tests were carried out on the joints with a one-side weld and turn-around weld. The plate thickness is 9 mm and the weld size is 10 mm. Moreover, finite element stress analyses were conducted on the test specimen models and parametric models with different main plate and gusset plate thickness. Their results show that fatigue cracks for out-of-plane gusset joints with a one-side fillet weld initiate from both weld toes at the start and end points of weld beads and non-penetration weld of the gusset side. Also, the crack initiation points are different depending on the weld arrangement; however, their fatigue strengths are almost same.

Mechanical behavior of transverse fillet welded joints of high strength steel using digital image correlation techniques