Panel Zone Shear Research Articles

The Influence of Box-Strengthened Panel Zone on Steel Frame Seismic Performance

During the Northridge earthquake, extensive brittle failures on the weld zones of the beam bottom flanges in the rigidity connection of steel special moment frames (SMFs) were detected. One of the primary reasons is the high-tensile strain demand created at the beam bottom flange zones due to positive bending. The weak panel zone of the I-section column exhibits more shear deformation, which promotes and accelerates the brittle fracture of the beam bottom flange weld zones. A box-strengthened panel zone can minimize the shear deformation of the panel zone of the I-section column, which may also reduce the inter-story displacement of steel SMFs and enhance their seismic behavior. In order to investigate this fact, in this research we carried out a model test of a steel frame with a box-strengthened panel zone to examine SMFs’ seismic performance and inter-story displacement, as well as testing the contribution of panel zone shear deformation to inter-story drift. Numerical methods were then used to investigate the influence of the axial compression ratio and beam-to-column linear stiffness ratio on the effect of shear deformation on the box-strengthened panel zone. Design recommendations are given based on the research results.

Cyclic behavior of dual-steel beam-to-column welded flange-bolted web connections

Cyclic loading tests on dual-steel beam-to-column welded flange-bolted web connections were conducted to quantify their moment resistance, plastic deformation and energy dissipation capacities. The test program consisted of five one-sided connection specimens, where Q355 grade beams and Q690 grade columns were used, to study the effects of beam-to-column welded flange connection details and panel zone shear strength on the connection seismic performance. Two types of welded connection details were considered; one was the traditional complete-joint-penetration (CJP) welded connections by use of backing bars, and the other type was those with the bottom backing bar further reinforced by a fillet weld. Three column web thicknesses were designed to arrive at strong, intermediate and weak panel zones, respectively. It was found that the CJP weld with the backing bar reinforced only under the bottom beam flange produced satisfactory performance and accommodated plastic rotations larger than 0.03 rad, while a maximum plastic rotation of 0.04 rad could be developed in the high-strength steel panel zone before fracture occurred. These results evidenced that those dual-steel connections could still sustain high seismic deformation demands.

Hysteretic behaviour of welded connections with highly inelastic panel zones

AbstractThe current practice in capacity‐designed steel moment resisting frames (MRFs) worldwide allows for limited shear yielding in the column web panel zone. As such, inelastic deformations concentrate near the beam ends, thereby leading to flexural strength deterioration due to local buckling often at modest lateral drift demands. Experiments on post‐Northridge welded connections suggest that prior to a story drift angle of 5% rad, panel zone kinking does not induce fracture for panel zone shear distortions of up to 10γy. Within such a context, this paper presents an alternative design of a welded moment connection with highly inelastic panel zones. The connection features simplified weld details including a customised beveled backing bar that can be kept in place after the completion of the complete joint penetration welds at the beam flange‐to‐column flange joint. Full scale experiments suggest that the hysteretic response of the connection remains stable up until a story drift angle of 8% rad. The specimen did not exhibit visible structural damage prior to story drift angles of 4% rad, which are characteristic to a maximum considered earthquake. Modest local buckling occurred near the beam ends only after a story drift angle of 5% rad, which is a typical drift threshold in current collapse assessment methodologies. This paper summarises the primary findings of the experimental program for one of the test specimens.

Parametric study of 3D steel moment connections with built-up box column subjected to biaxial cyclic loads

In this numerical research, the variation of cyclic behavior of beam-to-box column connection was studied. Dimensional and load conditions were parametrically evaluated with the goal of assessing the applicability and use of this biaxial moment connection according to the Seismic Provisions, such as bending strength and rotation capacity, secant and tangent stiffness, dissipated energy and strong column-weak beam relationship. A total of 83 different models of 3D connections were developed using in ANSYS software with the load at the top of the column. Results show a cyclic behavior not controlled by axial load. However, the variations of clear span to depth beam ratio caused degradation of the strength, secant and tangent stiffness as well as in dissipated energy. The 80% of plastic moment of beam and rotation at 4% interstory drift were reached for all models analyzed according to criteria established in AISC 341. Finally, the configurations designed with low levels of axial load are controlled by the design of the web panel zone shear, while configurations designed for high levels of axial load are controlled by the strong column-weak beam criterion. • The hysteretic response curves of the joints with end-plate connections and built-up box column subjected to cyclic loading were plumped. • The beam can concentrate the inelasticity effectively in a wide deformation range. • The behavior exhibited is acceptable for 7 < L/d < 20 ratio. • A numerical prequalification was possible.

Parameter Optimization and Bending Performance Analysis of a Corrugated Steel Plate-UHPC Composite Bridge Deck with PZ Shear Connectors

Composite bridge decks consisting of steel plates and concrete are used to minimize fatigue cracking and damage of asphalt pavement of orthotropic steel bridge decks subjected to wheel loads. This paper presents a methodology to optimize the parameters and mechanical performance of a corrugated steel plate-ultrahigh-performance concrete (UHPC) composite bridge deck with panel zone (PZ) shear connectors using the improved non-dominated sorting genetic algorithm (NSGA-II). A 3-D finite element model is established in ANSYS Workbench software to conduct numerical parameter analysis, and ABAQUS software is used to analyze the optimized model’s mechanical performance. The results show a significant improvement in the mechanical performance of the optimized composite bridge deck, with a 27.66% decrease in the maximum stress in the UHPC layer. The vertical displacement of the optimized composite bridge deck increases sharply when the load reaches 90% of the ultimate load, and a significant change in the strain is caused by the sliding displacement between the UHPC layer and steel plate. The bottom part of the corrugation yields first in the middle span, followed by failures of the ribs. In addition, as the tensile stress increases, damage occurs first in the UHPC layer near the PZ shear connectors in the shear bending area and the bottom in the bending area, expanding significantly to the entire bending and loading areas. The results indicate that the parameter optimization of the corrugated steel plate-UHPC composite bridge deck using NSGA-II improves the structure’s bending performance.

Seismic demands of steel moment resisting frames with inelastic beam‐to‐column web panel zones

AbstractThis paper intends to provide quantitative seismic response characteristics of steel moment resisting frames (MRFs) with inelastic beam‐to‐column panel zone joints. Two modeling approaches are proposed for this purpose along with a methodology to consider the fracture potential at the bottom beam flange in steel MRFs due to panel zone kinking. Both approaches, which are validated with available experiments, preserve the behavioral insights of inelastic panel zones. Nonlinear static and dynamic analyses are then conducted to quantify the seismic demands of 32 prototype steel MRFs while their panel zones exhibit various levels of inelastic deformations. Engineering demand parameter hazard curves are developed to interpret the results for a risk‐targeted seismic performance. The results demonstrate that steel MRFs with panel zone shear distortions of 10 to 15 times the shear distortion at yield, , have a mean annual frequency of collapse ranging from to , which is up to two times lower than corresponding results with code‐compliant steel MRFs (i.e., It is shown that steel MRFs with inelastic deformations of 10 in their panel zones, (a) enjoy up to 50% reduction in residual story drift ratios at a design basis earthquake; (b) their beam‐to‐column connections do not experience fractures due to panel zone kinking; and (c) local buckling in steel beams is very limited even at low probability of occurrence earthquakes. The above hold true when the current detailing and fabrication practice is employed. The findings have implications on seismic design and the post‐seismic repairability of steel MRFs.

Characterization of the panel zone shear behaviour in steel beam‐to‐column joints

AbstractNominated for the Eurosteel 2021 Best Paper AwardThis short report has been prepared in the context of the Eurosteel 2021 Best Paper Award. It summarizes developments completed and in progress at the University of Liège designed to characterize the complete shear behaviour of the panel zone in steel beam‐to‐column joints in terms of stiffness, resistance and ductility. This work is part of a larger research project which aims to predict the complete rotational response of the joint to failure.

Critical Comparison of Assessment Codes for Steel Moment Resisting Frames

AbstractMany existing steel multi‐storey frame buildings worldwide were designed prior to the introduction of modern seismic design provisions or based on outdated hazard maps considering low values of seismic intensity. This often resulted in buildings showing low performances with respect to earthquake loads. Assessment codes, such as the Eurocode 8 Part 3 and the ASCE 41, have been conceived to provide tools to assess the seismic performance of existing structures, to evaluate their adequacy with respect to the current safety standards and the need for seismic retrofit. However, recent research studies have revealed the necessity for a revision of these codes. In particular, for steel moment resisting frames, the current European regulation shares many similarities with older versions of the American codes, but has failed to incorporate changes based on the state‐of‐the‐art knowledge. In addition, the undergoing update of other parts of the Eurocode motivates a full revision of the current standards. This paper compares the assessment procedures of the European and American codes. Two low‐code steel Moment Resisting Frames were considered for case study purposes and the assessment was performed based on three local Engineering Demand Parameters (EDPs), i.e., column's rotation, beam's rotation and panel zone's shear distortion, and the inter‐story drift as global EDP. Incremental Dynamic Analyses were performed for the development of component and system fragility curves. The present work aims to identify some challenges and to provide some preliminary insights for the revision of the Eurocode 8 Part 3.

Parametric Analysis and Stiffness Investigation of Extended End-Plate Connection.

Extended end-plate (EP) bolted connections are widely used in steel structures as moment-resisting connections. Most of these connections are semi-rigid or in other words flexible. The paper aims to study the behavior of such connections under the effect of column top-side cyclic loading using the finite element (FE) method. For semi-rigid connections, it is very vital to determine the moment-rotation relationship as well as the connection stiffness. These beam-column connections have been parametrically studied, the effect of joint type, shear forces, diameter of bolt, thickness of end-plate, and end-plate style were studied. Parametric studies show that the panel zone shear force is the key factor and has a significant effect on the connection stiffness. Finally, based on the component method, the stiffness of the bending component is improved, and the initial stiffness calculation model of the connection under column top-side cyclic loadings is established. The results show that the calculation model is in good agreement with the finite element analyses, and this proves that the calculation model proposed in this study could act as a reference method.

Joint behavior and design procedure of a through plate connection for steel beam to hollow or concrete‐filled tubular columns

SummaryThe through plate connection has a practical reliable configuration for fully restrained connections for a steel I‐beam to hollow or concrete‐filled tubular columns in seismic areas. Based on experimental programs of authors on interior planar moment connections via through plate technique, this paper presents the outcome of the studies focusing on the joint behavior and the shear transfer in the panel zone of through plate connection. Based on the conducted approved three full‐scale tests, the behavior of connection components and panel zone shear force were investigated accurately in order to provide useful information and key parameters to facilitate design calculations and proportioning the connection. The contribution of each component in the total shear capacity of the panel zone region was determined. Load transfer mechanisms were explained and by quantifying the portion of load transfer paths, the calculation approach was described for design purpose. The proposed design procedure was validated for a wide range of beam to column connections using finite element models. Verified numerical models were used to conduct parametric studies. The numerical results revealed that the proposed analysis method can predict well the induced demand in the connection components and also the design procedure is suitable and secure for all cases.

Investigating partial tension field action in gable frame panel zones

Gable metal frames are popular, cost-efficient structural systems for commercial and industrial buildings. The use of relatively thin web material typically leads to shear buckling of the column panel zone when such frames are subjected to lateral loads. Previous experimental research has shown that the exterior corner of a panel zone in gable frame knee joints may not be stiff enough to fully develop tension field action (TFA), but that some post-buckling strength is developed. This paper presents a theoretical model for TFA in knee joints based on plastic analysis, and an accompanying equation for predicting the post-buckling panel zone strength for positive bending (wherein the tension field is oriented from the interior to the exterior corners). The TFA was found to primarily depend on three design parameters, namely, flange flexural strength, panel aspect ratio, and panel slenderness. To calibrate the proposed equation, a parametric analytical study was conducted using the finite element method. The modeling scheme accounted for material and geometric nonlinearity and was validated with experimental test data. The study involved 98 prototype gable frame configurations and allowed the investigation of the impact of the aforementioned three design parameters on the TFA. The proposed equation was found to predict the panel zone shear strength for the prototype frames with an average error of 1% and an error standard deviation of 5%. Therefore, the equation can be used to calculate the post-buckling shear strength of panel zones for the range of design parameters considered in the parametric study.

Experimental study on panel zone behavior of diaphragm-through connections to concrete-filled tube columns

In order to verify the accuracy of the panel zone shear capacity calculation method of diaphragm-through connections which were proposed in previous research, the low cycle repeated load tests of six cross-shaped specimens were carried out. The seismic performance of the panel zone’s stress distribution, failure mode, hysteresis curve, and skeleton curve are comprehensively studied and analyzed. The results showed that the steel tube web and core concrete were mainly participating to bear the horizontal shear force, and the “steel frame” composed of the steel tube flange and through-diaphragm was negligible for the shear resistance; the core concrete strut calculated width and height were all one-fourth of the height and width of the panel zone. The test results are in good agreement with the results of the calculation method, which indicated that the calculation method proposed in the previous research results had good accuracy and applicability, and would use for the panel zone shear capacity calculated in the connections design.

Experimental study on seismic behaviour of cover-plate joints in high strength steel frames

Improved configurations of beam-to-column joints are required to avoid brittle fractures in earthquakes in the design of high strength steel frames, and the cover-plate beam-to-column joints are expected to be effective to reinforce the welded flange-bolted web joints with negligible additional requirements for construction space and have potential for applications in seismic design of high strength steel frames. A total of 6 specimens of high strength steel double-sided cover-plate beam-to-column joints, considering three different combinations of 345 MPa or 460 MPa steel beams and 460 MPa or 730 MPa steel columns, were designed according to the Chinese code and tested subjected to cyclic loads with axial compressions in columns in consideration. The failure modes, the resistance, the stiffness and the ductility of the specimens were analyzed, and the influences of the panel zone thickness, cover-plate length, attached fillet weld in web connection and shape of the weld access whole were evaluated. According to the test results, continuity plates with sufficient thickness in high strength steel cover-plate joints were necessary to avoid unexpected failure modes, and the panel zone shear rotation would make a considerable contribution to the total story drift angle and the plastic story drift angle of the high strength steel frames. All the 6 specimens reach a story drift angle larger than 0.035 rad with 4 of them larger than 0.04 rad, indicating that the high strength steel cover-plate joint may develop considerable ductility. However, the evaluation methods of joint ductility in high strength steel frames should be further discussed because of the significantly increased elastic deformability of high strength steel members. Based on the test results, design recommendations were proposed for high strength steel cover-plate beam-to-column joints.

Cyclic tests on high strength steel flange-plate beam-to-column joints

Improved beam-to-column joint configurations, with the beam plastic hinges shifted away from the column faces, were required in high strength steel frames to guarantee the seismic performance, and the flange-plate beam-to-column joints are expected to be one of the improved joint configurations that have good prospects in high strength steel frames because of the potential reinforcing effects and the negligible additional requirements for construction space. However, there have been few investigations on the high strength steel flange-plate beam-to-column joints and a lack of detailed design method for flange-plate joints. Considering three different combinations of Q345 or Q460 steel beams and Q460 or Q890 steel columns, a total of 6 full-scale specimens of flange-plate beam-to-column joints with middle columns in steel frames were designed and tested subjected to anti-symmetrical cyclic loads. The failure modes, the resistance, the stiffness and the ductility of the specimens were analysed, and the influences of the joint configurational parameters, including the panel zone thickness, the flange-plate lengths, the attached fillet welds in web connections and the fillet welds arrangements around the flange plates, were investigated. According to the test results, continuity plates with enough thickness were necessary in high strength steel flange-plate joints to avoid unexpected failure modes, and the panel zone shear rotation would make a considerable contribution to the total story drift angles and the plastic story drift angles of the high strength steel frames. Five of the tested specimens reached a story drift angle larger than 0.035 rad and one of them was larger than 0.04 rad, indicating that the flange-plate joint configurations could develop a considerable ductility, which, however, may still be insufficient when adopted in structures with high ductility demand. Based on the test results, design recommendations were proposed for flange-plate beam-to-column joints in high strength steel frames.

Experimental investigation of unequal-depth-beam-to-column joints with t-shape connector

This paper presents the seismic behavior of unequal-depth-beam-to-column joints connected by a T-shape connector. Three specimens are examined under cyclic loading tests. The primary experimental parameters are joints with or without T-shape connectors and beam depth ratio (Db2/Db1) with values of 0.5 and 0.75. The panel zone shear strength of unequal-depth-beam-to-column joints connected by a T-shape connector is 20% higher than that of common unequal-depth-beam-to-column joint under the same conditions. The influence of beam depth ratio on the panel zone shear strength of unequal-depth-beam-to-column joints connected by a T-shape connector is limited. The contribution of the T-shape connector web on the flexure moment of whole beam is less than 3%, indicating that the T-shape connector web does not resist the flexure moment but resists the shear force. Hysteresis curves of the panel zone for unequal-depth-beam-to-column joints connected by T-shape connectors are stable, showing excellent ductility and energy dissipation capacity. The equivalent viscous damping coefficients corresponding to the three specimens range from 0.47 to 0.51 in the ultimate stage. A design method for the T-shape connector is proposed and the calculation formulas are deduced.

The importance of panel zone shear strength on seismic behavior of improved slotted-web beam connections

It is commonly believed by structural engineering researchers that the slotted-web beam connection rectifies many common weaknesses, and hence this connection is recommended whenever possible. Suitable ductility without considerable strength loss is the most important advantage of this type of special moment connection. The shear force present in beam flanges with lateral torsional buckling are mentioned as the main causes of weld fracture in most connections. The separation of flange from beam’s web results in separation of the force shares of beam’s flange and web; also, removal of the shear from beam’s flanges will cause uniform distribution of stress through the width of the beam flange. In this study the seismic behavior of improved slotted-web beam connections is compared with similar samples numerically and experimentally. Results suggest that in case of proper use of beam flange stiffeners, this type of connection does not show any loss of strength and provides suitable ductility. Since shear strength of the panel zone is effective on beam-to-column weld strains, participation of the panel zone in seismic behavior of this type of connection is of interest. Results show that high participation of panel zone effect causes the possibility of weld fracture in beam web to increase and the maximum strength of the connection to decrease. Performance comparisons are made based on envelope curves and percentage of energy dissipation of the specimens. Suitable ductility at this connection proves that this connection shall be classified as special moment connection.

Embedded column base connections subjected to seismic loads: Strength model

Seismically designed mid- to high-rise steel moment resisting frames in the United States are commonly constructed with the lowest portion of the first story column embedded into a concrete footing to transfer large moments and forces. Despite their prevalence, these Embedded Column Base (ECB) connections have not been experimentally examined until recently, such that strength estimation methods for other types of connections are usually adapted for their design. Based on recent experiments, current approaches for designing ECB connections are examined, and a new strength characterization method is presented. Mechanisms for internal force transfer within the connection are postulated; these include horizontal bearing of the column flange against the concrete, panel zone shear, and vertical bearing of the embedded base plate against the concrete. The proposed approach has two components: (1) a process for moment distribution between the horizontal and vertical bearing mechanisms, and (2) idealized stress distributions for estimation of associated limit states. The proposed method is able to characterize the experimentally observed specimen strengths with good accuracy, such that the average test-predicted ratio is 1.01, with a coefficient of variation 0.06. No significant bias in accuracy of the method is observed with respect to test variables. Limitations of the study are discussed; these arise from its empirical aspects which may not be generally extrapolated to configurations significantly different from the experiments upon which the method is based.

Calculation method for the shear bearing capacity of diaphragm-through connections

This article presents the results of experimental, numerical, and theoretical studies into the shear behavior of panel zone of diaphragm-through connections between concrete-filled square steel tubular columns and steel beams. The current design code does not cover the yield and ultimate shear strengths of such connections in China. Five tee-shaped diaphragm-through connections were fabricated and tested that they comply with the principle of “strong members and weak panel zone.” Three-dimensional nonlinear finite element models were developed to study the shear behavior of the panel zone under low-frequency cyclic loading. Based on the test results, the force transfer mechanism and the effect of different factors on the panel zone shear capacity were analyzed. The width and deformation of compression strut of core concrete were taken into account. A simple manual calculation method was also proposed for evaluating the shear strength of panel zone of diaphragm-through connections. Good agreement was found between theoretical and test results for both yield and ultimate shear strengths for connections.

Panel zone behavior of diaphragm-through connection between concrete-filled steel tubular columns and steel beams

The diaphragm-through connections are some of the most widespread connections between concrete-filled steel tubular columns and steel beams. In this work, five tee-shaped diaphragm-through connections were fabricated so that they comply with the principle of “strong members and weak panel zone.” Low-frequency cyclic loading was applied to the specimens to investigate the panel zone behavior of the connections. Based on the test results, the force transfer mechanism and the effect of different factors on the panel zone shear capacity were analyzed. In addition, different methods of calculating the panel zone shear strength were compared with the experimental data. The results show that the shear capacity of the panel zone of the connection is borne mainly by the steel tube webs and the core concrete. The steel frame composite with steel tube flanges and diaphragms strengthens the plastic deformation ability after yielding. It was found that in the existing computational methods for panel zone shear capacity of the connection, the calculated results are in agreement with the test results for the shear capacity of the steel tube webs, but the predicted values are not consistent with the concrete component capacity.

Experimental evaluation of the effect of vertical connecting plates on panel zone shear stability

Vertical connecting plates exist in the panel zones of spatial moment frames, which are used to link beam webs in the perpendicular direction. However, current provisions take no consideration of their effect on the panel zone shear stability. This paper aims to evaluate the effect of vertical connecting plates on panel zone shear stability through experimental studies on cruciform beam-to-column subassemblages with/without connecting plates under cyclic loading. The connecting plates are found to be effective in mitigating the shear buckling potential of the panel zone and thus improving the hysteresis behavior of slender panel zones. Based on current seismic provisions, a modified approach for evaluating the panel zone shear stability through its equivalent width-thickness ratio is proposed and proved to be appropriate and on the conservative side.