Weld Access Hole Research Articles

Evaluation of progressive collapse resistance performance of steel OMF with WCPF connections

A welded cover plated flange (WCPF) connection, which is a pre-qualified connection detail improving a weak weld access hole and the ductility of a welded unreinforced flange-bolted web (WUF-B) connection, has a simple and efficient advantage in construction. In this study, a new modelling approach of the WCPF connection by employing 1-D element was proposed for the evaluation of progressive collapse resistance capacity performance. The model was developed by substituting the average width of trapezoidal shapes of cover plates welded to the top and bottom flanges and by assessing the equivalent flange thickness based on the moment of inertia. The proposed model was verified through comparisons with experimental and 3-D numerical results, showing discrepancy within 5.7%. To evaluate the performance of the WCPF connection, a prototype structure was adopted from the previous study for the appraisal of the WUF-B and reduced beam section (RBS) connections. The alternative load path method was performed using an energy-based approximate analysis considering the dynamic effect of sudden column loss. The performance of the structure was evaluated in terms of structural robustness and sensitivity. Furthermore, the results were compared to those of the structures with the WUF-B and RBS connections analyzed in the previous study. The structure with the WCPF connections showed 33% more improved structural robustness and 11% less sensitivity to progressive collapse when one column was removed. In a two-column removal scenario, only the structure with WCPF connections indicated to have proper progressive collapse resistance capacity. The WCPF connection was deemed more reliable than WUF-B and RBS ones.

Study of mechanical properties of H-shaped beam-column joints considering panel zone

In order to clarify the influence of panel zone (PZ) strength on the mechanical properties of each component (column, beam and PZ) of H-shaped steel beam-column joint, the equations of mathematical physics for the mechanical relationship of framing member end considering panel zone were established, and five groups of T-shaped beam-column joint specimens with different strength are tested to study the influence of panel zone to beam strength ratio (PBSR) on the deformation performance, bearing capacity and stiffness of the specimens. Through the finite element analysis, the effect of PBSR and weld access hole on the deformation of joints, the shear and flexural capacity of beams is discussed. Finally, based on the analysis of deformation and bearing capacity of the specimens and models, the reasonable value of PBSR is proposed.

Brittle fracture prediction method considering mixed modes for column-to-beam connections

This study entailed an improvement in fracture assessment based on mixed-mode loading. Brittle fractures can be evaluated using the Weibull stress regardless of the differences in plastic constraints. However, the Weibull stress is proposed for cracks subjected to open loading (mode I), and it does not consider the effects of in-plane (mode II) or out-plane shear loadings (mode III). Structural connections under large deformations are subjected to modes I, II, and III at the crack tip. Fracture tests on beam-to-diaphragm connections in buildings have indicated that failure occurs when ductile cracks propagate from the strain concentration region of a weld access hole, where mode II dominates. Additionally, they cannot be appropriately evaluated using the conventional Weibull stress approach. This study investigated the relationship between mode differences and fracture initiation for several specimens modeled as beam-to-diaphragm connections. A mixed-mode ratio with stress intensity factor was used as an index to evaluate the mode differences. The fracture prediction considers the differences in modes by correcting the evaluated values on the basis of the mixed-mode ratio. The correction results shows more reasonable fracture prediction than conventional methods for beam-to-column connections under different modes.

Balanced design philosophy of superior high-performance steel cover-plated beam-to-column joints

Superior high performance (SHP, 460 MPa or 690 MPa grade) steel, combining high strength, low yield-to-tensile strength (Y/T) ratio, excellent ductility, corrosion resistance and fire resistance was recently developed in China. The seismic response and design of SHP steel beam-to-column joints reinforced with cover plates under cyclic loads are investigated in this paper. Three full-scale SHP460 specimens were carefully designed and tested, with two parameters, including the axial compression ratio and weld access hole, being varied and studied. The test setup and procedures, together with the key obtained results, including load–deformation curves, failure modes, loading resistance, stiffness, as well as ductility are fully reported and discussed. The components of the story drift angle θd are thoroughly analysed, and the contribution of each part to energy dissipation is evaluated. Digital image correlation (DIC) is used to quantify the deformation of the panel zone (PZ), which is more accurate than traditional contact measurement methods. Furthermore, the experiments were supplemented by numerical simulations; finite element models were firstly developed to replicate the experimental behaviour and then employed to perform parametric studies to generate further numerical data on SHP steel beam-to-column joints covering a wide range of axial compression ratios, thicknesses of PZ and material properties. Based on the test and numerical data in this paper, in conjunction with available results of other researchers, a strength and ductility-based balanced design strategy is proposed. It is beneficial for understanding, predicting, and controlling the failure modes and yield mechanisms between the shear yielding of PZ and the flexural yielding of beam and can be described by the balanced coefficient βpz.

Seismic performance study on Q460 high-strength steel welded cruciform beam-column connections

Four Q460 high-strength steel welded cruciform beam-column connection specimens were designed. Among them, different forms of weld access holes were adopted for three specimens, and the locally expanded beam flange configuration was adopted for the other one. Quasi-static tests were carried out on the specimens. Seismic performance of the specimens was studied. The test results show that the specimens have good seismic performance. The ultimate failure modes of each specimen are all shown as the fracture of the beam flange steel base metal or welding material near the weld access hole. Ductility of high-strength steel welded connection can be improved by changing the form of weld access hole. Seismic performance of the expanded beam flange connection specimen was relatively better, which was mainly reflected in the fact that the failure at the weld access hole was delayed in late loading period. Finite element analysis (FEA) was conducted on each specimen. The FEA results were almost consistent with the test results. Analysis shows that the maximum von Mises stresses around the weld access holes of each specimen occurred near the weld access hole toes. The von Mises stress value of each specimen in the middle part of the beam flange width was almost the same. The difference of the von Mises stress values in the beam web height direction of the specimens with different configurations was mainly manifested in the range of three times of the weld access hole height below the upper weld access hole.

Parametric Analysis of the Static Behavior for Stainless-Steel Beam-Column Connections

To study the influence of geometric parameters on flexural capacity and stiffness of beam-column connections using stain-steel S31608 and get the key influence parameters, on the basis of test data, using the finite element analysis software ABAQUS, parameter analysis on three main geometrical parameters of flexural capacity and stiffness of stain-steel beam-column connections was conducted. The analysis results show that when flange thickness of I-shaped bars increases, bearing capacity and initial stiffness of the joints increase with large amplitude; when slipping coefficient increases, bearing capacity and initial stiffness of the joints increase with small amplitude; when weld ac-cess hole changes, bearing capacity increases and initial stiffness increase with small amplitude, but can decrease stress concentrate phenomenon; when “Dog-bone” is used, the position of plastic hinge appearance will out-shift, but bearing capacity and initial stiffness decrease with large amplitude. Using the weld access hole of FEME350 and increasing the flange thickness of I-shaped bars is a good way to improve the static behavior of stain-steel beam-column connections.

Fracture analysis of high-strength steel beam-column connections with initial defects

In order to predict the ductile fracture of beam-column connections with initial defects, the finite element models of the existing Q460C high-strength steel local connection specimens were established, and J-integral, VGM and SMCS model were used to predict the fracture. Compared with the test results, the predicted results of the J-integral, VGM and SMCS model had good accuracy which verified the applicabilities of J-integral, VGM and SMCS model in fracture prediction of connections with initial defects. The finite element analyses were carried out on three full-scale cruciform Q460D high-strength steel frame beam-column connection specimens with three kinds of weld access holes. The influences of initial defect location, initial defect length, initial notch radius and weld access hole form on fracture index were studied. The results indicated that with the same initial crack length, fracture was more likely to occur at crack at flange HAZ; when the beam end load was constant, the required fracture toughness JI value increased with the increase of the initial crack length; with the same initial notch depth and initial notch radius, fracture was more likely to occur at notch at flange HAZ; the sharper the initial notch end was, the greater the stress triaxiality was and the more likely the specimen was to fracture; the weld access hole form had a significant influence on the deformation capacity of cruciform beam-column connection specimens, but had little influence on the strength of the connection specimens.

Improvement of weld details to avoid brittle fracture initiating at the toes of weld access hole of the beam end — prediction of ultimate strength of welded joint with conventional detail

Improvement of weld details to avoid brittle fracture initiating at the toes of weld access hole of the beam end — prediction of ultimate strength of welded joint with conventional detail

Numerical study of the robustness of steel moment connections under catenary effect

The local fracture will directly result in the consequent decrease in the vertical resistance of the beam-to-column assembly in the steel frame structure, which emphasizes the necessity of the ductile fracture prediction in the numerical study. In this paper, a monotonic plasticity and ductile fracture model is used to characterize the stress state and loading path dependency of the yield surface, as well as the combined effects of the shear stress and hydrostatic pressure on the damage evolution. On the basis of the validated material model, five push-down tests of the beam-to-column assemblies with different moment connections are chosen for the validation of this modeling method in terms of overall vertical force–displacement curves and the local crack initiation and propagation. Thereafter, the numerical studies of the weld access hole reveal that the gentle slope of transition cutting and larger distance between toe of weld access hole and flange weld will raise the connection ductility. The relationship between ultimate chord rotation and these two variables can be formulated by the empirical formulas. As for the bolted web-to-column connection, the deformation capacity can be improved by using compact bolt arrangement and larger bolt size. The implementation of the shear tab with long-slotted holes will also enhance the connection ductility under catenary mechanism. In general, these findings will be benefit to improve the robustness of the steel frame structure, along with the quantitative estimation of connection ductility for checking the structural safety.

Dynamic performance of retrofitted steel beam-column connections subjected to impact loadings

In this paper, three steel beam-column connections (welded flange-bolted web (WFB) connection, welded flange plate (WFP) connection and reduced beam section (RBS) connection) were experimentally examined under impact loadings. The impact tests using drop-hammer were carried out to simulate the dynamic behaviour of structural progressive collapse. The influence of strengthening or reducing methods on the impact resistance of steel frame substructure was discussed. The failure modes and the dynamic responses of the impact load and deformation time histories as well as the dynamic rotation and energy dissipation of the substructures were investigated. Test results showed that the upper flange of all specimens experienced local buckling near the plastic hinge section, while no welding seam cracked. For retrofitted connections, the out-of-plane and distortional deformation of steel beam flange and web at the plastic hinge section were measured. All the three connections with weld access holes recommended by American Federal Emergency Management Agency (FEMA) had good rotation abilities and impact loading resistances, and their ultimate rotations were not less than the FEMA350 design limits. The ductility and energy dissipation of two retrofitted beam-column connections were improved, which were better than those of un-retrofitted connections. The finite element analysis (FEA) models of steel beam-column connections were also established using ABAQUS software. The internal force development of connections during the impact loading was examined and the results showed that the strengthening or reducing methods had a profound influence on the formation of catenary action of beam-column connections under the dynamic progressive collapse scenario.

Experimental and numerical study on impact behavior of beam-column substructures of steel frame

In this paper, three welded flange-bolted web (WFBW) beam-column connections with three types of weld access holes (fan-shaped, enlarged and FEMA weld access holes) were experimentally examined under impact loading. The design of such connections was based on the North American seismic code FEMA350 and the Chinese design codes. The impact tests on of the connections were conducted to experimentally study the dynamic collapse of a steel frame under a column removal scenario. The dynamic responses including failure modes and time history process of the substructures were obtained and presented. Test results show that the weld access hole has a significant effect on impact behavior of the connections under impact loading. Different failure modes of the specimens were observed and discussed. The specimen with FEMA weld access hole is found to have a great advantage of improved structural ductility, impact resilience as well as energy dissipation and no obvious reduction of the plastic rotation capacity over the other two specimens. The specimens with enlarged and FEMA weld access holes show better rotation capacity to resist impact loads, while its ultimate rotation reach the seismic design limit in FEMA350 standard for WFBW connection. The steel frame with WFBW connection is difficult to give full allowance to catenary action due to the premature failure of connection. Furthermore, the finite element analyses give reasonable accuracy when compared with the test results. The simulation results can be used in the future to predict failure modes and ductile fracture of steel frame connections with different types of weld access holes.

EXPERIMENTAL RESEARCH AND FEM ANALYSIS ON BEHAVIOR OF BEAM-COLUMN CONNECTIONS MADE OF STAINLESS-STEEL

In order to study further the resistance and rotation capacity of beam-column connections made of stain-steel S31608, this paper presents the experimental results of connection details under monotonic loading. stainless-steel bolts A4-80 and bearing connection instead of friction type connection are adopted for beam-column connections to improve connection form. An efficient and accuracy FEM model is proposed for numerical simulation under monotonic loading based on the material stress-strain relationship of stain-steel structure and bole A4-80. The connection strength and stress concentration at the end of the weld access hole and the root and the longitudinal direction of the wing plate of a connection are analyzed and compared between the connections. The comparison between FEA results and experimental data shows that the maximum bearing capacity is 251.6 kN and 246.3 kN, and that the maximum displacement is 197.9mm and 196.1mm respectively. Thusly, the nonlinear FEA method is satisfactory in simulating the behavior of bolt connections under monotonic loading and utilizable for later parameter analysis appropriately.

Cyclic Seismic Performance of Weak-Axis RBS Welded Steel Moment Connections

In this study, cyclic seismic performance of weak-axis reduced beam section (RBS) welded steel moment connections was experimentally investigated. Experimental results of this study again showed that the weak-axis RBS moment connection designed based on the procedure proposed by Gilton and Uang (J Struct Eng 122:1292–1299, 2002) performs well and developed an excellent seismic performance much better than 4% story drift with 80% of beam plastic capacity. However, it was also shown that the sharp corner of C-shaped fillet weld, used for attaching the beam web to the shear plate, can be the origin of crack propagation owing to stress concentration there. Slight trimming of the sharp corner is recommended to reduce notch effect. One specimen in this study eventually failed due to low cycle fatigue fracture as a result of cyclic flange local buckling that occurred at the butt joint between the beam flange and the horizontal continuity plate. The size of the weld access hole beneath the butt joint should be minimized if possible to suppress the occurrence of flange local buckling around the butt joint. The factors affecting the size of C-shaped fillet weld and the beam shear eccentricity for the weld design were also examined through a case study and simple analytical modeling. The sectional factor governing the beam shear eccentricity was shown to be the plastic section modulus ratio of beam section at RBS center to the beam flanges at welded joint. The elastic method neglecting the ductile behavior of the C-shaped fillet weld group was shown to be too conservative and should not be used in design in order to minimize welding heat affection to the thin beam web as well.

Seismic behavior of composite beam connected to HSS column with large width-to-thickness ratio

This paper discusses out-of-plane deformations in a HSS (Hollow Structural Section) column connected to a composite beam. Width-to-thickness ratio of HSS column is an important parameter in the flexural deformation capacity of the connection. Beam web connection moment transfer efficiency in HSS column connection is poor and significantly less effective when compared to a connection with W-shape columns. This condition is more severe in the case of composite beam connected to thin walled HSS columns having large width-to-thickness ratio. In this research, the force flow pattern and ultimate flexural capacity of web connection are evaluated by considering main parameters affecting the out-of-plane deformations namely: width-to-thickness ratio of HSS column, height-to-thickness ratio of beam web, yield strength ratios of beam and column, height-to-width ratio of connection, slab strength, stud layout and geometry of weld access hole. Results from the analysis are utilized to illustrate the location of neutral axis and structural condition of web connection in different width-to-thickness ratios and different concrete slab strengths. Also, equations for evaluation of ultimate flexural capacity of web connection are derived; interaction curves of Moment-Axial force acting at the web are drawn. It was found that in the HSS column with large width-to-thickness ratio of 29, axial force subjected to the web connection results in significant reduction of web flexural capacity. Experimental tests showed that plastic rotation capacity of composite beam decreased to almost half of the capacity of bare steel beam. In order to improve seismic behavior, a gap was provided between concrete slab and column face. However, experimental tests revealed that the application of a gap between concrete slab and column face solely did not improve the rotation capacity. The Finite element study showed that despite the existence of a gap, headed studs contribute to the composite action and modification of stud layout is needed. Investigation about the contribution of studs located on the loaded beam and transverse beam has been conducted. Recommendations for seismic application of composite beam connected to HSS column with large width-to-thickness ratio have been presented.

Low-cycle fatigue performance assessment of current Japanese steel beam-to-column connections determined by ductile fracture

A methodology for low-cycle fatigue (LCF) performance assessment of beam-to-column connections commonly used in current Japanese steel moment-resisting frames, such as welded flange-bolted web connections and welded connections with rectangular hollow section columns, is presented in this paper. The proposed assessment methodology is based on an empirical relationship between the number of cycles to failure and beam rotation amplitude obtained from a database of cyclic loading test results. In the empirical relationship, the effects of decreasing the moment transfer efficiency at the beam web-to-column connection due to the slip behavior of the bolts, the out-of-plane deformation of the column flange and the loss of web section due to the weld access hole are considered. The proposed approach can be applied to evaluate the comprehensive fatigue performance of current Japanese beam-to-column connections, considering the moment transfer efficiency of the beam web-to-column connection details and the steel grade.

Finite Element Analysis of Weak-Axis Composite Connections Under Cyclic Loading

This paper describes a numerical study on weak-axis composite connection through the nonlinear finite element program ABAQUS. After the simulation and validation of experimental results, a total of 16 models were created to investigate the influence of the different parameters on the structural performance, and their hysteresis responses, rupture index distribution of beam flange welds were discussed in detail. The RBS connection scheme could develop extensive inelastic deformation in RBS region, thus reducing the weld rupture possibility. The thicker the concrete slab, the larger the bending moment under positive bending, and the higher the RI values at the beam bottom flange weld and also the neutral axis. The structural behavior was insensitive to the variation of the parameter reinforcement ratio as the reinforcements did not work well, and it is recommended to arrange reinforcements according to the construction requirements. Changing the weld access hole form has a little influence on the bearing capacity and rotation capacity, but the PEEQ and RI distributions are sensitive to this parameter. The design option of long access holes could provide a further means to reduce the fracture possibility of beam flange groove weld to a reasonable level, thus achieving a favorable performance of weak-axis column bending connections in a composite moment-resisting frame.

Development of a damage model for assessing fracture failure of steel beam-to-column connections subjected to extremely low-cycle fatigue

Abstract This paper presents numerical analysis on fracture failure of steel beam-to-column connections subjected to low-cyclic fatigue loading. A numerical approach is developed and implemented in the finite element program using the concept of lumped damage mechanics to estimate the extent of fracture damages until complete rupture failure occurred in beam and column hinges. In this framework, a damage variable is introduced for each end of beam elements, and can be linked to the extension of the fatigue fracture in the real structural components. The damage evolution law is based on the Manson–Coffin law and a new crack-driving variable to emulate the state of ultimate failure. The model also describes crack closure effects due to weld access hole at the edge of beam connected to column surface. The analytical model is validated using component tests of steel beam-column connections with weld access hole subjected to cyclic loadings with constant and variable amplitudes. Limitations of the model are also discussed for wider applications on the failure simulation of steel frame systems subjected to seismic loading.

Permissible Parameter Ranges of Access Hole Geometries for WUF-W Connections

The welded unreinforced flange-welded web (WUF-W) connection is one of seven prequalified connections for special moment frames (SMF) specified in AISC 358-10 (2010). Previous studies reported that the cyclic behavior of WUF-W connections was strongly affected by weld access hole geometry, and some WUF-W connections did not satisfy the requirements for SMF connections. For investigating in detail the effect of access hole configurations on the cyclic behavior of WUF-W connections, this study conducts three-dimensional nonlinear finite element analyses. This study shows that the seismic behavior of WUF-W connections are strongly affected by two configuration parameters, access hole slope and length of flat portion. To satisfy the requirement for SMF connections, this study proposes a range of the access hole slope and length of flat portion for WUF-W connections considering different span-to-depth ratios, beam depths, and material types.

액세스 홀 형상변수가 WUF-W 접합부 반복거동에 미치는 영향

The welded unreinforced flange-welded web (WUF-W) connection is one of seven prequalified connections for special moment frames (SMF) specified in AISC 358-10 (2010). Previous studies reported that the cyclic behavior of WUF-W connections was strongly affected by weld access hole geometry, and some WUF-W connections did not satisfy the requirements for SMF connections. For investigating in detail the effect of access hole configurations on the cyclic behavior of WUF-W connections, this study conducts three dimensional nonlinear finite element analyses. This study shows that the seismic behavior of WUF-W connections are strongly affected by two configuration parameters, access hole slope and length of flat portion. To satisfy the requirement for SMF connections, this study proposes a range of the access hole slope and length of flat portion for WUF-W connections considering different span-to-depth ratios, beam depths, and material types.

Experimental investigation of beam-to-column connection with SHN490 steel under cyclic loading

Seismic performance of beam-to-column connections used in the middle-low rise buildings was investigated through the cyclic loading test. Four joint specimens were prepared in accordance with the variables of material and connection type. In two cases of welded connection, the brittle fracture in weld did not occur but cracked at heat-affected zone (HAZ) and/or near weld access hole. In the connections with extended end-plate, punching failure followed by end-plate failure occurred at the flange of column around bolt head. The moment capacities based on failure modes were calculated and compared with the test results. The connections were classified as rigid, semi-rigid, flexible in terms of bending stiffness and strength.