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Web openings facilitate the passage of pipes and enable plastic hinge transfer. However, because these openings reduce the ultimate load at certain values, reinforced flange plates are introduced into the beam–column connections with web openings. In this study, five experimental specimens were constructed and tested, including one base specimen with only web openings, one base specimen with only flange plates, and three specimens with both flange plates and web openings. The failure modes, load–displacement responses, deflection shapes, and deformation capacity were mainly considered. Subsequently, after experimental verification, the thickness and length of the flange plates, as well as the position and diameter of the web openings were studied by numerical simulation. The results indicate that the catenary contribution coefficients and internal energies of the specimens with reinforced flange plates were higher than those of the base specimens. We also concluded that the optimal thickness of the flange plate is equal to that of the beam flange, and the optimal diameter is the maximum web opening that meets the specification requirements. In addition, the mechanical properties gradually increased with an increase the distance a from the web opening to the beam end for a ≤ 190 mm and then decreased for a > 190 mm. • Beam–column connections with flange plates and web openings (FW) are prepared. • The catenary internal energies of FW specimens exceed those of base specimens. • The dimensions of flange plates affect the mechanical properties of FW specimens. • The deformation capacity of FW specimens increases with the web opening diameter. [ABSTRACT FROM AUTHOR]

When a steel frame is subjected to an abnormal load, a sudden local failure due to the loss of a load carrying member may result in progressive collapse of the entire structure. In this study, experiments and numerical simulations were performed to investigate the anti-collapse performance of double half-span assemblies (a column connected with two half-span beams) with welded unreinforced flange–bolted web (WUF-B) connections in a column removal scenario. Three types of bolted webs—two bolts in one row, three bolts in one row, and four bolts in two rows—were considered. For the post-peak response, the connections exhibited a significant resistance recovery owing to the catenary action. The bolt-bearing areas on the beam web were prone to fracture owing to excessive compression, and the failure modes of the web varied significantly with the bolt arrangement. The test results demonstrate that increasing the number of bolt rows is a fairly effective approach for enhancing the anti-collapse performance of the WUF-B connections. Numerical models were used to further investigate the effects of the bolt arrangement on the anti-collapse performance of the WUF-B connections. The results indicate that the bolt arrangement can directly affect the response of the connections after the first peak load, especially in the catenary phase. [ABSTRACT FROM AUTHOR]

• Investigated the cyclic behavior of CSPSWs with two- and four-sided constraints. • Specimens were analyzed using a finite element model validated by experiments. • Seismic performance of CSPSW-2 and CSPSW-3 with two-sided constraints was similar. • Effect of initial damage on the seismic performance of CSPSWs was analyzed. Corrugated steel plate shear walls (CSPSWs) support vertical or horizontal corrugated plates attached to boundary frames through two- or four-sided connections. While two-sided constraints offer better applicability and convenience, this study aims to investigate the seismic behavior of CSPSWs with both two- and four-sided constraints. The investigation considers the coupling effects of direction, aspect ratio, thickness, and axial compression ratio. The study analyzes hysteresis curves, capacity characteristics, stiffness, ductility, and energy consumption for various failure modes. The results indicate that two-sided-constrained specimens exhibit lower mechanical properties compared to four-sided-constrained specimens, especially the initial stiffness. However, both constraint types show X-shaped tension fields diagonally along the CSP under low-cycle reciprocating loading. The horizontal and vertical directions of the corrugated plates have no significant impact on the seismic performance of the four-sided-constrained system, whereas they directly affect the stiffness and lateral load of the two-sided-constrained system. Additionally, an increase in plate thickness results in greater design requirements, particularly for surrounding frame members. Furthermore, when the axial compression ratio does not exceed 0.4, the specimen exhibits good seismic performance and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

• Withstanding local damage and collapse is critical for steel-frame structures. • Tests on a novel connection with flange openings are reported. • Specimens include flange openings with various diameter, number, and distance. • Special fracture and failure modes occurred in the connection types. • Specimens with V-shaped reinforcing plates are studied to resist external load. Improving the ductility of the structure to withstand local damage and prevent progressive collapse is critical for steel-frame structures. In this study, a novel principle of beam-to-column connections was developed, which arranged openings at the beam flange to form a flange-opening section (FO). First, experimental investigations were conducted on two FO substructures, considering their deformation capacity, failure modes, internal force evolution, and resistance mechanism development. Second, numerical simulations verified by experiments were conducted to further investigate the number n , distance l , and diameter d of the flange openings, and the results were compared with those of the case that had no weakening of mechanical properties. Third, because some flange openings weakened the mechanical properties of the structure, specimens with V-shaped reinforcing plates (FOV) were studied. The results indicated that the mechanical properties of the FO specimens increased with n , decreased with an increase in d , and increased with l. The mechanical behavior of the new beam-to-column connections using flange openings and reinforcing plates was studied to relocate the plastic hinge, realize a second path, and successfully improve the progressive collapse resistance of the steel frame structure. [ABSTRACT FROM AUTHOR]

Although the reduced beam section (RBS) connection is an excellent seismic design for transferring plastic hinge, it is prone to fracture under the condition of large deformation. In addition to good seismic response, the performance of RBS connections needs to be improved to ensure good anti-progressive collapse response. In this study, a novel principle is proposed, in which the RBS connection is used to meet the plastic hinge transmission, and kinked reinforced bars are installed in the beam–column connection to realize a second path. Experimental and numerical investigations were conducted on a frame substructure with kinked reinforced bars, considering their diameter d , kinked height a and length l of the reinforced bars. The deformation capacity, vertical force vs. deformation response, failure mode, and contributions of the flexural and catenary actions on the reinforced bars were evaluated. The test results demonstrate that the kinked reinforced bars started to work when the reduced-beam-section connection with reinforced bars (RRBS) is in a plastic state. When the reinforced bars with a > 1.5 d were installed at the beam end, the bearing capacity of the RRBS specimens increased with an increase in the diameter d and decreased with an increase in the length l of the reinforced bars. In addition, When the cracking first occurred at the reduced section, the bearing capacity decreased with an increase in the kinked height a. It is suggested to select the kinked height of the reinforced bar according to the deformation capacity of the beam. • Tests on a novel principle with kinked reinforced bars are reported. • Specimens include bars with various diameters, kinked heights, and lengths. • Various fracture and failure modes occurred in the connection types. • The effect of the reinforced bars on catenary is proved to be considerable. • The kinked height should match the deformation capacity during beam cracking. [ABSTRACT FROM AUTHOR]

• Tests on a novel principle with kinked reinforced bars are reported. • Specimens include bars with various diameters, kinked heights, and lengths. • Various fracture and failure modes occurred in the connection types. • The kinked height should match the deformation capacity during beam cracking. • The plastic zone range and installation space should be considered for the length. Various disasters may trigger a progressive collapse of frame structures, resulting in a high demand for new preventive structural strategies. Among the strategies adopted, increasing the joint rotation capacity to improve catenary action and forming a second path in the joint area are the most effective. In this study, a novel principle is proposed, in which the web opening is used to meet the rotation capacity, and kinked reinforced bars are installed in the beam–column joint to realize a second path. Experimental and numerical investigations were conducted on a frame substructure with kinked reinforced bars, considering their diameters, kinked heights, and lengths. The deformation capacity, vertical force vs. deformation response, failure mode, and contributions of the flexural and catenary actions on the reinforced bars were evaluated. The test results demonstrate that the kinked reinforced bars in the reduced-web-section connection (RRWS) specimens started to work after the plastic state. Although they had little influence on the flexural action, they were very important to the catenary action. When the kinked height a was less than 2 d , the bearing capacity and ductility of the specimen increased with a , but further increasing the kinked height a beyond 2 d would reduce both the bearing capacity and the ductility. In addition, the failure modes of the specimens were related to whether the plastic hinge was formed first or the reinforced bar had a major role first. Therefore, it is suggested to select the kinked height of the reinforced bar according to the deformation capacity of the beam, and the diameter of the bar as half of the kinked height. [ABSTRACT FROM AUTHOR]

• The paper reports tests on specimens with castellated steel beams. • Specimens include various opening diameter, spacing, and opening position. • Various modes of fracture and failure took place in the connection types. • Larger spacing of openings has minor influences on mechanical properties. • The recommended position of the first opening is equal to the beam height. In addition to strengthening or weakening the connections, castellated steel beams can realize plastic hinge rotation, which is a common strategy for improving the resistance of steel structures against progressive collapse. This paper presents experimental and numerical investigations of a substructure with castellated steel beams under a column removal scenario considering the diameter D of the openings, first opening position A , and spacing B between openings. The deformation capacity, vertical force–deformation response, failure mode, and contributions of the flexural and catenary action were studied as having different parameters for the openings. The test results demonstrate that the first web opening underwent the greatest deformation, changing from a circular to shuttle shape at the cracking moment, whereas the second and subsequent openings exhibited only small deformations in all specimens. The vertical force vs. deformation response can be divided into four states: elastic, plastic, catenary transition, and catenary states. The final resistance against progressive collapse was dependent on the catenary action caused by excessive axial tension. Moreover, the bearing capacity and deformations in the specimens having a small diameter of openings, D < 0.6 h , decreased with an increase in the opening diameter, whereas the respective properties in the specimens having a large diameter of openings, D > 0.6 h , increased with an increase in D. The recommended distance from the edge of the first opening to the surface of the column is equal to the depth h of the beam section. A large value of spacing B between the openings has a minor influence on the bearing resistance in the collapse analysis. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to evaluate the axial compressive behaviour of circular hollow section (CHS) stub columns with initial crack defects. A total of 96 specimens – 12 stub columns with one crack, 48 stub columns with two cracks, and 36 stub columns with three cracks – were tested under axial compression loading. The failure modes, load-carrying capacities, overall deflections, and strain intensities of all the specimens were examined. The design parameters were the tube thickness, long crack length, short crack length, crack spacing, and crack number. Additionally, a finite-element analysis was performed using the verified models in combination with the experimental data to evaluate the effects of the main influential factors. The initial cracks formed in the circular thin-walled stub columns accelerated the local buckling and changed both the bearing capacity and deformation capacity. The ultimate loads of the stub columns increased with the tube thickness, decreased slightly with an increase in the long crack length, and decreased with an increase in the crack spacing. The effects of the short crack length and crack number on the bearing capacity were complex and were coupled with the tube thickness. An adjustment coefficient was introduced into the predictive formula to estimate the ultimate bearing capacity. Through this, the ultimate bearing capacity can be accurately predicted. • Tests conducted on circular hollow section (CHS) tubes with initial crack defects. • Specimens include various tube thickness, fracture length, fracture spacing. • Various buckling and failure modes occur for the tubes with initial cracks. • Initial cracks accelerate the local buckling and change the bearing capacity. • Introduce adjustment factor into predictive formula to predict ultimate loading. [ABSTRACT FROM AUTHOR]

• The behaviours of the RWS connections in progressive collapse are investigated. • The RWS connections trend to fracture in two area with extreme stress focus. • Two flexural failure were observed in the RWS connections depending on web opening parameters. •.The RWS connections developed catenary action with an interrupted failure • The RWS connections performed higher deformability than the welded web connections. The spread of an initial local failure from load-carrying member to other members in system when subjected to abnormal load, eventually resulting the progressive collapse of an entire structure. This paper presents an experimental and parametric study on the anti-collapse performance of moment resisting frames (MRFs) with reduced-web-section (RWS) connections under critical column removal scenario. Factors influencing robustness and rotational capacity in these connections under Vierendeel failure are analyzed. A total of 14 laboratory tests on steel beam-column connections with complete joint penetrations are presented; one test was conducted with solid beam connections, while the others were designed to have RWS connections with different circular web openings geometric parameters. Comprehensive finite models are then implemented to further interpret the obtained test results. The test results demonstrated that vertical resistance against the applied load atop the failed columns was totally composed of flexural action (FA) in the early stages, and it became catenary action (CA) as the vertical displacement of the failed column increased. There are two typical failure modes, continuous failure in the beam-column joint region generated by the weld line fracture and interrupted failure in RWS connections generated by the fracturing of a perforated section, and the different failure modes determine whether the system can develop meaningful catenary action when the initial fracture occurs. Specimens with openings exhibited multiple peak loads because of the repeated occurrence of local damage in the beam-column connection. RWS connections with local failure near the openings were capable of developing deformability and resistance associated with CA when the dimensions and location parameters of the opening are controlled within a suitable range, and the rotational capacities of these connections were larger than the connection with solid beams. [ABSTRACT FROM AUTHOR]

• Tests are conducted on beam-to-column connections with or without reduced beam section (RBS), including bolted and welded web connection methods. • RBS connections exhibit numerous advantages in progressive collapse performance. • RBS connection via tensile deformation of RBS to dissipate inelastic energy, and its rotational capacity is much greater than that provided by reference guidelines. • Welded web connections exhibit better progressive collapse performance than bolted web connections in designing RBS connections. • Weakened parameters of RBS influence the mechanical properties. In this study, nine laboratory tests were conducted to estimate the performance of earthquake-resistant structures, i.e., reduced beam section (RBS) connection, under a scenario in which the middle column is removed. Four types of joints were tested, namely, welded unreinforced flange – bolted web connection without RBS (WUF-B-NRBS), welded unreinforced flange – bolted web connection with RBS (WUF-B-RBS), welded unreinforced flange – welded web connection without RBS (WUF-W-NRBS), and welded unreinforced flange – welded web connection with RBS (WUF-B-RBS), to investigate the effect of RBS and different beam web connection methods. The experimental results involving the responses of general behavior, resistance mechanisms, failure modes, deformation shapes, and limit displacements are presented in detail. A performance comparison of different connection types indicated that the RBS connection exhibits the optimum performance against progressive collapse, and its practical rotational capacity is >1.9 and 2.7 times larger than that provided by Federal Emergency Management Agency (FEMA) 350 and Department of Defense (DOD) guidelines, respectively. Additionally, in the design of the RBS connection, the welded web connection joint exhibited good load-carrying capacity, whereas the bolted web connection joint performed poorly owing to early fracture near the bolt holes. Furthermore, the research parameters were extrapolated within and beyond the limits using ABAQUS. This demonstrated that by increasing the values of horizontal distance from the column flange to the beginning of the beam flange reduction, a , or the length of the beam flange reduction, b , is beneficial to structural load-carrying capacity and ductility. However increasing the value of depth of the beam flange reduction, c , has the opposite effect. Based on the comparison, the recommended design details of RBS connections are presented. [ABSTRACT FROM AUTHOR]

Steel frame structures with ordinary weld connections often suffer from brittle fractures; to mitigate this issue, measures have been taken to integrate plastic hinges and improve the ductility of the steel connections. A new reduced beam section (RBS) connection, consisting of radius cuts in the beam flanges and circular openings in the beam webs, is proposed to allow for more ductile connections. RBS connections may increase structural deflection and crack width in the steel frame structure under large deformations. Therefore, it is extremely important to consider the bearing capacity and progressive collapse resistance of steel frame structures with RBS connections. In this study, nine different specimens with double-span frames were constructed and tested under a central column removal scenario: one without an RBS (RBS0), one with flange reductions (RBS1), and seven with web and flange reductions (RBS2). The mechanical behaviours of the different specimens were determined, including their failure modes, vertical force-deformation responses, and contribution of catenary action to resist progressive collapse. The results indicated that the RBS0 specimen with brittle failure did not effectively resist progressive collapse. RBS1 exhibited superior ductility and resistance compared to RBS0; however, its resistance to progressive collapse after cracking required further improvement. RBS2 with web openings formed an arch structure to dissipate energy through continuous deformations. Further, two important factors in RBS2 that influenced its mechanical properties were the diameter and the distance of the web opening, which were related to the development of arching and catenary action. Unlabelled Image • Tests are conducted on specimen groups with or without reduced beam sections. • Specimens with flange reductions, and with web and flange reductions are included. • Various fracture and failure modes occur for the connection types. • The web opening diameter and distance influence the mechanical properties. • The web openings form an arch structure to dissipate energy through deformation. [ABSTRACT FROM AUTHOR]

A new type of joint with Z-type cantilever beam splices was proposed for assembled steel frame structures in this study. The basic specimen was designed based on the theory of bolt sliding energy dissipation, and three groups of specimens were obtained by changing key parameters. That is, there is no section weakening (Z -BASE), flange weakening of cantilever beam near column (Z -RBS), flange weakening of steel beam near splicing (Z-SRBS), and flange and web weakening of steel beam near splicing (Z-RBS-RWS). The effects of reducing beam section and beam web on the anti-progressive collapse performance of assembled steel frame joints with Z-type cantilever beam splices were studied. The test results were described in detail in general behavior, failure modes, deflection shapes, limit displacements, and resistance mechanisms. According to the test results, specimen Z -RBS had the best anti-progressive collapse performance, and its ultimate load and initial failure displacement were 116% and 114% higher than specimen Z -BASE, respectively. In addition, specimens Z -SRBS and Z-RBS-RWS also had better anti-progressive collapse performance than specimen Z-BASE. Moreover, the validity of the results was verified and study parameters were analyzed using ABAQUS. The assembled steel frame joints with Z-type cantilever beam splices had better anti-progressive collapse performance than ordinary cantilever beam assembled steel frame joints. And the bearing capacity and ductility of the structure were improved by increasing the distance from the cantilever beam splices to the failed middle column, a, and reducing the aperture of the bolt on the cantilever beam splices, b. However, reducing the number of bolts on the cantilever beam splices, c, exhibited the opposite influence. Based on the above comparisons, the proposed design details of assembled steel frame joints with Z-type cantilever beam splices are given. • Anti-progressive collapse performance of a new type of beam-column joint was assessed. • Specimen Z-RBS had the best anti-progressive collapse performance. • Simulated results obtained by explicit dynamic approach correlated well with the test results. • The influence laws of different parameters were compared and summarized. [ABSTRACT FROM AUTHOR]

In this study, beam–column connections with various web openings were prepared to improve the mechanical characteristics of welded steel frames. First, several specimens were constructed and tested after adding various web openings, including circular, square, hexagonal, semicircular, and elliptical web openings. We mainly focused on analysing failure modes, deflection shapes, load–displacement responses, and deformation capacities. The height, width, and position of the web openings were further studied through numerical simulations following experimental verification, and the results were compared for specimens with and without various forms of web openings. The catenary internal energies and contribution coefficients of the specimens with web openings were found to be greater than those of the base specimens; the values of the hexagonal and semicircular web openings were greater than those of commonly used circular openings. The bearing and deformation capacities initially increased and then decreased with increasing opening height. When only the opening distance b was changed, the load–displacement responses of the specimens overlapped in the elastic state; the bearing and deformation capacities increased with increasing b. We also found that the vertical loads of circular or near-circular web openings were smaller than those of polygonal openings with fewer edges. • Beam–column substructures with web openings are analyzed. • Progressive loading is applied to various test specimens. • Finite element models are developed based on the test results. • Various web opening parameters are analyzed in terms of vertical load. • Circular and nearly-circular openings are determined to be suboptimal. [ABSTRACT FROM AUTHOR]