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Cyclic behaviour of elliptical-shaped reduced web section connection
Abstract
In this paper, an RWS connection with an elliptic opening in the web is proposed, and its performance is investigated through an experimental and numerical study. A full-scale elliptical RWS connection was experimentally tested under cyclic loading, to evaluate the performance of the connection and to use for verifying the validity of numerical models. In order to determine the optimum ranges for geometrical parameters of the elliptical cut, a parametric study was carried out using the verified FE models. Based on the results, the appropriate ranges for the cut parameters were recommended. Then, the cyclic behaviour of the connection with optimum parameters was compared with the conventional RBS and with different types of RWS connections. The results emphasised that the elliptical RWS connections according to the present recommendations provide appropriate cyclic performance in terms of ductility, rupture index, buckling stability, and ability to prevent the formation of plastic hinge near the column face. In addition, the flexural capacity of the proposed connection satisfied the requirements of the codes for special moment-resisting frames.
... The authors, as a part of their studies on RWS connections, proposed and investigated elliptical-shaped RWS connections [31]. Based on the experimental tests and numerical analysis, they presented the optimum ranges for the geometrical parameters of elliptical-opening in the beam web of RWS connections. ...
... According to Refs. [31,42], the parameters "c" and "h" are the geometrical parameters effective in the performance of R-RBS and E-RWS connections, respectively. EC8 Part 3 [42] has provided recommendations for the cutting parameters of R-RBS connections (Table 5). ...
... However, there are no acceptable criteria in regulations for the designing of E-RWS connections. Davarpanah et al. [31] have conducted an extensive numerical study on the reduced region parameters of E-RWS connections and suggested the following ranges to select the variables a, b and h. ...
One of the disadvantages of the reduced beam section (RBS) connection is the possibility of lateral-torsional buckling in the beam. Based on previous researches, reducing the cross-section along the web rather than the flange is one of the effective ways to prevent this phenomenon. The authors, in some part of their study on reduced web section (RWS) connections reported in references, have proposed new details about RWS connections by creating an elliptical opening in the beam web and presented recommendations for optimum ranges of the geometrical parameters. The main aim of this paper is to investigate the cyclic performance of an eight-story three-bay welded moment frame having elliptical-shaped RWS (E-RWS) and to compare it with that of the frames having the conventional full- or reduced-beam sections. For this purpose, at first, two connections with the E-RWS and with the common radial-cut (R-RBS) were experimentally tested under the cyclic loading and their performances were examined. The results showed the priority of the E-RWS over the R-RBS in terms of strength, stiffness, ductility, and lateral-torsional stability. Following that, a step-by-step design process for the E-RWS connection was presented. At last, by using an FEM analysis verified by the experimental data, the cyclic performance of an E-RWS frame was compared with that of the full- and RBS frames. According to the results of this study, the creation of an elliptic opening in the beam web can replace the reduced-beam section connections as a suitable method, which can improve the seismic behaviors of MRFs.
... Consequently, a strong column weak beam mechanism was developed, which considerably enhanced the seismic behavior of the entire connection. Other researchers [37][38][39] continued investigating steel beam-to-column connections under seismic loading numerically and experimentally while changing the opening shape (circular, elliptical based and elongated), opening size, and column face distance and introducing closely spaced web openings. They concluded that introducing a web opening can result in increasing the ductility and dissipating seismic energy of these connections. ...
Steel beams with web opening have become a popular structural element nowadays owing to their several structural and architectural benefits. This study numerically investigates a study of the behavior of steel beams with a web opening subjected to fatigue loading using the finite element software ANSYS. Simply supported I-section steel beams with a single web opening were studied under a fully reversed, uniformly distributed vertical load. Fatigue loading, material properties, and boundary conditions are discussed in detail. Finite element analysis was used to determine the effect of the web opening on the normal stress induced in the steel beam and consequently on fatigue stress life. Then, a parametric study was performed to investigate the effect of two geometric parameters (opening size α and opening location β). In addition, suitable fatigue categories were suggested to guarantee safety against fatigue failures. Further, an analytical method for predicting the synthetic SN curves for steel beams with web opening was introduced. The proposed method was validated using SN curves obtained from FE results and was proven safe and slightly conservative for steel beams with a single web opening of various sizes and locations, as well as spans.
... This method was utilized in cases where strength degradation and fracture do not occur. This method was used by many researchers [21][22][23][24][25][26][27][28][29] to assess the different configurations when no detailed fracture model is available. The numerical models and locations having larger RI indicate a higher potential for failure. ...
In January 2017, collapses of the numerous roofs were reported due to excessive snowfall in many provinces of Turkey. In this study, the reasons behind the collapses of the steel roofs of 19 factory buildings were investigated. The steel roofs supported by the precast reinforced concrete columns indicated a similar collapse pattern to each other under the unexpected heavy snow loading. The failure mechanisms of the roofs under the snow loading were simulated numerically. Nonlinear finite element models of a typical industrial building were developed and analyzed under an incremental vertical loading that is identical to snow loading. As a result of the analysis, the vertical load carrying capacity of the roof system and the snow load level causing the collapse of roof were determined. The resulting snow load was compared with the snow load values provided by the code specifications. In addition, the collapse mechanism of the steel roof system was analytically determined and compared with the collapse modes observed in the field and the causes of the failure were evaluated. The failure mechanism and the buckling modes obtained from analyses were found very similar to those observed during the site inspections. The main reasons of the roof failures may be attributed to excessive amount of snow caused by climate change and discrepancy of designed project and as-built project due to lack of building inspection control during the construction of the buildings.
... In cases where strength degradation does not occur, rupture index (RI) was selected to evaluate and compare the different configurations in the numerical models. This method was used by many researchers [22,[33][34][35][36][37][38] to assess the different configurations when no detailed fracture model is available. The numerical models having larger RI indicate a higher potential for failure. ...
This paper is aimed to investigate the interaction of flange and web slenderness ratio, overstrength factor and also to improve the behavior of long links. Pursuant to these goals, 150 numerical models of different long links were developed and exposed to cyclic loading protocol mandated by AISC 341. Link length ratio, flange and web slenderness and stiffener configurations are selected as parameters. The results revealed that the flange slen-derness ratio can be relaxed to 0.38(E/F y) 0.5 for long links if the web slenderness ratio is <1.5 (E/F y) 0.5. The shear capacity of long links decreases as the link length ratio increases. The results of shear capacity showed the overstrength factor required by AISC 341 overestimates the shear capacity; therefore, two different equations to predict the overstrength factor for long links are proposed. The stiffener configuration recommended by AISC 341 limits the potential of long links. To mitigate this drawback, different stiffener configurations are proposed to empower the behavior of long links. Using additional one stiffener at each link ends can enhance shear strength, energy dissipation and plastic rotation capacities by 25%, 447% and 322%, respectively. When two additional stiffeners are introduced, these ratios modify to 29%, 479% and 332%. Moreover, rupture index values are utilized to verify proposed stiffener configurations further.
... A bilinear stressstrain profile was assumed with young's modulus of 210 GPa, tangent modulus of 2.1 GPa and Poisson's ratio of 0.3. Based on former numerical investigations done by many scholars [27], [28], and according to guide runs, mesh element size of 20 mm was chosen to model the tested beam. This element size wasn't too large to cause major changes in the obtained results and at the same time it wasn't too small to make the solution run last for too much time. ...
In the last decades, steel beams with web opening were used extensively as useful structural and architectural elements due to their many advantages. In this research, steel beams with web opening subjected to static loading were modelled using the multi-purpose finite element software ANSYS and the finite element results were compared with previous research. Then, steel beams with a single web opening subjected to fatigue loading were investigated numerically. The effect of changing the location of web opening on the fatigue assessment of H section steel beams with web opening was studied taking normal stress into account. It was clear that, normal stress fatigue life of the steel beams was affected significantly by changing web opening location along the beam span when compared to a beam with solid web while the beam span, opening size and steel section were kept constant. The most convenient location of web opening along the beam span was found to be at mid span.
... Also, the capability of RWS models to reach higher story drifts (six percent) was evaluated by [82][83] both in experimental and numerical ways. The behavior of RWS connections via numerical or experimental studies in the recent years are assessed by many researchers among which [107] developed a novel RWS connection with vertical slits; [108] investigated the RWS connection with an elliptic opening in the web; [109] evaluated the cyclic performance of an eight-story welded moment frame with elliptical-shaped RWS and compared it to the conventional RBS connections; Yu and Li [110] evaluated the steel frames with RWS connections and WFP connections using the probabilistic seismic demand analysis and seismic capability analysis; Lin et al. [111] investigated the behavior of RWS in progressive collapse under critical column removal scenario, the results demonstrated the capability of the mentioned connections in terms of rotational capacity; Erfani et al. [112] studied the lateral load carrying behavior of steel moment resisting frames with reduced web beam sections and propounded an algorithm to select appropriate opening size; Bi et al. [113] scrutinized the castellated beam-to-column connections with four regular hexagonal web openings under cyclic loading with and without floor slab, the results indicated the importance of the space between web openings, and depth-to-thickness ratio of the web. Moreover, due to the limitations imposed on beam span-to-depth ratio in different codes which result in the impossibility of the use of short beams in some of the prequalified rigid connections, Hoseinzadeh Asl and Jahanian [114] investigated using web opening located at the mid-span of the deep steel beams in rigid connections in order to lead the plastic hinge away from the column face. ...
Connections are considered to be one of the most prominent components of steel moment frames and have received studious attention in recent years. The core problem of welded connections is premature brittle fracture of weld in the critical beam-to-column connection region. Within the framework of this issue, various approaches have been proposed to solve the mentioned problem. Intentional weakening of the beam web or flange is in line with the purpose of leading the plastic hinge away from the column face, hence, increasing the ductility. The aim of this research is to investigate the behavior of interior connections subjected to monotonic lateral loading in case of presence of openings in beam web or flange. To do so, an ordinary fully welded rigid connection, reduced beam section, reduced web section, and drilled flange connection models are simulated numerically, utilizing finite element software, ANSYS. The results indicate that scrupulous selection of opening sizes are of great importance to fulfill the desired outcome which is avoiding the brittle failure of connections. Furthermore, the use of drilled flange, reduced beam section, or reduced web section connections satisfy the expected performance and it is proposed to use them according to practicability, architectural and economic considerations as well as site conditions. Shear deformation and local buckling is observed in reduced web section connections while in drilled flange connections, stress concentration around the opening is critical.
... On the other hand, the presented results are only applicable for American wide flange fully welded RBS elements. However, the proposed methodology can be easily adopted to develop similar databases for other types of connections (such as Drilled Flange [72] and reduced web section [73]) and different cross sections. Based on the results from the developed database, the following conclusions can be draw: ...
The concept of Reduced Beam Section (RBS) connections in steel framed buildings have been widely adopted in previous studies as well as European and American Design codes (EN1998-3, ANSI/AISC 358-16 and FEMA 350) as a means of providing safe ductile fuse behaviour in the beam in order to protect the column from any significant damage. However, modelling the hysteretic behaviour of RBS connections under earthquake excitations can be challenging due to their non-linear complex behaviour. This paper presents a database of detailed and accurate modified-Ibarra–Krawinkler (mIK) models that can reliably capture the cyclic hysteresis behaviour of fully welded RBS connections over a wide range of different RBS geometries. An experimentally validated Finite Element (FE) model was developed using ABAQUS to accurately predict the cyclic hardening and strength degradation of RBS connections. Subsequently, a comprehensive parametric study was conducted on 1480 different American wide flange RBS and full section beams under cyclic loading. The results were then used to assess the influence of key RBS design parameters on the structural performance of the connections. It was shown that the conventional method of predicting mIK parameters cannot accurately capture the actual hysteresis behaviour of some RBS connections and may lead to unreliable predictions. Using the results of the validated FE models, a comprehensive database of 1480 different beams was developed which provides: (1) the beams full cyclic moment–rotation-hysteresis at the plastic hinge location up to 0.07 rad rotation following the SAC loading protocol, (2) appropriate mIK parameters to accurately capture the beam’s cyclic response in OpenSees, for non-linear dynamic analysis. The results of this study should prove useful in seismic design and assessment of RBS connections.
... Although RI can not be used as a criterion for fracture initiation different configurations can be compared to evaluate which one has the highest potential of the fracture (Bozkurt et al. 2019). For this purpose, the rupture index is utilized by many researchers to evaluate the level of damage (Vatansever and Kutsal 2018, Nazaralizadeh et al. 2020, Abar et al. 2020, Davarpanah et al. 2020, Nia and Moradi 2020, Özkılıç 2020a, b, Özkılıç et al. 2021b. Rupture index is defined in Eq. (3). ...
Eccentrically braced frames (EBFs) are utilized as a lateral resisting system in high seismic zones. Links are the primary source of energy dissipation and they are exposed to high deformation, which may lead to buckling. Web stiffeners were introduced to prevent buckling of shear link. AISC 341 provides the required vertical stiffeners for a shear link. In this study, different stiffener configurations were examined. The main objective is to improve the behavior of short links using different stiffener configurations. Pursuant to this goal, a comprehensive numerical study is conducted using ABAQUS. Shear links with different stiffener configurations were subjected to cyclic loading using loading protocol mandated by AISC 341. The results are compared in terms of energy dissipation and shear capacities and rupture index. The proposed stiffener configurations were further verified with different link length ratios, I-shapes and thickness of stiffener. Based on the results, the stiffener configuration with two vertical and two diagonal stiffeners perpendicular to each other is recommended. The proposed stiffener configuration can increase the shear capacity, energy dissipation capacity and the ratio of energy/weight up to 27%, 38% and 30%, respectively. Detailing of the proposed stiffener configuration is presented.
... In addition to local instability, another drawback of the large openings is the early failure of the beam section due to the significant effect of the shear-flexure interaction in the T sections remaining at the top and bottom of the large opening. Therefore, in order to reduce the depth of the web perforation, Davarpanah et al. [10,11] introduced and studied the horizontal elliptical-shaped RWS connections. They suggested ranges for the purpose of choosing the geometric variables of the elliptical-cut and the reduced region to ensure that the formation of the plastic hinge is away from the column edge. ...
Extensive research has been carried out on steel moment frames to improve the cyclic performance of seismic resisting connections with reduced beam section (RBS). The RBS connections are conventionally known by the radial reduction of the beam flange. Where the contribution of the beam flange to the flexural resistance is greater than that of the beam web, some researchers have proposed reduced web section (RWS) connections, instead. The present study dedicates to the RWS connections with vertical-slits (VS), as a cost-effective alternative with multiple design parameters. This paper aims to obtain proper ranges for the geometric design parameters of the VS-RWS connection. In this order, two full-scale specimens of the bolted end-plate VS-RWS connection were experimentally tested under the SAC cyclic loading to evaluate the performance of connections, and then a parametric study was carried out using the verified numerical models. The parameters consist of the distance between the column face and the beginning of the reduced region, the length of the reduced region, as well as the depth and width of the vertical-slits. Based on the results, certain recommendations for the ranges of the geometric parameters of VS-RWS have been suggested. In order to obtain the story drift of the frame caused by the VS-RWS beam flexural deformation using the conjugate beam method, the original VS-RWS was replaced with an equivalent constant-cut reduced beam section (CC-RBS). At last, a simple design procedure for VS-RWS connections was provided according to AISC-358.
This paper presents the details and analysis of a fire test conducted on a reduced web section (RWS) connection for steel framed construction. The test was completed in the fire laboratory at Tampere University in order to assess how these connections, usually selected and designed for their seismic performance, behave under fire conditions. RWS connections were first devised for fixed joints in steel framed buildings, with a view to moving the plastic hinge away from the column face during an extreme event such as an earthquake, thus improving the ductility of the structure. Until now, there was very little known of their behaviour under fire conditions. Accordingly, the current paper provides a detailed description and analysis of the fire test on a RWS connection, during which the arrangement lasted for around 16 minutes of standard fire exposure. It also describes the development of a numerical model, which is validated against the test data. The purpose of the model is to enable a more thorough examination of the various parameters and variables that may exist in a real structure, subjected to a real fire.
Tearing failures often occur at the bolt position of the recombinant bamboo beam under a large bending moment and shear force due to its poor compressive strength perpendicular to the grain. In this study, three H-shaped weakened connections were designed to explore the mechanical performance of the recombinant bamboo frames under low cyclic loading. The weakened forms of the web were selected as variables, including elliptical, rhombic, and arc holes. Load-displacement hysteresis curves, skeleton curves, stiffness degradation, ductility analysis, equivalent viscosity damping coefficient, and failure modes of the recombinant bamboo frame with three weakened connections were compared and analyzed. The results show that the weakened connections achieved the purpose of the outward movement of the plastic hinge. The moment and shear force will lead to the stress concentration of connection with the rhombic hole, and buckling failure of connection with the arc hole is easy to occur. Comparatively, the ultimate bearing capacity and energy-dissipating capacity of connection with the elliptical hole are the best among the three weakened connections. In conclusion, the weakened shape and position have a great influence on seismic performance.
Reduced web section (RWS) connections can prevent lateral-torsional buckling and web local buckling experienced by reduced beam section (RBS) connections. In RWS connections, removing a large portion of web can result in shear demand intolerance induced to plastic hinge region. The present study aims to resolve the problems of RBS and RWS connections by proposing two new connections: (1) RBS with stiffener (RBS-ST) and (2) RBS with reduced web (RW-RBS) connections. In the first connection (RBS-ST), a series of stiffeners is connected to the beam in the reduced flange region, while the second connection (RW-RBS) considers both a reduction in flanges and a reduction in web. Five beam-to-column joints with three different connections, including RBS, RBS-ST, and RW-RBS connections were considered and simulated in ABAQUS. According to the results, RBS-ST and RW-RBS connections can decrease or even eliminate lateral-torsional buckling and web local buckling in RBS connection. It is important to note that RW-RBS connection is more effective in long beams with smaller shear demands in the plastic hinge region. Moreover, results showed that RBS and RW-RBS connections experienced strength degradation at 4% to 5% drift, while no strength degradation was observed in RBS-ST connection until 8% drift.
A link element incorporating a nonlinear axial-shear-flexural (PVM) yield function is established for idealized beams with reduced web section (RWS), focusing on the static response when a column loss is triggered. The proposed model is considered in terms of the lowest level of model reduction, that is, axially restrained beams subjected to mid-span point loading (MPL) with boundary springs. A monotonic loading test was conducted on the perforated beams to calibrate the proposed model. The main features of the new approach include the consideration of the multi-surfaces concept and an anisotropic hardening rule is employed in the plastic hinge. The proposed model can predict the load–displacement relationship before the failure limit. The internal force evolution of the inner hinge is analyzed to determine the change in the load transfer mechanism of the RWS connection with rectangular openings. The numerical results show that the traditional equivalent rectangular opening method should be improved to reflect the large deformation response of the circular web opening beams. The proposed model can offer a practical tool for the progressive collapse design of steel frames with web opening beams under column removal scenarios.
The development of plastic hinges in a steel frame structure with steel beam-to-column end-plate connection joints by strengthening the end-plate area is a widely used design concept. This study explores the realization of this design concept with a beam web opening and without end-plate stiffening. The factors that impact the mechanical properties and failure modes of these joints are the end-plate thickness, opening diameter, opening position, and opening type. These parameters are tested for monotonic loading of six beam-column joints, and 220 finite element models are parametrically analysed. Additionally, the development of plastic hinge of the beam based on the development trend of maximum strain of each component section is studied. The initial rotational stiffness, ductility, bearing capacity, deformation capacity, and failure mode are used as the evaluation criteria to assess the behaviour of this joint. The research indicates that a castellated steel beam-to-column end-plate connection can realize the occurrence of plastic hinge and exhibit good ductility and load-bearing performance. This study highlights the premise that the beam web opening and end-plate thickness parameters must be within a specific range to achieve accurate results; additionally, the division method of the interval of parameters is described. The influence of end-plate thickness on the working mechanism of the connection is clarified, and the mechanical properties and failure modes of connections under different parameter intervals are studied. This study proposes a method for calculating the initial rotational stiffness of the connection to achieve good accuracy by considering the participation of the components on the beam in the rotation of the connection.
Extensive research has been carried out on steel moment frames to improve the cyclic performance of seismic resisting connections with Reduced Beam Section (RBS). The lateral-torsional buckling and reducing of the flexural resistance of the beam are the disadvantages of conventional RBS connections with radial cutting in the flange. Therefore, some researchers have suggested the reducing of the web in lieu of the flange as an effective strategy to prevent these phenomena. The present study aims to investigate the cyclic behavior of the reduced web section (RWS) connections with vertical-slits (VS) as a cost-effective alternative with multiple design parameters through an experimental and numerical study. Two full-scale specimens of the bolted end-plate VS-RWS connection were experimentally tested under the SAC cyclic loading to evaluate the performance of connections, and then in order to obtain proper ranges for the geometric design parameters, a parametric study was carried out using the verified numerical models. The parameters consist of the distance between the column face and the beginning of the reduced region, the length of the reduced region, as well as the depth and width of the vertical-slits. Based on the results, the appropriate ranges for the geometric parameters of VS-RWS have been recommended. In order to obtain the story drift of the frame caused by the VS-RWS beam flexural deformation using the conjugate beam method, the original VS-RWS was replaced with an equivalent constant-cut reduced beam section (CC-RBS). At last, a step-by-step design procedure for VS-RWS connections was provided according to AISC-358.
The reduced beam section (RBS) connections are widely used in construction buildings due to their desirable ductility and strength. The current reduced web section (RWS) connections are produced by a reduction in the beam web as circular or rectangular cuts or as horizontal slits. This article has proposed a new detail for the RWS bolted connection by creating vertical-slits in the beam web. The aim of this investigation is the evaluation of its cyclic performance in comparison with the conventional RBS connection. Two specimens, one with vertical-slits in the web (VS-RWS) and the other one with a radial-cut in the flange (RC-RBS), were experimentally tested and the results were compared. Moreover, numerical models were employed to evaluate the behavior of connections in detail. These two connections were able to move the plastic hinge region away from the column face, exhibit good hysteresis behavior, and satisfy the AISC requirements for special moment-resisting frames. The results also showed that the flexural capacity of the proposed VS-RWS connection is 10% higher than that of the conventional RC-RBS one, while their ductility and energy dissipation were almost the same. An important advantage of VS-RWS over RC-RBS is its ability to prevent the lateral-torsional instability. Besides, a numerical study was conducted to investigate the performances of various cut shapes RWS connections with certain overall dimensions and location of the cutting region in terms of hysteresis curves, rupture index and end-plate deformations.
The effect of different panel zone design ratios (Rv/Vpz) on reduced-beam-section connections
as part of steel moment resisting frames under cyclic and monotonic loading is investigated.
As design specifications suggest an overestimated value for the (Rv/Vpz) ratio in some
cases. To achieve this objective, the balanced design proposed in the specifications is compared
to other design concepts in the guidelines. Then a finite element (FE) analysis is conducted representing
the beam-to-column connection assemblies under cyclic and monotonic loading to investigate
the effect of different panel zone strength ratios. The FE simulation is validated and compared
to test results from the literature, then a parametric study is carried out. The parameters included in
the study are; the column flange thickness, the panel zone aspect ratio, and the strong column weak
beam ratio. Each connection configuration is investigated according to; the amount of energy dissipation
achieved, the participation in energy dissipation between the beams and the panel zone, the
stable hysteretic behavior and its fracture potential. Results from the analytical study show that for
assemblies with thick column flanges the design specifications overestimate the panel zone strength.
Therefore, a range for the validity of the panel zone design strength formula is suggested.
Cold-formed steel members have been used extensively in buildings, bridges, railways, high way products and other purposes. Since experimental tests for cold-formed steel members are time consuming and expensive, numerical and theoretical models have emerged as suitable alternatives for solving such problems, and have increasingly been the focus of attention of researchers in recent years. This study involves different aspects of the use of OPENSEES and ABAQUS for macro and micro modelling of cold-formed steel walls. In the first step, a finite element framework using ABAQUS is proposed to show the micro modelling of cold-formed steel walls. In the second step, the simplified framework using OPENSEES is presented to show the macro modelling of cold-formed steel walls. Then in the third step of the study, the two proposed methods are verified against the experimental data and finally, the results are compared and discussed. This study is planned to identify the advantages and disadvantages of the macro and micro modelling of cold-formed steel walls in terms of time of modelling, analysis and accuracy of the results. Results showed that both numerical methods have advantages and disadvantages which should be considered in each analysis.
The widespread brittle failure of welded beam-to-column connections caused by the 1994 Northridge and 1995 Kobe earthquakes highlighted the need for retrofitting measures effective in reducing the strength demand imposed on connections under cyclic loading. Researchers presented the reduced beam section (RBS) as a viable option to create a weak zone away from the connection, aiding the prevention of brittle failure at the connection weld. More recently, an alternative connection known as a reduced web section (RWS) has been developed as a potential replacement, and initial studies show ideal performance in terms of rotational capacity and ductility. This study performs a series of non-linear static pushover analyses using a modal load case on three steel moment-resisting frames of 4-, 8-, and 16-storeys. The frames are studied with three different connection arrangements; fully fixed moment connections, RBSs and RWSs, in order to compare the differences in capacity curves, inter-storey drifts, and plastic hinge formation. The seismic-resistant connections have been modeled as non-linear hinges in ETABS, and their behavior has been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in an earthquake with ground motions having a 2% probability of being exceeded in 50 years. The study concludes that RWSs perform satisfactorily when compared with frames with fully fixed moment connections in terms of providing consistent inter-storey drifts without drastic changes in drift between adjacent storeys in low- to mid-rise frames, without significantly compromising the overall strength capacity of the frames. The use of RWSs in taller frames causes an increase in inter-storey drifts in the lower storeys, as well as causing a large reduction in strength capacity (33%). Frames with RWSs behave comparably to frames with RBSs and are deemed a suitable replacement.
In this paper, a novel beam-to-column steel moment connection, named “double reduced beam section (DRBS)” is introduced and the seismic performance of the connection is assessed using finite element modeling. The connection is composed of double dog bone sections close to the column face to widen the plastic hinge region; consequently, reducing the resultant equivalent plastic strain. The region between the two reduced beam sections is laterally connected to the slab to protect the plastic hinge from lateral torsional buckling. A parametric study was conducted on the influence of cut parameters on the connection's seismic behavior. The results showed that, following the limitations and guidelines stated in this research, the DRBS connection exhibits outstanding hysteresis behavior. The deformation capacity of the connection was increased up to 40% in the DRBS connection, compared to the common reduced beam section (RBS) connection. Plasticization of both reduced beam sections postponed the failure buckling modes, resulting in 50 to 75% increase in the absorbed seismic energy before buckling, compared to the traditional RBS connection. Moreover, adding a second cut to the ordinary RBS connection distributed the strains over the two reduced sections, leading to 35 to 60% reduction in the equivalent plastic strain at the reduced sections, at 6% inter-story drift.
During the recent years, resistance mechanisms of reinforced concrete (RC) buildings against progressive collapse are investigated extensively. Although a general agreement is observed about their qualitative behavior in technical literature, there is not such a comprehensive point of view regarding the quantitative methods for predicting collapse resistance of RC members. Therefore, in the present study a simplified theoretical method is developed in order to predict general behavior of RC frames under the column removal scenario. In the introduced method, the robustness of the frame is extracted based on the capacity of the beams. The proposed method expresses ultimate arching and catenary capacities of the beams and also obtains the corresponding vertical displacements. Based on the calculated capacities, the introduced method also provides a quantitative assessment of structural robustness and determines whether or not the collapse occurs. The capability of the method is evaluated using experimental results in the literature. The evaluation study indicates that the proposed theoretical procedure can establish a reliable foundation for progressive collapse assessment of RC frame structures.
This paper provides numerical results investigating the behaviour of steel web-perforated beams with different shaped single openings located close to beam-to-column connections under monotonic and cyclic loading. In particular, the beams considered feature circular and patented elliptically-based perforations. Non-standard elliptically-based perforations have been proposed previously and are optimally designed to maximise resistance against Vierendeel moments and web-post buckling under static loads at the ultimate limit state. Comprehensive parametric nonlinear finite element analyses using the commercial FE package ANSYS were conducted. Initially, a FE model of the beam-to-column WUF-B moment connection was developed and calibrated against pertinent experimental results found in the literature. Next, parametric analyses were undertaken to assess the RWS/WUF-B connection regarding strength (moment), deformation (rotation) and column web shear panel zone deformation for different shapes of beam web perforations, hole sizes, and their locations. The study concludes that larger web openings are capable of moving the plastic hinge away from the column face and the CJP weld. Also, interstory drifts can be controlled with the wise use of the beam web opening size, shape, and distance from the face of the column, as suggested in the paper. Following, a step-by-step design process for RWS/WUF-B connection is presented.
Development of 4 new 5 strategies in order to prevent the progressive collapse of structures is the main focus of many studies during 6 recent years. Due to the available complexities, most of these investigations are concentrated on static behavior of structures while most of the 7 events leading to progressive collapse of structures are inherently dynamic incidents. In the present study, a theoretical method is developed in 8 order to compute the dynamic resistance of reinforced concrete (RC) subassemblages, which are accepted as an idealized part of RC frames in 9 the literature. The proposed method calculates the arching and catenary capacities of RC subassemblages under the middle column removal 10 scenario. The high strain rates due to dynamic behavior of RC members are also considered in the proposed method. An extensive evaluation 11 study is performed in three different stages in order to provide a comprehensive assessment of the introduced approach. Regarding the 12 performed evaluations, the developed theoretical method could provide a reliable framework for progressive collapse analysis of RC frames 13 under the dynamic removal of the columns.
In recent years, researchers study alternative connection designs for steel seismic-resistant frames by reducing the beam section in different ways including that of creating an opening in its web (RWS connections). A similar design is applied in the fabrication of perforated (i.e. cellular and castellated) beams mostly used to support the service integration, as well as the significant mass reduction in steel frames. This paper presents a comprehensive finite element (FE) analysis of extended end-plate beam-to-column connections, with both single and multiple circular web openings introduced along the length of the beam while subjected to the cyclic loading proposed by the SAC protocol from FEMA 350 (2000). The three-dimensional (3D) FE solid model was validated against FE and experimental results and the chosen configuration was capable of representing the structural behaviour of a partially restrained connection, without the necessity to be idealised as fully fixed. The study focuses in the interaction of such connections and the mobilisation of stresses from the column to the perforated beam. The parameters introduced were the distance from the face of the column, S, and the web opening spacing, So, with closely and widely spaced web openings. It is found that RWS connections with cellular beams behave in a satisfactory manner and provide enhanced performance in terms of the stress distribution when subjected to cyclic loading. The design of partially restrained RWS connections should be primarily based on the distance of the first opening from the face of the column.
This paper presents results of an investigation into the effect of span length on progressive collapse behavior of seismically designed steel moment resisting frames which face losing one of their columns in the first story. Towards this aim, several nonlinear static and dynamic analyses were performed for three frames designed for a high seismic zone considering various span lengths. The analysis results revealed that beams and columns of the studied frames had adequate strength to survive one column loss in the first story. However, in order to determine the residual strength of the frame, a series of nonlinear static analyses called pushdown analyses were performed. It was shown that by decreasing the span length to half, strength of the studied frames increases 1.91 times based on the performance-based analysis perspective. Besides, results of nonlinear static analyses revealed that by increasing the applied loads, the investigated structures are more susceptible to progressive collapse when they lose an internal column.
The Vierendeel mechanism is always critical in perforated steel beams with single large web openings, where global shear forces and Vierendeel moments coexist. Thus far, the main parameters that affect the structural behavior of such beams are the depth of the web opening, the critical opening length of the top T-section, and the web opening area. A comprehensive finite-element (FE) study of four sizes of perforated steel sections with three different sizes of 11 standard and novel nonstandard web opening shapes was undertaken, and their primary structural characteristics are presented in detail to provide a simple design method for general practice. The different geometric parameters were isolated and studied to understand the significance of their effects and in turn advance the knowledge on the performance of perforated steel beams. An elaborate FE model was established, with both material and geometrical nonlinearity, allowing load redistribution across the web openings and formation of the Vierendeel mechanism. The reduction of the global shear capacities, because of incorporation of the local Vierendeel moments acting on the top and bottom T-sections, was obtained directly from the FE analysis. Following that, a comparison of the global shear-moment (V/M) interaction curves of the steel sections with various web opening shapes and sizes was established, and empirical generalized V/M interaction curves were developed. Moreover, the accurate position of the plastic hinges was determined together with the critical opening length and the Vierendeel parameter. This work has shown that the shape of the web opening can also significantly affect the structural behavior of perforated beams, as opposed to the equivalent rectangular shape predominately used so far. In addition, the effect of the position of the web opening along the length of the perforated beam was revealed. The importance of the parameters that affects the structural performance of such beams is illustrated. The thorough examination of the computational results has led to useful conclusions and an elliptical form of a web opening is proposed for further study. The outcomes are considered relevant for practical applications. DOI: 10.1061/(ASCE)ST.1943-541X.0000562. (C) 2012 American Society of Civil Engineers.
This paper presents an experimental and analytical study on the behaviour of perforated steel beams with closely spaced web openings. Seven specimens including two typical cellular beams (i.e. circular web openings) and five perforated beams with novel web opening shapes were tested to investigate the failure mode and load strength of the web-post between two adjacent web openings. Fourteen numerical test specimens were developed and analysed by the finite element method and the results were compared with the full scale experiments. The effect of web opening spacing/web opening depth of web-posts was studied to investigate the effective ‘strut’ action of the web-post buckling. The effect of the web opening depth/web thickness was also studied to investigate the stability (slenderness) of the web-post subjected to vertical shear load. Two hundred and twenty-fine elastic-plastic finite element analyses were then employed in a comprehensive parametric study to propose an empirical formula which predicts the ultimate vertical shear load strength of web-posts formed from the particular web opening shapes.Perforated beams with standard circular, hexagonal and elongated web openings are mostly used nowadays. Various non-standard web opening shapes are introduced through this paper for first time. These new pioneering web opening shapes improve the structural performance of the perforated beams when examined under the web-post buckling failure mode. In addition, the manufacturing procedure of these non-standard web openings show great advantage in comparison with the manufacturing way of the more popular cellular beams.
In order to enhance the strength and ductility of post-Northridge connections with beam depths varying from 450 mm to 912 mm, two parallel horizontal long voids were opened on their beams web. Results showed that the proposed beam end configuration (BEC) is effective in moving the plastic hinge away from the column face. Adding web stiffeners and two tubes at the center of voids were effective in preventing excessive beam flange/web buckling. Based on the analytical results a step by step design procedure is proposed to determine the most suitable geometry for the BEC to achieve adequate connection strength and ductility.
Opening in beam web short away clear of beam-to-column connection is an effective method to improve the aseismic behaviors of steel moment resisting frames (MRFs). The pseudo-dynamic (PSD) test and the quasi-static test on the aseismic behaviors of full-size steel MRFs with opening in beam web are carried out. The PSD test shows that the tested frame can satisfy the design requirement and its stiffness isn’t weakened by the web opening. It can be judged from the strain distribution around the beam-to-column connection that the seismic energy is dissipated by local deformation in the weakened area of the beam due to the opening in the case of severe earthquake action, and the expected failure mode of a ductile frame (‘strong column but weak beam’ and ‘strong connection but weak component’) is reached. In the quasi-static test, the failure mode of the tested frame is in conformity with the judgement, i.e., Vierendeel mechanism is formed in weakened areas due to web opening and brittle weld fracture is avoided, which results in an improvement of the aseismic behaviors of steel MRF. Based on numerical analysis, the non-linear analysis model of steel MRF with opening in beam web is provided. Some experimental tests are numerically re-analyzed by applying the proposed model and the numerical results are in conformity with the test results, which verify the validity of the model. A 17-story steel MRF building, damaged during the Northridge earthquake and measured in detail after the earthquake, is selected as the studied case. Push-over analysis shows that the ultimate displacement of the modified building with web openings increases a lot due to the opening and the building’s ductility is improved greatly. Plastic hinge distribution in time-history analysis indicates that brittle weld fracture can be avoided in the frame including connection with opening and the maximum plastic zone moves to the weakened areas. It can be concluded that the aseismic behaviors of steel MRF are improved due to the opening in beam web.
Corrugated steel plate shear wall (CSPSW) as an innovative lateral load resisting system provides various advantages in comparison with the flat steel plate shear wall, including remarkable in-plane and out-of-plane stiffnesses and stability, greater elastic shear buckling stress, increasing the amount of cumulative dissipated energy and maintaining efficiency even in large story drifts. Employment of low yield point (LYP) steel web plate in steel shear walls can dramatically improve their structural performance and prevent early stage instability of the panels. This paper presents a comprehensive structural performance assessment of corrugated low yield point steel plate shear walls having circular openings located in different positions. Accordingly, following experimental verification of CSPSW finite element models, several trapezoidally horizontal CSPSW (H-CSPSW) models having LYP steel web plates as well as circular openings (for ducts) perforated in various locations have been developed to explore their hysteresis behavior, cumulative dissipated energy, lateral stiffness, and ultimate strength under cyclic loading. Obtained results reveal that the rehabilitation of damaged steel shear walls using corrugated LYP steel web plate can enhance their structural performance. Furthermore, choosing a suitable location for the circular opening regarding the design purpose paves the way for the achievement of the shear wall's optimal performance.
In recent years, the prequalified rigid connections of radius-cut reduced beam section (RBS) have been widely used in the design and construction of steel moment frames. Despite extensive investigations performed on the seismic performance of RBS connections, there is little research into the impact of these connections upon the elastic story drift in steel moment frames. In the current study, a precise formulation (partially based on a previous research) has been developed so as to evaluate the amount of stiffness variation or amplified elastic drift introduced by radius-cut RBS connections in a story of steel moment frames. Herein, by defining a novel and accurate method along with the method of virtual work, the amplified elastic drift of a 2-dimensional one-story single-span moment frame due to utilizing radius-cut RBS connections is calculated. The reliability and accuracy of the presented approach are validated using finite element modeling of the moment frame. Sensitivity analyses are also conducted upon the RBS connection parameters to derive the most effective parameters on the amount of elastic drift in steel moment frames. Then, by employing a statistical approach called response surface method (RSM) and combining findings of this study with some premises considered in a previous research, rigorous amplification factor of elastic drift formulas based on utilizing each of IPE and HEA beams in a story (from the first to the last one) with RBS connections are developed. Ultimately, two simple, linear, and functional amplification factor of elastic story drift formulas for each set of IPE and HEA story beams with RBS connections are proposed for designers. The scope of these formulas will be expanded to plate girders as well.
The Accordion-Web Reduced Beam Section (AW-RBS) connection consists of a corrugated web, replacing the flat web, within a limited area near the column face, which reduces the beam flexural strength and forces the plastic hinge to form in the corrugated zone. This paper presents a seismic design procedure in the framework of the U.S. design standards for a double-cell AW-RBS connection, which consists of two box sections oriented such that an accordion web is formed within a limited area in the beam. The analytical evaluation of the flexural strength of the beam with a corrugated web was first presented. Then, a step-by-step design method was proposed to size the connection. Quasi-static cyclic tests were conducted on two relatively identical specimens including double-cell AW-RBS connections. A detailed numerical model of a connection with deep beams and columns designed in accordance with the proposed design procedure was developed and a nonlinear analysis was performed to investigate the seismic response of the connection and verify the adequacy of the proposed design method for the beam sizes frequently used in steel moment-resisting frames. The results confirmed the satisfactory response of the double-cell AW-RBS connection under cyclic loading. The stable plastic hinge formed in the reduced area of beams as predicted in design and no yielding was observed in the beam-to-column groove weld. The findings of the numerical simulations confirmed that the AW-RBS connection with deep beams and columns could potentially exceed the plastic rotation limit for ductile moment connections without significant instability and strength degradation.
Cold-formed steel (CFS) shear walls are the primary lateral load resisting components in lightweight steel framed (LSF) structures. The development of increasing complex LSF structures, laterally supported by CFS walls, demands sophisticated modelling techniques for design and optimization that typically involves inherent material and geometric nonlinearities caused by large deformations. Determining the performance of CFS shear walls and accurately establishing their behavioural model are the foundations of obtaining effective responses of CFS structure under extreme loading conditions. Great progress has been made on the theories and applications of the numerical models for analysis of the lateral behaviour of CFS wall systems during the past several decades, and quite a great number of numerical models have been developed for simulating the behaviour of CFS shear walls in the literature. This study provides a comprehensive review on the numerical developments made in this area as published in leading journals, high impact conferences and codes' provisions in the area, and looks at the challenges and gaps that need to be addressed in future research studies. The numerical models for analysing the lateral behaviour of CFS shear walls including their strengths, weaknesses, limitations employed behavioural models, contributing factors, and parameters and functions influencing their performance are discussed and compared with each other. The existing models are grouped into two categories: micro modelling methods, which simulate fine-scale details; and macro modelling methods, which amalgamate details into selected categories for further simplification.
Seismic behavior of beam-to-column connections can be improved by shifting the location of inelasticity away from the
column’s face. Such connections can be achieved by reducing the flange area at a specific distance from the beam-column
connection, called reduced beam section (RBS), or by reducing web area by introducing a perforation into the web, called
reduced web section (RWS). This paper presents a parametric study that is carried out on the effect of the perforation size,
perforation location, and the beam span length in the RWS connections, using finite element modeling. Next, an interaction
formula is derived for design purposes, and a step by step design method is developed. Finally, a frame is analyzed to verify
the reliability of the proposed design process and assess the impact of the RWS connections on the behavior of special moment
frames. The study concludes that RWS connections can effectively improve seismic performance of special moment frames,
causing plastic hinges to form around the perforation away from the column’s face.
This study investigates an innovative method of avoiding brittle fracture at the beam-column connection welds of steel moment frames in earthquakes. The reduced web section (RWS) approach introduces large openings into the web to shift the location of inelasticity away from the connections. The configuration of the openings governs the mode and capacity of inelastic mechanism in the beam. In this paper, experimental results are reported for five RWS specimens that were subjected to quasi-static cyclic loading. Four specimens were designed to develop Mode-A mechanisms; three had a single unique opening at midspan, and one had two openings near the beam-column connections. The other specimen was designed to develop a Mode-B mechanism without having web post buckling (observed in the Phase 1 specimens Shin et al., 2017), which had a wide opening and two brass plates clamped to the web. The application of web openings was successful in achieving the intended inelastic mechanisms; inelastic deformation was due to yielding, buckling, and/or fracture of the webs around the opening(s) and plastic hinging of the T-sections above and below the opening(s). The three specimens with a single opening at midspan exhibited the most stable load-drift responses; the specimens displayed a loss of strength during the 3 or 4% drift cycles (due to local buckling and/or fracture of the webs) and subsequent transition from “full” to “S-shaped” hysteretic loops, but they regained full strength by the end of testing at story drifts up to 7%.
Avoiding fracture in the beam-column connections of steel moment frames is critical to their seismic performance. Both Reduced Web Section (RWS) and Reduced Beam Section (RBS) methods apply the capacity design principle to shift the location of yielding into the beam and away from the beam-column connection. In the RWS approach, large openings are introduced into the web of the beam, so that the arrangement and configuration of the openings determine the mode of inelastic mechanism that develops within the beam. In this paper, experimental and numerical results are discussed for five RWS specimens that were subjected to reversed cyclic displacements. Also, the concept and potential inelastic modes of RWS beams are introduced, and beam shear equations corresponding to the assumed plastic mechanisms are derived. Of the five specimens, one had only two openings close to the beam-column connections, while the others had multiple openings distributed over the beam span. Most of the specimens exhibited stable hysteretic behavior up to approximately 6% story drift.
A reduced beam section (RBS) is a new type of connection in steel moment resistant frames. In addition to the major benefits, RBS has its own weaknesses, such as web local buckling and lateral torsional buckling. The purpose of this paper is to improve the performance of European I-beam profile (IPE) with an arched cut in the flange, using a diagonal stiffener of the beam web. With the help of laboratory tests and numerical models, it was found that the use of a diagonal stiffener in the area of an arched cut increased the energy dissipation and plastic rotation capacity of RBS connection.
The effectiveness of using the reduced beam section (RBS) and welded haunch for seismic rehabilitation of pre-Northridge steel moment connections was investigated through cyclic testing of six full-scale specimens-three of them incorporated lightweight concrete slabs. Test results showed that, unless the low-toughness E70T-4 groove weld was replaced by notch-tough weld metal, introducing RES to the beam bottom flange alone could not prevent brittle fracture in the groove weld of the top flange. The presence of a concrete slab or removing steel backing only improved the cyclic performance slightly. Although two RES specimens with weld replacement performed well, a new type of ductile fracture along the "k" line of the beam was observed. With E70T-4 groove welds in place, however, the welded haunch specimens performed better than the RES specimens. No brittle fracture occurred when the slab was present. The composite slab only increased the beam positive flexural strength by about 10%.
The effect of panel zone yielding on the potential for fracture of welded-bolted steel connections is investigated, with the objective of gaining a better understanding of the inelastic behavior of the panel zone region and of critically assessing current seismic provisions for steel panel zone design. The research objectives are addressed through detailed, three-dimensional, nonlinear, finite-element analyses of connection subassemblies. The characteristics of the analysis configurations used in this research are derived from the geometry of a typical pre-Northridge fully restrained beam-colum steel connection. Important geometric parameters are varied over the practical range of interest in order to evaluate their effect on connection behavior. To assess the influence of the parameters of interest, a number of different stress, strain, and combined stress/strain indices are employed. These quantities are sampled at connection plastic rotations ranging from 0.0025 to 0.03 rad. Results from the finite-element analyses show that, although beam plastic rotation demands are smaller in connections with weak panel zones, the stress conditions at the beam-column interface are more critical at higher connection plastic rotations. Therefore, although the panel zone can effectively contribute to overall connection ductility, a weak panel zone can also lead to a greater potential for brittle and/or ductile fracture at higher connection plastic rotations. The finite-element analyses also suggest that current design provisions may not be appropriate when applied to panel zones in exterior joints.
Rectangular Hollow Sections (RHS) have superior structural performance compared to conventional steel sections. However, the application of RHS in structural steel framework is limited because suitable connection configurations have not been developed between such members. Also adequate information on the moment–rotation characteristics of connections between RHS members is not available for design. To overcome these problems, a new and efficient connection is proposed which is easy to fabricate and convenient for erection. The connection employs channel connectors welded to the column flange and bolted to the beam to transfer beam flange forces into the column webs thereby avoiding the need to provide internal diaphragms in the column. An opening in the web facilitates the installation of bolts and can be used to pass service lines. The bolts are loaded in shear, so as to obtain improved performance of the connection under cyclic loading. By choosing suitable dimensions for the channel connectors, the strength and stiffness of the connection can be varied. The behaviour of the connection is evaluated by cyclic tests and non-linear finite element analysis. Test results are presented in the form of hysteretic curves and failure modes. In the case of channel connectors of high strength, failure occurs at the beam net section away from the face of the column, similar to beams with Reduced Beam Sections (RBS). It is shown that the connection has adequate ductility and hysteretic energy dissipation capacity. The moment–rotation characteristics of the connection can be expressed in terms of the three-parameter power model, for semi-rigid frame analysis.
The results of an experimental study of the seismic performance of improved, welded unreinforced beam-to-column moment connections are presented. The study involved the inelastic cyclic testing of I I full-scale connection specimens to evaluate the effects of weld access hole geometry, beam web attachment detail, panel zone strength, continuity plates, and composite slab on connection performance. With a high toughness weld metal and modified detailing, it is demonstrated that a welded unreinforced flange moment connection can reliably achieve an inelastic rotation of 0.03 rad or more prior to failure. The modified details include the use of a weld access hole with a modified geometry and a welded beam web. The test results indicate that a strong panel zone enhances inelastic connection performance. Based on the results of the study recommendations are given for the seismic-resistant design of improved welded unreinforced connections for steel moment-resisting frames.
This paper presents the results of an experimental program for bolted moment connection joints of circular or square concrete filled steel tubular (CFST) columns, and H-shaped steel beams using high-strength blind bolts. In order to investigate the static performance and failure modes of the blind bolted connection, an experimental program was conducted involving four sub-assemblages of cruciform beam-to-column joints subjected to monotonic loading. Moment–rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. The test parameters varied were the column section type and the thickness of the end plate. The results showed that the proposed blind bolted connection, which behaves in a semi-rigid and partial strength manner according to the EC3 specification, displays reasonable strength and stiffness. The rotation capacity of this type of connection to square or circular CFST columns exceeds 70 mrad and this satisfies the ductility requirements for earthquake-resistance in most aseismic regions. The blind bolted connection is shown to be a reliable and effective solution for moment-resisting composite frame structures.
The effectiveness of using both the welded haunch and rib plates for the seismic rehabilitation of pre-Northridge steel moment connections for a 13-story office building in Los Angeles was studied. Full-scale cyclic testing of two pre-Northridge moment connections with simulated welding defects was conducted and used as a benchmark for the rehabilitation scheme. Four rehabilitated moment connections were then tested to validate the proposed scheme. A correlation study using a nonlinear finite element program (ABAQUS) was also performed. Both the experimental and analytical results showed that the use of welded haunch and rib plates significantly reduced strain demands at the beam flange groove welds. Doubler plates that were offset from the column web were effective in resisting shear in the panel zone region. Test results also showed that the inclination angle of the haunch, which was recommended to be within 30±5 degrees in an AISC Design Guide, can be extended to 50 degrees.
Steel moment connections reinforced with cover plates have received considerable attention in the US since the Northridge earthquake, both in laboratory testing and in new steel moment frame construction. This paper presents experimental data on 12 large scale connection test specimens reinforced with cover plates. Ten of the 12 test specimens showed excellent performance, developing large plastic rotations under cyclic load. Two test specimens failed, however, indicating that cover plated connections are not fool-proof. This type of connection has limitations that must be considered in design and construction. The paper provides a critical assessment of cover plated connections, identifying potential benefits as well as concerns and limitations. Design implications of the experimental data are discussed.
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