Reduced Web Section Research Articles

Capacity design assessment of composite reduced web section (RWS) connections

A gap in current design approaches demands explicitly introducing a capacity design approach when designing steel-concrete composite reduced web section (RWS) connections. This paper addresses this gap by presenting test-validated finite element models and parametric investigations, focusing on the presence and absence of composite action over the web opening, the diameter, and the end-distance of the web opening. Additionally, the first-ever comprehensive experimental and numerical database from the literature on bare steel and composite RWS connections is compiled and thoroughly analysed to develop the capacity design assessment for such connections. Both parametric investigations and the database highlight the significance of the capacity design ratio between the connected components in achieving a desirable ductile mechanism. This is crucial, as evidenced by the results: a 15 % increase in the connection's moment capacity led to an average 21 % difference in dissipated energy, favouring the web opening with a diameter of 50do over 80do, in RWS connections with the presence of composite action. The results show that proper consideration of the capacity design approach in designing RWS connections ensures a stable yield mechanism is developed, resulting in the redistribution of global action and capping deformation demands on non-ductile elements. This enhances connections' rotational capacity and ductility by forming the Vierendeel mechanism. Lastly, the paper presents a detailing recommendation for employing RWS connections in both existing and new structures for seismic purposes.

Experimental investigation using demountable steel-concrete composite reduced web section (RWS) connections under cyclic loads

This paper presents an experimental study of demountable steel-concrete composite reduced web section (RWS) connections for use in seismic areas. Four composite connection specimens were subjected to sagging and hogging moments to investigate the performance of RWS connections under reversible actions. For such purpose, a single web opening was created near the beam-column joint. Focus was made on the effects of perforation location and composite beam-slab action induced by bolted shear studs within the protected zone. Results indicate that employing RWS connections for seismic retrofit is a viable solution capable of achieving a performance similar to that observed for RBS connections in new buildings. Notably, a Vierendeel Mechanism is formed, allowing for plasticity development in the beam. All RWS connections were capable of achieving an interstory drift larger than 4%, thereby complying with the performance targets set by ANSI/AISC 358-16, ANSI/AISC 341-16 and EC8. Moreover, the deformation of beam-slab shear-transfer bolts was small enough to allow for disassembly after the tests, indicating that the proposed solution could enable reuse and post-earthquake retrofitting.

Experimental and numerical investigation of reduced web section connections in fire

AbstractThis 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.

An evaluation of slenderness limitations of H-beams for special moment connections

This paper presents the results of seismic connection testing and finite element analyses (FEA) on the slenderness limitations of steel H-beams in special moment-frame (SMF) connections. The effectiveness of FEA models was first validated by the full-scale testing of a reduced-web-section (RWS) connection, and a post-earthquake bolted-web-welded-flange (BWWF) connection. FEA simulations were then performed to study the beam section properties and seismic connection performance. The result shows that if a H-beam has a compact section, the adopted connection will develop strength and ductility meeting the AISC seismic requirements, even though the plastic section modulus ratio between the beam flanges and whole section is less than 70%. The result also suggests the effectiveness of adding a web opening to a BWWF connection. These findings call for a re-examination of the requirements of highly ductile members in SMF connections.

Hysteretic Behaviour of Composite Reduced Web Section (RWS) Connections for Seismic Applications

ABSTRACT Whilst there has been research about reduced web section beams; RWS, their seismic behaviour when they are overlaid by slabs is not well understood. This study addresses this by assessing a high-definition finite element representation of non-seismically detailed RWS connections with slabs. The composite action is investigated, focusing on effects of the size and location of the web openings. These connections can reach a 4% interstorey drift, thus comprising special moment frames in accordance with AISC 341. Moreover, beam, column, and joint tearing were avoided entirely, and at the most, brittle failure of bolts in the end plate was observed.

Mechanical performance of hybrid high-strength steel composite cellular beam under low cyclic loading

This study aimed to compensate for the impairments in structural load-carrying capacity and stiffness caused by conventional reduced web section beams, and to meet the strength design requirements for engineering. A new hybrid high-strength steel composite cellular beam (HHS-CCB) using high-strength steel in the beam flange and ordinary steel in the web was proposed. A composite cellular beam between the rigid joint and inflection point in the frame structure was selected as the research object, and low cyclic loading tests were conducted on one homogeneous ordinary steel composite cellular beam (HOS-CCB) and four HHS-CCB specimens. The effects of the hybrid use of high-strength steel and ordinary steel on the failure modes, load-carrying capacities, strength and stiffness degradation, ductility, and energy-dissipation capacities of the composite cellular beams were investigated. The test results show that with reasonable values for the diameter of the web opening and for the distance from the first opening at the beam end to the column surface (abbreviated as the hole edge distance), the HHS-CCB specimens exhibit local plastic damage at the first opening at the end of the beam but maintain a good ductility, stiffness degradation, strength degradation, and energy dissipation capacity, while significantly improving the structural load-carrying capacity loss owing to the web opening. Compared with HHS-CCB specimens using HHS in both the upper and lower flanges, the HHS-CCB specimens using HHS only in the lower flange show superior mechanical properties. Considering the poor plastic deformation capacity of HSS, the steel plate strength of the flange should not be much higher than that of the web to ensure the full development of plasticity in the cross-section, and Q460 steel or Q550 steel is generally recommended. A nonlinear finite element (FE) model was developed using ABAQUS software to predict the hysteresis behavior of specimens. Numerical simulation shows that the simplified FE model can be used to simulate the hysteresis performance of HOS-CCB and HHS-CCB.

Seismic performance of RWS moment connections to steel box-columns and H-beams with general sections

In this study, full-scale seismic testing and 3D finite element analysis were carried out on reduced web section (RWS) connections. A steel H-beam-to-box-column connection was designed to have two parallel long openings in the beam web. The opening was rectangular with semicircles at both ends. The design used the adjacent beam flanges to take shear forces with the beam web with openings, which made it possible to apply RWS connections with general sections. The design parameters were then selected to delay the occurrence of local plate buckling in the beam flanges near the beam web with openings, which ensured that the connections developed sufficient plastic deformation before reaching the maximum strength. The results showed that the refined design could move the plastic hinges of the connections away from the column faces. Moreover, after a complete loading cycle with a drift angle of 4% rad, the connections still had a moment strength of >80% of the beam plastic moment strength. The connection performance met the AISC seismic requirement. This design refinement makes it possible to further apply RWS connections to steel moment frames in building retrofits.

Building retrofit with reduced web (RWS) and beam (RBS) section limited-ductility connections

Softening of beams near the moment connection can be regarded as one of the most convenient methods for retrofitting non-seismically designed buildings. This can be done by drilling the beam web near the connection (aka RWS–Reduced Web Section) or cutting the beam flanges (aka RBS–Reduced Beam Section). Thus, becoming a cost-effective option for retrofitting and erection of new buildings, while optimising use of steel; making the most of this high environmental impactful material. This study presents a comprehensive investigation of the effects of using extended end-plate bolted RWS and RBS connections in building behaviour when subjected to strong ground motion. For that purpose, incremental dynamic analyses (IDA) were performed in a low height building fitted with RWS and RBS connections capable of limited ductility. This was done with the aim of characterising the seismic behaviour of buildings with deficient earthquake design after being subjected to seismic upgrade. It is observed that empirical fragility curves show that probabilities of exceeding 1%, 2% and 4% inter-story drifts are significantly lower (more than 25%) for the building that is designed with RWS connections instead of RBS connections; while the probability of collapse is reduced by at least one third. This indicates that deployment or RWS connections can reduce the risk of both; severe structural damage and, large economical loss due to damage of non-structural elements when seismic demands are moderate.

Prediction model for catenary action of welded RWS connections using PVM link element

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.

Experimental and numerical study on the seismic behavior of steel plate shear wall with reduced web section beams

In this paper, a new steel plate shear wall with a reduced web section beam is proposed. The proposed model, including a middle link beam with elongated circle opening, offers advantages such as the ease to integrate building services within the floor zone resulting in shallow structural depth, reducing demands on columns and beam-to-column connections, increasing the ductility by forming Vierendeel mechanism around the opening, and changing the pattern and mechanism of yielding. To investigate the structural performance of this system, experimental and numerical studies were carried out. Five 1/3- scale specimens were fabricated and tested under quasi-static cyclic loading. Results indicated that the steel plate shear wall with middle link beam (ML-SPSW) specimens had stable hysteresis curves and experienced 3% story drift without any reduction in bearing capacity. All proposed models could tolerate 6% drift with about a 30% reduction in maximum achieved load without a sudden or significant drop in strength or stiffness. The energy dissipation and ductility capacity were superior and the gravity bearing system (columns) and panel zones remained intact until the end of cyclic loading. Furthermore, nonlinear finite element (FE) models of tested specimens were developed and verified against the experimental results. Numerical simulations and test results showed good agreement. In order to further ascertain the validity of the proposed system, supplementary results were obtained from numerical models. Finally, a parametric study and a design algorithm were proposed to determine the proper size of the beam perforation.

The Effect of Degree of Composite Action on Reduced Web Section (RWS) Connections

AbstractDue to the concerns regarding the effects of the composite action on the seismic performance of beam‐to‐column connections leading to premature brittle fracture of the beam bottom flange, this paper introduces a comprehensive finite element (FE) analysis studying the effect of the degree of composite action to the performance of the bolted extended end‐plate (BEEP) RWS connections subjected to cyclic loads. Circular web openings with diameter equal to 0.8 of the beam's depth and two different parameters, namely the distance from the face of the column, S, and the degree of composite action, are investigated. Based on the results, it is confirmed that the degree of composite action of RWS connections is an important factor in seismic‐resistant design. It is concluded that the low degree of composite action with the use of a structural fuse, such as an RWS connection with localised beam web opening, can potentially avoid bottom flange fracture damage. It is found that composite RWS connections can also be employed to improve the seismic performance on steel structures.

Parametric study of reduced web section of beam to column welded connection with castellated beam having hexagonal openings and subjected to cyclic loading

In this paper, a finite element (FE) analysis is carried out on a beam to column welded connections with multiple hexagonal web openings. The openings are distributed along the length of the beam which is subjected to cyclic loading protocol proposed by the SAC and FEMA 350 (2000). This study focuses on the interaction of the connections from columns to the perforated beam and mobilization of stresses. Two parameters were addressed: the distance from the face of the column (S), and the web opening spacing (So) including closely spaced opening. The study revealed that the design of mostly controlled reduced web section (RWS) connections should be fundamentally based on the distance of the first opening from the face of the column. Three values of the distance (S) are presented (200 mm, 350mm, and 520 mm). A model with an ideal distance (S) of 350 mm has resulted in an ultimate rotation of 0.039649 rad, which is less than other models, in which rotations were 0.049386 rad and 0.050000 rad, respectively.

Experimental behaviour of non-seismical RWS connections with perforated beams under cyclic actions

The use of perforated (in particular cellular and castellated) beams has become widespread as their manufacturing processes keep minimising wasted material and has become cost-effective by reducing self-weight of steel structures, while allowing for larger clear spans. Although their behaviour to time-invariant vertical loads has been extensively investigated and validated in laboratory setups, their response to reversible actions has not been explored to the same extent. This paper presents results of cyclic load tests of beam-column reduced web section (RWS) connections, considering setups representative of what is observed in low-rise buildings in the UK; a region with sparse seismicity. Results show that RWS connections on these frames can achieve stable hysteresis loops without significant strength degradation, due to the simultaneous occurrence of yielding of the critical cross-section and development of a Vierendeel mechanism on the edges of the perforations (web openings). Also, inelastic action is mostly observed within the beam, thus being successful in protecting the beam-column connection. Performance particularly exceeds what is observed for a benchmarking RBS connection styled according to the same underlying assumptions, hinting that RWS connections could be a more suitable solution for structural retrofitting in regions where seismicity is sparse.

Performance improvement of rigid connection by reduced web section with cellular beam and column subjected to cyclic loading

Performance improvement of rigid connection by reduced web section with cellular beam and column subjected to cyclic loading

Comparison of steel frames with RWS and WFP beam-to-column connections through seismic fragility analysis

Reduced web section (RWS) connections and welded flange plate (WFP) connections can both effectively improve the seismic performance of a structure by moving plastic hinges to a predetermined location away from the column face. In this paper, two kinds of steel frames—with RWS connections and WFP connections—as well as different frames with welded unreinforced flange connections were studied through seismic fragility analysis. The numerical simulation was conducted by using multiscale FE modelling. Based on the incremental dynamic analysis and pushover analysis methods, probabilistic seismic demand analysis and seismic capability analysis were carried out, respectively. Finally, combined with the above analysis results, probabilistic seismic fragility analysis was conducted on the frame models. The results showed that the RWS connection and WFP connection (without double plates) have little influence on reducing the maximum inter-storey drift ratio under earthquake action. RWS connections slightly reduce the seismic capability in non-collapse stages and improve the seismic collapse resistance of a structure, which exhibits good structural ductility. WFP connections can comprehensively improve the seismic capability of a structure, but the seismic collapse resistance is worse than that of RWS connections when the structure has a large number of storeys. The frame with WFP connections has a lower failure probability at every seismic limit state, while the frame with RWS connections sacrifices some of its structural safety in non-collapse stages to reduce the collapse probability.

Performance improvement of rigid connection by reduced web section with cellular beam and column subjected to cyclic loading

The behaviour under cyclic loading of a cellular beam and cellular column on the beam-to-column rigid connection was studied. The main focus was at the connection when openings were implemented to the beam and column members. The study aims to determine the increase of the yield and ultimate strength of the whole rigid connection, the ductility of connection and the energy dissipation in each loading cycle. Finite element analysis with both nonlinear material and geometry was conducted. The results indicated that the implementation of a cellular member could increase the yield strength of the overall rigid connection by 28.81%, the ultimate load by 30.93% and the stiffness by 36.21% compared to the original.

Anti-collapse performance of steel frames with RWS connections under a column removal scenario

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.

Cyclic behavior of welded elliptical-shaped RWS moment frame

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.

Lateral load resisting behavior of steel moment frames with reduced web section (RWS) beams

Many studies have been conducted on the monotonic and cyclic behavior of beams with Reduced Web Section (RWS) moment connections. However, the use of these structural elements in Steel Moment Resisting Frames (SMRF) have not been much considered. This paper presents a numerical investigation on the lateral load carrying behavior of steel moment resisting frames with reduced web beam sections. For this purpose six multi-story multi-bay structures with different seismic design category, framing type and geometric configurations are designed and modeled numerically. A design procedure for calculating the proper size of opening in the beam web is presented. Then, nonlinear static analysis is conducted on the frames with reduced web beam sections and results are compared with the ones corresponding to the conventional moment resisting frames. Based on the results, the average reduction in initial stiffness and ultimate base shear of the models with perforated beams are 2.5–8.5% and 3.5–6%, respectively. This is while the investigation of yielded areas in these models showed that the plastic zone moved from beam-column connection zones to the openings which is consistent with “Strong column-weak beam” rule. Therefore, the proposed design algorithm can be considered as an effective way to select the proper perforation size which decreases demand for plastic deformation at beam-column connections without causing further decrease in stiffness and strength of the frame.

Cyclic performance of bolted end-plate RWS connection with vertical-slits

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.