Reduced Web Section Research Articles

Cyclic behaviour of elliptical-shaped reduced web section connection

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.

Local buckling analysis of cold-formed steel webs with stiffened rectangular openings

The cold-formed steel members often require web openings to allow for building services such as mechanical piping, electrical wiring, and air conditioning systems pass through the ceiling and therefore reduce the building overall height and as a result, lateral forces induced on the building. Stress distribution in members with openings is different from members without holes and therefore characteristics, shape and modes of their buckling are dissimilar which results in reduced buckling capacity and ultimate strength. In order to compensate some of the lost capacity, edge and intermediate stiffeners are fabricated into the web which complicates the characteristics and buckling mode. In this study, a set of analytical solutions for the local buckling of cold-formed steel webs with rectangular openings stiffened by intermediate and edge stiffeners subjected to compression, bending and their combination is developed, and summarized. The main variables are elastic modulus, Poisson's ratio, height of openings to height of web, aspect ratio of openings, moment of inertia of intermediate and edge stiffeners to moment of inertia of reduced web section, and stress distribution gradient above or under the hole. The proposed solutions can be used for a wide range of rectangular web openings. Analyses are conducted using energy based methods and the results are compared with numerical data obtained from the commercial finite element software (Abaqus). The numerical results demonstrate that one of the eight proposed formulas with minor modification can be successfully used to predict the critical buckling stress.

Seismic behaviour of RWS moment connections to deep columns with European sections

The design of reduced web section (RWS) connections is becoming more often, while the research is focusing on both areas: (a) the performance of beams with large web opening areas near the supports, and (b) the seismic behaviours of steel beam-to-column connections of different types when subjected to cyclic loads. The beam web opening is used as a mechanism to counterbalance the low inelastic capacity of the welds and to shift the stresses from the welding and shear panel zones to the weak beam section in line with the concept of “weak beam-strong column” often employed for the seismic-resistant design of Moment Resisting Frames (MRFs). However, limited data yet exists on the design and seismic behaviour of such connections and those are only for UKB and UKC section profiles. This paper presents an extensive FE study of the seismic performance of fully welded RWS moment connections to deep columns. The effect of using different beam spans is also investigated together with the effect of web opening size and position (web opening at different shear-moment interactions). European HE and IPE profiles are employed for this study in an effort to introduce RWS connections in Eurocode 8, and understand potential variations in design when using European sections as previously reported in RBS connections. Finally, a step-by-step design procedure is presented based on AISC 358 (AISC 358[3]).

Comprehensive FE Study of the Hysteretic Behavior of Steel–Concrete Composite and Noncomposite RWS Beam-to-Column Connections

This paper investigates the behavior of reduced web section (RWS) steel–concrete composite (SCC) beam-to-column connections with circular web openings through a comprehensive finite element (FE) analysis following experimental and computational studies. Results showed that the presence of a circular web opening is effective to move the plastic hinge away from the column shear panel zone and the main connection components including the welding beam-column welding area, and hence, significantly improve the ductility and energy dissipation of the connection without critically affecting its capacity. The composite action was not considered in the literature to account for the severest case (slab acts as load only) in terms of load carrying capacity. However, this study proves that the composite effect has a decisive role in the calculation of the ductility and rotational capacity, and if not considered may result in an overestimated ductile behavior. On the other hand, in cases where composite action is not provided, depending on the particular flooring system, noncomposite steel connections may be considered where the ductility and energy dissipation gains are definitely higher but the load carrying capacity is lower. This paper establishes the comparison between composite and noncomposite connections and concludes that the contribution of the composite action to the load carrying capacity is higher with the increase of the beam web opening diameter. Therefore, the calculated negative load carrying capacity tends to be very conservative if the composite effect is neglected when a large opening diameter is used.

Pushover Analysis of Steel Seismic Resistant Frames with Reduced Web Section and Reduced Beam Section Connections

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 providing ductility to connections. Researchers presented the reduced beam section (RBS) as a viable option to prevent 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 (MRFs) of 4-storeys, 8-storeys and 16-storeys. The frames are studied with three different types of connections; fully-fixed moment connections, RBS connections and RWS connections, in order to compare the differences in capacity curves, inter-storey drifts and plastic hinge formation. The seismic-resistant connections have been modelled as non-linear hinges in ETABS, and their behaviour have been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in a 2 in 50 earthquake. The study concludes that RWS connections perform satisfactorily when compared with frames with fully-fixed moment connections in terms of providing consistent inter-storey drifts 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. Frames with RWS connections behave comparably to frames with RBS connections and are deemed a suitable replacement.

Seismic performance of reduced web section moment connections

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.

Seismic toughness and failure mechanisms of reduced web-section beams: Phase 2 tests

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%.

Seismic toughness and failure mechanisms of reduced web-section beams: Phase 1 tests

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.

Comparative Study of Steel Beam Column Connection under Cyclic Loading

A structure is an assembly of various elements or components which are fastened together through some type of connections. Steel beam column connection may fail due to large earth quake. Plastic hinge formation is the main failure of a steel beam column connection. There are two methods for improving the steel beam column connection (i) connection reinforcement/strengthening (ii) beam weakening by reducing the cross-sectional area of the beam at a certain distance from the connection. When reducing the cross section area plastic hinge is formed away from column face. The main objective of this study is to compare reduced beam section (RBS) and reduced web section (RWS) pattern and find out the location of plastic hinge. For steel beam column plastic hinge is located near column. When reducing the cross section area the location of plastic hinge will shift from the column. Aim of this project is to locate the position of plastic hinge apart from column face, and also evaluate the stress and deformation.

Analytical Investigation of Replaceable Links with Reduced Web Section for Link-to-Column Connections in Eccentrically Braced Frames

Analytical Investigation of Replaceable Links with Reduced Web Section for Link-to-Column Connections in Eccentrically Braced Frames

Increasing Seismic Energy Dissipation of Steel Moment Frames Using Reduced Web Section (RWS) Connection

Connections of steel moment frames are vulnerable to brittle failure. Providing a perforation near the beam-ends is suggested as a potential method to improve seismic behavior of these structures. This article presents a numerical study on the energy dissipation of steel moment connections with perforated beam. Models with elongated circular openings of different dimensions and location are analyzed and compared based on the global and local damage indices, predicted failure time and dissipated energy. Results show that an RWS connection with a proper opening size can develop reasonable inelastic deformations and provide an acceptable seismic improvement to moment-resisting frames.

Seismic Behaviour of RBS and AW-RBS Moment Resistant Connections in Double I-Beams

Moment resistant steel connections are widely used in steel structures and play a significant role in reliability of structures, especially in earthquake-prone regions. After the Northridge earthquake, the invention of Reduced Beam Section (RBS) connections was a turning point in the design of the moment-resistant steel connections. In the present study, the seismic behavior of the RBS connections with reduced flange width as well as the AW-RBS connections with reduced web section in the double section beams are investigated. The results of a numerical study conducted using ABQUS finite element modeling software to investigate the ductility, energy absorption and plastic behavior of the RBS joints under cyclic loads are presented. Results showed promising performance with regards to energy absorbance and ductility for the AW-RBS connections.