Flush End-plate Connections Research Articles

Numerical study on the anti-progressive collapse performance of steel frame-steel plate shear wall structures

Although the lateral behaviour of the steel frame-steel plate shear wall (SF-SPSW) system has attracted much attention, there has been relatively lesser research conducted on its performance with respect to anti-progressive collapse. This study considers six SF-SPSW substructures with different column failures to be the targets of research. A simplified and detailed analysis method using Cartesian connectors instead of bolts is presented, which can improve the analysis efficiency of the collapse-resistant performance of SF-SPSWs with flush end-plate connections. Results indicate that SF-SPSW subjected to progressive collapse may resist the external load by flexure mechanism, arch compression mechanism, Vierendeel mechanism, catenary mechanism, and tensile mechanism of the steel plate. After the pseudo-failure column is removed, the remaining structures can be rebalanced and will not collapse under design loads. However, their failure modes and resistance mechanisms will vary with the location of the pseudo-failure column. Also, the addition of stiffened triangular steel plates at the failure region can improve the collapse-resistant capacity reserve of the SF-SPSWs; the design parameters of these triangular steel plates are analysed and discussed.

Structural behaviour of steel-timber versus steel-concrete composite joints with flush end plate

An innovative structural floor comprising of steel frames and cross-laminated timber slabs (i.e. steel-timber composite) has been introduced recently as a sustainable alternative to conventional composite floors with reinforced concrete slabs. To assess the structural performance of the steel-timber and compare it to steel-concrete composite and bare steel, push-down tests were performed on geometrically identical full-scale cruciform subassemblies with flush end plate connections. The width of slab and type of connections between the CLT slabs and the size of bolts connecting the flush end plate to the column were the variables in the testing program. The size of bolts and width of CLT slabs had minor (or no) influence on the hogging bending moment resistance. However, increasing the bolt size and CLT slab width increased the stiffness of the STC beam-to-column connections. Furthermore, the CLT-to-CLT connection type had significant influence on the stiffness and flexural capacity of the STC subassemblies under hogging bending moment. The results of the laboratory tests showed that the rotational stiffness and hogging flexural resistance of the semi-rigid STC joints with flush end plates are comparable to those of SCC joints. The ductility of the STC joints with a flush end plate is also comparable to identical SCC joints, providing that tensile failure in timber slabs can be avoided.

New equations for predicting initial stiffness and ultimate moment of flush end-plate connections

In this study, new equations are developed for predicting the initial stiffness and ultimate moment of flush end-plate connections (FECs). FECs exhibit partially restrained behavior, which affects the distribution of forces and the displacement of a steel frame. Thus, the influences of the nonlinearity of connections on second-order moments are incorporated into structural analysis. FECs bolted to column flanges and welded to beams are investigated. The experimental data of FECs are collected, including initial stiffness and ultimate moment. Finite element analyses are used for analyzing the mechanical behavior of FECs and identifying the fracture mechanism of FECs. The finite element model of FECs is developed using ABAQUS software, and it is verified through comparison with the experimental results of previous studies. The mechanical behavior of FECs is investigated. An improved semi-empirical equation for the initial stiffness is suggested, and it provides good accuracy. A new type of fracture mechanism for FECs is suggested. An equation for estimating the ultimate moment is derived from the suggested fracture mechanism, and it shows good agreement with experimental data.

The Influence of Steel Connection on Fire Resistance of Composite Steel-Framed Buildings

Steel connections play a significant part in enhancing the robustness of structures in the event of a fire. Therefore, it is important to examine the impact of steel connections on the fire resistance of composite steel framed buildings. In this paper, both the behaviour of steel connections and their effect on composite steel frames are analysed using the non-linear finite element computer software VULCAN at various temperatures. The chosen frame is subjected to ISO834 fire. A comparison between end plate connections, pinned connection and rigid connection has been carried out. By applying different compartment fires, some cases are studied to show the behaviour of steel connection when the fire is applied at certain beams. In addition, different plate thickness has been analysed to examine the behaviour of the chosen steel connection under ISO834 fire. From the analytical results, it was found that the beam with extended end plate is stronger and has better performance in terms of axial forces than those beams with flush end-plate connection. Furthermore, that extended end plate connection has highest limiting temperatures compared to the flush end plate connection. In addition, it was observed that the performance of end-plate connections is very close to rigid connection and very far from pinned connections. Furthermore, plate thickness has less of an effect on the influence of steel connection in regards to fire resistance. The article will conclude that the behaviour of composite steel framed buildings is largely dependent on the steel connection due to their high impact under fire condition. It is recommended to consider the extended end-plate in the design proposals because of its higher fire resistant properties compared to the flush end-plate connection. Finally, this paper shows that steel connection has an important effect on the fire resistance of composite steel framed buildings.

Moment-rotation-temperature model of semi-rigid cruciform flush endplate connection in fire

This paper aims to develop a model for predicting the moment-rotation-temperature (M-R-T) relationship of semi-rigid cruciform flush endplate (CFEP) connections in fire. For this purpose, a nonlinear finite element (FE) analysis was conducted to simulate the CFEP connections in the fire using ABAQUS. The FE model was verified with the experimental results conducted by others. Based on the validated FE model, a parametric study was carried out by considering effect of several parameters, such as the number of bolt rows, column section, beam section, distance of bolt rows, gauge distance, endplate thickness, bolt diameter, yield and ultimate stress of column, yield and ultimate stress of beam, yield and ultimate stress of endplate, yield and ultimate stress of bolt, and moment ratio. Accordingly, the results of the parametric study were used to establish the M-R-T model of CFEP connections at both ambient and elevated temperature. The performance of the M-R-T model was compared with the test results in the literature. The comparative study showed that the proposed model can accurately capture the M-R-T relationship of CFEP connections in fire.

Seismic Behavior of a Novel Blind Bolted Flush End-Plate Connection to Strengthened Concrete-Filled Steel Tube Columns

Modified blind bolts (Hollo-Bolt) and a locally strengthened steel tube column in the panel zone were created to overcome the moment-resisting problem for the bolted connections between concrete-filled hollow section columns and open section beams and to enhance the performance of connections. The cyclic loading was conducted on a total of six modified anchored blind bolted flush end-plate connections to concrete-filled steel tube (CFST) columns. The key parameters investigated were the tube wall thickness, end-plate thickness, blind bolt anchorage method, and beam section. The failure mode, hysteretic behavior, strength, stiffness, ductility, and energy dissipation capacity of the connections were analyzed and evaluated with all details. The results indicated that connections with modified anchored blind bolts and locally strengthened steel tubes could avoid the premature failure of CFST column and exhibit an improved behavior with a favorable strength, stiffness, and stiffness degradation. The test observations reveal two representative failure modes, and the tube wall thickness and blind bolt anchorage method have a significant effect on the resultant failure mode. Moreover, the use of thin endplate and weak beam can effectively enhance the hysteretic behavior of joints, ductility, and energy dissipation capacity; and the change in anchoring method has little effect on the stiffness. Finite element (FE) analysis models were established for the aforementioned connections. The numerical models were validated against the experimental results and exhibited good agreement. Finally, based on the component method, an initial stiffness calculation method was established for the connections.

Influence of link length on re-centring capability of dual eccentrically braced frames

Repair costs and downtime of a structure hit by an earthquake can be reduced, by implementing the concepts of removable dissipative members (bolted links which are intended to provide the energy dissipation capacity and to be easily replaceable) and re-centring capability (which is provided by the more flexible moment resisting frames) in a dual structure, obtained by combining steel eccentrically braced frames (EBFs) with removable bolted links, with moment resisting frames (MRFs). The seismic performance, re-centring capability and link replacement feasibility of a dual re-centring EBF with removable flush end-plate bolted links were already studied and experimentally validated. In this case, very short shear links were used in order to achieve the flush end-plate connection over-strength, so the connection can be kept elastic in order to make the link removal possible. Re-centring capability of EBFs with other types of removable links has not been yet approached. One of the main objectives of an ongoing research project is to extend the validation of re-centring capability and link replacement feasibility on extended end-plate bolted links. This type of connection geometry provides a larger connection capacity, thus shear links can be designed longer. The present paper numerically investigates the influence of using different link lengths (and connection detailing) on the recentring capability of two height levels structures.

Seismic performance evaluation of a novel bolted flush end-plate beam splice connection

This paper describes a three-dimensional (3D) finite-element (FE) model developed to assess the seismic behaviour of a novel prefabricated beam-to-beam connection termed a double-bolted flush end-plate beam (DBFEB) splice connection under cyclic loading. The seismic response was analysed and evaluated in terms of the hysteretic behaviour, rigidity, resistance degradation, ductility, energy dissipation capacity and equivalent damping coefficient. It is shown that the required performance can be achieved by controlling the end-plate thickness as well as the bolt grade and diameter; these parameters were therefore chosen as the key geometric variables investigated here for parametric study. Also this type of new connection provided an appropriate level of strength and stiffness and can be categorised as a semi-rigid connection based on Eurocode 3, as investigated in the previous work published by the authors. Subsequently, a bilinear simplified hysteretic moment–rotation (M–θ) model for the DBFEB connection was proposed and its defining parameters were obtained by conducting several parametric analyses on the results of the 45 most proportional 3D FE model specimens of this type of connection that were selected for the regression analysis.

Improved steel frame performance against progressive collapse with infill panels

Local failure of one or more components due to abnormal loading can induce progressive collapse of a building structure. Herein, improved structural robustness is targeted to improve steel frame performance against progressive collapse. A multi-scale analysis model is constructed; then, the anti-collapse performance of a plane steel frame structure with a flush end plate connection is comprehensively analyzed using nonlinear static analysis. To enhance the anti-collapse capability of the steel frame structure, reasonable addition of infill panels in indirect- and direct-influence areas is proposed. Infill panels properly arranged in direct influence area can give full play to the Vierendeel mechanism, and effectively improve combined ability of the remaining structure. And then 1/8–1/6 of the net span is recommended as the length of the infill steel panel for the steel frame structure with flush end plate connection.

Cyclic behaviour of infilled steel frames with different beam-to-column connection types

Although numerous researchers demonstrated the significant difference in performance between the various beam-to-column connection types, most of the previous studies in the area of infilled steel frames focused on the behaviour of frames with welded connections. Therefore, there is a need for conducting studies on infilled steel frames with other common connection types (extended endplate with and without rib stiffeners, flush endplate and shear connections). In this paper, firstly, a two-dimensional finite-element model simulating the cyclic response of infilled steel frames was presented. The infill-frame interaction, as well as the interactions between connections' components, were properly modelled. Using the previously-validated model, a parametric study on infilled steel frames with five different beam-to-column connection types, under cyclic loading, was carried out. Several parameters, including infill material, fracture energy of masonry and infill thickness, were investigated. The results showed that the infilled frames with welded connections had the highest initial stiffness and load-carrying capacity. However, the infilled frames with extended endplate connections (without rib stiffeners) showed the greatest energy dissipation capacity and about 96% of the load-carrying capacity of frames with welded connections which indicates that this type of connection could have the best performance among the studied connection types. Finally, a simplified analytical model for estimating the stiffness and strength of infilled steel frames (with different beam-to-column connection types) subjected to lateral cyclic loading, was suggested.

Numerical investigation of semi-rigid connection ultimate capacity

With the advances in computational analysis techniques and development of new design methods, new interests have arisen in structural engineering. In the last few years, with the increasing numbers of terrorist attacks, the study of robustness, progressive structural collapse and ultimate resistance of structures has grown exponentially, with various studies being published all over the world. In order to perform this study through computational analysis, it was necessary to develop a calibrated numerical model capable of representing the behaviour of structures in their final stage of resistance. This article presents an evaluation of semi-rigid connections through a numerical model considering the implementation of collapse and damage progression criteria calibrated against experimental tests. Afterwards, a parametric study was developed by varying the bolt diameters and endplate thickness of a flush endplate semi-rigid connection. The main parameters and criteria that rules the simulation of flush end-plate joints subject to damage were assessed, allowing that many different kind of studies with similar components could be performed, such as impact, explosion and column loss analysis. As an outcome, the bending moment-rotation curves of these connections are presented and it is shown that those with a larger bolt diameter were able to produce greater rotation, while an increase in the endplate thickness was able to provide a greater bending moment capacity.

Experimental and numerical behaviour of blind bolted flush endplate composite connections

This research presents an experimental investigation and finite element model on the performance of composite beam-to-column flush end plate connections utilising blind bolts. Previous research recommended improvements to the design of these connections if they are required to withstand a low probability high consequence earthquake of a 1-in-2500 years return period. Therefore, two full-scale sub-assemblages of cruciform composite joints were tested under static and cyclic loading. The test results were used to establish the load-displacement characteristics of the connection. The experimental results demonstrated improved stiffness and strength when compared with a previous study. Two finite element models were developed and validated with the experimental data. Parametric studies were performed to investigate the influence of the thickness of equal angles, end plate thickness, shear connection ratio, reinforcement ratio and slab thickness on the connection behaviour.

Component tests and numerical simulations of composite floor systems under progressive collapse

This paper presents experimental and numerical studies on the behaviour of components and composite floor system under column removal scenarios. Shear connectors, double angle-cleat connections and flush end plate connections were extracted from a three-dimensional composite floor system and tested under different loading conditions. The load-displacement curves of these components were compared with the results predicted from existing models. A simplified numerical model was developed to simulate the behaviour of composite floor systems subject to progressive collapse, in which the properties of springs were determined from component tests. The model was then validated against experimental results in terms of load-displacement relationship and failure mode. Finally, parametric studies were conducted to investigate the effects of slab thickness, aspect ratio and reinforcement. Numerical results suggested that the aspect ratio of slabs has the most significant effect on the load capacity of composite floor systems under progressive collapse scenarios.

Flush Endplate Connections in Fire: Time-Dependent Behavior of Tension Bolts

Steel connections play a crucial role in maintaining the integrity and stability of steel building frames especially when exposed to fire temperatures. The behavior of flush endplate connections in fire is shown to be governed by tension bolt failure as bolts lose their strength and stiffness more rapidly at higher temperatures. As a result, the ability to predict the development of stresses in tension bolts of flush endplate connections at different stages of fire is of special importance. One of the factors influencing bolt stresses in fire is the thermal creep or time-dependent inelastic response of steel to elevated temperatures. Therefore, time- and temperature-dependent behavior of tension bolts of flush endplate connections in fire is the focus of this study. Stress-time histories in tension bolts are obtained by explicit consideration of thermal creep of steel in FE models of flush endplate connections at elevated temperatures. To better understand the effect of thermal creep on tension bolt behavior, the correlation between time-dependent rotational deformation of flush endplate connections and bolt stresses is also investigated. Further, the isochronous representation is utilized to study the rotational deformation and the tension bolt stresses under various applied moments ranging from 50% to 95% of the moment capacity and fire temperatures ranging from 450°C to 600°C with 25°C increment. Through such representation, it is indicated that the connection behavior is not only dependent on bolt strength degradation and applied moment, but also affected by the time duration of applied moments and temperatures. Also, with the inclusion of thermal creep of steel, the connection experiences higher rotation and excessive endplate deformation with stress relaxation leading to top tension bolt failure at earlier stages of fire. More specifically, for time exposure greater than or equal to 60 min, the failure temperature of the connection decreases from 600°C to around 550°C. Therefore, neglecting thermal creep of structural steel may result in an unsafe prediction of the overall response of flush endplate connections in fire.

Behaviour of End-Plate Connections in 3D Frames Under Fire Conditions: Experimental Study

Due to high vulnerability of steel structures to elevated temperatures and the need for taking adequate and effective measures to reduce human and financial losses in fires, a thorough understanding of such behaviour is of utmost importance. In this research, a half-scale 3D model, comprising moment-resisting frames, equipped with flush end-plate connections, in one direction, and braced frames in the other, was subjected to a scaled ISO 834 standard fire. The maximum attained temperature was 1055 °C. The results showed that the structure tolerates high temperatures for an appreciable amount of time before collapsing. Moreover, for thick flush end-plates, which were used in this study, the collapse was initiated by bolt failure, giving rise to the idea of using more/stronger bolts and weaker end-plates to delay the overall collapse of the structure.

Study on the Influence of Connection Configuration on Composite Joints

Steel–concrete composite joints possess higher bearing capacity, initial stiffness and redundancy than bare steel joints. The configuration of beam-column connection would influence the behavior of composite joints, such as rigidity, rotation capacity and so on. In this paper, the test of two fully welded rigid composite joints and two flush endplate semi-rigid composite joints was introduced. The loading conditions in the tests involved sagging moment and hogging moment. The mechanical behavior of composite joints under bending moment was studied in detail, especially on the influence of connection configuration. The test results indicated that the experimental phenomena and failure mode of fully welded composite joint and flush endplate composite joint under hogging moment were similar to each other. The buckling of bottom flange of steel beam determined the behavior of composite joint under hogging moment, such as initial stiffness and bending strength. It indicated that using flush endplate connection instead of fully welded connection in composite joints had little influence on the behavior of the joint under service loads if the failure mode of joints is governed by the same component. Four models for moment-rotation relation of composite joints are compared with experimental results. Based on the comparison, a new combination model of power function expression and linear expression is developed. With proper optimum shape parameter and descending stiffness, the new model could present the moment-rotation relation of composite joints, regardless of connection configuration or loading condition.

APPLICATION OF PARTIAL STRENGTH CONNECTION IN THE DESIGN OF MULTI-STOREY BRACED STEEL FRAME USING TRAPEZOIDAL WEB PROFILED SECTION

Eurocode 3 offers the opportunity to design steel frames as „semi-continuous‟ by including the moment resistance of „partial strength‟ connections in plastic hinge analysis of the frame. Semi-continuous construction with partial strength connections offers many benefits for braced frames such as shallower and lighter beams, standardized connections with less complicated geometry, and more robust frames than simple construction. It is expected to give significant savings in frame weight. This paper presents findings on a series of two-bay, four-bay and six-bay braced frames of two-, four-, six- and eight-storey with span ranging from 6 m to 9 m by comparing between Hot-rolled (HR) steel beams designed using simple construction and Trapezoidal Web Profiled (TWP) steel beams designed using the semi-continuous construction method. Flush end-plate and extended end-plate connections were used as partial strength joints whereas for the simple construction, partial depth flexible end-plate connections were used as pin joints. The semi-continuous design method can reduce the frame weight between 13.4% and 20.5% compared to simple construction.

Three-dimensional numerical and linearly distributed multi-parameter fitted analytical modeling of hybrid beam–column with partially welded flush end-plate connection

The flexural behavior of partially welded flush end-plate connections incorporating built-up hybrid beams and columns is analytically and numerically investigated. An experimentally obeying three-dimensional finite element model is first constructed. To circumvent the laborious effort of three-dimensional simulation and experimental work, a new experimentally and numerically complying equation approach is introduced for the construction of a continuous moment–rotation ( M–θ) description. For the proposed equation, two essential terms are required: the rotational stiffness, Sj,ini, obtained by employing the component method and the maximum moment, Mmax, produced using the proposed linearly distributed multi-parameter fitting technique. To demonstrate the applicability of the proposed equation, a variation in the geometric configuration of connections within the practical range is considered. Excellent agreement is noted when comparing all M–θ relationships produced by the proposed equation to those by the finite element method and experiments. In addition, the stress distribution and main deformation modes are numerically obtained, where the ranking of stress criticality is offered for all structural parts. The depth, width, flange, and web thicknesses, as well as the yield stress of the beam, have a major influence on Mmax, as predicted by the proposed equation. Also, bolts have been identified as the most critically stressed component.

Time-Dependent Response of Flush Endplate Connections to Fire Temperatures

AbstractThis paper summarizes results of a comprehensive computational study on the time-dependent or creep behavior of flush endplate beam-column connections subjected to elevated temperatures due...

Structural Performance of Isolated Steel Beam-to-Column Connection

The present study attempts to determine the main characteristics of a new proposed steel connection retrofitted by an elastomeric isolator. Its stiffness, strength, and ductility are investigated. The elastomeric isolators were designed according to the Japanese Society of Base Isolation with the aim of improving the energy dissipation of the connection. Experimental tests were conducted to evaluate the moment rotation (M-θ) curve of the proposed connection as well as of fully-rigid (SidePlate) and semi-rigid (flush end-plate) connections. The behaviour of beams with flexible and fixed-end connections was also studied by classical methods of analysis. The initial stiffness and classification index of the connections were identified by an analytical calculation in compliance with the methods suggested by Eurocode 3 Part 1-8 and ANSI/AISC 360-10. The results confirmed that the new proposed connection can be classified as a flexible connection in terms of its initial stiffness; however, it developed 90% of the plastic moment capacity of a connected beam. Besides, it showed that the isolated connection did address the AISC drift angle capacity requirement of θSD for a special moment frame (SMF).