Connected Steel Frames Research Articles

Cyclic moment-rotation model for bolted double-angle connections with composite floor systems

This paper presents a simplified moment-rotation model for cyclic response of bolted double-angle beam-to-column connections in composite steel frames with concrete on metal decking floors. The proposed model employs mechanics-based equations to determine model parameters, along with empirical observations from previous studies and data from recent large-scale multi-bay frame experiments. Several design variables and construction details, such as orientation of the metal decking, concrete reinforcement layout, and deck splicing details around the connection, were considered in the proposed model. Comparisons between the connection model and experimental results showed reasonable agreement in moment-resisting capacity up to 8% interstory drift. Notably, the proposed model adequately simulated varying responses based on connection details not captured by existing moment-rotation models. Analyses of 2- and 4-story frames using the proposed model showed up to 1.3 times higher ductility and 47% lower initial rotational stiffness compared to those using the existing ASCE 41 connection models with strengths of 20% and 35% of the plastic moment capacity of the girder. These results indicate the potential overestimation of stiffness and moment-resisting capacity, and the underestimation of ductility when using existing moment-rotation models due to insufficient modeling parameters to represent actual behavior. Therefore, the proposed model demonstrates its applicability in incorporating various design variables and construction details of bolted double-angle connections with composite concrete on metal deck floors. This model can be used to account for the non-negligible strength and stiffness of bolted double-angle connections in steel gravity framing under seismic loads.

Seismic behaviour of self-centring hybrid steel frames equipped with SMA plates under mainshock–aftershock sequences

This paper focuses on the mechanical behaviour, seismic application in steel frame connections and steel structure of shape memory alloy (SMA) plates. This study commenced by examining the hysteretic response of SMA plates subjected to cyclic tension tests, considering two different loading paths. Subsequently, a self-centring steel frame connection equipped with SMA plates and washers (SC-PW) was examined via quasi-static cyclic loading tests, and comparatively satisfactory self-centring behaviour was observed. However, the degradation of the initial stiffness of the SC-PW due to an initial imperfection was observed. An improvement strategy was proposed to overcome the degradation of the hysteretic behaviour (e.g., initial stiffness) of the SC-PW. Disc springs with a larger stiffness and preloads were introduced to overcome the degradation of the initial stiffness of the SC-PW, and the validation was confirmed via detailed finite element (FE) analyses. To improve the computation efficiency, a simplified FE model was developed to reproduce the hysteretic responses of the connection. Based on the simplified FE model, a six-storey prototype structure, i.e., a self-centring hybrid steel frame (SCHSF), equipped with the improved connection was developed, and the structural dynamic responses were investigated via nonlinear response history analyses, where mainshock–aftershock sequences were considered. The influence of the SMA material properties on the seismic behaviour of the prototype structure was investigated.

Experimental study on seismic behavior of high strength steel flange-plate connections with box columns

The flange-plate beam-to-column connections are a promising option for reinforced moment-resisting connections in ductile steel frames and have potential applicability in high strength steel frames. However, there have been few investigations on flange-plate connections with high strength steel box columns. In this study, experiments were conducted to evaluate the seismic behavior of high strength steel flange-plate connections with box columns. Seven specimens were designed and tested under anti-symmetrical cyclic loads, comprising three different combinations of Q355 or Q460 steel beams and Q460 or Q690 steel columns. While the expected beam failure mode was observed in five specimens, two specimens experienced ESW joints failure, and one specimen experienced CJP weld failure. These findings highlight the possible impact of welding quality defects in engineering applications. The test results about bearing capacity, rotation stiffness, deformation capacity, and energy dissipation were reported and analyzed. Under the similar design conditions, the use of higher strength steel members results in a decrease in the initial stiffness of the specimens, as well as changes in yielding modes, deformation proportion, and energy dissipation capacity. Six flange-plate connections met the deformation and bearing capacity requirements for special moment frames in AISC 341 with the ultimate story drift angle not less than 0.06 rad. The proposed criteria for determining the minimum size of flange plates was verified in this study, and design recommendations were made for flange-plate connections in high strength steel frames.

Large-size shape memory alloy plates subjected to cyclic tension: Towards novel self-centring connections in steel frames

In this study, the hysteretic behaviour of shape memory alloy (SMA) plates under cyclic tension-release loadings was examined to promote their seismic applications, with an emphasis on large-size SMA plates with different geometries. Based on a series of SMA plate coupons extracted from base plates with different geometries, the thermal characteristics were investigated, and the phase transformation behaviour of the SMA plates was characterised. Subsequently, cyclic tension-release tests were conducted on the SMA plates in the laboratory, and the key mechanical performance indexes including the transformation strength, post-yield behaviour, self-centring capabilities, and energy dissipation abilities were carefully investigated. According to the results, SMA plates have a comparatively encouraging self-centring ability and moderate energy dissipation capabilities within a specified strain range. However, larger SMA plates show less satisfactory self-centring behaviour and are prone to brittle fracture at the edges. Based on the test programme, a numerical investigation was conducted to offer further insight into the potential applications of large-size SMA plates in the seismic field. A practical modelling procedure, namely the hybrid finite element (FE) modelling technique, was proposed and used to reproduce the degradation and cumulative residual deformation in the SMA plates. Moreover, nonlinear response history analyses (NL-RHAs) were performed on a prototype steel frame equipped with SMA plates in the connections to verify the feasibility of using large-size SMA plates in steel structures.

Location of semi-rigid connections effect on the seismic performance of steel frame structures

In design steel frames, combining semi-rigid and rigid connections can result in better structural performance, particularly in seismic locations. In this study, the effects of semi-rigid beam-to-column connections located on the seismic performance of steel frame structures are investigated. The analysis uses six and twelve-story moment resisting steel frames (MRSF) with rigid, semi-rigid, and dual beam-column connections. These frames are designed according to the Egyptian design codes. Drain-2Dx computer program and seven earthquake ground motions are used in the non-linear dynamic analysis. The rotational stiffness of beam-to-column connections is indicated through the end fixity factors with a value equal to 0.6. The performances of these frames are evaluated through the roof drift ratio (RDR), the maximum story drift ratios (SDR), and the maximum column axial compression force (MACF). The results indicated that the quantities of fundamental periods, roof drift ratio, the story drift ratio, and the column axial compression force are related to stiffness, rigidity, and the number of semi-rigid connections in steel frames.

Evaluation of machine learning models for load-carrying capacity assessment of semi-rigid steel structures

The paper investigates the potential application of machine learning methods to estimate the load-carrying capacity of semi-rigid connected steel structures. The database is developed using the advanced analysis based on beam-column and zero-length elements. The input variables are member cross-sections and parameters of the high-order nonlinear functions describing semi-rigid connection behaviors. Twelve machine learning algorithms, including three linear regression models, support vector machines, deep learning and seven tree-based ensemble algorithms, were evaluated. Three practical semi-rigid connected steel (including two-dimensional planar and three-dimensional space) structures were studied. The numerical results revealed that the distribution of the load-carrying capacity responses of the structures was non-normal and heavy-tailed. The class of linear regression methods was less efficient than the tree-based ensemble algorithms. Among the seven tree-based ensemble approaches, the extreme gradient boosting method presented the best performance in determining not only the lowest (mean squared, mean absolute and mean absolute percentage) errors but also the highest coefficient of determination. It was followed by the light gradient boosting machines and categorical gradient boosting algorithms. Three linear regression methods (linear regression, Lasso and Ridge), light gradient boosting machines, categorical gradient boosting and extreme gradient boosting provided the competitive computing cost. The extreme gradient boosting algorithm was therefore recommended for the accurate prediction of load-carrying capacities of semi-rigid connected steel frames.

Experimental study on mechanical behavior and resilient performance of steel frame connection with low-yield-point steel fuses

In order to avoid the brittle failure of welded region at the beam-column connection of steel frame under strong earthquake action and achieve resilient objective, the steel frame connection with replaceable low-yield-point steel cover plates (SF-LYCP) was developed. Cyclic tests were conducted on original and repaired full-scale specimens to explore the mechanical behavior and quick recovery performance. The various materials and configurations of cover plates were focused on. The failure modes, strain development, global and local hysteresis curves, energy dissipation behavior and the replacement performance of the damaged fuses were comprehensively compared. The results showed that the cover plates of specimens with the same weakening degree (C-LY100, C-LY160, C-Q235B and C-Q345B) all played the role of structural fuses through concentrating the damage and protecting the primary frame members. The SF-LYCPs had plumper hysteresis curves, more accumulated energy dissipation and superior ductility. The damaged low-yield-point steel cover plates of C-LY100 and C-LY160 were replaced within only 50 mins to form the repaired specimens under laboratory conditions, proving the possibility of recovery. The performance of the structures with replaced cover plates basically coincided with the one of the original structures, which satisfied the design objective of resilience.

Effect of Semi-Rigid Joints on Design of Steel Structure

Abstract: Limit state design method has presented a new era of safe and economic construction for steel structures. New standard IS 800:2007 for design of steel structures has provided an opportunity for modern design philosophy, design specifications and provisions as per Limit State Method of design in our country. In design of steel structures, steel connections are important elements for controlling behaviour of structure. It is essential that to understand behaviour of steel frame, connectors are required to develop full or a little higher strength compared to members being joined in order to achieve a safe and an economical design. A connection rotates through angle Or caused by applied moment M. This is angle between beam and column from their original position. Several moment-rotation relationships have been derived from experimental studies for modelling semi-rigid connections of steel frames. These relationships vary from linear model to exponential models and are nonlinear in nature. Connections possess semi rigid end conditions in actual behaviour. In the present dissertation, the effect of semi rigid joints on design of steel structures is studied. The behaviour of semi rigid connections and its modelling is discussed. The analysis of the frames is done using ANSYS 2016 and the comparative results of rigid, semi rigid and pinned end conditions has been presented in graphical form. From the results of analysis the design of various semi rigid connections is carried out. Further buckling analysis of stepped columns has been carried out in order to obtain effective length parameters for semi-rigid connections. The design examples has been solved using AISC and IS 800-2007. The comparison is done for fixed, semi rigid and pinned end condition. Keyword: semi-rigid joint, frame analysis, rotational stiffness, buckling length, genetic algorithm.

Seismic behavior of hollow-core infilled steel frames; an experimental and numerical study

This study describes an experimental program designed to investigate the influence of the presence and orientation of hollow-core wall panels as well as beam to column connection rigidity on the seismic performance of steel frames infilled with hollow-core wall units. For this purpose, four half-scale, single-story, and single-bay specimens, including three infilled steel frames and one bare moment frame, were subjected to cyclic lateral loading. The bare steel frame and two infill specimens had rigid connections, while the last one had pinned connections. One of rigid connections specimen was constructed with hollow-core wall panels placed vertically, whereas the other was fabricated with wall panels with the horizontal core. The experimental results indicated that the vertical placement of hollow-core wall units controlled structural damage and improved the seismic performance through the rocking mechanism within the steel frame. In addition, the strength, stiffness, and energy dissipation capacity of the infilled pinned connections frame were less than those in rigid connections specimen. In another part of this study, a parametric study was conducted with finite element method using ABAQUS software. The parametric nonlinear analyses study revealed that the infilled frames with hollow-core wall panels placed vertically had less initial stiffness and more strength than those with horizontal core panels. On the other hand, the initial stiffness and strength of the infilled steel frame, bare steel frame, and infill contribution were reduced by the decrease in the rigidity of the steel frame connections, regardless of infill aspect ratio and the relative stiffness of the hollow-core panels to the surrounding steel frame.

Static experimental analysis and optimization of innovative pre-engineered tubular section beam-column connections in cold-form steel frames

The lack of connection configuration forms is one of the main bottlenecks, restricting the application of pre-engineered lightweight cold-form steel structures with tubular steel section. In this study, two innovative pre-engineered tubular steel section beam-column connections (namely JD1 and JD2) were proposed and designed in terms of the configuration and geometry. The developed finite element modeling of the proposed connections was implemented, and the refined finite element model was confirmed by comparison to static loading tests of two types of connection joints, JD1 and JD2. The mechanical properties and the geometry effect of the components of the JD1 and JD2 were systematically analyzed to determine the optimized configuration. The bearing capacity and stiffness of connection JD2 with upper and lower ribbed angle steels increased by 45.2% and 71.2%, respectively, compared to those of connection JD1 with lateral angle steels. The bearing capacity of the newly designed pre-engineered connection is close to that of the traditional welded joint. Nevertheless, the initial stiffness of the welded joint is obviously larger than that of the connections JD2 and JD1. The new pre-engineered fabricated connection was systematically compared with the traditional welded connection in terms of the construction convenience, economy, and mechanical properties. The connection form can be comprehensively considered based on the mechanical performance and construction requirements in construction applications.

Evaluation on story-based stability in multistory frame under various restraining conditions

To estimate the critical buckling load, the effective length approach isolates a critical column inside a frame and analyses the rotational and translational stiffness of its end restraints. Although designers proportion leaning columns with K = 1, which is the correct K-value based on the column failure mode, buckling analysis fails to predict these values due to the influence of nearby columns and beams. In current design practise, beam-to-column and column-base connections in steel frames are typically idealised as wholly pinned or totally stiff connections. Various studies have demonstrated, however, that the semi-rigid behaviour of the systems beam-column connections affects the internal efforts in the structural parts, therefore the buckling critical loads and corresponding effective lengths of the compressed elements were also taken into account. In this study, a numerical analysis of the Effective length of column in multi-storey frames with single bay and dual storey (G + 2) is tried with variation in storey heights using rigid and semi-rigid jointed frames with rigid and semi-rigid jointed frames is undertaken. Webber's empirical equations are efficient in rigid frame systems for calculating the effects of adjoining columns and their critical buckling loading of the isolated column. The effective length K factor with the variance in critical length with different storey heights acquired a greater value when compared to other models. Moment rotations in semi-rigid jointed frames were influenced by differences in fixity factors in semi-rigid frames. The rigidity coefficient dropped as the stiffness coefficient increased, leading in an increase in the effective length factor.

Cost-based optimization of steel frame member sizing and connection type using dimension increasing search

Cost-based optimization of steel frame member sizing and connection type using dimension increasing search

Seismic Fragility Curves for Performance of Semi-rigid Connections of Steel Frames

A steel frame with a semi-rigid connection is one of the most widely used structural systems in modern construction. These systems are cheap to make, require less time to construct and offer the highest quality and reliable construction quality without the need for highly skilled workers. However, these systems show greater natural periods compared to their perfectly rigid frame counterparts. This causes the building to attract low loads during earthquakes. In this research study, the seismic performance of steel frames with semi-rigid joints is evaluated. Three connections with capacities of 50, 70 and 100% of the beam’s plastic moment are studied and examined. The seismic performance of these frames is determined by a non-linear static pushover analysis and an incremental dynamic analysis leading finally to the fragility curves which are developed. The results show that a decrease in the connection capacity increases the probability of reaching or exceeding a particular damage limit state in the frames is found. Doi: 10.28991/cej-2021-03091714 Full Text: PDF

Experimental Research on Mechanical Performance of New Modular Steel Frame Joint

Aiming at the problems of large interlayer displacement angle and low rotational stiffness of modular steel frame connection nodes, a new type of grouted interlayer joint was proposed, and the experimental study was carried out to observe the failure form and mechanical performance of the node. In order to study the stiffness and bearing capacity characteristics of the new grouting interlayer connection, 4 different joint specimens were tested and studied. The influence of the bolt connection at the node on the bearing capacity, rotation stiffness and ultimate rotation capacity of the grouting node is analyzed. The test results show that the bolt connection can ensure the integrity of the node and improve the stiffness of the node; Whether the column is filled with concrete has little effect on the mechanical properties of bolted joints, but has a more obvious effect on boltless joints, and the initial stiffness is increased by 20%.

Study on seismic performance of prefabricated self-centering beam to column rotation friction energy dissipation connection

Under severe earthquakes, a significant number of unexpected plastic hinges and brittle failure were found in conventional rigid beam to column welded connections of steel frames. To improve the seismic performance of steel frames, an innovative prefabricated self-centering beam to column (SCBC) connection was proposed and experimentally validated in this paper. The SCBC connection consisted of disc springs at the bottom flange of beam and a rotation friction hinge (RFH) at the beam end. The bottom disc springs could not contact with slab systems and provided restoring moment, whereas the RFH was designed to dissipate seismic energy. Firstly, its configuration form and design methodology were introduced. Then cyclic tests of a 1/4 scale SCBC connection specimen was carried out and the responses of the SCBC connection was compared to that of the RFH. Finally, the restoring force model of the SCBC connection was established through theoretical analysis. The experimental and analytical results demonstrated full flag-shaped hysteretic curves of the SCBC connection under cyclic loadings, verifying the desirable energy dissipation capacity and reliable self-centering capability of the SCBC connection. The calculation results based on the restoring force model were in good agreement with the test results, showing that the proposed restoring force model could reasonably predict the hysteretic behavior of the SCBC connection.

Experimental Study and Numerical Simulation of Plane Steel Frame with Rubberized Connecting Technology Subjected to Seismic Effect

This paper representsexperimental and numerical study the behavior of the rubberized steel frame connections. One single-bay, one-story without elastic buckling are cyclically tested. The experimental specimens are simulated and analyzed by the ABAQUS program. Four specimens of steel plane portal frame are investigated under horizontal reversed cyclic loads. The specimen connections are developed by using different diameters of composite steel bolts/rubberinstead of conventional steel bolts to connect the beams with columns. The yield and ultimate strength, ductility, envelope curves, and damping ratio of these specimens are analyzed and compared. The finite element method is used to establish and verify the results of the laboratory test. The results of the experimental and numerical tests gave a large load-carrying capacity, reduction in the stresses, excellent ductility and energy dissipation capacity, and remarkably improved damping ratio.

A Study on the Application of Two Different Material Constitutive Models Used in the FE Simulation of the Cyclic Plastic Behavior of a Steel Beam-Column T-Stub Connection

Seismic actions inevitably cause cyclic plastic deformations in steel frame connections, which is a common cause of failure in steel structures. Nonlinear finite element (FE) static analysis has been employed in the study of the cyclic plastic behavior of a T-stub connection based on the reported cyclic test on the corresponding extensively tested T-stub connection made of Q235 steel. In particular, the isotropic-hardening and Chaboche constitutive models were employed to predict both the stress distribution and plastic development on the T-stub and the hysteretic curves of the entire T-stub connection. The two constitutive models were calibrated by four material tests to describe the yield and hardening behaviors of the Q235 steel used to make this T-stub connection. The two sets of simulation results obtained from the simulations of the two FE models employed by the two different constitutive models were compared with each other and with the experimental results. The comparisons reveal that the simulation results are similar and in good agreement with the experimental results when the cumulative plastic deformation in the T-stub is small. However, the results of the FE analysis using the Chaboche model are in better agreement with the experimental results when the cumulative deformation in the T-sub is large. This study can provide a reference for FE simulation of the cyclic plastic behavior of steel connections, including the T-stub connection.

Behavior of Connections in Cold-Formed Steel Frames under Cycling Loading

AbstractCold-formed steel (CFS) sections can be designed in many configurations and, compared to hot-rolled steel elements, can lead to more efficient and economic design solutions. While CFS momen...

Experimental and numerical study on impact behavior of beam-column substructures of steel frame

In this paper, three welded flange-bolted web (WFBW) beam-column connections with three types of weld access holes (fan-shaped, enlarged and FEMA weld access holes) were experimentally examined under impact loading. The design of such connections was based on the North American seismic code FEMA350 and the Chinese design codes. The impact tests on of the connections were conducted to experimentally study the dynamic collapse of a steel frame under a column removal scenario. The dynamic responses including failure modes and time history process of the substructures were obtained and presented. Test results show that the weld access hole has a significant effect on impact behavior of the connections under impact loading. Different failure modes of the specimens were observed and discussed. The specimen with FEMA weld access hole is found to have a great advantage of improved structural ductility, impact resilience as well as energy dissipation and no obvious reduction of the plastic rotation capacity over the other two specimens. The specimens with enlarged and FEMA weld access holes show better rotation capacity to resist impact loads, while its ultimate rotation reach the seismic design limit in FEMA350 standard for WFBW connection. The steel frame with WFBW connection is difficult to give full allowance to catenary action due to the premature failure of connection. Furthermore, the finite element analyses give reasonable accuracy when compared with the test results. The simulation results can be used in the future to predict failure modes and ductile fracture of steel frame connections with different types of weld access holes.

Study on the Component-Based Model of an All-Welded Beam-Column Connection for Progressive Collapse Analysis

The mechanical behavior of all-welded beam-column connections of steel frames during progressive collapse was numerically studied using finite element simulations. The validation of the numerical model was based on a previous test model. The analysis results indicated that the stiffness of the all-welded beam-column connection in the elastic-plastic stage was mainly provided by the shear stiffness of the panel zone, and the axial compression on the column had a substantial impact on the capacity and ductility of the all-welded beam-column connection. An improved component-based model of the all-welded beam-column connection was proposed. To verify the accuracy of the proposed model, a beam-column assembly with an all-welded connection was established and the influence of the catenary action, column axial compression, beam-column stiffness ratio, and dynamic performance was parametrically analyzed. The validation results showed that the proposed model was able to simulate the behavior of all-welded beam-column connections at large structural deformation.