Moment Frame Connections Research Articles

Seismic Behavior of Steel Moment Frame Connections with Repairs in the Plastic Hinge Region

Seismic Behavior of Steel Moment Frame Connections with Repairs in the Plastic Hinge Region

Special moment frame connections with shear-yielding haunches

Steel special moment frame connections with shear-yielding haunches can be used for seismic retrofit and for new construction. In this study, shear-yielding haunch connections were investigated through experimental testing and finite element analysis. Three specimens were tested, each with a W1000 × 591 beam and W1000 × 554 column. The cyclically loaded specimens completed cycles at 0.04 rad prior to low-cycle fatigue of the haunch plates. The monotonically loaded specimen reached 0.064 rad drift. The experimental specimens had 10 to 15% post-yield stiffness, and the fuses reached the ultimate material strength prior to tearing. M-factors for the connection were determined to be 4.7 for life safety and 6.3 for collapse prevention. Finite element models were used to quantify force transfer through the connection and to investigate the retrofit-specific detail. The experiments and finite element models confirmed that a relatively simple design procedure produced acceptable designs.

Laboratory and ultra-low cycle fatigue evaluation of the seismic performance of BFP connection with different amounts of pre-tension in bolts

Bolted Flange Plate Moment Connections (BFP) are one of the most practical connections, used as prequalified connections in special steel moment frames. Using three full-scale BFP connections designed according to AISC, this paper has explored the effects of bolt pre-tension levels experimentally under SAC cyclic loading protocol. The bolt pre-tension level has been defined as α coefficient to indicate the pre-tensioning level in three specimens. The bolts of the first specimen were not pre-tensioned, called snug-tightened bolts, and considered as reference connections. The bolt pre-tension levels of the second and third specimens were established in accordance with the minimum and allowable limits of AISC design code and ultimate strength of the bolt, called pre-tensioned and fully pre-tensioned, respectively. The moment capacity, total energy absorption, and strain variation of the bolts have been investigated. Meanwhile, using the ultra-low cycle fatigue failure index obtained from experimental specimens, the capacity of modeled BFP connections in finite elements has been compared with the laboratory samples in terms of failure location and connection capacity. The experimental results revealed that final resistance in BFP connections occurs in the cycle of 7% of the drift angle of SAC protocol loading, and the location of the connection failure is around the farthest hole from the column, which is consistent with the failure results from ultra-low cycle fatigue in finite element modeling for BFP connections. The measure of moment resistance in the pre-tensioned connection (Both connections were minimum pre-tensioned according to the regulation and ultimate strength of the bolt) has increased by about 50% compared to the without pre-tensioned connection. The amount of energy absorption of the pre-tensioned connection with the ultimate strength of the bolt has increased by 176% of the energy absorption capacity of the connection without pre-tensioned and 14% of the energy absorption capacity of the connection with the minimum allowable pre-tensioning of the regulation. The extent of energy absorption in the three connections was equal to 38, 92, and 105 KJ.

Seismic performance of the RBS connection with trapezoidal corrugated web (TCW-RBS)

This paper presents an evaluation of the performance of the trapezoidal corrugated web (TCW) reduced beam section (RBS) connection under cyclic loading. A series of experiments were conducted on three TCW-RBS specimens. The tests were carried out up to a 10% story drift ratio, and it was observed that the connection met the code-based limitations for a reduction in strength until reaching an 8% drift, surpassing the existing criterion for qualified connections in special moment frames. Additionally, nonlinear finite element analysis was utilized to investigate the influence of web angles on the behavior of TCW-RBS connections. The findings revealed that increasing the web angle resulted in a decrease in the maximum moment by up to 11%, while simultaneously enhancing the connection's ductility by up to 37%. Furthermore, the axial strain results in the web of the beam indicated that the corrugated web had a negligible impact on the flexural behavior of the connection due to the accordion effect. Notably, the maximum strain values in the flanges near the column face were three times lower than those in the reduced section zone, contributing to a reduced sensitivity of the welds to potential fractures.

Seismic shear and flexural performance of new RCS joints with W-FDP, W-FBP, and small hoops

New through-beam joint details were developed for New high-strength Reinforced Concrete and Steel beam (New RCS) special moment frames. The columns hadfy = 690 MPa andfc′ = 84 MPa. The new joint details enhanced the joint strength for the large force demand seen in high-rise buildings in regions of high seismicity and minimized the construction difficulty associated with conventional joint transverse reinforcement. The new joint details included Wide Flange Doubler Plates (W-FDPs), Wide Face Bearing Plates (W-FBPs), and small rectilinear hoops. Three large-scale beam-column joint specimens with the proposed design details were tested using lateral cyclic loading to examine their seismic shear and flexural performance. Test results showed that the W-FDPs were effective in preventing joint bearing failure. Using W-FDPs, FBPs, or W-FBPs, and small hoops effectively mobilized the joint shear strength. The 2015 ASCE model modified to consider the proposed details provided a conservative estimation of the joint shear strength of the specimen that failed in joint shear. Moreover, the model was successfully used to design specimens to prevent joint shear failure and to produce desired beam-hinging behavior that met the requirement of AISC 341 for beam-column connections of special moment frames. The beam eccentricity did not significantly affect the hysteretic behavior of the specimen up to the 4% drift ratio.

Experimental and analytical performance of replaceable shear fuse connections for heavy beams

Experimental testing and finite element analysis were used to quantify the inelastic rotation capacity of replaceable shear fuse connections that exceed the current prequalification limits in AISC 358–22. Three experimental specimens with W1000 × 591 beams were tested per the procedures in AISC 341 Chapter K. Fuse plate geometry and the number of fuse plate bolts varied between specimens. All three specimens completed at least one cycle at 0.04 rad, with one specimen completing a cycle at 0.06 rad under the standard AISC special moment frame connection loading protocol. Using extra bolts on the fuse plate to match the bolts at the top flange in one configuration resulted in higher strains in the fuse yielding regions. Finite element models confirmed that about 90% of the moment at the face of the column was transmitted by the horizontal couple at the beam flange levels and that bolt lines should be more centered on the external connection plates. The connections had high post-yield stiffness and had strain hardening factors of up to 1.52. A more transparent procedure for addressing strain hardening in design was developed.

Performance Assessment of Hybrid Steel Frames under Near-field Seismic Excitations

Assessment of the seismic performance of steel structures is topical research for a variety of earthquakes. Moment-resisting rigid steel frames are generally designed and used for high seismic zones. However, the famous Northridge in 1994 and Kobe in 1995 earthquakes exposed the shortcomings of moment frames. During these events, the beam-column connections of rigid moment frames were severely damaged. Since then, an alternative of welded connections called bolted or semi-rigid connections is considered for designing or retrofitting of steel moment frames. From the last few years, the semi-rigid connections combined with rigid connections, termed as hybrid or dual frames have become widely popular for earthquake designers and engineers due to enhanced ductility and reduced cost of construction. Earlier research work was focused on far-field (FF) earthquakes, whereas, the near-field (NF) earthquakes are crucial for civil engineering structures. In this paper, an extensive numerical study is carried on rigid and hybrid steel moment frames for NF and FF earthquakes. For this purpose, a ten-story rigid steel frame is analyzed and designed for seismic requirements as per Indian Standards. The rigid connections of frames are replaced by semi-rigid connections with a moderate degree of semi-rigidity. The six different patterns (locations of semi-rigid connections) of hybrid frames are considered here to compare the seismic performance of hybrid frames under near field earthquakes. The nonlinear response-history analyses are executed using the SAP2000 software at two scaled PGAs defined as low (i.e., 0.2g) and high (0.5g) level. An ensemble of three time-histories, each for both types of earthquakes are considered for the numerical simulation. Response quantities of interest, namely, the maximum value of base shear, story displacement, inter-story drift ratio, the total number of plastic hinges, and the square root of the sum of squares of maximum plastic hinge rotations are considered for the decision of a most appropriate pattern for hybrid frames. The results of the numerical study indicate that the response behavior for the NF earthquakes is distinctly different both in nature and magnitude. It is observed that the seismic demands under the NF earthquakes are substantially more as compared to those obtained for FF earthquakes for all cases of hybrid frames. Further, it is also found that the pattern and number of semi-rigid connections in the hybrid frame have a vital role in seismic performance.

Experimental investigation on seismic behavior of steel welded connections considering the influence of structural forms

The traditional welded connections of steel moment frames are prone to brittle fracture in earthquakes due to the high stress concentration at the beam end, which significantly affects the seismic performance of steel frame structures. A novel type of steel connection with local structural forms is proposed to avoid brittle fracture. The proposed connection is developed by both of cover plate strengthened at the beam flange and the opening weakened at the beam web. The quasi-static tests of 8 welded steel connections were carried out to investigate and validate the proposed connection. The failure mode, hysteretic behavior, strength and cyclic degradation behavior, ductility and rotation behavior, stiffness behavior, and energy dissipation behavior of 8 connections were analyzed and further discussed. Moreover, the effects of different local structural forms, such as length of cover plate and diameter of web opening, on the proposed connection were experimentally investigated in detail. Also, the seismic performance of the proposed connection was comprehensively compared with the traditional connection. The results show that the proposed connection can achieve the plastic hinge away from the face of the column, thereby avoiding the brittle failure at the beam end, exhibiting excellent seismic performance. The comparisons demonstrate that the proposed connection presents a satisfactory ductility and plastic rotation behavior. A good cumulative plastic rotation and cumulative energy consumption can be observed in the proposed connection. However, the traditional connection shows a poor energy dissipation behavior. In addition, the strength and stiffness behavior of the proposed connection are not much different from the traditional connection, but the hysteretic, ductility, plastic rotation, and energy dissipation behavior can be considerably improved. The results confirm that the proposed connection is verified for seismic behavior and can be considered as a reasonable steel welded connection. Consequently, the proposed connection can be recommended to be directly adopted in the beam-to-column connection for steel frame structures under seismic design.

Experimental and FE study on strengthened steel beam-column joints for progressive collapse robustness under column-loss event

Strengthening of connections in steel framed structures is often required to mitigate the risk of progressive collapse initiated by column removal event. Steel framed buildings with simple shear connections between beams and columns are vulnerable to progressive collapse. Therefore, strengthening such structural systems for existing buildings as well as the designing of robust connections in the new structures is vital. This study was undertaken with the prime objective of investigating experimentally and numerically the efficient strengthening schemes for simple shear beam-column connections in order to minimize the risk of collapse in the incidence of sudden column loss. The experimental and numerical study includes testing a control test frame of a one-third scale single story shear-connection sub-assemblage consisting of two bays. A steel frame with an intermediate moment frame (IMF) connection was used as a target frame. Two schemes of strengthening beam-column connections were adopted for upgrading the control frame. The first scheme employed welded double side plates within the connection region, and the second scheme used pretensioned high-strength hot-rolled steel rods within the connection region. All specimens were subjected to dynamic loading in the vertical direction which essentially simulates extreme load cases like an explosion in which columns are removed. The efficacy of the strengthening schemes was evaluated based on the results of experiments and numerical simulation of the tested specimens.

Seismic performance of steel moment and hinged frames with rocking shear walls

The addition of a rocking structural system will soften the connection between a foundation and superstructure and help the beam-column connections to become softer than typical ones. These structures, with the addition of rocking structural systems, follow the elastic gap opening mechanism to soften the structural seismic response. Post-tensioned prestressed tendons and dampers are used in rocking systems to enable the structure to return to its initial position (self-centering) and to dissipate seismic energy, respectively. The current study investigated the use of a rocking shear wall system in steel moment-resistant and hinged frames and determined the amount of damage and the economic effects on the structures. For this purpose, 3D models of 3-, 9-, and 20-story SAC-project steel frames were modeled and validated according to FEMA-355C and then a hybrid rocking shear wall was added to them. The structures were designed and modeled according to common seismic codes and were analyzed using nonlinear time history when subjected to a series of records from FEMA-355C. The results showed that the use of a hinged frame attached to a rocking concrete shear wall (HFR) increased the fundamental period and inter-story displacement and decreased the amount of steel used in the 3-, 9-, and 20-story models compared to similar models with fixed connections in moment frames (MFR). The HFR shear wall models exhibited better seismic performance than MFR models, which increased their load-bearing capacity and reduced their weight, which reduced construction costs.

Investigation on behavior and seismic performance of reduced beam sections

Engineers prefer reduced beam section (RBS) connections in steel moment frames built in earthquake zones due to their many benefits. The RBS shape design significantly affects joint behavior. This paper examines the effect of RBS geometry on joint behavior and seismic performance using ANSYS finite element analysis software. RBS connections are investigated using European profiles and steel grades due to the limited number of studies using European profiles in the literature. The simulation study is carried out in three stages. In the first stage, an experimental study in the literature is simulated, and the reliability of the created finite element model is checked. In the second stage, geometric changes are made to the verified numerical model, and the obtained new models are examined under monotonic loading to observe the effect of RBS geometry on moment-rotation behavior. In the third stage, the effect of the change in the RBS geometry on the seismic performance is investigated under cyclic loading. As a result of the study, the effects of various changes made in the RBS geometry on the joint behavior and seismic performance are presented graphically. By using the results of the analysis under monotonic loading, the regression analysis is carried out, and the formulas giving the elastic-plastic stiffness, elastic moment capacity, and elastic rotation angle of the support are derived. Besides, simulation models show that the RBS joints' seismic performance met the minimum criteria specified in the earthquake code (AISC/ANSI 341-16) when European steel profiles and quality are applied.

Damage identification in connections of moment frames using time domain responses and an optimization method

Damage identification in connections of moment frames using time domain responses and an optimization method

Cyclic behaviour of laterally skewed special moment frame connections having composite concrete slabs

StahlbauVolume 90, Issue 7 p. 527-527 Empfehlungen der Redaktion Cyclic behaviour of laterally skewed special moment frame connections having composite concrete slabs First published: 05 July 2021 https://doi.org/10.1002/stab.202170705Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume90, Issue7July 2021Pages 527-527 RelatedInformation

Steel Structures Research Update: Seismic Performance of Nonorthogonal Special Moment Frame Beam-to-Column Connections

Ongoing research on the seismic behavior of nonorthogonal special moment frame beam-to-column connections is highlighted. Featured is a comprehensive experimental and computational study under way at the University of Arkansas and led by Dr. Gary Prinz, Associate Professor in Structural Engineering. The research team includes PhD students Hossein Kashefizadeh and Damaso Dominguez. Dr. Prinz’s research interests include mechanics and simulation of ductile fracture, seismic design solutions for steel structures, and computer simulation of structures under dynamic loading. He received a National Science Foundation Faculty Early Career Development (CAREER) award to investigate a new micromechanics-based approach to ductile fracture simulation in additively manufactured steels for improved seismic structural fuse design. Dr. Prinz has also been awarded AISC’s Milek Fellowship. The four-year Milek Fellowship is supporting this research on the seismic performance of skewed special moment frame (SMF) connections. The research team is partway through the third year of the four-year study. Selected results from the computational parametric study are highlighted along with a preview of the experimental investigation.

Evaluation of the capacity of steel special bolted moment frame connections subjected to simulated column removal

The eight bolted stiffened extended endplate (8ES) and bolted flange plate (BFP) moment connection are two common rigid joints that are widely used in special steel moment frames (moment resisting frames with high ductility). In this study, to investigate these connections' behaviour and capacity, first, verification of finite element assumptions was carried out using the Abaqus software. Then, based on the verification models, by changing different parameters, 17 specimens were designed following the AISC Manual using two beams and three columns to determine the maximum capacity values in a column loss scenario. The finite element analysis represents that the 8ES connection's failure begins near the joint area and at the vicinity of the rib stiffener, and the BFP connections provided no warning of failure before brittle fracture of bolts at the large displacement due to catenary action mode. The plastic equivalent strain, Von-Mises stress, and middle column force–displacement curve were discussed. Finally, a formula is presented based on the numerical results to determine the displacement at the maximum capacity of these connections, a formula is presented based on the numerical results using the Least Square Method (LSM). Finally, the modification factors are presented for the theoretical formula to determine these connections' maximum capacity under column removal demands.

Cyclic behaviour of laterally skewed special moment frame connections having composite concrete slabs

AbstractThis study presents a numerical investigation into the cyclic performance of skewed special moment frame (SMF) connections that include composite concrete slabs. The study uses advanced finite element simulations to investigate the behaviour of shallow (W14×), medium (W24×) and deep (W33×) steel column sections with three levels of beam skew (10, 20 and 30 degrees) for both bare‐steel and composite (steel‐concrete) construction. To account for complex torsional boundary conditions that may affect the skewed connection response, prequalification‐type analyses were conducted considering the middle storey of a three‐storey, two‐way moment frame configuration. In the analyses, all skewed configurations achieved at least 0.04 rad of connection rotation during the cyclic loading protocol prior to a 20 % reduction in moment capacity. When a composite concrete slab was added, column twisting and column flange yielding increased at large skew angles (30 degrees) during positive moment cycles.

A new friction-slip connection for moment frames with continuous beams

This paper presents a new configuration for connections in moment frames with continuous beams, which can be used as a friction-slip connection. Some studies on friction-slip connection with this new practice have been performed analytically.In moment frames with continuous beams, two beams are continuously passed next to the column. In current practice for connections in these frames, two vertical connection plates are placed on column flanges; the beams are connecting to these plates via their wings. A new configuration is proposed in this study with the advantage of an in-plane load path. The verification of the new proposed configuration has been done for the welded connection analytically, then some studies have been performed on eight models with friction-slip connection with the new practice. The effects of friction coefficient, design moment, and bolts' pretension load are assessed for two groups of beam sizes. In the new detail, regardless of the size of the beam, the friction joint works as expected. Changing the design moment will change the slip threshold force; as long as the design moment is constant, the change in the pretension load of the bolts or friction coefficient does not change the connection performance. The group slip occurred similar to the theoretical amounts. The amount of energy dissipation for these connections in comparison with corresponding welded connections is considerable; it will increase by increasing the design moment of the connection. So while these friction joints are used as an energy-dissipating system, the structural elements remain elastic.

Behaviour of Steel Deep Beams in Moment Frames with Web Opening Subjected to Lateral Loading

Due to the sharp change of the lateral load moment diagram in deep beams, the commonly proposed rigid connections may be incapable of proper transferring the plastic region away from the connection face into the beam. That is why prequalified connections of steel moment frames, proposed by different design codes, impose geometrical limitations on the beam span-to-depth ratio, which limits the application of the prequalified connections for short deep beams. The aim of this paper is to suggest details on leading the plastic area away from the column face by making a rectangular web opening at the mid-span of the deep beam. In order to stabilize the weakened area, stiffeners are used around the opening. 52 finite element models of deep beams with different geometries of the web openings are investigated. The results show that the use of deep beams with web opening located at mid-span in a steel moment frame is an efficient method to relocate the plastic hinge away from the connections, resulting in increased ductility. A parametric study is carried out on the effect of stiffeners dimensions, web thickness, and corner radius of web opening on behavior of deep beams in moment frames. A step-by-step design algorithm is also propounded for detailing of the web opening and the stiffener size.

Cyclic behavior of steel moment connections with built-up columns in weak direction

In many countries, due to fabrication restrictions in producing large hollow tubular rolled sections, use of built-up sections is a common practice. One of those built-up sections being a suitable choice as column in two directional steel moment frames is the double-I that attain high moment of inertia about their two main axes. In this study, using a through-plate concept, a new detailing and corresponding design procedure proposed for moment connections with double-I built-up columns in weak axis direction. A series of finite element analyses performed in order to envisage the connection behavior and its load transfer mechanism. To ensure the accuracy of the results, a computer model similar to the experimental prototype assembled and analyzed via finite element method. The numerical results illustrate reasonable agreement with the experimental results. In addition, the influence of the pertinent parameters on the proposed connection such as thickness and height of the column reinforcing plate, and thickness and height of the trough plate examined. The outcome of this research reveals that the proposed connection satisfies the rigidity, strength and ductility criteria according to AISC seismic provisions for special moment frame connections

Investigation of different steel intermediate moment frame connections under column-loss scenario

Abstract This paper investigated experimentally the progressive collapse risk of three one-third scale single story, two-bay steel frames under column-loss event. Progressive collapse was simulated by applying a vertical loading on the middle column. In these tests, three different types of steel beam-to-column connections were studied. These included: one shear-connection specimen that signified the prevalent type of steel beam-column joints, and two different steel intermediate moment frame (IMF) connections conforming to ANSI/AISC 358–16. The three tested specimens along with another two 2D steel frames with IMF connection, tested in the literature, were used to calibrate 3D finite element (FE) models prepared using ABAQUS software. The validated FE models were then employed to investigate the risk of progressive collapse for eleven different types of steel IMF beam-column joints under middle column-loss scenario. Out of the eleven specimens, eight connections were designed as per ANSI/AISC 358–16; two joints were in accordance with EN 1993-Eurocode 3 and the last connection was in conformance with the 2007 Turkish-Earthquake Code (TEC-2007). Performance of different IMF connections was compared based on their modes of failure and load-displacement response in both flexural and catenary action stages.