Connections In Moment-resisting Frames Research Articles

Numerical validation on novel replaceable reduced beam section connections for moment-resisting frames

This study presents replaceable reduced beam sections with connection detail for MRFs under residual drift. The proposed detail includes end-plated mid-spliced reduced beam sections. Pursuant to this goal, the proposed detail has been investigated under cyclic loading protocol required by AISC 341-16 by using ABAQUS finite element program. Seismic response of the proposed connection detail was compared from PEEQ and Rupture Index standpoint. The obtained findings indicate that the proposed mid-spliced replaceable reduced beam section satisfies all requirements indicated by AISC 341-16.

Experimental study on interior precast concrete beam–column connections with lap-spliced steel bars in field-cast RPC

Reactive powder concrete (RPC) has an ultra-high bond strength with steel bars, which offers new and innovative opportunities for precast concrete structures. This experimental study aimed to develop an alternative precast interior beam–column connection for moment-resisting frames in seismic regions. A two-stage experimental program involved a series of lap-splice tests and two beam–column connection tests to assess the viability of lap-spliced steel bars in field-cast RPC (LS-RPC) used in a precast beam–column connection. In the first part of the study, the lap-splice tests were conducted to determine the minimum lap length of LS-RPC and the influences of embedment length, hoop ratio, and hoop type (rectangular or spiral). In the second part, the application of LS-RPC in the precast beam–column connection was performed to verify its reliability and its seismic performance with the expectation that this alternative precast interior beam–column connection for moment-resisting frames would be practical for application in seismic regions. It was determined that the application of highly ductile fiber-reinforced concrete in the potential plastic hinge zone could improve the seismic performance of the connection.

Seismic performance of a novel self-sustaining beam-column connection for precast concrete moment-resisting frames

In this paper, a novel prefabricated reinforced concrete (PC) self-sustaining beam-column connection for moment-resisting frames was developed to achieve the targets of short erection time, high construction efficiency, low-cost and satisfactory seismic performance. The connection design eliminates the need of temporary supports for the PC beams and slabs during the assembly process in site, and reduces the amount of lateral supports for PC multi-storey columns and formwork for cast-in-place concrete. As the designed thickness of PC U-shells at the beam ends was about 1/3 of the beam width, there could be a marked effect on the achieved integrity of such connections, especially under seismic loading. To investigate the seismic performance of this PC connection, five large-scale PC self-sustaining beam-column connections specimens and one reference conventional RC connection were designed and tested under reverse cyclic loading. The test parameters included the length and area of the flexural reinforcing bars placed at the bottom of PC U-shells, and the anchorage measures (stirrups) inside the PC U-shell. The five precast specimens exhibited similar crack distributions and failure patterns due to the gap-opening between the PC beams and column surface, which was attributed to the reduced effective width and depth of beam cross-section. The test results showed that the use of longer flexural reinforcing bars had little influence on the load-carrying capacity, but contributed to the initial stiffness and energy dissipation capacity. The load-carrying capacity increased by 24% when the area of flexural reinforcing bars increased by 50% in the U-shell region. The incorporation of stirrups in the overlapping region of beam flexural reinforcing bars and longitudinal rebars improved their bond-slip behaviour in specimen PC-S. Compared with specimen PC-C, the energy dissipation capacity of specimen PC-S was improved by 16.5%. Finally, the failure pattern and load-carrying capacity of the PC specimens were analysed and discussed using a simplified mechanical model.

Cyclic behavior of hexagonal castellated beams in steel moment-resisting frames with post-tensioned connections

In this article, behavior of ten beam specimens, including five hexagonal castellated beams and five typical wide flange beams, in the post-tensioned semi-rigid beam-to-column steel connections of moment-resisting frames has been analyzed theoretically and numerically by well-known finite element software (ABAQUS 6.11-PR3) under the earthquake simulated by cyclic loading up to 4.4% lateral drift. Hexagonal castellated beams provide lower weight and higher bending strength in comparison with typical wide flange beams in post-tensioned semi-rigid steel connections. The inelastic deformations of the bolted top and bottom angles provide reliable level of energy dissipation, and the steel strands provide self-centering capability and revert the moment-resisting frame to its initial position without residual drift after a severe earthquake. The results of finite element analysis verified against experiment have proved that the theoretical method based on the previous researches accurately predicts the behavior of hexagonal castellated beams in the post-tensioned connections. All beam specimens did not suffer from the flange buckling and web shear buckling under the standard cyclic loading up to 4% lateral drift; likewise, hexagonal castellated beams in the post-tensioned connections showed adequate strength against web-post failure and vierendeel mechanism up until 4% drift. In order to investigate the ultimate failure modes of the specimens, they have also been subjected to an added half-cycle loading up to 4.4% lateral drift beyond the standard loading. The further drifts have leaded to the web-post buckling in most specimens with hexagonal castellated beams and flange buckling in all specimens with wide flange beams. In addition, the parametric study is suggested as a further investigation to comprehensively understand the behavior of hexagonal castellated beams in the PT connections and it is required to reach more general conclusions. This research has developed a benchmark to design hexagonal castellated beams in the PT semi-rigid connections, but a step-by-step design guideline is still required to add it to design codes and specifications for steel structures.

Development and Seismic Behavior of Precast Concrete Beam-to-Column Connections

A new precast concrete beam-to-column connection for moment-resisting frames was developed in this study. Both longitudinal bar anchoring and lap splicing were used to achieve beam reinforcement continuity. Three full-scale beam-to-column connections, including a reference monolithic specimen, were investigated under reversal cyclic loading. The difference between the two precast specimens was the consideration of additional lap-splicing bars in the calculation of moment-resisting strength. Seismic performance was evaluated based on hysteretic behavior, strength, ductility, stiffness, and energy dissipation. The plastic hinge length of the specimens is also discussed. The results show that the proposed precast system performs satisfactorily under reversal cyclic loading compared with the monolithic specimen, and the additional lap-splicing bars can be included in the strength calculation using the plane cross-section assumption. Furthermore, the plastic hinge length of the proposed precast beam-to-column connection can be estimated using the models for monolithic specimens.

Self-centering MRFs with bottom flange friction devices under earthquake loading

A bottom flange friction device (BFFD) has been developed as an energy dissipation device for self-centering post-tensioned steel beam-to-column connections for moment-resisting frames (MRFs). The BFFD is located beneath the beam to avoid interference with a floor slab. Since the BFFD is attached to only one flange, a connection with a BFFD has an asymmetric behavior with different positive and negative moment capacities. To investigate the behavior of a self-centering MRF with BFFDs, static and dynamic analyses were performed, and the results were compared to those of a similar frame with connections that have a symmetric behavior. It was found that the asymmetric behavior of the MRF with BFFDs leads to increased inelastic strain in the beam top flange, which may lead to beam flange buckling. These inelastic strains can be reduced by using longer top flange reinforcing plates.

Evaluating performance of post-tensioned steel connections with strands and reduced flange plates

The seismic performance of post-tensioned steel connections for moment-resisting frames was examined experimentally and analytically. Cyclic tests were conducted on three full-scale subassemblies, which had two steel beams post-tensioned to a concrete-filled tube (CFT) column with high-strength strands to provide recentring response. Reduced flange plates (RFPs) welded to the column and bolted to the beam flange were used to increase the dissipation of energy. Test results indicated that (1) the proposed buckling-restrained RFP could dissipate energy in axial tension and compression, (2) the subassemblies could reach an interstorey drift of 4% without strength degradation, and (3) buckling of the beam occurred towards an interstorey drift of 5%, causing a loss of the strand force, the recentring response, and the moment capacity. A general-purpose non-linear finite element analysis program (ABAQUS) was used to perform a correlation study. The behaviour of the steel beam under both post-tensioning and flexural loadings was compared to the test results and predictions. Copyright © 2006 John Wiley & Sons, Ltd.

Improved Truss Model for Design of Welded Steel Moment-Resisting Frame Connections

Results are given from finite element analysis of 18 strong-axis steel welded beam-column subassemblages with connection reinforcement. For the type of connection configuration considered, Federal Emergency Management Agency (FEMA) recommends connection forces be obtained by locating the plastic hinge at 1/3 depth of beam away from the end of connection reinforcement region. Also, a recent study pointed the location of plastic hinge to be at a distance of depth of beam from the column face. However, the present study shows that the plastic hinge is located at 1/2 depth of beam away from the end of connection reinforcement region. It is observed that connection design forces obtained from the present study are higher as compared to those obtained using the FEMA recommendations. A noniterative procedure for the design of beam-to-column connections using a truss for obtaining connection forces is also presented, which uses this location of the plastic hinge.

Evaluation of maximum strength and optimum haunch length of steel beam-end with horizontal haunch

Since the 1995 Hyogoken-Nanbu Earthquake, the use of horizontally haunched beams has been increasing to prevent brittle fractures of beam flanges in the vicinity of steel-beam-to-boxed-column connections of moment-resisting frames. The author has already proposed a design method based on experimental studies. This method produces ductile beam-to-column connections, because it predicts the fracture mode and an optimum haunch length by comparing a beam’s local buckling strength with that of fracture perpendicular or diagonal to the beam-axis. However, strength-formulas for local buckling used in the method have recently been amended, so the design method needs to be revised and its applicability verified. The revised design method has been applied to test results of twenty-nine horizontally haunched beam specimens designed by the author and other researchers to confirm its effectiveness. Results show that the revised method closely matches the test results. Furthermore, it produces more accurate fracture modes and optimum haunch lengths, except where the haunches incorporate stiffeners. A formula for the optimum haunch length is also proposed. A rough value of the optimum haunch length is about 25 to 35% of the beam depth.

水平ハンチを有する鉄骨梁端部の最大耐力と最適ハンチ長さの評価

Abstract Since the 1995 Hyogoken-Nanbu Earthquake, the use of horizontally haunched beams has been increasing to prevent brittle fractures of beam flanges in the vicinity of steel-beam-to-boxed-column connections of moment-resisting frames. The author has already proposed a design method based on experimental studies. This method produces ductile beam-to-column connections, because it predicts the fracture mode and an optimum haunch length by comparing a beam’s local buckling strength with that of fracture perpendicular or diagonal to the beam-axis. However, strength-formulas for local buckling used in the method have recently been amended, so the design method needs to be revised and its applicability verified. The revised design method has been applied to test results of twenty-nine horizontally haunched beam specimens designed by the author and other researchers to confirm its effectiveness. Results show that the revised method closely matches the test results. Furthermore, it produces more accurate fracture modes and optimum haunch lengths, except where the haunches incorporate stiffeners. A formula for the optimum haunch length is also proposed. A rough value of the optimum haunch length is about 25 to 35% of the beam depth.

Seismic Response of Composite Moment-Resisting Connections. I: Performance

The 1994 Northridge, California, earthquake precipitated numerous unexpected fractures in welded steel moment-resisting frame connections, mainly in the regions of the bottom girder flanges. This two-part paper reports on research to determine if structural phenomena, primarily the effect of composite concrete floor slabs, contributed substantially to these failures. The results of cyclic experiments of one bare steel and two composite full-scale specimens representing typical pre-Northridge, interior moment-resisting connections are described, along with corroborating analyses. The structural performance of the test specimens is highlighted in this paper. The connections failed either brittlely at the welded interface of the bottom girder flange and the column flange, or with a low cycle fatigue failure emanating from the root of the bottom girder flange access hole. None of the connections achieved adequate levels of cyclic ductility, and the composite connections did not achieve their calculated streng...

Seismic Response of Composite Moment-Resisting Connections. II: Behavior

This two-part paper presents research to determine the effect of structural phenomena, especially the presence of composite concrete floor slabs, on the behavior of the type of fully restrained, steel moment-resisting frame connections that failed, primarily near the bottom girder flanges, during the 1994 Northridge, California, earthquake. In a companion paper, the results of three experiments, including one bare steel specimen and two with composite floor slabs, are outlined, along with corroborating analyses. In this paper, the structural phenomena that affected the behavior of these connections are documented. The results indicate that the strains near the bottom flange of the specimens with a slab are several times larger than those near the top flange, and that strain concentrations and a triaxial state of tensile stress precipitate failure in these connection topologies. These results help to explain the predominance of bottom flange failures, and they indicate that the potentially high strain levels leading to fracture and the inherently unsymmetrical topology of composite steel frame connections should be considered in the development of connection design provisions.

The SidePlateTM moment connection system: A design breakthrough eliminating recognised vulnerabilities in steel moment-resisting frame connections

The SidePlateTM moment connection system: A design breakthrough eliminating recognised vulnerabilities in steel moment-resisting frame connections

Seismic moment connections for MRFs

Abstract This paper provides an overview of the state of the art for the design of steel moment connections for moment-resisting frames (MRFs) for regions of high seismic risk. The need to design such connections to be ductile with the capacity to sustain full load reversals is indicated first. The generally accepted approach of ‘strong columns/weak girders’, i.e. designing the joints to develop inelastic activity in the connections and beams rather than columns, is emphasized. A major section of the paper is devoted to presenting experimental results to illustrate the observed behavior of beam-to-column connections and column panel zones under severe cyclic loadings simulating extreme seismic conditions. Procedures are given for seismic moment joint calculations pertaining to flange-beam connections, web connections, and panel zone design. Typical seismic moment connections of beam-to-column flanges as well as to webs and column splices are illustrated. Because of further developments since 1982, the original date of the paper, a new section on recent research and additional references has been added. The paper concludes by indicating some of the problems requiring further investigation.