Beam-to-CFT High-Strength Joints with External Diaphragm. I: Design and Experimental Validation

Transcription

1 Beam-to-CFT High-Strength Joints with External Diaphragm. I: Design and Experimental Validation Cristian Vulcu 1 ; Aurel Stratan 2 ; Adrian Ciutina 3 ; and Dan Dubina 4 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Abstract: The paper presents the outcomes of an experimental program developed and carried out with the aim of characterizing the behavior of two types of moment-resisting joints in multistory frames of concrete-filled high-strength steel rectangular hollow section (RHS) columns and mild carbon steel beams. The paper describes the design approach and displays the specific detailing for the two joint typologies: with reduced beam section (RBS) and with cover plates (CP). In spite of the various past and recent studies which were focused on the evaluation of full-strength welded beam-to-concrete-filled-tube (CFT) column joints, particular design procedures are missing at the European level. The objectives of the current research were to (1) development a design procedure for welded beam-to-cf-rhs joints, (2) experimental validation of the of the design procedure, and (3) assessment of the seismic performance. The monotonic and cyclic tests evidenced a good conception and design of the RBS and CP joints. In particular, the current study proved the feasibility of using higher steel grades in columns and joint components, and the use of an external diaphragm for the transfer the loads from the beam to the side walls of the RHS steel tube. The seismic performance of the joints was proved adequate, the joints sustaining rotation capacities larger than the 4 mrad at the significant damage performance level. DOI: 1.161/(ASCE)ST X American Society of Civil Engineers. Author keywords: Dual-steel solution; High-strength steel; Concrete filled tubes; Welded beam-to-column joints; Metal and composite structures. Introduction Seismic-resistant building frames designed as dissipative structures must allow for development of plastic deformations in specific members, whose behavior is expected to be predicted and controlled by proper calculation and detailing. Members designed to remain elastic during an earthquake, such as columns, are characterized by high strength demands. Dual-steel structural systems, for which high-strength steel (HSS) is used in predominantly elastic members while mild carbon steel (MCS) is used in dissipative members, can be reliable and cost efficient (Latham and Lapwood 1991; Samuelsson and Schroeter 25). A comprehensive review of the early studies and recent research advances of HSS structures is presented by Shi et al. (214). Due to the fact that current European seismic design code EN (CEN 24b) does not cover the specific configuration of dual-steel structural systems, 1 Lecturer, Dept. of Steel Structures and Structural Mechanics, Politehnica Univ. of Timişoara, Str. Ioan Curea 1, Timisoara 3224, Romania. cristian.vulcu@upt.ro 2 Associate Professor, Dept. of Steel Structures and Structural Mechanics, Politehnica Univ. of Timişoara, Str. Ioan Curea 1, Timisoara 3224, Romania (corresponding author). aurel.stratan@upt.ro 3 Associate Professor, Dept. of Steel Structures and Structural Mechanics, Politehnica Univ. of Timişoara, Str. Ioan Curea 1, Timisoara 3224, Romania. adrian.ciutina@upt.ro 4 Professor, Dept. of Steel Structures and Structural Mechanics, Politehnica Univ. of Timişoara, Str. Ioan Curea 1, Timisoara 3224, Romania; Senior Researcher 1, Laboratory of Steel Structures, Romanian Academy Timisoara Branch, Bd. Mihai Viteazul, No. 1, Timisoara 3223, Romania. dan.dubina@upt.ro Note. This manuscript was submitted on October 12, 215; approved on September 28, 216; published online on January 17, 217. Discussion period open until June 17, 217; separate discussions must be submitted for individual papers. This paper is part of the Journal of Structural Engineering, ASCE, ISSN the research project HSS-SERF (Dubina et al. 215), was carried out with the aim of investigating and evaluating the seismic performance of dual-steel building frames. A particular objective of the project was to find reliable structural typologies (e.g., momentresisting frames, concentrically braced frames, eccentrically braced frames), and connection detailing for dual-steel building frames, and to validate them by tests and advanced numerical simulations. Different types of bolted and welded connection solutions were considered for the beam-to-column joints, as well as different types of composite columns, i.e., fully encased wide flange (FE-WF) columns, partially encased wide flange (PE-WF) columns, and concrete-filled tube (CFT) columns. Within this framework, particular research activities were related to the investigation of two types of beam-to-cft column joints, i.e., with reduced beam section (RBS) and with cover plates (CP). The current paper addresses the experimental investigation of joint assemblies as well as the development of design procedures for the investigated joint typologies. The outcomes of the numerical investigation program (calibration of numerical models, validation of design procedure for joint components) represent the subject of the companion paper, Beam-to-CFT High-Strength Joints with External Diaphragm. II: Numerical Simulation of Joint Behavior (Vulcu et al. 216). Columns fabricated from steel hollow sections can be filled with concrete with the aim to combine the properties of the two materials, the final element being characterized by higher stiffness, strength, and ductility, as well as enhanced fire resistance in comparison with bare steel configurations. A particular advantage of the composite solution is related to the reduction of the column cross-sectional area, and by using steel tubes as permanent formwork, the construction speed is increased. It is to be highlighted that, regardless of the various advantages, a particular attention should be given to the joining aspect between beams and columns from the point of view of the connection technology and detailing. ASCE J. Struct. Eng.

2 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. The framing system with concrete-filled columns and welded joints has been investigated and applied on a large scale in Asia, Australia, and America. In particular, according to Morino and Tsuda (23), the typical connections between concrete-filled tubes (CFT) and I-beams, frequently used in Japan, are based on the use of stiffeners which can be either a through diaphragm, internal diaphragm, or external diaphragm. Furthermore, past as well as recent research activity has shown that full-strength beam-to-cft column joints can be obtained by the means of various stiffening solutions. In the light of recent research, several studies are to be mentioned. Accordingly, Chen and Lin (24) investigated the cyclic behavior of flange plate connections between steel beams and rectangular CFT columns, in which the flange plates were penetrated through the CFT columns. Additionally, the study of Shin et al. (24) was focused on the behavior of CFT column to H-beam welded moment connections with external T-stiffeners. Considering the use of HSS members, Fukumoto and Morita (25) conducted tests on the panel zone within beam-to-cft column moment connections made from high-strength material for the investigation of the elastoplastic behavior. Further, Park et al. (25) investigated the force transfer mechanism and the cyclic performance of wide flange beams to square CFT column joints reinforced with stiffening plates welded around the column. In addition, Cheng et al. (27) investigated the seismic performance of steel beam-to-cft column connections with floor slabs, and Huang et al. (214) investigated the behavior and design modification of RBS moment connections with composite beams. Furthermore, Wang et al. (211) investigated the seismic behavior of H-beam to circular tubular column connections stiffened by an outer ring diaphragm, employing a three-dimensional connection subassembly testing system. The RBS solution was studied by Zhang and Ricles (26a, b) for the investigation of the seismic behavior of reduced beam section (RBS) moment connections to a deep wide-flange column. In spite of the various past and recent studies which were focused on the evaluation of full-strength welded beam-to-cft column joints, particular design procedures are missing at the European level. Accordingly, the seismic design code EN (CEN 24b) does not cover such joint configurations, and more significantly, it does not cover the case of dual-steel structures with nondissipative members manufactured from high-strength steels. The same situation is reflected by the content of EN (CEN 25b) and EN (CEN 24a). The particular lack of informatio within the two documents, is related to the following topics: welded connections between members of different steel grades (MCS and HSS), design of a full-strength beam-to-cft column joint, and shear strength of the column web panel in case of concrete-filled rectangular hollow section columns. As a result, the current study aimed at investigating the structural and seismic performance of beam-to-cft column joints. The objectives of the current research were (1) to develop a design procedure for welded beam-to-cf-rhs joints, (2) experimental validation of the of the design procedure, and (3) assessment of the seismic performance. For this purpose, the experimental program on beam-to-column joints was developed considering: full-strength and rigid joints, hot rolled MCS beams, cold-formed HSS rectangular hollow section columns filled with concrete, and two welded joint typologies: with reduced beam section (RBS), and with cover plates (CP). Furthermore, the connection solution of beams and columns, for both RBS and CP joints, was based on the use of stiffening plates welded around the steel tube in the shape of an external diaphragm. Consequently, the current research is focused on the joining aspect between members made of different steel grades (MCS and HSS), and more particularly on the design, detailing, and prequalification of welded RBS and CP joints. The uniqueness of the current research configuration is related to the use of high-strength steel and the particular detailing for the two joint configurations. The aim of the experimental program was to validate by tests welded connections in moment-resisting frames and dual-braced frames designed using the dual-steel concept. The experimental investigations included: (1) material sample tests, with the objective of evaluating the characteristics corresponding to each part of the joint assemblies; (2) load introduction tests, with the objective of evaluating the efficiency of the shot fired nails in providing the load transfer from the steel tube to the concrete core; (3) nondestructive tests (NDT), for the quality control of welded connections; and (4) beam-to-column joint tests, with the objective of observing the behavior and characterizing the seismic performance of welded beam-to-cft column joints in terms of stiffness, strength, and ductility. This paper is focused on the presentation of experimental tests on beam-to-column joints, while the outcomes of the load introduction tests are not presented within the current paper, and more detailed information can be found elsewhere (Vulcu et al. 214a, b). The current experimental program allowed assessing the response of the tested joint assemblies, and the comparison and interpretation of results evidenced the following: influence of loading conditions and steel grade within the column, contribution of components to the joint rotation, and strength of the connection components. Furthermore, the seismic performance of the beamto-column joint assemblies was evaluated, as well as the acceptance criteria corresponding to multiple performance levels. Design and Detailing of the Beam-to-Column Joints A set of dual-steel multistory frames were designed (Tenchini et al. 214; Dubina et al. 215), allowing the identification of realistic member sizes for beams and columns. The investigated structural systems were represented by moment-resisting frames (MRF), dual concentrically braced frames (D-CBF), and dual eccentrically braced frames (D-EBF). The frames were characterized by 8 floors of 3.5 m height and 7.5 m span. The beams and braces were designed from MCS (S355), and the columns from HSS (S46, S7) and C3/37 concrete. The loads considered in the design were 4 kn=m 2 permanent load and 3 kn=m 2 live load. The seismic action was defined by seismic spectrum according to EN (CEN 24b) (spectrum type 1, a g ¼.32 g, soil type C). In the case of MRF structures, all frames were active in resisting lateral forces (the seismic masses corresponding to 1 bay), while for D-CBF and D-EBF structures each second frame was gravity-only (the seismic masses corresponding to 2 bays). This design approach which is typical to European and Japanese practice leads to smaller member size in comparison with the North American approach, where often only perimeter frames provide lateral strength and stiffness. For the design and detailing of the beam-to-column joint specimens, cross sections of members were chosen from the D-CBF, i.e., two combinations of HSS columns and MCS beams, as shown in Table 1. Based on the two HSS/MCS combinations, and the two connection solutions (reduced beam section RBS, and cover plates CP), a number of four joint configuration were designed. The RBS joint (Fig. 1) connects a wide-flange hot-rolled beam with a CFT column using field welding. A reduced beam section is used in order to alleviate stresses in the beam-column connection and control the location of the plastic hinge. An external diaphragm is shop-welded to the column in order to transfer the forces from beam to the side walls of the column. Beam flanges are welded to the external diaphragm using full-penetration butt welds. ASCE J. Struct. Eng.

3 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Table 1. Cross Section of Members for Welded Joints with CFT Columns HSS/MCS Member Cross section/material Combination1 S46/S355 Column RHS , S46; concrete infill C3/37 Beam IPE 4, S355 Combination 2 S7/S355 Column RHS , S7; concrete infill C3/37 Beam IPE 4, S355 The preparation details for full penetration welds between external diaphragm and beam flanges are shown in Fig. 3. As can be noted, the thickness of the external diaphragm obtained from design was higher than the flange thickness. Therefore, in order to avoid the concentration of the stresses due to thickness variation, the preparation details shown in Fig. 3 were proposed. The solution does not require weld access holes, and the advantage is that no preparations are necessary for beam flanges. A shear tab bolted connection between the beam web and vertical column stiffener was considered for erection only. The final connection of the beam web is realized using full-penetration weld, using the shear tab as backing plate. The design of the reduced beam section was performed based on provisions from AISC 358 (AISC 21a). The design procedure was adapted to the particular joint configuration employing CFT column reinforced with external diaphragm. An photograph of the RBS joint specimen is shown in Fig. 1. The CP joint (Fig. 2) connects a wide-flange hot-rolled beam with a CFT column using field welding. An external diaphragm is shop-welded to the column in order to transfer the forces from beam to the side walls of the column. Cover plates are used in order to reinforce the beam-column connection, forcing the plastic hinge to form in the beam. The cover plates are welded to the external diaphragm using full-penetration butt welds. The preparation details shown in Fig. 3 are based on the weld access-hole details recommended in FEMA-35 (FEMA 2). Here also the thickness of the external diaphragm obtained from the design was higher compared to the thickness of the cover plates. Therefore, in order to avoid the concentration of the stresses due to thickness variation, the preparation details shown in Fig. 3 were used. The advantage is that no preparations are necessary for cover plates. A bolted connection between the beam web and vertical column stiffener was considered for erection only. The final connection of the beam web is realized using fillet welds. A photograph of the CP joint specimen is shown in Fig. 2. Regarding the two joint configurations, the advantage of the RBS joint consists in simpler fabrication details and lower costs. The disadvantage of this configuration consists in lower strength (and consequently larger deformation demands), as well as susceptibility to lateral torsional buckling. The advantage of the cover plate joint consists in larger strength (and consequently lower deformation demands). This improves the performance of the structure. The disadvantage of this configuration consists in larger fabrication costs. It is to be noted that the details of the reduced beam section are as follows: a ¼ 9 mm, b ¼ 26 mm, c ¼ 35 mm, R ¼ 26 mm (radius). In addition, the weld material grade was used as follows: (1) filler metal G46 for the connection between S355 component and S46 component, respectively between S46 components, and (2) filler metal G69 for the connection between S355 component and S69 component, respectively between S69/S7 components. The quality assurance and control requirements of the specimens were those corresponding to execution EXC3, which was selected based on EN 19-1 (CEN 29) and EN 19-2 (CEN 28), and are common for residential and office buildings located Fig. 1. RBS joint configuration: (a, b) conceptual scheme; specimen image ASCE J. Struct. Eng.

4 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Fig. 2. CP joint configuration: (a, b) conceptual scheme; specimen image Fig. 3. Weld preparation details for on-site welded connections: RBS joint; CP joint V pl,rd VEd,hinge M pl,hinge M pl,rd (d) Fig. 4. Design steps for RBS and CP joints; RBS joints; CP joints; (d) RBS and CP joints ASCE J. Struct. Eng.

5 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Table 2. Summary of the Design Procedure for RBS and CP Beam-to-Column Joints Design step number RBS joint CP joint 1. Identification of members (beam, column) and the corresponding material properties 2. Selection of component size considering the following trial values The thickness of the external diaphragm should be equal or higher than the thickness of the beam flanges (t ed t f ), and the width (b ed ) should satisfy the following relation (b ed.4 b c ) with the aim of obtaining a stiff external diaphragm, where b c is the width of the column The minimum values of a, b, c dimensions [Fig. 1, and AISC (AISC 21)] should be considered as starting values for the geometry of the reduced beam section The thickness of cover plates should be equal or higher than the thickness of beam flanges (t cp t f ), and the width [b cp ; see Fig. 2] should satisfy the following relations: b cp > b c b cp < ðb c þ 2 b ed ) 3. Evaluation of plastic hinge location The position of the plastic hinge is related to the center of the reduced beam section The center of the plastic hinge is located at a distance equal to h beam =3 from the cover plate ending [see (Kim et al. 2)]; h beam being the height of the beam 4. Evaluation of the expected maximum bending moment and shear force at the plastic hinge location The expected maximum bending moment (M pl;hinge ) and shear force (V Ed;hinge ) in the plastic hinge [Fig. 4], are determined considering a fully yielded and strain hardened plastic hinge in the beam: M pl;hinge ¼ γ sh γ ov W pl f y V Ed;hinge ¼ V Ed;G þ 2 M pl;hinge L where γ sh ¼ 1.1 accounts for strain hardening; γ ov ¼ 1.25 is the material overstrength factor; W pl = plastic section modulus; f y = nominal yield strength; V Ed;G = shear force from gravity forces in the seismic design situation; and L = distance between the plastic hinges of the same beam 5. Welded connection between cover plates and beam flanges RBS joints do not involve the use of cover plates Actions are evaluated at the beam end Capacity is computed assuming that the flanges carry the moment only, while the web carries the shear force. The strength of the welded connection [based on EN (CEN 25b), Eqs. (4.3) and (4.4)] is determined as the sum of the strength of the four fillet welds between cover plate and beam flange: F w;rd ¼ 2 ðf w;rd;1 þ F w;rd;2 Þ V Ed;hinge ¼ V Ed;G þ 2 M pl;hinge L where a 1 and a 2 = throat thickness of the longitudinal and transversal welds; l 1 and l 2 = length of the longitudinal and transversal welds; f u = nominal ultimate strength; β w = appropriate correlation factor; and γ M2 is the partial safety factor for the resistance of welds 6. Welded on-site connection: beam to external diaphragm (RBS joints), and respectively cover plates to external diaphragm (CP joints) Actions are evaluated at the on-site connection [Fig. 1] Capacity is computed in terms of bending moment and shear force, based on the gross cross section of the beam (no weld access holes are considered) Actions are evaluated at the on-site connection [Fig. 2] Capacity is computed assuming that the cover plates carry moment only, while the web carries the shear force. Only the effective width b cp;eff;width ¼ b cp b c þ 1.4 b ed of the cover plate is assumed to carry loads [based on numerical simulations described in Vulcu et al. (216)] ASCE J. Struct. Eng.

6 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Table 2. (Continued.) Design step number RBS joint CP joint 7. External diaphragm Actions evaluated at column face Actions evaluated at column face The capacity in shear [Eq. (6.18) of EN (CEN 25a)] of the external diaphragm is computed assuming the formation of yield lines [Fig. 4] and neglecting the direct connection to the column wall: F v;rd ¼ 2 A v f p ffiffi Y 3 γm The capacity in shear [Eq. (6.18) of EN (CEN 25a)] of the external diaphragm is computed assuming the formation of yield lines [Fig. 4] and neglecting the direct connection to the column wall: F v;rd ¼ γ M 2 A v f p Y ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ 2 cos 2 α where A v = shear area along the yield line; α = angle between the yield lines and the axis of the beam; and γ M = partial safety factor for the resistance of cross sections 8. Column web panel 1. The shear force in the column web panel is determined using the procedure from EN (CEN 25b) [5.3(3)], corresponding to fully yielded plastic hinges in the beams framing into the joint. According to EN (CEN 24b), no over-strength is required (γ sh ¼ 1. & γ ov ¼ 1.) 2. The strength of the column web panel in shear is computed for both steel tube and concrete core The shear strength of the steel tube (V wp;s;rd ) is determined according to EN (CEN 25b) [ (2), Eq. (6.7)]: V wp;s;rd ¼ ; 9 A v f y p ffiffi A v ¼ A 3 γm b c þ h c The shear strength of the concrete core (V wp;c;rd ) is determined according to EN (CEN 24a) [ , Eq. (8.1)], but considering a coefficient of 1. instead of.85, according to Clause of the same code: V wp;c;rd ¼ 1; v A c f cd sin θ A c ¼ ; 8 ðb c 2 t t Þ ðh c 2 t t Þ cos θ hc 2 t θ ¼ arctg t ν ¼.55 z b c 1 þ 2 3. The capacity of the column web panel in shear V wp;rd [Fig. 4], according to EN (CEN 24b), should be taken as 8% of the two sections (concrete and steel) together. However, considering only the contribution of the steel section might lead to higher shear strength: V wp;rd ¼ max½v wp;s;rd ;.8 ðv wp;s;rd þ V wp;c;rd ÞŠ where A = cross-sectional area of the tube, b c and h c = width and depth of the steel tube; t t = thickness of the tube; ν = reduction factor; A c = crosssectional area of concrete [in particular the cross-sectional area of the concrete diagonal with compression forces from the column web panel; see Fig. 4(d)], f cd = design value of the cylinder compressive strength of concrete; θ = angle between the compressed diagonal and the horizontal direction; z = lever arm (in this particular case it represents the distance between the middle surface of the external diaphragms); N ed = design compressive normal force in the column; and N pl;rd = design plastic resistance of the column s cross section NEd N pl;rd 1.1 ASCE J. Struct. Eng.

7 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. in seismic areas. In particular, the following requirements were specified for the manufacturing of the welded connections: Compliance of welded components with the requirements specified in Clauses 1 and 11 of EN 19-2 (CEN 28) and weld imperfections quality level B for full penetration welds and quality level C for fillet welds, with reference to EN ISO 5817 (ISO 26); Welding in accordance with the requirements of EN ISO (ISO 25). Qualification of welding procedures as defined in European Standards defined in Tables 12 and 13 of EN 19-2 (CEN 28); and Visual inspection of all welds throughout their entire length. Additional surface testing by penetrant testing or magnetic particle inspection on the inspected weld according to Table 24 of EN 19-2 (CEN 28). The design procedure for the two joint typologies, in principle organized following the component method of EN (CEN 25b), is summarized in Table 2, and briefly illustrated in Fig. 4. The first step is related to the selection of component size, and estimation of the expected moment and shear force at the plastic hinge location. Further, the welded connections and joint components are designed and/or checked with the aim of obtaining an equal or higher capacity compared to the design values of the actions, which are computed at the component location based on the expected bending moment and shear force within the plastic hinge. The rotational stiffness of a joint can be determined from the flexibilities of its basic components, each represented by a stiffness coefficient k i. According to Table 6.11 of EN (CEN 25b), the stiffness coefficients can be assumed to be equal to infinite for the following components: beam web in tension, beam flange and web in compression, and plates in tension or compression. Furthermore, the stiffness coefficient for the external diaphragm can be assumed to be infinite if the design is made considering a full strength external diaphragm, and the following relation is satisfied: b ed.4 b c. It is to be noted that the relationship was obtained from the comparison between the stiffness of a plate in tension (full restrained at one edge and loaded at the opposite one), and the stiffness of the same plate but subjected to bending (full restrained on the lateral edges and with uniform Table 3. Experimental Program on Beam-to-CFT Column Joints distributed load at the front edge). The geometry of the plate was assumed as follows: b c length; b ed width; t f thickness. From the analogy, the stiffness coefficient of the bent plate could be assumed equal to infinite, if the stiffness is equal or higher to the stiffness of the plate in tension. As a result, for the investigated joint typologies, the stiffness is affected only by the column web panel in shear. According to Section of EN (CEN 25b), the stiffness coefficient of the column web panel corresponding to an unstiffened joint is k 1. Where the steel column web is encased in concrete, the stiffness of the panel may be increased to allow for the encasement, and the addition k 1;c to the stiffness coefficient k 1 may be determined with Eq. A.2 of EN (CEN 24a). Experimental Program The experimental program on beam-to-column joints with CF-RHS columns is summarized in Table 3. The variations in the configuration of the joints are given by the two joint typologies (RBS and CP), two steel grades for the rectangular hollow section tubes (S46 and S7), and two intended failure modes (beam and connection zone). In addition, two loading conditions were considered for each beam-to-column joint configuration, i.e., monotonic and cyclic loading procedure. As a result, the experimental program covered a total number of 16 beam-to-column joint assemblies. The specimen labelling, column and beam sections, joint typology, loading procedure, and intended failure mode are described for each particular case in Table 3. Considering the two joint typologies [RBS and CP; Figs. 5(a and b)] and two steel grades for the tubes (S46 and S7), a number of four beam-to-column joint configurations were designed [Fig. 5]. Additionally, in order to assess the overstrength of the connection zone and to observe the basic components of joints, tests were performed on the corresponding joints for which the beam was strengthened [Fig. 5(d)] with the aim to avoid the formation of the plastic hinge in the beam and to force failure in the connection zone. The specimens with reinforced beams were identical to corresponding standard configurations, except that: For RBS joints the beam flange was not cut, and additionally it was reinforced by welding plates of 15 mm thickness (Figs. 5, 13, and 14); and Number Specimen label Column/external diaphragm/vertical stiffener plate Beam/cover plate (CP) Joint type Loading Intended failure mode 1 S46-RBS-M RHS S46/Ext. diaphragm and IPE4 S355/- RBS Monotonic Beam 2 S46-RBS-C vertical stiffener S46 Cyclic 3 S7-RBS-M RHS 25 1 S7/Ext. diaphragm and IPE4 S355/- RBS Monotonic Beam 4 S7-RBS-C vertical stiffener S7 Cyclic 5 S46-CP-M RHS S46/Ext. diaphragm and IPE4 S355/CP S355 CP Monotonic Beam 6 S46-CP-C vertical stiffener S46 Cyclic 7 S7-CP-M RHS 25 1 S7/Ext. diaphragm and IPE4 a S355/CP S355 CP Monotonic Beam 8 S7-CP-C vertical stiffener S7 Cyclic 9 S46-RBS-R-M RHS S46/Ext. diaphragm and IPE4 a S355/- RBS-R Monotonic Joint components b 1 S46-RBS-R-C vertical stiffener S46 Cyclic 11 S7-RBS-R-M RHS 25 1 S7/Ext. diaphragm and IPE4 a S355/- RBS-R Monotonic Joint components b 12 S7-RBS-R-C vertical stiffener S7 Cyclic 13 S46-CP-R-M RHS S46/Ext. diaphragm and IPE4 a S355/CP S355 CP-R Monotonic Joint components b 14 S46-CP-R-C vertical stiffener S46 Cyclic 15 S7-CP-R-M RHS 25 1 S7/Ext. diaphragm and IPE4 a S355/CP S355 CP-R Monotonic Joint components b 16 S7-CP-R-C vertical stiffener S7 Cyclic a The section dimensions for IPE4 beam are: height 4 mm, flange width 18 mm, web thickness 8.6 mm, and flange thickness 13.5 mm. b For these specimens, the beam flanges were reinforced [Fig. 5(d)] in order to force the failure of the welded connections and/or the yielding of the joint components (i.e., cover plates, external diaphragm, and column web panel). ASCE J. Struct. Eng.

8 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. For CP joints extended cover plates were used (Figs. 5, 15, and 16). Test Set-Up, Instrumentation, Loading Protocols The conceptual scheme and a photograph of the experimental test set-up are shown in Fig. 6. A hydraulic actuator connected at the tip of the beam served as loading device. The column was supported at Pinned connections Fig. 5. Welded external diaphragm beam-to-column joints with reduced beam section; cover plates; standard joint specimens; (d) corresponding strong-beam joint specimens Hydraulic actuator Lateral support system (d) both ends using pinned connections. The horizontal and vertical displacements were blocked by the right support, and only the vertical displacements were restrained by the left support. In addition, the out of plane deformations of the beam were blocked through the use of a lateral support system. The instrumentation was considered at both global and local level. The global instrumentation allowed assessing the force in the actuator, the displacement at the tip of the beam, and the Fig. 6. Experimental test set-up: conceptual scheme; test assembly ASCE J. Struct. Eng.

9 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Fig. 7. Instrumentation of beam-to-column joint assemblies: global instrumentation; local instrumentation within dissipative zone, connection zone, and column web panel Fig. 8. Definition of the bending moment and rotation for the beam-tocolumn joint assembly horizontal and vertical displacement of the column ends [Fig. 7]. Local instrumentation was aimed to measure the deformations within the dissipative zone and the connection zone, as well as in the column web panel [Fig. 7]. In order to identify the sequence of yielding, the connection zone was whitewashed. The parameters used to control the tests were the interstory drift θ of test assembly and the bending moment M computed at column Table 4. Tensile and Charpy V-Notch Test Results for Steel Samples centerline. Monotonic loading was applied by progressively increasing the displacement at the tip of the beam. One unloadingreloading phase was considered for a better estimation of the initial stiffness. The ANSI/AISC 341 (AISC 21b) loading protocol was used for the cyclic loading. Fig. 8 illustrates the definition of the bending moment and rotation. As can be observed, the bending moment was computed as the product between the force applied at the tip of the beam and the distance to the column centerline. The rotation was computed as the ratio between the actual displacement measured at the tip of the beam and the distance to the column centerline. The actual displacement at the tip of the beam was computed using the value measured with the displacement transducer (DHTR), from which the following values were subtracted: (1) the horizontal displacement measured at supports, and (2) the horizontal displacement at the tip of the beam due to the rotation of the assembly as a rigid body (displacement transducers at the supports allowed to compute the rotation of the assembly as a rigid body). Material Properties A set of experimental investigations were performed on material samples with the aim of assessing the characteristics of all parts of the joint assemblies. Compression tests on concrete cube samples were performed at 28 days from concrete casting, obtaining an average characteristic strength in amount of 35.9 N=mm 2. Tensile tests Charpy V-notch tests Number Joint component Steel grade R eh (N=mm 2 ) R m (N=mm 2 ) A (%) A g (%) T ( C) KV (J) 1 IPE 4 flange S355 JR IPE 4 web a S355 JR Cover plates S355 J Splice plate S355 J RHS S46 M RHS 25 1 a S7 QL External diaphragm S46 NL External diaphragm S69 QL Vertical stiffener S46 NL Vertical stiffener a S69 QL Note: The splice plate was used for the RBS joints; it represented the plate welded on the web of the beam and which has the purpose to position and fix the beam to the columns during construction. a Prepared with 7.5-mm thickness. ASCE J. Struct. Eng.

10 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. In addition, tensile and Charpy V-notch impact tests were performed on the steel samples prepared from additional material (profiles and plates) associated to each component of the beamto-column joints. The results are summarized in Table 4. Consequently, the average values are shown for each component in terms of: yield stress (R eh ), tensile strength (R m ), elongation at fracture (A), and elongation at maximum force (A g ). The table shows also the results obtained from the Charpy V-notch tests, i.e., the average value of the absorbed energy (KV), and the temperature of the samples during the test. It is to be noted that the samples marked with footnote a were prepared with 7.5 mm thickness. The obtained results allowed assessing the properties of all joint parts and confirmed that the steel grades were in accordance with the code requirements and the requested steel grades. NDT Quality Control of Welded Connections As part of the experimental program, a set of nondestructive tests (NDT) were performed for the quality control of the welded connections realized between the main parts of the joint assemblies. It is to be noted that the NDT quality control was carried out using three particular methods: (1) liquid penetrant inspection, (2) magnetic particle inspection, and (3) ultrasonic testing. The first two methods did not evidence any discontinuities. As a result, the in-depth investigation was performed by ultrasonic testing. From the investigation of the welded connections, the ultrasonic testing method evidenced only local discontinuities (in the allowed range) for all joint assemblies, with the exception of S7-CP-R-M and S7-CP-R-C joint assemblies. In both cases, the investigation revealed a full-length discontinuity at the root of the welded connection between the plates of the external diaphragm. As a result, the failure of the external diaphragm, evidenced during the experimental investigation of S7-CP-R-M/C joints, can be justified. However, it is to be mentioned that the failure of the welded connection was not a premature one. As shown in Fig. 22, the failure of the welded connection occurred under a significant higher load level compared to the fully yielded and strain hardened plastic hinge which developed in the S7-CP-M joint specimen. Test Results Behavior of Standard Joints The primary test results are shown in terms of moment-rotation curve (computed at column centerline) and photographs of the failure mode. Figs present as comparison the responses of joint specimens under monotonic and cyclic loading. For all figures, the photographs of the failure mode are shown for joints subjected to monotonic and cyclic loading. Figs. 9 and 1 show the response of S46-RBS and S7-RBS joints. The yielding was initiated in the beam flanges within the RBS zone and was followed by large plastic deformations local buckling of flanges and web. No damage was observed in the external diaphragm and column web panel. Furthermore, Figs. 11 and 12 show the response of S46-CP and S7-CP joints. Yielding was initiated in beam flanges near cover plates and was followed by the local buckling of flanges and web. No damage was observed in cover plates, external diaphragm and column web panel. S46-RBS-C S46-RBS-M (d) Fig. 9. S46-RBS joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions ASCE J. Struct. Eng.

11 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved S7-RBS-C S7-RBS-M Fig. 1. S7-RBS joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions S46-CP-C S46-CP-M (d) (d) Fig. 11. S46-CP joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions ASCE J. Struct. Eng.

12 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved S7-CP-C S7-CP-M Fig. 12. S7-CP joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions S46-RBS-R-C S46-RBS-R-M (d) (d) Fig. 13. S46-RBS-R joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions ASCE J. Struct. Eng.

13 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Behavior of Corresponding Joint Assemblies with Artificially Strengthened Beams Figs. 13 and 14 show the response of S46-RBS-R and S7-RBS-R joints. The yielding was initiated in the heat affected zone (HAZ) of the beam flanges (between the reinforcing plate and external diaphragm) under compression and tension, and was followed by yielding of web and external diaphragm. Eventually, the beam flanges subjected to tension forces fractured in the HAZ. Figs. 15 and 16 show the response of S46-CP-R and S7-CP-R joints. In case of S46-CP-R joints, the yielding was initiated in the external diaphragm and was followed by local deformations of cover plates under compression and tension, and yielding of the column web panel. For the S7-CP-R joints, the yielding was initiated in the compressed cover plate and was followed by failure of the welded connection between plates of the external diaphragm, however corresponding to forces higher than the design capacity computed with the tested material properties S7-RBS-R-C S7-RBS-R-M Fig. 14. S7-RBS-R joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions (d) to the response under monotonic loading conditions. In addition, the experimental investigation of the joint assemblies under the two loading conditions offered valuable information on multiple levels. In particular, the response under monotonic loading conditions enabled the calibration of numerical models and validation of the analytical design procedure, while the response under cyclic loading conditions enabled the seismic performance evaluation of the joint assemblies. In case of the same type of loading and the same type of joint (e.g., RBS or CP), but with columns realized with different steel grades, it was observed that the performance of the joint assemblies, in terms of strength and ductility, was the same but with differences in terms of initial stiffness (Fig. 17). The columns realized from higher steel grade (S7) were characterized by a smaller cross section, and therefore the elastic rotation of the column was slightly higher, respectively the initial stiffness of the joints was slightly lower. Comparison and Interpretation of Results Influence of Loading Conditions and Steel Grade within the Column Considering the influence of the loading conditions, each of the four standard joint configurations [Fig. 5] subjected to cyclic loading evidenced similar strength, but lower ductility compared Contribution of Components to the Joint Rotation The measurements performed during tests allowed assessing the contribution of the following regions: plastic hinge, connection zone, and column web panel. In case of RBS joints, the instrumentation of the connection zone [Fig. 7] included the following regions: external diaphragm, welded on-site connection, and the beam flanges over the distance a [Fig. 1]. In case of CP joints, the instrumentation of the connection zone [Fig. 7] included the ASCE J. Struct. Eng.

14 S46-CP-R-C S46-CP-R-M Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. following regions: external diaphragm, welded on-site connection, and cover plates. Fig. 18 shows the contribution of components to the joint rotation under both monotonic and cyclic loading conditions. In particular, the results are shown for S46-RBS joints [Fig. 18] and S46-CP joints [Fig. 18]. As can be observed, the main plastic deformations occurred in the beam (dissipative zone). The contribution of the connection and column web panel to the overall joint rotation were observed to be low, with one remark, i.e., in case of RBS joints, the measurement of the deformation in the connection zone included also the beam flange situated between the reduced beam section and external diaphragm [see the displacement transducers labelled DWL and DWR in Fig. 7]. Due to the fact that some deformations developed in that particular part of the beam flange, the measurements were affected. However, the welded connection and the external diaphragm were characterized by an elastic response, as was observed within the numerical investigation program, see Vulcu et al. (216). In case of S7-RBS and S7-CP joint assemblies, the contribution of components to the joint rotation were observed to be similar, see Dubina et al. (215). Fig. 19 shows the contribution of components to the rotation of joint assemblies with artificially strengthened beams subjected to monotonic loading. As can be observed, the deformations within the reinforced part of the beam were proved to be low. Besides the elastic rotation of the beam and column, the main contribution to the overall joint rotation was given by the connection Fig. 15. S46-CP-R joints: connection zone before test; response to monotonic and cyclic loading; (c, d) failure mode under the two loading conditions (d) zone in case of RBS-R joints [Figs. 19(a and b)], respectively by the connection zone and column web panel in case of CP-R joints [Figs. 19(c and d)]. Under cyclic loading conditions, the contribution of components to the joint rotation was observed to be similar. Apart from the observations made during the experimental tests with regard to the yielding sequence and, respectively, the regions where plastic deformations were developed, the local joint instrumentation allowed the quantitative assessment for the contribution of components to the joint rotation. Consequently, the intended failure mechanism summarized in Table 3 was confirmed. In particular, the response of the four designed joint configurations [Fig. 5], was characterized by the development of large plastic deformations in the dissipative zone of the beam and the elastic response of the joint. Furthermore, the corresponding joint assemblies with artificially strengthened beam [Fig. 5(d)], were characterized by the development of plastic deformations and/or failure of the joint components (beam flanges in the heat affected zone, cover plates, external diaphragm, column web panel). Strength of the Connection Components With the aim of assessing the strength of the connection components, a comparison was made between the four standard joints [Fig. 5] and the corresponding joints with artificially strengthened beam [Fig. 5(d)]. For this purpose, the bending moment and rotation for each joint configuration were computed at the connection of the beam to the external diaphragm. ASCE J. Struct. Eng.

15 S7-CP-R-C S7-CP-R-M Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved S46-RBS-M S7-RBS-M Fig. 16. S7-CP-R joints: connection zone before test; response to monotonic and cyclic loading; (c, d) illustration of failure mode under the two loading conditions S46-CP-M S7-CP-M Fig. 17. Influence of the steel grade within the column on the response of: RBS joints; CP joints (d) Fig. 18. Contribution of components to joint rotation standard joints (note: rotation of the column web panel was computed based on the diagonal displacement transducers; see local instrumentation): S46-RBS; S46-CP (monotonic and cyclic) ASCE J. Struct. Eng.

16 Connection Column panel Reinforced beam Connection Column panel Reinforced beam Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved The strength of the connection zone for RBS joints is illustrated in Fig. 2. As can be observed, several points are marked on the curves. In case of the standard joints (S46-RBS-M and S7- RBS-M), the values represent the maximum bending moment corresponding to the fully yielded and strained hardened plastic hinge. In case of the joint assemblies with artificially strengthened beam, the values marked on the curves correspond to the following: (1) initiation of yielding within the beam flange near the connection to the external diaphragm, i.e., in the heat affected zone (HAZ), (2) initiation of yielding within the external diaphragm, and (3) fracture of beam flange near the connection to the external diaphragm (in the HAZ). A photograph (detail) of the component yielding is shown in Fig. 21. For these joint configurations, the yielding of the column web panel was not evidenced, see Vulcu et al. (216). In addition, Table 5 summarizes the yielding sequence, strength and over-strength (expressed as a percentage) of the connection zone corresponding to both joints with strengthened beam. As can be observed, corresponding to the maximum bending moment, the Connection Column panel Reinforced beam (d) Connection Column panel Reinforced beam Fig. 19. Contribution of components to joint rotation joints with artificially strengthened beam (note: rotation of the column web panel was computed based on the diagonal displacement transducers; see local instrumentation): S46-RBS-R-M; S7-RBS-R-M; S46-CP-R-M; (d) S7- CP-R-M S46-RBS-R-M S46-RBS-M S7-RBS-R-M S7-RBS-M Fig. 2. Strength of connection zone for: S46-RBS joints; S7-RBS joints other components were characterized by an elastic response. Furthermore, the yielding of the external diaphragm was initiated at 2.4% and respectively 43.9% additional load, while the complete failure of the joint assemblies (fracture of beam flanges in HAZ) occurred corresponding to higher load levels (43.4% for S46-RBS-R, 52.1% for S7-RBS-R). In the same way, the strength of the connection zone for CP joints is illustrated in Fig. 22. As can be observed, several points are marked on the curves. In case of the standard joints (S46-CP-M and S7-CP-M), the values represent the maximum bending moment corresponding to the fully yielded and strained hardened plastic hinge. In the case of the joint assemblies with an artificially strengthened beam, the values marked on the curves correspond to the following: (1) yielding of external diaphragm, (2) yielding of cover plates, (3) yielding of column web panel, and (4) failure of external diaphragm (in particular, failure of the welded connection). A photograph (detail) of the component yielding and/or failure is shown in Fig. 23. In addition, Table 6 summarizes the yielding ASCE J. Struct. Eng.

17 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. sequence, strength, and over-strength (expressed as a percentage) of the connection zone corresponding to both joints with strengthened beam. As can be observed, corresponding to the maximum bending moment, the other components were characterized by an elastic response. In case of the S46-CP-R joint, the yielding was initiated in the external diaphragm, cover plates and column web panel corresponding to 5.3, 71.5, and 83.8% higher load Table 5. Yielding Sequence and Over-Strength of Connection Zone for RBS Joints (Vulcu et al. 216 for Further Information) Yielding of component Value of the corresponding bending moment (knm) Over-strength with respect to standard joint (%) S46-RBS-R Yielding of beam flange in HAZ Yielding of external diaphragm Fracture of beam flange in HAZ S7-RBS-R Yielding of beam flange in HAZ Yielding of external diaphragm Fracture of beam flange in HAZ S46-CP-R-M S46-CP-M Fig. 21. Detail of component yielding/failure: S46-RBS-R joints; S7-RBS-R joints levels. In case of S7-CP-R joint, the yielding was initiated in the cover plates, external diaphragm, and column web panel corresponding to 36.3, 61.7, and 66.4% higher load levels. Furthermore, the complete failure of the joint assemblies (extended plastic deformations within S46-CP-R-M joint and failure of the external diaphragm of the S7-CP-R-M joint) occurred at 12.7 and 87.3% higher load levels. The yielding sequence and the strength of the connection zone for RBS and CP joints summarized in Tables 5 and 6 was established in association with the numerical investigation program, in particular based on the calibrated numerical models of each joint configuration, see Vulcu et al. (216). During the experimental investigations, only the large deformations could be observed, and therefore, the numerical simulations contributed to a better understanding of the behavior and response of the joint assemblies, e.g., observation of the yield initiation. Seismic Performance of the Joints The seismic performance of the joints subjected to cyclic loading was assessed by identifying the joint rotation corresponding to three performance levels (damage limitation, DL; significant damage, SD; near collapse, NC), assumed to be characterized by the following description [based on FEMA 356 (FEMA 2a)]: S7-CP-R-M S7-CP-M Fig. 22. Strength of connection zone for S46-CP joints; S7-CP joints ASCE J. Struct. Eng.

18 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Damage limitation: light damage, with the component retaining the initial strength and stiffness; Significant damage: significant damage, with some margin against total collapse of the component; and Near collapse: heavy damage, with low residual strength and stiffness of the component. Envelope curves were first constructed based on the provisions from FEMA P-795 (FEMA 211) for each cyclic moment-rotation data. In a second step, the rotations corresponding to the three performance levels were identified. It was considered that the damage limitation performance level corresponds to the yield rotation (θ y ) computed using the ECCS (1986) procedure (intersection of two lines with slopes equal to initial stiffness and 1% of it). The rotation related to the significant damage performance level was considered as corresponding to the drop of moment to.8 M max, but not more than.75 times the rotation at near collapse. Finally, the rotation associated with near collapse performance level, was considered as corresponding to a drop of moment to.2 M max, but not more than the maximum deformation attained during the test. Figs. 24 and 25 illustrate the envelope curves and the state of S7-RBS-C and S7-CP-C joints corresponding to the three Fig. 23. Detail of component yielding/failure: S46-CP-R joints; S7-CP-R joints Table 6. Yielding Sequence and Over-Strength of Connection Zone for CP Joints (Vulcu et al. 216 for Further Information) Yielding of component Value of the corresponding bending moment (knm) Over-strength with respect to standard joint (%) S46-CP-R Yielding of external diaphragm Yielding of cover plates 1, Yielding of column web panel 1, Extended plastic deformations 1, S7-CP-R Yielding of cover plates Yielding of external diaphragm 1, Yielding of column web panel 1, Failure of external diaphragm 1, performance levels. Furthermore, Table 7 summarizes the rotation of the four joint assemblies [Fig. 5] corresponding to each performance level. In relation to the performance of the joints, the following observations were made: The state of the joints corresponding to the three performance levels (Figs. 24 and 25) was observed to reflect in a realistic manner the definitionrelatedtoeachperformance level; and Corresponding to the significant damage performance level, all four joint configurations evidenced rotation capacities larger than the 4 mrad [a common code requirement for high-ductility MRF s; see EN (CEN 24b)], and therefore the seismic performance of the joints was considered acceptable. Conclusions The paper presents the outcome of an experimental program developed and carried out with the aim of characterizing the behavior of two types of moment resisting joints in multistory frames of concrete-filled HSS rectangular hollow section (RHS) columns and MCS beams. The paper also describes the design approach and displays the specific detailing for the two welded joint typologies: with reduced beam section (RBS) and with cover plates (CP). As a general conclusion, the monotonic and cyclic tests evidenced a good conception and design of the joints (RBS and CP), justified by several aspects: (1) elastic response of the connection zone, (2) formation of the plastic hinge in the beam, and (3) adequate response of joint components. Furthermore, the comparison and interpretation of results lead to the following observations/ conclusions: The joints subjected to cyclic loading evidenced similar strength, but lower ductility compared to the response under monotonic loading conditions; The performance of the joint assemblies, in terms of strength and ductility, was not affected by the use of columns made from higher steel grade (e.g., S7). Only the initial stiffness was ASCE J. Struct. Eng.

19 Downloaded from ascelibrary.org by THE UNIVERSITY OF NEWCASTLE on 1/19/17. Copyright ASCE. For personal use only; all rights reserved. Fig. 24. S7-RBS-C envelope curves; state of joint corresponding to: damage limitation; significant damage; (d) near collapse performance levels Fig. 25. S7-CP-C: envelope curves; state of joint corresponding to: damage limitation; significant damage; (d) near collapse performance levels slightly affected due to the smaller cross-section of the column (i.e., smaller moment of inertia), which lead to slightly higher elastic rotation of the column; For RBS and CP designed joints, the main plastic deformations occurred in the dissipative zone of the beam (plastic hinge), while the contribution of the joint components (connections, cover plates, external diaphragm, column web panel) to the overall joint rotation were observed to be low; Significant deformations within joint components were evidenced only in case of the joint assemblies with artificially strengthened beams, which confirmed the intended plastic mechanism; and ASCE J. Struct. Eng.