Complete Joint Penetration Welds Research Articles

Hysteretic behaviour of welded connections with highly inelastic panel zones

AbstractThe current practice in capacity‐designed steel moment resisting frames (MRFs) worldwide allows for limited shear yielding in the column web panel zone. As such, inelastic deformations concentrate near the beam ends, thereby leading to flexural strength deterioration due to local buckling often at modest lateral drift demands. Experiments on post‐Northridge welded connections suggest that prior to a story drift angle of 5% rad, panel zone kinking does not induce fracture for panel zone shear distortions of up to 10γy. Within such a context, this paper presents an alternative design of a welded moment connection with highly inelastic panel zones. The connection features simplified weld details including a customised beveled backing bar that can be kept in place after the completion of the complete joint penetration welds at the beam flange‐to‐column flange joint. Full scale experiments suggest that the hysteretic response of the connection remains stable up until a story drift angle of 8% rad. The specimen did not exhibit visible structural damage prior to story drift angles of 4% rad, which are characteristic to a maximum considered earthquake. Modest local buckling occurred near the beam ends only after a story drift angle of 5% rad, which is a typical drift threshold in current collapse assessment methodologies. This paper summarises the primary findings of the experimental program for one of the test specimens.

Qualification of Electroslag Welds made from HPS 485W (70W) and 345W (50W) Steels

Electroslag welding (ESW) is a highly efficient welding process for completing single-pass complete joint penetration welds that offers production gains over conventional welding processes. This gain in productivity requires very high heat inputs, often to the detriment of the base metal's heat-affected zone (HAZ) impact energy. U.S. bridge-welding codes recognize the ESW Narrow Gap (termed ESW-NG) process developed in the early 1980s to remedy the substandard weld and HAZ impact energies found in bridges across the United States fabricated with the original ESW process used roughly from 1967 to 1977. ESW-NG process is limited to certain base metals; particularly, ESW-NG with quenched and tempered (Q&T), and thermo-mechanically controlled processed steels are prohibited because they are not part of the ESW-NG process development. This study was specifically performed to evaluate whether the existing ESW-NG process could be qualified for use with grade HPS 485W (70W) Q&T bridge steel and hybrid weldments between grade HPS 485W (70W) Q&T and conventionally processed grade 345W (50W) bridge steels. None of the weldments met fracture critical impact requirements. The weldment of just Q&T steel and the hybrid weldment met nonfracture critical requirements. However, the weldment of just Q&T had tension and impact resistance results right on the margin, leaving little room for error.

Assessment of partial joint penetration welds on bolted end-plate connections

End-plate moment connections are a very common connection type used in today’s metal building industry. Bolted end-plate connections are especially popular because they can be engineered to meet design requirements for moment resisting connections used in seismically active areas. The current industry standard for end-plate moment connections is to use complete joint penetration (CJP) welds when making end-plate to flange welds. An alternative to CJP welds is partial joint penetration (PJP) welds, which leaves some portion of the base metals’ thickness unfused. PJP welds may save time and money in the fabrication of the end-plate connections but the use of PJP welds in this application is currently not considered in the Seismic Provisions for Structural Steel Buildings AISC/ANSI 341-10[1]. The objective of this research was to evaluate the effectiveness of properly detailed PJP flange welds on end-plate connections when subjected to seismic loading by using a pseudo-static loading protocol. Two of the same multiple row extended end-plate moment connection tests were conducted at the University of Oklahoma’s Donald G. Fears Structural Engineering Laboratory. The tested specimens were 44 in. (111.76 cm) deep, cantilevered beams connected to a column via a bolted end-plate. A concentrated load was applied on the beam’s tip creating a moment at the beam to column connection. This created forces acting on the flange to end-plate welds. The specimens were tested in accordance to AISC 341-10’s[1] criteria on cyclic tests for qualification of beam to column connections. Both six-bolt multiple row extended end-plate connections made with PJP welds met AISC 341-10’s[1] requirements for beam to column connection in Intermediate Moment Frames. The specimens’ flanges and webs deformed plastically, while no weld failures were observed during testing. The PJP welds used on the tested beams’ flange to end-plate connections performed favorably. It is the authors’ beliefs that these results may serve as a good starting point for further examination of PJP weld capabilities when subject to seismic loading. Further testing of PJP welds would help to understand their ultimate capabilities. To date the 44 in. (111.76 cm) deep test sections are to our knowledge, the deepest sections that examined PJP flange to end-plate connections subject to seismic loading successfully achieving a 0.02 rad story drift angle.

USING FILLET WELDS INSTEAD OF CJP GROOVE WELDS IN DIRECTLY-WELDED FLANGE FR MOMENT CONNECTIONS

The possibility to use fillet welds instead of complete joint penetration welds (CJP ) in directly- welded flange FR (fully restrained) connections is the main aim of this study. An experimental comparison has been made between these two types of welds. Fifteen specimens have been configured by welding plates to form butt, Tee and lap joint connections; three specimens with butt-joint, six with lap-joint, and six specimens were with T-joint. Fillet and CJP groove welds separately have been used to make these connections. After testing of all these specimens, the results indicated that the appropriately sized fillet weld is a good alternative to CJP groove weld when it is used for fully restrained FR moment connections.

Seismic Response of Partial-Joint-Penetration Welded Column Splices in Moment-Resisting Frames

Current standards require that welded column splice connections in special or intermediate moment resisting frames (SMRFs or IMRFs) feature complete-joint-penetration (CJP) groove welds to develop the full flexural strength of the column. CJP welds are often costly, requiring additional material, inspection and labor. Compared to beam-to-column connections, column splices have modest deformation demands. This suggests that perhaps with modern, toughness-rated weld filler materials and welding practices, PJP welded splices may offer acceptable performance under seismic loads. A study featuring five full-scale tests on PJP-welded column splices is presented. The test matrix investigates a range of parameters including column sizes as well as variations in connection details. Specimens were loaded cyclically in a three-point bend configuration subjecting the splice to demands consistent with those in severe earthquakes; a loading protocol was developed specifically for this purpose based on nonlinear time history simulations. All the full-scale specimens exhibited excellent performance. A series of finite element fracture mechanics simulations is also presented to assist with the generalization of test results. The test and simulation data are encouraging from the perspective of adoption of PJP welded splices in IMRFs and SMRFs in seismic regions. Limitations of the research are outlined, along with discussion of future work to develop the concept further.

Panel Zone Deformation Capacity as Affected by Weld Fracture at Column Kinking Location

Three full-scale specimens were tested to evaluate the cyclic performance of rehabilitated pre-Northridge steel beam-to-column moment connections. A Kaiser bolted bracket (KBB) was used on the beam bottom flange for all specimens, but different rehabilitation schemes (another KBB, a notch-tough beam flange replacement weld, or a double-tee welded bracket) were used to strengthen the top flange. All specimens were able to sustain an interstory drift angle of 0.04 radian, with large inelastic deformations in the panel zone. Two specimens experienced fracture at the replacement complete-joint-penetration (CJP) welds, mainly due to the large shear deformation in the panel zone. Because it may not be economically feasible to mitigate weak panel zones in seismic rehabilitation, an analytical model was developed to predict the panel zone deformation capacity and the associated strength. In this model, it was postulated that the ultimate panel zone deformation capacity corresponded to that when each column flange was fully yielded and excessive kinking would cause fracture of the beam flange CJP welds. This postulation was verified by the test data of two specimens that experienced weld fracture due to excessive panel zone deformation. It was shown that the deformation capacity is a function of db/tcf (beam depth-to-column flange thickness ratio). The effect of column axial load was also studied.

Probabilistic demand and fragility assessment of welded column splices in steel moment frames

SummaryAn assessment of seismic demands and capacities of welded column splice (WCS) connections in steel moment frames is presented. For demand assessment, nonlinear dynamic analyses are conducted for two case‐study buildings, that is, a 4‐story and a 20‐story moment frame. Results from the nonlinear dynamic analyses are assessed through a probabilistic seismic demand analysis (PSDA) framework to characterize recurrence rates of longitudinal flange stress in these connections. The PSDA is applied in two contexts. First, in the context of WCS connections constructed prior to the M 6.7 1994 Northridge earthquake, the PSDA is combined with sophisticated finite element‐based fracture mechanics analysis to compute the mean annual frequencies of fracture in these connections. The pre‐Northridge WCS are especially critical because they feature partial joint penetration and brittle materials that compromise their resistance to fracture. The analysis indicates that the mean annual frequencies of fracture in these connections may be unacceptably high for both the 4‐story and the 20‐story frames. This warrants a serious and urgent consideration of retrofit strategies. These findings are attributed to the brittleness of the pre‐Northridge splices (as indicated by the fracture mechanics simulations), as well as the force‐controlled nature of these components, wherein low‐intensity ground motions contribute disproportionately to fracture risk, as evidenced by fracture risk disaggregation. Second, in the context of new construction, the PSDA provides meaningful stress magnitudes for design. Currently, WCS connections employ complete joint penetration welds with the intent to develop the smaller column flange in yielding. The PSDA conducted in this study suggests that this requirement may be too stringent because stress demands in the splices corresponding even to high return periods (e.g., 2475 years) are significantly lower (~40 ksi), as compared with the stress required to yield the column (~55 ksi). Limitations of the study are outlined. Copyright © 2015 John Wiley & Sons, Ltd.

Fatigue and residual strength of concrete-filled tubular X-joints with full capacity welds

This paper presents the experimental findings on the fatigue performance and residual strength of the circular hollow section X-joints with a concrete-filled chord. The welding profile along the brace-to-chord intersection employs a recently proposed set of welding details, namely the full capacity tubular joint welds. The experimental investigation focuses on: 1) the stress concentration comparison corresponding to different stages of the specimen preparation, 2) the fatigue crack initiation life and propagation life; and 3) the comparison of the measured fatigue life with respect to the design S-N curves. The experimental measurement reveals that the fatigue crack propagation life contributes to a significant portion of the total fatigue life for both the hollow section tubular joints and the concrete-filled tubular joints. The total fatigue life of the test specimens complies with the life estimation based on the existing design S-N curves, originally developed for tubular joints fabricated using the complete joint penetration welds. The residual strength of the fatigue-cracked tubular joints follows approximately a linear relationship with respect to the percentage of the crack area along the brace-to-chord intersection.

Effect of various span lengths on seismic demand on column splices in steel moment frames

Steel moment frames have gone through intensive investigation to understand the cause of the damage since the 1994 Northridge–California earthquake. A research conducted by the SAC Joint Venture has helped to improve the current code requirements for steel special moment frame design. One major outcome of these research efforts was on the enhanced design requirements for column splices. For example, AISC 341 Seismic Provisions require that column splices in intermediate and special moment frames, when not made using complete joint penetration welds, be designed to develop the expected flexural strength of the smaller connected column and the shear demand associated with flexural hinging at the top and bottom of the spliced column. This paper focuses on the effect of various span lengths on seismic demands on column splices in steel moment-resisting frames. A comprehensive nonlinear analytic investigation was undertaken to evaluate the seismic responses of 4- and 9-story moment-resisting frames with constant and various span lengths subject to an ensemble of 20 strong ground motions. The results indicate that the structural response is sensitive to the span length and variable span length within the frame might significantly increase the seismic demand on column splices.

A Flexibility-Based Formulation for the Design of Continuity Plates in Steel Special Moment Frames

This paper introduces a rational approach for the design of continuity plates and associated welds in steel special moment frame (SMF) connections. The current AISC Seismic Provisions require welds attaching continuity plates to develop the full strength of the plate, resulting in the need to use complete-joint-penetration (CJP) groove welds. The combination of continuity plate thickness requirements, welding process and weld inspection often leads to costly detailing that may be overly conservative. The proposed design procedure, which is based on the relative flexibility between the column flange and continuity plate, aims to quantify the seismic force demand on continuity plates, thus allowing designers to efficiently size both the continuity plate thickness and the associated welded joints. In addition, the design procedure may allow the use of fillet welds or partial-joint-penetration groove welds as opposed to CJP welds, leading to a more economical design and fabrication. Formulation of the design procedure through analytical studies, including finite element analysis, is outlined.

Fatigue performance of tubular X-joints with PJP+ welds: I — Experimental study

This study examines the fatigue performance of tubular joints fabricated using a new type of enhanced partial joint penetration weld details under constant-amplitude brace in-plane bending actions. The experimental program includes four cyclic tests on two large-scale X-joints, each with a different surface treatment near the weld toe. The experimental results confirm the satisfactory fatigue performance of the tubular X-joints welded using enhanced partial joint penetration welds in comparison with the S-N curves developed for tubular joints with complete joint penetration welds, and demonstrate the significant improvement on the fatigue life rendered by the weld surface grinding and toe grinding. Root fatigue cracking occurs only in specimens with post-weld toe-grinding treatment which enhances the fatigue life for toe cracking.

Effect of weld details on the ductility of steel column baseplate connections

Results from six two-thirds scale tests on moment-resisting steel column base plates are presented. The test specimens incorporate Complete Joint Penetration (CJP) and Partial Joint Penetration (PJP) weld details between the column and the base plate. The test data indicate that both details are resilient to fracture and sustain inelastic column hinging to story drift ratios of 6%–9%, which exceeds the typical acceptance criteria of 4% drift ratio for seismically detailed special moment frames. In five of the six tests, fractures initiated in the Heat Affected Zone (HAZ) at the fusion line between the weld and column flange. In the sixth test, fractures initiated at the inside face of the column flange at the upper edge of the weld access hole of the CJP weld detail. Contrary to the initial expectations, the specimens with the PJP welds exhibited higher displacement ductility than those with CJP welds. This is attributed to the fillet reinforcing that strengthens the PJP welds and enables them to sustain stresses and strains necessary to fully develop yielding in the column flanges. The test data further support the adequacy of the FEMA 350 provisions for determining the required strength of the welds based on the probable moment demand with the material overstrength factor of R y = 1.1 and strain hardening factor of C p r = 1.2 .

Seismic behavior of steel beams and CFT column moment-resisting connections with floor slabs

This research investigates the seismic performance of four steel beams to concrete filled steel tube (CFT) column connections with floor slabs, including two interior and two exterior joints. The objective of this research is to evaluate firstly the composite effect of the steel beam and floor slab commonly used in Taiwan in practice. Secondly, the seismic behavior of new connection details such as the taper flange or larger shear tab in the beam-end is investigated to prevent complete joint penetration welds (CJP) of the girder flanges from the unexpected brittle failure found in the latter after the Northridge earthquake. In addition to the experimental investigation, the development and validation of analytical models for the assessment of the force–deformation behavior of the joint components are also conducted. The slab effect on the shear transfer in the panel zone is investigated as well.

Experimental Investigation of Reduced Beam Section Moment Connections without Continuity Plates

The AISC 2002 Seismic Provisions for Structural Steel Buildings recommend that usage and sizing of beam flange continuity plates across the column web shall be based on tests. The Recommended Seismic Design Criteria for New Steel Moment-Frame Buildings ( FEMA-350) state that unless project-specific testing is performed to demonstrate that continuity plates are not required, moment-resisting connections should be provided with continuity plates when the thickness of the column flange is below a minimum value. One of the preferred moment connections for seismic-resistant steel frames is the reduced beam section (RBS) moment connection, which has performed well under cyclic loads in laboratory testing. To demonstrate the effectiveness of the RBS moment connection without continuity plates in the panel zone, a series of four full-scale tests of exterior beam-column connections was carried out. All materials were A572 Grade 50 steel; the beams were W30×132, two of the assemblies used W14×283 columns, and the other two used W18×211 columns. The beams were welded to the columns using complete joint-penetration welds. All four tests demonstrated that the RBS connections without continuity plates developed a total interstory drift angle greater than 0.04 radians and met the requirements for special moment frames.

Special Issue on Behavior and Design of Steel Weldments

This special issue of the ASCE Journal of Materials in Civil Engineering is devoted to the subject of using welds to join steel members in frame structures. In particular, the focus of content is on the behavior of welded connections in building structures when subjected to strong ground shaking during severe earthquakes. It was primarily in multistory buildings that welds fractured during the 1994 Northridge, California Earthquake and also subsequently during the 1995 Great Hanshin Earthquake near the city of Kobe in Japan. Design details differ in significant ways between the steel building systems used typically in Japan and those used typically in the United States. It should be noted that the papers herein cover fundamental topics that are relevant to the experience of both nations, but the details discussed are most apropos to steel building systems used in the Western United States. Here I shall provide a very brief introduction to the problems discovered following the 1994 Northridge earthquake. A common strategy to resist drift in multistory buildings is to incorporate moment-resisting frames in the structural systems of the buildings. As the name implies, a moment-resisting frame is designed to provide continuity of shear force and bending moment through joints where girders and columns intersect. To achieve this desired behavior, steel moment frames require special connections between girder flanges and the columns so that flexural stresses from the girders can be transferred efficiently through the joint. Commonly, the girder-flange-to-column connections are complete joint penetration welds ~Fig. 1!.

Multiaxial fatigue of welded shaft-flange connections of stirrers under random non-proportional torsion and bending: Sonsino, C.M. and Pfohl, R. Int. J. Fatigue Sept. 1990 12, (5), 425–431

This study examines the fatigue performance of tubular joints fabricated using a new type of enhanced partial joint penetration weld details under constant-amplitude brace in-plane bending actions. The experimental program includes four cyclic tests on two large-scale X-joints, each with a different surface treatment near the weld toe. The experimental results confirm the satisfactory fatigue performance of the tubular X-joints welded using enhanced partial joint penetration welds in comparison with the S-N curves developed for tubular joints with complete joint penetration welds, and demonstrate the significant improvement on the fatigue life rendered by the weld surface grinding and toe grinding. Root fatigue cracking occurs only in specimens with post-weld toe-grinding treatment which enhances the fatigue life for toe cracking.