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[SEAOC] DUAL STRONG AXES SMRF CONECTION TEST[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: [SEAOC] DUAL STRONG AXES SMRF CONECTION TEST
- From: MNHKODell(--nospam--at)aol.com
- Date: Tue, 21 May 1996 18:49:52 -0400
MNH-SMRF SYSTEMS, INC. COMPLETES FIRST DUAL STRONG AXES TEST OF STEEL SPECIAL MOMENT RESISTING FRAME (SMRF) CONNECTION Costa Mesa, CA., May 6, 1996 - In January, 1995, MNH-SMRF Systems, Inc., completed initial development and full scale cyclic testing of the MNH-SMRF? uniaxial side plate connection system using all shop fillet-welded construction. An average plastic rotation of 5.2% radians was achieved during the three tests. The side plate connection eliminates troublesome T-joint complete penetration groove welds, and defuses the dilemma of uncertain column flange through-thickness properties, weak panel zone behavior, and peak triaxial stress concentrations found to be inherent with the pre-Northridge SMRF connection configuration. On May 3, 1996 MNH-SMRF Systems, Inc. completed the first-ever, full scale laboratory testing of a Dual Strong Axes SMRF connection at UCSD's Charles Lee Powell Structural Research Laboratories, under the direction of Professor Chia-Ming Uang. The test specimen consisted of W36x170 beams connected with side plates to a built-up cruciform column fabricated with W36x230 sections in each principal direction to form a 3-sided SMRF connection. All base metal was ASTM A572, Grade 50 steel. The MNH-SMRF? Dual Strong Axes connection was biaxially loaded by subjecting two beams in one direction to a static load of 30% of the beam flexural capacity, while cyclically loading the beam in the other direction to failure. The Dual Strong Axes connection concept is a continuation of the original MNH-SMRF? side plate connection research and is based on the earlier successful full scale tests at the University of California, San Diego. The MNH-SMRF? Dual Strong Axes connection allows the use of intersecting orthogonal frame lines in resisting earthquake loading without the use of weak axis connections, therefore maintaining the code required ?strong-column / weak-beam? criteria in each principal direction. The MNH-SMRF? Dual Strong Axes test was conducted following the industry standard ATC-24 protocol. The beam tip displacement at which significant yielding of the beam occurs (Delta-y) was determined to be approximately 1.4 in. The beam material strength (Fy) was determined by flange coupon testing to be 52.9 ksi. During the first cycle of the 3*Delta-y displacement amplitude (i.e., 4.2 in. beam tip displacement), the beam?s expected maximum plastic flexural strength of 38,870 in-kips (Mp = 1.1*Fy*Z) was exceeded when the specimen resisted the peak test load of 369 kips, corresponding to an applied moment at the plastic hinge location of 40,590 in-kips. Plastic hinging initiated prior to reaching the peak load of 369 kips. During the second cycle of the 3*Delta-y displacement amplitude, after the maximum load for this cycle began to decline, a crack at the tip of the bottom flange of the beam began to develop at the end of the bottom cover plate. The crack propagation across the beam flange was ductile and progressed through the last cycle of this load increment. During the plus excursion of the first cycle of the 4*Delta-y displacement amplitude (i.e., 5.6 in. beam tip displacement) the crack propagated through the entire flange width and into the web just beyond the web fillet (i.e., ?k? dimension). Due to the degradation of flexural capacity in the upward load direction, the test was completed by pulling the beam through a continuous downward tip displacement to a maximum of 10 in., approximately 7*Delta-y. No significant degradation of the vertical load carrying capacity was observed throughout the duration of the test. The tested MNH-SMRF? Dual Strong Axes connection exhibited the predicted behavior and strength of welds and connecting plates as determined by finite element analysis. The connection demonstrated the ability to sustain multiple inelastic cyclic rotations, achieving 3% radians beam plastic rotation at the predicted plastic hinge location, with no significant plastic deformation of any of the connection plate or weld elements. The observed performance of the MNH-SMRF? Dual Strong Axes connection indicated that the design intent to locate the energy dissipation outside of the cover and side plates was satisfied. The test demonstrated ductile behavior of the beam, as evidenced by significant flange and web local buckling, which continued through final rupture of the beam flange. All damage was confined to the base metal of the beam. The Dual Strong Axes test demonstrated that the MNH-SMRF? side plate connection can be used for biaxial applications and that orthogonal effects of earthquake forces can be successfully resisted. The MNH-SMRF? Dual Strong Axes connection has been developed to address the project requirements of the new, seismically base-isolated, Diagnostic and Treatment Facility (a 6-story building encompassing approximately 500,000 sq. ft) for the Los Angeles County/USC Medical Center Replacement Program. The use of a dual strong axes general frame and the stiffness of the MNH-SMRF? side plate connection system allows for the economical use of a steel SMRF superstructure in a seismically base isolated building. The 20,000 lb. test specimen for the Dual-Strong Axes connection was fabricated by Bickerton Iron Works at their Torrance, California fabrication plant. Funding for the testing program was shared by the County of Los Angeles and MNH-SMRF Systems, Inc. The project Architects are HOK and Lee, Burkhart, Liu of Santa Monica, and the Structural Engineer is KPFF, Los Angeles, CA. The MNH-SMRF? Dual Strong Axes connection test was witnessed by representatives of the Los Angeles County/USC Project Team (LAC+USC), Los Angeles County Department of Public Works and SMRF Technical Advisory Panel (LAC TAP), State of California Office of Statewide Health Planing and Development (OSHPD), and prominent consulting engineers. Other invited guests included representatives from AISC, the SAC Joint Venture and Los Angeles City Building Bureau. The MNH-SMRF? uniaxial connection system has been developed and qualified for a wide range of beam and column sizes. Both the MNH-SMRF? uniaxial and Dual Strong Axes connections address all of the industry's technical concerns. MNH-SMRF Systems, Inc., is an engineering service company supporting structural engineers and building owners in providing solutions for steel frame buildings, and is headquartered at 3151 Airway Avenue, Suite N-1, Costa Mesa, California, 92626. ...
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