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[SEAOC] LA County position on Welded Moment Resisting Frame[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: [SEAOC] LA County position on Welded Moment Resisting Frame
- From: seaoc-ad(--nospam--at)seaoc.org (Shafat Qazi)
- Date: Wed, 21 Aug 96 14:45 PDT
The following letter was emailed to me by an employee of LA county. This letter will also be available in our FTP area on our WWW server. Shafat August 14, 1996 TO WHOM IT MAY CONCERN: COUNTY OF LOS ANGELES CURRENT POSITION ON THE DESIGN AND CONSTRUCTION OF WELDED MOMENT RESISTING FRAME SYSTEMS (WMRF) GENERAL This memorandum supercedes a March 26, 1996 memorandum on the same subject. The publication of SAC Interim Guidelines(FEMA 267) in August 1995 was a major milestone in the Northridge Earthquake recovery effort for steel moment frames and provided recommendations on engineering procedures for modification and design of WMRF structures. We continue to support the SAC effort and consider the SAC Interim Guidelines the best document to date on the WMRF issue, however, clarification and amplification is necessary for the County's current and future projects. The SAC Interim Guidelines cautioned users that research "results may invalidate or suggest the need for modification of recommendations." This memorandum is to provide up-to-date information as the result of the County?s continuing and active effort to resolve the WMRF crisis. It shall apply to County capital projects and may be used for any new buildings in Los Angeles County. A Technical Advisory Panel(TAP) consisting of experts in the design, research, and quality assurance of welded steel construction was invited to assist County engineers in meeting the WMRF challenge. Members of this panel are identified in the attachment (Attachment I). COUNTY?S POSITION ON WMRF Welded moment resisting frame systems (special or ordinary) are not permitted unless the connections proposed meet the following requirements and are submitted to and approved by the County: 1. A minimum of three full size prototype specimens of the configurations to be used shall have passed full-scale cyclic loading tests and demonstrated plastic rotational capacity equal to or greater than 0.03 radians. More than three specimens may be required if any of the first three tests demonstrated "rapid deterioration" behavior described in ATC-24, "Guidelines for Cyclic Seismic Testing of Components of Steel Structures", Chapter 4 and Commentary. a. All tests using the same concept must be reported, regardless of the test results. Information required for the report is listed in the attachment (Attachment II). b. The requirement of 0.03 radian plastic rotation capacity is subject to modifications based the strength of the beam material, the location of the plastic hinge, the basis for which this location is determined, and to account for behavioral uncertainties of the connection assembly. Therefore, the applicability of this requirement to each connection system will be evaluated accordingly. 2. Nonlinear finite element analysis, e.g. MSC-NASTRAN, ANSYS, NISA-II, NIKE-3D, etc. to demonstrate that the behavior of prototype test specimens can be rationalized by known engineering principles and properties. 3. A clear and complete design methodology for all the components of the joint assembly and their effect on other components. Describe, based on engineering principles and material properties, how each specific design attribute and/or parameter is determined, designed and controlled to achieve predictable and repeatable connection behavior. These attributes should include geometry, types of materials, doubler plates, continuity plates, cover plates, side plates, ribs, notches, drilled holes, welds, bolts, shaved flanges, slotted webs and/or flanges etc. The County?s and TAP?s extensive review of all connection systems is required. This review will consist of examining the submitted documents and test results, meeting with the proposer, and TAP issuing recommendations and reports to the County. The TAP?s reports are issued by the Construction Quality and Contracting Division as TAP SMRF-Bulletins. The TAP SMRF-Bulletins will be used to complement and interpret the SAC Interim Guidelines when necessary. ISSUES REQUIRING CONSIDERATION IN THE DESIGN, ANALYSIS AND TESTING OF WMRF CONNECTIONS A number of issues need to be considered in the design, analysis and testing of connections. It should be recognized that each of these issues affects a specific connection type in different ways and to different degrees. These issues should be considered when evaluating the performance qualification of any connection system: 1. Major Contributing Factors to the General Behavior of Connections: · Through-thickness Strength of Column Flange · Participation of the Column Panel Zone in the Required Plastic Rotational Capacity · Location of Plastic Hinge · Shorter Spans/Amplified Rotation Angle · Axial Load on Column · Plastic Moment Interaction with Significant Beam Drag Force. · Beam Material Strength (Yield and Ultimate) · Column Material Strength · Column Depth · b/t Ratio of Column Flange · b/t Ratio of Beam Flange · Connection Plate Thicknesses · Rolling Direction of Connection Plates · Weld Materials, Weld Sizes, Configurations and Fit-up · Stress Concentrations in Connection Elements, Including welds · Control of Strain Levels in Critical Connection Elements · Beam Moment Demand at Each Critical Section 2. Configuration of Connection: · Two-sided Strong-axis · One-sided Strong-axis · Dual-strong-axes · Weak-axis and Skewed-axis · Effect of Bracing Members · Restrictive Effect of Concrete Slab on the Formation of Plastic Hinge · Effect of Perpendicular Gravity Framing 3. Testing: · Extrapolation of Test Results to Member Sizes Not Tested - Methods and Justification · Test Setup to Reflect Significant Service Conditions · Test Protocol · Location of Instruments on the Prototype Test Specimen 4. Construction and Quality Assurance: · Construction Sequence · Erection Fit-up · Welding Materials and Methods · Size of Welds · Notch-toughness of Weld · Weld Finishing (e.g. Grinding, Removal of Backing etc.) For comments or questions regarding the contents of this memorandum and/or TAP SMRF-Bulletins, please contact Y. Henry Huang, Supervising Civil Engineer III at (213)738-2832 or by fax at (213)386-4818. Very truly yours, HARRY W. STONE Director of Public Works THOMAS V. SCHRIBER, Division Chief Construction Quality and Contracting Division Attachments ATTACHMENT I TECHNICAL ADVISORY PANEL (TAP) MEMBERS: Mark Saunders, SE (Chairman) · Vice President, Rutherford and Chekene Consulting Engineers, San Francisco, CA. · Director, Structural Engineers Association of California, 1993-1995 · President, Structural Engineers Association of Northern California, 1992-1993 · Vice President, Applied Technology Council · Chairman, Technical Sub-committee 6 on steel, "National Earthquake Hazard Reduction Program (NEHRP) Recommended Provisions for the Development of Seismic Regulations for New Buildings" Karl Frank, Ph.D. · Member of Executive Committee, Research Council on Steel Connections · Professor of Civil Engineering, University of Texas at Austin Egor Popov, Ph.D. · Professor Emeritus of Civil Engineering, University of California, Berkeley · Member, National Academy of Engineering · Distinguished Teacher Award - University of California, Berkeley · Recognized by the Berkeley Citation - University of California, Berkeley · President (1984), Structural Engineers Association of Northern California · Member, Specification Committee, American Institute of Steel Construction Bob Schwein, CE · Principal, Schwein/Christensen Laboratories, Inc., Lafayette, CA. Additionally, valuable contributions were made by: Chia-Ming Uang, Ph.D. · Associate Professor, Department of Applied Mechanics and Engineering Science, University of California, San Diego ATTACHMENT II REPORTING REQUIREMENTS FOR TESTS OF STEEL MOMENT FRAME CONNECTIONS 1. Test location 2. Test date 3. Investigator(s) 4. Details of the specimen (in graphical form), including any specific attributes of the connection design, such as doubler plates, continuity plates, cover plates, side plates, ribs, notches, drilled holes, shaved flanges, slotted webs or flanges. 5. Design methodology: describe, based on engineering principles and material properties, how each specific design attribute in item 4 is determined and controlled to achieve predictable and repeatable connection behavior. 6. Material Properties: · Member Size, ASTM Specification and Grade, Mill and Location, Heat Number, Tonnage · Certified Mill Test Report for All Base Metal ? Complete Mechanical Properties Showing Yield Method, Specimen Type & Location of Test Coupon in Shapes ? Complete Chemical Analysis ? Compliance with Astm Specifications and Grade · Shop or Lab Coupon Tests ? Mechanical Properties (Flange & Web) ? Yield Strength & Method ? Tensile Strength ? Elongation ? Stress/strain Diagram ? Flange & Web Locations ? CVN at 70oF on Column Material · Weld Metal ? Manufacturer's Technical Data Sheets ¨ Chemical Analysis ¨ CVN at 0o F ¨ Mechanical Properties 7. Shop and Field Fabrication: · Welding Procedure, Process and Electrode Specifications · Qualification of the Welders · Quality Control Procedure · · Quality Assurance Procedure · Ultrasonic Testing Reports 8. Testing Procedure: · Loading Protocol · Location of Instruments on the Test Specimen · Failure Criteria 9. Test Results: · Force Versus Deflection Relationships · Elastic Rotation Based on Test Specimen Column Centerline Dimensions · Plastic Rotation Based on Test Specimen Column Centerline Dimensions · Actual Plastic Rotation at the Assumed Plastic Hinge Location · Basis for the Selection of the Location for Establishing the Plastic Rotation Capacity · Actual Flexural Capacity of Test Specimen Beam Based on Laboratory Coupon Tests of Flange and Web · Actual Strain Hardening Ratio at the Plastic Hinge Location · Description of All Plastic Deformation and Rapid Deterioration Exhibited by the Test Specimen, I.e., Weld Metal, Beam and Column. · Photographic Documentation of the Testing Sequence ...
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