TO: Don Gilbert
SEAOSC
FROM: Peter Maranian
SUBJECT: Dynamic Load Weld Task Group
Report No. 1341
Following some recent comments from Henry Huang, please find attached a revised synopsis on the above paper. Please replace the previous version with the attached latest version.
PJM:ag
O:\PETER\SEASCS\MISC\SYNOPSIS.DLW
DLW TASK GROUP
c/o SITECH LTD. AND c/o BRANDOW & JOHNSTON ASSOCIATES
P. O. Box 3532 1660 W. 3rd Street
Winnetka, CA 91306 Los Angeles, CA 90017
Tel. (818) 883-3741 Tel. (213) 484-8950
Fax (818) 888-2503 Fax (213) 483-5550
"Dynamic Load Welds for the Repair of Existing
Steel Moment Frame Building Damaged from Earthquake"
by
Synopsis:
During the course of the last two years, a group of volunteers called the Dynamic Load Weld (DLW) Task Group has been carrying out research and testing and soliciting knowledge from both within and outside of the industry on the development of effective and economic repairs of damaged steel moment frame buildings. This effort follows the January 17, 1994 Northridge earthquake and has been conducted on an impartial basis.
The group, led by Dr. Warner Simon, has primarily been directed towards developing weld repairs capable of sustaining the severe demands of stress, strain and strain rate associated with earthquakes. The work was also carried out with a view toward assisting other applications with similar problems.
Research and testing has resulted in repair methods being developed using shielded metal arc weld (SMAW) overlays applied over flux core arc welds to address the weld and material issues associated with the problem, while also achieving significant savings. The Dynamic Load Weld (DLW) uses a tough overlay designed to take, if necessary, the full dynamic load. In this way, the effects of weld damage are immobilized by applying the weld overlays. The technical advantages of the DLW process, without significantly gouging the original weld, outweigh the economic advantages, as secondary repairs frequently cause secondary defects and secondary stresses.
Small component tests were carried out to investigate the dynamic capability of the welds. The test specimens for the small component tests comprised tee specimens with large artificial defects. The specimens were then tested by drop weight and low cycle fatigue tests. The drop weight test specimens achieved substantial deformation before fracture. Specimens tested by low cycle columns fatigue test attained in excess of 600 cycles before failure. The artificial defects did not affect dynamic strength or fracture mode.
Two large scale beam single sided beam to column assemblies, with W21x68 beams and W12x106 columns, were tested using the pre-Northridge connection detail with SMAW weld overlays applied over flux core arc welds. In the first test, without a doubler plate at the panel zone, significant yielding occurred in the column panel zone with minimal distortion occurring in the beam flanges. The specimen performance was excellent, significantly exceeding SAC requirements for testing. In the second test, a doubler plate was used at the panel zone such that yielding did not occur in the panel zone allowing significant buckling of the beam flanges. The specimen performance again was very good, significantly exceeding SAC requirements for testing with final fracture occurring well away from the welds. Although the tests have shown excellent results, at this point in time, the use of overlays should be considered as a repair method only, i.e. restoring the connection to its pre-existing condition or better. More testing, including small component tests on larger thicknesses and large scale tests on larger members is necessary before it may be considered a retrofit method.
The use of weld overlays has been approved by the Department of Building and Safety of Los Angeles for the repair of a steel moment frame building in Los Angeles (Initially for repair of E.Q. damaged beam-to-column connections). Specific tests will be required on small component and full-size members, to qualify for retrofitting and new structures. Subject to further research and testing, the use of weld overlays may also be found to be suitable for new construction and also apply to other applications; e.g. bridges, offshore structures, marine, and railroad applications.
The research, development and testing is fully reported in DLW Task Group's Report No. 1341, entitled "Dynamic Load Welds for the Repair of Existing Steel Moment Frame Buildings Damaged From Earthquakes" by the above listed authors.
The report also includes research on Major Historical Events, discussion on parent metal toughness, and recommendations to mitigate potential for lamellar tearing, and other contributing factors, with emphasis on improved performance and the cost savings over conventional repair methods.
Contributors involved in the research development and testing include the following:
Dennis Amos, Westinghouse (GTAW overlay on steam generators); Jim Anderson, USC (Column to beam tests, correlation of subsize to full size); Robert Bianci, Syndication Concepts (Cost Accounting); John Bird, Ministry of Defense, Metallurgist, UK (Carried out original crack arresting properties on GTAW weld substrate); Gregg E. Brandow, Brandow & Johnston Assoc. (Testing); Rick Brantley, American Welding (Welding test and procedures); Yeuan Chou, City of LA (Building and safety regulations); Jack Compton, College of the Canyons/Welding Technology Department (Welding procedures and test; education in structural welding engineering); Christopher Farrar, Metrode Welding Consumables (Lamellar tearing); Mike Green, DWP (Structural engineering, laminations); Randy Haberman, Weldcraft (Welding equipment for Class E); David Harvey, Eclipse Aerospace (Metallurgy); Walt Hayes, Metals Technology (Developed Drop weight testing low cycle fatigue, methographic chemical analysis); Steve Jorgenson, Parsons (Class B and D repair procedures); Peter Keskine, West Valley Automatic Saw (Specimen machining trepanning set-up); Peter Maranian, Brandow & Johnston (Joint design, classes A and C; structural engineering assistance); Ron Mobley, Accurate Weld Testing, (Welding procedures, impact test, and welding tests); Barry Schindler, John A. Martin Associates (LCF parameter and standards); Ed Simon, California Resources
(Procurement of base metal, GTAW wire); Warner Simon, Sitech Ltd. (Experience in industries other than building Class A, C, and E repair procedures, donating the original concept and development); John Sumpter, British Admiralty (Fracture Mechanics. Carried original crack arresting properties on GTAW weld substrate); Ray Zenk, Bragg Rigging (Cost Studies).
If you are interested in obtaining a copy of the 59-page report, please forward forty-five dollars
($45 which includes postage and packaging) to the following address:
Sitech Ltd.
P.O. Box 3532
Winnetka, CA 91306
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