Contractor tackles new seismic code welding with dual-arc machines
May 16, 2002
This article is a case study that outlines how a California contractor retrofit existing buildings in southern California, using new construction codes to prevent further earthquake damage, while staying profitable, expanding, putting more welders in the field, using new welding procedures and consumables, and buying new equipment.
Here's a dual challenge for a construction company:
Solution: Use a total life cycle cost approach and a creative mind, as Builders Steel Inc. has done.
But let's back up and start at the beginning.
On Jan. 17, 1994, a major earthquake hit Northridge, Calif., in the densely populated San Fernando Valley north of Los Angeles. Some 12,500 buildings were moderately or severely damaged. Local officials and engineers were alarmed at the extent and types of damage sustained by structures.
Specifically, it appeared that welded steel moment-frame buildings—buildings based on a horizontal steel beam both welded and mechanically fastened to a vertical steel column—were suffering brittle failures in the beam-to-column welds. These welds previously had been thought to be almost invulnerable to earthquakes.
The net result was a new set of recommended moment-frame joint designs and welding procedures (FEMA-350 through 353), developed by the Federal Emergency Management Agency (FEMA) in the late 1990s after extensive research and testing.
This brings us to John Reed, the president of Builders Steel Inc., Riverside, Calif., a company specializing in structural and miscellaneous steel fabrication, including erection. The 16-year-old company employs about 50 people. It increasingly has been involved in seismic construction to the new FEMA codes, which now are used widely in California, for both new buildings and retrofitting of existing structures.
In early 2000 Reed was struggling with a problem. He wanted to expand by putting more welders in the field, with an eye toward several upcoming jobs; yet it was essential to remain productive and profitable under the new, restrictive FEMA codes. That led to the question of what new equipment to buy for his workers.
"We do a lot of self-shielded and gas-shielded flux-cored welding, mostly in wire diameters of 0.068 inch and above. We need some serious welding output power, anywhere from 200 to 300 amps, 20 to 30 volts," Reed said. Builders Steel had a Miller Electric XMT Rack (three XMT 304 units and one XMT 456) in the shop, and two older Miller Trailblazer gasoline-driven arc welding machines served the work force in the field.
The dilemma was resolved for Builders Steel at a seismic retrofit job for Costa Mesa, Calif.'s City Hall, which started in June 2001.
The retrofit is being conducted to the latest FEMA standards (except for welder certification). The City Hall is a five-story building with prestressed concrete slab floors extending out as balconies on each floor. Essentially, the retrofit involves installing what Reed calls a gigantic girdle around the building.
First, half-inch-thick steel plate is wrapped around the edge of each floor, extending 30 in. back from the to p edge and bottom. This steel wrapper is anchored to the floor with 7-in.-long, 7/8-in.-dia. studs.
Next, a gigantic frame of steel girders is erected on each side of the building. The frame then is welded to the steel wrapper at each floor. With the frame solidly anchored to the ground, the resulting girdle should prevent the side-to-side motion feared by earthquake experts.
The framework comprises a series of frames, each three columns wide, 56 ft. tall, and 50 ft. wide with diagonal braces (see photo on page 35). The beams making up the frames are American Society for Testing and Materials (ASTM) A572 grade 50 steel, all with 14-in.-wide flanges but of varying weights; the heaviest 14-by-276s (14-in. beams weighing 276 lbs. per ft.) have 2-in.-thick flanges.The company partially assembles the frames in its shop, then ships modules to the site for final assembly and erection. Another interesting twist is that all beam and column girders are rotated 90 degrees from normal so that beam flanges are flush to the sides of the building.
Welding these frames together is an interesting aspect of the job. Reed gives the details.
"All the welding being done here is essentially to the FEMA code, which supersedes the American Welding Society D1.1 structural code. The typical joint, for example a column splice, is welded in three places, the web and both flanges, with full-penetration welds. The joint is beveled all the way to the back. It has a backup bar on the root side of the weld.
"After the weld is made from the front side, what we call the A side, the backup bar is taken off and the weld is back-gouged down to the root. It's magnetic particle-inspected for cracks. If it passes, it's back-welded: We make a weld on the B side of the weld where the backup bar was. We then complete the weld from the A side, about 15 passes total, and inspect ultrasonically from the A side.
"Everywhere the floor plate meets the frame, it is welded on both top and bottom. That's a fillet weld between the beam and the plate across the full width of the frame," he said.
"These welds are really critical. We can't have any kind of slag inclusions or discontinuities in the weld at all or it doesn't generate the full strength of the column. The weld must be as strong as the rest of the column material, and if you have any voids, then the beam might not be strong enough to meet the engineer's calculations."
Welds in the flat position are made with AWS E70TG-K2 wire, which has a high deposition rate. Overhead and other out-of-position welds are accomplished with AWS E71T-8, an all-position wire. Both are 5/64-in.-dia. wires. Carbon arc back-gouging is used with 3/16-in. carbons.
Do the new FEMA regulations require a change in welding equipment? "It depends on what you're running now," Reed said.
"You have to run the AWS E71T-8 class wire or the AWS E70TG-K2, and you absolutely need a constant voltage-type machine to do that. We've found with the E71T-8 particularly that it is extremely critical to set the correct voltage and amperage to make it run properly. You want to be able to set the proper values with a CV machine as opposed to a constant current-type machine."
This leads to Reed's equipment choices for his expanded work force for this job. He said he evaluated at least five different machines and approaches. But he was not looking just at purchase prices, and that is one key to his company's success.
Reed has worked out a system of evaluating equipment, which focuses on total life cycle costs. The goal, he said, is to find out a piece of equipment's total cost per arc per hour over its entire life.
The formula includes the following variables:
Thinking about these calculations led Reed to select a multiarc machine. The machine finally purchased came from Miller Electric and is called the Du-Op. It is rated at 550 amps at 30 volts of direct current (VDC) with a 40 percent duty cycle for single weld mode, and 275 amps at 31 VDC on the same duty cycle in dual welding mode. The 2,005-lb. unit is powered by a low-maintenance Deutz diesel engine.
This approach gives Builders Steel two arcs from one machine, with only one set of maintenance requirements. Reed reported that the cost per hour of operation, on a per-arc basis, was low enough to offset the much higher initial cost of purchasing the machine, and even undercut the operating costs of the gas engine drives he had already paid for.
Then Reed got even more creative. He realized that transportation to the job for the welding machine is another significant cost, one not often factored into fabricators' calculations. His solution was to buy a trailer and put a second unit on it, giving his company four arcs working from a single truck.
Considering that the cost of a truck is higher than the cost of any welding machine, the result is a huge edge for Builders Steel over competitors that haul one welding machine per truck, Reed said.
Reed now has three of the dual-arc machines. They have proven equal to the severe power demands of the FEMA code welding, even working two shifts a day right through the Southern California summer.
But why should fabricators in Atlanta, Philadelphia, and elsewhere worry about how to weld to California seismic standards?
"The FEMA regulations probably aren't universal even in California yet," Reed said. "But as I understand it, FEMA anticipates that the American Institute of Steel Construction, the American Society for Testing and Materials, the American Society for Nondestructive Testing, and AWS will all review and possibly adopt these standards into their codes. These codes are universal, not local, and are usually adopted by engineers in every locale across the country—usually for school and hospital construction first.
"Everybody thinks of California as being the land of earthquakes, and it probably is, frequencywise," he said. "But I also know that the biggest earthquake ever recorded in the United States was in St. Louis. This could be coming to a town near you before too long."
Among the features of the new Federal Emergency Management Agency-recommended moment-frame joint designs and welding procedures (FEMA-350 through 353) are:
Builders Steel Inc., 3670 Placentia Lane, Riverside, CA 92501, phone 909-369-5720, fax 909-369-5721, e-mail email@example.com.
Miller Electric Mfg. Co., 1635 W. Spencer St., Appleton, WI 54912-1079, phone 920-734-9821, Web site www.MillerWelds.com.
Federal Emergency Management Agency, 500 C St. S.W., Washington, DC 20472, phone 202-646-4600, Web site www.fema.gov.
American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126, phone 800-443-9353, fax 305-443-7559, Web site www.aws.org.
American Institute of Steel Construction, One E. Wacker Drive, Suite 3100, Chicago, IL 60601-2001, phone 312-670-2400, fax 312-670-5403, Web site www.aisc.org.
American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, phone 610-832-9585, fax 610-832-9555, Web site www.astm.org.
American Society for Nondestructive Testing, P.O. Box 28518, 1711 Arlingate Lane, Columbus, OH 43228-0518, phone 800-222-2768, fax 614-274-6899, Web site www.asnt.org.