BRIDGES 1998

Bridges Article December 28, 2000
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Imagine a concrete reinforcement job so consuming that contractors opted not to bid it until they found a tool that could make it feasible and affordable.

Last year, the California DOT (CalTrans) requested bids for a $1.5 million seismic retrofit project of the I-134 Arroyo Seco Bridge in Pasadena, Calif.

CalTrans’ design called for continuous rebar reinforcement. This required a design, fabrication and installation of 770 tons of rebar to support new structural concrete and 500 cu yd of shotcrete—all without stopping traffic.

The bridge, which was built in 1954 and widened in 1970, is on an eight-lane interstate running from North Hollywood to Pasadena. It’s a 1,300-linear-ft concrete arch span suspension bridge that traverses a dry river bed and is 125 ft above ground at its highest point.

Consequently, all work was performed from beneath the structure and contractors hesitated to bid this project due to logistics and the bridge’s height.

Risky business

Placing the continuous rebar bands by welding would be costly and time-consuming in some cases, unsafe in others. Using couplers to form all bends also would have been too time consuming and costly. But field bending of rebar after placing it through cored holes could create a substantial savings in couplers required to create a continuous band of support.

The challenge was to find a way to accurately bend positioned rebar in place, to specifications, within confined quarters at high elevations, while remaining on time and under budget. After studying the project, Rebar Engineering concluded that using a portable rebar bender was essential to successfully complete the job.

According to Chris Rubio, project field supervisor for Rebar Engineering, the project included encasing the original concrete structure in an additional 3 ft of concrete. Each beam face was widened by 1 ft, 6 in.

With 11 piers, 72 girders and 24 columns to reinforce, the company installed lengths of rebar ranging from size #3 to #11, into approximately 44,000 holes of varied diameters pre-drilled through existing concrete.

On the site, they used three SPX Power Team, Owatonna, Minn., portable Jimmy Rebar Benders which can bend rebar to an ACI-approved bending radius (90 degrees, 135 degrees or 180 degrees) after rebar is positioned and/or after concrete is poured. A B7135 model was used for hairpin bends and two B8090L for stirrups and U-bends made from #7 rebar.

“In essence,” said Rubio, “we did the same thing on site with our rebar bender as in our fabrication shop.”

Teamwork essential

In this job task sequence was important, therefore, the iron workers progressed in twos. One worker inserted the U-bend rebar into two parallel holes pre-drilled through the concrete column or girder, while the other helped pull the rebar through the opposite side. Once a series of rebar U-bends was in place, another ironworker used the rebar bender to bring the two ends together with two opposing ACI-certified 90 degrees bends.

Workers did this by slipping the rebar bender over the rebar and activating a 10,000 psi hydraulic pump. After bending the rebar, the workers slipped the bender off and then onto the adjacent rebar to repeat the process. Another worker followed and mechanically coupled the two bent ends together to form a continuous band. According to Rubio, workers could create as many as 150 bends in one day. To accomplish that with welds or couplers would’ve taken two or more days longer and an increased the cost by 60% according to Rubio.

Ralph Salamie, P.E., project manager McCarthy, said, “The rebar bender enabled the completion of the continuous bands that run through the pier caps and beams with the half the number of mechanical couplers.”

According to ironworkers from the site, the rebar bender simplified the job since they spent less time in confined quarters and used less effort.

“The tool accurately bent the rebar in a matter of seconds while we looked on. It was quick, easy and accurate,” said general foreman Jeff Patrick.

About the author: 
Gregorski is Technology editor for Roads & Bridges
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