Oxford Street Parking Facility, Cambridge, MA

The crane of choice was a Liebherr HS 853 HD, in duty cycle configuration, with a 56-foot boom, and a counterweight of 48,500 lbs., sitting upon steel plates to help distribute the weight more evenly across the reinforced concrete surface. The clamshell chosen was a Hawco 4-cubic yard bucket, weighing 12,300 lbs.

One of the most critical components of the job, however, would be the proper selection of the wire rope to be used. Given the weight of the Hawco bucket, and the estimated 14,500 lbs. of soil it would lift each time, Jim knew he needed to specify a high capacity cable; one that would minimize downtime and maximize wear longevity. The cable also had to be rotation resistant, which would be required at the lower portions of excavation to prevent cabling. Further, because the Liebherr’s hoist drum was grooved, the wire rope could not exceed 26mm in diameter.

" But we also had a budget to adhere to." he emphasized. "So we couldn’t go overboard on cost."

J.F. White contacted one of its wire rope suppliers, Cableworks, Inc. of Putnam, CT; a distributor of wire rope, slings and fittings with 20 years of service to contractors throughout New England. Their representative, Dave Black, came to the job site to take a look at the project.

" Given the unique nature of the job, and the high stress load that was going to be put on the rope, I knew they’d need a high quality cable," Dave said as he eyed the top of the crane boom, some 60-feet high. "The first rope that came to mind was Bridon."
" Bridon American manufactures a premium high performance crane rope," he asserted. "They test the minimum breaking strength of each production length of it they produce, and they also "twistcheck" the rope to make sure it has the proper resistance to rotation. Plus, you get what you pay for."

Working the numbers together, using a design factor appropriate for duty cycle use, they determined they needed a wire rope with a minimum breaking strength of nearly 67 tons. They narrowed the choice down to one product; Bridon’s Endurance Dyform 34LR Grade 2160 which, at 26mm, provides a breaking strength of 74 tons.

So how is the job going? "Excellent," Jim said as he surveyed the action from the construction office above the site. "Our crane operator, James Black, is very experienced, which certainly contributes to reducing wear on the equipment and keeping us up and running. We’ve had a great safety record on this job, and we’re right on schedule."

Only one person is a little disappointed. "Well, considering the load that wire rope is under," Dave said, "I thought I’d be able to sell him replacement cable every month or so. He’s got over 500 hours on the original rope and he’s only had to trim a few feet that were showing signs of wear. At this rate, it could last him six months!"

" Guess he won’t be making quite as much commission off of this job," Jim said smiling.

" That’s okay with me," Dave said. "Next time he needs wire rope, he’ll know who to call."

Here’s a unique challenge: How to build a 4-story, 730-space parking garage, complete with basement level and roof – underground – in the midst of crowded buildings on Harvard University’s campus? There was only one choice…top-down construction.

Now consider that the ground level - which would eventually serve as the roof of the parking garage - is a reinforced concrete slab/composite steel deck only nine inches thick. Many questions had to be answered. What size and weight crane would the roof support? What size bucket would you use that will deliver the capacity you need for workflow, yet still be an acceptable weight load? And what type of wire rope would you use that is strong enough to support a 15-ton single line load, is rotation resistant, and durable enough to endure daily duty cycle use? All very important issues which required an experienced team of professionals.

" I live for this stuff," says Jim Cahill, Project Manager for J.F. White Contracting Co., who has been with the Framingham, MA-based company for 16 years. "Ever since I was a kid, I’ve always loved cranes…everything about them. And this project required a lot of planning."

The $50 million Oxford Street Parking Facility broke ground in October 2002. It is currently on schedule to be completed in December of 2004. In the meantime, some 400,000 tons of soil, including layers of fluvial wash, marine and glaciomarine deposits, have to be excavated, hoisted and trucked away. A series of openings in the concrete slab, called gloryholes, would be used to access and clear the initial level of topsoil. Then the crane would lower the excavation equipment – in this case, six Gradall 2200 units – into the holes so they could feed the soil toward the openings, where the crane would hoist the material out and load it into one of the choreographed fleet of hauling trucks making some 40-trips daily to and from the site.

The garage would be constructed one level at a time. When the first level was emptied of soil, a concrete floor would be poured – still leaving the gloryholes open – and the work would continue onto the next lower level.

During the first phase of the project, as the perimeter walls were being constructed, Jim was busy consulting with the engineers relative to the weight limits the concrete slab would allow, helping him to determine the size crane to use. He, along with his team of 12 on-site associates, also analyzed the timeline to determine what size clamshell bucket needed to be used – again keeping the weight factor in mind.