Case Study: Sound Partnership Nets 2+U Office Tower a Solid Foundation Project boreilly Mon, 10/11/2021 - 19:06
Omega Morgan Crane Service Inc and Apex Steel Inc were tasked with setting the foundation using a single crane and creative rigging with the help of rental equipment specialists, Lifting Gear Hire.
The Situation:
For crane superintendent Eldon Ash and senior engineer Kai Farrar of Omega Morgan Crane Services Inc. and owner Kevin Koester of Apex Steel Inc along with engineer Ron Roberts, the engineering of the structural columns supporting the proposed 38-story office complex provided a challenge in ensuring the y-shaped columns could distribute the weight of every floor above evenly among the foundation while maintaining a 72-degree angle of installation. More than a year of planning, engineering, testing and simulations went into the design of the project, dubbed 2+U (2 and U for its location on 2nd Avenue and University Street) before ground was broken on site.
Faced with several challenges that could have stalled the project before it even began, the engineers of Omega Morgan and Apex Steel went over several options to determine the best way to perform the required lifts when available space and increased weights of the columns caused the original lift plan to be scrapped.
“Initially, we were going to use two cranes and then we were going to use a crane and a tri-lifter, but as the load got heavier and heavier and as the site got tighter and tighter for access, we had to come up with some more innovative ways to pick and stand these things up and that’s when I came up with this idea,” said Faarrar.
The Challenge:
Charged with leveraging their skill and experience to come up with a way to utilize a limited amount space and a strict schedule of road closures to set the foundation for Skanska’s office tower project, Omega Morgan and Apex had to adapt a skip-around schedule based on which roads would be closed to complete the project while avoiding falling behind schedule.
The engineering of the supports, which start on the 2nd floor and run up through the next five stories installed at a 72-degree angle, left no room for error in the construction and placement to ensure the stability of the building above. Further, engineering the lifts of each section of the columns posed its own problem. With the columns being assembled in a sort of “Y” shape, the assembled height and weight made it essential to install them in sections. Fully assembled, each column came in with the base, installed separately, weighing in around 50,000 pounds with two arms run at a 72-degree angle that span around 60-70 feet tall with a final weight of 165,400 pounds for the heaviest columns. The rigging itself weighed 4,700 lbs. Ensuring all pieces lined up properly to evenly distribute the weight with only enough space for one crane, calculations had to be precise.
Once on-site, further challenges crept up that called for on-the-fly adjustments. The position of the crane had to be modified to avoid swinging the counterweight too close to a tree trunk, which would break branches. The crane was moved 5’ away to be able to tie the branches back and not contact them. This move required the crane be set on a wooden ramp to level it out given the slope of University Avenue.
Once the columns were fabricated and weighed, the numbers came in significantly heavier than planned. The tight nature of the site inside the building did not allow space for two cranes with the capacity required. It became clear that a rigging scenario in which a single crane could pick and upright the columns would be necessary. Because of the tight space on site, it was not possible to use a boom suspension system to stabilize a longer boom to get enough capacity to make the picks, limiting the boom length to 118’ with no boom suspension. The short boom and head room required that the single crane rigging setup be as short as possible.
Equipping a crane with a 37.5-ton air chain hoist and a pair of 60-ton sheave blocks, the crew was able to perform the work typically done with the aid of a tailing device while utilizing only one crane and saving on the head room required to perform the lift.
“One thing that was unique about this rigging scenario was that using the rolling blocks and the chain lift in this way, as the load goes through its rotation, the head height at the final rotation, is minimized compared to other systems that are similar like a tri-block that runs the secondary line down, but the rigging height that you end up with was too much for our project. This rolling block/hoist system really minimizes the head room once the columns are upright,” said Faarrar. “Because the site was so tight, we couldn’t use any kind of boom suspension like a mega wing or guy wires since they stuck out too far and would’ve interfered with the building core and a lot of the structural things in there, so we had to stick to short-length, main boom only and couldn’t have any tall rigging,” he added.
The Solution:
Farrar engineered the rolling block setup to create the safest, most efficient pick possible that allowed them to run the lift with one crane and save on the space required compared with other options available elsewhere. Limited on viable options, the use of a tri-block system would no longer work in this application, so the creative use of an air chain hoist paired with rolling blocks saved both cost and time. Keeping a spare 50-ton air chain hoist on site, which never left its shipping container, ensured there would be minimal risk of unplanned downtime in the event of a mechanical breakdown.
Omega Morgan and Apex were both contracted by Skanska to assist in the lift and to hook the rigging for the crane operator. As the owner of Apex Steel, Kevin Koester saw this as a personal project and stayed heavily involved, arranging for a test run of lifting the columns days before the lift was planned. Running a pared down crew of only five guys, each of whom would play pivotal roles during the planned lift, to see the best practice for lifting and placing the columns. The initial test runs ran smoothly and, while performing the install, it was determined that extra support bracing would not be required as previously thought. Koester worked directly with Farrar and Lifting Gear Hire, running through the extensive catalog to hand-pick the gear that would be used on site and arranged for equipment to arrive on site the same day as the columns to avoid causing further delays with the road closures.
The Result:
Through the collaboration of all three parties, the job went off without a hitch and the use of the air chain hoist and rolling block rigging solution made the entire project possible given the limitations faced on site. “Using single crane picks where possible and not having the use of a tailing device like you normally would, the rigging allowed the single crane to work and allowed the job to even be done,” said Koester.
To overcome the inevitable obstacles faced on any job, having the right equipment from a reliable partner is as pivotal as the crew’s knowledge and expertise in their craft. The teams of Omega Morgan and Apex Steel Inc along with their collaboration with Lifting Gear Hire, were able to easily traverse every hurdle along the way and reached a safe and successful installation of the support columns on the 2+U project.
Equipment Required:
(1) 37.5-ton Air Chain Hoist – JDN 37TI w/ 35’ HOL (35’ Rope Control)
(1) 50-ton Air Chain Hoist – JDN 50TS w/ 35’ HOL (35’ Rope Control)
(2) 60-ton WLL Single Sheave Blocks – 24” Dia. Wire Rope Size 2”
Editor's Note: Scranton Gillette Communications and the SGC Infrastructure Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the Roads & Bridges' Editorial Team.
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