Hydraulic trucks, telehandlers, boom trucks, forklifts or cranes can all lift a truss, but when placing it you want the machine hoisting it to be as precise and nimble as possible.
Builders across the U.S. are taking notice of how Potain self-erecting cranes can make their jobs easier and more efficient, said David Polce, regional business manager of Potain tower crane products for the Eastern and Southern parts of the country.
When operating a self-erecting tower crane to lift a truss, selecting the height under hook — the distance from the ground to how high the building will be — is crucial.
“That’s going to vary because you need to leave about 25 ft below the hook where you’re rigging, in the span of how long your truss is going to be, so it can pick it up securely and evenly and move it across the area of the jobsite,” Polce advised.
He added that crane operators need to consider the size of the truss or panel and the conditions outside.
“You want to factor in the wind that is going to be pushing against that object you’re moving,” Polce cautioned. He mentioned crane operators are always looking at the size and type of the truss, panel or wall. Some pieces are determined as “fully dressed,” which is a solid object, or as “open,” where wind can pass through in between its parts.
“We measure the panel (or truss) size in meters squared and look at how far it’s being moved across a certain area, which is the radius, and the width,” Polce said. “We then take that into consideration, and we have like a ‘tic-tac-toe’ (noughts and crosses) chart in our manuals that shows you at what wind speeds you can efficiently move that panel to where it needs to be.”
He adds this practice — using load charts for crane-user recommendations — works as a guide for lifting both panels and trusses, and that it’s the biggest metric to look at.
Take measures to prevent trusses sailing away from a crane. “Everyone thinks it’s the weight that’s the biggest concern. When the truss starts sailing away from you and starts swinging, or even trolleying, that can take the crane and lift you off your foundation and tip over.”
He warned you don’t want the load taking control of the crane, instead of the crane controlling the load.
Solving truss challenges with cranes
Polce said using self-erecting tower cranes to hoist trusses completes these tasks faster and more efficiently. But the challenge, he added, is coordinating which builders get the crane and when. He said it’s important the general contractor factor in a self-erecting crane as part of the bidding process to take full advantage, and reap cost and time savings, of using this type of equipment to manage the whole job. He can control who uses the crane and when. In doing so, he can keep track of how the work is progressing.
Polce reiterated that smaller cranes work on post-frame projects. Many jobsites require working in tighter spaces with limited room for truss-lifting machinery. “That’s the benefit of using the ‘MA or HUP series’ cranes; you can put these in tight places,” Polce said. “Operators can put these cranes into those smaller spaces and reach the backside of the structure where trusses need to be placed. Many of these post-frame projects are custom homes built into the side of a mountain (for example) or on a 30-degree slope where it is impossible to use (road) a telehandler and move it in position to set trusses.”
Compact cranes are also ideal for framing homes in residential neighborhoods or in remote areas with limited yard space. “The benefit is that these cranes stand right beside the building and [hoist and jib] goes up and over instead of a mobile hydraulic boom truck or where it has to ‘square it out’ and reach at an angle,” Polce explained.
These “mini-cranes” can complete truss lifting and placement for two side-by-side houses at the same time without moving. Multiple configurations on the cranes give the operator more lifting options to place trusses of varying sizes and weights into place. In addition, these are “taxi cranes,” as Polce calls them, that can lift A/C units as easily as larger trusses, performing three to four jobs a day completing homes or apartment complexes.
Making the jobsite more efficient
Polce said using compact self-erecting cranes to hoist trusses makes the jobsite more operational and efficient. Many use telehandlers to place trusses in pole barn frames with workers helping on scaffolding.
“These buildings are 80 ft to 100 ft and they put them up very rapidly,” Polce said, adding this kind of combination is not ideal when lifting trusses into place. “You’re putting in one truss after another. I’ve talked to many pole barn builders and the disadvantage they say is that they’re not very high up, usually one story.”
He adds they’re then driving that telehandler down 80-100 ft and there may be no integrated counterweight to distribute weight evenly for balance. This feature is designed and built into many small, self-contained or self-erecting cranes with these movements while hoisting in mind. The telehandler is moved often to reach another area where the next truss goes in. The smaller cranes have greater reach and don’t have to be moved, so the hazard of moving machinery around several times is eliminated.
Polce said the crane becomes the centerpiece of a post-frame job and a contractor can eliminate the use of several telehandlers or other heavy-lifting tools.
“The crane ‘runs’ your jobsite for you,” he said. “These may be controlled remotely too for even more convenience. The operator on top of the building is free to move, setting the trusses in and putting loads down. The crane can place in other materials before the trusses are ready, staying steps ahead to increase efficiency and finish a post-frame structure faster.”