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Temporary Bracing for Metal Buildings

A recent spate of metal building collapses during construction has building erectors pushing for increased temporary bracing awareness

Double X Brace
Doubling up bracing in a bay prevents having to brace in multiple bays and interfering with construction.

Have you ever seen a new-born foal crumple back to the ground after it has first stood? Its gangly legs go in all directions while it falls awkwardly, slowly and finally plops onto the ground. That’s kind of what the collapse of a metal building under construction is like, except it’s neither cute nor funny, but frightening and dangerous.

Metal buildings are engineered to use material efficiently and, when completed, be able to withstand any wind or storm that a conventional steel building can. But, while being erected, metal buildings are vulnerable to collapse unless erectors take precautions because the structure is so dependent on every element to meet the load requirements.

“Temporary bracing is essential on any metal building regardless of its size,” says T.K. Frahm, project manager for Butler Manufacturing, Kansas City, Mo. Frahm has a lifetime of experience in metal building construction as both a contractor and for manufacturers. “A metal building won’t be fully supported until all the roof and wall panels are actually on, including the permanent bracing. The temporary bracing is necessary to hold everything in place, but also to help plumb and square the building.”

Many erectors make the mistake of believing that the building isn’t vulnerable to wind until the panels go on, thinking that the minimal surface area of the structural steel isn’t enough to catch the wind.

“Because it has so many individual elements, we commonly see the wind load in an exposed structure is higher than on an enclosed structure,” says John Rolfes, PE, SE, vice president of CSD Structural Engineers, Milwaukee.

A New Guide

Rolfes and Frahm are part of an effort by the Metal Building Institute (MBI) to develop standards for temporary bracing and implement them across the industry. Rolfes’ firm is writing the guide in cooperation with a team of MBI members, led by Metal Building Contractors & Erectors (MBCEA) presidentKeith Wentworth, on an instructional video that will be part of the Craftsman video series the group has developed to help contractors improve their skills. Frahm is also on that team.

X-bracing in between bays and laterally across the building holds the structure plumb and square while construction is completed

“Part of our mission for this design guide,” says Rolfes, “is for more normal metal buildings— not incredibly big spans, no unique characteristics that create stability issues during erection—your average, plain jane building that might be 60 or 80 feet wide and 200 feet long. Most of our work lies in providing prescriptive guidelines on what kind of temporary bracing is required.”

DJ van Rooyen, manager of Steel Worx, Groveland, Fla., is a metal building erector who works nationally and takes on complicated projects. He is also a member of MBCEA and vocal about the need for temporary bracing education. “On bigger structures, the exposure is less,” he says, “because the manufacturers are managing all aspects of the structure. Collapses mainly happen on the mid-sized projects that have exposure but no management of the temporary bracing.”

“Just because a temporary bracing scheme worked fine for a smaller building doesn’t mean it will extrapolate to a larger building,” says W. Lee Shoemaker, Ph.D., PE, director of research and engineering for the Metal Building Manufacturers Association (MBMA). “Metal buildings continue to get larger and that is where temporary bracing deficiencies usually come to light.”

Temporary bracing is so essential to MBCEA that the AC478 Accreditation program for metal building assemblers includes the requirement for erectors to have procedures to develop temporary bracing plans.

Who’s Responsible

“The metal building engineer, along with the engineer of record for the design of components not supplied by the manufacturer, are responsible for designing the building for the condition when the building is fully erected,” says Rolfes. “In the MBMA Common Industry Practices, the responsibilities of the engineer of record, owner, contractor, metal building manufacturer and erectors are addressed. The erector is responsible to ensure the structure is stable and safe during the process of erection.

An X-brace cable is attached to the foundation bolts with turnbuckles between cables and Crosby clamps holding the cable tight. Everything is properly sized to withstand the structural forces during construction.

“What we have is an erector who may or may not have significant knowledge about the design of the structure, but is responsible for the stability during erection. Historically, there has been a considerable amount of problems during erections with collapse or partial collapse of building structures and potential injuries or loss of life associated with that. And, obviously, commercial loss. There is more and more of a push to get an engineer involved so a complete and competent design is put forth for the temporary bracing of the structure during erection to ensure that it’s stable.”

In practice, the process depends on the size of the building. For smaller and less complicated buildings, there tends to be a clean hand-off from the metal building manufacturer to the erector who is responsible for putting the building up safely. Larger and more complicated buildings will likely have more input from the manufacturers.

According to Frahm, the driving reason for these distinctions in responsibility is liability. The manufacturers shouldn’t be held liable for something— the erection process—they can’t control.

But there is a greater reason than liability. “The reason MBMA members aren’t involved in the responsibility for the erection of a metal building,” says Shoemaker, “is because they recognize that each erector is going to have their own practices, their own methods they use, the equipment they have, the number of people on their crews. It’s really dependent upon how the erector chooses to operate. They want to give the erector the flexibility they need to do the job correctly.”

Those distinctions in responsibility make sense. Let the people who are experts in their areas, control their areas of expertise.

Van Rooyen is very complimentary of the help he gets from Bluescope Buildings North America in larger projects, where the company assists with temporary bracing schemes. Even so, he has an inhouse engineer who is responsible for completing a scheme for every building. Most erectors aren’t large enough to carry such a position, so they have to seek outside help.

“The benefit for us is I’m shifting liability from my shoulders to my engineer,” he says. “The small guys don’t have that knowledge or flexibility and isn’t going to pay for an engineer. The onus needs to rest on the manufacturers more than it is now. There needs to be a more equal split between getting it done.”

That difference between the capability and flexibility of a company the size of Steel Worx and a small erector is a marketing differentiator for van Rooyen, but also a constraint. “Even on smaller projects,” he says, “we’re almost 15 percent higher on the price than the other bidders.” He has to sell that difference and stresses risk mitigation as a major part of it.

One change van Rooyen would like to see from manufacturers is for them to call out the top loads on columns. “Our primary concern,” he says, “is the well-being of our guys. Steel collapses give the industry a bad name, but guys get hurt in the process. What’s the point of doing all the other training, but we don’t adequately brace the structures? In America, we deal with extreme weather conditions. The same way as they provide loading for the foundation, the manufacturers should provide top loads on the columns. They have the engineers for them to have a spreadsheet spit out suggested temporary bracing methods. They can specify it the same way they can the engineering on a foundation. They don’t tell you what size the concrete needs to be, but the foundation engineer uses that information to design the foundation.”

Flange braces are essential to keeping the structure stable and protecting workers

The Kit

Even though MBCEA is working to establish prescriptive bracing methods for standard buildings, everyone agrees there is no single way to do a temporary bracing scheme. Frahm has some rules of thumb that he uses as guidelines. Among them are that “you want to have 10,000 pounds of force in a straight pull.” That means that the rating for the cable, turnbuckle, clamps, hooks and eyes need to be able to manage 10,000 pounds of force. If the loads on the frame are greater than that, you’ll need more than one cable.

He and van Rooyen prefer to run cables from tops of columns to foundation bolts. Frahm aims— as a rule of thumb—to run bracing in every fifth frame at the minimum, but every third frame if the forces require it.

Cross-bracing in frames can get in the way of construction, but Frahm notes, “If you plan well enough, work with the general contractor and the other trades, you can make it work.”

“Our approach,” says van Rooyen, “is we get the top loads on the columns in frame line and grid line directions. We determine how many kips [one kip equals 1,000 pounds of force] we need to carry. We position the cables in frame lines out of the way so we can travel freely in both directions. We determine which bays we want to brace, and instead of having bracing in every bay, we double brace in some bays. The bracing stays in place until all the cladding is on. All roof and wall panels.”

Neither Frahm nor van Rooyen were bullish on using dead men or helical ground anchors, although they saw the necessity of them in certain instances. “With ground anchors, you then have to find out what the soil borings are,” van Rooyen says. It’s simpler to anchor to the foundation bolts.

No matter what method, the temporary bracing scheme should be planned ahead of time and written out. An engineer needs to be involved in the plan so that forces are adequately accounted for. That includes the forces created by the temporary bracing itself.

The MBCEA Temporary Bracing Guide will have complete information on what you need to know for bracing and should be available later this year.