May 28, 2010
PETER BOYLE / MBS STEEL LTD
FEATURE | Steel
Major steel joist manufacturers are capable of producing 100-foot joists
Twenty years ago, most steel buildings used 30- to 40-foot-long steel joists and a 60-foot-long joist was considered a long span. Field splicing (bolting and/or welding joists together on site) was required for spans greater than 80 feet up to about five years ago.
Times have changed.
Today, major steel joist manufacturers have the capability of producing joists 100 feet long — exciting news for any architect or interior designer who values column-free space.
“We’ve been telling architects for a while that we could do longer spans and eventually they believed us,” says Peter Boyle, chief designer of Brampton, Ont.-based MBS Steel Ltd. “It provides them with a lot more design flexibility.”
Boyle says big manufacturers like MBS and Canam Canada can produce joists in the 100-foot range without splicing shorter joists together because the fabrication process has been reconfigured to accommodate the longer steel members.
Buildings specified with longer-span joists often don’t cost more to build than conventional structures because fewer support columns are required. That translates to less foundation work, which can reduce overall building costs, says Boyle.
There are downsides to longer spans, however. Erectors require larger, more expensive cranes — a 200-ton crane rather than a 100-ton model, for example — to lift the longer, heavier joists and trusses. But Boyle says those erectors can often make up that price difference because fewer lifts are required to complete the job.
He points out the cost of field splicing to make longer joists can price a fabricator right out of a job. “In each field splice, there is a lot more material, a lot more labour in the field and the erector then charges more and costs snowball.”
“It is much easier for us make a long span on a jig than it is to design and draft splices. It means the shop doesn’t have to cut the material and assemble it to make sure the splice works properly.”
Where field splicing is required, welding is preferred, a simpler process and less pricey than bolting.
Increasing length and weight of a steel member is not without its problems — mainly higher shipping costs and more complicated transit methods and routes — particularly when steel members are 100 feet long or more.
But the cost of a police escort on highways and roadways is still often less than the price for splicing joists together on site, explains Boyle. “Some projects don’t have the room to lay out long items away from the immediate erection site.”
He adds that erectors charge more to assemble on site — a price paid by the manufacturer. “Unless the project is a long way from our plant, we usually try to ship in one piece.”
If shipping costs seem high for Canadian manufacturers, talk to American companies trying to compete in the Canadian marketplace. Transporting any steel member near 100 feet long is impractical.
Supplying spliced joists is often not an option for American manufacturers either, Boyle points out. “Their erector has to spend a lot more time splicing in the field and some sites don’t have the space for laydown work.”
The longest members MBS Steel has ever shipped were 105 feet long by 12 feet deep. Even though an escort was required at the front and back of the load, shipping proved “much more economical” than field splicing.
MBS is currently supplying 105-foot and 78-foot joists for the construction of a 190-foot long by 300-foot wide three-storey fitness centre in Mississauga. The job also requires some trusses about 80 feet long.
“Five years ago, it would have been more expensive because we would have had to splice the joists together. And, because of site restrictions, we would have faced problems where to lay down the steel.”
Not every long-span design can accommodate the longer joists because the steel members have to be fabricated with a deeper depth than conventional joists to support the greater spans, says Boyle.
“That means the building height has to be higher and that is not always an option.”
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