The committee of 20 includes dealers (Morrow, the US Liebherr tower crane distributor and rental house), crane rental companies – General Crane of Orlando and Sims Crane, among others – as well as operators, end users, developers, general contractors, third party equipment inspection services and an attorney, according to panel chairman Richard Horton, president of Miami’s Green Construction.
Construction continutes to boom in Miami
The workgroup has now informally agreed to the recommendations, which broadly fall into four categories: codes and standards, hurricane preparedness, inspection and enforcement and crane operator qualifications. A final vote is expected this month.
“Southern Florida doesn’t have a government entity to regulate cranes and heavy equipment as does the state of California, the city of New York and the city of Chicago,” says Brian Silbernagel, workrgoup member and corporate safety director for North America Liebherr distributor Morrow Equipment.
Silbernagel attended the first and second meetings of the workgroup, and said that although a tower crane fatality formed the group, the participants were interested in discussing topics outside the remit of tower crane safety. This includes hurricane preparedness and operator certification.
First, the workgroup has agreed that tower crane foundations and tiebacks should be designed to American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures, ASCE 7-02.
Horton says that although it is not unusual for the cranes to meet this specification, nobody has enforced compliance to date. “There has been a relaxation in enforcement and in approving cranes in high-rises to the extent to which not all of the forces that affect the structure recorded by crane manufacturers are being properly applied,” he says.
“There has been evidence in other areas, not necessarily here in Miami, that tiebacks have been inadequately designed as far as matching in with the structure,”Horton says. “There are other issues with foundation design. These things are the most critical in our ordinance,” he adds.
There are several engineering issues with this change, according to Michael Quinn, workgroup member and structural engineering manager of Liebherr dealer Morrow Equipment.
First, most of the tower cranes sold in the USA are designed in Europe to European standards. The European standard for the maximum out-of-service wind is the equivalent of about 94 mph, or 10 mph more above a height of 100m. These figures are well short of the 150 mph required by ASCE 7-02.
It might be possible to strengthen the crane by reducing the freestanding height of the crane above the lowest building tie-in, Quinn says, but there are limits there as well. Under the European standards, it is generally possible to stand about nine or ten towers above the tie-in. But even the reduced crane’s hook height must be sufficient to lift slip forms and pumping equipment – at least 40ft (12m), Quinn estimates. There is a further complication on multi-crane sites where crane jibs could clash if they were mounted at the same height.
Quinn says he is working with Liebherr to present a solution to the problem by the workgroup’s next meeting in mid-November.
In advance of a hurricane, the group has discussed having telescopic mobile cranes retract and stow their booms. But Silbernagel says that consensus has not been reached about what to do with crawler cranes in the event of a hurricane. Some participants advocated they should lower their lattice booms over the road; others argued that such positioning might block the travel routes for emergency service vehicles.
The city’s building boom is not only residential apartment blocks, but also commercial space.
Inspection
The workgroup has agreed that the Miami-Dade building department will be responsible for reviewing foundations, tieback designs and freestanding heights, which must be produced by the structural engineer of record for the building, according to Horton.
Installed cranes will not be permitted to be used until the building department has reviewed the “shop” (engineering) drawings, Horton says. “It’s just like roof trusses and storefront glass. There are all subsidiary approvals once you have the building permit.”
According to Silbernagel, the department will report back about whether it has the resources it needs to carry out these checks at this month’s meeting.
OSHA already requires annual examinations of cranes currently in use. Silbernagel says that the workgroup is looking for more frequent examinations – perhaps every six months, although the frequency had not been established at time of going to press.
Operator qualifications
The workgroup is planning on importing California’s work on operator qualifications. In particular, it is likely to require all operators to be certified to a level equivalent to NCCCO. These are intended to act in the short-term, before an expected state-wide law on operator certification in 2008.
“We don’t need to re-invent the wheel, especially when the state is coming out in 2008 with crane certification,” Horton says, which is likely to require operators to reach the NCCCO level.
The recommendations will be put to a formal vote this month. From there, a team of lawyers will turn the technical language into regulatory language. It is likely to be sent to the Miami-Dade county commission for a formal vote early next year.
