The latest revision to the American standard for tower cranes contains significant changes that affect how engineers should take into account wind loading on jobsites, including those prone to hurricanes. The standard also calls for more rigorous inspections than in the past, now requiring a major teardown and rebuild every five years.
Tower cranes now must be engineered to withstand wind conditions detailed in ASCE 7, the American Society of Civil Engineers' standard on minimum design loads for buildings and other structures; it was previously a recommendation. "The volume specifies that ASCE 7 wind speeds must be used for calculating foundations and freestanding heights," said Peter Juhren, corporate service manager for crane supplier Morrow Equipment Co. LLC, Salem, Ore., in a recent telephone interview. Juhren, who is also chairman of the tower-crane subcommittee for the ASME B30.3 standard published by the American Society of Mechanical Engineers, warned that even though the latest version was released in 2012, many people are still not aware of the changes.