More than two years after the National Institute of Standards and Technology released its 30 recommendations for improving the safety of tall buildings based on its post-9/11 investigation of the World Trade Center towers, the prescriptive recommendations are finally making their way into the model building codes.
In June, the International Code Council released a supplement to its International Building Code that incorporates a number of changes and additions based, in part, on the NIST WTC investigation recommendations. The changes include:
An additional exit stairway for buildings more than 420 feet in height.A minimum of one fire service access elevator for buildings more than 120 feet in height.Increased bond strength for fireproofing (nearly three times greater than what is currently required for buildings 75-420 feet in height and seven times greater for buildings more than 420 feet in height).Field installation requirements for fireproofing to ensure that: installation complies with the manufacturer's instructions; the substrates (surfaces being fireproofed) are clean and free of any condition that prevents adhesion; testing is conducted to demonstrate that required adhesion is maintained for primed, painted or encapsulated steel surfaces; and the finished condition of the installed fireproofing, upon complete drying or curing, does not exhibit cracks, voids, spalls, delamination, or any exposure of the substrate.Special field inspections of fireproofing to ensure that its installed thickness, density, and bond strength meet specified requirements, and that a bonding agent is applied when the bond strength is less than required due to the effect of a primed, painted, or encapsulated steel surface. The inspections are to be performed after the rough installation of mechanical, electrical, plumbing, sprinkler, and ceiling systems.Increasing by one hour the fire-resistance rating of structural components and assemblies in buildings 420 feet and higher.Explicit adoption of the “structural frame” approach to fire resistance ratings that requires all members of the primary structural frame to have the higher fire resistance rating commonly required for columns. The primary structural frame includes the columns; other structural members having direct connections to the columns, including girders, beams, and trusses; and spandrels and bracing members designed to carry gravity loads.Luminous markings delineating the exit path (including vertical exit enclosures and passageways) in buildings more than 75 feet in height to facilitate rapid egress and full building evacuation.
NIST's lead WTC investigator Shyam Sunder said a broad industry coalition is planning to submit two more model code changes to be considered for the next edition of IBC in 2009.
The first recommends that structures be designed to mitigate disproportionate progressive collapse and ensure, for the first time, minimum structural integrity and robustness requirements for structures as complete systems.
The second code change would require the use of a nationally accepted standard for conducting wind tunnel tests routinely used for determining wind loads in the design of tall buildings.
For more, visit www.nist.gov.
