SEISMIC RESTRAINT SYSTEM

Transcription

1 1. GENERAL 1.1. Description: SECTION SEISMIC RESTRAINT SYSTEM This specification covers design and installation of seismic bracing and anchorage required for conduit, cable tray, bus duct, and equipment. Contractor is responsible for design and installation of seismic bracing and anchorage systems Description of systems: 1.2. Quality Assurance: Transverse and longitudinal bracing for seismic forces on suspended electrical systems including conduit, cable tray, bus duct, and equipment Anchorage of floor and roof mounted electrical equipment Seismic design requirements: provide bracing and anchoring for equipment, conduit, cable tray, designed, constructed, and installed to resist stresses produced by lateral forces specified under the authority below: IBC 2009, for Seismic Design Category C Design and install seismic anchorage and bracing for all floor or roof mounted equipment weighing 400 pounds or more and all suspended or wall mounted equipment weighing 20 pounds or more For this project, the following seismic coefficients shall be used in calculating the required lateral force: SDS = (IBC) SD1 = (IBC) Ss= (IBC) S1=0.051 (IBC) Site Class: D Seismic forces shall be presumed to act through the center of mass of the equipment in a direction that will produce the largest single anchor force Submittals: Shop drawings and calculations: Layout and mounting detail drawings showing system and proposed brace locations for all systems including pre- SEISMIC RESTRAINT SYSTEM

2 engineered systems The specific detail for each type of brace or anchor must be referenced on a plan that identifies the required. Supplying a book of details without referencing the proper detail to a specific location on a plan is not acceptable Structural calculations for required lateral force level for each component All submittals, including pre-approved systems, shall be signed and sealed by a licensed engineer, licensed in the state in which the project is located Product data: Technical data on seismic control devices Include rated load, rated deflection, and overload capacity for each vibration isolation device Illustrated and indicate style, material, strength, fastening provision, and finish for each type and size of seismic restraint component used Tabulate types and sizes of seismic restraints, complete with report numbers and rated strength in tension and shear as evaluated by an agency acceptable to authorities having jurisdiction Annotate to indicate application of each product submitted and compliance with requirements. 2. PRODUCTS 2.1. Suspended Bracing Systems: Acceptable manufacturers: Pre-engineered systems: Base: Optional: Unistrut International Seismic Application Technology (ISAT) B-Line SEISMIC RESTRAINT SYSTEM

3 Other manufacturers desiring approval shall comply with Document Custom engineered systems designed using specified criteria and common building materials Equipment Anchors and Supports: 3. EXECUTION Drilled-in-place concrete anchors shall have an approved ICBO Evaluation Services Report Cast-in-place anchors shall comply with ASTM-A36, ASTM-A307, or ASTM-F Anchors permanently exposed to weather or corrosive environments shall be stainless steel or hot-dipped galvanized Structural steel for supports: ASTM-A Cold formed metal and connection material: Unistrut or equal Any details provided are based on assumed equipment and arrangement. Contractor shall be responsible for design and acquiring approval for support and anchorage of equipment and arrangement which varies from equipment and arrangement assumed in detail provided General Requirements: Design and install all bracing and anchoring for equipment, conduit, cable tray, and bus ducts in accordance with the requirements of this specification Every run which requires bracing shall have a minimum of two Transverse Braces and one Longitudinal Brace A run is defined as suspended pipe, duct or trapeze rack having a minimum 5 foot (1.52 m) straight run length Brace spacing shall not exceed the maximum allowable brace spacing as engineered by the manufacturer or custom bracing designer Bracing may be omitted from conduit and cable tray runs less than 5 ft (1.52 m) in length Bracing may be omitted from conduit and cable tray runs where rod hung supports of less than 12 in (305 mm) in length are required All unbraced suspended utility systems having 2 diameter conduit and larger or systems weighing more than 5 lb/ft shall be installed with a minimum 6 in (152 mm) clearance to suspended ceiling vertical hanger wires. SEISMIC RESTRAINT SYSTEM

4 The conduit and cable tray shall be installed such that the lateral motion of the members will not cause damaging impact with other systems or structural members or loss of vertical support A longitudinal brace at a 90 degree change in direction may act as a Transverse Brace if it is located within 2 ft (610 mm) of the change in direction A Transverse Brace may act as a longitudinal brace if it is located within 2 ft (610 mm) of a change in direction and if the brace arm and anchorage have been sized to meet or exceed the requirements of the Longitudinal Brace When bracing equipment or a utility system that is suspended from an overhead deck, brace back to the overhead deck or to the supporting structure supporting the deck. Do not brace to another element of the structure which may respond differently during a seismic event Obtain approval from the Structural Engineer prior to attaching to any brace elements to structural steel or wood framing When utilizing cable bracing, tension the cable to remove slack without inducing uplift of the suspended element. Tension seismic bracing system prior to system start up and adjust if necessary after equipment start up As a general rule, do not mix rigid bracing with cable bracing in the same run. However, once bracing has transitioned a 90 degree change in run direction, the bracing may switch from rigid to cable or vice versa if required due to a significant change in overhead deck elevation or to provide an implementable bracing scheme in a congested area Install brace members at an angle of 45 degrees from horizontal within a tolerance of plus 2 1/2 degrees or minus 45 degrees provided the brace length is accounted for in design. Brace angle may be increased to 60 degrees provided the brace spacing is reduced to 1/2 that required for a 45 degree brace Seismic bracing may not pass through a building separation joint. Utility systems that pass through a separation joint must be seismically restrained within 5 ft (1.52 m) from the point of connection. Any hardware designed to accommodate seismic movement across the span of the separation joint shall be installed per manufacturer s installation and listing instructions With approval of the Structural Engineer, utility systems that are suspended from the overhead deck may be braced to load bearing concrete or CMU (concrete masonry) walls provided that the walls and the overhead decks will respond similarly during a seismic event Each layer of a multiple layer trapeze rack shall be braced individually based on the weight of the individual layer Conduit and cable tray constructed of non ductile material (plastic, fiberglass, or no hub cast iron), shall have brace spacing reduced to 1/2 of the spacing allowed for ductile materials. SEISMIC RESTRAINT SYSTEM

5 Where brace elements are through-bolted, the mounting hole in the element is to be no more than 1/16 in (1.6 mm) in diameter larger than the bolt or threaded rod Seismic braces shall directly brace system and not the hanger Suspended Electrical Systems: Install seismic bracing for all conduit 2 1/2 in (63.5 mm) trade size or greater All trapeze assemblies supporting conduits and cable trays shall be braced considering the total weight of the elements on the trapeze. For the purposes of calculating weight, all conduits are to be treated as full Brace all trapeze racks which support conduit 2 1/2 in (63.5 mm) trade size or larger. Brace all other conduit rack and cable tray trapezes having a minimum weight in excess of 10 pounds (4.54 kg), per lineal foot. Include a minimum 10% additional capacity for future additions Seismic bracing may be omitted from cable trays and conduit suspended by rod hung supports 12 in (305 mm) or less in length from the top of the element to the bottom of the structural attachment of the hanger provided lateral motion will not cause damaging impacts to other systems or loss of system vertical support All vertical risers involving conduit 2 1/2 in (63.5 mm) in diameter or larger shall include lateral restraint at maximum 30 ft intervals and at the top and bottom of the riser Floor or Roof Mounted Equipment: Provide one anchor on each leg or corner. Support with a minimum of three 3/8 in diameter anchors Friction shall be neglected when designing anchors for shear Vertical seismic forces, when required, shall be presumed to act concurrently with horizontal seismic forces. END OF SECTION SEISMIC RESTRAINT SYSTEM