ISAT's OSHPD OPA-0485
|
| • • • • • • • |
1997 Uniform Building Code 2001 California Building Code NPC Upgrades, California Senate Bill 1953, “Hospital Seismic Safety Act” The BOCA National Building Code, 1999 International Building Code 2000 Unified Facilities Criteria 1-200-01, Dept. of Defense FEMA 302 |
Lateral Force Formulas
The ISAT Applications and Design Manual provides seismic restraint requirements engineered for use within a broad range of horizontal accelerations. Primary end user input must first draw upon data specific to the project type, location, and the projects seismic design specifications. Once these parameters have been determined and certain basic calculations performed, ISAT’s engineered Bracing Tables and Detail Drawings can be used as a ready reference for the seismic bracing of suspended utilities within the specific facility.
Beginning with the 1997 UBC and 1998 CBC substantial revisions were adopted for the formulas used to determine minimum seismic restraint requirements for non-structural components. OSPHD, however, elected to delay adoption of the revised code formulas until issuance of the 2001 CBC, Volume 2, Chapter 16A. The implementation date for use of the new formulas for OSHPD facilities is November1, 2002.
The new 1997 UBC and 2001 CBC code formulas calculate “Total Design Lateral Force”(TDLF), and require utilization of the following parameters:
Total Design Lateral Force Variables
|
• Soil Profile Type Seismic Coefficient, Ca |
See the ISAT Project Worksheet located at the back of the Manual for the specific code formula. To obtain project worksheets for use with other codes, please contact ISAT Technical Service.
As a point of comparison, under the 1994 Uniform Building Code the maximum horizontal force factor was .45g for the seismic restraint of rigidly supported utilities in an essential facility. As a result of the new 1997 UBC and 2001 CBC formula, the new maximum horizontal force factor for elements attached at roof elevation on non-essential facilities is 1.89 g’s after having divided Total Design Lateral Force by 1.4 to convert to Allowable Stress Design.
To provide uniformity of installation on a specific project, the horizontal acceleration calculated for utilities suspended from the underside of the roof deck (worst case) maybe used as the basis for selecting seismic restraint systems for all floors of the structure. However, to achieve economy of installation, the horizontal acceleration for each floor may be computed separately and designs meeting the minimum horizontal acceleration for each floor can be employed as drawn from the ISAT bracing tables.
ISAT Engineered Bracing Tables
The cumulative result of the new formula is the need to provide engineered seismic restraint systems covering a substantial range of possible horizontal ground accelerations.
In response to this need ISAT has generated concise tables of the minimum restraint requirements for a broad array of ground accelerations as applied to commonly suspended utilities. In order to efficiently apply the Bracing Tables it will be necessary that the user acquire all seismic parameters specific to the project as defined by the engineer of record and/or the project architect. These parameters should commonly be identified on the plans or within the construction documents.
To obtain assistance in performing calculations, complete the ISAT Project Worksheet at the back of the Manual and fax to ISAT Technical Service.
ISAT Technical Support
ISAT’s technical staff is available to provide project support services and is dedicated to assisting contractors and project teams achieve code compliance in a cost effective manor. Technical support services are co-coordinated through ISAT affiliated distributors. Services available include but are not limited to the following:
|
• Submittal Preparation |
Design Considerations
1. Information within the ISAT Manual is intended only as a guideline for the design of seismic restraint systems. It is not intended as the basis for the design of the suspended utility nor is it intended to be all inclusive of every element of the suspended utility. Certain elements of systems such as trapeze assemblies, support frames for suspended mechanical equipment or pipe anchors and guides for steam lines may require additional design, analysis and detailing by a California Registered Structural Engineer.
2. Seismic restraint layout drawings maybe required, prepared by persons familiar with and experienced in the design and layout of support and seismic bracing systems in order to offer a more complete design package to the installing contractor.
3. Any deviation from the ISAT bracing tables or ISAT installation details shall only be made using sound design practices by a qualified engineer with the approval of the engineer of record and the code authority having jurisdiction, subject to local code requirements.
4. It is the responsibility of the engineer of record to confirm suitability of the structure to accept the vertical support loads and seismic reactions generated as a result of these designs.
5. All ISAT brace assemblies employ seismic bracketry covered under ICBO Evaluation Services Report PFC-5566. No deviations or substitutions allowed without the express written consent of ISAT. Any unauthorized deviation or substitution voids all engineering.