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4.4 Structural Considerations

Steel bracing in the Milwaukee Courthouse
Steel bracing in the Milwaukee Courthouse

LRFD and ASD. Both Load Resistance Factor Design (LRFD) and Allowable Stress Design (ASD) are acceptable design procedures for GSA buildings. If LRFD is chosen, the design narrative must specifically address floor vibration.

Cast-in-Place Systems. Systems that have fewer limitations in cutting openings during future alterations are preferred over other systems.

Precast Systems. Precast floor framing systems should only be used for GSA office buildings when the design can be demonstrated to adapt well to future changes in locations of heavy partitions or equipment. Precast systems may be considered for low-rise structures such as parking garages, industrial buildings, and storage and maintenance facilities.

Pre-tensioning and Post-tensioning. As with precast floor framing, these systems should only be used when the design can be demonstrated to not impede future flexibility.

Base Isolation. Base isolation shall be considered for Seismic Design Categories C and D and buildings located in Regions of High Seismicity for two to fourteen story buildings, particularly on rock and firm soil sites which are stable under strong earthquake ground motion. The base isolation system must be shown to be as cost effective as conventional foundation systems. The effects of the base isolation system on the framing, mechanical, and electrical systems shall be included in the evaluation of cost effectiveness.

Passive Energy Dissipation Systems. Passive energy dissipation systems shall be considered for Seismic Design Categories C and D and buildings located in regions of moderate to high-risk seismic zones.

Innovative Mitigation Methods. Innovative mitigation methods that deviate from the requirements of FEMA 356 shall be permitted, provided an analytical procedure acceptable to GSA shows that the required performance level is attained. When new and innovative rehabilitation techniques are proposed for a specific building, a peer review panel, acceptable to GSA, shall determine the adequacy of the mitigation techniques proposed by the engineer.

Progressive Collapse
Refer to Chapter 8: Security Design.

Floor Vibration
The floor-framing members shall be designed with a combination of length and minimum stiffness that will not cause vibration beyond the “slightly perceptible” portion of the “Modified Reiher-Meister Scale” or an equivalent vibration perception/acceptance criteria.

Seismic Instrumentation for Buildings
For Seismic Design Categories C, D, E, F and buildings located in Regions of High Seismicity, every existing building over six stories in height with an aggregate floor area of 60,000 square feet (5574 m2) or more, and every building over 10 stories in height regardless of floor area, shall be provided with USGS approved recording accelerographs. USGS developed guidelines and a guide specification for federal agencies for the seismic instrumentation

The W.F. Bennett Federal Building in Salt Lake City is the first federal building to use buckling-restrained brace technology.
The W.F. Bennett Federal Building in Salt Lake City is the first federal building to use buckling-restrained brace technology.

of their buildings. The guidelines describe the locations and the types of instruments used for several “typical” buildings. Typical costs were also developed for existing buildings. The Seismic Instrumentation of Buildings (with emphasis on federal buildings), Special GSA/USGS project, USGS Project No: 0-7460-68170, can be downloaded as a PDF file at http://nsmp.wr.usgs.gov/celebi/gsa_report_instrumentation.pdf.

Workmen on the roof of the Winder Building, Washington, D.C. install a window as part of a renovation project.
Workmen on the roof of the Winder Building,
Washington, DC install a
window as part of a renovation project.

 Geotechnical Considerations
The requirements for the geotechnical engineering investigation and report are listed in Appendix A: Submission Requirements.

Footings shall not project beyond property lines.

 Nonstructural Elements
All nonstructural elements, components and equipment located within a building or on the site must be anchored to withstand gravity, wind, seismic, temperature, and other loads as required by IBC for new buildings and FEMA 356 for existing buildings.


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