Potential of PBEE in the Selection and Comparative Performance of Structural Systems

Potential of PBEE
in the Selection and Comparative Performance
of Structural Systems
Ron Mayes – SGH Inc
The development of structural systems with improved performance characteristics began with
the introduction of base isolation (1970’s and 1980”s), energy dissipation devices (viscous,
hysteretic and friction, 1980’s and 1990’s), buckling restrained braces and active control systems
(1990’s). The presentation will overview the development and implementation of these structural
systems in the United States and assess current and future capabilities that can be used to assess
the relative performance of different structural systems.
Conveying the value of higher-performance seismic design to clients, building users and
the general public has always been a difficult task. The design philosophy of current building
codes as given in its commentary states: “These provisions are intended to safeguard against
major failures and loss of life, NOT to limit damage, maintain functions, or provide for easy
repairs.” This often comes as a surprise to many building owners, who believe they are getting
an “earthquake proof” building when they hire a competent structural engineer to design a code
conforming building.
The next-generation performance-based seismic design procedures developed under the
PEER and ATC 58 projects will express performance directly in terms of the quantified risks that
the building owner or decision maker will be able to understand. In a workshop held in the early
stages of the ATC 58 project, a representative sample of these users indicated their preference to
define these risks in terms of the future life loss, facility repair costs and downtime that could
result from design decisions.
The presentation will include results from the response of the six three story buildings with four
different framing schemes to look at the relative damage losses that may occur in a standard
office building and a high tech manufacturing facility. The four framing schemes were a
buckling-restrained braced frame, viscously damped frame, moment frame and a base isolated
braced frame. The buckling-restrained braced frame and the viscously damped frame were also
designed as essential facilities where the R-Factor for the buckling-restrained braced frame was
reduced from 7 to 3.5 and the force capacity of the viscous dampers was increased from 133 kips
to 220 kips. The ATC 58 methodology is applied to the results of this study and the presentation
will compare the professions current capability of expressing relative structural performance and
that provided by the PEER/ATC 58 methodology. The PEER/ATC 58 methodology will
revolutionize the way in which the design engineer will be able to communicate with the owner.
It will also be extremely valuable information for “Green Design” as it will express damage costs
in very clear terms. At this time the LEED Rating system for green designed buildings
completely ignores the earthquake performance of a building.