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Wind Some, Lose Some - Amusement Structures

[Subject Prev][Subject Next][Thread Prev][Thread Next] From 1996 Blue Book

Wind and Seismic Forces
Wind and seismic forces are fundamentally different. Wind force results from
aerodynamic pressures applied to an exterior surface of a structure, whereas seismic
forces result from the inertial response of a structure to the accelerations and
displacements from earthquake ground shaking. Wind pressures and the resulting
forces tend to have somewhat predictable upper limits; the upper limits of seismic
inertial forces, on the other hand, tend to be unpredictable. Furthermore, the seismic
design forces set forth in these Requirements are based on inelastic behavior in the
structure; the forces resulting from the inelastic behavior are much lower than the
seismic forces that would occur if the structure remained elastic.
Seismic ground shaking can cause several reversing cycles of inelastic deformation.
Thus, even when wind pressures govern the stress (strength) or drift design, the
structural lateral force resisting system must conform to the special detailing
requirements for seismic systems in order to accommodate the inertial forces and
displacements from an earthquake. These detailing requirements are intended to
allow the lateral force resisting system to deform inelastically without catastrophic
failure and to provide the necessary inelastic energy absorption and toughness
necessary to resist actual seismic forces. Actual seismic forces are expected to
exceed the specified seismic design forces.

James Bela

Oregon Earthquake AwarenessTM        /        The Quake NorthwestTM
"We Have Nothing To Fear But Shear Itself"        /        "We're All Subducting In This Together"