doi:10.3850/978-981-08-7920-4_S2-G11-cd
Decoupling Lateral Spread Response from Structural Inertial Loading: A Design Case Study
Thomas McCormack1 and Rick Thrall2
1Portland, OR, USA.
2PBS Engineering and Environmental, Vancouver, WA, USA..
ABSTRACT
This paper presents the case history of a new 8-story building on Oregon’s seismically active
coast, sited next to a 40-foot deep dredged ship channel and overlying highly liquefiable soils.
A steel pipe pile foundation was designed to support gravity loads, vertical and lateral earthquake
forces, and to stabilize the underlying soils against lateral spread by “pinning.” The pile
foundation was designed in accordance with recently published liquefaction design guidelines
that recommend “decoupling” the effects of lateral spread from the effects of the structural
inertial loading, along with the use of different performance criteria for these two seismic effects.
Separating these two seismic effects is a rational technique because the peak vibration response
is likely to occur in advance of maximum lateral spread displacement. Significant economy
was achieved by using this approach and design procedure. In accordance with the published
design recommendations, the development of a plastic mechanism under the action of the
spreading forces was allowed. Approximately ninety 24-inch diameter concrete-filled pipe piles
were drilled into underlying sandstone to achieve base fixity and uplift resistance, while the pile
headswere fixed by embedment in four-foot thick pile caps. In addition, pile analysis considered
the effect of inelastic deformation on lateral deflections, and the effect of P-delta moment on pile
stress and pinning capacity.
Keywords: Liquefaction, Lateral spread, Pile pinning, Deep foundations, Earthquake.
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