1455
On Seismic Performance and Load Capacities for Pile Design
A propos des performances sismiques et les capacités de charge pour la conception de pieux
Chang D.-W., Sung S.-H
Tamkang University, Taipei, Taiwan
Lee S.-M.
CECI Engineering Consultant Inc., Taipei, Taiwan
Zhussupbekov A., Erlan Saparbek E.
LN Gumilyov Eurasian National University, Astana, Kazakhstan
ABSTRACT: This paper suggests alternative seismic design procedures using probability analysis and wave equation solutions. The
assessments of an existing pile foundation and a new design is suggested by checking up the maximum moment of the pile with the
moment capacities for the seismicity of interest. The pile displacements correspondent to the moment capacities can be found and
used as the allowable pile displacements. For a preliminary investigation on seismic design of the pile foundations in an engineering
project, one can establish a monographic procedure considering both load capacities and seismic performance of the piles. The design
could be carefully verified through a good use of the monographs.
RÉSUMÉ:
Cet article suggère des procédures alternatives de conceptions sismiques utilisant l’analyse de probabilité et des solutions
d’équations d’ondes. Les évaluations d’une fondation sur pieux
existante et une nouvelle conception sont proposées en vérifiant le
moment maximum du pieu avec la capacité de moment pour la sismicité d’intérêt. Les déplacements de pieux correspondants aux
capacités de moment peuvent être trouvés et utilisés comme les déplacements de pieux admissibles. Pour une enquête préliminaire sur
la conception sismique de fondations sur pieux dans un projet d’ingénierie, on peut établir une procédure monographique en tenant
compte et des capacités de charge et des performances sismiques des pieux. La conception pourrait être soigneusement vérifiée par
une bonne utilisation des monographies.
KEYWORDS: seismic performance, load capacity, pile design
1. INTRODUCTION
Performance Based Design (PBD) has received considerable
attentions from geotechnical society in the past decade. For
pile foundations, the design procedure needs statistical
investigations on bearing resistances and deformations of the
piles. Possible changing of the loads and the material
parameters are often considered. In addition, the uncertainties
of the methods for calculations, laboratory and/or in-situ
measurements, and the type of construction may also be
included. For piles susceptible to the earthquake impacts,
seismic performance of the piles ought to be analyzed carefully.
Since the dynamic strength parameters of the soils were often
found large than the static ones, the study on seismic effects to
pile capacities are generally fucusing on soil liquefaction. For
example, the soil parameter reduction coefficient, DE (JRA,
1996) can be used to reduce the soil strength and/or the soil
stiffness for liquefaction occurred due earthquake excitations.
In general, pseudo-static superstructural loads are carried in the
seismic design for pile capacities. According to the suggestion
of Honjo
et al.
(2002), PBD analysis can be made by LRFD
method and reliability analysis as well as probability analysis.
While the first two methods were used by many investigators
in studying the static performances of pile foundations, a
probability method named as PBEE (Performance Based
Earthquake Engineering) analysis, suggested by US Pacific
Earthquake Engineering Research Center, has been adopted by
Kramer (2008), Bradley
et al.
(2008) and Chang
et al.
(2009,
2010) to investigate the seismic performance of bridge pile
foundations. For design practice, the seismic performance of
piles can be monitored using pseudo-static or dynamic analysis.
While the former is easier to conduct, the latter requires much
longer time of computations, especially for FEM analysis.
Therefore an effective but rather fast solution is desired. Such
analysis is now available by Chang
et al
(2006, 2008) as
EQWEAP solving the free-field ground responses (w/ the
lumped mass analysis) and using them to obtain the
corresponding pile displacements out of the discrete wave
equations. In this paper, the possible connections between the
seismic performance and the calculated bearing capacities of
the piles are discussed based on the simplified modeling.
2. PERFORMANCE BASED EARTHQUAKE
ENGINEERING ANALYSIS
An excellent overview of the PBEE analysis can be found in
Kramer (2008). The so called Framing equation declares that
the annual rate of exceednace (
) of a decision variable (DV)
for any engineering project can be analyzed as a triple-integral
based on those consequent probabilities from the intensity
measured (IM), the engineering demand parameter (EDP) and
the damage measure (DM). The integral can be decomposed to
solve for the rate of exceednace for IM, EDP and DM,
respectively. Based on rational simplifications, analytical
equations were suggested to compute the corresponding
probabilities of these indices at different seismic levels. For
instance, the seismic design code in Taiwan requires that the
structures need to be analyzed at moderate earthquake, design
earthquake and the maximum consideration earthquake, which
implies that within a 50 yrs design life, the corresponding
probabilities of occurrence of these quakes are 80%, 10% and
2%, and the return periods are 30, 475 and 2500 years,
respectively. With the local hazard curves (
vs PGA, see
Figure 1) suggested by Cheng (2002), one can find the
corresponding PGAs at different seismic levels, ex, the ones in
Taipei are found to be 0.12g, 0.29g and 0.51g, respectively.
