Structural Concrete - Hassoun

CHAPTER20
SEISMIC
DESIGN OF
REINFORCED
CONCRETE
STRUCTURES
Collapse of frame concrete structures due to an earthquake. Courtesy
of Murat Saatcioglu and John Gardner.
20.1 INTRODUCTION
Ground motions during an earthquake can severely damage the structure. The ground acceleration
when transmitted through the structure is amplified, and it is called the response acceleration. The
amplified motion can produce forces and displacements that can be larger than the motions the
structure can sustain.
Many factors influence the intensity of shaking of the structure such as earthquake magnitude,
distance from fault or epicenter, duration of strong shaking, soil conditions of the site, and frequency
content of the motion.
A structure should be designed, depending on the type of structure and its function, to have
acceptable levels of response generated in an earthquake. Economy of design is achieved by allowing
the structure to deform above elastic limit.
20.2 SEISMIC DESIGN CATEGORY
Building Code Requirements for Structural Concrete (ACI 318) [1] gives the procedure for design
and detailing of structures subjected to earthquake loads but does not address the calculations of
seismic forces. In this chapter the International Building Code (IBC 2012) [2] will be utilized for
the calculation of seismic forces.
The IBC 2012, Section 1613, defines six seismic design categories (SDC): A, B, C, D, E,
and F. IBC 2012, Section 1613.3.5, also defines four risk categories: I, II, III, and IV. To relate the
SDC and the risk category, the design spectral response acceleration S DS and S D1 are used. S DS is the
design spectral response acceleration coefficient for short periods and S D1 is the design response
acceleration coefficient for a 1-second period. Design spectral response acceleration coefficients
are related to severity of the design earthquake ground motions at the site.
A seismic design category will determine which type of lateral force analysis must be performed
and which type of lateral force resisting system must be used.
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