Civil Engineering Reference
In-Depth Information
2
Response of Structures
2.1 General
The objectives of this chapter are to address and unify defi nitions of the fundamental response param-
eters considered to be most infl uential in structural earthquake engineering, and to highlight the factors
infl uencing these fundamental response parameters. The parameters postulated in this topic to be the
basic building blocks of understanding and controlling earthquake response of structures are Stiffness,
Strength and Ductility. As presented in the following chapter, stiffness is the most pertinent parameter
in responding to the requirements of serviceability under the small frequent earthquake. In an analogous
manner, strength is utilized to control the level of inelasticity under the medium-sized infrequent earth-
quake, hence it maps onto the damage control limit state. Finally, collapse prevention under the large
rare earthquake is most affected by ductility, thus completing the hazard- limit state - response parameter
triads discussed in Section 1.4 of Chapter 1. The material in this chapter is presented in a strictly hier-
archical framework of material, section, member, connection and system characteristics most infl uential
in affecting stiffness, strength and ductility. The chapter concludes with a treatment of the two important
quantities of overstrength and damping, which are consequential to the three fundamental parameters
discussed above. This chapter therefore articulates the general guidelines of Chapter 1 into operational
quantities, and prepares for a thorough understanding of Chapters 3 and 4 on earthquake strong- motion
and structural analysis tools, respectively.
2.2 Conceptual Framework
2.2.1 Defi nitions
In order to establish a common nomenclature and in recognition of the plethora of confl icting defi nitions
in the literature, generic and rigorous defi nitions of the main terms used in this topic are given herein.
Focus is placed on the three response characteristics used hereafter as the most important parameters
that describe the behaviour of structures and their foundations when subjected to earthquakes. These
are stiffness, strength (or capacity) and ductility. Prior to defi ning the three quantities, it is instructive
to reiterate the defi nition of two more fundamental quantities, namely ' action ' and ' deformation ' . The
former is used in this topic to indicate stress resultants of all types, while the latter is used to indicate
strain resultants. The three quantities of stiffness, strength and ductility are treated in detail in subse-
