| = 18. CHAPTER 18 — EARTHQUAKE-RESISTANT STRUCTURES | |
| = 18.1 — Scope | |
| == 18.1.1 This chapter shall apply to the design of nonprestressed | |
| and prestressed concrete structures assigned to | |
| Seismic Design Categories (SDC) B through F, including, | |
| where applicable: | |
| | |
| (a) Structural systems designated as part of the seismic-force- | |
| resisting system, including diaphragms, moment | |
| frames, structural walls, and foundations | |
| (b) Members not designated as part of the seismic-force-resisting | |
| system but required to support other loads while | |
| undergoing deformations associated with earthquake | |
| == 18.1.2 Structures designed according to the provisions | |
| of this chapter are intended to resist earthquake motions | |
| through ductile inelastic response of selected members. | |
| = R18.1 — Scope | |
| Chapter 18 does not apply to structures assigned to | |
| Seismic Design Category (SDC) A. For structures assigned | |
| to SDC B and C, Chapter 18 applies to structural systems | |
| designated as part of the seismic-force-resisting system. For | |
| structures assigned to SDC D through F, Chapter 18 applies | |
| to both structural systems designated as part of the seismic-force- | |
| resisting system and structural systems not designated | |
| as part of the seismic-force-resisting system. | |
| Chapter 18 contains provisions considered to be the | |
| minimum requirements for a cast-in-place or precast | |
| concrete structure capable of sustaining a series of oscillations | |
| into the inelastic range of response without critical | |
| deterioration in strength. The integrity of the structure in the | |
| inelastic range of response should be maintained because | |
| the design earthquake forces defined in documents such as | |
| ASCE/SEI 7, the 2018 IBC, the UBC (ICBO 1997), and | |
| the NEHRP (FEMA P749) provisions are considered less | |
| than those corresponding to linear response at the anticipated | |
| earthquake intensity (FEMA P749; Blume et al. 1961; | |
| Clough 1960; Gulkan and Sozen 1974). | |
| The design philosophy in Chapter 18 is for cast-in-place | |
| concrete structures to respond in the nonlinear range when | |
| subjected to design-level ground motions, with decreased | |
| stiffness and increased energy dissipation but without critical | |
| strength decay. Precast concrete structures designed in | |
| accordance with Chapter 18 are intended to emulate cast-in- | |
| place construction, except 18.5, 18.9.2.3, and 18.11.2.2, | |
| which permit precast construction with alternative yielding | |
| mechanisms. The combination of reduced stiffness and | |
| increased energy dissipation tends to reduce the response | |
| accelerations and lateral inertia forces relative to values that | |
| would occur were the structure to remain linearly elastic and | |
| lightly damped (Gulkan and Sozen 1974). Thus, the use of | |
| design forces representing earthquake effects such as those | |
| in ASCE/SEI 7 requires that the seismic-force-resisting | |
| system retain a substantial portion of its strength into the | |
| inelastic range under displacement reversals. | |
| The provisions of Chapter 18 relate detailing requirements | |
| to type of structural framing and SDC. Seismic design | |
| categories are adopted directly from ASCE/SEI 7, and relate | |
| to considerations of seismic hazard level, soil type, occupancy, | |
| and use. Before the 2008 Code, low, intermediate, | |
| and high seismic risk designations were used to delineate | |
| detailing requirements. For a qualitative comparison of | |
| seismic design categories and seismic risk designations, | |
| refer to Table R5.2.2 . The assignment of a structure to a SDC | |
| is regulated by the general building code (refer to 4.4.6.1 ). | |
| [ Lanjut Ke 18.2—General ... ] | |
| | |
| | |
