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Structural Concrete - Hassoun

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820 Chapter 20 Seismic Design of Reinforced <strong>Concrete</strong> Structures<br />

2. SDCs C indicates moderate/intermediate seismic risk zones with moderately strong ground<br />

shaking.<br />

3. SDCs A and B indicate low seismic risk zones with SDC A corresponding to the lowest<br />

seismic hazard zone.<br />

For structures in high seismic risk (SDCs D, E, and F) special requirements in flexural design<br />

and detailing are required. Special moment frames (ACI Code, Sections 18.6–18.9) and special<br />

structural walls (ACI Code, Section 18.5) should be used as the structural system of a building.<br />

For the structures in moderate seismic risk (SDC C) some special provisions are required for<br />

satisfactory intermediate seismic performance (ACI Code, Sections 44.6.4, 4.4.6.5.1 and 4.4.6.5.2).<br />

Structure can be designed as intermediate moment-frame or intermediate structural-walls systems.<br />

Structures from a higher category can also be utilized.<br />

For the structures in low seismic risk (SDC A), no special requirements in flexural design and<br />

detailing are required (ACI Code, Section 4.4.6.3). Ordinary moment frames and ordinary structural<br />

walls and systems should be utilized as the structural system of a building.<br />

For structure assigned to SDC B, additional requirements apply (ACI Code, Section 4.4.6.4).<br />

SDC B structures shall satisfy ACI Code, Chapter 18.<br />

20.5.1 Structures in the High Seismic Risk: Special Moment Frames<br />

A special moment frame is a structural system that is designed and detailed to sustain strong earthquakes.<br />

Special provisions for designing and detailing are given for<br />

1. Flexural members of special moment frames such as members subjected to only bending.<br />

2. Special moment-frame members subjected to bending and axial load such as columns.<br />

3. Joints of special moment frames.<br />

Strong column–weak girder connection. Courtesy of Murat Saatcioglu and John Gardner<br />

20.5.1.1 Flexural Members of Special Moment Frames<br />

20.5.1.1.1 General Requirements<br />

1. If factored axial compressive force P u < A g f ′ c∕10, then the member is considered to be subjected<br />

to bending. Area A g represents the gross area of the concrete member.

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