ABSTRACT
When applying strength design procedures, engineers can obtain building structures that have adequate strength but unsatisfactory serviceability; that is, they exhibit excessive deflection. Thus, the size of many flexural members is determined by deflection response rather than by strength. The purpose of this chapter is to outline efficient procedures for estimating deflection, discuss factors affecting the variability of deflections, suggest procedures for use in the design process to reduce the expected deflection, and enable design engineers to proportion building structures closer to both strength and
serviceability requirements. The result could be more economical structures compared to those designed too conservatively because of concerns about deflection or those designed without adequate deflection control resulting in expensive repair costs. Throughout this chapter, the discussion assumes that a competent design is prepared according to ACI 318 Building Code (ACI Committee 318, 2005) and that construction follows good practices. It should be noted that the ACI Code provides minimum requirements for design. The engineer should determine (in consultation with the owner) whether these minimum requirements are adequate for the project in question; for example, certain types of brittle partitions such as unreinforced masonry may require smaller deflection limits, and certain types of sensitive equipment may require more stringent limits than those given in the code.
