Detailing Evaluation of Existing Concrete Structures

This paper discusses the historical evolution of reinforcement detailing in RC structures as stipulated in the ACI Code since 1956. The provisions for the required development length, splice length, hooks and bend diameters are compared for the 1956 ACI code, 1963 code, 1971 code, 1989 code and the current code. It is shown that the development lengths and splice lengths have increased significantly since 1956. At the same time, the bend diameters have been significantly relaxed to eliminate concerns of potential cracking of concrete due to tight bend radii. The detailing changes have been even more dramatic for structures expected to perform in moderate to high seismic regions (Chapter 21 of ACI 318). FEMA 356 and ATC-40 provide guidance for estimating the effect of insufficient development/splice length for seismic evaluation of structures designed for pre-70 codes. However, no guidance seems to exist for evaluation of the effect of tight bend diameters of standard hooks and tie hooks specified in the pre-70 codes. Note that evaluation of detailing is an integral part of strength evaluation of existing structures. Currently, there does not seem to be a uniform approach for detailing evaluation of pre-70 structures. Therefore, some guidelines are required in order to bring consistency to structural evaluation for general industry use.