This is a recorded webinar from April 2, 2019.
ASCE 7-16 includes two significant new items related to the seismic design of diaphragms. First, a new Section 12.10.3, Alternative Design Provisions for Diaphragms including Chords and Collectors, has been added to Section 12.10, Diaphragm Chords and Collectors. The new section provides for an alternative determination of diaphragm design force level, which is mandatory for precast concrete diaphragms in buildings assigned to Seismic Design Category (SDC) C or above. The alternative is permitted to be used for other precast concrete diaphragms, cast-in-plane concrete diaphragms, and wood diaphragms supported on wood framing. All diaphragms other than precast concrete diaphragms in SDC C, D, E, or F buildings may continue to be designed using the design force level in ASCE 7-16 Section 12.10.1, which is unchanged from ASCE 7-10.
To go hand-in-hand with the alternative diaphragm design force level, ASCE 7-16 includes a precast diaphragm design procedure in Section 14.2.4, which is based on extensive research. The procedure must be used whenever the design force level of Section 12.10.3 is used. The requirements of Section 14.2.4 are in addition to the requirements of ACI 318-14 Section 18.12, Diaphragms and Trusses.
The procedure gives the designer three diaphragm design options for selecting the target performance of a diaphragm when subject to earthquake excitation. The Elastic Design Option (EDO) seeks to keep the diaphragm elastic in the Maximum Considered Earthquake (MCE). The Basic Design Option (BDO) seeks to keep the diaphragm elastic in the design earthquake while permitting controlled inelastic behavior in the MCE. The Reduced Design Option (RDO) permits controlled inelastic behavior even in the design earthquake. The choice of options is not unrestricted, but depends on the seismic design category, the number of stories, the diaphragm span, and the diaphragm aspect ratio.
The webinar will explain the alternative diaphragm design force level as well as the precast diaphragm design procedure of ASCE 7-16, which has now been adopted by ACI 318-19, which in turn references two new standards developed by ACI Committee 550: ACI 550.4, Qualification of Precast Concrete Diaphragm Connections and Reinforcement at Joints for Earthquake Loading and ACI 550.5, Code Requirements for the Design of Precast Concrete Diaphragms for Earthquake Motions.
Table of Contents
1. Identify the new alternative diaphragm seismic design force level of ASCE 7-16.
2. Explain why the alternative force level was found necessary.
3. Describe how to use the newly introduced diaphragm design force reduction factor.
4. Summarize the new precast concrete diaphragm design provisions of ASCE 7-16.
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