Derivation of strut-and-tie models for the 2002 ACI Code


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Title: Derivation of strut-and-tie models for the 2002 ACI Code

Author(s): James G. MacGregor

Publication: Special Publication

Volume: 208


Appears on pages(s): 7-40


Date: 10/29/2002

This paper documents the decisions made by ACI Committee 3 18 to introduce strut-and-tie models into the 2002 ACI Code. Sections 3 and 4 of this paper review code statements concerning the layout of strut-and-tie models for design. The format and values of the effective compression strength of struts are presented in Sec. 5. The first step was to derive an effective compression strength which gave the same cross-sectional area and strength using Appendix A as required by another code for the same concrete strength and same unfactored loads. The final selection of design values of the effective compression strength considered test results, design values from the literature, values from other codes, and ACI Code design strengths for similar stress situations. A similar derivation of the effective compression strengths of nodal zones is summarized in Sec. 6 of the paper. The description of the geometry of nodal zones in code language proved difficult. The design of ties is described in Sec. 7 of this paper and requirements for nominal reinforcement are in Sec. 8. Nominal reinforcement is provided to add ductility, to improve the possibility of redistribution of internal forces, and to control cracks at service loads.