scope:

Aim and contents of this Special Publication

The implementation of strut-and-tie models in ACI 318-2002 with Appendix A is an important step in direction towards a more consistent design concept. Even more, it is a major achievement for the engineers in practice and should trigger efforts to apply strut-and-tie models in daily practice. Therefore, the main objective of this Special Publication is to show with design examples the application of strut-and-tie models according to the Appendix A of ACI 318-2002.

This Special Publication contains five parts. After the introduction (Part i), Part 2 gives an insight into the development of Appendix A of ACI 318-2002 and of the discussions in ACI Committee 3 18 E "Shear and Torsion". The scope and aim of the Appendix A is described and extensive explanations are given in addition to those already presented in the Commentary of Appendix A.

Part 3 presents a summary of important tests, which justify the use of strut-and-tie models for the design of structural concrete. Among the tests are the classical examples for D-regions like deep beams, corbels and dapped beam ends.

Part 4 forms the major part of this Special Publication presenting nine different examples designed with strut-and-tie models using Appendix A of ACI 318-2002. Most of these examples were taken from practice:

 - The Example 1 (deep beam), Example 2 (dapped beam end) and Example 3 (double corbel and corbel at column) are classical D-regions, which have been designed with strut-and-tie models since long, and for which even tests were carried out, as described in Part 3.

 - The Example 5 (beam with indirect supports) and Example 6 (prestessed beam) deal with well known D-regions of beams, which so far have mostly been dealt with in codes by rules for the shear design.

 - The Examples 7 (pier table) and Example 9 (pile cap) deal with D-regions of 3D-structures, for the design which most codes give only rare information.

Some examples were selected to demonstrate the potential of strut-and-tie models to solve uncommon design problems, such as like Example 4 (deep beam with opening) and Example 8 (high wall with two openings).

All examples show the approach of finding a model, which is the first and an important step in a design with strut-and-tie models. The examples also point out where problems in dimensioning or in detailing and anchoring the reinforcement occur and how the design could be improved.

Part 5 gives a summary and discusses some issues which are either common for all examples or turned up in several examples. After a brief review of the procedures for finding a model, the uniqueness of a model is discussed and why different models may be selected by several engineers. The other issue addresses the transition between D- and B-regions of beams and is of general importance for many examples, because many D-regions are part of a larger structure and have to be "cut out" of it, i.e. the correct actions and forces have to be applied at the border of the D-region. Finally in Part 5 the importance of detailing is pointed out as it was demonstrated in several examples,