Title: Load-Spread Spectrum in Strut-and-Tie Modeling of Structural Concrete
Author(s): Mohamed E. El-Zoughiby
Publication: Structural Journal
Appears on pages(s): 3-15
Keywords: concentrated loads or reactions; deep beams and walls; discontinuity regions; equilateral-triangle; load path method; load-spread spectrum; regular-hexagon; strut-and-tie modeling; strut-tie angle
The development of a strut-and-tie model (STM) using the load path method requires considering only concentrated loads or reactions. Distributed loads can be lumped into a series of (at least two) concentrated loads applied at nodes. The load-spreading (or strut-tie) angle is a key parameter in laying out an STM. Reducing the strut-tie angle to below a limiting value greatly increases the strut-tie forces, and when, by geometry, the angle is zero, no compression stresses would be permitted in a strut that is superimposed on a tension tie; strain incompatibilities with difficulty fit large struts within the space available. Two simple limiting rules—equilateral-triangle and regular-hexagon—are developed and used to define the three phases proposed for the load-spread spectrum in the strut-and-tie modeling method. The one-panel model, with(out) including web reinforcement in addition to the crack-control reinforcement required by codes, is assumed to represent the first two phases, while the two-panel model with one vertical tie represents the last phase. Sample examples are presented to justify and demonstrate the ease of implementation of the developed two rules.