This course presents a numerical procedure for computing a three-dimensional interaction diagram for reinforced and prestressed concrete sections of arbitrary cross-sectional shape. From the three-dimensional failure surface two-dimensional interaction diagrams can be extracted for use by design and research engineers. Construction of the failure surface is accomplished by computing section capacities corresponding to numerous orientations and positions of the neutral axis in relation to the concrete section being analyzed.
The course covers several topics including the numerical procedure, a discussion of nonlinear stress-strain curves versus the traditional rectangular stress block, the k3 factor which is important in column analysis, construction of two-dimensional interaction diagrams from the three dimensional failure surface, and comparisons of this numerical procedure to column and beam test results from past investigations.
At the conclusion of the course, the student will learn:
• The numerical procedure described in this course and used by FDOT's Biaxial Column Program;
• The benefits of using nonlinear stress-strain curves;
• The difference in results between nonlinear stress-strain curves and the rectangular stress block;
• the importance of the k3 factor and casting position;
• the advantages of constructing a true three dimensional diagram instead of using curve fitting solutions;
• Differences between different types of interaction diagrams.
The numerical procedure discussed in this course is utilized by the Florida Department of Transportation's Biaxial Column v3.0 program. It is highly suggested that before reading this course and then again after reading this course the student try out this program if possible. The program is free but it does require a java and MathCad 15 to be installed on your computer. For those that have MathCad 2001 you may request an older compatible version from the author.
A free version of the program can be found here:
This program is excellent for evaluating short concrete columns which are biaxially loaded or concrete beams which are biaxially loaded. It does not perform shear or tie reinforcement design.