Reinforced Concrete Sections under Moment and Axial Load

Concrete International, Oct 2007 by Alaoui, Sanaa S, Klingner, Richard E

Because shear calculations are not extensive, they are not automatically conducted. Rather, shear capacities are calculated only as needed based on the input in the "Shear Calculations" sheet. Once an analysis has been run, any changes in input require that the analysis be rerun. If only changes in shear are of concern, however, the analysis need not be rerun because shear data are updated instantaneously.

PROGRAM VALIDATION

Using a variety of beam, column, and wall sections, the program was checked against hand calculations and also against previous programs6,7 developed for the same purpose, but using a different programming language. Agreement was excellent.1

Example

As an example of the input and output of the program, the flanged shearwall shown in Fig. 3 was analyzed in bending about its strong axis. The input spreadsheet is shown in Fig. 4. The concrete has a specified compressive strength of 4000 psi (27.6 MPa), and is modeled using Scott, Park, and Priestley's curve for low strain rates. The reinforcement has a specified yield strength of 60 ksi (420 MPa), an initial modulus of 29,000 ksi (200 GPa), a strain of 0.01 at the start of strain-hardening, and an ultimate strength of 100 ksi (690 MPa) at a strain of 0.1.

The moment-curvature response and moment-axial force interaction diagram for this wall are shown in Fig. 5 and 6, respectively. The latter includes the moment-axial force interaction curve as governed by shear assuming an effective height of 10 ft (3 m).

Acknowledgments

The RECONASANCE program was begun in Spring 2004 by the first author as a class project in CE 383N (Advanced Reinforced Concrete Structures) at the University of Texas at Austin. In that project, some work (the three sheets for concrete stress-strain relationships and the sheet for shear calculations) was initially done by another student, D. Williams. His contributions are gratefully acknowledged.

References

1. Alaoui, S.S., "RECONASANCE: REinforced CONcrete Analysis Spreadsheet enhANCEd," MS Report, Department of Civil, Architectural, and Environmental Engineering, The University of Texas at Austin, Austin, TX, Dec. 2004, 60 pp.

2. Hognestad, E.; Hanson, N.W.; and McHenry, D., "Concrete Stress Distribution in Ultimate Strength Design," ACI J ournal , Proceedings V. 52, No. 4, Dec. 1955, pp. 455-479.

3. Kent, D.C., and Park, R., "Flexural Members with Confined Concrete," Proceedings, ASCE, V. 97, No. ST7, July 1971, pp. 1969-1990.

4. Scott, B.D.; Park, R.; and Priestley, M.J.N., "Stress-Strain Behavior of Concrete Confined by Overlapping Hoops at Low and High Strain Rates," ACI Journal , Proceedings V. 79, No. 1, Jan.-Feb. 1982, pp. 13-27.

5. ACI Committee 318, "Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (318R-05)," American Concrete Institute, Farmington Hills, MI, 2005, 430 pp.

6. Mahin, S., "RCCOLA: Reinforced Concrete Column Analysis," Earthquake Engineering Research Center, University of California, Berkeley, CA, 1972, 89 pp.

7. Farahany, M., "User-Oriented Computer Program for Flexural Behavior of General Reinforced Concrete Sections," MS Report, Department of Civil, Architectural, and Environmental Engineering, The University of Texas at Austin, Austin, TX, Dec. 1983, 125 pp.