Assessment and Simplification of American Association of State Highway and Transportation Officials Sectional Shear Design Using V-M Interaction Diagram
Ju Dong Lee
Appears on pages(s):
American Association of State Highway Transportation Officials (AASHTO) shear design; reinforced concrete; shear database; shear design; shear-flexure interaction; shear strength
This study presents the use of V-M interaction diagrams to estimate the ultimate shear and moment demands of reinforced concrete (RC) beams. The method of analysis presented can be beneficial for both design and analysis as it provides a visual aid for gaining clearer insight into the determination of the maximum load-carrying capacity of a considered section, as well as its failure mode. To simplify the construction of such V-M interaction diagrams and remove the often-needed iterative procedure, the current American
Association of State Highway and Transportation Officials
(AASHTO) shear sectional design model based on the Modified
Compression Field Theory (MCFT) was modified. As a result, the simplified process uses the strains of flexural reinforcement and moment demands at three events, which can be obtained by a simple elastic analysis. The maximum shear strengths were predicted for 1012 RC beams without transverse reinforcement using two current AASHTO shear design methods and the proposed simplified method. Overall predictions at failure from the V-M interaction diagram approach for all three methods showed great agreement
with the test results with a reasonable coefficient of variation.
Further investigation of the experimental variables revealed an overly conservative trend in beams with smaller effective depth and a/d ratio due to insufficient consideration of size effect and arch action. The noticeable trend by a/d ratio was somewhat moderated in the proposed method. Although the proposed method showed the most accurate predictions compared to the two AASHTO methods, an unconservative aspect existed for many cases so that a strength reduction factor of 0.75 was suggested. Also, the current strength
reduction factor of 0.9 in AASHTO for shear was evaluated and
considered appropriate. Given the satisfactory performance in
estimating the maximum shear capacity, the proposed simplified AASHTO method using the V-M interaction diagram can serve as an alternative shear strength design and analysis method for slender RC beams.