Explaining the riddle of tension stiffening models for shear panel experiments

Analyses of reinforced and prestressed concrete structures based on a smeared crack approach generally include a tension stiffening relationship to estimate the average concrete tensile stress after cracking. Many such equations have been developed over the years and show significant differences between them. In this study, three of these equations are compared and it is shown that the variation between the equations can be explained by the different bond conditions of the specimens tested to calibrate the equations. An expression is proposed to quantify this effect and sample results are shown. Use of this relationship should allow more realistic estimates of crack width and stiffness at service loads to be obtained.