## 4 Evaluation of Design Provisions  
In this section, the interface shear resistance according to design codes is evaluated based on the test results in the database summarized in Section 3. The design provisions considered include six major international codes, namely, _ACI 318-19; PCI Design Handbook; AASHTO LRFD; CSA-S6; Eurocode 2_; and _Fib Model Code 2010_. Details of test specimens and experimental and predicted results on interface shear resistance are presented in the Appendix A. Predicted interface shear resistance is compared with experimental results in original papers to evaluate the accuracy of design provisions. The columns of the Appendix A include the source of test data, specimen name, compressive strength of concrete \(f_{c}^{\prime}\), area of the concrete section resisting shear transfer \(A_{cv}\), area of the shear reinforcement crossing the interface \(A_{vf}\), reinforcement ratio \(\rho\), yield strength of reinforcement \(f_{y}\), clamping stress \(\rho f_{y}\) (\(\rho f_{y}\) is calculated using the upper limit of the yield strength of the reinforcement \(f_{y}\) for each code), peak measured shear stress \(v_{test}\), calculated interface shear resistance \(v_{cal}\) (\(v_{cal}\) is calculated utilizing \(\rho f_{y}\)), and ratio \(v_{test}/v_{cal}\) for each test specimen and each of the design provisions. In addition, the mean, maximum, and minimum values, standard deviation (STD), and coefficient of variation (COV) of \(v_{test}/v_{cal}\) are reported for each group of specimens. The peak measured shear stress \(v_{test}\) is defined as \(V_{test}/A_{cv}\), where \(V_{test}\) is the peak measured shear force. Interface shear resistance \(v_{cal}\) is calculated with the above-mentioned design provisions and proposed equation in this study (the proposed equation is presented in Section 6). The statistical results of \(v_{test}/v_{cal}\) are not separated by concrete type, but for different concrete types (normal-weight, sand lightweight, or all lightweight concrete), appropriate equations are utilized. From the calculation results listed in the Appendix A, ratios \(v_{test}/v_{cal}\) are plotted against the compressive strength of concrete \(f_{c}^{\prime}\) and the clamping stress of shear reinforcement \(\rho f_{y}\), as shown in Figures 5-8. The vertical axis of each graph ranges from 0 to 6.0 for each of the six design provisions evaluated. Ratios \(v_{test}/v_{cal}\) greater than 6.0 are not indicated in the graphs, but they are listed in the Appendix A. These figures are plotted to compare the peak measured shear stress \(v_{test}\) with the interface shear resistance \(v_{cal}\) calculated utilizing equations from codes for specimens with different interface types (M-U, M-P, J-R, J-M) and different concrete types (NW, SLW, ALW). From Figures 5-8, the evaluation and comparison of shear resistance for each interface had the following trends:  
Monolithic uncracked: All four codes provided conservative predictions of the interface shear resistance (that is, \(v_{test}/v_{cal}\) greater than 1.0) for the entire ranges of \(f_{c}^{\prime}\) and \(\rho f_{y}\). The _AASHTO LRFD_ tended to provide the most accurate overall predictions of the interface shear resistance. Larger conservative estimates were observed in all four design provisions at low values of clamping stress and high values of compressive strength of concrete. Monolithic precracked: The _ACI 318-19_ strength predictions were conservative at all clamping stresses and compressive strengths of concrete. The predictions of the _CSA-S6_ and _PCI_ provided some \(v_{test}/v_{cal}\) values less than 1.0. Figure 6 illustrates that for these two codes, values less than 1.0 occur for specimens made with lightweight concrete and for low clamping stress. Although the _AASHTO LRFD_ again tended to be more accurate than other codes, the _AASHTO LRFD_ strength estimates were unconservative.