# Assessment of Existing Bond Models for Externally Bonded SRP Composites
## 4 Results and Discussion
### Comparison of Models
Furthermore, after analyzing the values of all statistical parameters, we found that [PERSON] et al. [21] and [PERSON] and [PERSON] [28] models were the most accurate. Similarly, among the technical guidelines, fair exactness ensured JCI 2003, SIA 166/2004, CNR-DT200R1/13, and the fib bulletin 90/2019; they could be successfully used to predict the bond strength of SRP composites to concrete. The older fib bulletin 14/2001 and especially TR55/2000, tended to underestimate the bond capacity too much. Models by [PERSON] et al. [22], [PERSON] and [PERSON] [26], [PERSON] et al. [27], and [PERSON] [29] not only overestimated the bond prediction but also had a very high percentage of unsafe design. As shown in Table 5, the general trend for masonry-bonded SRP composites was similar to that for concrete-bonded. Similar models tended to overestimate or underestimate prediction. However, a general increase in the mean of the ratio of predicted to experimentally measured results could be observed. It ranged from one ([PERSON] [17], [PERSON] and [PERSON] [20]) to several dozen percent ([PERSON] [14], fib Bulletin 14/2001 [34], and CNR-DT 200 [37]). Only two models showed a decrease in the mean value ([PERSON] and [PERSON] [26] and [PERSON] et al. [27]); however, they still overestimated the bond strength, and the result was characterized by the highest standard deviation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model** & **Mean** & **SD** & **PCC** & **\% Uncertainty** \\ \hline Fib Bulletin 14/2001 [34] & 0.821 & 0.268 & 0.632 & 23\% \\ JCI 2003 [35] & 0.941 & 0.263 & 0.738 & 39\% \\ SIA 166/2004 [36] & 0.911 & 0.219 & 0.756 & 34\% \\ CNR-DT200R1/13 [37] & 0.928 & 0.264 & 0.718 & 43\% \\ Fib Bulletin 90/2019 [38] & 0.962 & 0.233 & 0.755 & 45\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model** & **Mean** & **SD** & **PCC** & **\% Uncertainty** \\ \hline [PERSON] [14] & 0.911 & 0.209 & 0.330 & 58\% \\ [PERSON] and [PERSON] [15] & 0.869 & 0.202 & 0.339 & 23\% \\ [PERSON] et al. [16] & 1.34 & 0.322 & 0.416 & 87\% \\ [PERSON] [17] & 0.764 & 0.202 & 0.339 & 29\% \\ [PERSON] [18] & 1.04 & 0.339 & 0.215 & 68\% \\ [PERSON] and [PERSON] [19] & 1.34 & 0.435 & 0.215 & 81\% \\ [PERSON] and [PERSON] [20] & 0.764 & 0.202 & 0.339 & 29\% \\ [PERSON] et al. [21] & 1.13 & 0.277 & 0.358 & 74\% \\ [PERSON] et al. [22] & 1.87 & 0.393 & 0.453 & 90\% \\ [PERSON] and [PERSON] [23] & 1.208 & 0.663 & \(-\)0.087 & 71\% \\ [PERSON] et al. [24] & 0.726 & 0.232 & 0.232 & 16\% \\ [PERSON] et al. [25] & 0.719 & 0.223 & 0.223 & 45\% \\ [PERSON] and [PERSON] [26] & 1.78 & 0.664 & 0.116 & 87\% \\ [PERSON] et al. [27] & 1.73 & 0.499 & 0.499 & 87\% \\ [PERSON] and [PERSON] [28] & 1.04 & 0.222 & 0.441 & 74\% \\ [PERSON] et al. [29] & 1.91 & 0.47 & 0.424 & 90\% \\ [PERSON] et al. [30] & 0.954 & 0.218 & 0.414 & 68\% \\ [PERSON] and [PERSON] [31] & 1.271 & 0.351 & 0.380 & 84\% \\ TR55/2000 [33] & 0.655 & 0.231 & 0.229 & 13\% \\ Fib Bulletin 14/2001 [34] & 1.20 & 0.392 & 0.218 & 77\% \\ JCI 2003 [35] & 0.943 & 0.238 & 0.379 & 65\% \\ SIA 166/2004 [36] & 0.954 & 0.22 & 0.404 & 65\% \\ CNR-DT200R1/13 [37] & 1.41 & 0.432 & 0.232 & 81\% \\ Fib Bulletin 90/2019 [38] & 1.09 & 0.249 & 0.411 & 77\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of results—predicted to experimental bond strength ratios for SRP composites bonded to masonry. Against the background of all the results in Table 5, the prediction error of the Italian Standard CNR-DT200R1/13 may be surprising. Average predictions increased by more than 50%. It results most likely from assuming an overestimated value of the \(k_{G}\) coefficient. Based on Appendix D of the cited standard, it was adopted as a mean value \(k_{G}=0.093\) mm, but it was characterized by high variation (recommended for design, 5% fractile is 0.031 mm). Evaluating only the mean parameter presented in Table 6, the assessment of the possibility of using the analyzed models in predicting the SRG bond would be similar to the SRP.