# Assessment of Existing Bond Models for Externally Bonded SRP Composites
## 4 Results and Discussion
### Comparison of Models  
The first feature visible in the graphs is the scattering of results. The more they were concentrated around the bisector, the more accurate the model. In this respect, the best models were [PERSON] et al. [21] and the newer [PERSON] and [PERSON] [28], [PERSON] et al. [30], as well as [PERSON] and [PERSON] [31]. The largest dispersion of results concerned the [PERSON] et al. [22], [PERSON] and [PERSON] [23], and [PERSON] and [PERSON] [26] models. The common feature of the three models was that they did not depend on the anchorage length or the effective anchorage length. This proved the importance of this quantity in the analysis. The [PERSON] [17] model was an exception in this respect. Another interesting observation concerned the [PERSON] [14] and [PERSON] and [PERSON] [15] models. They undervalued the predicted bond for higher values of an experimentally obtained ultimate bond. This may have resulted from the omission of the concrete strength in the analysis that characterized these two models. [PERSON] et al. [22], [PERSON] and [PERSON] [26], and [PERSON] et al. [29] were among the models that overestimated the bond capacity. The [PERSON] model was calibrated on bond tests of CFRP sheets, and this may be the reason for its characteristics. Interesting in this regard are the results based on the [PERSON] et al. model [27] (Figure 15). It underestimated the bond capacity in terms of low forces and, at the same time, dangerously overestimated for higher forces. Groups of models that underestimated the bond included [PERSON] [17], [PERSON] and [PERSON] [20], [PERSON] et al. [24], [PERSON] et al. [25], and the British TR55/2000 standard [33]. The described graph observations were confirmed by the results of the statistical analysis presented in Tables 4-6. The following parameters were used to evaluate and were analyzed in the manuscript bond prediction models: mean value of the predicted, theoretically to measure experimentally bond strength ratio (\(F_{ub,predicted}/F_{ub,test}\)), standard deviation (SD), and Pearson's correlation coefficient (PCC). Additionally, to evaluate the safety of the prediction, the percentage of results was given. Parameters are listed separately for the SRP bonded to concrete (Table 4), SRP bonded to masonry (Table 5), and SRG bonded to concrete (Table 6). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model** & **Mean** & **SD** & **PCC** & **\% Uncertainty** \\ \hline [PERSON] [14] & 0.699 & 0.263 & 0.220 & 15\% \\ [PERSON] and [PERSON] [15] & 0.746 & 0.218 & 0.503 & 13\% \\ [PERSON] et al. [16] & 1.14 & 0.241 & 0.751 & 66\% \\ [PERSON] [17] & 0.761 & 0.193 & 0.748 & 20\% \\ [PERSON] [18] & 0.763 & 0.244 & 0.629 & 17\% \\ [PERSON] and [PERSON] [19] & 0.980 & 0.313 & 0.629 & 45\% \\ [PERSON] and [PERSON] [20] & 0.763 & 0.195 & 0.747 & 11\% \\ [PERSON] et al. [21] & 0.873 & 0.234 & 0.676 & 27\% \\ [PERSON] et al. [22] & 1.55 & 0.372 & 0.734 & 91\% \\ [PERSON] and [PERSON] [23] & 0.937 & 0.478 & 0.408 & 36\% \\ [PERSON] et al. [24] & 0.754 & 0.197 & 0.729 & 8\% \\ [PERSON] et al. [25] & 0.528 & 0.166 & 0.657 & 0\% \\ [PERSON] and [PERSON] [26] & 2.00 & 0.906 & 0.476 & 89\% \\ [PERSON] et al. [27] & 1.81 & 1.22 & 0.573 & 68\% \\ [PERSON] and [PERSON] [28] & 0.882 & 0.202 & 0.726 & 30\% \\ [PERSON] et al. [29] & 1.63 & 0.389 & 0.728 & 95\% \\ [PERSON] et al. [30] & 0.752 & 0.196 & 0.716 & 13\% \\ [PERSON] and [PERSON] [31] & 1.14 & 0.246 & 0.745 & 67\% \\ TR55/2000 [33] & 0.502 & 0.197 & 0.609 & 3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of results—predicted to experimental bond strength ratios for steel-reinforced polymer (SRP) composites bonded to concrete. In the group of SRP models bonded to concrete, the mean closest to 1.0 can be found in the [PERSON] [23], and [PERSON] [19] models; however, it was accompanied by one of the highest standard deviations and correlation coefficients. In this situation, a good agreement of the mean should be considered as aleatory.