## 5 Bonded Anchor Tests
### Short-Term Tests and Loading Rate Sensitivity  
Apart from the concrete curing history, and possible imperfections due to the installation procedure, a crucial influence factor is the loading rate sensitivity of the short-term pull-out capacity [53]. Both concrete and adhesive polymers are rate-dependent materials [21; 54; 55]. Thus, it is crucial to control the loading rate in all applications. Prior to the sustained load test investigation, a systematic loading rate effect study was performed to quantify the effect of the loading rate on the pull-out capacity. All tests were performed for both adhesive products in confined and unconfined configurations using concrete slabs with dimensions of 150 \(\times\) 100 \(\times\) 30 cm cast in the same batch as the specimens used for the material characterization and the cylindrical slabs for the time-to-failure tests. Tests were carried out using the testing load frame with a 630 kN servo-hydraulic jack. The tensile load was applied at the top of the anchor, controlled by one of two linear variable differential transformers (LVDT: HBM IWA/20 mm-T) with a nominal measuring range of 20 mm. Two LVDT's were installed close to the steel confinement plate in case of \"confined\" tests, and close to the concrete surface in case on \"unconfined\" tests to ensure stable post-peak response and a constant displacement rate. For this purpose, bonded anchors with the same geometry and embedment depth were used as tested under sustained load. Since this study is focused on the sustained load behavior of bonded anchors in a confined configuration, only the related loading rate effect results are discussed here. Apart from the so-called \"quasi-static\" rate (0.008 mm/s) that according to approvals has to reach the peak load between 1-3 min, another two loading rates were considered: (i) \"low rate\" with the speed of 0.0008 mm/s, and (ii) \"high rate\" with the speed of 0.08 mm/s. The resulting mean pull-out capacities with regard to the loading rate are listed in Table 4 including the corresponding coefficients of variation (CoV). Each value is the average of four tests. As it can be seen from Table 4, the results indicate the presence of a statistically significant loading rate effect. Based on linear regression in a plot of peak load versus logarithmic loading rate, the loading rate sensitivity can be quantified. An increase in loading rate by a factor of 10 causes an increase in pull-out capacity by 4.8% and 3.1% for Products 1 and 2, respectively. It has to be noted that the rate effect may follow another functional form if a wider loading rate range is taken into account. Typically, standard confined pull-out tests to determine the short-term capacity are performed either in load or displacement control. However, not much attention is placed on the actual load rate as the effect on the peak load in the range of \"normal\" loading rates is of the same order as typical experimental scatter. For sustained load tests (with and without failure), a completely different experimental set up is used in which the load is applied by pressurized air, hydraulics, or even torque in combination with spring systems. Most of the reported literature data sets on sustained load tests are carried out using hydraulic jacks or compression springs to sustain the load, often in combination with hand pumps [10]. Even if automatic hydraulic loading systems are available, they typically can \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Product** & **Low Rate** & **Quasi-Static Rate** & **High Rate** \\ \hline Product 1 & 117.4 kN \(\pm\) 2.6\% & 129.3 kN \(\pm\) 5.1\% & 146.6 kN \(\pm\) 1.9\% \\ Product 2 & 78.9 kN \(\pm\) 6.7\% & 85.8 kN \(\pm\) 4.4\% & 89.3 kN \(\pm\) 6.0\% \\ \hline Time to peak & 27 min & 2.4 min & 0.3 min \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Result of the loading rate effect on pull-out capacity in confined configuration. not be operated in displacement control.