## 2 Materials and Methods
### Testing Procedure  
Sustained load specimens were first loaded to a target sustained load within about 20 min (short-term loading). Then, the load was held constant for 24 to 52 days (sustained loading). The target sustained window was 24 days. Although this testing period may seem short for creep testing, the objective of this research was to determine if failure would occur under high sustained load. After 24 days, the rate of deflection increase reduced to less than 0.025 mm/day (0.001 in./day) on average and the research team felt the beam would not fail under additional testing. This was verified by a few specimens that were tested for an extended time period to evaluate behavior beyond 24 days. The applied load was checked and adjusted (if needed) every 12 h for the first 3 days and daily afterwards. For beam series I, after the sustained loading was finished, the beam was loaded to failure in a short time. For beam series II (excluding B10-SL), multiple levels of sustained load were applied. If no failure occurred under sustained load, the load was increased by 2.5 to 5% and then held constant for a time period of 2-3 days. The goal of this stepped loading approach was to determine shear-controlled beam near-failure behavior under sustained load and capture the tertiary phase of creep. Figures 7 and 8 show the details of loading histories. Figure 6: Stress–strain curves for longitudinal reinforcement. Figure 7: Beam series I loading histories. Tables 3 and 4 summarize the results of beam series I and series II including sustained load intensity, defined as the ratio of sustained load to the peak load of the control specimens (BC1 for series I and BC5 for series II). The tables also include the actual sustained load intensity which is the ratio of sustained load to the actual peak load of the specimens. The tables give the failure deflection when a beam experienced a sudden shear failure. In the tables, the creep coefficient is defined as the ratio of deflection increase during sustained loading to the initial deflection. The measured initial deflections, which is the elastic and inelastic deflection experienced in the specimens during the initial short-term loading, are also reported in the tables. The initial loading occurred in a slow process (over 20 min). The initial deflection was defined as the deflection measured at the end of the loading period. The sustained loading period and deflection increase are highlighted in Figures 9 and 10. The figures indicate that the beams that underwent sustained loading showed a load-deflection behavior different from that of the control specimen and much greater deflection at failure. For beams series I, BC1 served as a control specimen and was tested under monotonically increasing load to failure. BC1 failed at a load per loading point (P) of 19.62 kN (4410 lb) and a deflection of 12.75 mm (0.502 in.). The failure mode was a sudden shear-controlled failure, as seen in Figure 11. The remaining beams in series I were loaded with sustained loads equal to 82% (B2-SL), 87% (B3-SL) and 93% (B4-SL) of the strength of the  
Figure 10: Load vs. deflection response of beam series II. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & **BC1** & **B2-SL** & **B3-SL** & **B4-SL** \\ \hline Sustained load kN (lb) & - & 16.01 (3600) & 17.13 (3850) & 18.24 (4100) \\ Sustained load intensity & - & 0.82 & 0.87 & 0.93 \\ (sustained load/peak load of BC1) & - & 0.79 & 0.86 & 0.88 \\ Actual sustained load intensity & - & 0.78 & 0.86 & 0.88 \\ (sustained load/measured peak load) & 18.36 (4352) & 20.28 (4559) & 20.01 (4498) & 20.68 (4659) \\ Ratio of the peak load to the peak load of BC1 & 1 & 1.05 & 1.03 & 1.07 \\ Deflection at the peak load mm (in.) & 12.37 (0.487) & 13.88 (0.547) & 20.47 (0.806) & 18.22 (0.717) \\ Deflection at failure mm (in.) & 12.37 (0.487) & 40.39 (1.590) & 44.78 (1.763) & 37.41 (1.473) \\ Initial deflection under short-term loading deflection (\(\delta_{\mathrm{s}}\)) mm (in.)