# Calibrating of a Simulation Model to Predict the Flexural Capacity of Pre-Stressed Concrete Beams
## 3 Results and Discussion
### Calibration  
After performing various calibration analyses, the most important parameters for fitting the flexural model were: pre-stress level, modulus of elasticity of the concrete and bond strength. The most important results for each of these parameters are described below. * Level of pre-stressing losses  
The simulation results show that the pre-stressing loss level that best replicates the response obtained in the experimental tests is 35%, and thus, it was necessary to apply a higher level of losses than that included on the data sheets. Thus, in the case of joint TB35-5 (Figure 7a), the level increases from a theoretically estimated 21.9% to 35% (+12%), while in T18-1, the increase is from theoretical 17.7% to 35% in the simulation (+13.3%). Furthermore, as shown in Figure 7b, the load losses are linearly correlated with the ultimate and cracking strength levels achieved by the element analyzed. Therefore, it is clear that this factor is the key parameter that governs the strength of the elements. Figure 6: Load–deflection diagrams for different tests in T18-1 (**a**) and TB35.5 (**b**) joists with 3 repetitions for each joist. Figure 7: Load–deflection diagrams for different simulated pre-stressing levels in joist TB35.5 (**a**) and evolution of cracking strength and ultimate strength with pre-stressing losses (**b**). This finding show that the manufacturing of elements analyzed results in a higher level of pre-stressing loss than that estimated theoretically, which suggests that, if it were possible to limit such losses in the final products through an optimization of the process, the strength of the elements would be increased at no additional cost to the company. * Modulus of elasticity The model calibration results show that the variation of this parameter has no impact on the final strength level of the model, when mainly controlling the first part of the curve (Figure 8). Thus, the simulation suggests that the modulus of elasticity value that best fits the experimental test is 32,000 N/mm\({}^{2}\) for both types of joists (T18.1 and TB35-5). * Bond strength In addition to the response of the curve, we calibrated the bond strength between the reinforcement and the concrete to control the crack pattern of the model. Thus, the optimal bond value that best fits the crack patterns of the experimental tests was 12 MPa (Figure 9). This value is close to the default value generated by the tool for a steel rebar (13.4 MPa) and is far from the value generated for cold cables (0.6 MPa) and hot rolled bars (2.0 MPa). Thus, for specimens of this type, the most advisable solution is to use the model configured for \"Ribbed Reinforcement\" elements to generate the bond model. Figure 8: Load–deformation diagrams simulated for different modulus of elasticity in joist TB35.5. Figure 9: Crack distribution in the simulation with different bond strength levels (**a**) and that obtained in the experimental test (**b**) for joist T35.5. The rupture crack is shown in red color. The tensile strength and fracture energy were found not to be significant determinants of the response of the model to the flexural tests analyzed, and we hence opted to leave the default values. Regarding the compressive strength, no modifications were made since we used the values from the company's quality control tests on compression. Table 3 shows the calibration values of the model that best replicate the experimental structural response, and which were used to simulate the other pre-stressed linear elements. Results of the Simulation of the Elements with the Parameters Obtained from the Calibration and Comparison with the Experimental Tests  
Having calibrated the models, all the parts tested experimentally were simulated in order to compare the overall level of fit obtained following the adjustments.