## 7 Laboratory Tests and Numerical Simulations Result and Discussion
### Experimental Test Results  
Figure 17 shows the results of the experimental tests performed on the two beams in terms of the midspan load-displacement curve. The behavior of the two beams in static scheme 1 (Figure 10a,b) is almost identical (continuous black and blue curves). The failure load is about 240 kN for both beams (120 kN on each half joint). The type of collapse presents both analogies and differences: a longitudinal disconnection on the casting joint between the web and flange arises at the end of the damaged side for both beams. The beam with orthogonal reinforcement collapses with a brittle mechanism tearing away the strengthened zone from the rest of the beam without developing a large plastic field as shown in Figure 18a,b. In the beam with inclined reinforcement, the flange-web disconnection extends almost to the midspan leading to a more ductile behavior (see Figure 18d). The beam with orthogonal reinforcement was tested on load scheme 2 after the failure in load scheme 1. The dashed black curve, shown in Figure 17, is relative to the test in static scheme 2, shown in Figure 10c,d. In this scheme, the sound-dapped end reaches a collapse load of about 175 kN and the collapsed end is shown in Figure 18c. Figure 17: Laboratory test results. Figure 18: Collapse mechanisms. (**a**) Beam with orthogonal reinforcement in static scheme 1. (**b**) Beam with orthogonal reinforcement in static scheme 1 after removal of steel jacketing. (**c**) Beam with orthogonal reinforcement in static scheme 2. (**d**) Beam with inclined reinforcement in static scheme 1. The beam with inclined reinforcement could not be tested in scheme 2 because the failure mechanism due to the test on static scheme 1 extends to the midspan of the beam, Figure 18d. Therefore, the beam could not be used anymore. The collapse load calculated with STM for the sound-dapped end with orthogonal reinforcement is 150 kN. The sound side tested in the laboratory provided a resistance of 175 kN (17% higher than STM). The theoretical result is therefore in excellent agreement with the laboratory tests because STM tends to predict failure loads lower than real ones (on the safe side) being a plasticity lower bound solution. The collapse load calculated with STM for the sound-dapped end with inclined reinforcement is 160 kN. No laboratory test can confirm this value as this beam cannot be tested in this scheme. The authors are confident that the result obtained with STM (160 kN) would also have been confirmed. The failure loads of the damaged end without jacketing, calculated with STM, are, respectively, 65 and 70 kN for orthogonal and inclined reinforcements. The steel jacketing increased them by +85% and +72% respectively, reaching 120 kN for both reinforcements layouts. The results are shown in Table 4.  
Steel jacketing, therefore, improved noteworthy the resistance of damaged ends. Nevertheless, it was not able to restore the +120% necessary to reach the sound resistance because of a failure mechanism that took place outside the jacketed area and that will be described in the following paragraph. As can be seen in Figure 18, in both experiments no evident signs of damage is visible in the web under the jacketing plates. The strengthening system acts as a rigid block that shifts the collapse zone to the first section where the jacketing is not applied. The collapse follows the opening of a crack between the flange and the web of the T beam along the casting joint. The authors did not find in the literature any experimental test on half-joints of T beams realised in two casting phases; therefore, this study introduces two novel issues: interaction between half joint and flange of T section and the presence of flange-web construction joint. Construction joints are an area of intrinsic weakness in the structure especially if the surface is not prepared to increase its roughness such as in this case. Real bridge beams are almost always cast in two stages, and the slab is realised a second time.