## 9 Conclusions  
With this work, the authors aimed to investigate an innovative strengthening system for gerber saddles. Analytical calculations, laboratory experimental tests, and numerical simulation are performed on two different beams with different reinforcement layouts in the dapped end. A review of the state of the art showed that few studies have been conducted on the supporting part of bridge gerber saddles. Most of the studies found in the literature focus on the supported part of gerber saddles. The strengthening systems evidenced in the literature are prevalently performed with FRP/CFRP or with pretensioning systems. The first is effective for moderate levels of damage and is not highly invasive; the second is effective for more intense levels of damage but has considerable invasiveness. On this basis, the authors propose a system that should be more efficient than FRP/CFRP, but at the same time less invasive than the introduction of prestressing. Moreover, tests on beams with strengthened dapped ends were almost exclusively conducted on beams with rectangular cross-sections: T-shaped sections with casting joints were never tested before. This aspect represents an absolute novelty point of this study. Thus, in the present study, some significant innovations are introduced: a T-shaped beam section with the presence of a flange web casting joint; the casting of the beam in two phases; and the study of the end subjected to negative bending moment. The beams were designed to be approximately 1:3 scale compared to the common size of real gerber saddles. The collapse load is estimated with an STM in both the undamaged and damaged dapped end. The damaged gerber saddles were designed to support a load equal to about 45% of the sound ones. This level of damage is very high since normally in reinforced concrete decks the permanent loads exceed 50% of the total applied loads. Therefore, the designed damage would result in the collapse of the bridge under only permanent loads. Reinforcement corrosion damage was simulated by changing the diameter of the corroded stirrups; for example, an undamaged stirrup \(\Phi\Theta\) or \(\Phi\Omega\) was replaced with a damaged stirrup \(\Phi\Phi\). This operation uniformly reduced the area of the stirrups whereas in real conditions corrosion is more concentrated in the part of the stirrup within the half joint as it is more exposed to water leakages. The authors decided to simulate corrosion with diameter change because of the scheduling of the financed research that did not allow the use of accelerated corrosion techniques. Web stirrups almost always maintain their original area at the connection with the beam flange (in the casting joint). The application of the steel strengthening failed to raise the strength of the damaged dapped end to the level of the undamaged ones, as it was intended, but the collapse load still increased from about 45% to about 80% percent of the value of the undamaged dapped end. The strengthening system thus proved to be able to increase the strength of the gerber saddle in a nonnegligible way. Both laboratory specimens collapsed with a similar failure mechanism involving a longitudinal crack dividing the web from the flange of the beams. The weakness of the shear-friction resistance of the joint between the web and flange may be a collateral effect of the stirrups damage simulation mode and should not be probable in real operating conditions. The authors believe that the \"block tearing\" collapse mechanism seen in the experimental tests needs to be furtherly investigated to understand whether this mechanism is only due to the low amount of stirrups crossing the casting joint, or if the steel jacketing causes its initiation. From the experimental tests, hand calculations and numerical calculations performed, the following considerations can be made:  
* Both strengthened gerber saddles reached collapse by a similar mechanism involving the failure of the casting joint and a shear crack in the web with an inclination of about 60\({}^{\circ}\).