# Large-Scale Experimental Static Testing on 50-Year-Old Prestressed Concrete Bridge Girders
## 5 Discussion  
The girders of the C.so Grosseto Viaduct studied in the present work have 50 years of service life in an urban environment and, consequently, have experienced all the aforementioned deterioration causes affecting this structural typology. The results reported in this paper concern the tests performed on the first group of girders and aim at characterizing their structural conditions up to failure. In particular, the tests were designed to investigate their flexural capacity response adopting a three-point bending test scheme. The choice of the test setup considered the presence of the damages induced during the dismantling operations. The girders were selected having damages located away from the most stressed area and most prone to experience rupture. The damage due to corrosion noticed at the edges of the girders was considered not to influence the outcome of the experimental tests. Figure 19: Tensile shear strain of the B8-P47/46 beam. Figure 20: Force-tensile shear strain for SH3 and SH8 for the B4-P47/46 and B9-P47/46 beams. The material properties obtained from the design documentation and laboratory tests performed at the time of construction were reported, such as the strengths of precast concrete, cast in situ slab and prestressing steel. A noticeable difference in terms of compressive strengths with the current material characterization were found. The results obtained for the samples extracted from both the slab and the beams show a resistance of 40% lower than what was reported on the tests performed at the time of construction. Given the importance of these parameters to correctly interpret the static tests results, the material characterization study will be extended, paying particular attention to all the phases of sampling and extraction of the cores. The results of the test on steel confirm what was reported in the design project. The static tests conducted on the three complete girders showed a similar behavior in terms of deflection, maximum capacity and failure mechanism. The maximum midspan deflections up to collapse recorded for all the tests reveal a ratio less than 1/100 of the span that is typically addressed to PC beams. The crushing of the cast in situ concrete slab for the B3 and B8 and B4-P47/46 girders and of the top flange of the B9-P47/46 girder was reported, highlighting a non-ductile rupture behavior. The girder B4-P47/46 shows a double peak revealing an initial crushing of the cast in situ slab, followed by the crushing of the top slab of the PC beam at a lower load that determined the global collapse (Figure 11c). In all the four tests, the crush of the slab occurred close to the loading system and not at the maximum bending moment section, probably due to the confining action exerted by the transverse steel beams; indeed, a diagonal crack on the most compressed zone departed from the bottom flange of the same steel beam, as can be observed in Figure 11. In Figure 10, the non-ductile performance of the girders is apparent, with no evidence of yielding of the prestressing steel. The girders tested, after adopting the two-loading phases, did not show residual damages such as visible cracks at the end of the unloading, except for a residual deflection due to non-recoverable deformations. Moreover, no significant difference in terms of maximum loads was registered. On the other hand, the two-phase tests adopted for B3-P47/46 and B8-P47/46 and also for the B9-P47/46 girders allowed us to evaluate the decompression loads disregarding the value of the tensile strength of concrete. The crack opening values reported in Section 4.2 can be compared to the results of specific tests on strands and concrete in order to estimate the prestressing losses more accurately. For reinforced concrete beams, cracks directly affect the moment of inertia of the cross-section and the flexural stiffness decreases accordingly.