# Large-Scale Experimental Static Testing on 50-Year-Old Prestressed Concrete Bridge Girders
## 4 Test Results
### Deflection Responses  
The deflection of girders under loading is a significant parameter; it can be used for the calibration of structural models able to properly assess the stiffness and resistance characteristics. Figure 10 shows, for each girder, the load-deflection curve obtained at the midspan of the girders (position D05 according to Figure 9) during each loading phase. From the slope of the curves, it is possible to observe the linear elastic response branch up to flexural cracking followed by crack propagation stage up to failure. Referring to the first, second and third load test (Table 1) on specimens composed by precast beam and cast-in situ slab, all curves show similar flexural stiffness and a cracking load of 24, 20 and 17 kN, respectively. The B3-P47/46 specimen reached its maximum capacity before collapsing with a load of 78.2 kN, related to an applied bending moment of 1438.9 kNm at midspan. The maximum applied loads for B8-P47/46 was 81.1 kN, corresponding to a bending moment of 1492.2 kNm. The B4-P47/46 specimen was loaded up to a failure load of 71.4 kN, corresponding to a bending moment of 1313.8 kNm. The B9-P47/46 PC beam collapsed after reaching a maximum load of 64.6 kN, corresponding to a bending moment of 1188.6 kNm. At the maximum applied load, B3-P47/46, B8-P47/46, B4-P47/46 and B9-P47/46 exhibited maximum midspan deflections of 167 mm, 150 mm, 135 mm and 145 mm respectively. The curve of the B3-P47/46 beam shows a load reduction at 75 kN associated to a holding phase required for the visual inspection stage of the cracking pattern. The drop recorded in the response of the B4-P47/46 beam at 72 kN can be associated to a first crushing of the cast in situ slab.  
All girders collapsed in a non-ductile mode with a bending failure mechanism due to concrete crushing in the top compression zone. Figure 11 shows the failure zone for all the tested girders in detail.  
Figure 10: Load versus midspan deflection with dots located at the estimated first cracking and peak loads for each girder.  
Figure 12 shows the deflection of each girder at the elastic stage (15 kN) and at the post cracked phases (30, 45 and 60 kN). For girders tested with two loading phases, the load at 60 kN refers to the second loading phase. The deflection was measured in the position of sensors from D01 to D09, according to the layout reported in Figure 9. As expected, the girder B9-P47/46, from which the cast in situ slab was removed, experienced a higher deflection due to a reduced flexural stiffness compared to the other girders. The deflections of the first three beams are similar for low load levels and become slightly different with increasing load.  
Figure 11: Failure zone details for: (**a**) B3-P47/46, (**b**) B8-P47/46, (**c**) B4-P47/46, (**d**) B9-P47/46 and the corresponding position.  
Figure 12: _Cont._  
In order to remove vertical displacements from the deflection of the beams due to support settlement, transducers were placed in the support zone (devices V01 and V02 in Figure 9). During the load tests, not relevant settlements were measured at the support level, but their values were taken into account. As an example, the vertical displacements recorded for the B8-P47/46 beam are reported in Figure 13.