# Fast Falling Weight Deflectometer Method for Condition Assessment of RC Bridges
## 3 Results and Discussion  
In the center of the deck (test points 37-48, Figure 8), deflection test values are between 599 and 638 \(\upmu\)m, while tests performed on the abutment (test points 1-24, see Figure 8) show deflection values between 272 and 285 \(\upmu\)m (N-W side) and 238 e 248 \(\upmu\)m along (S-E side). Considering, instead, the approach pavement (test points 25-36), higher values of deflection were measured, that is, 981 e 1094 \(\upmu\)m (S-E side) and 1212 e 1368 \(\upmu\)m (N-W side).  
The average value of stiffness in the center of the deck was of 0.16 GN/m, while, on the two abutments, an average value of di 0.41 GN/m was measured (Figure 13). The approach pavement had an average stiffness value of 0.091 GN/m.  
The above stiffness is significant to evaluate the condition and deterioration of bridges over time, throughout repeated tests [5,44]. Moreover, the stiffness values of the abutment are greater than those measured on the center of the deck and on the approach pavement. In Figure 14 are plotted the values of the stiffness on the deck of the bridge.  
Figure 12: Comparison between experimental and numerical time history of geophone displacements. Geophone 1 (**a**), Geophone 2 (**b**) and Geophone 4 (**c**).  
Figure 13: Average values of stiffness for the tested points.  
The indexes introduced in Section 2.1 indicate the condition of the layers placed at different depths. Those are plotted in Figures 15-18. The Federal Highway Administration (FHA) gives tables [41] with the limits of acceptability of the indexes for road pavement, depending on the kind of material. Reinterpretation of the deflection basin parameters can be used to investigate other non-standard situations, such stone pavement, airport pavement instrumentation and pavement management system [45; 46; 47].  
It can be highlighted that the Fast-FWD allows us to induce a significant vertical impulse to the deck, like the one induced by a big sclerome  
Figure 14: Deflection basin on the: abutment (**a**), centerline of the bridge (**b**) and approach pavement (**c**).  
Figure 15: Contour of stiffness values.  
analyzed throughout different indexes. The more significant is probably the stiffness K. The maximum displacements of the Fast-FWD test are from the 33% (Figure 12c) to the 49% (Figure 12a) greater than the one attended from the FE model. This is a clear indicator of the degradation of the deck.  
The contours of Figures 16-18 show the variation of the vertical stiffness and of the Basin Indexes. The color maps are derived by the point measures made, as shown in Figure 8. The interpolation of the tests was carried out with the software Surfer rel. 8.  
Figure 16 illustrates that vertical stiffness varies in the range 0.00-0.65 MN/m. Figures 17 and 18 illustrated, respectively, SCI, BDI and DCI in \(\upmu\)m, indicators that reveal the condition of the investigated pavements and structural layers.  
The variation of these indexes on the surface of the bridge is an interesting indicator of the response of the surrounding structural layer. This is more significant for bridges in which the depth of the pavement is very thin. All the indexes represented in the graphs bellow present some range of variation in a different zone of the deck that represents a different structural response induced by aging.  
By providing the reduced depth of the road pavement on the bridge deck, the Base Distress Index (BDI) can be considered an interesting indicator for the structural response. For example, the BDI in the centerline varies between 20 and 80. Thus, the BDI, here, is a relevant indicator of the differential corrosion of the reinforcement of the bridge. An accurate record of the response of the bridge is recommended at different abscissa in various positions (both on the crossbeams and on the slab).  
Figure 16: Contour of the Surface Condition Index (SCI).  
Figure 17: Contour of Base Distress Index (BDI).  
Figure 18: Contour of Deep Condition Index (DCI).