PSI - Issue 64

Antonio Bilotta et al. / Procedia Structural Integrity 64 (2024) 2109–2116 "Bilotta A. et al." / Structural Integrity Procedia 00 (2019) 000 – 000

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temporary instruments will be used to check if the response of the structure changes during the periodic testing, ensuring accurate and periodic monitoring of the sensors' operation over time. 3.3. SHM Layouts For all the bridges considered in this study, one or two spans, representative of repetitive deck layout, were selected for the SHM. Considering the structural similarity among the ramp viaducts, the SHM layouts are chosen to allow eventually comparisons through the recorded dataset within the eight viaducts. However, distinction can be done between the superstructure (i.e., deck) and the substructure (i.e., piers and pier caps) SHM layout. In the superstructure SHM layout, a six-point measurement accelerometer arrangement was designed, detailing reconstructing the structural response due to traffic loads, as well as the main vibration parameters of the deck (i.e., mode shapes and fundamental frequencies for both flexural and torsional behavior). The considered accelerometers on the bridge deck are summarized in Figure 5. More in detail only few triaxial accelerometers are used that also consider the horizontal degree of freedom, exploiting the stiff in-plane deck behavior. On the contrary, to catch both the flexural and the torsional response of the deck, vertical measurement points are needed along the bridge span on both the sides. Figure 5 shows the described layout in both plan, longitudinal and transverse view. The displacement transducers are used in several configurations depending on the presence of the half joints. In fact, when simply supported beams are arranged on the pier caps, bearing displacements are monitored using transducers in two orthogonal directions. On the contrary, 45-degree transducers are used in case of half joints (see details in Figure 6). Regarding the static measurement points of the bridge deck, two inclinometers are used to assess the rotational response at the ends of the span. In the middle span, deformometers are used to evaluate local measurements in terms of flexural mean curvature along a gage length equal to 250mm for one of the two beams of the deck. This local measure allows to identify high stresses/deformation due to flexural response under traffic loads due to excessive loads, degradation of materials, loss of prestressing load. If possible, due to environmental limitations arising during the installation step, laser distometers are included at midspan to record the absolute (relative to the ground) vertical displacement. In the substructure SHM layout, a rough sensor configuration is usually needed because, under ordinary traffic load condition, bridge pier experiences relatively low deformations respect to the vertical ones of the deck. On the contrary, acceleration and displacements at the top of the pier can have large increase when vehicle braking, seismic/wind actions occur. Mainly for this reason, a specific triaxial accelerometer is used at the pier top, also with a dedicated biaxial inclinometer.

Slab

Beams

Beams

Accelerometer Inclinometer

Deformometer

Disp. transducers

(in case of half joint bearings)

(in case of half joint bearings)

Figure 5 Typical layout of superstructure SHM system. The features of this secondary SHM layout are shown in Figure 6 as a conceptual sketch. Finally, two distinct thermal and humidity sensors are included respectively into the bridge deck and the selected pier. Figure 7 depicts various sensors in their in-situ conditions. Notably, specific measurement points for displacement transducers are visible at the bearings, alongside the particular geometric arrangement pertinent to bearing monitoring.