# Bridge Expansion Joint in Road Transition Curve: Effects Assessment on Heavy Vehicles
## 4 Test Results and Discussion
Considering the significant difference found between the three BEJs in terms of IRI values, it is evident that BEJ1 has the most critical unevenness. Several in situ measurements were carried out to evaluate the dynamic consequences on heavy vehicles running on BEJ1. All of the recorded accelerometer signals were made uniform to a homogeneous time duration of \(T\) = 4.587 s and considering a time sampling equal to 5.6 \(\times\) 10\({}^{-4}\) s (\(\Delta t\)). Thus, a whole number of \(N\) = 8192 samples was registered for each signal. In addition, for all of the vertical acceleration measures, the reference time \(t_{0}\) corresponds to test vehicle transit on a transversal road section located at about 29 m before the BEJ. Table 5 shows the time of the three axes' passages on the joint for each loading test, captured by means of a high frame rate camera. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Number** & \(t_{1}\) **(s)** & \(t_{2}\) **(s)** & \(t_{3}\) **(s)** \\ \hline
1 & 0.999 & 1.184 & 1.230 \\
2 & 1.273 & 1.509 & 1.567 \\
3 & 1.038 & 1.231 & 1.278 \\
4 & 1.258 & 1.491 & 1.549 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Time of bump between axes and joint. Figure 15: International roughness index (IRI) values calculated on a segment of 10 m.  
Figure 16 shows the recorded accelerometer signals provided by the accelerometers on the front, medium and rear axles (number of tests = 1), with the indication of the three bump axle times. Positive peak values higher than 1 g were found for all of the test vehicle's axles, confirming the loss of tire/pavement contact due to the passage on BEJ1. Analyzing the maximum positive vertical accelerations obtained for each configuration test (Table 2), it was found that the medium axle was the most critical one (Figure 17). In addition, Figure 17 highlights the importance of the moving speed: increasing the vehicle velocity results in an increment of vertical acceleration on vehicles and passengers. Figure 16: An example of accelerometer signals (front, medium and rear axles: Test Number 1) and axles’ bumps transiting over the bridge expansion joint. All of the collected data were also analyzed in the frequency domain, and the results were represented using the acceleration power spectral density (PSD) function. This procedure permitted studying the principal oscillation and vibration components of the vehicle due to the bump (Figure 18). According to Figure 18, the main oscillation components are:  
* Vehicle roll oscillation: body roll \(f\cong 1.0\) Hz (\(T\cong 1\) s) (sprung mass);
* Primary vehicle oscillation: body bounce \(f\cong 2.0\) Hz (\(T\cong 0.5\) s) (sprung mass);
* Vehicle pitching oscillation: pitching\(f\cong 3.0\) Hz (\(T\cong 0.33\) s) (sprung mass);
* Primary vehicle axles oscillation: axle hop \(f\cong 10\)-\(20\) Hz (\(T\cong 0.1\)-\(0.05\) s) (unsprung mass);
* Tire oscillation and vibration: \(f\cong 40\)-\(60\) Hz (\(T\cong 0.025\)-\(0.017\) s) (unsprung mass);
* Power and other part in vibration: \(f>100\) Hz (\(T<0.001\) s) (vibration). Lower frequency responses (1-4 Hz) characterize the vehicle's body (sprung mass) bounces, or pitches and rolls. High-frequency responses (10-50 Hz), instead, correspond to axle hop vibrations. Acceleration measurements and their processing permitted identifying all vibrational components induced in the vehicle test by the geometric irregularity of BEJ1. In particular, the most important ones, which have a frequency range 1-4 Hz, determine the complete lifting from the pavement of the rear axles of the running ordinary heavy vehicles. Consequently, this phenomenon reduces the adherence of wheel-pavement, until the complete loss of adherence. Furthermore, in the paved areas adjacent to the joint, more accentuated irregularities appear, due to the considerable dynamic increment of the loads transmitted to the pavement.