PSI - Issue 84

Francesco Ballio et al. / Procedia Structural Integrity 84 (2026) 151–158

156

a

b

0.8

0.4

0.6

0.3

0.4

0.2

 h (cm)

F (kg)

0.2

0.1

0

0

0

200

400 t (s)

600

800

0

200

400 t (s)

600

800

Fig. 5. Temporal evolution of (a) backwater rise; (b) hydrodynamic load.

3.2. Temporal evolution of backwater rise and hydrodynamic load The entrapment of driftwood and the consequent formation and growth of the accumulation increase the backwater rise at the bridge and the hydrodynamic load the flow exerts on the bridge. Fig. 5 shows the temporal evolution of the backwater rise and hydrodynamic load for the present and prior experiments (the load was not measured in the prior experiments, so they do not appear in panel b). During all the runs, the backwater rise increased in time due to the progressive entrapment of new driftwood. In run 1, the hydrodynamic load did not increase much due to the relatively limited size of the accumulation; instead, the load increase was quite significant in run 2. 3.3. Relationships between the accumulation size, backwater rise, and hydrodynamic load Figs. 6 and 7 present the increase of the backwater rise and of the hydrodynamic load with the size of the accumulation, expressed, respectively, in terms of projected area upstream of the bridge measured from above (A Ua ) and total volume determined by the wood continuity principle (W cont ). In order to quantify the relative increase, both the backwater rise and the hydrodynamic load were normalized with reference to their initial values, respectively  h 0 and F 0 , that were determined as the average values within the first 10 s of an experiment. The expected enhancement of the investigated quantities by the driftwood accumulation is evident from the plots.

a

b

3

3

2

2

 h/  h 0

F/F 0

1

1

0

0

0

500

1000

1500

2000

0

500

1000

1500

2000

A Ua (cm

2 )

A Ua (cm

2 )

Fig. 6. Increase of (a) backwater rise; (b) hydrodynamic load as a function of on the upstream area measured from above.