https://orcid.org/0000-0002-4920-6216
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ABSTRACT
Empirical equations for predicting local scour depth around bridge piers only consider the effects of hydraulic parameters and do not take into account the uncertainties involved in them. Empirical equations also assume steady-state condition which means the flood peak flows for a long time. In the present study, a methodology is presented for the reliability assessment of bridge piers against scouring considering the uncertainties involved in effective parameters and duration of the flood. Additional necessary experimental studies were also carried out to develop an equation for time development of scouring around a protected pier by a collar. Monte Carlo simulation technique was used for estimating the probability of bridge failure. In addition, Fault Tree analysis was employed for combining the interactions of various parameters and calculating the overall probability of failure. For unprotected piers, results showed that at lower flow intensities, flood time has a lower influence on probability of bridge failure. It was also concluded that the collar protection increases the reliability of bridge piers significantly, especially at lower flow intensities. Furthermore, the model was applied to find a relationship between the reliability index and safety factors under various flow conditions.
Notation
| ds | = | scour depth [m] |
| dse | = | equilibrium scour depth [m] |
| Kσ | = | sediment gradation adjustment factor |
| Kν | = | V/Vc − 0.04 relative shear stress adjustment factor |
| V/Vc | = | relative shear stress |
| V | = | the mean velocity [m/s] |
| Vc | = | the critical approach velocity for initiation of sediment motion |
| D | = | pier diameter [m] |
| T | = | t/te |
| t | = | time [s] |
| te | = | equilibrium time of scour depth [s] |
| Tc | = | (dse/0.35KσKν − 0.31)−3.33 |
| p() | = | probability of event |
| pf | = | probability of failure |
| g(x) | = | the limit state function |
| x | = | the vector of basic random variables |
| dp | = | depth of the pier foundation [m] |
| Nf | = | the number of simulation cycles |
| N | = | the total number of this cycles |
| COV | = | Coefficient of variance |
| tl | = | lag time [s] |
| H | = | flow depth [m] |
| d50 | = | median riprap size |
| SF | = | safety factor |
| β | = | reliability index |
Disclosure statement
No potential conflict of interest was reported by the authors.