Circular Piers Research Articles

Experimental Investigation of Bridge Scour under Pressure Flow Conditions

Recent studies have revealed that the frequency and magnitude of floods tend to increase due to climate change. Hence, excessive scouring due to flood events puts river bridges at greater risk of failure. This paper presents the initial findings of an experimental study to improve the understanding of the main characteristics of bridge pier scour under pressurized flow encountered during flooding. The experiments were carried out in four main groups according to two deck alignments with circular and oblong pier shapes. For each group of experiments, thirty-six tests were conducted under partially and fully pressurized flow conditions using four approach flow depths and three discharge values. The validity of the structured design approach for pier scour estimation implemented in the guidelines was investigated. The results showed that the bridge pier scour depths were up to 29.4% and 49.4% greater than the sum of the vertical contraction and local scour depths for 100 L/s for partially and fully pressurized flow conditions, respectively. However, as the discharge increased to 120 L/s, the bridge pier scour depth became 38.3% and 17.8% smaller than the sum of the vertical contraction and local scour depths for partially and fully pressurized flow, respectively. So, the structured design approach was determined to be safe for high discharge values. Furthermore, it was found that tests with a circular pier resulted in higher bridge pier scour depths than the sum of the vertical contraction and local scour depths up to 19.3% even for 120 L/s. Conversely, smaller bridge pier scour depths than the sum of the vertical contraction and local scour depths were observed up to 17.8% for tests with oblong piers. Thus, it can be concluded that the pier shape has a profound effect on scour holes and oblong piers cause smaller scour depths than circular piers in pressurized flow conditions. This study showed that the flow–pier–deck interaction significantly affects the depth and width of the scour hole, especially for small discharges and fully pressurized flow conditions.

Reduction of local scour around a circular bridge pier using the collars and sacrificial piles in non-uniform sediment

In the present study, circular and octagonal collars together with sacrificial piles are tested for their efficiency as protection devices against local scour in the non-uniform sand bed of geometric standard deviation 2.29 and median grain size 1.18 mm. To examine the effect of width and elevation on scour depth, experiments are conducted with circular and octagonal collars of widths 1.5b and 2b placed on the bed and 0.25y above the bed where b is the pier diameter and y is the flow depth. The octagonal and circular collars of width 2b placed in flush with the bed achieved maximum scour reductions of 78.33 % and 75 %, respectively. The efficiency of the collars decreased when their width is reduced and when they are placed above the bed. Among the sacrificial piles in transverse and staggered arrangements, a maximum scour reduction of 55 % is observed when the piles are placed transverse to the flow at a distance of 2b from the pier center. The efficiency of the sacrificial piles decreased when they are moved away from the pier center. A maximum scour reduction of 86.67 % is seen for the combination of the octagonal collar of width 2b on the bed and piles in the transverse arrangement. A new empirical equation is proposed for temporal and equilibrium scour for collar around the pier, including the armor effects. The sensitivity analysis revealed that bc/b is the most sensitive parameter followed by H/y, ks and Tc where where bc is the collar width, H is the location of the collar from the water surface, ks is the shape factor and Tc is dimensionless time.

The influence of collar parameters on local scour mechanism around the circular pier at the bend

Analysis of bridge failures due to scouring has been extensively studied by different researchers in recent years and as a result various methods of controlling local scour cavity have been given. Since most of the research in this field has been done on straight paths and also the complexity of the flow pattern in bends, studying the scouring pattern around the bridge piers located in the bends has become a necessity. Therefore, one of the main objectives of this study is to investigate the scouring around the circular piers which are protected by collars at the river bends. The performance of the collar significantly depends on its level around the pier, which has been studied in this study. The results showed that the optimal performance of this structure, in positions 60°, 90° and 120° at the level of 0.2 pier width under the bed with 3 mm thickness (0.06 of pier width) by approximately 68, 63 and 70% of the maximum pier scour depth was reduced compared with collarless pier, respectively. By analyzing the results of this research, it was observed that the optimum level range of collar around the pier at various bend angles is the initial bed level up to 0.4 times the pier width at the bottom of the incipient level of the bed. Moreover, getting closer to the plate placement level toward the initial bed elevation enhances the collar’s function in decreasing scouring.

Effects of submergence ratio on flow around a circular pier in combined wave–current flows using particle image velocimetry

The present study illustrates an experimental investigation of flow hydrodynamics in the vicinity of a submerged circular pier across various submergence levels under only current and wave–current combined flow conditions. The instantaneous velocity data are collected using particle image velocimetry for three distinct frequencies of waves to determine the influence of wave superimposition on the current-induced turbulence parameters. The distribution of phase averaged turbulence quantities, such as mean velocities, Reynolds shear stress, turbulent kinetic energy, flow patterns, and vorticity analysis by Q-criterion, are presented. The results provide insight into the impacts of wave frequency and submergence ratio on the formation of horseshoe vortices, trailing vortex, and reverse flow zones. From the results it is observed that a decrease in the submergence level of the structure causes the formation of strong horseshoe vortices and reverse flow zones in the absence of waves. Also, an increase in wave frequency intensifies the turbulence kinetic energy at the upstream of the pier and eddy generation behind the pier. The present findings highlight the effects of pier submergence and wave characteristics, such as frequency, wave height, and wave period, on flow patterns and turbulent flow characteristics and aid in the design of marine structures. Furthermore, experimental data serve as a valuable resource for validating theoretical or mathematical models related to combined wave–current environments.

Numerical investigation of impact response of bridge pier subjected to off-center vehicle collision

The increased risk of vehicle collisions on bridge piers causes damage to bridge structures and traffic congestion. In extreme cases, severe collisions caused by trucks lead to bridge collapse and loss of lives. Many studies have been conducted to investigate the dynamic responses of bridge piers subjected to vehicle collisions. Most of them focused on head-on (center-to-center) collisions based on the assumption that they represented the worst scenarios. However, off-center collisions were most often observed in vehicle collision accidents. In this study, bridge piers with different cross-section geometries (i.e., circular, and square) subjected to off-center vehicle collisions are numerically investigated. The results show that off-center vehicle collisions result in more severe spalling damage to the circular piers than head-on collisions. However, the curved surface of the circular piers effectively avoids inducing torsional response under off-center collisions. On the other hand, off-center collisions on square piers induce torsional response, thus more significant deformation, and damage than head-on collisions. Further mechanism analyses are conducted to explain the influence of off-center collisions, focusing on truck type and rectangular cross-section. Furthermore, some meaningful suggestions are put forward to resist off-center vehicle collisions for bridge piers in design process or in service.

Multi-spring model for tubular rocking steel bridge piers subjected to earthquake loading

Recent decades have seen increased interest in using the controlled rocking concept in seismic resisting systems. Unlike conventional systems, where lateral deformation of a member is achieved through the formation of plastic hinges in critical regions, in the rocking systems this is achieved through a gap opening mechanism. Due to gravity load and/or post-tensioning forces, the rocking systems exhibit a self-centering behavior. Conducting a continuum finite element analysis to investigate the seismic response of such a system is quite expensive in terms of computational resources. On the other hand, a simplified macro model using two springs to simulate the gap opening/closing mechanism cannot accurately predict the dynamic response of the system. This study utilizes a multiple-spring model to simulate the nonlinear seismic response of circular tubular steel piers. An efficient optimization procedure based on a genetic algorithm is developed to calibrate the parameters of the springs. The results of continuum finite element analyses are compared with those obtained from the multi-spring model to verify the accuracy of the model. The proposed method is shown to be advantageous for accurately simulating the seismic response of a bridge model subjected to multi-directional ground motions, particularly the hysteretic force-displacement relationship, and dynamic response time history.

Experimental, Analytical, and Numerical Evaluation of Bridge Pier Scouring

Abstract Due to the rising number of incidents of bridge failure, scouring around bridges has received a lot of attention. Accurate scour depth prediction is a challenge for researchers and experts, despite massive global research efforts. Estimation the scour depth is crucial for both a safety and economy. Numerous factors affect the scour depth. In this work, the scour depth of three distinct pier geometries – circular, oblong, and rectangular – is thoroughly investigated, and the effect of water depth and discharge on the scour depth of a given geometry is evaluated. Three pier shapes were the subject of a total of 27 trials, nine of which combined three discharges with varying flume water depth. Experimental observation of scour depth shows good agreement with analytical and numerical scour depth values. A comparative examination of analytical, experimental, and numerical findings indicates that numerical models can effectively estimate scour depth, offering a cost-effective and time-saving methodology. Results showed that circular and oblong pier geometry shows lesser scour depth than rectangular pier geometry for a specific combination of flow depth and discharge. Scour depth decreased with increasing flume water depth for the same discharge. For the constant flume water depth, higher discharge results in greater scour depth.

Extraction of flow features around a bridge pier with an evolving scour hole using Lagrangian coherent structures

Local scouring around a bridge pier poses a severe threat to the safety of the bridge. A better understanding of flow features around the bridge piers is necessary for accurate prediction of the scour depth. The ridges of the finite-time Lyapunov exponent, called Lagrangian coherent structures (LCSs), were used to extract the flow features around a circular bridge pier with an evolving scour hole. The velocity field required for the LCSs computation was obtained using a three-dimensional Reynolds-averaged Navier–Stokes simulation. The simulation results were validated with the published experimental and numerical findings. The computed LCS stretching field extracted all the flow features around the bridge pier that were previously reported in the literature. In addition, the LCSs extracted the region of flow acceleration on both sides of the pier. The forward LCSs upstream of the pier extracted a particle trapping region, providing insight into the volume of fluid converting into the downflow. They extracted anchor-like structures inside the scour hole upstream of the pier. The analysis of velocity variations along the width and depth of the flow domain revealed that a change in the velocity profile is triggering the formation of LCS. The behavior of non-inertial particles released and integrated into the flow field revealed the significance of LCSs in particle transport. Using the LCS method, the study extracted the flow features that were difficult to extract with traditional flow visualization methods.

Effects of pier inclination angle and direction on local scour at rectangular and circular piers

Effects of pier inclination angle and direction on local scour at rectangular and circular piers

Cyclic shear testing of artificially corroded reinforced concrete short circular piers

Chloride-induced deterioration of reinforced concrete (RC) structures is an increasingly vital topic among asset management and structural maintenance fields, as many RC bridges and other structures are reaching the end of their initial design lives. Deterioration of the transverse reinforcement in RC piers leads to the direct loss of shear and confinement-related mechanical properties as degradation advances with time. This research investigates the seismic response of fourteen short RC circular piers subjected to artificial chloride-induced corrosion. Each pier is designed to trigger a shear-dominated failure and artificially corroded at two current densities. A maximum average mass loss of 10.5% and 43.0% was measured in the longitudinal and spiral reinforcement, respectively. The influence of confinement effectiveness, spiral diameter, and aspect ratio on the rate of shear capacity degradation are included as test parameters in this study. Results indicate that shear deformation begins to govern performance at moderate to severe deterioration, which precedes the onset of brittle shear-dominated failure modes. Ultimate deflection is more adversely affected by increasing corrosion than all other measured properties, with a maximum observed reduction of 70.9% compared to a maximum 37.5% reduction observed in peak shear capacity. Several existing theoretical models are introduced and evaluated on their ability to predict the shear capacity of the experimental tests. Based on the results, those models directly evaluating the circular section without needing an equivalent section transformation offer the most accurate and reliable predictions.

Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio

This paper presents new data on scour around a vertical pier in cohesive soils. It specifically focuses on the temporal evolution of local scour hole around the pier with increasing the clay/silt ratio content. Series of flume tests were performed using soil mixtures made with 85% fine sand and 15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite clay, and various combinations of both with different proportions. The water velocity during the tests was kept constant and slightly above the erosion critical velocity of the fine sand used in the mixtures. A 3D laser scanner was employed to continuously record the geometry of the scour hole. Results show that increasing the Kaolinite clay in the fine fraction reduces significantly the scour. The mixture with a range around 7.5–10% of kaolinite clay fines content provides the threshold composition for cohesive soil behaviour effect in scouring process, recognized through scour pattern change. As the clay content increases, notable reductions are observed in the dimensions of the scour hole. Furthermore, the temporal evolution of maximum scour depth measured in flume was in agreement with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion Function Apparatus) method.

The universal two-fifths law of pier scour

Understanding scour at bridge piers is crucial for safeguarding public safety, ensuring infrastructure resilience, and planning effective maintenance. Despite over six decades of extensive studies aiming to develop predictive formulas for the equilibrium scour depth at bridge piers, more than 20 000 highway bridges in the United States have been spotted “scour critical.” The traditional reliance on existing empirical formulas has posed a severe challenge for researchers, hindering to achieve a unified relation for the equilibrium scour depth from a fundamental scientific tenet. This perspective article presents a breakthrough—a universal law governing the equilibrium scour depth at a circular pier embedded in a sediment bed, specifically in clear-water scour condition. Derived from a phenomenological model, the universal law reveals that the equilibrium scour depth to pier diameter ratio obeys a consistent two-fifths scaling law with the introduction of a newly coined pier-scour number. This number accounts for all the key parameters involved in a local scour phenomenon, including the approach mean flow velocity, threshold shear velocity for sediment grain motion, approach flow depth, pier diameter, and sediment grain size. Importantly, the scaling law contains an additional term involving the drag coefficient raised to the power of 2/5, addressing the impact of the pier shape on the equilibrium scour depth. The derived universal law undergoes the validation through an extensive dataset of experimental measurements on circular pier scour.

Efficacy of the Combined Use of Bed Sill and Sacrificial Piles to Control Local Scour around Circular Bridge Piers

In this study, the results are presented and discussed from laboratory test campaigns specifically designed to investigate the behavior of sacrificial piles as a countermeasure against local scouring at a circular bridge pier and clear-water conditions with flow intensity slightly below the threshold of sediment motion. Sacrificial piles are assessed on the upstream side of the pier in two transverse and triangular arrangements. Piles can reduce scouring by deflecting the flow and creating a low-velocity wake region behind them. The efficiency of the piles against local scouring depends on the diameter of the piles, the number of piles, and the angle of the wedge. The investigation was aimed at evaluating the effectiveness of the sacrificial piles as a function of different dimensionless groups. It was found that the triangular arrangement of sacrificial piles has better results than the transverse arrangement. The results showed that the triangular sacrificial piles reduced the maximum local scour depth at the pier to 37.2% in the best configuration. Combined countermeasures were tested, which were composed of sacrificial piles and a bed sill downstream of the pier; in the best configuration, the scour depth reduction in front of the pier reached 51.1%. The increased efficiency of the combination of bed sill and sacrificial piles (BSSP) is an advantage that can reduce the risk of pier failure when the duration of the flood is short. This last result shows that a combination of BSSP may be a very effective countermeasure against local scouring at bridge piers. Finally, the coherent turbulent flow structure around the best combination of BSSP was investigated, and its effect on the bed scouring pattern was studied. A 3D analysis of the bursting process was used. Turbulence characteristics, as well as the occurrence and transition probabilities of bursting events, were calculated. The obtained results confirmed the quite effective effect of the combination of these two countermeasures in reducing the scour depth.

Seismic collapse assessment of single-column bridge piers using the applied element method

Several single-column-bent bridges have collapsed in the past under earthquakes. Different factors associated with poor structural design and/or construction including inadequate and/or prematurely terminated longitudinal reinforcement (LR), insufficient concrete confinement, or insufficient transverse reinforcement (TR) were identified and reported. Different alternative designs or retrofitting solutions were also proposed and examined. One of the well-known samples of this bridge type was the elevated Hanshin Expressway Bridge (HEB), which collapsed in the 1995 Kobe earthquake. In that incident, 18 circular single-column piers (SCPs), monolithically connected to the deck, failed and collapsed. Here, the seismic progressive collapse behaviour of SCPs of the HEB was investigated using non-linear dynamic analyses of three-dimensional numerical models created by way of the applied element method (AEM). The results obtained agreed well with field observations after the earthquake. Two alternative design solutions for improving the seismic response of the original model were also considered and the efficiency of the solutions was assessed. Results showed that the AEM is capable of modelling the progressive collapse procedure for concrete bridges with sufficient accuracy. The results proved greater effects of the anchorage length of the LR as well as the space between the TR in the collapse behaviour of the pier.

Evolution of coherent structures in the flow around a circular pier with a developing scour hole: A numerical study

Large-eddy simulations (LES) were used to simulate the flow features around a circular pier with evolving scour hole. The bathymetry corresponding to four stages of scour hole evolution, published in the previous literature, was used in the flow domain to recreate the flow at a particular stage of scour hole development. The growth of coherent structures and their interactions in a developing scour hole were investigated. The formation of secondary vortices inside the scour hole and their interactions with the primary horseshoe vortex (HV) made the HV system highly dynamic. High-level pressure fluctuations were observed inside the core of HV. The simulation captured the bimodal aperiodic oscillations in the HV at all stages of scour hole development. The mechanisms responsible for the formation of scour hole behind the pier were discussed. High levels of mean and instantaneous bed shear stress values were observed beneath the horseshoe vortex. These values were found to have decreased with an increase in the scour hole depth. The LES also captured the detachment of vortices from the legs of HV and their convection in the pier downstream.

An Experimental Study on the Effect of Distance and Sheltering Area of a Group of Linearly Arranged Sacrificial Piles on Reducing Local Scour around a Circular Bridge Pier under Clear-Water Conditions

One of the major problems associated with bridge piers is ensuring their safety against local scouring caused by the erosive action of flow. Numerous countermeasures have been developed and tested to solve this problem, among which sacrificial piles are highly recognized due to their high performance, economy, durability, and ease of construction. Several factors affect the performance of sacrificial piles, such as their number, size, degree of submergence, and geometric arrangement parameters. In this study, the performance of a group of linearly arranged cylindrical sacrificial piles in reducing local scour around a circular bridge pier was investigated by varying the number of piles (or sheltering area) and distance between piles and the pier under clear-water conditions. Three values of distance between piles and the pier and three values of sheltering area (or number of piles) were tested. The efficiencies of sacrificial piles in different configurations were presented in terms of the percentage reduction in maximum scour depth at an unprotected pier under the same hydraulic conditions. The results of this experiment show that when linearly arranged sacrificial piles are placed close to the pier (at distance D; D is the pier diameter), an increase in the number of piles (or sheltered area) results in an increased scour depth, and when placed far from the pier (2D and 3D), an increase in the number of piles results in a decrease in scour depth around the pier. In addition, for 40% and 60% sheltering conditions, scour depth increased with an increase in the spacing between piles and the pier, while for 80% sheltering conditions, optimum protection was observed at a distance of 2D. Overall, two piles placed at distance D provided optimum protection with a scour depth reduction of 41.6%, while minimum protection was recorded when the same were placed at a spacing of 3D from the pier (25.5%).

Seismic fragility of circular piers in simply supported RC bridges: A proposal for capacity assessment

Bridges are crucial structures of a roadway system, always exposed to both natural and anthropic hazards. Several approaches have been investigated in the past two decades to evaluate the seismic vulnerability of bridges; the development of fragility curves represents a sound tool to evaluate their performances at a large scale. This study aims at the estimation of seismic fragility curves for a structural element of a very common bridge typology in Italy, that is the single circular cross-section pier of a simply supported Reinforced Concrete (RC) bridge. Two analytical methodologies for deriving fragility curves are applied to a case study model. The first one is the Capacity Spectrum Method (CSM). This method accounts for the non-linearities and the seismic energy dissipation, in fact it is based on a non-linear static analysis and the definition of Damage States (DSs) on the capacity curve of the piers. By contrast, the second one is the Response Spectrum Analysis (RSA), that is a methodology based on a linear method. By using both methods, a parametric study is carried out, varying the bridge’s geometrical and mechanical properties within standard ranges, to evaluate their effect on the seismic vulnerability of the pier. This study refers to four DSs and proposes a multilinear regression model to directly evaluate the pier’s seismic performances based on the geometrical and mechanical properties of the bridge to which it belongs.

Study on the seismic characteristics of piers considering site conditions and hydrodynamic effect

Sea-crossing bridges face complex site environments compared to onshore bridges, with the marine environment significantly influencing seismic responses. Despite this, current seismic design for these bridges relies on onshore earthquake records. Therefore, investigating the impact of seawater layers and site conditions on sea-crossing bridge seismic performance is crucial. This paper investigates the influence of characteristics of offshore ground motion, site conditions, and hydrodynamic effect on the seismic performance of piers. Initially, based on the validated finite element model, 5 offshore and onshore strong ground motion records from K-NET were selected for assessing the seismic performance of piers. Subsequently, the effects of the water depth and site conditions on the seismic responses of piers were investigated. Finally, the effects of the section size, section shape, and boundary conditions on the piers were investigated. The result shows that the seismic response of piers under offshore ground motion exceeds that under onshore ground motion. In addition, the seismic response of the pier increases with greater water depth, while they exhibit a slight decrease with increasing soil depth. Notably, the larger the section size, result in higher the hydrodynamic pressure, and square piers experience greater hydrodynamic pressure compared to circular piers.

Reducing Scour Hole Dimensions around Bridge Circular Piers Using Hexagonal Collars

Reducing Scour Hole Dimensions around Bridge Circular Piers Using Hexagonal Collars

Equation for time-dependent local scour at pier-like structures with eccentric in-line arrangements

Excess scour developing around tandem and eccentric piers of side-by-side bridges may aggravate bridge failure. Thinking differently, this combination of pier-like structures may increase scour and shift sediments towards the bank, which may help in self-dredging. Therefore, accurate estimation of temporal scour depth (dst) around such piers has a very high priority nowadays. However, little work has been done in this regard. Most of the previous equations predict dst only for an isolated pier. Here, two to three piers are placed eccentrically in line in addition to isolated piers to derive equations empirically for accurate prediction of dst considering circular, triangular and square pier shapes. The present experimental results for an isolated circular pier are validated using equations from the literature, cross-validated with other published experimental data. Predictive equations are proposed for two to three piers with eccentrically in-line arrangements, taking their intermediate spacings as key variables. These equations are established based on dimensional analysis and non-linear regression. Overall analysis reveals that the estimated temporal scour depths based on the proposed integrated equation are closely within the ±80% accuracy band. The proposed equations can be used to predict temporal scour accurately for selected combinations of piers within the given experimental ranges.