Circular Piers Research Articles

Experimental study on hydrodynamic interaction between dam-break waves and circular pier

This paper focuses on the hydrodynamic interaction between dam-break waves and circular pier. Firstly, a series of dam-break waves under dry-bed and wet-bed conditions were conducted, the evolution of wave front profiles are obtained experimentally. Then, experimental studies on hydrodynamic interaction between these dam-break waves and a circular pier were carried out systematically. After that, the pressures and their vertical distributions on the front, back and lateral side of the circular pier are obtained and analyzed in detail. In which, sudden rise of pressures on the front side, obviously oscillatory pressures on the back side, and negative pressures on the lateral side are observed. Furthermore, the forces and moments on the circular pier are presented, and their characteristics are explored. Among which, the maximum force and moment occur in the impulse stage when there are fluctuations upstream of the wave front, otherwise they occur in the quasi-stationary stage. In addition, the corresponding dimensionless coefficients are obtained and their evolutions are revealed elaborately. Finally, the calculation formulas for maximum force and moment on circular pier, considering the variation of wave front profile, are proposed, and related coefficients are suggested. This study could provide reference for the improvement of calculation method.

Assessing local scour at rectangular bridge piers

The scour depth at bridge piers depends on a large number of variables. This study aims at revisiting the influence of rectangular piers' shape on local scouring. The scour around circular and rectangular bridge piers with length to width (L/D) of 1, 3, 4.5, 6, 7.5, and 9 was experimentally and numerically investigated at shallow water conditions (water depth to pier width (h/D) ratio varied from 1.4 to 2.32). Fifty-two experimental runs were carried out with a mobile bed made of non-ripples uniform sand with a median sediment grain size (d50) of 0.6 mm. The results show that L/D would influence the dimensionless scour depth (ys/D). The rectangular pier with L/D of 4.5 had the maximum ys/D and at L/D of 7.5 and 9 the ys/D was highly reduced. The Flow 3D model was used to verify the effect of downflow, shear stress, streamwise velocity and turbulence (energy and intensity) on the ys/D. The numerical results emphasized that the maximum scour would occur in terms of downflow and shear stress at L/D of 4.5. A new empirical equation (R2 = 0.904 and RMSE = 0.238) for predicting the maximum ys/D at rectangular piers was obtained. Compared with the similar formulas in the literature for predicting ys/D, accurate predictions at the rectangular pier with L/D of 1–9 were registered in this study.

Clear Water Scour at Circular Piers: A New Formula Fitting Laboratory Data with Less Than 25% Deviation

Clear Water Scour at Circular Piers: A New Formula Fitting Laboratory Data with Less Than 25% Deviation

Structural assessment of the pedestrian bridge accessing Civita di Bagnoregio, Italy

The paper presents the results of the vibration tests carried out on the pedestrian bridge accessing Civita di Bagnoregio, Italy. The structure was in bad health condition. The external beams were damaged due to deterioration exacerbated by the combined actions of rain and wind. The circular piers were also damaged with several cracks where the concrete cover was spliced and the reinforcement bars were exposed. The analysis presented in the paper focuses on the highest five piers, which seemed to show an irregular behavior during a preliminary experimental campaign. The results of the experimental campaign presented in this paper showed that the structural behavior of the bridge was qualitatively similar to the expected one. The reduced stiffness, due to the observed widespread damage state, amplified the vibrations uniformly along the structure. The Italian Guidelines for the risk and safety assessment of bridges and viaducts, issued in 2020, have been applied and tested in this study and the results are presented in the paper.

Seismic Performance of the PVA Fiber Reinforced Concrete Prefabricated Hollow Circular Piers with Socket and Slot Connection

The seismic performance of prefabricated hollow circular piers with socket and slot connection was evaluated through model tests and numerical simulations. The quasi-static tests with cyclic lateral load and constant axial load were conducted on three large pier specimens. The piers of these three specimens were cast by polyvinyl alcohol (PVA) fiber concrete, and the piers were connected to the cover beams by slotted connections and to the bearing platform by socketed connections. The seismic performance of the specimens was investigated in terms of failure modes, hysteresis curves, skeleton curves, stiffness degradation, energy dissipation, and residual deformation. The test results showed that, within a certain range, increasing the axial compression ratio is able to enhance the shear bearing capacity of prefabricated hollow piers and increase the cumulative energy dissipation, but it is not beneficial to the ductility. In addition, the increase in the shear span ratio significantly reduces the shear bearing capacity of piers and increases the residual deformation of the specimen, but the ductility is significantly improved. In addition, the numerical model of the prefabricated hollow pier was established by ABAQUS. The result of the numerical simulation was consistent and similar to the experimental result in terms of damage modes and load–displacement curves. Finally, the parametric analysis of the prefabricated hollow piers was carried out on the basis of the numerical model.

Seismic performance of concrete-encased column connections for concrete filled thin-walled steel tube piers

An improved type of concrete-encased column connections (CECCs) for circular concrete filled steel tube (CFST) piers is proposed in this paper, which does not require the use of base plates and anchor bolts. The seismic performance of the proposed CECC for circular CFST piers was experimentally investigated. Four CECC specimens were tested under a constant axial load and cyclic lateral loads to investigate the effects of the reinforcement ratio in the steel tube and the thickness of outer reinforced concrete component. The test results show that all test specimens failed flexurally primarily and the lateral load versus displacement hysteresis curve was generally full, indicating a good energy dissipation capacity (with a ductility coefficient >3.5). The strength degradation, stiffness degradation, and energy dissipation coefficient were calculated to study the seismic performance of proposed CECCs. The axial and lateral load versus the strain development of steel tube and anchor bars curves were further investigated to analyze the load transfer mechanism. The calculation methods for the sectional strengths of both CFST section and bottom section are proposed, which are found to be in good agreement with the test results.

Seismic performance of prefabricated steel tube-confined concrete circular pier

In this study, a prefabricated steel tube-confined concrete (PSTC) circular pier with a bottom grouted sleeve connection was developed to correct some limitations in typical precast concrete (PC) piers, such as over-dense grouting sleeves and insufficient energy dissipation capacity, thus promoting their use in high seismic hazard zones. To validate the performance of the proposed design, four scale models of an actual circular bridge pier, including two PSTC, one PC, and one cast-in-place (CIP) specimens, were fabricated and their seismic response under cyclic loading was investigated via quasi-static experimental and numerical tests. The seismic performance indices, hysteretic energy dissipation characteristics, skeleton curve, flexural strength, stiffness degradation, residual displacement, and ductility of the different specimens were compared. The experimental and numerical results indicated that, compared with the CIP and PC circular piers, the flexural strength and energy dissipation capacity of the PSTC piers were significantly improved owing to the confinement provided by the steel tube to the concrete core, their ductility and initial stiffness effectively increased, and the pier body stiffness (pier body curvature) was more uniformly distributed. Moreover, parametric finite element analyses of the PSTC pier under low-cycle reciprocating load were used to determine the influence of the steel tube thickness and strength on the seismic performance of the pier. It was found that an increase in the thickness and strength of the steel tube also increases the flexural strength, yield load, yield displacement and initial tangent stiffness of the PSTC circular pier. Consequently, this study demonstrates that PSTC piers are reliable and suitable for prefabricated bridge construction in high seismic hazard areas.

Hydrodynamic shape optimization of an auxiliary structure proposed for circular bridge pier based on a developed adaptive surrogate model

Reducing the hydrodynamic force for a cylindrical structure is extremely important in oceanic engineering applications. In this study, an auxiliary structure, shaped by two controlling parameters, is proposed to be placed in front of a typical circular bridge pier, desiring to mitigate the hydrodynamic loads on the pier. Two-dimensional numerical simulations are carried out through the open source CFD (computational fluid dynamics) program OpenFOAM to optimize the shape of the auxiliary structure by using a developed adaptive surrogate model, where the optimal auxiliary structure is identified by searching optimal hydrodynamic indexes, i.e., the drag and lift coefficients. The salient observations show that: (1) High efficiency is embodied in the whole optimization procedure by way of adopting the developed adaptive model; (2) The optimal auxiliary structure is featured with convex surfaces and can reduce the vortex scale and accelerate the vortex dissipation; (3) Investigation of the hydrodynamic performance proves that the optimal auxiliary structure can effectively decrease the drag and lift coefficients; and (4) The excellent performance emanating from the optimal auxiliary structure retains for a large range of the Reynolds numbers. It is hoped that the presented concept of the optimal auxiliary structure can provide guidance on mitigating the hydrodynamic loads for other oceanic engineered structures.

Flow fields around tandem and staggered piers on a mobile bed

An experimental investigation on flow fields within the scour holes upstream and downstream of circular piers positioned in tandem and staggered arrangements is reported and compared with isolated piers on mobile beds with uniform sediment. The instantaneous bed elevations and instantaneous three dimensional (3D) velocities were measured using a 5 MHz Ultrasonic Ranging system and 16 MHz micro down looking acoustic Doppler velocimeter, respectively. The velocity and flow depth were measured at different locations under near equilibrium bed scour conditions. The measured 3D velocities were processed for the computation of flow parameters, such as velocity fields, streamline patterns, vorticity fields, and circulation. Furthermore, turbulence intensities, turbulent kinetic energy, Reynolds shear stresses, and bed shear stresses around the piers for all three pier configurations were computed from the detrended velocity signals to identify significant differences in the flow parameters and turbulence in the tandem and staggered pier arrangements as compared to those for an isolated pier. A recirculation zone was found near the bed in front of the rear pier in the tandem case from the streamline patterns. The vortices in the bi-vortex system were observed to be opposite to each other in the gap between the three piers in the staggered case. A strong secondary vortex also was observed apart from the primary vortex at the foot of the pier (θ = 0°) in all the three configurations. The strength of the horseshoe vortex (combination of primary and secondary vortices) was found to be higher at the front piers of the staggered arrangement as compared to those of the tandem piers, followed by the isolated pier. The bed shear stresses were found to be higher for the staggered piers than for the tandem piers in the direction of flow (θ = 0°). However, a 50% reduction in the bed shear stresses was observed behind the tandem piers at θ = 180°. The study reported in this paper provides the foundation for further investigation of countermeasures against local scour around tandem and staggered bridge piers on a mobile bed with non-uniform sediment.

A comparative study on equilibrium scour volume around circular cylinders in clay–sand mixed cohesive beds, at near threshold velocity of sand – an experimental approach

Abstract Local scour around a bridge pier is a complex phenomenon resulting from the interaction of the three-dimensional turbulent flow field around hydraulic structures. An accurate estimation of scour depth below the stream-bed is important during design since it determines the foundation levels and the expansion of the bridge foundation structures. The present study reveals the results of flume experiments on equilibrium scour depth and scour volumes around circular bridge pier models in clay–sand sediment mixtures. The scouring process in a cohesive sediment mixture is a complex interaction between clay–sand network structure and bed shear stresses. The bed shear stress reduces inside the scour hole as scour depth increases, and this is related to the different modes of scouring in clay–sand mixtures. An exponential equation for the non-dimensional scour volume is proposed considering all the experimental runs to get a specific understanding of the surrounding volume of scour hole from maximum equilibrium scour depth in a clay–sand mixed cohesive bed, when the approach flow velocity is near to the critical velocity for mixed sand. The proposed equations are validated using the pre-existing data from the literature dealing with experimental investigations on bridge scour using clay–sand mixed cohesive sediment and show good agreement with observed data.

Study on Further Improvement of Anti-tsunami Ability of a New Type Bridge Pier

Compared with circular, square and diamond piers, the N60 pier proposed in our previous study has been numerically proven to be effective in reducing tsunami force. The relatively stronger vortices behind the N60 pier are responsible for the not-small-enough tsunami force on the N60 pier. The asymmetry in shape makes the N60 pier fail to reduce flood force because flood propagates in the opposite direction of tsunami bore. A series of new type piers named [Formula: see text] are proposed to further improve the anti-tsunami ability of the N60 by computational fluid dynamics (CFD) method among which the N60-60 pier is proven to be most effective in reducing tsunami force, and its tsunami force mitigation mechanism is analyzed numerically. Further, the physical experiments were conducted to validate the N60 pier and the new type pier N60-60. Results show that compared with circular, square and diamond piers, the N60 pier is indeed capable of reducing tsunami force, and compared with the N60 pier, the new type N60-60 pier is capable of further reducing tsunami force. The order of magnitudes of tsunami forces on piers is: N60-60 [Formula: see text] N60 [Formula: see text] circular [Formula: see text] diamond [Formula: see text] square.

Reduction of scour around circular piers using collars

AbstractRiver dynamics and sediment transport play an important role in river bed morphology. Building a bridge pier along the river alters the cross‐section of the river and causes the change in flow processes. These changes are mainly responsible for pier scour. In this paper, the usage of collars to reduce scour around circular piers has been investigated. The collars with different diameters and depth positions have been studied using previous data and additional data collected in the present study to assess their effectiveness in reducing scour. Using a wide range of measured data, an empirical equation to compute the maximum scour depth around the circular piers in the presence of collars has been proposed. The proposed equation has been validated and proven to be applicable to a wide range of pier layouts. It has been found that the maximum efficiency can be achieved by fixing the collar at bed level and adopting a collar diameter 1.5–2.5 times of pier diameter.

Parametric study for hydraulic design of air-bubble injections to control scour around circular bridge piers

ABSTRACT Several countermeasure techniques have been presented to control bridge scour-induced failure. Air-bubble injection, a new method compatible with the environment, was introduced to combat destructive vortices that cause bridge piers to be scoured. Extensive experiments were conducted to determine the appropriate air-bubble injections for the least scours at a bridge pier. Two different clear-water flow intensities with air-bubble injections were assessed in different radial positions around and also on the upstream half of the bridge pier. The vertical position of air injections and air discharge were determined previously to be optimal. The long-term experiments revealed that the well-designed air-bubble injections reduced the local scour around the bridge pier. It was found that the complete air-bubble injection around the bridge pier is the best configuration and able to reduce the scour depth about 44% over the case with no air injection (non-protected pier). Moreover, the appropriate arrangement of bubble injections to lessen the scour depth is the nearest radial position of the injection to the bridge pier and with increasing the radial distance of injections to the pier, the bubble plumes move downstream by the main flow. The results indicate that bubble plumes would be effective in both flow intensity, u*/u*c = 0.7 and 0.9, as examined in the present study.

Performance of coastal circular bridge pier under joint action of solitary wave and sea current

As an important transportation infrastructure, coastal bridges are widely established in coastal areas, the piers of which are always subjected to waves and currents and are prone to damage, especially under extreme marine conditions. Since ocean waves and currents coexist and twist with each other, it is necessary to take both them and their interaction into account to better understand the interaction between the pier and the marine environment. To reveal the interaction mechanism among waves, currents and piers under extreme marine conditions caused by hurricanes or tsunamis, the joint action of solitary wave and sea current on the piers are studied based on a numerical model with the immersed boundary (IB) method in this paper. The calculation capability of this model is verified and a series of simulation cases are systematically carried out depending on this model. The prominent factors of the environmental conditions including current velocity and wave height and the piers with different diameters and arrangements are considered. The flow field, the wave run-up, the velocity, the pressure and the hydrodynamic load on the piers are investigated, the results of which indicate that the total force on the pier under the joint effect of solitary wave and sea current is several times the sum of the forces under solitary wave and current. The higher the velocity of the sea current is, the more significant the wave and current coupling effect is. When the tandem pier is with the small gap, the forces on the streamwise and transverse tandem piers are smaller and larger than those on the single pier, respectively, and with the increase of the gap, the force on the tandem pier tends to be that on the single pier. The small gap in the streamwise tandem piers and the large gap in the transverse tandem piers are beneficial to the stability of piers.

Scour model for circular compound bridge pier

Abstract Scour is a complex phenomenon, whose complexity increases with the change in the geometry of the obstruction. Most investigations have been carried out on the scour process at a uniform pier. However, in reality, many bridge piers behave as non-uniform depending on the exposure of their foundation into the flow field. All the experimental investigations were carried out in the present study to understand the effect of pier geometry, the position of footing top with respect to bed level, and sediment mixtures (uniform and non-uniform) on local scour under clear water conditions. A total of 106 experiments were conducted in the present study with a different combination of pier models, sediment mixture, and footing top with respect to bed. A maximum scour depth model was developed using 182 data points consisting of experimental data (106) and extracted from the literature (76). To develop a model, a state-of-the-art artificial intelligence (AI) based modeling technique known as gene expression programming (GEP) was employed in this study. The GEP model was developed by using 130 data points and independent 52 data points for the model validation. The performance of the proposed scour model for the compound bridge pier was found to be satisfactory.

Investigation of Local Scour Hole Dimensions around Circular Bridge Piers under Steady State Conditions

The local scour around bridge piers is one of the main causes of bridge failures. In this study, scour hole dimensions around circular bridge piers were investigated under clear water scour conditions for various steady flow rates. The experiments were performed with four different bridge pier diameters and seven different flow rates by using uniform sediment with a median diameter of 1.63 mm and geometric standard deviation of 1.3. After each experiments the bathymetry of scour hole was determined. New empirical equations to estimate scour hole length, scour hole width and scour hole volume (V) are proposed by using experimental findings and experimental data available in the literature. The experimental results were also compared with those calculated using several empirical equations given by previous studies. Since there is a lack of data about scour hole dimensions, the experimental findings presented in this study are useful for the researchers investigating the local scour process, and have contributed to the few experimental data in the literature.

Machine learning driven seismic performance limit state identification for performance-based seismic design of bridge piers

Performance-based earthquake engineering requires the identification of different damage states in structural components. Bridge piers are one of the most critical components in the bridge system that dictate the overall performance of bridges under seismic loading. The ability to predict different damage states of a bridge pier following an earthquake can be useful in restoring service or prescribing appropriate remediation. Machine learning techniques are becoming attractive in earthquake engineering for predicting failure modes of buildings and bridges. This study implements several machine learning techniques to capture different performance limit states such as spalling, core crushing, and bar buckling of reinforced concrete bridge piers under seismic loading. Using experimental data from the large scale testing of bridge piers, this study compares different machine learning techniques for predicting drift capacity performance limit states of circular and rectangular bridge piers. Model tuning using grid search algorithm and 5-fold crossvalidation is performed to optimize model predictions over a wide tuning parameter search space. The efficiency of different methods is compared using a reserved 20% testing dataset to determine the optimal machine learning regression method for each limit state. This study compares the respective bar buckling and concrete spalling drift limit state models against existing physics-based empirical models, where the machine learning models are found to have significantly improved accuracy and precision.

Reliability assessment and sensitivity analysis of vehicle impacted reinforced concrete circular bridge piers

Impact collisions of vehicles with reinforced concrete (RC) bridge piers are an increasingly common event. The collision creates a dynamic effect on the concrete pier not generally considered in design practices, making the piers vulnerable to extensive damage. Not all bridge piers collapse upon impact, and some are kept in service without adequate investigations as to their continued structural viability. Unfortunately, little attention has been provided to investigate the justification of damaged piers kept in service post-impact. A limit state model to identify the probability of failure in the damaged pier is developed and alternative approaches for solving the limit state models are analyzed. In addition, reliability indices and probabilities of failure to quantify damage incurred from vehicular impact are determined. Deterministic analyses do not capture the uncertainties involved in assessing the non-linear dynamic behavior of RC piers under impact loading. To limit the uncertainty associated with determining RC pier’s performance under vehicular impact, sensitivity analyses of the variables controlling impact performance are scrutinized, and a sensitivity ranking to outline the relative importance of the variables to the pier’s performance is developed. The proposed process for determining the reliability of damaged RC piers provides an additional design tool for structural designers, forensic structural engineers, and practitioners for use in analyzing the impact performance of RC bridge piers in a useful, convincing, and economical way.

Experimental Investigation of Scouring Around Circular Piers with Different Opening Ratios

Experimental Investigation of Scouring Around Circular Piers with Different Opening Ratios

Damage assessment of circular bridge pier incorporating high-strength steel reinforcement under near-fault ground motions

Bridge piers are typically the most vulnerable to damage during an earthquake, and the entire seismic performances of the bridge is determined to some extent by the hysteretic energy of its piers. It was discovered that partially embedding high-strength reinforcements in bridge piers is a reliable and efficient method to increase the ductility performance. The term “high-strength reinforcement” refers to reinforcement with a yield strength of (500 MPa) or above. The use of certain high-performance materials can help to enhance bridge pier seismic performance. Because of their strong and impulsive impact on structures, near-fault ground vibrations deserve special attention. These features are distinct from far-field ground vibrations, which are the basis of practically all seismic design requirements. The goal of this study is to evaluate the effects of near-fault ground vibrations on reinforced concrete bridge piers, as well as to develop a framework for evaluating bridge columns near active faults. The impact of Forward-directivity pulses effect on the behavior of a continuous steel box girder bridge pier is investigated in this work using fragility analysis. Damage measures such as pier displacement ductility and rotational ductility of pier are used to generate fragility curves and Probabilistic seismic demand model for bridge pier using high strength reinforcement bars under the ensemble of near-field forward- directivity earthquakes. The damage model presented may be assumed to be a well-versed model which may address the variability in earthquake ground motion while performing the bridges pier seismic vulnerability evaluation. Two sets of near-field forward-directivity records with peak ground velocity to peak ground acceleration ratio (high PGV: PGA > 150 cm/s/g and low PGV: PGA < 150 cm/s/g) are employed to carry out incremental dynamic analysis. The findings show that even at low PGA levels, near-field directivity pulses result in a substantial chance of pier damage exceedance.