Circular Bridge Piers Research Articles

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.

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.

Improvement of energy damage index bounds for circular reinforced concrete bridge piers under dynamic analysis

AbstractAn improvement of energy damage index bounds for circular reinforced concrete (RC) bridge piers under dynamic time history analysis is presented in this study. The energy‐based damage model has been defined as a ratio of hysteresis dissipation energy to input energy for performance evaluation of circular RC bridge pier systems. Based on the energy balance equation, the mentioned damage model can consider all energy aspects, including kinematic energy, strain energy, hysteresis energy, damping energy, and input energy. Additionally, the effect of ground motion duration, amplitude, and frequency content is appropriately considered in this damage model. For this purpose, the damage limit state bounds for two empirical RC bridge piers are statistically evaluated under the 22 far‐field ground motion sets of FEMA‐P695 for simulation of strong‐earthquake motion and consideration of record‐to‐record variability. First of all, appropriate validation between empirical and numerical fiber element models is implemented to estimate accurate results. Then, damage data at each performance level through strain limit states are collected by developing energy incremental dynamic analysis curves. Statistical results on collected damage data are presented in all performance levels to determine damage index bounds by the convolution of fragility curve distribution. Hence, five damage index bounds at five performance‐level are suggested, including very slight, slight, moderate, extensive, and complete damage. Finally, the effect of the other damping ratios on the modified energy damage model is carried out by using the beta coefficient in the formula. In the end, the modified energy damage model is compared with other damage indices to investigate the efficiency of the proposed damage model.

Field Study on Wood Accumulation at a Bridge Pier

Transported large wood (LW) in rivers may block at river infrastructures such as bridge piers and pose an additional flood hazard. An improved process understanding of LW accumulations at bridge piers is essential for a flood risk assessment. Therefore, we conducted a field study at the River Glatt in Zurich (Switzerland) to analyze the LW accumulation process of single logs at a circular bridge pier and to evaluate the results of previous flume experiments with respect to potential scale effects. The field test demonstrated that the LW accumulation process can be described by an impact, rotation, and separation phase. The LW accumulation was described by combining two simplified equilibria of acting forces and moments, which are mainly a function of the pier diameter, pier roughness, and flow properties. We applied the resulting analytic criterion to the field data and demonstrated that the criterion can explain the behavior of 82% of the logs. In general, the field observations confirmed previous results on the LW accumulation probability in the laboratory, which supports the applicability of laboratory studies to investigate LW–structure interactions.

Earthquake Response Modeling of Corroded Reinforced Concrete Hollow-Section Piers via Simplified Fiber-Based FE Analysis

The effect of corrosion-induced damage on the seismic response of reinforced concrete (RC) circular bridge piers has been extensively investigated in the last decade, both experimentally and numerically. Contrarily, only limited research is presently available on hollow-section members, largely employed worldwide and intrinsically more vulnerable to corrosion attacks. In this paper, fiber-based finite element (FB-FEM) models, typically the preferred choice by practitioners given their reduced computational expense, are validated against previous shake-table and quasi-static cyclic tests on hollow-section RC columns, and then used to investigate the influence of corrosion-induced damage. To this end, modeling strategies of varying complexity are used, including artificial reduction of steel rebar diameter, yield strength and ductility, as well as that of concrete compressive strength to simulate cover loss, and ensuing dissimilarities quantified. Pushover and incremental dynamic analyses are conducted to explore impacts on collapse behavior, extending experimental results while accounting for multiple corrosion rates. Produced outcomes indicate a minimal influence of cover loss; substantial reductions of base shear (up to 37%) and ultimate displacement capacity (up to 50%) were observed, instead, when introducing relevant levels of deterioration due to corrosion (i.e., 30% rebar mass loss). Its predicted impact is generally lower when considering more simplified assumptions, which may thus yield non-conservative predictions.

Effectiveness of CFRP seismic-retrofit of circular RC bridge piers under vehicular lateral impact loading

The effectiveness of Carbon Fiber Reinforced Polymer (CFRP) seismic-retrofit of circular Reinforced Concrete (RC) bridge piers under vehicular lateral impact loading is addressed in the present work performing experimental tests. Sixteen 1/3 scale RC bridge piers with circular cross-sections characterized by three different configurations of longitudinal and transverse reinforcements were tested with and without CFRP seismic-retrofit. In the first case, tested columns represent common shear-deficient RC bridge piers designed with obsolete design practice or for non-seismic areas. In the second case, CFRP wrapping is applied according to common seismic-retrofit practices to increase the shear capacity and ductility of columns.Experimental tests were carried out under static and lateral impact loading with propped cantilever conditions reproducing a typical short-span viaduct bridge pier configuration. In the static tests, the lateral load was applied monotonically through a hydraulic jacket under equivalent impact conditions. In impact tests, the lateral impact load was applied through a colliding truck equipped with a rigid hammer at the typical vehicular impact location adopting two different impact velocities (3 and 4.5m/s). A critical investigation of the transient dynamic characteristics, damage evolution, and post-impact damage is conducted by comparing the results obtained with and without CFRP seismic-retrofit, and under static and dynamic loading conditions. It is shown that CFRP seismic-retrofitting of circular RC bridge pier can also be effective in reducing the vulnerability under lateral impact loading. The CFRP-retrofit approach adopted in this study meets the requirement of multi-hazard prevention improving the robustness of the bridge. Finally, a semi-empirical equation for predicting the maximum displacement under impact loading is derived based on experimental results. The proposed equation adopts the results of a static test as a proxy for assessing the dynamic behavior allowing for the design of the required shear and flexural load-carrying capacity.

Vorticity fields around a pier on rigid and mobile bed channels

ABSTRACT Experimental investigation with reference to vorticity fields around circular bridge pier having diameter, d = 8.8 cm, at different angles, namely, θ = 0°, 90°, and 180° with respect to center of pier diameter, on rigid and mobile beds, is compared for identical flow conditions. The instantaneous velocity measurements were carried out using 16 MHz down looking micro-Acoustic Doppler Velocimeter (ADV) at different grids along the flow depths. The sediments having mean size, d50 = 0.75 mm, and geometric standard deviation, σg = 1.29, are used in experimentation. The results reveal that, on both rigid and mobile bed, with increasing the angle, the strength of primary vortex is decreased. On the other hand, the strength of secondary vortex has been found to increase with the angle, that is, the primary vortex is found to be strong in front of the pier, whereas the secondary vortex is predominant behind the pier. Further, the strengths of primary and secondary vortices are found to be ≈30% more on rigid bed than mobile bed for same flow condition.

Effect of Sediment Feeding on Live-Bed Scour around Circular Bridge Piers

The effect of sediment feeding was investigated in the case of live-bed scour around circular bridge piers under flood waves to provide contributions for future experimental procedures. Circular piers of three different diameters were tested in a long rectangular flume containing uniform sediment layer 25 cm thick, by generating 7 different triangular hydrographs with different durations ranging between 6 and 20 minutes and the peak discharges varying from 18 to 38 L/s. Experiments were first conducted without sediment feeding and total load was collected at predetermined time intervals. Then the same experiments were performed by feeding with the same amount of collected sediment. Time dependent scour depths were measured using UVP. Bed degradation was also determined by using an empirical equation existing in the literature. It was found that feeding with the rates equal to the transported ones did not significantly change the scour depth and total sediment load within the limits of the experiments. No significant bed degradation was observed, except at the upstream end. It was revealed that the sediment feeding may not be required in the experiments where temporal evolution of the scour depth is studied in a sufficiently long flume containing sufficient sediment. Doi: 10.28991/cej-2021-03091699 Full Text: PDF

Seismic behaviour of concrete bridge piers with various types of transverse reinforcement

Past bridge failures due to earthquakes have been found to be due to inadequate seismic design of the bridge piers. It is thus essential to investigate the effect of lateral confinement on the seismic behaviour of bridge piers. The aim of this study was to evaluate, experimentally and numerically, the seismic performance of reinforced concrete bridge piers with various types of transverse reinforcement. For this purpose, three scaled-down (1 : 4) circular bridge pier specimens were tested under constant axial and quasi-static cyclic loading (QSCL). A control specimen was made with spiral lateral reinforcement, while the other two specimens were made with stirrups with cross-ties and strips with cross-ties. The hysteresis loops, envelope curves, energy dissipation and stiffness degradation of all three specimens were determined in order to evaluate their seismic behaviour. Compared with the control specimen, the specimen with strips and cross-ties showed increased lateral load capacity, cumulative energy dissipation and higher initial stiffness due to the effect of increased confinement. The results of finite-element analysis showed good agreement with the experimental results. The findings of this study indicate that strips with cross-ties can be used in bridge piers when a high lateral load carrying capacity and energy dissipation are required.

Aspects of Downstream Bed Sill Location for Investigating the Countermeasure with Local Scour around Cylindrical Bridge Piers

ABSTRACT The countermeasures versus local scour around bridge piers are essential for safe bridge hydraulic design. In this study, laboratory experiments were conducted to investigate the effectiveness of downstream bed sill location as countermeasure method to decrease the local scour under clear water conditions for single cylindrical pier. Four flow intensities were tested (from 0.48 to 0.96 of the threshold velocity of sediment) with five different bed sill locations (from 0 to 4 pier diameter). The measured scour depths were compared with that observed at the exposed pier (four tests for unprotected pier) to estimate the percentage reduction in scour depth for each flow intensity and to assess the aspects of bed sill location. The results revealed a significant effect of bed sill location on decreasing the scour depth with in downstream distance equal to pier diameter. Accordingly, the percentage decrease in scour depth was ranged from 4 to 30%. New empirical formula has been proposed to estimate scour depth near circular bridge piers according to different bed sill configuration.

Scour protection around bridge pier and two-piers-in-tandem arrangement

ABSTRACT In the present study, experiments were carried out on circular model bridge piers individually as well as with two-piers-in-tandem arrangement under clear water scour conditions predominantly caused by formation of horseshoe vortex. Independent collar plates around bridge piers and a continuous collar plate covering both the piers were installed as countermeasures against scouring. In case of two piers, efficacy of scour-protection devices for front and rear piers was checked for the overall stability. Performance potential was noted to be about 67% and 100% for continuous collar plates of sizes 2.5D and 3.0D around two piers at average bed level with spacing of 2.0D; where D is the diameter of the pier. During degradation of general bed level, a group of three continuous collar plates was employed around both the piers to ensure considerable reduction of scour. A group of three collar plates of sizes 2.5D and 3.0D having an inter-plate spacing Cs equal to D/4 with the middle plate placed at the average bed level reduced scour by 79 and 82%, respectively, in comparison to the scour depth for an unprotected pier. A mathematical model was developed by multivariate regression analysis to prediction the scour depth for both the pier arrangements.

Development of performance limit states for concrete bridge piers with high strength concrete and high strength steel reinforcement

Current design codes and guidelines do not permit reinforcing the plastic hinge region of bridge piers using high strength steel (HSS) rebars. This is due to the lack of adequate research on the seismic response of HSS reinforced bridge piers. The objective of this study is to develop analytical expressions for predicting the drift at the onset of different performance limit states for high strength concrete (HSC) bridge pier reinforced with HSS reinforcement. Utilizing damage data obtained from incremental dynamic analysis of HSC circular bridge piers reinforced with HSS, this study developed drift ratio relationship accounting for the aspect ratio, concrete and steel material properties, axial load ratio, and reinforcement ratio, using validated finite element models. Analytical equations are developed for estimating the drift at the inception of rebar yielding, concrete spalling, and bar buckling using multivariate regression analysis. The proposed equations showed reasonable precision when corroborated against experimental results.

Study of flow turbulence around a circular bridge pier in sand-mined stream channel

Experiments were performed in a sand bed channel to investigate the effects of a mining pit on the hydrodynamics around circular bridge piers. Mean velocity profiles, Reynolds stresses, kinetic energy fluxes and scales of turbulence were analysed at critical locations along the channel bed as well as in the proximity of the pier. At the approach location where flow had passed over the pit and was approaching the pier, substantial increments in the near-bed velocities, bed shear stress and Reynolds stresses were observed. Dredging of the pit increased the strength of the horseshoe vortex in the scour hole region and also amplified the shedding frequency of trailing vortices at the rear of the pier. These effects may be instrumental in the alteration of local scour as well as erosion and deposition patterns around bridge piers.

Sacrificial Piles as Scour Countermeasures in River Bridges A Numerical Study using FLOW-3D

Scour is defined as the erosive action of flowing water, as well as the excavating and carrying away materials from beds and banks of streams, and from the vicinity of bridge foundations, which is one of the main causes of river bridge failures. In the present study, implementing a numerical approach, and using the FLOW-3D model that works based on the finite volume method (FVM), the applicability of using sacrificial piles in different configurations in front of a bridge pier as countermeasures against scouring is investigated. In this regard, the numerical model was calibrated based on an experimental study on scouring around an unprotected circular river bridge pier. In simulations, the bridge pier and sacrificial piles were circular, and the riverbed was sandy. In all scenarios, the flow rate was constant and equal to 45 L/s. Furthermore, one to five sacrificial piles were placed in front of the pier in different locations for each scenario. Implementation of the sacrificial piles proved to be effective in substantially reducing the scour depths. The results showed that although scouring occurred in the entire area around the pier, the maximum and minimum scour depths were observed on the sides (using three sacrificial piles located upstream, at three and five times the pier diameter) and in the back (using five sacrificial piles located upstream, at four, six, and eight times the pier diameter) of the pier. Moreover, among scenarios where single piles were installed in front of the pier, installing them at a distance of five times the pier diameter was more effective in reducing scour depths. For other scenarios, in which three piles and five piles were installed, distances of six and four times the pier diameter for the three piles scenario, and four, six, and eight times the pier diameter for the five piles scenario were most effective.

Effect of Interaction between Bridge Piers on Local Scouring in Cohesive Soils

Local scour at the piers is one of the main reasons of bridge foundation undermining. Earlier research studies focused mainly on the scour at a single bridge pier; nevertheless, modern designs of the bridges comprise wide-span and thus group of piers rather than a single pier are usually used to support the superstructure. The flow and scour pattern around group of piers is different from the case of a single pier due to the interaction effect. Reviewing the literature of local scour around bridge piers group revealed that the local scour around bridge piers group founded in cohesive soil bed was not investigated, and most of the scour studies were related to scour in cohesionless soils. The objective of the present study is to investigate the effect of the interaction between two in-line (tandem) circular bridge piers of variable spacings founded in cohesive soil on the local scour. A set of laboratory flume experiments were conducted under the clear-water scour condition to investigate this effect. This study is the first that investigates experimentally the scour around group of bridge piers in cohesive bed. It was found that the maximum scour depth at the upstream pier of the two in-line piers occurred at a spacing of two times the diameter of the pier, scour at the downstream pier was reduced due to a sheltering effect, the interference effect will be reduced for pier spacings larger than three times of the pier diameter. A recent pier scour equation was used to estimate the scour depths at the two in-line piers in cohesive soil and compare the estimated value with the measured scour depths in the laboratory. The comparison indicated that the proposed scour equation overestimates the scour depths at both the upstream and the downstream pier.

Three-dimensional numerical simulation of local scour around circular bridge pier using Flow-3D software

The problem of local scouring around circular bridge pier has been studied numerically by Computational Fluid Dynamics (CFD) using Flow-3D model to represent the evolution of local scour and the maximum depth of the scour hole which is important in the bridge pier design. The aim of this study is to verify the ability of the numerical simulation model Flow-3D to accurately simulate and predict the scour depth around the bridge pier. This verification is conducted by comparison the numerical results with Melville laboratory experimental model. The maximum scours depth around the circular pier obtained from numerical results after 30 min is 3.6 cm, while the scouring depth obtained from Melville model is 4 cm. According to these results, the error rate ratio between the numerical and experimental models is close to 10%. The results showed a good validation with experimental results. Finally, the proposed Flow-3D model considered an effective tool in predicting and simulating the scour depth around bridge pier and considered an economic method to predict potential results.

Seismic Performance of Bridge Piers Reinforced with Shape Memory Alloys in Plastic Hinge Region

The recent earthquake reconnaissance reports revealed that a large residual displacement had led to the devastation of bridge piers due to serviceability concerns. Shape Memory Alloys (SMA) is the distinctive category of smart materials, which can sustain enormous deformations and reappear to a parent shape after removal of loading or by removal of heat. Replacing the typical steel reinforcement with SMA reinforcement in the potential plastic hinge regions of bridge piers could reduce the residual displacement of a pier. This study is focused on the numerical investigation of circular bridge piers with SMA-based reinforcement in the plastic hinge regions to mitigate the residual displacement. The numerical model of a bridge pier is validated using the experimental results of SMA-reinforced bridge pier. Dynamic time history analyses are performed to compare the performance of SMA-reinforced bridge piers with steel-reinforced bridge piers under the effect of various earthquake ground motions. The results are represented in terms of displacement, base shear, and ductility. Moreover, the influence of several parameters on the performance of bridge piers is investigated, i.e., aspect ratio, axial load ratio, and compositions of SMA. The numerical results have indicated the effectiveness of bridge piers reinforced with SMA by reducing the residual displacement after major earthquake events.