Circular Piers Research Articles

Application of an evolutionary technique (PSO–SVM) and ANFIS in clear-water scour depth prediction around bridge piers

The mechanism of the local scour around bridge pier is so complicated that it is hard to predict the scour accurately using a traditional method frequently by considering all the governing variables and boundary conditions. The present study aims to investigate the application of different hybrid soft computing algorithms, such as particle swarm optimization (PSO)-tuned support vector machine (SVM) and a hybrid artificial neural network-based fuzzy inference system to predict the scour depth around different shapes of the pier using experimental data. The important independent input parameters used in developing the soft computing models are sediment particle size, a velocity of the flow and the time taken in the prediction of the scour depth around the bridge pier. Different pier shapes used in the present study are circular, round-nosed, rectangular and sharp-nosed piers. The accuracy and efficiency of the two hybrid models are analyzed and compared with reference to experimental results using model performance indices (MPI) such as correlation coefficient (CC), normalized root-mean-squared error (NRMSE), normalized mean bias (NMB) and Nash–Sutcliffe efficiency (NSE). The ANFIS model with Gbell membership and the PSO–SVM model with polynomial kernel function yield good results in terms of MPI. The performance of PSO–SVM with polynomial kernel function with CC of 0.949, NRMSE of 7.47, NMB of − 0.009 and NSE of 0.90 reveals that the hybrid ANFIS model with Gbell membership function yields slightly better than that of the PSO–SVM model with CC of 0.950, NRMSE of 6.92, NMB of − 0.002 and NSE of 0.91 for the optimum bridge pier with circular shape, whereas the performance of PSO–SVM model is better than that of ANFIS model for optimum bridge piers with rectangular and sharp nose shape. The PSO–SVM model can be adopted as accurate and efficient alternative approach in predicting scour depth of the pier.

Comparison of Scour and Flow Characteristics Around Circular and Oblong Bridge Piers in Seepage Affected Alluvial Channels

The present study examines scour geometry and turbulent flow characteristics around circular and oblong piers in alluvial channel with downward seepage. Experiments were conducted in plane sand bed of non-uniform sand under no seepage, 10% seepage and 15% seepage conditions. Scour depth at oblong pier is significantly lesser than the scour depth at circular one. However, the scour depth at both piers reduces with downward seepage. The measurements show that the velocity and Reynolds stresses are negative near the bed at upstream of piers where the strong reversal occurs. At downstream of oblong pier near the free surface, velocity and Reynolds stresses are less positive; whereas, they are negative at downstream of circular pier. The streamline shape of oblong pier leads to reduce the strength of wake vortices and consequently reversal flow at downstream of pier. With application of downward seepage turbulent kinetic energy is decreasing. The results show that the wake vortices at oblong pier are weaker than the wake vortices at circular pier. The strength of wake vortices diminishes with downward seepage. The Strouhal number is lesser for oblong pier and decreases with downward seepage for both oblong and circular piers.

Effects of a downstream submerged weir on local scour at bridge piers

This paper describes 64 experiments conducted in a sand-recirculating flume using coarse sand (d50 = 0.85 mm), investigating the interference of local scour between a circular pier (diameter D = 48 mm) and a downstream submerged weir (weir height z = 30 mm) with different separation distances L. The experimental results show that, for clear-water scour, the scour depth at the pier can be reduced by up to 54% by the downstream submerged weir when L = 0. This reduction decreases with increasing L until it approximately vanishes at L = 6D. For live-bed scour, besides the upstream bed aggradation, the downstream submerged weir can affect the local scour at a pier through two mechanisms: (i) superposition of local scour areas; and (ii) altering flow patterns. The mechanism (i) can increase the scour depth at the pier significantly when the pier is located in the upstream scour area of the submerged weir. The mechanism (i) vanishes at a distance L1, where the pier is located out of the upstream scour area of the submerged weir. The mechanism (ii) is similar to that of the clear-water scour tests, and can reduce the scour depth at the pier. The reduction effectiveness of mechanism (ii) decreases with increasing L until it becomes zero at a distance L2. Based on the experimental data, L1 and L2 are found to be 2D and 12D, respectively. For safe design, L1 < L < L2 is suggested to avoid the mechanism (i) and take the advantage of the mechanism (ii) for reducing the scour depth at the pier.

Seismic Assessment of Existing Hollow Circular Reinforced Concrete Bridge Piers

ABSTRACT Experimental works in literature have paid proper attention to the seismic response of hollow circular piers only quite recently, despite their widespread use in existing bridges. Herein, experimental cyclic tests on two scaled reinforced concrete piers with hollow circular cross-section, representative of typical existing Italian bridges, are carried out. Design criteria, adopted setup, experimental response, and damage evolution are discussed. A focus on shear–critical piers is performed, collecting an experimental database of tests from literature. The more specific existing shear strength models are compared with the collected data. Model by Ranzo and Priestley [2001] has finally shown promising results.

Numerical study of local scour around bridge piers

Numerical models have more flexibility avoiding the critical limitation in physical ones. The predictive capability of the hydro-morphological model around bridge piers in clear-water conditions have been investigated using mathematical modelling flow 3D 11.2 as there is a lack in using that model. The objective of the study to investigate the effect of cross section of the pier on the predictive capability of the model. Computations has been performed and the results are compared with several sets of experimental data available in the literature. The Van Rijn sediment transport model and (RNG) k-ε model are used. However, this study strongly demonstrates that a 3D hydro-morphological model can effectively predict the scour around piers with different cross section, there is significantly under predicts for the scour depth at the nose of the pier with different pier shapes. It is found that for the circular pier the capability of the model depending on the flow properties not only the geometry of the pier.

Multiple linear regression and genetic algorithm approaches to predict temporal scour depth near circular pier in non-cohesive sediment

Pier scour is a major problem for the safe and economical design of bridges. Large number of field and laboratory studies have been conducted to investigative the effect of significant variables. Present study is an attempt to develop a generalized scour prediction equation to investigate temporal variation of scour around circular bridges utilizing the data generated from our experimental study as well as data collected by earlier researchers. Nearly 1100 laboratory experimental data-sets were compiled and utilized to develop the generalized scour equation using MLR and GA. The scour depth predicted using GA was found to be more accurate than MLR. Further, the equation developed in the present study was compared to the previously proposed equations. It was found that the present equation complies with observed data better than the previously proposed equations. About 20% and 35% data-sets are found to be within the ±25% error line using previously proposed equations, while GA-based relationship gave about 52% of the data points within ±25% error line.

Numerical investigation of the drag force for cross-sea bridge based on the two-way fluid-structure interaction

The substructure of cross-sea bridge has its unique structural form, the calculation of drag force is related to working, designing, constructing and maintaining of the bridge in the marine environment. So in order to guarantee the construction and use safely, accurate and convenient calculation method of drag force is necessary. The calculation method of drag force theory is studied in this paper, with using shear stress transport model to set up eddy viscosity model, which is adopted to establish the numerical water tank and analysis the whole process of eddy generation and shedding in the wake area. Considering the features of cross-sea bridge substructure, the effect of the flow velocity, the depth of water and the section form of pier on the drag force is researched. The difference between the superposition method and integral calculation method, which are used for calculating the drag force of group pile cap composite structure, is studied. The results show that the water flow velocity is square relation with the drag force, and the depth of water is linear relation with the drag force. The drag coefficient C D of round-ended pier is 1.35, which is between the values of circular pier and rectangular pier. Due to the shield and interference with each component, the drag force calculated by integral method is less than the other one, and the lift force can be considered in the integral method.

Prediction of scour depth and dune morphology around circular bridge piers in seepage affected alluvial channels

Prediction of scour depth is one of the most significant problems in designing of bridges. Due to complexity of scour phenomenon, available empirical equations do not always offer accurate scour depth prediction. In this work, experiments were conducted on non-uniform sands using two piers of different diameter with and without seepage conditions. It has been found that, the scour depth at upstream of piers is decreased with application of downward seepage. The observed scour depths are compared with scour depth predicted by various prediction methods and it has been observed that the available equations are not suitable for seepage conditions. The present work thus introduces a new empirical equation for prediction of scour depth at piers with inclusion of seepage. The features of migrating dune like bedforms at downstream of piers due to deposition of scoured bed material are also explored. Height of deposition is found to be increased with downward seepage. The empirical equation describing morphology of dunes behind piers is also developed by incorporating downward seepage parameter.

Estimation of maximum scour depths at upstream of front and rear piers for two in-line circular columns

Previous investigations indicate that scour around bridge piers is one of the most important factors for the failure of waterway bridges. Hence, it is essential to determine the accurate scour depth around the bridge piers. Most of the previous studies were based on scour around a single pier; however, in practice, new bridges are usually wide and then piers comprise two circular piers aligned in the flow direction that together support the loading of the structure. In this study, the effect on maximum scour depth of the spacing between two piers aligned in the flow direction was investigated experimentally under clear water scour conditions. The results show that the maximum scour depth at upstream of the front pier occurs when the spacing between the two piers is 2.5 times the diameter of the pier. Two semi empirical equations have been developed to predict the maximum scour depth at upstream of both front and rear piers as a function of the spacing between the piers, in terms of a pier-spacing factor. If the new equations for the pier-spacing factor are used with some of the existing equations for scour at a single pier, the predicted scouring depths are in good agreement with observed results. The S/M equation exhibited the best performance among the various equations tested and was recommended for use in prediction of the equilibrium scour depth. The findings of this study can be used to facilitate the positioning of piers when scouring is a design concern.

Comparison of Three Commonly Used Equations for Calculating Local Scour Depth around Bridge Pier under Ice Covered Flow Condition

A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.

Model test study on seismic performance of new type column-plate hollow high pier

There are many disadvantages in the design of high pier in high intensity zone for traditional circular end-shaped hollow pier. The design concept of multi-column grid pier can improve the seismic performance of high-strength pier. The column-plate hollow high piers not only retain the good seismic performance of the lattice pier, but also improve the longitudinal and transverse stiffness of the hollow high piers, which lays a foundation for the application of the column plate bridge piers to the design of railway bridges. To understand the seismic performance of such piers systematically, a local model of plate pier is made on the basis of the column plate pier of the Zongmu Gou Bridge in this paper. The destructive mode and hysteresis characteristics of the pier are studied by means of pseudo-static test. It provides reference for the seismic design of the piers. The test results show that the column-plate structure as a whole has strong seismic performance. Under seismic loading, the inter-column plates can be completely sheared and destroyed, and the frame columns remain flexible. The energy consumption of the inter-column plate during the destruction process ensures the normal operation of the frame column.

Maximum scour depth around bridge pier in gravel bed streams

Precise prediction of scour near the circular uniform pier may lead to the economic design of piers and avoid disastrous instances. Present study mainly deals with cohesionless sediment with gravel particles. Authors checked the three latest bridge pier scour models in this study. Three new relationships are proposed by authors for computing maximum scour depth, maximum scoured length and maximum effected scoured width in cohesionless sediment at equilibrium scour condition. Maximum scour depth equation is validated by the available literature data, and this relationship is applicable for both gravel as well as the sand bed. Graphically and statistically the new maximum scour depth relationship gives better agreements between observed and computed values of maximum scour depth. Relationships for maximum scoured length and maximum effected scoured width are only applicable for gravel and coarse sand bed and also gives better agreement with computed values.

Experimental investigation of clear-water temporal scour variation around bridge pier in gravel

Variation of temporal scour depth around circular piers under clear-water scour condition was studied experimentally for a variability of configuration studies, including different size of circular piers. A total of 96 experiments were carried out with more than 800 data sets of temporal scour depth in non-uniform gravel bed. The experimental data were used to calculate the temporal scour depth at different planes i.e. 0°, 90°, 180° and 270°, 0° plane indicates the maximum and 180° plane indicates minimum scour zones. Some of the previous methods of estimating temporal scour depth at 0° plane are studied in this study. Three temporal scour depths equations for 0°, 90°, 270° and 180° planes have been proposed in this study. The predictions of the temporal scour depth improved after the revised methods of Kothyari et al. (J Hydraul Eng 133(11):1229–1240, 2007). Results of the present proposed equation for 0° plane were compared with latest available relationships in literature and found in good agreements with observed values.

The effect of combined countermeasures on main local scouring parameters using physical models

Details of an experimental study for 22 clear-water scour tests around bridge piers are presented in three combinations of flow-altering countermeasures against bed erosion. The combined countermeasures are as follows: (1) berm and geometry; (2) berm, geometry, and centered slot; and (3) berm, geometry, and off-centered slots. First, four different cross-sections were selected for the model piers (A series). The results of this group have shown that the lenticular model can decrease the scour depth remarkably. The efficient height of a berm was then determined through B series of tests for circular cylindrical model pier. Then, it was found that the first combination (C series) could not decrease the bed erosion significantly. Also, the second combination (D series) mainly decreased the scour depth only in the circular and round-nosed rectangular geometries. Finally, the third combination (E series) used for the first time with considering its structural aspects can be considered as the most effective countermeasure only for the common geometries of the model piers. The results showed that the combination of different countermeasures would not be an efficient tool for all geometries of model piers.

Splitter plate as a flow-altering pier scour countermeasure

Results of an experimental study on the countermeasure of scour depth at circular piers are presented. Experiments were conducted for pier scour with and without a splitter plate under a steady, uniform clear-water flow condition. The results of pier scour without splitter plate were used as a reference. Different combinations of lengths and thicknesses of splitter plates were tested attaching each of them to a pier at the upstream vertical plane of symmetry. Two different median sediment sizes (d 50 = 0.96 and 1.8 mm) were considered as bed sediment. The experimental results show that the scour depth consistently decreases with an increase in splitter plate length, while the scour depth remains independent of splitter plate thickness. In addition, temporal evolution of scour depth at piers with and without a splitter plate is observed. The best combination is found to be with a splitter plate thickness of b/5 and a length of 2b. Here, b denotes the pier diameter. An empirical formula for the estimation of equilibrium scour depth at piers with splitter plates is obtained from a multiple linear regression analysis of the experimental data. The flow fields for various combinations of circular piers with and without splitter plate including plain bed and equilibrium scour conditions were measured by using an acoustic Doppler velocimeter. The turbulent flow fields for various configurations are investigated by plotting the velocity vectors and the turbulent kinetic energy contours on vertical and horizontal planes. The splitter plate attached to the pier deflects the approach flow and thus weakens the strength of the downflow and the horseshoe vortex, being instrumental in reducing the equilibrium scour depth at piers. The proposed method of pier scour countermeasure is easy to install and cost effective as well.

Experimental investigation on the cyclic behaviors of corroded coastal bridge piers with transfer of plastic hinge due to non-uniform corrosion

Coastal bridge piers exposed to marine environments always suffer from non-uniform corrosion along the elevation. Severe degradation in the splash and tidal zone would significantly affect the seismic performance of the structure with a specific phenomenon of the plastic hinge transferring from the column end to the splash and tidal zone. In a companion paper of the authors [1], a theoretical method to identify the time-dependent failure mode and equivalent plastic hinge length of the aging bridge piers under seismic excitation in the whole life cycle was conducted. In this study, cyclic loading tests of six reinforced concrete circular bridge piers with different levels of corrosion are carried out to investigate the seismic performance of such types of structures and validate the proposed method. The test specimens and the experimental setup are first introduced. Based on the measured hysteretic curves, the experimental results of the curvature distributions, hysteretic characteristics, loading-resistance capacity, ductility, energy dissipation, equivalent viscous damping ratio and equivalent plastic hinge length are analyzed and discussed. The test results demonstrate the accuracy of the analysis results for the seismic failure modes presented in the companion paper. It is also indicated that the seismic performance of the non-uniformly corroded columns exhibited a small variation before the transfer of the plastic hinge location, while an obvious reduction was observed for moderately and severely corroded structures.

Three-dimensional velocity measurements around bridge piers in gravel bed

ABSTRACTThe experimental results of time average velocity components measured around circular pier models during transient scour stage using acoustic Doppler velocimeter are shown for flow pattern and turbulence characteristics. Totally, four experiments were performed under clear water scour conditions in a model of gravel bed stream. Four circular pier models of diameter 6.6, 8.4, 11.5, and 13.5 cm were used for this study. Detailed controlled measurements on velocity components, and turbulence intensities near the pier and in scour hole at 0° and 180° plane are shown. Flow structure around a pier model in the presence of a scoured region was compared with the flow structure similarly noticed around all pier model runs by utilizing the observations taken at 0° and 180° plane from flow axis. Size of the primary vortex at 0° plane with largest diameter pier model in place (R4 run) is found to be maximum and was approximately 61% larger than that for smallest diameter pier model in place (R1 run). The time-averaged velocity components of turbulence intensities plots at 0° and 180° planes are also presented around each pier.

Calculation Method of Hydrodynamic Forces on Circular Piers during Earthquakes

Calculation Method of Hydrodynamic Forces on Circular Piers during Earthquakes

Experimental investigation on flow and scour characteristics around tandem piers in sandy channel with downward seepage

Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition.

EVALUATION OF LOCAL SCOUR DEVELOPMENT AROUND PRISMATIC AND NON-PRISMATIC BRIDGE PIERS WITH DIFFERENT SHAPES

In this study, laboratory experiments were conducted to evaluate the local scour around piers. Effects of many parameters on the maximum depth of scour and scour pattern around piers have been studied. The study considered the effects of upstream flow conditions, shape of pier, side slope angles, and type of soil. Three cross sections for pier (circular, elliptical and oblong) were used for different velocities and discharges to find the scour depth. Two types of uniform cohesionless soil with median grain sizes of d50=0.25 (bed soil of Al-Kufa river), and d50=0.66 were used as bed material. Four angles of pier side slope were selected 0° (prismatic pier) and 5°, 10° and 15° (non-prismatic piers). It has been observed that for circular cross section pier, the maximum reduction for the scour depth at the upstream of the pier with a side slope of 15° for the soil of d50=0.25mm was about 63.64% and for the soil of d50=0.66mm was about 54.55%. The reduction value was increased up to 80% and 75% for the same angle of pier side slope (Ɵ=15°) with oblong cross section for the soil of d50=0.25mm and d50=0.66mm respectively.