Single Bridge Pier Research Articles

Numerical Simulation of the Flow and Local Scour Process around Single and Complex Bridge Piers

The present work is focused on the flow and clear-water scour process around single and complex bridge piers using the computational fluid dynamics (CFD) approaches. In CFD, the use of large time steps may accelerate the simulation process but the effects of the unsteady flow structures may not be considered in the computations. In this case, the computational method is defined as a steady-state solution. In the present study, the capability and accuracy of the steady-state solution of the flow equations are investigated by employing the SSIIM code which is numerically stable for large time steps. For this purpose, several simulations were performed for different piers and bed configurations and the corresponding numerical results were compared with experimental ones obtained from referenced bibliography. Overall, the steady-state solution of the flow equations could predict fairly well the scour geometry at the upstream side and lateral sides of the bridge pier but not downstream side of the pier. Moreover, the local scour around a single pier was also predicted by performing an unsteady-state solution (where the vortex shedding effects are taken into account) by using the Flow-3D code. The major difference between the results from the two mentioned CFD codes was observed downstream of the pier such that, compared to the physical model, the scour depth was under-predicted by the steady-state calculations while it was over-predicted by the unsteady-state calculations.

Soil-structure interaction effects in single bridge piers founded on inclined pile groups

This paper investigates the seismic response of bridge piers founded on inclined pile groups in different soil deposits, evaluating effects of soil-structure interaction induced by different pile group geometries and piles inclinations. Analyses are performed in the frequency domain by means of the direct approach taking advantage of a numerical model developed by the authors for the analysis of inclined pile groups. Both the superstructure and piles are modelled with beam elements and the soil is schematized as a visco-elastic medium constituted by independent infinite horizontal layers. The soil-pile and the pile-soil-pile interaction are captured in the frequency domain by means of elastodynamic Green's functions that also allow including the hysteretic and radiation damping. The significance of kinematic stress resultants in piles, the foundation filtering effect and the rotational component of the input motion due to the coupled roto-translational behaviour of the soil-foundation system are also investigated; to this purpose kinematic interaction analyses are performed. These analyses revealed essential for the understanding of the general phenomena governing the dynamic response of the whole soil-foundation-superstructure systems. Results of numerical investigations highlight that conventional design approaches suggested by codes do not provide reliable predictions of the superstructure displacements and stress resultants.

Reducing local scour at bridge piers using an upstream subsidiary triangular pillar

The objective of this experimental study was to examine the effect of an upstream subsidiary triangular pillar on the development of local scour at a single circular bridge pier. The triangular pillar was placed such that its apex faced the approach flow and its base length was equal to the pier diameter (D) in all experiments. The experiments were conducted to investigate the effect of the spacing between the base of the subsidiary pillar and the bridge pier (S) and the apex angle (α) of the triangular pillar on the dimensions of the scour hole and its temporal development at different Froude numbers. The experiments were conducted in a rectangular flume under clear-water scour conditions at Froude number ranging between 0.1 and 0.3. Relative spacing (S/D) of 0, 0.5, 1, 1.5, 2, and 3, as well as apex angle (α) of 60°, 90° and 120° were tested. The results show that the maximum scour depth at the pier could be minimized using three different combinations of spacing and apex angle. The highest reduction in the maximum scour depth (dsm) of approximately 28 % was possible using S/D of 3 and α of 90° compared to the pier-alone case. Overall the performance of the 90° apex angle pillar surpassed the other two angles.

Effect of pier shape and pier alignment on the equilibrium scour depth at single piers

The equilibrium scour depth at uniform single bridge piers depends on a large number of variables, including the pier horizontal cross-section shape and its alignment angle towards the flow direction. The influence of these variables has been studied by only a few researchers, mostly, on the basis of tests that were far from approaching equilibrium. This experimental study aims at revisiting the influence of piers׳ shape and alignment on local scouring for length–width ratios smaller than or equal to 4, by increasing the experimental evidence. Fifty five long-duration laboratory tests were run under steady, clear-water flow, close to the threshold for initiation of sediment motion. Five pier shapes were considered: circular, rectangular square-nosed, rectangular round-nosed, oblong, and zero-spacing (packed) pile-groups; the tested skew-angles were 0°, 30°, 45°, 60°, and 90°. It was concluded that i) the shape factor can be taken as 1.0, for rectangular round-nosed and oblong cross-section piers, and as 1.2, for rectangular square-nosed and packed pile-group cross-section piers, ii) the shape factor does not vary significantly with the duration of tests, this way confirming the robustness of the shape factors reported to date, iii) the effect of shape is present at skewed piers although the associated coefficients remain in the narrow range of 1.0–1.2, and iv) for length–width ratios smaller than 4, the shape factor is of the same order of magnitude as the skew angle factor and should not be neglected.

Analysis of High Velocity Free Surface Flow Interaction with a Bridge Pier in a Trapezoidal Channel using CFD

This study uses the computational fluid dynamics (CFD) code ANSYS-CFX-12, to simulate 3D flow through a straight trapezoidal cross section channel containing a single bridge pier. The fluid flow condition is assumed to be steady state, isothermal and incompressible, with symmetry along the centerline of the channel, and the simulation uses the k - ε turbulence model. The study investigates the impact of variations of aspect ratio (channel bed width/flow depth), bed and side slopes of the channel, discharge (represented by a Froude number), and the length and thickness of the bridge pier on the free surface flow profile, both along the centerline and the on the wall of the channel. The code is based on the finite volume method, and uses the volume of fluid (VOF) approach to predict the free surface flow profile. Prediction of the free surface flow profile is essential for the design of high velocity channels. Prior prediction of flow profiles can inform and improve the design of expensive structures, such as high velocity channels and bridges, in particular the height of channel walls and bridge decks. Firstly, the code was validated against the numerical and experimental work of Stockstill (1996) for a channel containing three piers, and found to agree well. Then, the method was applied to the design test case, and mesh convergence tests to establish the required mesh size were carried out. The simulations were conducted in parallel over 32 cores on the Plymouth University High Performance Computer Cluster (HPCC). Finally, a parametric study was carried out and analytical expressions derived for maximum flow depth at the centre-line and at the side wall of the channel. Useful non-dimensional curves and equations derived from regressions of the study data are provided, which can be used as a guideline for the design of high velocity channels containing a bridge pier. For data regressions the statistical package software Statistical Product and Service Solutions (SPSS) was used.

Assessment of Soil-Structure Interaction in Seismic Bridge Pier Analysis Using Force and Displacement Based Approaches

Abstract The seismic analysis carried out assuming foundation to be perfectly rigid and bonded to the soil underneath is far from truth and therefore, the soil-structure interaction effect on the dynamic behavior of the bridge pier should be considered. The assessment of soil-structure effect on the design force generated has been estimated using Force based, Capacity Spectrum and Direct Displacement based methods considering fixed and flexible foundations. For this purpose a single cantilever bridge pier of constant diameter with varying heights has been considered for the analysis in different type of soils and earthquake zones. The study has revealed that soil-Structure Interaction index is negative in some cases, especially in soft soil, implying base shear demand being greater than that of fixed base contrary to the traditional views.

Simple method for real-time seismic damage assessment of bridges

Seismic damage of bridges may pose a severe threat to motorway users, and preventive closure until post-seismic inspection may be viewed as the only safe option. However, such a measure may incur pronounced losses by obstructing transportation of rescue teams. On the other hand, allowing traffic on earthquake-damaged bridges is a difficult decision with potentially dire consequences. Hence, the main dilemma for the motorway administrator is whether to interrupt the operation of the network, calling for timely development and implementation of a RApid REsponse (RARE) system. The development of such a RARE system requires an effective means to estimate the seismic damage of motorway structures in real time. This paper contributes towards such a direction by introducing a simple method for real time seismic damage assessment of motorway bridges. The proposed method requires nonlinear dynamic time history analyses using multiple seismic records as seismic excitation. Based on the results of the analyses, statistical models are estimated, and nonlinear regression equations are developed to express seismic damage as a function of statistically significant intensity measures (IMs). Such equations are easily programmable and can be employed for real-time damage assessment, as part of an online expert system. In the event of an earthquake, the nearest seismic motion(s), recorded by an online accelerograph network, will be used in real time to estimate the damage state of motorway structures, employing the developed equations. The efficiency of the proposed method is demonstrated using a single bridge pier as an illustrative example. Based on finite element (FE) analysis results, three nonlinear regression models are estimated correlating three damage indices (DIs) with statistically significantly IMs.

Experimental and numerical investigation of the effect of different shapes of collars on the reduction of scour around a single bridge pier.

The scour phenomenon around bridge piers causes great quantities of damages annually all over the world. Collars are considered as one of the substantial methods for reducing the depth and volume of scour around bridge piers. In this study, the experimental and numerical methods are used to investigate two different shapes of collars, i.e, rectangular and circular, in terms of reducing scour around a single bridge pier. The experiments were conducted in hydraulic laboratory at university of Malaya. The scour around the bridge pier and collars was simulated numerically using a three-dimensional, CFD model namely SSIIM 2.0, to verify the application of the model. The results indicated that although, both types of collars provides a considerable decrease in the depth of the scour, the rectangular collar, decreases scour depth around the pier by 79 percent, and has better performance compared to the circular collar. Furthermore, it was observed that using collars under the stream’s bed, resulted in the most reduction in the scour depth around the pier. The results also show the SSIIM 2.0 model could simulate the scour phenomenon around a single bridge pier and collars with sufficient accuracy. Using the experimental and numerical results, two new equations were developed to predict the scour depth around a bridge pier exposed to circular and rectangular collars.

Three-dimensional analysis of coherent turbulent flow structure around a single circular bridge pier

The coherent turbulent flow around a single circular bridge pier and its effects on the bed scouring pattern is investigated in this study. The coherent turbulent flow and associated shear stresses play a major role in sediment entrainment from the bed particularly around a bridge pier where complex vortex structures exist. The conventional two-dimensional quadrant analysis of the bursting process is unable to define sediment entrainment, particularly where fully three-dimensional flow structures exist. In this paper, three-dimensional octant analysis was used to improve understanding of the role of bursting events in the process of particle entrainment. In this study, the three-dimensional velocity of flow was measured at 102 points near the bed of an open channel using an Acoustic Doppler Velocity meter (Micro-ADV). The pattern of bed scouring was measured during the experiment. The velocity data were analysed using the Markov process to investigate the sequential occurrence of bursting events and to determine the transition probability of the bursting events. The results showed that external sweep and internal ejection events were an effective mechanism for sediment entrainment around a single circular bridge pier. The results are useful in understanding scour patterns around bridge piers.

Influence of unsteady flow hydrograph shape on local scouring around bridge pier

Accurate estimation of scour depth is needed for economic and safe determination of bridge pier foundation depth. Most design criteria are based on maximum scour depth due to the steady design discharge without flow time limit. In this paper, the results are presented of an experimental investigation on local scouring around a single bridge pier under steady and unsteady flow regimes. For unsteady flow, triangular shape hydrographs with repeatable peaks have been chosen. Results show that both sharp and flat increases to the peak of hydrographs have a negligible effect on scour depth for the same base time. An equation is obtained to compute the scour depth due to a specific triangular hydrograph with specific base time, peak flow characteristics and pier diameter. Also, an equation is introduced to represent temporal variation of scour depth with respect to the steady flow condition.

Nonlinear finite element analysis of barge collision with a single bridge pier

Vessel collisions with bridge piers are one of the most frequent accidents that may lead to bridge failure. To reliably assess bridge response and damage due to barge impact, and design the bridge piers to resist such impact, the impact force should be accurately defined. In most of the previous works of numerical simulation of barge collision with bridge piers for defining the barge impact force, the pier was assumed to be rigid or elastic and the interaction between the barge and the pier was neglected. As pier plastic deformation and damage will absorb impact energy and also prolong the interaction time, the impact force acting on the bridge pier might not be accurately predicted with rigid and elastic pier assumption. In this paper, a detailed numerical model of barge–pier impact is developed in LS-DYNA. The bridge pier is modelled with nonlinear materials to more realistically generate the bridge pier characteristics. Barge–pier impact force time history, barge crush depth and pier displacements are calculated in this paper. The reliability of the numerical model is calibrated with some results available in the literature. Based on numerical results simplified formulae are derived to predict the impact force time history with respect to the collision conditions. Numerical results are compared with the previous works. The adequacy of current code specifications is also discussed.

Developing a Family of Curves for the HEC-18 Scour Equation

Accurate pier scour predictions are essential to the safe and efficient design of bridge crossings. Current practice uses empirical formulas largely derived from laboratory experiments to predict local scour depth around single-bridge piers. The resulting formulas are hindered by insufficient consideration of scaling effects and hydrodynamic forces. When applied to full-scale designs, these formula deficiencies lead to excessive over prediction of scour depths and increased construction costs. In an effort to improve the predictive capabilities of the HEC-18 scour model, this work uses field-scale data and nonlinear regression to develop a family of equations optimized for various non-cohesive soil conditions. Improving the predictive capabilities of well-accepted equations saves scarce project dollars without sacrificing safety. To help improve acceptance of modified equations, this work strives to maintain the familiar form of the HEC-18 equation. When compared to the HEC-18 local pier scour equation, this process reduced the mean square error of a validation data set while maintaining over prediction.

The Dynamic And Earthquake Response Of ABridge Pier Model At The Volvi EuropeanTest Site

This paper presents results of the measured and predicted response of a bridge pier model-structure which is constructed at the Volvi-Greece European Test Site for Earthquake Engineering. Despite the disadvantage of being unable to produce significant in-situ levels of ground motion, when desired, as can be generated by an earthquake simulator, this is in part compensated at the Test Site by the realistic foundations conditions, which are present for model structures that are built there and are supported on the soft soil deposits in-situ. The current extension of the in-situ facility includes the possibility of subjecting the model structures to low to medium intensity man-made dynamic excitations. At this point in time the model structures that are built at the test site include: a) A 6-story Reinforced Concrete building with masonry infills; b) A single bridge pier specimen built for the purposes of the currently running Euro-Risk program, which is supported by the European Union. The variation of the fundamental dynamic characteristics of the 6-story 1/3 3-D frame model structure was measured over a period of ten years. Masonry infills were added to this model structure at a certain period of its life span. So far, only one earthquake of moderate intensity has subjected the 6-story model structure to seismic loads and excited the permanent instrumentation system. The current sequence of experiments includes man-made dynamic excitations for both the 6-story structure and the single bridge pier model. The main objective of the recent tests, which are partially presented in this paper and involve the bridge pier model, is to include influences on the dynamic structural response arising from the flexible foundation support conditions.

Study of Time‐Depenbent Local Scour around Bridge Piers

Estimation of maximum possible scour depth around bridge piers is an important step in the design of bridge pier foundations. Under known hydrological characteristics such as peak discharge and time-to-peak value of design flood hydrograph, smaller scour depths can be obtained compared to the equilibrium scour depths corresponding to clear water conditions. To examine such a phenomenon, time variation of local scour depths around bridge piers has to be determined. To this end, sets of experiments are performed using single cylindrical and square bridge pier models in the laboratory under clear water conditions with uniform bed materials. Semiempirical time-dependent analysis of local scour depths around bridge piers has been conducted using the sediment continuity equation for the scour hole around bridge piers. For design purposes, nondimensional scour prediction curves were prepared in terms of various sediment and flow properties.