Pier Models Research Articles

Seismic evaluation method on shear strength models for round-end hollow piers of high-speed railway bridges

Round-end hollow pier has been widely used in China's high-speed railway (HSR) lines. Experimental studies have shown that the HSR round-end hollow pier may experiece bending shear failure in the transverse direction of bridge, which is a brittle failure. Although it is of great significance to clarify the shear strength model for HSR round-end hollow piers, their seismic shear performance and failure mode criterion are still unclear. Considering the existing seismic design codes of bridges are mostly applicable to ordinary bridge components, this paper proposes a shear strength model for HSR round-end hollow piers based on the truss model limiting equilibrium theory, and quasi-static test results. According to the proposed shear strength model, a bending-shear coupling numerical pier model was established using OpenSees. Then the accuracy of the proposed shear strength model is verified. The study results show that the proposed shear strength model can accurately obtain the shear strength of HSR round-end hollow piers compared with other evaluation methods. Besides, the numerical simulation results illustrate that the HSR round-end hollow pier is not prone to damage under the design seismic excitation. Corresponding to the extreme seismic excitation with the peak ground acceleration of 0.75 g, the HSR round-end hollow pier experiences bending shear failure, which can be accurately determine by the proposed shear strength model.

A rapid evaluation method based on natural frequency for post-earthquake traffic capacity of small and medium span bridges

To improve the efficiency of evaluating the traffic capacity of bridges after the earthquake, a rapid method based on natural frequency for evaluating post-earthquake traffic capacity of small and medium-span bridges is proposed. Firstly, OpenSees software is selected to establish the seismic numerical analysis model of the pier, and the pressure of the main girder on the pier is equivalent to concentrated mass to extract the dynamic characteristics of the pier. The horizontal thrust on the pier top is adopted to simulate seismic action by the pseudo-static method, and the horizontal thrust is controlled by the maximum horizontal displacement. The value range of pier parameters is determined according to the definition of the regular bridge and relevant design data, then the design parameters and maximum horizontal displacement of each pier are sampled by the Latin hypercube sampling method to obtain various combined working conditions. Subsequently, the natural frequency, residual displacement and bearing capacity of the pier under different working conditions are obtained through numerical simulation. The relationship between natural frequency and residual bearing capacity of the pier after the earthquake is established in light of the simulation results of pier models. Then, the vehicle load is arranged on the basis of the most unfavorable loading principle, and the bearable maximum vehicle weight of the bridge is estimated from the bearing capacity of each pier, so that the traffic capacity of the bridge after the earthquake can be quickly evaluated by the change of natural frequency of piers. Finally, the reliability of the pier numerical model and residual displacement calculation method are verified by the test results of piers. The application process of the evaluation method proposed in this paper is illustrated by two typical examples of a simply supported beam bridge and a continuous beam bridge, which proves the feasibility of this method.

Damage assessment of RC bridge piers under rockfall impact and evaluation of a steel-sand protective structure

The damage and collapse of the reinforced concrete (RC) piers subjected to rockfall impact occur frequently in mountainous areas. In the present scrutiny, a full-scale numerical model of a bridge pier is established to examine the mechanical behaviors of RC piers against rockfall, which is planned to be explored in three aspects: residual strength analysis, structural damage evaluation, and protection measures. The dynain file method is introduced to reach the realization of the stress initialization of the impacted pier. The RC pier model and the dynain file method, constructed and realized through the software LS-DYNA respectively, are illustrated in detail as well as their validations. The complicated collision process between the rockfall and the RC pier is first interpreted. Subsequently, the study on the pier residual axial capacity is carried out based on the dynain file approach. Further, a calculation model for the residual axial capacity of the impacted pier is proposed by considering the rock mass, velocity, concrete strength, and pier diameter. The influential parameters on the maximum impact force and residual axial capacity of the impacted pier are also displayed and discussed. Furthermore, the damage index of the bridge pier under the rockfall impact is established based on the residual axial capacity, and the pier's impact-damage degree is analyzed through the isodamage curves. Finally, a steel-sand composite structure is introduced to protect the RC pier from rockfall impact. The obtained results demonstrate that the dynain file method can be suitably applied in the residual axial capacity analysis of RC piers subjected to rockfall. The proposed calculation formula can be appropriately adopted to evaluate the post-impact residual axial capacity of RC piers. The detailed parameter analysis indicates that the pier diameter has a remarkably influential effect on the rockfall impact force and the pier's residual axial capacity. Additionally, the composite protective structure can enhance anti-collision performances.

Seismic Behavior of Box Steel Bridge Pier with Built-In Energy Dissipation Steel Plates

Based on the design concept of earthquake-resilient structure, a new-type of box-shaped steel piers with embedded energy-dissipating steel plates was proposed. Quasi-static tests of 6 box-shaped steel pier specimens under variable axial pressure and cyclic horizontal loading were carried out. By analyzing the failure mode, load-displacement hysteretic curve, skeleton curve, displacement ductility coefficient, stiffness degradation characteristics, strength degradation coefficient, and cumulative hysteretic energy, the effects of setting energy-dissipating steel plate, axial compression ratio, and thickness of energy dissipation steel plates on the seismic performance of new-type steel piers were discussed. Finite element models of steel bridge piers were established and compared with the test results. The analysis results using FEM agree well with the test results. Results show that the setting of energy-dissipating steel plates can effectively improve the ductility, deformation capacity, and energy-dissipating capacity of box-shaped steel piers, and effectively delay buckling deformation and cracking of wall plates. The steel plate near the bolt hole of the wall plate at the root of the new-type of box-shaped steel piers is easy to crack due to stress concentration, resulting in a rapid reduction of the maximum bearing capacity of the specimens. With the increase of axial compression ratio, the bearing capacity, energy-dissipating capacity, and earthquake-resilient capacity of the specimens increase. The smaller the thickness of the replaceable energy-dissipating steel plates, the smaller the bearing capacity and faster the stiffness degradation of the specimens become, while the ductility and energy-dissipating capacity of the specimens are improved. The axial compression ratio and the thickness of the energy-dissipating steel plate have relatively little effect on the strength degradation of the specimens. In order to facilitate the popularization and application of the new-type steel piers, formulas were also established to calculate the bearing capacity and displacement ductility factor of the new-type of box-shaped steel piers.

Exploring the performance of experimentally benchmarked RC bridge pier models when subjected to sequential seismic shocks

In this paper we explore the performance of RC bridge piers to seismic ground motion sequences, using both experimental and numerical models. Four RC columns were tested on the University of Bristol’s shake table. These columns contained both well-confined and poor-confined cases. Spectrally matched by near-field without pulse (NFWP), near-field pulse-like (NFPL) and far-field (FF) ground motion records where employed in a sequential/progressive fashion ranging from (I) slight damage (II) extensive damage (III) complete damage and (IV) aftershock cases. These experimental test results are then used to develop a benchmarked OpenSees model of this bridge pier. The importance of the concrete tension constitutive model is highlighted. The differences between sequential (progressive damage) and neglecting sequential seismic events are discussed. The benchmarked model is then used for a heuristic case using incremental dynamic analyses. A comparison is made between drift and energy dissipation performance measures, that suggests drift cannot identify the increased system damage induced by sequential events.

Cross-sectional blockage effect on the drag force of a scaled round-ended pier model under directional flow

Flume testing of a scaled model under steady flow is an essential reference for accessing the flooding-induced drag force on a prototype pier, but is highly susceptible to the cross-sectional blockage effect. Round-ended bridge piers have a non-axisymmetric cross-section, of which the drag force varies significantly with inflow direction. A flume testing program was carried out to illustrate the cross-sectional blockage effect under different inflow directions. CFD numerical simulations were then conducted to understand the blockage effect on the drag force, flow field and hydrodynamic pressure of the round-ended pier with different blockage ratios and inflow directions. The major findings include: 1) the blockage effect affects the drag force of the scaled model and changes with inflow direction; and 2) the limit of occurrence of the cross-sectional blockage effect is defined by the critical blockage ratio and given as a function of inflow direction. An empirical approach was finally developed to correct the cross-sectional blockage effect on the drag force of the round-ended pier model under directional flow. The influences of the blockage ratio and inflow direction were included in the empirical calculation of the drag force on the prototype from the scaled model test.

Data-driven reliability assessment of dynamic structures based on power spectrum classification

The power spectral density function is a widely used tool to determine the frequency components and amplitudes of environmental processes, such as earthquakes or wind loads. It is an important technique especially in the engineering field of vibration analysis and in determining the response of structures. When using a large amount of data, a load model can be generated, which describes the characteristics of the underlying stochastic process. This load model enables artificially generated excitations to be created within the framework of Monte Carlo simulations. If multiple data records are utilised, a problem that can occur is that the individual records have a high variance in the frequency domain and are therefore too dissimilar from each other, even though they appear to be similar in the time domain. A load model derived from this data does not represent the entire data set, because not the whole spectral range is covered. Therefore, every attempt must be made to group the records according to their characteristics and thus combine similar data to derive two or more load models accordingly. In this work, an approach is proposed to classify real earthquake ground motion records using the k-means algorithm based on similarities within the data ensemble as determined by the Bhattacharyya distance. The silhouette method enables the identification of the optimal number of groups for the classification. The classified data thus form a subset of the entire data set from which load models can be generated and can be applied separately to the structure under investigation, leading to more accurate simulation results. The advantages of this classification approach are illustrated by means of an academic example and a seismic-isolated bridge pier model as a non-linear dynamic system.

Quasi-static test of the lattice-type railway bridge pier with replaceable connection component

Replaceable components are beneficial to functionality rapid restoration of structures after earthquakes, which is a good option for seismic design of resilient bridges. In this study, a lattice-type bridge pier with replaceable connection component was proposed for railway bridges. Large initial stiffness was provided by using steel truss connection system as replaceable connection component between two concrete columns. A 1/12-scaled bridge pier model was designed and fabricated to investigate its cyclic responses by quasi-static testing. It was proved that the replaceable connection component can be easily assembled between concrete columns and work well together with them. During testing, cracks occurred at the concrete columns and crack zone extended with the increase of loading displacement. At the later loading stage, some of steel rods of the connection component between the concrete columns began to yield, the hysteretic loop of the bridge pier showed obvious pinching effect. However, concrete columns were prevented to be severely damaged due to the sacrifice of replaceable connection components. There were differences in the strain distribution of the replaceable connection component and not all the replaceable components yielded during testing. Thus, steel rods with varied strength should be used in replaceable components for the lattice-type railway bridge pier. Otherwise, it should balance the stiffness and ductile in seismic design for the lattice-type railway bridge pier with replaceable connection component.

Cyclic Testing on Seismic Behavior of Segmental Assembled CFST Bridge Pier with External Replaceable Energy Dissipator

In 2009–2022, to meet the requirement of resilient bridge pier structure (e.g., earthquake resistance, energy dissipation, isolation, resilience) for rapid repair after earthquakes and to improve the suitability of precast segmental bridge piers in medium- and high-intensity areas, a segmental assembled CFST bridge pier with external replaceable energy dissipator was proposed. Based on ABAQUS finite element analysis software, the finite element model of the CFST pier is established to analyze the force of the external replaceable energy dissipator, and the feasibility of the external energy dissipator is verified. Thereafter, two groups of segmentally assembled CFST pier model structures were tested for seismic behavior under reciprocating loading. Non-linear mechanical behaviors, such as restoring force-displacement hysteresis, loss of prestressing, and opening of the indirect joint of a segmented precast assembled pier, are analyzed. The results show that compared with a CFST pier with an energy dissipator, the lateral bearing capacity of the CFST pier with an external energy dissipator is increased by 32.8%, the energy dissipation capacity is also significantly improved, the opening size of joints between segments is reduced, and the overall damage of the CFST pier is concentrated on the energy dissipator, which is convenient for rapid disassembly and replacement. At the same time, the seismic performance of the CFST pier after replacing the energy dissipator is analyzed. The results show that the replacement of the external energy dissipator will not affect the seismic performance of a segmental assembled pier.

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.

Seismic Performance Analysis of Segmental Assembled Concrete-Filled Steel Tubular Pier with External Replaceable Energy Dissipation Ring

In order to develop a new type of prefabricated bridge structure system with green, efficient and recoverable function, which complies with the new requirements of rapid repair of pier function after earthquake, and improves the applicable performance of prefabricated assembled pier in medium and high-intensity seismic areas, a precast segmental concrete-filled steel tubular (PSCFST) pier with an external energy dissipation ring is proposed. Based on ABAQUS analysis software, a four-segment PSCFST pier model is established, and the pseudo-static comparative analysis is carried out between the traditional PSCFST pier and the PSCFST pier with the external energy dissipation ring. The results show that compared with the traditional PSCFST pier, the lateral bearing capacity of the PSCFST pier with an external energy dissipation ring is increased by 60%, the energy dissipation capacity is increased by about 20 times, and the damage is concentrated in the energy dissipation ring, the damage is controllable, and the rapid repair after the earthquake can be realized by replacing energy dissipation devices and other measures. At the same time, the seismic performance of pier models with three different control parameters (initial prestress, material strength of energy dissipation ring and section width of energy dissipation ring) under reciprocating loading is analyzed. The results show that the initial prestress does not affect the cumulative energy consumption of the pier; the increase in the material strength of the energy dissipation ring improves the overall stiffness and improves the energy dissipation capacity of the PSCFST pier; the reduction in section width will affect the overall equivalent stiffness and unloading stiffness of the segmental pier, and the energy dissipation capacity will be significantly reduced.

Analysis of the Seismic Behavior of a Wall Pier of a Covered Bridge Based on the Multi-Layer Shell Element

To investigate the seismic behavior of the wall pier of a covered bridge, the multi-layer shell element in OpenSEES was used to carry out the numerical analysis under a horizontal low cyclic loading in the weak axis direction. The effects of the mesh divisions of the wall pier models were evaluated and the hysteretic curves, skeleton curves, bearing and energy dissipation capacity, stiffness degradation and displacement ductility of the wall pier with different lateral loading modes were mainly researched. The results demonstrate that the discretization of layers along the thickness direction of the multi-layer shell element model has a very limited effect on the hysteretic and skeleton curves. The mesh division of the horizontal direction depends on that of the vertical, and the vertical mesh spacing shall be longer than the plastic hinge with a length of 0.5744 m. The arrangement of the loading points is critical for the seismic behavior of the wall pier. The pier suffering the force from the five points presents a relatively strong energy dissipation and larger ductility, but this layout may cause a more concentrated force at the local position. When the loading points are evenly distributed, the capacity and displacement changes sharply and the ductility diminishes. Successively, the seismic performance indexes at the local position of the wall pier tend to be more consistent with the increasing loading points. The deformation and energy dissipation capacity of the nearby position with the denser side loading points becomes larger, but this has a minor impact on the seismic performance of the position far from the points. The wall pier without the bent cap and with three bearings set is supposed to be more reasonable for the covered bridge through the overall analysis of seismic performance.

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.

An online platform for bridge-specific fragility analysis of as-built and retrofitted bridges

Bridges are the most critical and usually the most vulnerable structural component of a road network exposed to various hazards. Damage due to recent earthquakes worldwide highlighted the substantial direct and indirect financial losses related to partial or total collapse of critical bridge components and pointed to the need for reliable assessment of their seismic performance. This paper presents a ‘toolkit’ developed for bridge-specific fragility analysis of bridges; it is implemented on a “two-track” online platform, including ad-hoc developed software for online bridge-specific fragility curve derivation, as well as the option to select an appropriate set of generic fragility curves from a database including a broad range of bridge classes. Three alternative options for the estimation of component-specific limit state thresholds are provided; selection from extensive lists with available thresholds for piers, bearings and abutments, and calculation of limit state thresholds for as-built and retrofitted piers based on (a) closed-form relationships, or (b) inelastic pushover analysis and capacity assessment of a parametrically defined pier model (carried out online). Details regarding the software developed, the methodology for bridge-specific fragility curves, and all critical features are presented and discussed herein. The application of the online software is illustrated through two case studies involving the derivation of fragility curves for bridges with different structural systems and properties.

Study on seismic behavior of a self-centering railway bridge pier with sacrificial components

Railway bridge pier with large cross-section will vibrate significantly during strong earthquake events. Sacrificial components can be used to improve the lateral stiffness and control the initial uplift of the self-centering pier during earthquakes. This study investigated the seismic isolation mechanism and behavior of a self-centering railway bridge pier with sacrificial components by experimental and numerical methods. Based on an actual railway bridge, a 1/30 scaled bridge pier model was designed for pseudo-static test. Constant axial load and cyclic lateral load were applied for the scaled bridge pier model. Test results showed that sacrificial components were fractured when the loading displacement exceeded 25 mm. The hysteretic behaviors of the self-centering pier exhibited significant difference before and after the failure of sacrificial components. It was found that the bridge pier concrete cracked but steel bars did not yield during the test. This indicated that the failure of sacrificial components of the self-centering bridge pier can effectively protect the pier from severe damage during earthquakes. Furthermore, a Four-spring model was proposed with assistance of the Opensees software platform, and it was verified by pseudo-static test results. It is demonstrated that the proposed model can simulate the self-centering piers with sacrificial components under cyclic lateral loading.

Study on the Seismic Performance of Prefabricated Single-Segment Steel Jacket Bridge Piers

To study the seismic performance of prefabricated single-segment steel jacket piers connected by grouting sleeves, two scaled symmetrical pier models with different anchorage lengths of the longitudinal reinforcement in the grouting sleeves and a comparative symmetrical cast-in-place (CIP) model were designed. OpenSees finite element models were established and shaking table tests were carried out on the three scaled pier models. The seismic response of each pier was compared and analyzed. Results showed the stiffness of the two prefabricated piers was greater than that of the CIP pier, and other seismic responses were less than those of the CIP piers, The dynamic responses of the two prefabricated bridge models were similar and changing the anchorage length of the reinforcement in the grouting sleeve had little effect on the seismic performance of the prefabricated pier. The simulation results were in good agreement with the experimental results. In the parameter analysis, the counterweight of the pier top had the greatest influence on the seismic performance of the prefabricated pier. The anchorage length of the longitudinal reinforcement in the grouting sleeve could be 6–14 times the diameter of the longitudinal reinforcement. Moreover, the seismic performance was found to be optimal when the thickness of the steel jacket was 5–7 mm.

Shaking table test on single segment prefabricated concrete bridge pier connected by grouting sleeve

PurposePrefabricated pier technology has the advantages of quick construction time, relatively little traffic interference and relatively small environmental impact. However, its applicability under earthquake conditions is not yet fully understood. The seismic performance and influence parameters of a prefabricated concrete pier connected by embedded grouting sleeve (GS) in a pile cap are investigated in this study.Design/methodology/approachTwo prefabricated pier scale model specimens with different reinforcement anchorage lengths and two comparative cast-in-place (CIP) pier model specimens are designed and manufactured for a seismic simulation shaking table. With the continuous increase of input ground motion strength, the changes in basic dynamic characteristics, damage development, acceleration and displacement variation laws, and pier bottom strain responses are compared among the specimen. The finite element software ABAQUS is used to simulate the test pier.FindingsThe crack location of the two prefabricated pier specimens is almost the same as that of the CIP pier specimens; CIP pier specimens show more penetrated cracks than prefabricated pier specimens, as well as an earlier crack penetration time. The acceleration, displacement and strain response of the CIP pier specimens are more affected by earthquake activity than those of the prefabricated pier specimens. The acceleration, displacement and strain responses of the two prefabricated piers are nearly identical. The finite element results are in close agreement with the acceleration and displacement response data collected from the test, which verifies the feasibility of the finite element model established in ABAQUS.Originality/valueA GS connection method is adopted for the prefabricated pier, and on the premise of meeting the minimum reinforcement anchorage length required by the code, this study explores the influences of different reinforcement anchorage lengths on the seismic performance of prefabricated piers in high-intensity areas. A shaking table loading test is used to simulate the real changes of the structure under the earthquake. This work may provide a valuable reference for the design and seismic performance analysis of prefabricated pier, particularly in terms of seismic stability.

Effects of Dynamical Change in Water Level on Local Scouring around Bridge Piers Based on In-Situ Experiments

To evaluate the stability of bridge piers affected by the local scouring, the existing formulas for estimating the maximum local scour depth have been developed based on the results of experiments conducted under a constant water level. However, the applicability of these formulas to the cases where the water level rises and falls, such as a water level change in a real river, is not clear. In this study, water flow experiments were conducted on cylindrical and oval bridge pier models to investigate the effect of iterated water level change on the progression of local scour around piers. Results of experiments with cylindrical and oval pier showed that the local scour depth and length increased by an iterated action of the water level change; however, these values converged after the number of iterated actions reached a certain time. The local scour length at upstream of the bridge pier was approximately 1.8 times larger than the theoretical value, which was calculated through the local scour depth and angle of repose in water. The local scour length is an important parameter for defining the streambed protection zone, which is one of the measures against local scour, and we showed that the streambed protection zone needs to be defined more widely.

Experimental Characterization of the Flow Field around Oblong Bridge Piers

The prediction of scour evolution at bridge foundations is of utmost importance for engineering design and infrastructures’ safety. The complexity of the scouring inherent flow field is the result of separation and generation of multiple vortices and further magnified due to the dynamic interaction between the flow and the movable bed throughout the development of a scour hole. In experimental environments, the current approaches for scour characterization rely mainly on measurements of the evolution of movable beds rather than on flow field characterization. This paper investigates the turbulent flow field around oblong bridge pier models in a well-controlled laboratory environment, for understanding the mechanisms of flow responsible for current-induced scour. This study was based on an experimental campaign planned for velocity measurements of the flow around oblong bridge pier models, of different widths, carried out in a large-scale tilting flume. Measurements of stream-wise, cross-wise and vertical velocity distributions, as well as of the Reynolds shear stresses, were performed at both the flat and eroded bed stages of scouring development with a high-resolution acoustic velocimeter. The time-averaged values of velocity and shear stress are larger in the presence of a developed scour hole than in the corresponding flat bed configuration.

Effects of Different Geometric Parameters of Complex Bridge Piers on Maximum Scour Depth: Experimental Study

This research experimentally investigated local scour depth around complex bridge piers in a clear-water condition. The term “complex pier” is used to define a bridge pier composed of three different sections: a column, cap of pile, and group of pile. Eighty-two experiments were carried out using six types of complex pier models to understand the impacts of the pile cap longitudinal extension from column, arrangement (or configuration) of pile group, extension occurring upstream of pile group, and thickness of pile cap. Through the experiments, a mathematical relationship between the upper limit of the pile cap undercut elevation and pile cap thickness was presented. In fact, the proposed formulation aimed to assess the undercutting elevation of pile cap. It was found that the variation of pier-foundation geometry significantly affected the maximum scour depth. The result showed that increasing pile cap thickness thereby decreased the pile cap undercutting elevation. When the piles number in line with flow increased, the maximum scour depth decreased.