Seismic Response Of Bridge Piers Research Articles

Centrifuge shaking table study on the hydrodynamic effects on a pile foundation bridge pier in soft soil under earthquakes

Previous investigations have shown that water-pier interaction has a considerable effect on the seismic response of bridge piers in deep water. However, most of those studies assumed that the foundation is rigid and there are few studies on the hydrodynamic effects on the piers considering soil-structure interaction under earthquakes. To investigate the hydrodynamic effects on bridge piers built on soft ground, series of centrifuge shaking table tests were conducted. In the tests, a pile foundation bridge pier was scaled down by a factor of 1:50. The height of the pier was 340 mm, and the length of the pile was 200 mm. The pile foundation pier was installed in soft soil contained in a laminar shear box. Three depths of water, i.e., no water, 150 mm and 300 mm, were considered. The dynamic responses of pier displacement, acceleration and bending moment of the pier and piles, hydrodynamic pressure on the pier, soil pressure on the pile and pore-water pressure in the soil were measured. The results show that the natural frequency of the pier decreases as the water depth increases, and the displacement of the pier with a water depth of 300mm is significantly reduced in comparison with that of no water. However, water increases the acceleration and bending moment of the pier and the pile. The results also show that as the water depth increases, the hydrodynamic pressure acting on the pier and the dynamic soil pressure exerted on the pile both increase under earthquakes.

Seismic response of caisson-supported bridge piers on viscoelastic soil

The paper presents a parametric study on the seismic response of bridge piers founded on gravity caissons. Despite the wide use of caissons in bridge engineering, until a few years ago this foundation typology has been less investigated than piles and shallow foundations in both static and dynamic field. In most of the published studies, the seismic design of bridge piers was carried out without accounting for soil-structure interaction or by means of an uncoupled approach in which the superstructure was solved independently from the soil-caisson subsystem. In this study, coupled systems made of soil, caisson, pier and deck were analyzed in the time domain by a 3D finite element approach, considering rigid and massive caissons embedded in linear viscoelastic soils. In addition to unravelling the contribution of kinematic and inertial interaction to the total response of the caisson-bridge-pier systems, the study focuses on a particular aspect of kinematic interaction, overlooked in practical design and in most of previous studies, represented by the kinematic bending arising in the bridge pier due to the pier-to-deck joint rigidity. For some critical combinations of soil compliance, caisson geometry, pier height and input motion characteristics, the pier-deck constraint could induce kinematic bending moments in the pier as important as the inertial ones. A closed-form equation was finally proposed to predict the maximum kinematic moment in the bridge pier as a function of the key model parameters identified through the parametric study.

Seismic response of bridge pier supported on rocking shallow foundation

In the seismic design of bridges, formation of plastic hinges plays an important role in the dissipation of seismic energy. In the case of conventional fixed-base bridges, the plastic hinges are allowed to form in the superstructure alone. During seismic event, such bridges may be safe from collapse but the superstructure undergoes significant plastic deformations. As an alternative design approach, the plastic hinges are guided to form in the soil thereby utilizing the inevitable yielding of the soil. Rocking foundations work on this concept. The formation of plastic hinges in the soil reduces the load and displacement demands on the superstructure. This study aims at evaluating the seismic response of bridge pier supported on rocking shallow foundation. For this purpose, a BNWF model is implemented in OpenSees platform. The capability of the BNWF model to capture the SSI effects, nonlinear behavior and dynamic loading response are validated using the centrifuge and shake table test results. A comparative study is performed between the seismic response of the bridge pier supported on the rocking shallow foundation and conventional fixed-base foundation. Results of the study have established the beneficial effects of using the rocking shallow foundation for the seismic response analysis of the bridge piers.

Seismic response of bridge piers on pile groups for different soil damping models and lumped parameter representations of the foundation

SummaryThis paper presents a wide parametric study aimed at elucidating the influence, on the computed seismic response of bridge piers, of two related aspects of the model: (1) the adoption of the classical hysteretic or the causal Biot's damping models for the soil and (2) the use of two different lumped parameter models of different complexity and accuracy to approximate the impedances of the pile foundation. A total of 2072 cases, including different superstructures, pile foundations, soil deposits, and seismic input signals, are studied. The results are presented so that the influence of the different parameters involved in the analysis can be assessed. From an engineering point of view, both lumped parameter models provide, in general, sufficiently low errors. The choice of the most adequate model for each case will depend not only on the configuration of the structure and the soil‐foundation system but also on the assumed soil damping model, whose influence on the computed seismic responses is relevant in many cases. The nonphysical behaviour provided by the classical hysteretic damping model for the soil at zero frequency generates issues in the process of fitting the impedance functions. It is also found that larger deck displacements are predicted by Biot's model due to the higher damping at low frequencies provided by the classical hysteretic damping model.

Nonlinear response of bridge piers on inclined pile groups: the role of rocking foundation input motion

This paper presents first results of an on-going research focused on the effects of piles layout and inclination on the nonlinear seismic response of bridge piers. The analysis methodology, based on the substructure approach, is firstly presented. The soil-foundation system is studied in the frequency domain according to a numerical model developed by the authors while the inertial interaction analysis of the superstructures is carried out in the time domain to capture the nonlinear structural behaviour. A suitable lumped parameter model is used to approximate the frequency dependent behaviour of the soil-foundation impedances in the time domain analyses. The procedure is applied to some case studies constituted by single bridge piers founded on medium stiff and soft clayed soil deposits. Pile groups with piles of different inclinations are considered, as well as piers with different fundamental periods and yielding bending moments of the base cross sections, to simulate systems with different ductility capacity. Analyses results show the key role of the foundation rocking on the superstructure response and demonstrate that inclined pile foundations may have a significant impact on the superstructure response, reducing the pier head displacements and ductility demand.

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.

Networked pseudodynamic testing of bridge pier and precast pile foundation

Using the internet-based network platform NetSLab, the seismic response of bridge pier and precast concrete pile foundation was investigated in this study. NetSLab was developed based on client/server concept along with a data model and communication protocols, and is capable of transferring control and feedback data and signals among geographically distributed laboratories or computers connected by the Internet. In this study, the bridge column was simulated numerically whereas the full-scale prestressed/precast pile model was tested physically with predetermined moment distribution along the pile model and neglecting pile group effects. The hybrid experimental results indicate that the sudden spalling of the thick concrete cover of the precast pile may cause unstable response of the bridge pier and pile foundation system under simulated earthquake loading, particularly when the bridge is subjected to near fault ground motions. The research also demonstrated the enhanced testing capabilities of the networked pseudo dynamic testing concept.

Seismic Response of Bridge Pier in Deep Water Considering close Fluid-Structure Interaction Effects

Based on the Navier-Stokes equations which are set up with the arbitrary Lagrange-Euler description, a finite element model considering close fluid-structure interaction (FST) is established to analyze the seismic response of bridge piers in the deep water. The influence of close FSI on the bridge pier is analyzed including the relative displacement, shear force and bending moment. In addition, the close FSI and its effects are discussed with respect to different water levels. The results of the case study indicate that the displacement and internal force will become larger obviously when the FSI is considered. Effects of the close FSI on seismic response of the pier are related to the frequency characteristics of the input earthquake wave. The larger the peak displacement of input earthquake wave, the larger the FSI effects on the displacement response of the pier are and the smaller the FSI effects on the internal force response of the pier. Additionally, the effect of the water level on internal force response of the pier is more remarkable than that on the displacement response of the pier.

Seismic response of bridge pier on rigid caisson foundation in soil stratum

An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from finite element (FE) analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modification of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.

Seismic response of bridge piers on elasto-plastic Winkler foundation allowed to uplift

When the bridge piers with shallow foundation are subject to intensive earthquake excitations, uplift of foundations will occur and the foundation soil will partly become plastic. It is very difficult to use an accurate method to simulate the uplifting and yielding of supporting soil. An improved Winkler foundation model, which could be used to consider the uplift and yield, was employed in the analysis. The 1940 El Centro earthquake record is inputted to a rigid pier with shallow foundation so that the non-linear history response is obtained. From the non-linear analysis, it is concluded that the non-linear effect is very remarkable when uplifting and yielding of supporting soil are considered. Compared with the linear analysis, the stiffness of bridge pier–soil system degrades in each cycle after considering uplifting and yielding. It is shown that the non-linear analysis can get larger rotational angles and smaller bending moments compared with the linear analysis.

Effects of soil-structure interaction on inelastic seismic response of bridge piers: M. Ciampoli & P. E. Pinto, Journal of Structural Engineering — ASCE, 121(5), 1995, pp 806–814

Effects of soil-structure interaction on inelastic seismic response of bridge piers: M. Ciampoli & P. E. Pinto, Journal of Structural Engineering — ASCE, 121(5), 1995, pp 806–814

Effects of Soil-Structure Interaction on Inelastic Seismic Response of Bridge Piers

The investigation reported in the paper is an attempt to assess the relevance of soil-structure interaction (SSI) effects on the dynamic response of bridge piers responding in the inelastic range and, in particular, on the maximum required ductilities in the critical regions of the superstructure. The problem is dealt with reference to a simple structural configuration: a vertical cantilever carrying a mass at the top, representing realistic cases of bridge piers of common geometry with spread footing foundations. A relatively large number of parameters has been considered in the analysis, with a total of 240 cases examined, and with ductility demands on the piers ranging between 1.5 and 7. The results indicate that although in most cases SSI produces an increase of the maximum displacements, this effect is not very significant, and the inelastic demand in terms of curvature essentially remains unaffected by soil-structure interaction, showing a tendency to decrease. Finally, the stability of these conclusions against rather extreme variations of the parameters is confirmed by the results of additional bounding analyses, characterized by unusually soft soil conditions and by a seismic excitation multiplied by a factor of two.

Influence of foundation compliance on the seismic response of bridge piers

The paper summarises the results of dynamic analyses of some single-stem and double-stem bridge piers responding to a range of earthquake ground motions, including both natural and synthetic earthquake records. The influence of foundation flexibility was modelled by an 'extended leg' analogy and by a more refined approach in which the soil is replaced by an equivalent spring system. A bilinear moment-curvature loop was assumed to model the plastic hinge behaviour. The curvature ductility factor demand of bridge piers with different foundation flexibilities was determined and compared with the rigid foundation case.