Earthquake Response of Bridge Piers and Their Foundations

Teknik Dergi, 2014

An isolated bridge pier having rubber bearings is modeled by finite element technique and dynamic responses under effects of earthquake accelerations are obtained by linear solution methods in time and frequency domain; the results are evaluated by probabilistic distributions. For this purpose, stationary accelerations characterized by Kanai-Tajimi power spectrum are simulated for different soil types and twenty nonstationary records in each soil group are obtained by modulating the amplitudes in harmony with Erzincan NS 1992 component. The pier responses and deck displacements are obtained in time domain for different support and soil conditions by using simulated horizontal and vertical accelerations. Furthermore, variances of the responses are obtained in frequency domain by assuming stationary stochastic behavior and by using power density and cross-power spectra of the applied simultaneous motions. The results are evaluated by those of the time domain solutions and peak respons...

2016

The dynamic response of structures to earthquake loading depends mainly on: the characteristics of the incident seismic waves; local site conditions, such as topographic irregularities and heterogeneity of the soils; the presence of stiff and heavy embedded foundations; the deformability of the soil supporting the structures. These phenomena can be relevant for bridges that usually have deep foundations and extent over considerable distances. In this paper the dynamic response of a bridge pier subjected to polarized shear waves is investigated. Different wave patterns are considered and the corresponding free-field ground motion is calculated with reference to a linear elastic halfspace. The pier is founded on a rigid caisson and soil-structure interaction is solved using the Winkler type model developed by Gerolymos and Gazetas.

Earthquake Engineering & Structural Dynamics, 2011

This study investigates the seismic behavior of bridge with strengthened pier, and also the behavior of bridge when foundation strengthening was imposed. Seismic responses of bridge were compared by conducting pseudo-dynamic test, in which, foundation was selected as an experimental part. Two cases of foundation specimens have been constructed in order to represent a normal foundation and a strengthened foundation. Damage in the piles was observed in the normal foundation with pier strengthening case, whereas the pier was damaged in the strengthened foundation case.

Journal of Structural Engineering, 2009

Recent earthquakes such as Loma Prieta, Northridge, and Kobe have demonstrated a need for a new design philosophy of bridge piers that avoids damage in order to ensure post-earthquake serviceability and reduce financial loss. Damage Avoidance Design (DAD) is one such emerging philosophy that meets these objectives. DAD details require armoring of the joints; this eliminates the formation of plastic hinges. Seismic input energy is dissipated by rocking coupled with supplemental energy dissipation devices. In this paper the theoretical performance of a DAD bridge pier is validated through bi-directional quasi-static and pseudodynamic tests performed on a 30% scale specimen. The DAD pier is designed to rock on steel-steel armored interfaces. Tension-only energy dissipaters are used to increase tie down forces and further reduce dynamic response. The seismic performance of the DAD pier is compared to that of a conventional ductile pier. Results show that one can have 90 percent confidence that the DAD pier will survive a design basis earthquake without sustaining any damage, whereas for the conventional design substantial damage is sustained.

Rocking as an acceptable mode of seismic response has been investigated extensively and has shown to potentially limit local displacement demands. Rocking can act as a form of isolation, reducing displacement and force demands on a bridge, thereby allowing for design of smaller footings and members. A series of preliminary shaking table tests of a simple inverted pendulum reinforced concrete bridge column was conducted for horizontal and vertical components of excitation. The underlying soil is modeled in these tests with a simple neoprene material on which the pier is allowed to rock. Results presented illustrate the effects of multi-directional earthquake excitation on the elastic response of bridge columns. Comparisons of analytic simulations of the elastic rocking response and fixed base response illustrate the benefits of foundation uplift.

2006

Circular reinforced concrete highway bridge piers, designed in accordance with the requirements of Caltrans, New Zealand and Japanese specifications, are experimentally investigated to assess their seismic performance. Pseudodynamic tests are performed on 30% scaled models of the prototype bridge piers. Each specimen is subjected to a sequence of three different earthquake ground motions scaled appropriately to represent: (i) the Design Basis Earthquake (DBE) with a 90 percent confidence; (ii) the Maximum Considered Event (MCE) with a 50 percent confidence; and (iii) the MCE with a 90 percent confidence. Test results show that when bridge piers are designed to the specifications of the three countries, satisfactory performance with only slight to moderate damage can be expected for DBE. For the MCE, severe damage without collapse is likely for the Caltrans and Japanese piers. However, the NZ pier may not be able to survive MCE motions with sufficient confidence to ensure the preservation of life-safety.

2006

Rocking as an acceptable mode of seismic response has been investigated extensively and has shown to potentially limit local displacement demands. Rocking can act as a form of isolation, reducing displacement and force demands on a bridge, thereby allowing for design of smaller footings and members. A series of preliminary shaking table tests of a simple inverted pendulum reinforced concrete bridge column was conducted for horizontal and vertical components of excitation. The underlying soil is modeled in these tests with a simple neoprene material on which the pier is allowed to rock. Results presented illustrate the effects of multi-directional earthquake excitation on the elastic response of bridge columns. Comparisons of analytic simulations of the elastic rocking response and fixed base response illustrate the benefits of foundation uplift.

Structural Engineering International, 2013

Seismic performance of Reinforced Concrete (RC) bridge piers can be improved when their deformation demands are partially alleviated at the cost of a limited amount of rotation in the pier foundation due to soil-pile interaction. Until recently, damage to the foundation was undesirable in the capac ity design framework. However, with the advent of performance-based design, engaging the foundation in a controlled manner is now considered a desirable means by which to control damage to the piers at advanced performance levels. This approach is particularly relevant in the common highway overpass (usually short two span bridges) where embankment contributions determine the seismic demands to the central piers, as the embankment-abutment interaction dominates the lateral translation of the bridge superstructure. This paper explores this option as a design scenario, whereby, through the implementation of appropriate structural and geometrical configuration of the pier-foundation system, it may be feasible to improve the seismic performance of a bridge by engaging more components to distribute the deformation rather than relying on damage localization in a few critical elements. Concepts are illustrated through correlation of the calculated responses with field records obtained from an instrumented bridge overpass, used as benchmark example.

ASCE Journal of …, 2008

1 Research Assistant, Mid-America Earthquake (MAE) Center, Department of Civil Engineering at the University of Illinois at Urbana-Champaign, 205 N. Mathews Ave, Urbana, IL, 61801, E-mail: nburdette@gmail.com 2 Bill and Elaine Hall Endowed Professor, Director, MAE ...

Collapses of bridges founded in liquefiable soils are still observed after most major earthquakes; see for example the bridge collapses following the 1964 Niigata (Japan) and Alaska earthquakes, 1975 Haicheng (China) earthquake, 1976 Tanshang (China) earthquake, 2008 Wenchuan (China) earthquake, 2010 Maule (Chile) earthquake. One of the observations is that the middle of the bridges collapses by falling of the deck without any noticeable damage to superstructure. It has long been argued that the cause of the bridge failure is due to liquefaction induced soil flow (also commonly known as lateral spreading of the ground) which pushed the pier causing large displacement of the pier which eventually dislodges the deck. This paper reviews the bridge failures observed in the past earthquakes from China, India, Japan and critically analyses the postulated hypothesis behind the failure. Parallels will be drawn with the recent findings on dynamic soil foundation structure interaction. Piles are most common foundations for supporting small to medium span bridges and they are designed with required factors of safety against bending due to lateral loads (inertia and kinematic loads due to lateral spreading) and axial capacity (shaft resistance and end-bearing). Recent research identified a few weaknesses in the conventional design approach for pile foundations: (a) when soil liquefies it loses much of its stiffness and strength, so piles subsequently act as long slender columns, and can simply buckle (instability failure) under the combined action of axial load and inevitable imperfections (e.g. out-of-line straightness, lateral perturbation loads due to inertia and/or soil flow). In contrast, most codes recommend that piles be designed as laterally loaded beams; (b) Natural period of pile supported bridge structures may increase considerably (few times) owing to the loss of lateral support offered by the soil to the pile and the damping ratio of the structure may increase to values in excess of 20%. These changes in dynamic properties of the bridges can have important design consequences, the most important one being displacement demand on the pier. The aim of the paper is to revisit the failure of bridges in light of the current understanding. It is concluded that the immediate need is not only to rewrite the design code to incorporate these effects, particularly buckling instability, but also to requalify and, if necessary, strengthen the existing important pile foundations in liquefiable soils. Research needs are also highlighted.

2010

In this study, the oscillation behavior and the seismic reinforcement effect of an existing bridge with high pier are investigated by dynamic analysis method. The bridge pier is retrofitted by ground anchor and damper. The PC cables and the dampers are assumed to be strung between the column of the pier and the ground anchors. Focusing on whether to introduce an initial tension and a damper, the analysis is conducted and, the analysis results show that this reinforcement method has a significant positive effect in improving the aseismicity of the bridges with high piers. Introduction Bridges serve as important constituent elements of highway and railway networks and, when damaged by earthquakes, have a direct negative effect on earthquake relief and reconstruction. Of particular note, the recent Northridge Earthquake of 1994, the HyogokenNanbu Earthquake of 1995, the Taiwan Chi-Chi Earthquake of 1999, the Iran Earthquake of 2001, the Chuetsu Earthquake of 2004, and the Wenchuan Eart...

International Journal of Trend in Scientific Research and Development

In this study, seismic analysis of soil-foundation interaction under a bridge pier are studied with different earthquake excitations. In 2016, August 25, a magnitude of 6.8 happened near Bagan region. Pakokku Bridge, the longest of the bridges over the Irrawaddy, is situated on 37.8 miles from the epicentre of 2016 Chauk earthquake. That is why the safety performance of long-span Bridge (Pakokku Bridge) especially for the safety of the foundation system subjected to soil-foundation interaction is necessary to investigate for unexpected future seismic excitation. Firstly super structural loadings on the pile cap are estimated by using STAAD PRO V8i. And then, p-y curves are determined by Reese (1974) method for the static and National Cooperative Highway Research Program (NCHRP) for dynamic conditions. Based on the development of p-y curves, theoretical ultimate soil resistance pcr and pcd due to wedge and flow failure are determined to produce critical depth xcr. After that, finite element software ABAQUS is used for the analysis of soil-foundation interaction under a bridge pier in static condition. And then, the behaviour of soil foundation interaction under a bridge pier is carried out due to Chauk earthquake. In this study, the behaviour of soil-foundation interaction such as deflections and settlements are produced. According to the analysis results in static condition, it is found that the vertical and horizontal displacements at the pile tip are 2.28mm and 0.14mm respectively. In dynamic condition, the vertical and horizontal displacements at the pile tip are 3mm and 2.94mm are found at 0.12g. After that, maximum ground acceleration of 0.5g is 14.5mm and 2.94mm in horizontal and vertical displacement of pile tip. Maximum shear stress and strain are found out the base of the pile cap. Finally it is found that the soil-foundation interaction under a bridge pier during earthquake motions presented in this study is reliable and reasonable with the limitation of AASHTO Standard Specifications for Highway Bridges.

Korea is located in a slight-to-moderate seismic zone. Nevertheless, several studies pointed that the peak earthquake magnitude in the region can be reached to approximately 6.5. Accordingly, a seismic vulnerability evaluation of the existing structures accounting for ground motions in Korea is momentous. The purpose of this paper is to develop seismic fragility curves for bridge piers of a steel box girder bridge equipped with and without base isolators based on a set of ground motions recorded in Korea. A finite element simulation platform, OpenSees, is utilized to perform nonlinear time history analyses of the bridges. A series of damage states is defined based on a damage index which is expressed in terms of the column displacement ductility ratio. The fragility curves based on Korean motions were thereafter compared with the fragility curves generated using worldwide earthquakes to assess the effect of the two ground motion groups on the seismic fragility curves of the bridge piers. The results reveal that both non-and base-isolated bridge piers are less vulnerable during the Korean ground motions than that under worldwide earthquakes.

Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2019

In this paper, a simplified procedure for the evaluation of the seismic performance of bridge piers founded on caissons subjected to strong ground motions is outlined. To this end, the upper-bound semi-empirical relationships proposed in [1] are considered for the estimation of the seismic performance, expressed in terms of the maximum and permanent values of the deck drift ratio attained during and at the end of the seismic event. These drifts were related to the period ratio Teq/T0 between the fundamental periods of the deck-pier-caisson-soil system and of the soil column in free-field conditions. The deck drift and the period ratios were extracted from the results of an extensive parametric study, where 14 different systems were subjected to 6 real high-intensity seismic records. In the parametric study, 3D dynamic analyses were performed with the Finite Element Method in the time domain, in terms of effective stresses but assuming undrained conditions and adopting an elastic-plastic constitutive model to reproduce the irreversible soil behaviour under cyclic loading. As 3D dynamic numerical analyses are not expected to become an everyday design tool, the period ratios Teq/T0 are evaluated through empirical and analytical relationships available in the literature as well and then compared with the ratios obtained from the parametric study, to assess the possibility of using simplified relationships while still getting a reliable estimate of the deck drift ratio. It is shown that these relationships can be profitably adopted provided that a fair estimate of the equivalent shear wave velocity, depending on the intensity of the seismic inputs, is used.

Journal of Civil Engineering and Architecture, 2015

This dissertation is dedicated to the study of the seismic performance of an existing long reinforc ed concrete (RC) bridge localized in a region of moderat e seismicity. The RC bridge is 440 m long with 6 spans and piers with very different lengths, 3 of which are monolit hically connected to the deck. In order to better understand the roles of the high size and low size piers in the overall response of the bridge under seismic loading several analyses were carried out in the longit udinal direction. These analyses comprised in first place the linear dynamic approach, secondly, a non-linear static approach and finally a non-linear dynamic approach. The aim of the linear elastic analysis was to obtain the design for the ultimate limit state considering the largest value of the ductility factor for the piers. To achieve this goal the location of t he bridge was chosen in a region with a seismic action similar to t he one defined for Lisbon. EC-8 response spectrum for Lisbon (DNA, National Document Application, 2011) was us ed to define the s eismic action and the N2 method was used to check the design. For this situation, pier 4, the smallest of t he bridge, is the more critical element, and due to this reason the design was essentially concentrated in this element. Starting from here, minimum and maximum values of reinforc ement were adopted for all other piers and, using non-linear static analyses, sensitivity was performed to check the influence of steel quantities in the overall behavior of the bridge. To check the importance of the static vers us dynamic non-linear analysis in the situation of a RC bridge with very different piers lengths, the study was then performed using non-linear dynamic approach. To do s o a s eries of strong motion records compatible with the EC-8 response spectrum was generated and subjected to the structure in a dynamic non-linear behavior. Various combinations of amount of steel rei nforcement for flexural efforts in piers were studied with the objective of optimizing the cost-performance in the light of seismic loading having in mind t he elastic method proposed in E C8. Results were compared with a static non-linear N2 method and a non-linear dynamic analysis to confirm the validity of t he former method for the present case where the period of vibration is quite high as the case of this long structure.