Fault Ground Research Articles

Influence of Collapse Definition and Near-Field Effects on Collapse Capacity Spectra

In the present article, the impact of both near fault ground motions and a finite ductility threshold on the collapse capacity is studied. Single-degree-of-freedom systems with non-deteriorating bilinear hysteretic behavior, vulnerable to P-delta effects, are considered. Defining collapse as excessive ductility is investigated, and the difference to collapse associated with instability is elaborated. Medians of individual record dependent collapse capacities are presented as function of the initial structural period for characteristic structural and ground motion parameters. Analytical expressions for influence coefficients, which account for a differing ground motion set, and finite ductility thresholds, respectively, are derived via non-linear regression analysis.

Performance-based seismic rehabilitation of existing steel eccentric braced buildings in near fault ground motions

SUMMARY The devastating effects observed in the recent earthquakes, in terms of loss of lives as well as immediate and long-term economic losses, have prompted the need to provide documents concerning the assessment and improvement of the structural performance of existing buildings at the time of an earthquake. In this regard, performance engineering is defined as performance-based seismic design and rehabilitation. There are many reasons for rehabilitation of existing buildings. Changing the building's usage is one of the most common reasons. In the present study, the residential steel buildings were subject to performance-based rehabilitation, converting to educational use. Several steel frames with dual lateral-resistant systems (MRF–EBF) and different numbers of stories were initially designed as residential buildings. The frames were rehabilitated according to the current seismic rehabilitation codes and regulations. Cover plates were used to strengthen structural elements. Variations in structural responses were evaluated before and after retrofitting by the use of nonlinear analysis. Moreover, the performance of rehabilitated structures was evaluated, considering the gross features observed in near-field records. Copyright © 2013 John Wiley & Sons, Ltd.

Influences of pre-existing fracture on ground deformation induced by normal faulting in mixed ground conditions

Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground deformation are not fully understood. In this work, six centrifuge tests are reported to investigate the influence of pre-existing fracture on ground deformation induced by normal faulting in sand, clay and nine-layered soil with interbedded sand and clay layers. Shear box tests were conducted to develop a filter paper technique, which was adopted in soil model preparation to simulate the effects of pre-existing fracture in centrifuge tests. Centrifuge test results show that ground deformation mechanism in clay, sand and nine-layered soil strata is classified as a stationary zone, a shearing zone and a rigid body zone. Inclination of the strain localization is governed by the dilatancy of soil material. Moreover, the pre-existing fracture provides a preferential path for ground deformation and results in a scarp at the ground surface in sand. On the contrary, fault ruptures are observed at the ground surface in clay and nine-layered soil strata.

Seismic Response of Elevated Liquid Storage Tanks Using Double Concave Friction Pendulum Bearings with Tri-Linear Behavior

In the current paper, the seismic response of elevated liquid storage tanks using double concave friction pendulum bearings (DCFP) considering bi-linear and tri-linear behaviors have been investigated. After deriving the coupled differential equations of motion, the MATLAB programming language is employed to solve the differential equations in each time step in order to obtain the time history response of isolated tank under near fault ground motions. The advantages and disadvantages of tri-linear behavior over bi-linear one on the response of isolated tanks is scrutinized by studying the effects of main parameters such as isolation period, tank period with fixed base, tank aspect ratio and base mass ratio on the tank response. It is demonstrated that change in bearing behavior form bi-linear to tri-linear dramatically affects the bearing maximum displacement while the peak value of other parameters such as sloshing displacement or tower shear force may experience less variations.

Shake table tests of steel embedded composite columns under moderate near-fault motion

Shaking table tests were conducted on steel-embedded composite columns with core structural steel on near fault ground motion (NFGM) to investigate their seismic behavior. Four composite columns and one reinforced concrete (RC) column with diameters of 400 mm and heights of 1400 mm were tested on a shake table, and one specimen was studied with a pseudodynamic test. A sliding steel frame, called the inertial force rig, was designed and implemented to completely support the inertial mass of the column and the shaking table system. The composite column with a higher steel ratio required more volumetric confinement steel in the plastic hinge region. For the steel embedded composite columns with an axial steel ratio of less than 2%, The same amount of confining steel as in the normal reinforced concrete columns was sufficient to obtain the required ductility for the composite columns with low steel ratio. Composite columns with an embedded steel tube at the center showed better displacement ductility than RC columns with similar steel ratios, but showed smaller energy absorption capacity. The effect of the lap splice in a composite column was not significant because the spliced reinforcing bars had a lower area than RC columns with a 50% lap splice. The shake table test specimen showed much less ductility than the pseudo-dynamic test specimen and more energy dissipation capability, while the maximum capacity of the composite column was the same for the different test methods.

GIS-based evaluation on the fault motion-induced coseismic landslides

Earthquake-induced potential landslides are commonly estimated using landslide susceptibility maps. Nevertheless, the fault location is not identified and the ground motion caused by it is unavailable in the map. Thus, potential coseismic landslides for a specific fault motion-induced earthquake could not be predicted using the map. It is meaningful to incorporate the fault location and ground motion characteristics into the landslide predication model. A new method for a specific fault motion-induced coseismic landslide prediction model using GIS (Geographic Information System) is proposed herein. Location of mountain ridges, slope gradients over 45 o , PVGA (Peak Vertical Ground Accelerations) exceeded 0.15 g, and PHGA (Peak Horizontal Ground Accelerations) exceeded 0.25 g of slope units were representing locations that initiated landslides during the 1999 Chi-Chi earthquake in Taiwan. These coseismic landslide characteristics were used to identify areas where landslides occurred during Meishan fault motion-induced strong ground motions in Chiayi County in Taiwan. The strong ground motion (over 8 Gal in the database, 1 Gal = 0.01 m/s 2 , and 1 g = 981 Gal ) characteristics were evaluated by the fault length, site distance to the fault, and topography, and their attenuation relations are presented in GIS. The results of the analysis show that coseismic landslide areas could be identified promptly using GIS. The earthquake intensity and focus depth have visible effects on ground motion. The shallower the focus depth, the larger the magnitude increase of the landslides. The GIS-based landslide predication method is valuable combining the geomorphic characteristics and ground motion attenuation relationships for a potential region landslide hazard assessment and in disaster mitigation planning.

Response spectrum analysis for regular base isolated buildings subjected to near fault ground motions

This paper presents a response spectrum analysis procedure suitable for base isolated regular buildings subjected to near fault ground motions. This procedure is based on the fact that the isolation system may be treated separately since the superstructure behaves as a rigid body on well selected isolation systems. The base isolated building is decomposed into several single-degree of freedom systems, the first one having the total weight of the building is isolated while the remainder when superposed they replicate approximately the behavior of the superstructure. The response of the isolation system is governed by a response spectrum generated for a single isolated mass. The concept of the procedure and its application for the analysis of base isolated structures is illustrated with an example. The present analysis procedure is shown to be accurate enough for the preliminary design and overcomes the limits of applicability of the conventional linear response spectrum analysis.

Abandonment and the Law of Contract

Abandonment and the Law of Contract

Parametric analysis of optimum isolator properties for bridges susceptible to near-fault ground motions

This paper examines the selection of optimum isolator properties, namely characteristic strength, Qd, and post-elastic stiffness, kp, for bridges located in near-fault regions. First, a two-phased sensitivity analysis is conducted to evaluate the influence of bridge, isolator, and near-fault ground motion parameters on optimum levels of Qd and kp based on minimizing maximum isolator displacement and force. In the first phase of sensitivity analyses, a screening via design of experiments principles is performed to assess the statistical significance of various parameters on the optimum isolator properties. The second phase includes rigorous sensitivity analyses to assess the trends in optimum Qd and kp as a function of the bridge, isolator, and near-fault ground motion parameters. Next, nonlinear time history analyses of typical seismically isolated bridges are conducted for a suite of near-fault ground motions across a range of values of the identified parameters to enable the development of parametric equations for optimum Qd and kp to minimize isolator force or displacement. The parametric equations are validated using an alternate suite of near-fault ground motions. Furthermore, the dispersion about the predictive equations are quantified and assessed. It is observed that the developed equations produced reasonable estimates of optimum isolator properties with a relatively consistent dispersion across the modeling parameters. Moreover, it is observed that for near fault ground motions with high intensity and strong directivity, supplemental energy dissipation devices are required to minimize the isolator displacements.

Effect of lead core heating on the seismic performance of bridges isolated with LRB in near‐fault zones

SUMMARYIn this paper, the effect of lead core heating and associated strength deterioration on the seismic response of bridges isolated with lead rubber bearings (LRB) is investigated as a function of the characteristics of the isolator and near fault ground motions with forward rupture directivity effect. Furthermore, the ability of bounding analyses to provide a design envelope for maximum isolator force and maximum isolator displacement is verified. For this purpose, a series of nonlinear dynamic analyses are conducted for LRB isolated bridges where both deteriorating and non‐deteriorating force‐deformation relationship of LRB were employed. The analyses are performed for both simulated and recorded ground motions. It is found that while the temperature rise in the lead core generally increases with increasing magnitude and number of near fault ground motion velocity pulses, it decreases with larger distances from the fault. It is also found that bounding analysis method provides conservative (envelope) estimates of maximum isolator displacement and maximum isolator force for design purposes that fulfill its intended purpose. Copyright © 2012 John Wiley & Sons, Ltd.

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.

Identification of Lightning Disturbance in UHVDC Transmission Lines Using Correlation Degree Based on Short Time Window Data

In this paper, the simulation of ±800kV UHVDC transmission line in which fault lightning stroke and non-fault lightning stroke, line short circuit occur shows: because there is fault current lumped parameter access to earth during the fault lightning stroke or ground fault, the voltage waveform decrease suddenly and cross repeatedly the zero line in 5ms time window；There is no fault current accessing to earth during non-fault lighting stroke, the disturbance caused by lightning is too less than value of the pole voltage. The voltage waveform comes from the protect position change up and down around the direct voltage line and decays to the pole voltage line in the 5ms time window at last. In the case of the fault lightning or ground fault non-lightning, the correlation degree of transient component and pole voltage line in the time window is little. On the contrary, it is large during the non-fault lighting. Above this, the correlation degree is calculated using 5ms samples. This kind of algorithm can resist random noise effectively,calculating speed is very fast. Many PSCAD simulations show that the algorithm can identify lighting disturbance correctly.

An analytical study of residual displacements in RC bridge columns subjected to near-fault earthquakes

One of the important measures of post-earthquake functionality in bridges is residual displacement. This study focused on the analyses of six reinforced concrete bridge columns subjected to near fault ground motion using fiber elements to estimate the residual displacement. Another part of the study was aimed at determining the residual drift ratio limit beyond which bridge columns would be unsafe. The ability of models to estimate residual displacement was assessed by comparison of the results of the analyses to experimental data. It was determined that fiber element models were generally successful in estimating residual displacements. To determine residual displacement limits, a large number of reinforced concrete bridge columns with different geometries and steel ratios were analyzed subjected to truck loading. The residual moment capacity of the column and the moment due to the trucks and the P-Delta effects were used in the study. The residual drift ratio limit was found to be 1.2% or more for typical bridge columns.

Electric Distributed Constant Measurement of Long Steel Structures When Fault Ground Connection Happened

Electric Distributed Constant Measurement of Long Steel Structures When Fault Ground Connection Happened

The Effect of Soil Structure Interaction on the Seismic Response of Spatial Structure Subjected to the near Fault Ground Motion

This paper is to analyze the seismic response of the spatial structure supported by the column subjected to the near fault excitation. Three analysis models, such as fix base model, the SSI model without considering the radiation damping and the SSI model considering the radiation damping, are analyzed simultaneously subjected to the near fault excitation. The statistical analysis is carried out for the displacement at the mid-span, the axial force of the upper chord, the web and the bottom chord for the models.

An Improved Contact Model for Pounding Simulation of Base-isolated Highway Bridge

A modified Hertz model with nonlinear damping (Hertz damp model) is proposed for capturing the seismic pounding response of adjacent structures. Relevant parameters in the model are theoretically derived and numerically verified. Then, this model is used to simulate pounding response of a base-isolated highway bridge subjected to near fault ground motions. At the same time, nonlinear viscous dampers are installed between bridge decks for pounding prevention. The appropriate damping coefficient of the dampers can be found by parametric studies. It is shown that nonlinear viscous dampers are effective in reducing the relative displacement between bridge decks. At last, the hysteresis curve, the maximal damper force and stroke are used to demonstrate the behavior of nonlinear viscous dampers. The results indicate that satisfied viscous dampers can be produced to eliminate pounding according to the current manufacturing skills.

Seismic Response of Base-Isolated Structures with LRB and FPS under near Fault Ground Motions

Seismic response of structures in the vicinity of causative earthquake faults can be significantly different than those observed further away from the seismic source. In the near fault zone, ground motions are significantly influenced by the rupture mechanism and slip direction relative to the site and by the permanent ground displacement at the site resulting from tectonic movement. Forward directivity and fling effects have been identified by the seismologists as the primary characteristics of near fault ground motions. Because of the unique characteristics of the near-fault ground motions and their potential to cause severe damage to structures designed to comply with the criteria mostly based on far-field earthquakes, the estimation of seismic response of base-isolated structures for a project site close to an active fault should account for these special aspects of near fault ground motions. This paper investigates the seismic response of base-isolated structures with LRB and FPS isolators under near fault ground motions. A seismic evaluation of the building, isolated with the LRB and FPS, is performed using a nonlinear three-dimensional analytical model. The parametric study is concentrated on base shear, accelerations and displacements of isolated models. Large displacement and velocity pulses in records of near fault ground motions can significantly change the results of seismic response of base-isolated structures.

A method for computing interstory drift spectra with consideration of gravity effects

Vertical loads such as gravity may have an important influence on the seismic response of buildings. In this paper, the continuous shear-beam model is extended to study the seismic demand of shear buildings with consideration of the gravity load effect under near-field ground motions. An analytical solution of the free motion equation of as gravity shear beam model is provided in terms of a Bessel series. A method for computing interstory drift spectra is proposed. The interstory drift spectra for two near-field records with distinct pulses are presented to illustrate the effects of gravity and the damping ratio. The interstory drift spectra are also used to analyze the spectral characteristics of near fault ground motion during the 2008 Wenchuan earthquake. The effects of the gravity load ratio, damping ratio and higher modes are investigated and discussed.

Seismic Response of Buckling Restrained Braced Frames under Near Fault Ground Motions

Seismic Response of Buckling Restrained Braced Frames under Near Fault Ground Motions

근단층지반운동에 대한 상부구조 질량 변화에 따른 RC 교각의 응답분석

근단층지반운동은 진앙거리가 약 10 km 이내인 지역에서 관측되는 장주기 성분의 펄스형태를 갖는 지반운동으로서, 도심지에서 발생할 경우 미국 Northridge(1994), 일본 Kobe(1995), 터키 Izmit(1999), 중국 쓰촨성(2008), 아이티지진(2010) 등과 같이 매우 큰 피해를 야기시킨다. 이에 강진지역에서는 NFGM에 대한 많은 연구가 수행되었으나 우리나라와 같은 중약진 지역에서는 매우 미흡한 실정이다. 이 연구에서는 근단층 지반운동을 받는 철근콘크리트 교각의 거동과 내진성능을 평가하기 위하여 6기의 실험체에 대하여 진동대 실험을 수행하였다. 주요 실험 변수로는 심부구속 철근비와 상부질량 크기로서 진동대 실험 결과 심부구속철근비가 적거나 상부질량이 클수록 교각의 내진성능이 저하됨을 알 수 있었다. 또한 진동대 실험 결과를 분석하여 지진동을 받는 교각의 강성변화에 대한 심부구속철근비와 질량의 영향을 분석하였으며, 변위연성도와 강성과의 관계식을 제안하였다.