Seismic Analysis Model Research Articles

Improved equivalent bracing model for seismic analysis of mid-rise CFS structures

An improved equivalent bracing model of cold-formed steel shear wall with concrete-filled rectangular steel tube column as reinforced end studs was proposed, for seismic analysis of mid-rise cold-formed steel structures. The model can consider end stud's compression buckling and beam-column joint's behavior. Elements and parameters of the model were described, comparisons between the model and pinned equivalent bracing model were performed. The results show that: (1) compression buckling can be simulated by setting an axial spring at the bottom of end stud; the reinforced end stud can be defined as a composite section, and the sectional properties can be determined according to the principle of equivalent flexural rigidity; the spring's axial stiffness can be determined by the shear capacity Fp of the wall and its corresponding deformation Δa; (2) beam-column joint's behavior can be simulated by rotational spring, which can be defined by pinching4 model after its constitutive relationship has been determined by experiments or the moment-rotation prediction model proposed in this study; (3) the shear behavior of the wall can be represented by equivalent diagonal braces with nonlinear springs whose restoring force properties can be defined by pinching4 model according to the load-displacement hysteretic curve obtained from full-scale cyclic loading test or numerical simulation etc.; (4) the model can predict actual seismic performance of mid-rise cold-formed steel structure more accurately than pinned equivalent bracing model; moreover, a wall's yield limit directly affects the response modification factor R, the model can thereby provide more reliable design objectives for the structure.

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Subsurface fault geometries in Southern California illuminated through Full-3D Seismic Waveform Tomography (F3DT)

More precise spatial descriptions of fault systems play an essential role in tectonic interpretations, deformation modeling, and seismic hazard assessments. The recent developed full-3D waveform tomography techniques provide high-resolution images and are able to image the material property differences across faults to assist the understanding of fault systems. In the updated seismic velocity model for Southern California, CVM-S4.26, many velocity gradients show consistency with surface geology and major faults defined in the Community Fault Model (CFM) (Plesch et al. 2007), which was constructed by using various geological and geophysical observations. In addition to faults in CFM, CVM-S4.26 reveals a velocity reversal mainly beneath the San Gabriel Mountain and Western Mojave Desert regions, which is correlated with the detachment structure that has also been found in other independent studies. The high-resolution tomographic images of CVM-S4.26 could assist the understanding of fault systems in Southern California and therefore benefit the development of fault models as well as other applications, such as seismic hazard analysis, tectonic reconstructions, and crustal deformation modeling.

The Development of the Calculation Module of ANSYS and Its Engineering Application

The damping radiation effect of infinite foundation is considered by using the Damping Solvent Extraction Method (DSEM) based on the Finite Element Method, the nuclear plant and the infinite foundation is coupled based on solving the interaction force between interface and the displacement coordination assumption, the time domain seismic analysis model of nuclear plant foundation is established. In order to improve the practicability, the developed model is functionally embedded in the general finite element software ANSYS by using the secondary development function UPFs, APDL and UIDL. Finally, the influence of different frequency harmonic wave on the accuracy and efficiency is analyzed through numerical example, and the parameter range of the applicable engineering application is also put forward, and then, Seismic adaptability analysis of china’s one million kilowatt pressurized water reactor nuclear power plant foundation is carried out, the calculation results show good reliability and engineering practicability.

Winkler model for pile seismic analysis considering end constraints effects

Beam on nonlinear Winkler foundation (BNWF) analysis of pile foundation subjected to vertically propagating earthquake ground motions is presented in this paper. The BNWF is considered a simplified approach that is capable to model nonlinear soil-pile-structure interaction. Soil nonlinearity is simulated by p-y curves according to American Petroleum Institute (API) procedure. The analyses are carried out using the open source finite element platform OpenSees. Results are verified against centrifuge experiments and numerical finite element simulations published in the literature. In this paper pile tip and head constraints effects on bending moments and displacement responses are investigated. Three types of pile tip constraints are applied: floating, end bearing, and fixed supports. Pile top constraint is modeled as either free or fixed head. Three different earthquake ground motions are applied in the model. Effect of superstructure mass is investigated for the three considered earthquake records and the different assumed pile end and head constraints. The results indicate significant influence of pile tip and head constraints on pile bending moment and displacement responses. A significant effect of superstructure mass on the analyses results is also observed. The analyses show that earthquake record characteristics remarkably influence pile response behavior. Different earthquake records scaled to the same peak ground acceleration give different pile seismic responses.

3次元非線形FEM解析による杭集約モデルの杭周水平地盤ばねの算定式

1. Introduction Pile foundation response during earthquakes is strongly affected by nonlinear soil-pile foundation interactions. The damages to pile foundations during the 1995 Hyogo-ken Nanbu Earthquake and the 2011 Tohoku-Chiho Taiheiyo-Oki Earthquake were obviously attributed to nonlinear interactions of soil-pile foundation-superstructure. In addition, the vibration properties of soil and superstructure made the damages complicated. Therefore, in order to sophisticated seismic evaluation of the pile foundation, the nonlinear lateral soil resistance around pile should be properly evaluated and it should be incorporated in the seismic response analysis model. However, only few studies have been reported on the evaluation method of the nonlinear lateral soil resistance around pile. Therefore, the purpose of this study is to propose the simple formula to calculate the initial stiffness and the nonlinear lateral soil resistance around pile. The parameters of the simple formula are the shear wave velocity, the internal friction angle and the diameter of the pile. An additional purpose is to propose the simple formula to calculate the group factor of the nonlinear lateral soil resistance around pile for integrated pile model. 2. Method In this study, the nonlinear lateral soil resistance around piles is calculated using the soil-pile system modeled by 3D-FEM. When calculating the soil spring around piles, the piles are modeled as excavated soil and uniform forced displacement is given to the whole of the piles. The soil springs that are calculated are normalized in the diameter of the pile and the shear stiffness. The normalized soil springs are then approximated using a second-order logarithmic function. From the relationship between coefficient calculated by approximation and the internal friction, the simple formulas are determined. The group factors of the soil spring for the integrated pile model are calculated. The integrated pile model is, obtained by modeled as one pile which has integrate the mass and stiffness of all piles. The simple formulas are determined from the relationships between the group factor and two of the influencing factors. Two of the influencing factors are the number of piles and the spacing of the piles. 3. Conclusions The major findings obtained from this study are summarized as follows: (1) The simple formula for determining the initial stiffness of the soil spring is shown in Eq.(4). (2) The simple formula for determining the nonlinear lateral soil resistance around pile is shown in Eq.(5) and Eq.(8). The soil spring defined in the simple formula correspond to soil spring calculated by 3D-FEM. (3) The simple formulas for determining the group factor of the soil spring for the integrated pile model are shown in Eq.(10), Eq.(11) and Eq.(12). The group factors defined in the simple formula correspond these calculated by 3D-FEM. (4) The calculation formulas proposed in this study are greatly useful in modeling pile foundation for the seismic response analysis.

The role of the Modal Assurance Criterion in the interpretation and validation of models for seismic analysis of architectural complexes

The seismic vulnerability assessment of historical buildings is usually a very complex task because of the large number of uncertainties in the characterization of their structural behaviour. The unique structural configurations, the adoption of old construction techniques and the presence of stratified structural modifications occurred over the centuries make the definition of an appropriate and reliable numerical model very challenging. The available analysis approaches distinguish the local response of selected macro elements from the global response of the structure. The problem of discriminating if the investigated structure shows a global behaviour or a local response has been often reported in the literature. However, the definition of a quantitative measure to discriminate the global modes from the local ones and, in the latter case, the associated macro elements, is currently missing.The Modal Assurance Criterion is a vector correlation index frequently used in experimental dynamics to quantify the similarity of mode shapes. In the present paper, it is used to define an original and quantitative approach to the discrimination between local and global modes. Results of application of the proposed procedure to an explanatory case study are reported, pointing out how the proposed method can guide towards the selection of the most appropriate analysis method.

A Markov model for seismic hazard analysis along the Hellenic subduction Zone (Greece)

A homogeneous finite–state discrete–time Markov model is applied for the earthquake occurrence in the Hellenic Subduction Zone (Greece), a region accommodating high seismic activity, being a key structure from a seismotectonic point of view. An attempt is made to provide a stochastic representation of the earthquake process and to assess the seismic hazard through the application of the Markov model. The model is applied on a complete data sample comprising strong () eart h-quakes that occurred in the study area since 1911 up to present. The continuous magnitude scale is divided into appropriate intervals to specify discrete states of the model. As the stochastic behavior of the model is governed by its transition probability matrix, we firstly estimate its well–known maximum likelihood estimator. The estimation of the transition probability matrix leads to the estimation of important indicators of the Markov chain, including hitting times and failure rate functions. The mean number of steps for the first occurrence of an anticipated earthquake (belonging to the class with the stronger events, which we are more interested in) is estimated along with its variance. In a next step, we calculate the confidence interval of the aforementioned estimators.

Seismic Analysis of Confined Masonry Shear Walls Using the Wide Column Model

Confined Masonry (CM) structural system consists of masonry walls enclosed by reinforced concrete (RC) confining elements (tie-columns and tie-beams) and is usually supported by reinforced concrete floors and roof. This technology has been widely used for construction of low-and medium-rise buildings in Latin America, Europe, South Asia, and Middle East, and it has a proven record of good performance in damaging earthquakes. CM construction is not currently practiced in India and is not addressed by Indian design codes. Seismic analysis of CM wall panels can be performed using Wide Column Model (WCM), also known as Equivalent Frame Model. WCM is a macro model where a wall structure and the supporting floors and roof are idealized as a bare frame. CM walls can be modelled as wide columns with transformed section properties accounting for composite action of masonry and RC tie-columns. Beams in these bare frames have rigid segments simulating the effect of wall stiffness, and flexible segments that simulate the effect of floor and roof slabs. WCM has been recognized as a viable model for seismic analysis of CM buildings in Latin American countries, however this model is not well known in India. The results presented in this paper are based on linear elastic analyses of typical multi-storey CM solid walls and walls with openings. The output parameters include shear forces, bending moments, stiffness, and lateral displacements. A comparison of the results obtained using the WCM and the Finite Element Method (FEM) has been presented. WCM can be useful for seismic analysis of CM buildings since it does not require significant computational effort and can be applied using a variety of software packages.

A theoretical strut model for severe seismic analysis of single-layer reticulated domes

This paper focuses on proposing an efficient theoretical strut model to predict the post-buckling behaviors of members of single-layer reticulated domes under severe earthquake. The model was established based on finite element (FE) method and it can well reflect the performance of individual member during the complete loading period by using one element, especially the inelastic post-buckling behaviors. By using the model, the failure behavior of single-layer reticulated domes under severe earthquake can be well captured. With the help of this model, the interaction between individual member buckling and structural global instability can be accounted, and then the influence on plastic internal forces redistribution due to the degradation of bearing capacity of members under large displacement can be well depicted. The model is suitable for severe seismic analysis as it involves a wider range of strain than the existing phenomenological models. At last, the efficient model is verified by several experiments and good agreement is found between the simulated and experimental results.

Resilience of Civil Infrastructure by Optimal Risk Mitigation

This paper puts forward a framework for optimal mitigation of regional risk to enhance the resilience of civil infrastructure. To meet this objective, probabilistic models, methods, and software are developed and applied. The work is conducted within a new reliability-based approach, in which reliability methods compute risk. This contrasts several contemporary approaches for risk analysis. Risk, in this context, denotes the probability of exceeding monetary loss. Evaluating such probabilities requires probabilistic models for hazards, response, damage, and loss. This motivates the following contributions in this paper. First, a new computer program is developed that is tailored to conduct reliability analysis with many interconnected probabilistic models. It orchestrates the interaction of models through an object-oriented architecture. Second, a library of probabilistic models for regional seismic risk analysis are developed. The library includes new models for earthquake location and magnitude and building response, damage, and loss. Third, probabilistic methods for multi-hazard risk analysis are developed and applied in a large-scale regional analysis. The results are cost exceedance probabilities and insights into the seismic risk of the region. Finally, sensitivity measures are developed to identify the buildings whose retrofit yields the most reduction in regional risk, i.e., the most resilience of the region.

Characterizing the Kathmandu Valley sediment response through strong motion recordings of the 2015 Gorkha earthquake sequence

We analyze strong motion records and high-rate GPS measurements of the M 7.8 Gorkha mainshock, M 7.3 Dolakha, and two moderate aftershock events recorded at four stations on the Kathmandu basin sediments, and one on rock-outcrop. Recordings on soil from all four events show systematic amplification relative to the rock site at multiple frequencies in the 0.1–2.5Hz frequency range, and de-amplification of higher frequencies (>2.5–10Hz). The soil-to-rock amplification ratios for the M 7.8 and M 7.3 events have lower amplitude and frequency peaks relative to the ratios of the two moderate events, effects that could be suggestive of nonlinear site response. Further, comparisons to ground motion prediction equations show that 1) both soil and rock mainshock recordings were severely depleted of high frequencies, and 2) the depletion at high frequencies is not present in the aftershocks. These observations indicate that the high frequency deamplification is additionally related to characteristics of the source that are not captured by simplified ground motion prediction equations, and allude to seismic hazard analysis models being revised – possibly by treating isolated high frequency radiation sources separately from long period components to capture large magnitude near-source events such as the 2015 Gorkha mainshock.

On the Safety and Performance Demonstration Tests of Prototype Gen-IV Sodium-Cooled Fast Reactor and Validation and Verification of Computational Codes

Abstract The design of Prototype Gen-IV Sodium-Cooled Fast Reactor (PGSFR) has been developed and the validation and verification (V&V) activities to demonstrate the system performance and safety are in progress. In this paper, the current status of test activities is described briefly and significant results are discussed. The large-scale sodium thermal-hydraulic test program, Sodium Test Loop for Safety Simulation and Assessment-1 (STELLA-1), produced satisfactory results, which were used for the computer codes V&V, and the performance test results of the model pump in sodium showed good agreement with those in water. The second phase of the STELLA program with the integral effect tests facility, STELLA-2, is in the detailed design stage of the design process. The sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger performance test, the intermediate heat exchanger test facility, and the test facility for the reactor flow distribution are underway. Flow characteristics test in subchannels of a wire-wrapped rod bundle has been carried out for safety analysis in the core and the dynamic characteristic test of upper internal structure has been performed for the seismic analysis model for the PGSFR. The performance tests for control rod assemblies (CRAs) have been conducted for control rod drive mechanism driving parts and drop tests of the CRA under scram condition were performed. Finally, three types of inspection sensors under development for the safe operation of the PGSFR were explained with significant results.

A finite element model for seismic response analysis of deformable rocking frames

SummaryA new finite element model to analyze the seismic response of deformable rocking bodies and rocking structures is presented. The model comprises a set of beam elements to represent the rocking body and zero‐length fiber cross‐section elements at the ends of the rocking body to represent the rocking surfaces. The energy dissipation during rocking motion is modeled using a Hilber–Hughes–Taylor numerically dissipative time step integration scheme. The model is verified through correct prediction of the horizontal and vertical displacements of a rigid rocking block and validated against the analytical Housner model solution for the rocking response of rigid bodies subjected to ground motion excitation. The proposed model is augmented by a dissipative model of the ground under the rocking surface to facilitate modeling of the rocking response of deformable bodies and structures. The augmented model is used to compute the overturning and uplift rocking response spectra for a deformable rocking frame structure to symmetric and anti‐symmetric Ricker pulse ground motion excitation. It is found that the deformability of the columns of a rocking frame does not jeopardize its stability under Ricker pulse ground motion excitation. In fact, there are cases where a deformable rocking frame is more stable than its rigid counterpart. Copyright © 2016 John Wiley & Sons, Ltd.

Nonlinear dynamic analysis and seismic fragility assessment of a corrosion damaged integral bridge

Purpose In this paper the impact of corrosion of reinforcing steel in RC columns on the seismic performance of a multi-span concrete integral bridge is explored. A new constitutive model for corroded reinforcing steel is used. This model simulates the buckling of longitudinal reinforcement under cyclic loading and the impact of corrosion on buckling strength. Cover concrete strength is adjusted to account for corrosion induced damage and core concrete strength and ductility is adjusted to account for corrosion induced damage to transverse reinforcement. This study evaluates the impact which chloride induced corrosion of the reinforced concrete columns on the seismic fragility of the bridge. Fragility curves are developed at a various time intervals over the lifetime. The results of this study show that the bridge fragility increases significantly with corrosion. Design/methodology/approach This paper firstly evaluates the impact which chloride induced corrosion of the columns has on bridge fragility. Finally, fragility curves are developed at various time intervals over the lifetime of the bridge. The results of this study show that the bridge fragility increases significantly with corrosion. Findings 1) It was found that columns dominate the system fragility at all levels of deterioration. Therefore, it highlights the importance of good column design in terms of both seismic detailing and durability for this integral bridge type. 2) In terms of foundation settlement coupled with corrosion, it was found that settlements on the order of the discrete levels adopted for this study increased the system fragility at the slight, moderate and extensive damage states but their impact at the complete damage states is negligible. 3) Ageing considerations are currently neglected in widespread regional risk assessment and loss estimation packages for transport infrastructure. The result of this study provides a methodology that enables bridge managers and owners to employ in seismic risk assessment of existing aging bridges. Originality/value The modelling technician developed in this paper considers the impact of detailed corrosion damaged of RC column on nonlinear dynamic response and fragility of a corroded integral bridge under earthquake loading. The current modelling technique is the most comprehensive 3D fibre element model for seismic analysis and risk assessment of corroded bridges.

Collapse risk and residual drift performance of steel buildings using post-tensioned MRFs and viscous dampers in near-fault regions

The potential of post-tensioned self-centering moment-resisting frames (SC-MRFs) and viscous dampers to reduce the collapse risk and improve the residual drift performance of steel buildings in near-fault regions is evaluated. For this purpose, a prototype steel building is designed using different seismic-resistant frames, i.e.: moment-resisting frames (MRFs); MRFs with viscous dampers; SC-MRFs; and SC-MRFs with viscous dampers. The frames are modeled in OpenSees where material and geometrical nonlinearities are taken into account as well as stiffness and strength deterioration. A database of 91 near-fault, pulse-like ground motions with varying pulse periods is used to conduct incremental dynamic analysis (IDA), in which each ground motion is scaled until collapse occurs. The probability of collapse and the probability of exceeding different residual story drift threshold values are calculated as a function of the ground motion intensity and the period of the velocity pulse. The results of IDA are then combined with probabilistic seismic hazard analysis models that account for near-fault directivity to assess and compare the collapse risk and the residual drift performance of the frames. The paper highlights the benefit of combining the post-tensioning and supplemental viscous damping technologies in the near-source. In particular, the SC-MRF with viscous dampers is found to achieve significant reductions in collapse risk and probability of exceedance of residual story drift threshold values compared to the MRF.

Shear Deformation and Sliding-Based Fiber Beam-Column Model for Seismic Analysis of Reinforced Concrete Coupling Beams

AbstractConventional RC coupling beams have been widely used as key energy-dissipation components in frame-core tube structural systems for high-rise buildings. A model with sufficient efficiency, accuracy, and practicality is urgently needed for the seismic analysis of high-rise structures. According to test results, both the shear deformation and shear sliding mechanisms are critical to assessing the seismic performance of coupling beams. However, available shear models for beams and columns cannot give satisfactory results in modeling both mechanisms in finite-element analysis (FEA). To address this problem, this study takes into account the section shear force–shear strain and shear sliding laws in the traditional displacement-based fiber beam-column element, which is implemented into a general FEA package. A new section shear force–shear strain law, which can consider the pinching effect, strength and stiffness deterioration, shear capacity degradation, and arbitrary complex loading path is first pro...

A simplified 3 D.O.F. model of A FEM model for seismic analysis of a silo containing elastic material accounting for soil–structure interaction

The purpose of this study is the evaluation of dynamic behavior induced by seismic activity on a silo system, containing bulk material, with a soil foundation. The interaction effects between the silo and bulk material, as well as the effects produced between the foundation of the silo and the soil, were taken into account. Proposed simplified approximation, as well as the finite model, were used for analysis. The results, from the presented approximation, were compared with a more rigorous obtainment method. Initially, the produced simplified approximation, with elastic material assumption for the grain, could determine the pressures on the dynamic material along with displacements along the height of the silo wall and base shear force, etc., with remarkable precision. Some comparisons, via a change of soil and/or foundation conditions, were also made regarding the seismic pressure of the dynamic material pressure, displacement and base shear forces for both squat and slender silos. Comparing the analytical predictions to results from the numerical simulations produced good results. It can be concluded that the model can be used effectively to perform a broad suite of parametric studies, not only at the design stage but also as a reliable tool for predicting system behavior under the limit state of the system. The results and comprehensive analysis show that displacement effects and base shear forces generally decreased when soil was softer; however, soil structure interaction (SSI) did not have any considerable effects on squat silos and therefore need not be taken into practice.

Post-earthquake assessment and management for infrastructure systems: learning from the Canterbury (New Zealand) and L’Aquila (Italy) earthquakes

Both the April 6, 2009 L’Aquila (Italy) earthquake, and the 2010–2011 Canterbury (New Zealand) earthquake sequence provided unprecedented opportunity to enhance the understanding on earthquake performance of infrastructure systems, and to analyse still-opened issues affecting the post-earthquake assessment and management of infrastructure. This paper provides a succinct and holistic overview on the physical and functional performances of the gas, water, waste water, road and electric networks (this one to a limited extent for the L’Aquila case-study), following the moment magnitude (Mw) 6.3 L’Aquila earthquake, and two main events of the Canterbury earthquake sequence, namely: the Mw 7.1 September 4, 2010 Darfield and the Mw 6.2 February 22, 2011 Christchurch earthquakes. A structured format, based on internationally recognised taxonomies and damage descriptors, is introduced to present the assets and to report on the earthquake-induced physical impacts for both above-ground and underground components. Functional impacts, interdependency issues and resilience attributes observed during the emergency management and recovery phases for the same infrastructure systems are furthermore discussed in the paper. It is envisaged that the data and overview on the seismic performance and management of infrastructure systems presented in the paper can be used to test the effectiveness of existing models and to inform the development of new models for seismic risk assessment and resilience analysis. Also, the structured framework presented within this paper can form the basis for defining specific and standardised survey tools for post-earthquake assessment of infrastructure systems.

A GLE-based model for seismic displacement analysis of slopes including strength degradation and geometry rearrangement

Seismic performance of natural slopes, earth structures and solid-waste landfills can be evaluated through displacement-based methods in which permanent displacements induced by earthquake loading are assumed to progressively develop along the critical sliding surface as a result of transient activation of plastic mechanisms within the soil mass. For sliding mechanisms of general shape the earthquake-induced displacements should be computed using a model that provides a closer approximation of sliding surface. When large permanent displacement are induced by seismic actions, due to substantial shear strength reduction, and significant changes in ground surface occur, an improved estimate of permanent displacement can be obtained using a model which accounts for shear strength reduction and mass transfer between adjacent portions of the slope resulting from geometry changes of ground surface during the seismic event.In this paper, a GLE-based model is proposed for seismic displacement analysis of slopes that accounts for shear strength degradation and for geometry rearrangement. Model accuracy is validated against experimental results obtained from shaking table tests carried out on small scale model slopes. Comparison of computed and experimental results demonstrates the capability of the proposed approach in capturing the main features of the observed seismic response of the model slopes.