To investigate the differences in east-west lithospheric deformation in the Qaidam Basin, we present thermo-rheological models of two profiles across the western Qaidam Basin (WQB) and eastern Qaidam ...Basin (EQB). The differences in east-west geodynamic deformation styles are also described, involving GPS motions, focal mechanisms (P axes), seismic anisotropy (SKS-wave splitting), and low-velocity zones (LVZs). The WQB is characterized by a warm destabilized cratonic basin with a weak lower crust, and the rheological structure changes from a rather weak crème brûlée-1 regime into a strong jelly sandwich-1 regime, from the Altyn-Qaidam boundary to the northeastern corner of the WQB. Combined with the limited distribution of the LVZs and the strong crust-mantle decoupling revealed by the unmatched pattern between P axes (N20ºE) and SKS-wave splitting (N110°E), the crust-mantle mixing related to the under-thrusting of the Tarim Basin along the Altyn Tagh Fault is suggested as the primary tectonic dynamic inducement of the destabilized WQB craton, which weakens the lithospheric strength greatly and contributes to the shallow brittle deformation. However, the EQB performs as a typical cold and rigid cratonic basin characterized by a jelly sandwich-2 rheological regime, which is sufficiently strong to maintain crust-mantle coupling. The LVZs beneath the EQB revealed by recent wide-angle seismic profiles have only a small effect on the
lithospheric
strength drop. The EQB could be regarded as a solid basin, anchored in the NE Tibetan Plateau, which shows a strong resistance to NE extrusion of the weak plateau material, leading to clockwise rotation.
The acoustic fluid‐structure interaction (FSI) formulation is a practical numerical approach for the seismic analysis of fluid‐filled tanks. However, there are no verification and validation studies ...reported in the literature that demonstrate the ability of an acoustic FSI numerical model to predict responses important to structural and mechanical design for intense translational and rotational earthquake inputs. Herein, an acoustic FSI formulation is implemented in the open‐source Multiphysics Object‐Oriented Simulation Environment (MOOSE), and is formally verified and validated using analytical solutions and code‐to‐code verification, and experimental data, respectively. The analytical solutions are for small amplitude, unidirectional seismic inputs. The code‐to‐code verification utilizes a previously verified and validated Arbitrary Lagrangian‐Eulerian (ALE) numerical model in the commercial finite element code LS‐DYNA. The validation studies utilize a comprehensive data set assembled from results of 3D earthquake‐simulator tests of a fluid‐filled vessel. The acoustic numerical model in MOOSE is verified and validated for hydrodynamic pressures and support reactions except for cases that involve significant convective response. For small amplitude inputs, numerically predicted wave heights match those of the analytical solutions. The numerical model is not verified and validated for wave height calculations under intense 3D seismic inputs. The run times for the acoustic FSI simulations in MOOSE are an order of magnitude, or more, shorter than for the corresponding ALE simulations in LS‐DYNA. The utility of the MOOSE acoustic FSI implementation is demonstrated by seismic analysis of a building equipped with a fluid‐filled, advanced nuclear reactor.
•We developed a novel seismic analysis framework (SAF) for offshore wind turbines.•We used target spectrum matching technique to adjust the ground motions.•We examined three distinct flexible ...foundation concepts.
This paper presents an investigation on the sensitivity of flexible foundation models of offshore wind turbines subjected to earthquake loadings. A novel seismic analysis framework (SAF) is developed and implemented in an open source aero-hydro-elastic analysis tool, “FAST”, for accurately modelling the effects of seismic loadings on offshore wind turbines. SAF has been validated through comparisons against experimentally validated numerical tools, GH Bladed and NREL Seismic. The behaviours of three flexible foundation models, namely, the apparent fixity (AF), coupled springs (CS) and distributed springs (DS) methods, subjected to earthquake loadings have been examined in relation to a fixed foundation. A total of 224 fully coupled nonlinear simulations of the foundation models are performed using a dataset of 28 earthquake records which are scaled using the target spectrum matching technique to represent the actual seismic effects of the selected sites. The results reveal that the AF model appropriately reflects realistic situations in comparison to the CS model. In addition, the amplitudes of vibration induced by the earthquake loadings are larger for flexible foundations compared to the rigid foundation. The main contribution to the out-of-plane bending moment of the support structure at the mudline comes from the wind loading for all the foundation models. This study has also found that the 2nd flap mode of blade is activated by the earthquake loadings for the AF and DS models but not for the rigid and CS models. As a result, the peak blade-root bending moment is found to be more sensitive to pseudo spectral acceleration (PSA) for the AF and DS models. Furthermore, the peak tower-top displacement and mudline bending moment increase linearly with PSA for all the examined models. This study contributes to the evaluation of the wind turbine responses subjected to earthquakes or combined multi-hazard loadings in the operational state.
This research work is aimed at studying the seismic behavior of a lightly reinforced precast concrete wall system that is typical in northern European regions characterized by little or no natural ...seismicity. To this end, the authors tested pseudostatically, under in-plane cyclic loads, six full-scale panels representative of those commonly used for low- to mid-rise precast residential multi-unit terraced buildings in the Groningen region. Damage mechanisms and hysteretic capacity curves of wall assemblies with and without openings in their layout are presented so as to examine the seismic performance of these panels and their connections at progressively increased drift amplitudes. All specimens collapsed by a premature shear failure of their panel-to-panel joints, demonstrating that this type of connection is the weakest link of the wall system tested. The paper also discusses the main trends observed in terms of stiffness degradation and energy dissipation with the number of applied cycles and the imposed drift level. Furthermore, the authors carried out an additional set of push-pull tests of four panel subassemblies with variable wall thickness, with a view to specifically investigate the seismic response of this type of joint under asymmetric out-of-plane loading. Test results show that this type of connection system is characterized by visible pinching and low energy dissipation capacity. Based on this large campaign of experimental tests, a simple and computationally efficient numerical model is proposed for large scale seismic fragility analysis of precast terraced structures built with this particular technology.
•A series of BRB-RCFs and the corresponding bare frames and BRB systems were designed.•The effectiveness of BRBs in BRB-RCFs with different numbers of stories and story shear ratios p was ...assessed.•The effect of BRBs on the overall performance of RC frames was investigated.
Due to the different mechanical behavior of buckling-restrained braces (BRB) and reinforced concrete frames (RCF), their coupled work in dual structural systems (BRB-RCFs) is complicated, especially their earthquake responses. A series of structures with different numbers of stories and different story shear ratios equipped with BRBs were designed and tested in simulation. Static nonlinear pushover analysis and cyclic loading were simulated to investigate the interaction between BRBs and RCFs. The capacity curves, the story distributions of shear force, axial forces on the columns, strength and stiffness, lateral displacement, interstory drift ratios and hysteresis behavior were evaluated. Adding BRBs in a RCF was found to alter the story distribution of shear force and to significantly increase the axial demands on RC columns in BRB-braced bays. The yield strength, initial elastic stiffness and energy dissipation capacity of BRB-RCF structures are all greater than the sum of the contributions from the braces and the frames independently. That synergistic interaction cannot be ignored in design.
•A time-domain model simulating the water-cylinder interaction is presented.•The exact dynamic stiffness relationship is obtained based on the exact solution.•The relationship is transformed into a ...high-order approximation in time domain.•The proposed model is implemented into software ABAQUS by the UEL subroutine.
Seismic analysis of many offshore structures is the three-dimensional (3D) water-cylinder dynamic interaction. The cylinder is commonly modeled as a beam by finite elements. If the 3D infinite water layer is also modeled by the finite elements, the high computational costs are unacceptable in engineering practice. Therefore, an accurate and efficient time-domain model is proposed to replace the 3D infinite water layer in the water-cylinder interaction analysis. Firstly, based on the frequency-domain analytical solution, the exact dynamic stiffness relationship between the hydrodynamic pressure and the structural displacement is constructed on the water-cylinder interface. Secondly, this relationship is transformed into a high-order approximation in time domain by using the temporal localization method. Thirdly, the high-order approximation is represented as a mechanical model system consisting of the spring, dashpot and mass elements, which is implemented into the finite element software ABAQUS by the user element subroutine. Finally, numerical examples are given to indicate the effectiveness of the proposed time-domain model and investigate the effect of hydrodynamic pressure on the seismic responses of the cylinder.
Identification of inversion tectonics and inverted structures is very important in petroleum exploration and production due to the positive or negative impacts they can exert on the hydrocarbon ...traps. In order to characterize the occurrence of multi-phase inversion tectonics and its effect in the Rag-e-Sefid Oilfield, located in the southern Dezful Embayment (SW Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Rag-e-Sefid anticline is created from multiple fault-propagation folds. The final shape and geometry of the Rag-e-Sefid anticline are affected by the Rag-e-Sefid and Nourooz-Hendijan-Izeh Faults activity. The deformation history in the north-western part of the Rag-e-Sefid anticline is older than the south-eastern part of it. The Rag-e-Sefid Fault set in the north-western and south-eastern parts of the Rag-e-Sefid Oilfield experienced activity at least during seven and four tectonic phases, respectively. Multiple fault-propagation folding and the fold axis rotation in the north-western part of the Rag-e-Sefid anticline controlled by the presence of several décollement surfaces and the occurrence of inversion tectonics along the pre-existing basement structures. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault and the Rag-e-Sefid Fault set in the north-western part of the Rag-e-Sefid Oilfield occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. The inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the southern Dezful Embayment. Based on the hydrocarbon migration in these regions from the Late Miocene to the present day, the N-S trending (Pan Africa trend) north-western part of the Rag-e-Sefid anticline has a larger share of oil and gas compared to the NW-SE trending (Zagros trend) south-eastern part. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on the hydrocarbon traps development in the foreland of a collisional orogen.
Earthquakes are not isolated events and, typically, dominated by a larger-magnitude excitation (Mainshock – MS) and many smaller-magnitude motions (Aftershock – AS). Most often, such destructive ...events bring more damage than a single strong motion. Nowadays, many existing non-seismic designed RC structures are classified as either functional-obsolete or sub-standards. The seismic performance of these aged structures can be even more critical if some phenomena, such as corrosion, occur. The present study aimed at evaluating the seismic vulnerability of typical existing RC structures subjected to earthquake sequences and various levels of corrosion. A probabilistic approach via the fragility analysis, and three different seismic intensity measures (IM), was carried out. A four-story RC building was used as a testbed for Incremental Dynamic Analyses (IDA) via an advanced Finite Element approach. Twenty as-recorded natural motions were selected from international databases and inserted into the three-dimensional model. A new seismic intensity measure was provided and compared to the world-wide accepted peak ground acceleration (PGA) and spectral acceleration at the first natural period of the structure (Sa(T1)); the modified spectral acceleration intensity (MASI). The limit states of limited damage (LD) and severe damage (SD) were considered as capacity thresholds. The outcomes of this numerical investigation showed that multiple excitations and corrosion significantly affect the seismic vulnerability of the investigated building; MASI appeared to be the most effective intensity measure to assess the seismic fragility of corroded RC buildings; modern seismic-based technical codes are no longer conservative for such detrimental phenomena.
•Newly formulated intensity measure based on the modified acceleration spectral intensity for RC corroded buildings.•Robust seismic fragility analyses of existing RC buildings with smooth bars subjected to various levels of corrosion.•Response of corroded RC buildings to sequential mainshock-aftershocks motions.
Abstract
Pseudostatic analysis can be an efficient approach to evaluating the dynamic response of structures for a preliminary design. In this paper, we present a pseudostatic method based on a ...pushover analysis to assess the seismic performance of bridge piers supported by rocking‐governed shallow foundations. The method has two stages. In the first stage, the capacity spectrum method (CSM) is applied to evaluate the maximum acceleration and displacement response of the bridge system. To have an appropriate system damping ratio in the CSM, we propose a method to consider various earthquake energy dissipation mechanisms for the pier and foundation. In the second stage, the footing settlement is evaluated based on the maximum footing rotation; an incrementally cyclic pushover analysis with a fixed footing rotation increment is performed to estimate the footing settlement. Examples are presented to demonstrate the applicability of the proposed method and the results of the proposed method are compared with the dynamic analysis results. Compared with the conventional CSM, the proposed method improves the estimation of system damping and can estimate the settlement after earthquakes.
PDF
