Results Of Response History Analysis Research Articles

A simplified analysis method for estimating the peak responses of recentering structures with viscous damping systems

AbstractRecentering structure with a viscous damping system is an emerging structural system with remarkable seismic resilience. This system can exhibit sufficient energy‐dissipating capacity during a major earthquake and eliminate the residual deformation through recentering mechanism afterward. However, the seismic response of the considered system is still confusing due to its complex dynamic behavior. Thus, it is hard to estimate the peak responses of the system during a major earthquake. This study proposes a simplified analysis method for estimating the peak responses of recentering structures with viscous damping systems based on an equivalent two‐stage substitute model. Considering the considerable strain energy of recentering structures during vibrations, this method proposes to employ effective stiffness based on the equal‐energy principle in an equivalent two‐stage substitute model. Based on this concept, corresponding equations are derived for capturing the peak transient responses of the considered system. Results of response history analysis validate that the proposed method can reasonably estimate maximum relative displacement, relative velocity, and absolute acceleration. Given its satisfactory accuracy, this method is promising while conducting seismic design of recentering structures with viscous damping systems.

Mid-height seismic isolation of equipment in nuclear power plants: Numerical simulations and design recommendations

Seismic isolation can mitigate earthquake demands on safety-class equipment and is being considered for application to some advanced nuclear reactors. For tall, slender vessels that could represent an advanced reactor, a steam generator or a heat exchanger, mid-height seismic isolation has been shown to be beneficial and practical. This paper focuses on numerical modeling of a mid-height isolated tall, slender vessel with two primary goals 1) investigate and quantify the benefits of mid-height seismic isolation for a range of support structure stiffnesses, isolation systems, and seismic inputs, and 2) provide analysis and design recommendations for isolation of safety-class equipment. Results of response-history analysis were in good agreement with experimental measurements and demonstrated that mid-height isolation can substantially reduce seismic demands on tall, slender vessels for a range of support structure stiffnesses, isolation systems, and seismic inputs. Importantly, the reductions in horizontal spectral accelerations in the mid-height isolated vessel from the non-isolated condition were not affected by the stiffness of the support structure. Recommendations are made for analysis and design of isolated equipment and testing of isolators used for equipment protection in nuclear facilities, which are also applicable to other industries.

Identification and Calibration of Advanced Hysteresis Models for Recycled Rubber–Fiber-Reinforced Bearings

Several studies have investigated the feasibility of reducing the implementation cost of base isolation. In this optic, recycled rubber–fiber-reinforced bearings (RR–FRBs) represent a suitable solution for structures in developing countries. Such devices can be produced using simple manufacturing procedures at a limited cost with respect to conventional isolators. Full-scale tests on RR–FRBs featured energy dissipation values similar to those associated with high-damping natural rubber bearings (HDRBs). Equivalent viscous damping, ranging from 10 to 15%, resulted from testing of RR–FRBs, with poor degradation after cyclic loading. On the other hand, a sensible softening response, associated with the axial–shear interaction, which is much more significant compared to that exhibited by HDRBs, was observed. As a result, the numerical description of the cyclic behavior of the RR–FRBs appears to be more challenging than that of HDRBs. In past studies, simple bilinear hysteresis models were adopted to describe the cyclic behavior of low-cost rubber bearings, thus completely neglecting the P-delta effects which significantly influence the dynamic behavior of such bearings. In this paper, advanced hysteresis numerical models, able to capture the nonlinear response of RR–FRBs, were examined and properly calibrated using a powerful optimization technique, the differential evolution algorithm. Preliminary results of the numerical analyses, performed in OpenSees, were described and compared with those of experimental tests on low-cost rubber bearings. The findings of this study represent the first step of a characterization procedure aimed to provide an accurate representation of the dynamic behavior of these particular bearings. Obviously, additional studies are needed to compare results of response history analyses with those of experimental tests for real structures on RR–FRBs. In this optic, the present paper, along with further studies, could provide a new impulse for the application of low-cost rubber-based devices in current practice.

Generalized response spectrum analysis based computational morphogenesis for metal gridshells with buckling-restrained braces subjected to seismic loading

Structural morphogenesis is widely used as a parametric tool to find an optimal structural shape of shell structures for a prescribed objective function and a given design load. However, the current optimization methods are limited to finding a geometry under only a specific static load like the dead load or an equivalent static seismic load for predefined geometrical shapes, and so can not be applied to free-form gridshells. This poses a challenge to achieving an efficient free-form shell structure in high seismic hazard areas. This paper aims to resolve this by presenting a computational morphogenesis method to obtain form-found shell structures by considering the dynamic seismic loads and the response reduction effects of seismic energy-dissipating devices using generalized response spectrum analysis. The method was applied to optimize the buckling-restrained brace layouts on target spherical metal gridshell structures with different diameter-to-height ratios. The resulting form-found structures had an efficient roof geometry, along with an efficient damper layout (to prevent member buckling and the dropout of finishing materials). Dampers were found to be more efficient if placed in the (relatively heavy) supporting structure instead of the roof, and a flattened but locally bulged roof shape proved to be the most efficient in mitigating the seismic response. The generalized response spectrum analysis significantly reduced the computation time while evaluating the displacement response with sufficient practical accuracy, although it slightly underestimates the acceleration response if compared to the conventional nonlinear response history analysis results.

Machine Learning for Enhanced Regional Seismic Risk Assessments

The ability to conduct accurate regional seismic risk assessments is key to informing a risk-reduction policy and fostering community resilience. This paper presents a machine learning-based framework to predict a building’s postearthquake damage state using structural properties and ground motion intensity measures as model inputs. The machine learning techniques assessed, namely, logistic regression, k-nearest neighbors, decision tree, random forest, AdaBoost, and gradient boosting, are trained using a dataset of nonlinear response history analysis results from 36 detailed structural models of modern reinforced concrete shear wall buildings ranging from four to 24 stories and subjected to approximately 500 ground motion records with a range of shaking intensities. The results indicate that the gradient boosting classifier is the most efficient algorithm by achieving a prediction success (F1-score) of 87%. The proposed framework also leverages synthetic data samples to support the prediction of severe damage state instances, that is, collapse. The percentage of observed collapse cases correctly classified by the gradient boosting algorithm is increased from 76% to 93% when synthetic data are also used for training. The framework is implemented in a portfolio of reinforced concrete shear wall buildings across the Metro Seattle region to quantify earthquake-induced damage and collapse risk. The framework shows great potential for enhancing regional seismic risk assessments by leveraging datasets of detailed nonlinear response history analysis results.

Effects of design and seismic parameters on horizontal displacement responses of sloped rolling‐type seismic isolators

The influences of design parameters, including sloping angles of bearing plates and friction damping forces, together with seismic parameters, including corner periods and effective peak accelerations that are usually used for characterizing a design response spectrum, on the maximum horizontal displacement responses of sloped rolling-type seismic isolators are numerically discussed in this study. Because the seismic isolators feature the constant acceleration control (or zero postelastic stiffness) performance, the equivalent linear model conventionally adopted in the equivalent lateral force procedure might not be adequate for predicting their maximum horizontal displacement response under a given seismic demand. Therefore, considering a small number to a large number of coefficients, several statistics-based empirical formulas that are able to approximate their maximum horizontal displacement response are proposed. Not only the accuracy but also the conservative property of the proposed empirical formulas are discussed by comparing their predictions with the nonlinear response history analysis results. To efficiently determine the horizontal displacement capacity of sloped rolling-type seismic isolators during the preliminary design stage, the statistics-based empirical formula considering a reasonable number of coefficients is recommended.

Seismic response analysis of single-degree-of-freedom yielding structures with fluidic self-centering systems

Analyses of single-degree-of-freedom yielding structures with fluidic self-centering systems are performed for a wide range of parameters and the results are utilized to (a) illustrate the effect of the added fluidic self-centering devices on the behavior of the structural system, and (b) to arrive at conclusions on the appropriate strategy for selection of the structural system and self-centering system properties for design. The results suggest that the primary structural system could be designed for a base shear force not less than 75% of the minimum base shear force prescribed in ASCE 7-2010 for the building exclusive of the self-centering system, and that the drift criteria would be satisfied and the residual drift will be minimal when the fluidic self-centering system is designed for a preload equal to about (or more than) 20% of the story shear yield strength and a viscous damping ratio of at least 10% of critical under elastic frame conditions. Simplified methods of analysis are then presented and verified by comparison to nonlinear response history analysis results. The simplified methods of analysis are found to be reasonably accurate for most practical cases of structural system and self-centering system parameters except for cases of long period structures and when near-fault, pulse-like ground motions are considered.

Characteristics and displacement capacity of reinforced concrete walls in damaged buildings during 2010 Chile earthquake

About 2 % of reinforced concrete (RC) buildings taller than nine stories suffered important structural damage during 2010 Chile earthquake. The typical structural configuration of residential buildings is characterized by a large number of RC structural walls which provides high lateral stiffness and strength. The first objective of this paper is to obtain global geometric and design parameters of RC structural walls in damaged buildings and correlate their values with the observed damage. The second objective is to compare the roof displacement capacity with the roof displacement demand in critical walls, and hence, try to explain the observed damage. The wall parameters were obtained from five representative damaged structural wall buildings; these are: wall thickness, aspect ratio, axial load, reinforcement ratios, and the ratio between horizontal reinforcement spacing and the vertical bar diameter. The roof displacement capacity is obtained using a plastic hinge approach, and the ACI 318-08 approach, since both methods are proposed in the current Chilean seismic code. The displacement demand is estimated from ground motions recorded in the vicinity of the buildings. It is found that values of wall parameters correlate well with the observed damage. The structural walls were subjected to relatively high axial loads, and some walls included a large amount of vertical reinforcement to provide the required strength, but had inadequate transverse reinforcement thus compromising ductility. Findings from this research suggest that the plastic hinge approach is inadequate to estimate the roof displacement capacity and lacks correlation with the observed damage. Moreover, the use of the ACI 318-08 approach to estimate the roof displacement capacity is also inadequate, but leads to better predictions of wall displacement capacity. As shown by the results of response history analysis, the failure of walls was triggered by high axial loads rather than flexural deformation.

Re-evaluation of equivalent lateral force procedure for prediction of displacement demand in seismically isolated structures

The accuracy of the equivalent lateral force (ELF) procedure described in codes and specifications for the analysis and design of seismically isolated structures is of concern, because this procedure is always used either directly under certain conditions or to establish a lower-bound limit on the results of response history analysis (RHA). A number of recent studies have resulted in conflicting conclusions with some showing the ELF procedure to produce accurate results and others showing the opposite. A review of these studies shows that they primarily differ in the selection and scaling of motions for RHA, and in the interpretation of the results. Accordingly, this study re-evaluates the accuracy of the ELF procedure based on RHA of a range of parameters of isolation systems subjected to bidirectional excitations and investigates the effects of (a) the selection of seed earthquake motions for RHA (near-fault pulse-like versus non-pulse-like), (b) the procedure for scaling the seed motions for RHA (weighted scaling versus spectral matching), (c) the specification of the response spectrum (geometric mean versus maximum direction spectrum), and (d) the measure of central tendency (average versus median). It is found for the isolation systems considered, the ELF procedure always provides reasonably good or conservative estimates of the isolation system displacement demands provided that non-pulse-like motions are selected and spectral matching is used for scaling. In other cases, the demands predicted by the ELF procedure could be un-conservative, especially for large effective period and low effective damping isolation systems.

Approximate Method for Transverse Response Analysis of Partially Isolated Bridges

Current analysis procedures for seismically isolated bridges frequently use an equivalent (approximate) linearization approach to represent the response of nonlinear isolation/energy dissipation devices. Linearization allows standard linear elastic analysis methods, e.g., the response spectrum method, to be conveniently used for design purposes. The linearization approach is by nature an iterative method implying the need to repeatedly correct and analyze a numerical finite-element model. A further simplification could be achieved using closed form equations to represent (1) the structure displacement patterns and (2) the restoring forces from structural elements. The paper explores such a possibility with reference to partially isolated continuous bridges, i.e., bridges with isolation devices at piers and pinned supports at abutments. The role and effect of higher modes of vibration on the system response are discussed, and an approximate method is proposed to account for such effects. An improvement of the classical Jacobsen’s approximation for the effective viscous damping ratio is also proposed using the results of response history analyses. The latter are carried out on two-dimensional numerical models of five case studies, generated from a real existing bridge supposed to be isolated with friction pendulum devices. Comparison of approximate predictions with response history analysis results is presented and discussed. Nonlinear dynamic analyses of a three-dimensional numerical model of the existing bridge were also carried out for comparison purposes.

Evaluation of Rayleigh damping and its influence on engineering demand parameter estimates

SUMMARYThe effects of Rayleigh damping model on the engineering demand parameters of two steel moment‐resisting frame buildings were evaluated. Two‐dimensional models of the buildings were created and response history analysis were conducted for three different hazard levels. The response history analysis results indicate that mass‐proportional damping leads to high damping forces compared with restoring forces and may lead to overestimation of floor acceleration demands for both buildings. Stiffness‐proportional damping, on the other hand, is observed to suppress the higher‐mode effects in the nine‐story building resulting in lower story drift demands in the upper floors compared with other damping models. Rayleigh damping models, which combine mass‐proportional and stiffness‐proportional components, that are anchored at reduced modal frequencies lead to reasonable damping forces and floor acceleration demands for both buildings and does not suppress higher‐mode effects in the nine‐story building. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of torsion on the behavior of peripheral steel‐braced frame systems

AbstractIn this study, the torsional response of buildings with peripheral steel‐braced frame lateral systems is evaluated. A three‐dimensional model of a three story braced frame with various levels of eccentricity is created and the effects of torsion on the seismic response is assessed for four hazard levels. The response history analysis results indicate that, unlike frame structures, the torsional amplifications in the inelastic systems exceed those of corresponding elastic systems and tend to increase with an increase in the level of inelasticity. The ability of two simplified procedures, elastic response spectrum analysis and pushover analysis, to capture the torsional amplifications in steel‐braced frames is evaluated. Copyright © 2010 John Wiley & Sons, Ltd.

Comparative Response Assessment of Minimally Compliant Low-Rise Base-Isolated and Conventional Steel Moment-Resisting Frame Buildings

In this study, the multihazard response of code-designed conventional and base-isolated steel frame buildings is evaluated using nonlinear response history analysis. The results of hazard and structural response analysis for 3-story moment-resisting frame buildings are presented in this paper. Three-dimensional models for both buildings are created, and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the performance of the isolated building is superior to the conventional building in the design event. However, for the Maximum Considered Earthquake, the presence of outliers in the response data reduces confidence that the isolated building provides superior performance to its conventional counterpart. The potential causes of the outliers have been carefully evaluated.

Comparative response assessment of minimally compliant low‐rise conventional and base‐isolated steel frames

AbstractIn this study, the multi‐intensity seismic response of code‐designed conventional and base‐isolated steel frame buildings is evaluated using nonlinear response history analysis. The results of hazard and structural response analysis for three‐story braced‐frame buildings are presented in this paper. Three‐dimensional models for both buildings are created and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the design objectives are met and the performance of the isolated building is superior to the conventional building in the design event. For the Maximum Considered Earthquake, isolation leads to reductions in story drifts and floor accelerations relative to the conventional building. However, the extremely high displacement demands of the isolation system could not be accommodated under normal circumstances, and creative approaches should be developed to control displacements in the MCE. Copyright © 2010 John Wiley & Sons, Ltd.

Evaluation of simplified methods of analysis for structures with triple friction pendulum isolators

AbstractTriple friction pendulum isolators, that exhibit behavior with amplitude‐dependent strength and instantaneous stiffness, represent a new development in seismic isolation. The application of simplified methods of analysis for this type of seismically isolated structures requires development of tools of simplified analysis and demonstration of their accuracy. This paper describes these tools and presents validation studies based on a large number of nonlinear response history analysis results. It is shown that simplified methods of analysis systematically provide good and often conservative estimates of isolator displacement demands and good estimates of isolator peak velocities. Copyright © 2009 John Wiley & Sons, Ltd.