Comparison of the Dynamic and Static Corner Frequencies in Ground Motion Simulation: Cases Study of Jiuzhaigou Earthquake and Northridge Earthquake

By using the stochastic finite-fault method based on static corner frequency (Model 1) and dynamic corner frequency (Model 2), we calculate the far-field received energy (FRE) and acceleration response spectra (SA) and then compare it with the observed SA. The results show that FRE obtained by the two models depends on the subfault size regardless of high-frequency scaling factor (HSF). Considering the HSF, the results obtained by Model 1 and Model 2 are found to be consistent. Then, similar conclusion was obtained from the Northridge earthquake. Finally, we analyzed the reasons and proposed the areas that need to be improved.

A Novel Design of Interval Type-2 Neuro-Fuzzy Controller for Flexible Structure

The aim of this research is to develop a novel design of interval type-2 neuro-fuzzy (IT2NF) controller for active vibration control of a flexible structure during an earthquake. For this purpose, two adaptive neural network based fuzzy logic controllers are designed and combined to create the novel design of an IT2NF controller to reduce the vibrations of two-storey flexible building model that occur during earthquake disturbance effects. Accordingly, dynamic modeling of a flexible structure is realized and simulated using the MATLAB / SimMechanics. Then, an experimental setup consisting of two-storey flexible structure, active mass damper (AMD) and shaker is established. Additionally, IT2NF controller is implemented in simulation and experimental models, and the effectiveness and performance of the IT2NF controller are tested under the scaled Northridge Earthquake acceleration. The obtained simulations and experimental responses are evaluated in terms of cart displacements, deflections, and accelerations of the flexible floors showing a good agreement between the simulations and the experimental results. The results show that the designed novel IT2NF controller reduced the total deflections of first and second floor by 72.3% and 68.7%, respectively, when compared with the uncontrolled system. Additionally, it is also found that the designed IT2NF controller is able to reduce the accelerations of the first and second floor by 64.8% and 54.6%, respectively. The proposed and designed control method reported in this study can be employed as an active vibration controller for multi-degree of freedom of flexible systems under the disturbances such as earthquake excitations.

Effect of Different Design Parameters on the Cyclic Response of Reduced Beam Sections (RBS) Moment Connections

After the 1994 Northridge earthquake, research has been conducted to develop new types of beamcolumn moment connections, such as Reduced Beam Section (RBS) connections. This study performs a sensitivity analysis of the cyclic response of RBS connections using detailed finite element simulation. The significance of the effect of twenty-one factors is assessed using a statistical design of experiment method. The input factors are related to the material properties or the geometry of the beam-column connection. A two-level fractional factorial design is used to create factor combinations for the sensitivity analysis. The cyclic response of RBS connections is assessed in terms of five response variables, including: the total dissipated energy, initial stiffness, strength degradation rate, maximum moment capacity and rupture index at 7.5% storey drift. The sensitivity analysis results show that the beam depth has the greatest influence on the cyclic response of RBS connections.

Effect of Different Design Parameters on the Cyclic Response of Reduced Beam Sections (RBS) Moment Connections

After the 1994 Northridge earthquake, research has been conducted to develop new types of beamcolumn moment connections, such as Reduced Beam Section (RBS) connections. This study performs a sensitivity analysis of the cyclic response of RBS connections using detailed finite element simulation. The significance of the effect of twenty-one factors is assessed using a statistical design of experiment method. The input factors are related to the material properties or the geometry of the beam-column connection. A two-level fractional factorial design is used to create factor combinations for the sensitivity analysis. The cyclic response of RBS connections is assessed in terms of five response variables, including: the total dissipated energy, initial stiffness, strength degradation rate, maximum moment capacity and rupture index at 7.5% storey drift. The sensitivity analysis results show that the beam depth has the greatest influence on the cyclic response of RBS connections.

Geotechnical lessons from the Mw 7.1 2018 Anchorage Alaska earthquake

The 2018 Mw 7.1 Anchorage, Alaska, earthquake is one of the largest earthquakes to strike near a major US city since the 1994 Northridge earthquake. The significance of this event motivated reconnaissance efforts to thoroughly document damage to the built environment. This article presents the spatial variability of ground motion intensity and its correlation with subsurface conditions in Anchorage, the identification of liquefaction triggering in the absence of surficial manifestations (such as sand boils or sediment ejecta), cyclic softening failure in organic soils, and the poor performance of anthropogenic fills subjected to cyclic loading. In addition to lessons from observed ground deformation and geotechnical effects on structures, this article provides case studies documenting the satisfactory behavior of improved ground subjected to cyclic loading and the appropriateness of current design procedures for the estimation of seismically induced sliding displacements of mechanically stabilized earth walls.

From scenario-based seismic hazard to scenario-based landslide hazard: fast-forwarding to the future via statistical simulations

Ground motion scenarios exists for most of the seismically active areas around the globe. They essentially correspond to shaking level maps at given earthquake return times which are used as reference for the likely areas under threat from future ground displacements. Being landslides in seismically actively regions closely controlled by the ground motion, one would expect that landslide susceptibility maps should change as the ground motion patterns change in space and time. However, so far, statistically-based landslide susceptibility assessments have primarily been used as time-invariant.In other words, the vast majority of the statistical models does not include the temporal effect of the main trigger in future landslide scenarios. In this work, we present an approach aimed at filling this gap, bridging current practices in the seismological community to those in the geomorphological and statistical ones. More specifically, we select an earthquake-induced landslide inventory corresponding to the 1994 Northridge earthquake and build a Bayesian Generalized Additive Model of the binomial family, featuring common morphometric and thematic covariates as well as the Peak Ground Acceleration generated by the Northridge earthquake. Once each model component has been estimated, we have run 1000 simulations for each of the 217 possible ground motion scenarios for the study area. From each batch of 1000 simulations, we have estimated the mean and 95% Credible Interval to represent the mean susceptibility pattern under a specific earthquake scenario, together with its uncertainty level. Because each earthquake scenario has a specific return time, our simulations allow to incorporate the temporal dimension into any susceptibility model, therefore driving the results toward the definition of landslide hazard. Ultimately, we also share our results in vector format – a .mif file that can be easily converted into a common shapefile –. There, we report the mean (and uncertainty) susceptibility of each 1000 simulation batch for each of the 217 scenarios.

Seismic Evaluation of the RC Moment Frame Structure using the Shake Table

This paper presents the findings of an experimental investigation on a reinforced concrete frame structure (ordinary moment resistant frame). The test model was subjected to lateral excitation employing the 1994 Northridge earthquake accelerogram. The reinforced concrete test model was fabricated in 1:3 reduced scale acquiring dimensional similarities. The utilized ingredient mix ratio was 1:1.65:1.75 and the water to binder ratio was 0.47. The dynamic characteristics (natural frequency and elastic viscous damping) were calculated using the free vibration record. Story shear, drift, and displacement profiles were drawn using multiple excitation records along with damage patterns and capacity curves. The natural frequency of 2.47Hz was calculated for the test specimen, which is equivalent to 1.41Hz for the prototype. Structural damping (elastic viscous) of 12.36% was calculated for the prototype.