Prediction of High-Damping Seismic Demands in Eastern North America

This article investigates high-damping seismic demands and associated damping reduction factors in Eastern North America (ENA). A database of hybrid empirical records with moment magnitudes M ≥ 6.0 is first studied to evaluate 5%- to 30%-damped seismic demands. A new magnitude- and distance-based equation is proposed to predict ENA spectral displacements and then used to characterize their sensitivity to variations in period, magnitude, epicentral distance and site conditions. The proposed equation is also used to assess damping reduction factors in ENA. The results contribute to improved assessment of seismic demands in ENA while accounting for added-damping in structural seismic design.     

Influence of Diaphragm Flexibility on Seismic Response of Unreinforced Masonry Buildings

The effects of diaphragm flexibility on the seismic response of low-rise unreinforced masonry buildings are examined using one-way stiffness- and strength-eccentric single-story systems subjected to unidirectional ground excitation. A wide range of diaphragm stiffnesses are considered. Results show that diaphragm flexibility can induce different effects depending on the configuration of the system and the level of diaphragm flexibility. When diaphragm is relatively stiff, amplified displacement demands can be imposed on the flexible side of the structure. When diaphragm is relatively flexible, peak displacements of in-plane loaded walls generally reduce. A diaphragm classification is developed to capture these salient effects.     

Surface Rotations on and Around a Semi-Parabolic Canyon in an Elastic Half-Space Induced by Out-of-Plane SH-Waves,I: Torsion

The surface displacement amplitudes excited by out-of-plane SH waves on and around a semi-parabolic canyon had solution that was introduced over twenty years ago. In 2015, such solution was updated to much (5 times) higher frequencies, using a transformation involving the Wronskian. The same excitations also introduce rotations on and around the parabolic canyon. This article is the first of two that discuss the torsional component of rotations, with the rocking components discussed in the subsequent article. The rotational amplitudes of motions, as much as the displacement amplitudes, play an important role in studying the surface responses of structures, and can lead to a better understanding of the behavior of surface topographies in the event of seismic excitation.     

Influence of Ground Motion Duration on Damping Reduction Factor

This article investigates the influences of the effective ground motion duration (GMD) on damping reduction factor. The GMD are associated with 25 Chi-chi earthquake ground motion records and harmonic sine wave. The study shows that damping reduction factor decreases with the increasing of the damping ratio, and decreases with the increasing of the effective duration of the ground motion and the number of cycles of harmonic excitation. A nonlinear multiple regression analysis based on the statistical mean values of the present study is employed, and a modified damping reduction factor considering the effects of GMD is suggested.     

Effect of Horizontal Component Definition on the Characterization of Vertical Ground Motions: Application to Eastern Canada

In this article, ground motions recorded on rock sites in eastern Canada are studied in order to characterize their vertical acceleration components. Emphasis is placed on the sensitivity of vertical-to-horizontal spectral ratios to: (i) inter-component intensity correlations and (ii) the use of geometric mean horizontal components at each site instead of considering them individually. Four different definitions of horizontal components are investigated. Vertical-to-horizontal spectral ratios are compared with the findings of other researchers. We illustrate how the results can be used to evaluate vertical acceleration demands on rock sites in eastern Canada.     

An Improved Displacement-Based Adaptive Pushover Procedure for the Analysis of Frame Buildings

The main purpose of this article is to develop an alternative adaptive pushover method in which multiple inelastic response spectra proportional to the instantaneous ductility ratio of the structure are employed to reflect the actual energy dissipation characteristic of the structure at a given deformation level. Based on the proposed methodology, two load patterns are independently applied to the structure and the envelope of the demand values is computed. The obtained results demonstrate that the proposed method provides improved predictions of the peak interstory and total drift profiles of the structure.     

Estimating the Seismic Performance of CFRP-Retrofitted RC Beam-Column Connections Using Fiber-Section Analysis

Over the past two decades, many experimental techniques have been developed to improve the efficiency of the externally-bonded fiber-reinforced polymers (FRPs) in order to improve the structural performance of reinforced concrete (RC) beam-column connections. Numerical analysis is also being used as a cost-effective tool to predict the experimental results and to further investigate the parameters that are beyond the scope and capacity of experimental tests. In this study, at first, a fiber-section modeling approach is developed for estimating the seismic behavior of RC beam-column connections before and after application of FRP retrofits. The accuracy of the analysis results were validated against a series of the available experimental data under both monotonic and cyclic loadings. It was pointed out that the proposed model can predict the strength and displacement of un-retrofitted and FRP-retrofitted RC beam-column connections up to the failure points. The verified model was then used to perform a parametric study pertaining to the effect of longitudinal reinforcement ratio on the efficiency of the adopted FRP retrofitting technique to improve the structural behavior of RC beam-column connections.     

The Diffraction of Rayleigh Waves by Twin Circular Cavities in a Poroelastic Half-Space

The diffraction of Rayleigh waves by twin circular cavities in a poroelastic half-space is investigated using the indirect boundary integral equation method (IBIEM). To satisfy the boundary conditions on the free surface, Green’s functions of compressional and shear wave sources in a poroelastic half-space are derived based on Biot’s theory. It is verified that the IBIEM has great accuracy and numerical stability. Then, the influences of the drainage boundary condition, incident wave frequency, porosity, and cavity spacing on the dynamic responses are investigated by numerical examples. The results show that the amplification effect of the twin cavities is greater in the case of undrained boundary conditions, lower frequencies, and smaller cavity spacings. The porosity of the saturated medium also influences the dynamic responses because the velocity of the Rayleigh wave will change with the porosity of the saturated medium.     

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.