基于光谱成像的彩绘文物新应用与新方法

目前基于光谱成像的彩绘文物分析主要集中在颜料分析、信息增强、隐含信息挖掘等方面,分析方法主要采用遥感图像处理软件。针对文物数据专门分析方法研究尚显不足的问题,提出基于光谱成像的彩绘文物新应用与新方法。主要包括基于最小噪声分离(MNF)变换感知修复区域的新应用,利用感兴趣区域分析与融合挖掘彩绘文物隐含信息以及基于稀疏非负矩阵欠近似彩绘文物线稿提取的新方法。通过在唐墓壁画、彩绘泥塑以及手绘绢画上的实验,发现光谱成像可以有效感知修复区域,提出的新方法可以有效挖掘隐含信息以及提取线稿,对基于光谱成像的彩绘文物分析研究具有重要意义。     

Comparison of the Spectral Representation Method to Simulate Spatially Variable Ground Motions

The spectral representation method (SRM) is widely used when simulating spatially variable ground motions. It has mainly two formulas, i.e., the random amplitudes and the random phases formulas. There exist three methods for decomposing the cross spectral density matrix: Cholesky decomposition, eigen decomposition, and root decomposition. Therefore, there are six forms with respect to the different combinations of the simulation formulas and the decomposition methods. To provide researchers and engineers with the guidance on choosing simulation method, the six forms are systematically investigated from five aspects: the power intensity, response spectra, and stochastic error of auto/cross spectral density, Fourier spectra, and difference indexes for Fourier amplitudes and phases. Finally, we give the following advice: the characteristics of the ground motions simulated by the random amplitudes formula are independent of the decomposition method, while the characteristics of the ground motions simulated by random phases formula are dependent of the decomposition method. Furthermore, the root decomposition is strongly recommended when utilizing the random phases formula.     

Impact of Modification on Ground Motion Characteristics and Geotechnical Seismic Analyses for a California Site

The impact of different modification techniques on ground motion characteristics and results of seismic geotechnical analyses is investigated for a site in California. Twenty-eight motions were selected and scaled and also modified using both time domain (TD) and frequency domain (FD) techniques. PGV and PGD of the TD-modified motions are found to be larger than their FD-modified counterparts, but slightly less than the scaled ground motion characteristics. Cyclic stress ratios and amplification factors are similar for all sets of motions. Newmark-type slope displacements caused by the scaled and modified ground motions are similar (within 25%) for a variety of sliding masses.     

Ground Motion Parameters for the 2011 Great Japan Tohoku Earthquake

The 2011 great Japan Tohoku earthquake is not only the most devastating but also, one of the best recorded earthquakes in the history of seismology. A thorough study of strong motion characteristics of this earthquake is conducted using 20 well established ground motion parameters (GMPs). The behaviour of these parameters with fault distance and average shear wave velocity is examined and attenuation relationships are developed using the 1172 surface level strong motion records. In addition, all GMPs are categorized on a statistical basis using principal component analysis, which is further used to rate the damage potential of ground motion records.     

Fuzzy-Sliding-Mode Supervisory Control of a Seismic Shake Table with Variable Payload for Robust and Precise Acceleration Tracking

Precise tracking of the earthquake acceleration profile in the presence of uncertainties is a challenge for the shake table control design. Design and implementation of a fuzzy-sliding-mode super- visory controller for an electric seismic shake table with variable payload is addressed in this paper. The proposed controller contains two layers including a proportional–integral loop and a fuzzy-sliding-mode supervisory controller. The controller is then implemented in the shake table and its performance is evaluated. The test results reveal successful performance of the proposed controller at robust tracking of some harmonic and seismic excitations in the presence of parametric uncertainties.     

Physical and Numerical Approaches for the Optimal Insertion of Seismic Viscous Dampers in Shear-Type Structures

This article presents the results of an exhaustive parametric analysis which compares the performances offered by various systems (which lead to both classical and non classical damping matrices) of added viscous dampers in shear-type structures. The aim of the research work here presented is the identification of the system of added viscous dampers which maximizes the dissipative properties under an equal “total size” constraint. The choice of the systems of added viscous dampers considered in the comparison is carried out both using a numerical approach (based upon the use of genetic algorithms) and a physically based approach (based upon the properties of classically damped systems). The comparison is carried out through the numerical evaluation of the dynamic response of representative shear-type structures to both stochastic and recorded earthquake inputs. The results obtained using both approaches indicate that a damping system based upon the mass proportional damping component of the Rayleigh viscous damping matrix (referred to as MPD system) is capable of optimizing simultaneously a number of different performance indexes, providing the best “overall” damping performances. The MPD system is characterised by viscous dampers (a) which connect each floor to a fixed point and (b) which are sized proportionally to the corresponding floor mass.     

Multi-Component Seismic Response Analysis – A Critical Review

Issues related to multi-components seismic response analysis are critically reviewed and their implications with respect to the current codified approaches are studied. The issues specifically addressed are: (1) the directions of earthquake forces to excite a structure when the direction of the potential epicenter is known; (2) different commonly used combination rules to obtain the critical response when responses are available in different directions; and (3) the applicability of the combination rules for elastic and inelastic analyses. Based on an extensive parametric study consisting of three-dimensional 1-, 3-, 8-, and 15- story buildings made of moment-resisting steel frames and 20 recorded earthquakes, it is observed that the principal components produce larger responses than the normal components. The 30% and SSRS rules generally underestimate the axial loads in columns. The 30% combination rule is slightly better than the SSRS rule. For both rules, the uncertainty in the estimation of the axial loads in terms of COV is very large (about 25%). The statistics obtained for axial loads and total base shear indicate that the combination rules are applicable for both elastic and inelastic cases. The critical response could be obtained for an orientation different from that of the principal components. The differences are found to be slightly greater for the scaled earthquakes producing a considerable inelastic behavior. Considering the enormous amount of efforts needed to address the directionality effect, it is believed that the responses obtained by the principal components will be acceptable in most cases; however, for critical structures the components should be rotated to obtain the critical responses.     

Subsoil Interventions Effect on Structural Seismic Response. Part II: Parametric Investigation

In the present article the effect of subsoil interventions on the response of soil-structure systems under strong earthquake shaking is studied. Several idealized configurations of commonly applied as well as innovative intervention techniques are examined, referring to increased or reduced stiffness of the initial subsoil conditions of the subsoil-foundation-structure system. Numerical analysis utilizing validated simulation procedures covers a large spectrum of structures and soil conditions. A parametric investigation of several key factors is also conducted. A comparative evaluation of the results in time and frequency domain is aiming in generalizing the conclusions to several earthquake and soil-structure combinations. Obtained results reveal a rather detrimental effect of the stiffness-increasing methods, whereas techniques related to modification of oscillation dynamic properties with flexible subsoil intervention schemes, present promising alternatives for an efficient mitigation of structural response to strong earthquakes.     

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

Response of masonry walls to out-of-plane excitation is a complex, yet inadequately addressed theme in seismic analysis. The seismic input expected on an out-of-plane wall (or a generic “secondary system”) in a masonry building is the ground excitation filtered by the in-plane response of the walls and the floor diaphragm response. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. The current article delves into the details and results of several nonlinear dynamic time-history analyses executed within a parametric framework. The study addresses masonry structures with rigid diaphragm response to lateral loads. The scope of the parametric study is to demonstrate the influence of inelastic structural response on the seismic response of secondary systems and eventually develop an expression to estimate the seismic input on secondary systems that explicitly accounts for the level of inelasticity in the primary structure in terms of the displacement ductility demand. The proposed formulation is discussed in the companion article.     

Direct Acceleration Feedback Control of Shake Tables with Force Stabilization

This study presents a new strategy for shake table control that uses direct acceleration feedback without need for displacement feedback. To ensure stability against table drift, force feedback is incorporated. The proposed control strategy was experimentally validated using the shake table at the Johns Hopkins University. Experimental results showed that the proposed control strategy produced more accurate acceleration tracking than conventional displacement-controlled strategies. This article provides the control architecture, details of the controller design, and experimental results. Furthermore, the impact of input errors in shake table testing on the structural response is also discussed.