Direct displacement-based design for seismic retrofit of existing buildings using nonlinear viscous dampers

This paper presents a direct displacement-based design procedure for seismic retrofit of existing buildings using nonlinear viscous dampers according to equivalent linear systems. Unlike conventional methods, the equivalent linear viscous damping provided by the nonlinear viscous dampers is derived based on the assumption that the average energy dissipated between the linear and the nonlinear viscous dampers is equal. Also, the equivalent period and viscous damping for the equivalent linear systems which are used for representing the behavior of bare frames (the buildings without dampers) are derived from the concept of average storage energy and average dissipated energy, respectively. It is shown from nonlinear time-history analyses that the nonlinear action of the retrofitted structures can be reasonably captured by the presented direct displacement-based procedure.     

二维物性界面深度重磁反演的一种非线性迭代解法──样条函数法

提出一种重磁导演非线性反演的直接解 ,它是基于迭代法求解一个非线性各分方程。当物性界面起伏分布△ｈ满足｜△ｈ｜〈√２－１）ｈ时,积分的补积函数可展成△ｈ的幂级数,考虑△ｈ高次项的影响,应用简单迭代法可将问题化成相应的线性积分方程,并可用Ｂ样条函数求解。在不同磁化方向的△Ｔ和Ｚα异常上和变密度界面引起的重力异常上实现了模拟反演。精度显著高于线性直接解。在南海东沙群岛地区进行了莫霍面的反演计算,效果良     

A hypoplastic model for site response analysis

Site response analyses must take into account the nonlinear behavior of soils. This is typically achieved using an equivalent linear approach or using numerical analyses with an appropriate constitutive model. In this work a family of hypoplastic models is proposed for use in site response analyses. These nonlinear models use a rate-type tensorial equation and are capable of reproducing plastic deformation of soils for cyclic loading under both drained and undrained conditions. A methodology for the calibration of hypoplastic parameter for dynamic loading is proposed. The hypoplastic constitutive models are implemented in a finite element code and the site response of the Lotung downhole array site is used to validate the use of hypoplastic models for site response analysis. The hypoplastic models reproduce accurately site response at the Lotung site. The advantages and disadvantages of the hypoplastic models compared to other models are discussed.     

Wavelet approximation of earthquake strong ground motion-goodness of fit for a database in terms of predicting nonlinear structural response

Reduced dimensionality representation of strong ground motion records as a superposition of a relatively small number of pulses is studied. Such representation is obtained by the expansion of velocity in orthogonal wavelet series using the Fast Wavelet Transform, and approximation by only the largest energy terms in the series. The Coiflet 5 wavelet family is used, which is orthogonal, smooth and nearly symmetric. The goodness of the approximation is examined for the EQUINFOS for USA Part I database, as representative of a large variety of strong motion records (it consists of 494 three-component records from 106 earthquakes recorded in the western US between 1933 and 1984). The goodness of fit is measured in terms of closeness of predicting several input and output characteristics of a nonlinear oscillator representing a structure: (i) energy of the input ground motion (proportional to integral of velocity squared), (ii) the peak input power, and (iii) the time of collapse of a bi-linear oscillator (considering also collapse due to dynamic instability). The results show very high degree of correlation of these characteristics as estimated from the actual record and from its approximations, even for small number of pulses (relative to the number that would represent the ground velocity exactly). Such reduced representation of strong ground motion is useful for extracting such pulses from strong motion records to study their nature, and for development of new algorithms for the synthesis of artificial earthquake strong motion records.     

Near-source ground motion attenuation relationship for PGA and PSA of the vertical and horizontal components

In this paper, empirical ground-motion models for the vertical and average horizontal components of peak ground-motion and acceleration response spectra from shallow crustal earthquakes are derived using near-source database. These attenuation relationships were derived using a worldwide dataset consisted of corrected and processed accelerograms of 678 strong-motion records recorded with 60 km of the rupture plane of earthquakes between M_w 5.2 and 7.9. Ground motion models are functions of earthquake mechanism, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, depth-to-top of the rupture, hanging wall effects and faulting mechanism.     

Investigating the transport dynamics and the properties of bedload material with a hydro‐acoustic measuring system

This article deals with the following two questions. Are acoustic measurements in running waters appropriate for a highly resolved investigation of the bedload transport? Which characterizations of the bedload regarding mass and shape are possible via the acoustic signals? The signals were recorded by means of data recorders (Tascam Inc. DAP1 Portable Data Recorder) and hydrophones (International Transducer Corp. ITC‐4001 A). The ITC‐4001 is a shallow water omnidirectional transducer containing a flexural disc transducer utilizing Channelite‐5400 ceramics mounted in a rugged corrosion‐resistant housing. These hydrophones were screwed onto the bottom side of stainless steel plates, serving as a contact surface for the bedload in motion above them. After more than 100 series of tests in the laboratory, which indicated the basic relations between the dimension, shape and weight of the bedload and the resulting signal, field tests of the measuring system were conducted. By artificially produced flood waves in the small brooks Riverisbach, Olewiger Bach and by a winter flood wave in the River Moselle, it is possible to elaborate similar structures of the signal course of the bedload movement. The highest transport rates can be observed at the beginning of the increasing limbs and behind the peaks of the waves. At the beginning of the waves, the increasing transport power of the water and the loose material can be considered as the cause for this result. The high stream velocity behind the wave peaks explains the increase in the bedload transport so that material from the channel beds is unfastened and will be mobilized. The characterization of the bedload regarding the shape and mass is still limited regarding the field measurements and could be solved only for homogeneous grain sizes and single stones under laboratory conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia

The results of a hydroacoustic monitoring experiment in the Kelut Crater lake, Indonesia, prior to its 1990 eruption, are presented, with the benefit of hindsight. Indeed, the underwater noise levels in three widely separated frequency bands, together with the lake water temperature, was radio-transmitted and almost continuously recorded from a period of quiescence of the volcano till the onset of its 10 February 1990, eruption, which destroyed the monitoring buoy. The comparative analysis of the noise variations in the three bands, together with seismic and temperature data, have shed light on the mechanisms underlying the pre-eruptive activity. The three acoustic levels had shown conspicuous, yet distinctive, changes prior to the eruption. Acoustic level in the low-frequency (1–50 Hz) band, which increased one year before the resumption of seismic activity and the lake warming up, is interpreted as the result of boiling at depth. The source of high-acoustic level in the audiometric (500–5000 Hz) range is clearly the bubbling of volcanic gases, occurring as a strong convective column in the middle of the lake. From the variations of this audiometric level, we have estimated that the degassing rate in the lake increased by a hundred-fold during the pre-eruptive period. Variations of ultrasonic (20–100 kHz) frequency acoustic level seem to be related with pressure and thermal changes within the hydrothermal system and its rock matrix beneath the lake. In conclusion, this experiment demonstrates the potential of hydroacoustic monitoring as an early warning system at crater lake volcanoes.