Predictive instantaneous optimal control of inelastic structures during earthquakes

A new inelastic structural control algorithm is proposed by incorporating the force analogy method (FAM) with the predictive instantaneous optimal control (PIOC) algorithm. While PIOC is very effective in compensating for the time delay for elastic structures, the FAM is highly efficient in performing the inelastic analysis. Unlike conventional inelastic analysis methods of changing stiffness, the FAM analyzes structures by varying the structural displacement field, and therefore the state transition matrix needs to be computed only once. This greatly simplifies the computation and makes inelastic analysis readily applicable to the PIOC algorithm. The proposed algorithm compensates for the time delay that happens in practical control systems by predicting the inelastic structural response over a period that equals the magnitude of the time delay. A one‐story frame with both strain‐hardening and strain‐softening inelastic characteristics is analyzed using this algorithm. Results show that the proposed control algorithm is feasibile for any inelastic structures. While the control efficiency deteriorates with the increase in magnitude of the time delay, the PIOC maintains acceptable performance within a wide range of time delay magnitudes. Finally, a computer model of a six‐story moment‐resisting steel frame is analyzed to show that PIOC has good control results for real inelastic structures. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluation of predictors of non‐linear seismic demands using ‘fishbone’ models of SMRF buildings

Predictors (or estimates) of seismic structural demands that are less computationally time‐consuming than non‐linear dynamic analysis can be useful for structural performance assessment and for design. In this paper, we evaluate the bias and precision of predictors that make use of, at most, (i) elastic modal vibration properties of the given structure, (ii) the results of a non‐linear static pushover analysis of the structure, and (iii) elastic and inelastic single‐degree‐of‐freedom time‐history analyses for the specified ground motion record. The main predictor of interest is an extension of first‐mode elastic spectral acceleration that additionally takes into account both the second‐mode contribution to (elastic) structural response and the effects of inelasticity. This predictor is evaluated with respect to non‐linear dynamic analysis results for ‘fishbone’ models of steel moment‐resisting frame (SMRF) buildings. The relatively small number of degrees of freedom for each fishbone model allows us to consider several short‐to‐long period buildings and numerous near‐ and far‐field earthquake ground motions of interest in both Japan and the U.S. Before doing so, though, we verify that estimates of the bias and precision of the predictor obtained using fishbone models are effectively equivalent to those based on typical ‘full‐frame’ models of the same buildings. Copyright © 2003 John Wiley & Sons, Ltd.     

渭干河流域"2002·7"特大洪水分析

渭干河是塔里木河流域第六大源流, 位于天山西部南麓, 渭干河干流起点有新疆最大的流域性控制工程--克孜尔水库. 2002年7月下旬天山中西部山区出现大暴雨(雪)过程, 渭干河流域山区降水持续时间长达30 h以上, 山区降水量50 mm左右, 导致5条支流和渭干河干流出现有水文记录以来的最大洪峰, 流量超过警戒流量和危险流量的2～3.5倍, 暴雨(雪)过程结束之后, 融雪型洪峰长时间居高不下. 洪水过程中, 各支流以及暴雨与融雪等多种洪峰遭遇现象很明显. 克孜尔水库入库洪峰流量达3 660 m3*s-1, 经水库调洪错峰, 出库峰值流量为1 000 m3*s-1, 削峰率72.7%.     

哈尔滨市磨盘山水利枢纽区三维渗流数值模拟模型研究

哈尔滨市磨盘山水库防渗型式拟采用垂直砼防渗墙及帷幕灌浆方案。为了分析左岸不同长度防渗对水库渗漏量及坝基渗透稳定性的影响。对磨盘山水利枢纽区渗流场进行了三维数值模拟研究。结果表明，随着左岸防渗长度的增大。渗漏量及下游渗流出口渗透比降基本呈线性趋势减小。当左岸防渗长度为200m时。渗漏量及各渗透比降均小于允许值，为推荐的渗控方案。     

Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999——2001 in the northeast margin of Qinghai-Xizang block

Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999.     

深圳市东湖矿泉水形成机理探讨

深圳市东湖矿泉水是自然界十分稀少的锶—锌—偏硅酸碳酸复合型矿泉水，通过对矿泉水赋存地的地质与水文地质条件的分析，并结合其水文地球化学特征，认为东湖矿泉水形成的主要控制性因素是构造作用和变质作用；在特定的水文地质条件下，深部碳酸盐类岩石受热硅化变质而产生大量CO2气体，使得各种化学元素在含有大量CO2的地下水的溶滤作用下不断迁移和富集而形成该区地下水中良好的元素组合。在其特征成分中，偏硅酸来自裂隙渗透水的溶滤和岩浆期后热液水的作用，微量元素锶主要来源于钾长石、钙长石，锌则主要来自岩浆活动以及岩脉中的黑云母、角闪石、辉石等铁镁硅酸盐矿物；并认为目前矿泉水含水层仍处于良好的地质环境保护下。     

易门式大型铜矿床构造成矿动力学模型

针对金属矿床隐伏矿定位预测的关键问题,在提出构造成矿动力学的分支学术方向的基础上,以易门式大型铜矿床为例,从成矿地质背景、矿田构造、构造地球化学和成矿构造应力场等方面进行构造成矿动力学研究,阐述在构造应力场控制下成矿流体运移和聚集的规律。构造地球化学研究认为,构造地球化学异常反映矿体的原生晕;构造地球化学异常受构造控制,其分带特征可指示成矿流体的流向,并提供矿床成因和隐伏矿(化)体相对埋深的信息。构造应力场的控矿特征主要表现在:构造应力场导致控矿构造的形成,并驱动成矿流体的运移;构造应力场控制了成矿能量场;应力和能量的高值集中区分布特点可反映某些构造型式。在此基础上建立构造成矿动力学模型,概括隐伏矿成矿预测准则,据此提出若干重点找矿靶区和靶位,其中部分靶区得到工程验证,表明构造成矿动力学方法对隐伏矿定位预测和评价具有重要的指导意义。     

The importance of plant root characteristics in controlling concentrated flow erosion rates

While it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimal distribution of linear control intensity over the frequency range

In this paper, a control strategy for structural systems is proposed and developed in the frequency domain. The algorithm is substantially based on a linear derivative feedback and a convolution of the control parameter, whose distribution in the frequency field is chosen in such a manner as to comply with the requirements of an ad hoc formulated constrained optimum problem, with the response data monitored until the instant of control action application. Some numerical testing is carried out by referring to given recorded accelerograms, showing a good performance of the proposed approach. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparative study of the inelastic response of base isolated buildings

This article presents a numeric comparative study of the inelastic structural response of base isolated buildings. The comparative study includes the following isolation systems: laminated rubber bearings, New Zealand one, pure friction and the frictional pendulum ones. The study is based on obtaining non‐linear response spectra for various design parameters using six earthquake records. Usually the base isolation of a new building seeks to maintain the structure in the linear elastic range. The response of old weak buildings or the response of new ones subjected to extreme earthquakes may not be, necessarily, in the aforementioned ideal elastic range. Consequently, it is important to characterize the response of isolated buildings responding inelastically. A conclusion from this research is that the isolators affect significantly the structural response of weak systems. Rubber isolators seem slightly less sensitive to plastification that may occur in the structure compared to friction isolators. Ductility demands in the structure are affected significantly by friction and neoprene protected systems, in particular sliding ones where larger demands are obtained. Copyright © 2002 John Wiley & Sons, Ltd.