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1.
Reinforced concrete columns with insufficient transverse reinforcement and non‐seismic reinforcement details are vulnerable to brittle shear failure and to loss of axial load carrying capacity in the event of a strong earthquake. In this paper, a procedure is presented after examining the application of two macro models for displacement‐based analysis of reinforced concrete columns subjected to lateral loads. In the proposed model, lateral load‐deformation response of the column is simulated by estimating flexural and shear deformation components separately while considering their interaction and then combining these together according to a set of rules depending upon column's yield, flexural and shear strengths. In addition, lateral deformation caused by reinforcement slip in beam–column joint regions and buckling of compression bars are taken into account and considered in the analysis. Implementation of the proposed procedure produces satisfactory lateral load–displacement relationships, which are comparable with experimental data. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
2.
This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three‐dimensional, multi‐storey, multi‐span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase‐delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
The feasibility and efficiency of a seismic retrofit solution for existing reinforced concrete frame systems, designed before the introduction of modern seismic‐oriented design codes in the mid 1970s, is conceptually presented and experimentally investigated. A diagonal metallic haunch system is introduced at the beam–column connections to protect the joint panel zone from extensive damage and brittle shear mechanisms, while inverting the hierarchy of strength within the beam–column subassemblies and forming a plastic hinge in the beam. A complete step‐by‐step design procedure is suggested for the proposed retrofit strategy to achieve the desired reversal of strength hierarchy. Analytical formulations of the internal force flow at the beam–column‐joint level are derived for the retrofitted joints. The study is particularly focused on exterior beam–column joints, since it is recognized that they are the most vulnerable, due to their lack of a reliable joint shear transfer mechanism. Results from an experimental program carried out to validate the concept and the design procedure are also presented. The program consisted of quasi‐static cyclic tests on four exterior, ? scaled, beam–column joint subassemblies, typical of pre‐1970 construction practice using plain round bars with end‐hooks, with limited joint transverse reinforcement and detailed without capacity design considerations. The first (control specimen) emulated the as‐built connection while the three others incorporated the proposed retrofitted configurations. The experimental results demonstrated the effectiveness of the proposed solution for upgrading non‐seismically designed RC frames and also confirmed the applicability of the proposed design procedure and of the analytical derivations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
From soil aggregates to riverine flocs: a laboratory experiment assessing the respective effects of soil type and flow shear stress on particles characteristics 
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下载免费PDF全文 Particles eroded from hillslopes and exported to rivers are recognized to be composite particles of high internal complexity. Their architecture and composition are known to influence their transport behaviour within the water column relative to discrete particles. To‐date, hillslope erosion studies consider aggregates to be stable once they are detached from the soil matrix. However, lowland rivers and estuaries studies often suggest that particle structure and dynamics are controlled by flocculation within the water column. In order to improve the understanding of particle dynamics along the continuum from hillslopes to the lowland river environment, soil particle behaviour was tested under controlled laboratory conditions. Seven flume erosion and deposition experiments, designed to simulate a natural erosive event, and five shear cell experiments were performed using three contrasting materials: two of them were poorly developed and as such can not be considered as soils, whilst the third one was a calcareous brown soil. These experiments revealed that soil aggregates were prone to disaggregation within the water column and that flocculation may affect their size distribution during transport. Large differences in effective particle size were found between soil types during the rising limb of the bed shear stress sequence. Indeed, at the maximum applied bed shear stress, the aggregated particles median diameter was found to be three times larger for the well‐developed soil than for the two others. Differences were smaller in the falling limb, suggesting that soil aggregates underwent structural changes. However, characterization of particles strength parameters showed that these changes did not fully turn soil aggregates into flocs, but rather into hybrid soil aggregate–floc particles. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Site effects characterize the filtering mechanisms within the soil sedimentary layers overlying bedrock. In regions of high seismicity such as California where strong motion records are relatively abundant, site coefficients can be developed by regression of recorded ground shaking parameters. In regions of low‐to‐moderate seismicity or of high seismicity but with a paucity of recorded strong motion data, such empirical models cannot be obtained in the same way. This study describes the theoretical development of a simple, rational manual procedure to calculate site coefficients, based on a single period approximation (SPA), and to construct displacement response spectra (RSD) for soil sites. The proposed simplified model, which takes into account the non‐linear behaviour of soil that is dependent on the level of shaking, impedance contrast at the soil–bedrock interface and the plasticity of soil material, has been verified by comparison with results obtained from non‐linear shear wave analyses and data recorded during the 1994 Northridge earthquake. The proposed model is believed to be a convenient tool for calculating non‐linear site responses and constructing site‐specific response spectra, which has the potential of being incorporated into code provisions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
Near‐collapse response of existing RC building under severe pulse‐type ground motion using hybrid simulation 下载免费PDF全文
下载免费PDF全文 Column shear‐axial failure is a complex response, which lends itself to physical experimentation. Reinforced concrete structures built prior to the mid‐1970s are particularly susceptible to such failure. Shear‐axial column failure has been examined and studied at the element level, but current rehabilitation practice equates such a column failure with structural collapse, neglecting the collapse resistance of the full structural system following column failure. This system‐level response can prevent a column failure from leading to progressive collapse of the entire structure. In this study, a hybrid simulation was conducted on a representative pre‐1970s reinforced concrete frame structure under severe seismic ground motion, in which three full‐scale reinforced concrete columns were tested at the University of Illinois at Urbana Champaign. The analytical portion of the model was represented in the computer program OpenSees. Failure occurred in multiple physical specimens as a result of the ground motion, and the hybrid nature of the test allowed for observation of the system‐level response of the tested columns and the remaining structural system. The behavior of the system accounting for multiple column shear‐axial failure is discussed and characterized. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Within the scope of the interdisciplinary Natural and Artificial Systems for Recharge and Infiltration research project dealing with riverbank filtration processes at the Berlin water works, a semi‐technical column experiment has been ongoing since January 2003. Here, a 30 m long soil column is infiltrated with surface water sampled from Lake Tegel (Berlin, Germany) under saturated flow conditions. Changes in pore water hydrochemistry sampled on 21 non‐equidistant distributed points are verified by coupled transport and reaction modelling. The objective of reactive transport modelling was to identify the main biogeochemical processes within the soil column during the flushing experiment as a conceptual model for riverbank filtration. Modelling was done with a combination of MATLAB and PHREEQC. The main processes identified are: (1) biogeochemical degradation due to interaction of natural surface water with the soil matrix; (2) continuous dissolution of refractory air bubbles from the soil column matrix. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
8.
This paper presents an efficient procedure to determine the natural frequencies, modal damping ratios and mode shapes for torsionally coupled shear buildings using earthquake response records. It is shown that the responses recorded at the top and first floor levels are sufficient to identify the dominant modal properties of a multistoried torsionally coupled shear building with uniform mass and constant eccentricity even when the input excitation is not known. The procedure applies eigenrealization algorithm to generate the state‐space model of the structure using the cross‐correlations among the measured responses. The dynamic characteristics of the structure are determined from the state‐space realization matrices. Since the mode shapes are obtained only at the instrumented floor (top and first floors) levels, a new mode shape interpolation technique has been proposed to estimate the mode shape coefficients at the remaining floor levels. The application of the procedure has been demonstrated through a numerical experiment on an eight‐storied torsionally coupled shear building subjected to earthquake base excitation. The results show that the proposed parameter identification technique is capable of identifying dominant modal parameters and responses even with significant noise contamination of the response records. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
S. T. Trudgill 《水文研究》1987,1(2):149-170
Three fluorescent dyes (Rhodamine WT, Lissamine FF and Amino G Acid) are compared for use in soil water tracing. Severe limitations are evident, but practical applications are possible. Background fluorescence, adsorption, desorption, pH and other non-adsorptive effects are reviewed in the contexts of soil column work and field tracing of soil water. Lissamine FF and Amino G Acid are to be preferred for soil column work because of their lower adsorption; Rhodamine WT exhibits higher adsorption but is useful in field situations where organic fluorescence backgrounds are high. Semi-quantitative work may be undertaken in soil columns once a priming and flushing procedure has been adopted. 相似文献
10.
开展场地地震动反应分析是众多海洋工程活动顺利实施和长期安全运行的重要保障,其中查明海底土小应变动力特性是十分关键的。文章借助海上原位钻孔取样和室内共振柱仪对辽东湾近海海底土小应变动力特性开展试验研究,探讨前人总结提出的滨海海底土初始动剪切模量Gmax预测经验公式在辽东湾海域的适用性,对比文章试验结果与周边海域已有海底土剪切波速测试结果,分析小应变范围内海底土动剪切模量的衰减特征和阻尼比发展演变趋势,并同时进行定量化模拟预测,评价海底土动剪切模量衰减曲线的归一化特征。研究结果表明：(1)共振柱试验得到的原状海底土剪切波速与周边海域已有海底土剪切波速测试结果吻合良好;(2)相比起陆地土,海洋土在小应变范围内归一化动剪切模量G/Gmax衰减得更慢,阻尼比增长得也更慢;(3)通过引入临界剪应变,不同土类和埋深对应的海底土小应变动剪切模量衰减曲线可以进行归一化。研究成果对合理开展海洋工程场地地震动反应分析评价具有一定的指导意义。 相似文献
11.
A wavelet‐based random vibration theory has been developed for the non‐stationary seismic response of liquid storage tanks including soil interaction. The ground motion process has been characterized via estimates of statistical functionals of wavelet coefficients obtained from a single time history of ground accelerations. The tank–liquid–soil system has been modelled as a two‐degree‐of‐freedom (2‐DOF) system. The wavelet domain equations have been formulated and the wavelet coefficients of the required response state are obtained by solving two linear simultaneous algebraic equations. The explicit expression for the instantaneous power spectral density function (PSDF) in terms of the functionals of the input wavelet coefficients has been obtained. The moments of this PSDF are used to estimate the expected pseudo‐spectral acceleration (PSA) response of the tank. Parametric variations are carried out to study the effects of tank height, foundation natural frequency, shear wave velocity of soil and ratio of the mass of tank (including liquid) to the mass of foundation on the PSA responses of tanks. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
12.
The objective of the study presented in this paper is to investigate the effects of masonry infills on the shear demand and failure of columns for the case when reinforced concrete frames with such infills are modeled by means of simplified nonlinear models that are not capable of the direct simulation of these effects. It is shown that an approximate simulation of the shear failure of columns can be achieved through an iterative procedure that involves pushover analysis, post‐processing of the analysis results using limit‐state checks of the components, and model adaptation if shear failure of columns is detected. The fragility parameters and the mean annual frequency of limit‐state exceedance are computed on the basis of nonlinear dynamic analysis by using an equivalent SDOF model. The proposed methodology is demonstrated by means of two examples. It was shown that the strength of the four‐story and seven‐story buildings and their deformation capacity are significantly overestimated if column shear failure due to the effects of masonry infills is neglected, whereas the mean annual frequency of limit‐state exceedance for the analyzed limit states is significantly larger than that estimated for the case if the shear failure of columns is neglected. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
13.
Rocking damage‐free steel column base with friction devices: design procedure and numerical evaluation 下载免费PDF全文
下载免费PDF全文 Earthquake‐resilient steel frames, such as self‐centering frames or frames with passive energy dissipation devices, have been extensively studied during the past decade, but little attention has been paid to their column bases. The paper presents a rocking damage‐free steel column base, which uses post‐tensioned high‐strength steel bars to control rocking behavior and friction devices to dissipate seismic energy. Contrary to conventional steel column bases, the rocking column base exhibits monotonic and cyclic moment–rotation behaviors that are easily described using simple analytical equations. Analytical equations are provided for different cases including structural limit states that involve yielding or loss of post‐tensioning in the post‐tensioned bars. A step‐by‐step design procedure is presented, which ensures damage‐free behavior, self‐centering capability, and adequate energy dissipation capacity for a predefined target rotation. A 3D nonlinear finite element (FE) model of the column base is developed in abaqus . The results of the FE simulations validate the accuracy of the moment–rotation analytical equations and demonstrate the efficiency of the design procedure. Moreover, a simplified model for the column base is developed in OpenSees . Comparisons among the OpenSees and abaqus models demonstrate the efficiency of the former and its adequacy to be used in nonlinear dynamic analysis. A prototype steel building is designed as a self‐centering moment‐resisting frame with conventional or rocking column bases. Nonlinear dynamic analyses show that the rocking column base fully protects the first story columns from yielding and eliminates the first story residual drift without any detrimental effect on peak interstory drifts. The study focuses on the 2D rocking motion and, thus, ignores 3D rocking effects such as biaxial bending deformations in the friction devices. The FE models, the analytical equations, and the design procedure will be updated and validated to cover 3D rocking motion effects after forthcoming experimental tests on the column base. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
14.
Seismic hybrid simulation of a nonductile RC building with severe damage to multiple columns 下载免费PDF全文
下载免费PDF全文 Reinforced concrete frame structures built prior to the mid‐1970s are susceptible to brittle column failure under seismic action, potentially leading to progressive collapse of the structure. The behavior of columns susceptible to brittle shear‐axial failure has been studied previously but rarely has the interaction between damaged columns and the surrounding three‐dimensional structure been investigated experimentally and at full scale. In this study, as the second in a series of hybrid simulations, two full‐scale reinforced concrete columns of a representative pre‐1970s structure were tested at the Multi‐axial Full‐scale Substructure Testing and Simulation (MUST‐SIM) laboratory. Through the use of hybrid simulation, the interaction of the columns with the surrounding structure is studied under a severe seismic motion including vertical excitation. The computational model representing the remainder of the representative 10‐story structure is created in the computer program OpenSees. During the hybrid simulation, both physical specimens experience significant loss of shear and axial strength, and the effects of these failures on the surrounding system are described. The three‐dimensional computational model in OpenSees allowed for analytical flexural‐axial failure of a third column in the structure to occur. The effects of these multiple failures on the response of a full structural system under seismic action are quantified, and the progressive collapse resistance mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
Yuyuan Li Ru Gao Rui Yang Hongan Wei Yong Li Heai Xiao Jinshui Wu 《洁净——土壤、空气、水》2013,41(11):1100-1107
The impacts of soil P leaching on water eutrophication have widely been concerned. However, there is no dependable method to quantitatively estimate the P leaching risk of soils. In this study, a simple soil column method was developed using two calcareous Fluvisols, silt loam and loam. The soil column was 20 cm in length and 5 cm in diameter, and distilled water was continuously supplied from the top. The volume and dissolved reactive P (DRP) concentrations of leachate were measured. Results showed that DRP concentrations in leachate increased slowly for the low soil Olsen‐P levels but rapidly for the high Olsen‐P levels. According to these two‐phase changes in the DRP versus soil Olsen‐P contents, the thresholds of P leaching risk were estimated to be 41.1 and 62.3 mg P kg?1 (Olsen‐P) for silt loam and loam, respectively. The P leaching intensity of soils increased by 3‐ to 540‐fold if the soil Olsen‐P contents accumulated from 6.6 to 155.5 mg P kg?1. The outcomes derived from this study regarding the determination of P leaching threshold and intensity by the soil column method also need a further verification on more soils with a wide range of physical and chemical properties. 相似文献
16.
A crucial aspect of physical geotechnical model tests (under both 1-g and n-g conditions) is the evaluation of the initial (low-strain) stiffness of the soil layers of the sample test deposit, especially in the case of coarse materials. While for uniform soil deposits this issue can be addressed in a straightforward manner, e.g. by determining the fundamental frequency through the transfer function of an applied white-noise excitation, the problem becomes cumbersome for multi-layered deposits. After reviewing a number of available theoretical solutions, this paper illustrates a simplified yet reliable analytical procedure for determining the shear wave velocity profile (Vs) in a single or bi-layer deposit, taking into account the inhomogeneity of the individual soil layers, under the hypothesis of vanishing shear modulus at ground surface. The fundamental natural frequency of the inhomogeneous bi-layer deposit is analysed using the Rayleigh quotient procedure. The associated shape function is evaluated by considering the equilibrium of the soil column under a pseudo-static lateral inertial excitation imposed at its base, accounting for both layering and inhomogeneity. A validation of the proposed method is provided by comparing numerical results obtained from both time- and frequency- domain analyses against experimental data on Leighton Buzzard sand, from a recently-completed research project conducted on the shaking table facility at BLADE Laboratory, University of Bristol (UK). 相似文献
17.
Many studies focus on the effects of vegetation cover on water erosion rates, whereas little attention has been paid to the effects of the below ground biomass. Recent research indicates that roots can reduce concentrated flow erosion rates significantly. In order to predict this root effect more accurately, this experimental study aims at gaining more insight into the importance of root architecture, soil and flow characteristics to the erosion‐reducing potential of roots during concentrated flow. Treatments were (1) bare, (2) grass (representing a fine‐branched root system), (3) carrots (representing a tap root system) and (4) carrots and fine‐branched weeds (representing both tap and fine‐branched roots). The soil types tested were a sandy loam and a silt loam. For each treatment, root density, root length density and mean root diameter (D) were assessed. Relative soil detachment rates and mean bottom flow shear stress were calculated. The results indicate that tap roots reduce the erosion rates to a lesser extent compared with fine‐branched roots. Different relationships linking relative soil detachment rate with root density could be established for different root diameter classes. Carrots with very fine roots (D < 5 mm) show a similar negative exponential relationship between root density and relative soil detachment rate to grass roots. With increasing root diameter (5 < D < 15 mm) the erosion‐reducing effect of carrot type roots becomes less pronounced. Additionally, an equation estimating the erosion‐reducing potential of root systems containing both tap roots and fine‐branched roots could be established. Moreover, the erosion‐reducing potential of grass roots is less pronounced for a sandy loam soil compared with a silt loam soil and a larger erosion‐reducing potential for both grass and carrot roots was found for initially wet soils. For carrots grown on a sandy loam soil, the erosion‐reducing effect of roots decreases with increasing flow shear stress. For grasses, grown on both soil types, no significant differences could be found according to flow shear stress. The erosion‐reducing effect of roots during concentrated flow is much more pronounced than suggested in previous studies dealing with interrill and rill erosion. Root density and root diameter explain the observed erosion rates during concentrated flow well for the different soil types tested. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
18.
The effects of soil–structure interaction (SSI) while designing the liquid column damper (LCD) for seismic vibration control of structures have been presented in this study. The formulation for the input–output relation of a flexible‐base structure with attached LCD has been presented. The superstructure has been modelled by a single‐degree‐of‐freedom (SDOF) system. The non‐linearity in the orifice damping of the LCD has been replaced by equivalent linear viscous damping by using equivalent linearization technique. The force–deformation relationships and damping characteristics of the foundation have been described by complex valued impedance functions. Through a numerical stochastic study in the frequency domain, the various aspects of SSI on the functioning of the LCD have been illustrated. A simpler approach for studying the LCD performance considering SSI, using an equivalent SDOF model for the soil–structure system available in literature by Wolf (Dynamic Soil–Structure Interaction. International Series in Civil Engineering and Engineering Mechanics. Prentice‐Hall: Englewood Cliffs, NJ, 1985) has also been presented. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
19.
Chiun‐lin Wu Wu‐Wei Kuo Yuan‐Sen Yang Shyh‐Jiann Hwang Kenneth J. Elwood Chin‐Hsiung Loh Jack P. Moehle 《地震工程与结构动力学》2009,38(2):205-224
Post‐earthquake reconnaissance has reported the vulnerability of older reinforced concrete (RC) columns lacking details for ductile response. Research was undertaken to investigate the full‐range structural hysteretic behavior of older RC columns. A two‐dimensional specimen frame, composed of nonductile and ductile columns to allow for load redistribution, was subjected to a unidirectional base motion on a shaking table until global collapse was observed. The test demonstrates two types of column failure, including flexure‐shear and pure flexural failure. Test data are compared with various simplified assessment models commonly used by practicing engineers and researchers to identify older buildings that are at high risk of structural collapse during severe earthquake events. Comparison suggests that ASCE/SEI 41‐06 produces very conservative estimates on load–deformation relations of flexure‐shear columns, while the recently proposed ASCE/SEI 41‐06 update imposes significant modifications on the predictive curve, so that improved accuracy has been achieved. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
钢管混凝土叠合边框内藏钢桁架剪力墙振动台试验研究 总被引：1，自引：0，他引：1
进行了4个钢管混凝土叠合边框剪力墙模型的模拟地震振动台试验,包括:1个高宽比为1.6的钢管混凝土叠合边框剪力墙,1个高宽比为1.6的钢管混凝土叠合边框内藏钢桁架剪力墙,1个高宽比为3.0的为钢管混凝土叠合边框剪力墙,1个高宽比为3.0的钢管混凝土叠合边框内藏钢桁架剪力墙。试验中输入Taft地震波,测试了各试件在不同峰值加速度下的时程地震反应及其动力特性,分析了剪力墙损伤过程及破坏特征。研究表明,钢管混凝土叠合边框内藏钢桁架剪力墙比普通钢管混凝土叠合柱边框剪力墙承载力高、刚度退化慢、延性好、抗震耗能能力强。 相似文献