Correction factors for SSI effects predicted by simplified models: 2D versus 3D rectangular embedded foundations

The effects of soil‐structure interaction (SSI) are often studied using two‐dimensional (2D) or axisymmetric three‐dimensional (3D) models to avoid the high cost of the more realistic, fully 3D models, which require 2 to 3 orders of magnitude more computer time and storage. This paper analyzes the error and presents correction factors for system frequency, system damping, and peak amplitude of structural response computed using impedances for linear in‐plane 2D models with rectangular foundations, embedded in uniform or layered half‐space. They are computed by comparison with results for 3D rectangular foundations with the same vertical cross‐section and different aspect ratios. The structure is represented by a single degree‐of‐freedom oscillator. Correction factors are presented for a range of the model parameters. The results show that in‐plane 2D approximations overestimate the SSI effects, exaggerating the frequency shift, the radiation damping, and the reduction of the peak amplitude. The errors are larger for stiffer, taller, and heavier structures, deeper foundations, and deeper soil layer. For example, for a stiff structure like Millikan library (NS response; length‐to‐width ratio ≈ 1), the error is 6.5% in system frequency, 44% in system damping, and 140% in peak amplitude. The antiplane 2D approximation has an opposite effect on system frequency and the same effect on system damping and peak relative response. Linear response analysis of a case study shows that the NEHRP‐2015 provisions for reduction of base shear force due to SSI may be unsafe for some structures. The presented correction factor diagrams can be used in practical design and other applications.     

矩形Cartogram自动构建方法探究

矩形Cartogram作为一种同时表达拓扑及数据属性的面域Cartogram,因其表达内容简单、直观的特点,具有较大的潜力。矩形Cartogram尝试用简单的矩形表示复杂地理所具有的拓扑及数据属性,这两个属性在其自动构建过程中往往是矛盾的,因此产生了很多截然不同的构造方法。对其自动构建方法进行研究,有助于地理信息与统计数据融合方法的探索。本文首先简要介绍了矩形Cartogram的研究背景、研究现状及其意义;归纳了矩形Cartogram的特点与评价标准,进而分析了两类构造矩形Cartogram的典型算法,总结了自动构建算法难点;最后探讨了现有矩形Cartogram研究存在的问题,并对其发展方向进行了展望。     

三维层状场地的精确动力刚度矩阵及格林函数

本文对Wolf二维层状场地精确动力刚度矩阵进行推广,给出了三维层状场地的精确动力刚度矩阵。刚度矩阵具有对称的特点,且因刚度矩阵是精确的,计算结果不受土层单元厚度的影响,可以大大提高计算效率。文中对刚度矩阵进行了数值验证。利用三维层状场地动力刚度矩阵,计算分析了基岩上单一土层场地的动力响应。最后作为动力刚度矩阵的另一重要应用,给出了表面或埋置矩形均布荷载或集中荷载的动力格林函数计算方法。     

均质地基上浅埋矩形基础极限承载力上限分析

基于土体塑性极限分析理论,推导一般黏性土地基上矩形基础承载力的上限解。为了证实上限解的合理性与适用性,采用大型通用有限元分析软件ABAQUS进行数值分析,并分别与Vesic理论解和Salgado et al理论解进行了对比。结果表明,推导的三维矩形基础上限解能较好地计算黏性土地基的极限承载力。     

空间直角坐标转换大地坐标的直接解法

根据地面点地心空间直角坐标与地心大地坐标的关系式,导出由空间直角坐标求解大地坐标的更为简洁的直接计算公式,并对计算误差进行分析讨论。理论分析和实际验算结果表明,该直接解法引起的纬度误差不大于10-5s,可以满足精密的大地测量需要。     

空间直角坐标计算大地坐标的抛物线逼近法

采用抛物线逼近法求解大地纬度和大地高,先计算空间点在椭球面上的子午面坐标,然后求解点的大地纬度和大地高。     

A new analytical model for consolidation with multiple vertical drains

Various analytical theories of consolidation for soils with vertical drains have been proposed in the past. Most conventional theories are based on a cylindrical unit cell that contains only a single vertical drain. This paper described a new analytical model where a vertical drain located at the centre (the ‘inner vertical drain’) and is surrounded by two or three vertical drains (the ‘outer vertical drains’), the number of which depends on whether the configuration is triangular or rectangular. Both types of drains are combined into a cylindrical unit cell, and the water is assumed to flow both inwards to the inner vertical drain and outwards to the outer vertical drains distributed around the circumference. The outer radial boundary of the unit cell is regarded as a permeable boundary, with a drainage capacity of two or three separate vertical drains for triangular and rectangular configurations, respectively. The smear effects and the drainage resistances for both the inner and outer vertical drains are considered in the analysis as well. In this way, the equations governing the consolidation process with multiple vertical drains are derived, and the corresponding analytical solutions are obtained for instantaneously loading, ramp loading and multi‐stage of instantaneously loading and multi‐stage of ramp loading. The present solutions are finally compared with several conventional solutions for a single vertical drain in the literature. The results show that the present model predicts the same average degree of consolidation as conventional models do, which verifies the correctness of this new model. Finally, the settlement predicted by the present solution is compared with the measured settlement from a field test at the Port of Brisbane, Australia, which shows a good agreement between them. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental study on the effectiveness of TLDs under wave loading

The objective of this study is to experimentally investigate the effectiveness of Tuned Liquid Dampers (TLDs) for suppressing the dynamic response of a platform structure subjected to wave loading and to explore the applicability of TLDs for suppressing the structural vibration of fixed offshore platforms. The experimental model is scaled according to a full size platform by matching its dynamic properties. Rectangular and circular TLDs of various sizes and water depths are examined.The experiments were performed in a 2-D wave flume. The effectiveness of TLDs is evaluated based on their response reduction. By observing the performance and the behavior of TLDs through laboratory experiments, the effects of a number of parameters including container shape, container size, number of dampers, frequency ratio, mass ratio, and incident wave characteristics are investigated.     

基于GPS基线向量计算机场跑道真方位角

本文介绍了GPS相对静态定位测量结合站心地平直角坐标系计算跑道真方位角的方法,通过坐标方位角加上改正值计算真方位角的方法进行验证,结合工程实例对该方法进行验证。该方法计算过程简单,可靠性好,省时省力。     

On the potential of Bartlett Lewis rectangular pulse models for simulating rainfall in Peninsular Malaysia

Abstract

The applicability of two versions of the Bartlett Lewis rectangular pulse model, the original and the modified model, is discussed for describing the temporal and spatial variation of rainfall patterns observed at 15 raingauge stations in Peninsular Malaysia over the period 1971–2008; 17 different sets of moment combinations are fitted to these models based on the generalized method of moments approach. The common statistics included in all sets are the mean, variance, lag-1 autocorrelation and the probability of dry based on the hourly rainfall data. The analysis was carried out on hourly rainfall data from all 15 stations for all months of the year. Two stations, Petaling Jaya and Kemaman, located on the west and east coasts of the Peninsula, respectively, are considered for illustration of the results, taking the months of July and November, which correspond to the driest and wettest months, corresponding to the southwest monsoon (May–August) and northeast monsoon (November–February), respectively. The best moment combination found for the illustrative results is based on the common statistics, as well as the mean and variance based on 24-h aggregated rainfall data, the inclusion of which successfully improved the model performance; the errors were significantly reduced. It was also found that the performance of the fitted models based on the mean absolute deviate error varies according to the type of Bartlett Lewis model applied: errors are much smaller for the fitted model based on the modified model as compared to the original model. In addition, the fitted statistics: mean, lag-1 autocorrelation and probability of dry are quite well fitted for several aggregated time scales; however, the variances are underestimated in both models for all aggregated time scales, particularly in the case of the original model. The results of extreme value analysis indicate that the modified model failed to reproduce the annual hourly and daily rainfall extremes satisfactorily.

Editor D. Koutsoyiannis; Associate editor C. Onof

Citation Hanaish, I.S., Ibrahim, K., and Jemain, A.A., 2013. On the potential of Bartlett Lewis rectangular pulse models for simulating rainfall in Peninsular Malaysia. Hydrological Sciences Journal, 58 (8), 1690–1703.