Shear modulus and damping ratio of grouted sand

An experimental comparative study of three different grouted sands in terms of their effects on the values of two dynamic properties is presented. The dynamic properties studied are the shear modulus and the damping ratio which are determined with resonant column tests and cyclic triaxial tests. The behaviour of a pure Fontainebleau sand is compared with the behaviour of a Fontainebleau sand grouted with a silicate grout, a micro-fine cement grout and a mineral grout. The effects of the grouting treatment, the type of grout, the confining pressure, and the strains, on the shear modulus and the damping ratio are studied. The test results have shown that grouting improves the stiffness of the sand especially for small strains. Whatever the type of material, confining stress improves the shear modulus whereas it has a negligible effect on the damping ratio. When strain increases, the shear modulus decreases and the damping ratio increases.     

Multiple‐tuned liquid column dampers for torsional vibration control of structures: theoretical investigation

This paper presents a theoretical investigation on the performance of multiple‐tuned liquid column dampers (MTLCD) for reducing torsional vibration of structures in comparison with single‐tuned liquid column dampers (STLCD). The analytical model is first developed for torsional vibration of a structure with an MTLCD under either harmonic excitation or white noise excitation. The experimental results are then used to verify the analytical model for coupled MTLCD‐structure systems under harmonic excitation. The performance of an MTLCD and its beneficial parameters for achieving the maximum torsional response reduction to white noise excitation are finally investigated through an extensive parametric study in terms of the distance from the centre line of the MTLCD to the rotational axis of the structure, the ratio of the horizontal length to the total length of liquid column, frequency bandwidth, head‐loss coefficient, the number of TLCD units in an MTLCD, frequency‐turning ratio and the spectral level of excitation moment. The results show that there is an optimal head‐loss coefficient and an optimal frequency bandwidth for an MTLCD to achieve the maximum torsional response reduction. It is also demonstrated that the sensitivity of an optimized MTLCD to the frequency‐tuning ratio is less than that of an optimized STLCD, and it can be further improved by increasing the bandwidth but at the cost of less torsional vibration reduction. Copyright © 2002 John Wiley & Sons, Ltd.     

钢管混凝土轴压长柱承载力的试验研究

通过对12个钢管混凝土长柱试件的试验分析，探讨了影响钢管混凝土长柱承载力的因素；引入切线模量概念，从理论上推导出钢管混凝土轴压长柱承载力的公式。     

Stone columns as liquefaction countermeasure in non-plastic silty soils

In many cases densification with vibro-stone columns cannot be obtained in non-plastic silty soils. Shear stress re-distribution concepts [1] have been previously proposed as means to assess stone columns as a liquefaction countermeasure in such non-plastic silty soils. In this study, centrifuge testing is conducted to assess the performance of this liquefaction countermeasure. Attention is focused on exploring the overall site stiffening effects due to the stone column placement rather than the drainage effects. The response of a saturated silt stratum is analyzed under base dynamic excitation conditions. In a series of four separate model tests, this stratum is studied first without, then with stone columns, as a free-field situation, and with a surface foundation surcharge. The underlying mechanism and effectiveness of the stone columns are discussed based on the recorded dynamic responses. Effect of the installed columns on excess pore pressures and deformations is analyzed and compared. The test results demonstrate that stone columns can be an effective technique in the remediation of liquefaction induced settlement of non-plastic silty deposits particularly under shallow foundations, or vertical effective stresses larger than about 45 kPa (1000 psf) in free field conditions.     

Study of total column atmospheric aerosol optical depth,ozone and precipitable water content over Bay of Bengal during BOBMEX-99

The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99 have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment. The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high, there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols over the study region.     

Reversed polarity patches at the CMB and geomagnetic field reversal

The International Geomagnetic Reference Field models (IGRF) for 1900–2000 are used to calculate the geomagnetic field distribution in the Earth’ interior from the ground surface to the core-mantle boundary (CMB) under the assumption of insulated mantle. Four reversed polarity patches, as one of the most important features of the CMB field, are revealed. Two patches with +Z polarity (downward) at the southern African and the southern American regions stand out against the background of ™Z polarity (upward) in the southern hemisphere, and two patches of ™Z polarity at the North Polar and the northern Pacific regions stand out against the +Z background in the northern hemisphere. During the 1900–2000 period the southern African (SAF) patch has quickly drifted westward at a speed of 0.20–.3° /a; meanwhile its area has expanded 5 times, and the magnetic flux crossing the area has intensified 30 times. On the other hand, other three patches show little if any change during this 100-year period. Extending upward, each of the reversed polarity patches at the CMB forms a chimney-shaped “reversed polarity column” in the mantle with the bottom at the CMB. The height of the SAF column has grown rapidly from 200km in 1900 to 900km in 2000. If the column grows steadily at the same rate in the future, its top will reach to the ground surface in 600–700 years. And then a reversed polarity patch will be observed at the Earth’s surface, which will be an indicator of the beginning of a magnetic field reversal. On the basis of this study, one can describe the process of a geomagnetic polarity reversal, the polarity reversal may be observed firstly in one or several local regions; then the areas of these regions expand, and at the same time, other new reversed polarity regions may appear. Thus several poles may exist during a polarity reversal.     

碎石桩复合地基承载力性状分析

按等置换率原则建立碎石桩复合地基有限元计算模型，在考虑基础刚度、荷载强度变化条件下对比分析了天然地基与复合地基附加应力分布特征、塑性区扩展规律；根据有限元计算结果分析了桩身荷载传递规律并与实测结果对比确定桩身应力随桩身呈指数衰减。计算结果还表明：桩土应力比不仅与桩土模量比有关，也与荷载水平及置换率有关；在鼓胀破坏情形下桩体侧向变形性质取决于桩周土而与置换率、模量比、桩长无关。     

带交叉筋十字形短柱抗震性能试验研究

在提出带暗柱异形柱基础上，进一步提出带交叉筋异形柱这一设计方法，通过3根十字形短柱抗震性能的试验研究，分析比较了普通十字形柱，带暗柱十字形柱和带交叉筋十字形柱的性能，试验表明加配交叉钢筋可明显提高十字形短柱的抗震性能。     

构造柱一圈梁体系外多孔砖内混凝土小型空心砌块六层足尺房屋抗震性能试验研究

本文简述了六层构造柱 -圈梁体系外墙用多孔砖、内墙用混凝土小型空心砌块足尺房屋抗震试验的设计 ,介绍了模型楼的试验结果 ,并对试验结果进行了分析 ,评价了此类房屋的抗震能力。最后 ,本文对此类房屋的工程实践提出一些建议     

中高层钢筋混凝土异形柱框架结构试验与理论研究

对-1/6比例12层大开间钢筋混凝土异形柱框架结构模型进行了振动台试验，探讨结构的地震反应和破坏形态，采用杆模型编制了钢筋混凝土异形柱框架结构的弹塑性时程分析程序，经比较，计算结果与试验值吻合较好，探讨了肢长肢厚比对该体系结构性能的影响，并提出了相应的设计建议。