The inclusion record of fluid evolution,crack healing and trapping from a heterogeneous system during rapid cooling of pegmatitic veins (Dronning Maud Land; Antarctica)

Granitoid (pegmatite and aplite) veins in metamorphic rocks and intrusive syenites of central Dronning Maud Land, Antarctica, are flanked by conspicuous light‐coloured alteration halos, which represent the damage zone of fracture propagation. The damage zone is characterized by a high density of sealed or healed microcracks, about 1 order of magnitude above background. Fluid inclusions along healed microcracks in quartz of both pegmatite and alteration halos are inspected by optical and scanning electron microscopy, and their composition is analysed by microthermometry and quadrupole mass spectrometry. The similar inclusion record in the granitoid vein and in the damaged host rock indicates the derivation of the fluids from the hydrous melt phase. The aqueous inclusions bear abundant daughter crystals, mainly silicates, and may represent a hydrous melt. The volatile composition is variable in the system H₂O–CO₂, with mostly subordinate amounts of N₂. Phase separation with partitioning of CO₂ into the fluid phase coexisting with the hydrous melt, and possibly immiscibility in the subsolidus range, govern fluid evolution during cooling. The variable CO₂/N₂ ratio suggests mixing with fluids from an external source in the host rock and vigorous circulation at an early stage of high transient permeability. Experiments have shown that healing of microcracks at high temperatures is a matter of hours to weeks, hence similar in time scale to the cooling of the cm‐ to dm‐thick granitoid veins. In this case, rapid cooling and concomitant crack healing in a system undergoing phase separation causes a broad compositional variability of the inclusions due to necking down, and the underpressure developing in closed compartments precludes a meaningful thermobarometric interpretation.     

2015尼泊尔地震后加德满都谷地世界文化遗产破坏特征

2015尼泊尔地震对加德满都谷地的世界文化遗产造成不可估量的损失。为了探究谷地文化遗产震害整体分布特征,对谷地世界文化遗产建筑的震害状况开展实地调查,划分了三类文化遗产震害等级标准,形成了六处世界文化遗产的震害图并对其进行统计分析,加德满都、帕坦和巴德岗三处杜巴广场震后保存基本完好的文化遗产建筑占各自总数的39.5%、53.3%、50%,斯瓦扬布纳特寺、昌谷纳拉扬寺和博达哈大佛塔主体保存基本完好,附属建筑不同程度地破坏。加德满都、帕坦和巴德岗三处杜巴广场地层的松软沉积层放大地震效应使建筑严重破坏,斯瓦扬布纳特寺、昌谷纳拉扬寺震害主要受地形特征影响。考察成果为我国同类遗产建筑的抗震防护提供参考。     

甲基三甲氧基硅烷对砂岩石刻封护性能的实验室研究

为了解砂岩石刻用甲基三甲氧基硅烷材料封护处理后的各项性能,选择四川省内风化较严重的摩崖造像区的砂岩作为实验样品,采用浸水、酸雾、盐老化、光老化、循环破坏等方法对材料的憎水性、透气性、耐老化性能进行实验测试。试验表明,砂岩样品用甲基三甲氧基硅烷封护处理后其憎水性、耐老化性都有较大的提高,透气性没有太大的改变,半涂样品经循环破坏处理后,表面出现开裂现象。通过研究表明,甲基三甲氧基硅烷材料处理砂岩后其憎水性和耐老化性都较好,但循环破坏实验提示,甲基三甲氧基硅烷材料处理石刻可能对其表面产生负作用,在石刻保护中应慎重使用。     

Performance and Risks of Salt-Accumulating Renders in Relation to Their Moisture Transport Properties

Salt-accumulating renders are usually applied in several layers with different specific properties of moisture transport. An extensive experimental programme was carried out to establish a relationship between those properties of individual layers and the performance of combined systems on a salt-laden substrate. Each of the 20 renders was characterized separately in absorption and drying tests, vacuum saturation tests, dry cup tests, mercury intrusion porosimetry, and ultrasound wave velocity measurements. Each of the 12 combined render systems was applied on a brick, which was then saturated with a concentrated NaCl solution by free capillary uptake. Subsequently the assembly was closed at the bottom and subjected to an accelerated drying test (50° C and 15% relative humidity). Moisture and salt profiles over the depth were taken regularly during 1 month. The results reveal very different degrees of effectiveness and levels of risk for the substrate, which are related to the moisture transport properties.     

DAMAGE AND DUCTILITY DEMAND SPECTRA ASSESSMENT OF HYSTERETIC DEGRADING SYSTEMS SUBJECT TO STOCHASTIC SEISMIC LOADS

Damage phenomena observed in structures subject to intense seismic events are the result of stiffness and strength degradation. This paper studies the damage assessment of hysteretic degrading structures described by means of the Bouc-Wen model, modified to represent the mechanical degradation induced by severe earthquakes. In order to consider randomness of seismic action, the analysis is performed by adopting a stochastic approach and the Park and Ang damage functional is also evaluated in stochastic way. A parametric analysis is carried out with the aim to analyse the effect of mechanical characteristics and measure parameters of earthquake intensity on seismic response and damage level. Damage spectra are finally obtained and they are used to develop, on the basis of the Performance Based Seismic Design, ductility demand spectra.     

A PROCEDURE FOR ESTIMATING INPUT ENERGY SPECTRA FOR SEISMIC DESIGN

In this paper, the damage potential of an earthquake ground motion is evaluated in terms of the total power of the acceleration of the ground motion. By assuming an appropriate spectral shape for the input energy spectrum, and using the well-known Parseval theorem for evaluating the total power of a random signal, the peak amplification factor for the equivalent input energy velocity spectrum can be determined. It is shown that the peak amplification factor for the input energy spectrum depends on the peak-ground-acceleration to peak-ground-velocity ratio and duration of the strong motion phase of the ground motion. Values for the equivalent input energy velocity amplification factor vary from about 2 to 10 for most of the recorded ground motions used in this study. Although a considerable scatter of data is observed in this study, the peak amplification factor predicted by the Fourier amplitude spectrum of the ground acceleration provides a fairly good estimate of the mean value of the peak input energy compared to that determined from inelastic dynamic time history analyses, particularly for systems with high damping and low lateral strength. The peak amplification factor derived in this paper provides a more consistent approach for estimation of seismic demand when compared to an earlier empirical expression used for the formulation of duration-dependent inelastic seismic design spectra, even though only a slight difference in the required lateral strength results from the use of the new formula.     

A DAMAGE MODEL FOR THE ANALYSIS OF THE SEISMIC RESPONSE OF MONUMENTAL BUILDINGS

In this paper the Author proposes a damage model for the analysis of masonry plates and shells, which is based on an improvement of a previous constitutive model. The modifications introduced, connected to the head joint damage, allow us to study the influence of masonry texture on the damage modes once the mechanical characteristics of the elements constituting the masonry and the results of tests on simple assemblages are known. Having a nonlinear constitutive model is certainly one of the basic elements for understanding the damage mechanisms in masonry buildings. If, in fact, an elastic-linear constitutive model may be used under normal loading conditions, in critical situations it is necessary to model the damage and the dissipation mechanisms that occur between the elements, stone (brick) and mortar, in correlation with their characteristics and kind of masonry. To validate the model a comparison is made between the numerical and experimental results, in the case of tests available in the literature in masonry panels subjected to out-of plane loading and in a real structure through the observation of the damage in Umbria (Italy) surveyed after the 1997 earthquake.     

Damage Assessment of Unreinforced Stone Masonry Buildings After the 2010–2011 Canterbury Earthquakes

The sequence of earthquakes that has affected Christchurch and Canterbury since September 2010 has caused damage to a great number of buildings of all construction types. Following post-event damage surveys performed between April 2011 and June 2011, an inventory of the stone masonry buildings in Christchurch and surrounding areas was carried out in order to assemble a database containing the characteristic features of the building stock, as a basis for studying the vulnerability factors that might have influenced the seismic performance of the stone masonry building stock during the Canterbury earthquake sequence. The damage suffered by unreinforced stone masonry buildings is reported and different types of observed failures are described using a specific survey procedure currently in use in Italy. The observed performance of seismic retrofit interventions applied to stone masonry buildings is also described, as an understanding of the seismic response of these interventions is of fundamental importance for assessing the utility of such strengthening techniques when applied to unreinforced stone masonry structures.     

Assessing the effects of conservation treatments on short sequences of DNA in vitro

Little is known about what effects conservation treatments used to preserve human and animal hard and soft tissues have on DNA preservation. We have developed a method to assess quantitatively the extent of lesions or strand breakage caused by conservation treatments on short sequences of DNA in vitro. The method developed enables the determination of the percentage of DNA preserved following exposure to a conservation treatment solution relative to control samples, thereby allowing the direct comparison of treatments based upon their preserving/damaging effects on a DNA sequence. Forty-three chemicals commonly used in the preparation and/or conservation of human and/or animal remains were examined. We found that the majority were damaging, in particular and as expected, acidic treatments and treatments carried out at elevated temperatures. A few, primarily organic solvents, were not damaging. The approach we have adopted can be applied to screen other treatments either used in the past or for future conservation applications as they are developed to assess their effects on DNA. How these results should be interpreted in terms of conservation and sampling is also discussed.