轴压比对中等高度LC结构剪力墙抗震性能的影响

轻骨料混凝土(L ight-we ight concrete,简称LC)剪力墙的轴压比是剪力墙抗震设计时一个重要的控制因素,直接关系到其延性性能。为使设计规程具有足够的理论依据,本文通过对六榀轻骨料混凝土剪力墙试件的试验,研究了在低周反复荷载作用下,着重考虑不同轴压比对中等高度有边框剪力墙的破坏形态和变形性能的影响效应,对其滞回特性进行分析,计算了各剪力墙的刚度退化率与延性系数,并将无竖缝剪力墙与带竖缝剪力墙的抗震性能进行了对比。     

剪切型多自由度体系瞬时输入能量的分布

通过对剪切型多自由度体系的地震能量反应分析,提出了描述多自由度体系整体脉冲能量反应的参数,瞬时输入能量等效平均速度,并在此基础上建立了瞬时输入能量分布系数的概念,提出了估计瞬时输入能量分布的方法。     

扩径率与入岩深度对岩基挖孔基础抗拔承载特性影响的试验研究

扩径率和入岩深度是影响岩基挖孔基础抗拔承载特性的两个重要因素。通过开展8个不同扩径率、不同入岩深度挖孔基础的现场真型上拔静载试验,从荷载位移变化规律、抗拔承载力和地基岩体破坏模式三方面分析了扩径率与入岩深度对基础抗拔承载特性的影响,结果表明扩径率对荷载位移曲线初始线性阶段影响显著。采用图解法分别获得代表基础低、中、高3种承载能力的抗拔承载力QL1、QDLI、QL2,分析表明,随着扩径率与入岩深度的增加,基础抗拔承载力均有不同程度提高,但两种因素对基础承载力影响机制不同,扩径率可明显提高初始弹性阶段的承载力QL1,而入岩深度可明显提高塑性阶段的承载力QDLI和QL2。通过分析地基破坏时地表岩体裂缝的分布特征,得出岩基中上拔岩体的破坏模式与基础结构型式无关,均是从基底开始出现裂缝,沿着一定角度的开口延伸至地面,直至地基发生破坏,并且破坏范围随着入岩深度的增加而减小。综合考虑基础施工安全性、经济性和机械化程度,建议优先选择加深入岩深度的措施来提高基础抗拔承载力。     

基于Hock-Brown强度准则的高应力判据理论分析

如何评价工程岩体中赋存的应力状态一直是工程设计人员所要面对的基本问题之一.应力状态评价需综合考虑岩体强度和岩体中赋存的应力两个要素,其评价结果反映了地下结构围岩在二次应力场作用下满足岩体强度准则时可能的变形破坏响应.通过对前人研究成果的分析,总结出高应力作用下地下结构的基本变形破坏规律.利用Hoek-Brown强度准则...     

奥地利Gosau群Bibereck组Campanian早期海水变深序列的地层学和地球化学

Schmidsippl剖面位于奥地利北钙质阿尔卑斯构造带内Gosau群典型地区。剖面出露的Bibereck组记录了一个海侵和沉积区海水变深过程。Bibereck 组之下是Santonian 晚期Hochmoos 组(Sandkalkbank段),主要为砂质、粉砂质灰色生物扰动构造发育的泥灰岩,含少量双壳类碎片。Hochmoos组之上为灰色泥灰岩和泥灰质灰岩。Bibereck组下部显示变深到近滨-远滨过渡带区域;向上,泥灰岩指示细粒泥质远滨沉积,水深大致50~150 m;之上出现浮游有孔虫含量超过90%的泥灰质灰岩,代表着半深海沉积环境。生物地层数据显示采样层位整体位于浮游有孔虫asymetrica elevata 带,由Globotruncanita elevata 和Dicarinellaasymetrica 的共同出现来界定。钙质超微化石Calculites obscurus、Lucianorhabdus cayeuxii、Arkhangelsk iella cymbiformis 的出现指示属于钙质超微化石带CC17b/UC12,相当于Campanian初期。地层深度剖面上,Ca/Al比值和Catot含量显示海水来源的Ca在0~5 m地层内几近于零,向上快速增加;(Fe/Al)/碳酸盐显示两个峰值,代表更还原条件,分别位于4 m和10 m位置;K/Al比值的下降被解释为更潮湿气候条件;剖面上部Ba含量的增加显示向更低原始生产条件的变化;陆源矿物在剖面7 m以下保持稳定,之上一直到剖面顶部不断下降。生物地层     

Field calibration and performance of sediment traps in a eutrophic holomictic lake

In wind-stressed and unstratified Lough Neagh low aspect ratio sediment traps, which allow for internal resuspension, collected sediment at a rate close to the natural sediment accumulation rate inferred from dated sediment cores. High aspect ratio traps grossly overestimated the natural rate of sediment accumulation as did, but to a lesser extent, burial rate measurements on an artificial stratigraphic marker. The former type of trap deployed over long exposure periods is therefore recommended as providing the best estimate of net downward particle flux in lakes such as Lough Neagh. However, it is emphasized that all sediment trap types, when operated in shallow turbulent lakes, will to a greater or lesser extent be contaminated by secondary or redeposited material and so will not provide a direct measure of primary sedimentation. Use of tube traps in lakes such as Lough Neagh should not, however, be discounted since they can provide a record of the quality of sedimenting material through time.     

Lippmann Diagrams: Theory and Application to Carbonate Systems

Since 1980 when F. Lippmann's seminal paper appeared, ourunderstanding of solubility equilibria involving ionic solidsolutions has been advanced by theoretical considerations as wellas careful experimental studies designed to determine excess Gibbsfunctions. A unified theory of solid-solution aqueous-solutionequilibria as well as the thermodynamic background of thephenomenon of ``stoichiometric saturation' are reviewed.It is shown that Lippmann diagrams effectively summarize thethermodynamic basis of solid-solute aqueous-solution equilibria ofsparingly soluble metal carbonate systems. Clearly, the predictivepower of these diagrams may be limited due to kineticrestrictions. Only when dissolution and precipitation areessentially reversible, favourable conditions to synthesizehomogeneous solid phases can be derived from studies of equilibria.     

Dimensionless input parameters in discrete element modeling and assessment of scaling techniques

A set of dimensionless input parameters were defined for DEM using a characteristic time which is a function of density and elastic modulus of particles and an arbitrary characteristic length. Dimensionless strain rate and mass damping ratio are inversely proportional to the characteristic time, and stress is normalized by elastic modulus to give dimensionless stress. It was demonstrated that the response of a model in the dimensionless scale is invariant with the choice of density, elastic modulus and the characteristic length if dimensionless strain rate and mass damping ratio are kept constant. Small time step is a prohibitive aspect of DEM. Scaling techniques are widely employed to enlarge the time step. Using the dimensionless scheme, it was learned that density scaling is equivalent to the use of a higher strain rate, and stiffness scaling results in a higher strain rate and an elevated stress state in the dimensionless scale.