斜拉桥H型混凝土桥塔的有限延性

由于塔梁之间的横向约束,在强地震动作用下斜拉桥的桥塔将产生较大的横向动力响应,为了满足规范规定的抗震性能目标,则须采用较大的桥塔配筋率.同时,桥塔基于弹性设计的思路,还会导致下部结构的工程量增加,其工程经济性值得商榷.为此采用IDA(incremental dynamic analysis)方法研究斜拉桥桥塔横桥向塑性变形分布规律和破坏模式.通过有限元分析和拟静力试验相结合的手段,对H型混凝土桥塔横向破坏机理进行验证,确定所要达到的性能目标,并得到与之对应的可以量化的性能指标.为斜拉桥的有限延性抗震设计提供理论和试验基础.

少筋混凝土重力式桥墩抗震设计方法研究

研究目的：对于我国高速铁路广泛采用的少筋混凝土重力式桥墩（配筋率ρ〈0.5%）,《铁路工程抗震设计规范》仅给出多遇地震下的一阶段强度设计方法,因而缺乏罕遇地震下的抗震验算方法。为此,本文首先采用拟静力试验探讨少筋混凝土桥墩的抗震性能与纵筋配筋率的关系,然后提出罕遇地震下的抗震验算指标及验算方法。研究结论：（1）少筋混凝土桥墩的抗震性能与纵筋配筋率密切相关,随着配筋率的增加,延性逐步向钢筋混凝土桥墩过渡;（2）对于配筋率在0.1%~0.5%之间的混凝土桥墩,抗震设计中应合理考虑其耗能能力,位移延性系数限值可在1.0~4.8之间线性内插;（3）提出了罕遇地震下少筋混凝土桥墩的单墩非线性分析模型及简化分析法,为便于设计人员使用,建议采用简化分析法;（4）本研究结果可为罕遇地震下少筋混凝土重力式桥墩的抗震设计方法提供参考。

罕遇地震下少筋混凝土桥墩最低配筋率研究

为了研究少筋混凝土桥墩在罕遇地震下的抗震性能,给少筋混凝土桥墩的配筋率设计提供理论依据,以高速铁路32m简支梁桥为研究对象,通过拟静力试验得到了少筋混凝土桥墩的抗震验算指标,基于有限延性抗震设计思想提出了相应的验算方法,并分析了3种场地条件、2种墩高下的桥墩抗震性能。结果表明:在场地较好的条件下,配筋率小于0.5%的中、低墩,在强震作用下可达到"大震不倒"的抗震性能要求;地震动峰值加速度为0.1g、0.21g、0.32g、0.38g、0.57g时,少筋混凝土中、低墩的最低配筋率分别为0.1%、0.2%、0.3%、0.4%、0.5%;场地条件对桥墩地震反应的影响显著,场地条件较差时,应提高桥墩的配筋率,并加强结构的抗震措施。

A型高墩大跨混凝土连续刚构桥地震反应影响分析

A型高墩大跨混凝土连续刚构桥的显著特点是墩高、跨度大、梁体及墩身质量巨大。文章分析了P-Δ效应、行波效应对A型高墩大跨混凝土连续刚构桥地震反应的影响及弹塑性地震反应特点,探讨了A型高墩大跨混凝土连续刚构桥的延性抗震设计方法。结果表明:A型高墩连续刚构桥按有限延性的抗震设计比较合理,P-Δ效应对A型高墩大跨连续刚构桥地震反应的影响较小,设计中可以忽略;行波效应对A型高墩大跨连续刚构桥地震反应的影响应结合具体的桥型、桥址场地类别,选取合理的地震动、恰当的行波速度进行分析。

基于拉伸型限位键的牺牲装置与性能试验

减、隔震支座中的剪切牺牲销钉,其脆性破坏模式易导致群钉共同承载时发生先后断裂,而产生难以协同的问题,销钉截面削弱部位也因应力集中而易导致正常使用状态下的疲劳问题.提出一种基于拉伸型限位键的水平限位牺牲装置,通过力转向块将水平限位力转变为作用在拉伸型限位键上的拉力,拉伸型限位键通过采用具有一定长度的截面削弱段使其具有有限的延性能力以防止脆性断裂,并通过大弧度光滑过渡减小应力集中,提高其抗疲劳性能.开展不同类型限位键和基于拉伸型限位键的限位牺牲装置静载性能试验,结果表明,拉伸型限位键具有更高的极限变形能力,延性变形能力可通过改变截面削弱段长度进行调节;限位装置整体承载性能与理论预期值符合较好,重复试验下的承载力离散性小,满足群钉协同承载要求.开展了拉伸型限位键和剪切型限位键的疲劳性能对比试验,结果表明新型拉伸限位键比剪切型限位键具有更优的抗疲劳性能.

Experimental and numerical study on flexural behaviors of steel reinforced engineered cementitious composite beams

To investigate the flexural behaviors of steel reinforced engineered cementitious composite （ECC） beams, the behaviors of the steel reinforced ECC beam and the conventional steel reinforced concrete beam subjected to flexural load are experimentally compared. The experimental results show that the flexural strength and ductility of the steel reinforced ECC beam are 24.8% and 187.67% times larger than those of the steel reinforced concrete beam, and the substitution of concrete with ECC can significantly delay the propagation of cracks. Additionally, a simplified constitutive model of the ECC material is used to simulate the flexural behaviors of beams by the finite element analysis （FEA）. The results show a good agreement between the simulation and test results. The crack width of the steel reinforced ECC beam can be limited to 0.4 mm under the service load conditions. The application of ductile ECC can significantly increase the flexural performance in terms of flexural strength, deformation capacity and ductility of the beams.

Extreme Stability of Functional Differential Equations with Finite Delay

This paper obtained some theorems that can ascertain the zero solution of functional differential equations are extremely uniformly stable, extremely asymptotically stable or extremely uniformly asymptotically stable. In the obtained theorems, the derivative of Liapunov function on t along the solutions of functional differential equations is not required to be always negative, especially, it may be even positive.

Finite-Time Stability of Nonautonomous Delayed Systems

The finite-time stability to linear discontinuous time-varying delayed system was investigated. By applying the method of upper and lower solutions, some sufficient conditions of this kind of stability were obtained. Furthermore, it also developed a monotone iterative technique for obtaining solutions which are obtained as limits of monotone sequences

Dry Stone Masonry Ductility During an Earthquake

Stone structures with dry joints, that is, without mortar, have shown a surprising behavior when earthquakes occur. An example of this behavior is the perennially of the so-called Inca wall in Peru, which despite having suffered several earthquakes over time has remained stable without collapsing. This article presents the research carried out on stone masonry wails with dry joint, without mortar, subject to a seismic action. In order to understand the behavior of the masonry without mortar, it designs a Grid mode/ of Finite Elements. From the results, it is concluded that these walls with a certain thickness have ductility that allows them to withstand high displacement and rotation values, thus accommodating the movement of the earth subject to an earthquake. The individual stone blocks move relative to each other through rotations and displacements, which are processed in the free joints of any mortar. The joints work as energy sinks. The free movements in the joints dissipate the energy transmitted by the earthquake, not causing in this way the rupture of the stone blocks. The goal of this article is to understand the p importance of lack of mortar in the seismic behavior of the mansonry.

An Improved Ductile Fracture Criterion for Fine-blanking Process

In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.

Finite Time Consensus Problem for Multiple Non-Holonomic Agents with Communication Delay

In this paper, finite time consensus problem is discussed for multiple non-holonomic mobile agents with constant communication delay. The objective is to design non-smooth distributed control laws such that multiple non-holonomic mobile agents can be all in agreement within any given finite time larger than communication delay. The authors propose a novel switching control strategy with the help of Lyapunov-based method and graph theory.