基于遗传-模拟退火算法的单层球面网壳结构破坏模式优化

将遗传算法和模拟退火算法相结合,以遗传算法作为基础,将模拟退火机制融入其中,提出遗传-模拟退火算法(GASA)。通过三个经典函数最小值求解,表明混合算法在优化行为、优化效率及稳定性方面均具有明显优势。以构件截面为优化变量,应用构形易损性理论,以结构集簇过程中自由簇构形度Q标准差最小为优化目标,建立单层球面网壳结构倒塌破坏模式优化模型。以一个原型跨度75m、相似比1∶10的单层球壳振动台试验模型为例,采用GASA算法对此试验模型进行倒塌模式优化分析,通过优化前后自由簇构形度变化规律和加速度时程分析结果的对比,表明提出的优化方法及优化模型能够实现单层球面网壳在地震作用下的倒塌模式从无征兆的动力失稳破坏转化为承载力强度破坏。     

考虑P-Δ效应的结构地震倒塌及影响因素分析

P-Δ效应是引起结构在地震作用下倒塌的主要原因之一。以钢框架结构为研究对象,采用增量动力分析法（IDA）和推覆法（Pushover）分析了结构在考虑P-Δ效应时的地震响应特征。结果显示：考虑P-Δ效应后,结构的整体刚度降低,结构下部较容易出现动力失稳,而上部经历卸载,层间位移较小;由于几何非线性与材料非线性的共同作用,骨架曲线会产生明显的负刚度;对具有负刚度的骨架曲线,用三段折线模型进行简化更为合适。基于完全弹塑性滞回模型,研究了不同骨架曲线参数对结构抗倒塌能力的影响。结果表明：二阶效应系数增大,结构发生倒塌的概率增加,而名义延性系数和屈服后刚度比增大则会使结构的抗倒塌能力增强。     

基于LSSVM对盾构施工诱发地面塌陷变形预测

成都地铁1,2号线盾构在砂卵石地层施工诱发多次地面塌陷事故,其地面塌陷变形曲线受多种因素影响,且各因素对地面塌陷变形曲线的影响表现出非线性特性,因此地面塌陷变形曲线很难用显示的数学表达式进行求解。最小二乘支持向量机是基于统计学习理论的机器学习方法,该方法能避免传统神经网络诸多缺陷,能够分析复杂因素对结果影响的潜在规律,据此引入最小二乘支持向量机,以地层物理力学参数、盾构埋深和地层损失数量为输入参数,建立地面塌陷变形曲线预测模型。经过样本检验,预测模型具有较强的泛化能力,预测结果精度和可靠性较高。     

超长隔震结构抗震性能与抗倒塌能力研究

采用增量动力分析(Incremental Dynamic Analysis,IDA)方法,得到了整体式与多塔式超长隔震结构进入各破坏状态的地震峰值加速度,分析了结构的抗震性能与抗倒塌能力。IDA分析结果表明:与多塔结构相比,整体式结构更易发生破坏,所以多塔结构的抗倒塌能力略强于整体结构,但两个结构在设计大震下的倒塌概率都小于5%,可以认为能达到大震不倒的安全要求。     

Retrofit of RC frames against progressive collapse using prestressing tendons

This study investigates the effect of prestressing tendons on the progressive collapse performance of a 6‐ and 20‐story reinforced concrete model structures. According to nonlinear static and dynamic analysis results, the analysis model structures turned out to be vulnerable to progressive collapse caused by sudden loss of a first story column. However, the RC structures reinforced by external prestressing tendons along floor girders showed stable behavior against progressive collapse. The retrofit effect increased as the initial tension and cross‐sectional area of tendons increased. The incremental dynamic analyses showed that the seismic performance of the model structure was also enhanced after the retrofit using tendons. Based on analysis results, it was concluded that the retrofit of existing buildings using prestressing tendons could be effective for increasing both progressive collapse resisting capacity and seismic performance of RC framed structures. Copyright © 2011 John Wiley & Sons, Ltd.     

System reliability evaluation of in-service cable-stayed bridges subjected to cable degradation

Abstract

The cables in a cable-stayed bridge are critical components supporting the long-span girders and ensuring their functionality. However, cables are prone to fatigue damage and atmospheric corrosion, which directly affect the bridge safety. This study presents a framework for system reliability evaluation of in-service cable-stayed bridges subjected to cable degradation. The effect of cable strength degradation on the system reliability is demonstrated through simulation on a parallel-series system representation. Learning machines are utilised to approximate the non-linear and dynamic response functions of critical components due to cable rupture, and the system reliability is finally evaluated from the event tree established by the β-unzipping method. Both short-span and long-span cable-stayed bridges are selected as prototypes to investigate the influence of cable degradation on the system reliability. On this basis it is revealed that cable degradation can significantly influence the collapse mechanism of a cable-stayed bridge and thereby lead to a significant reduction in the system reliability. This phenomenon is associated with cable spacing, where a spare cable system seems more sensitive to cable gradation. It is demonstrated that the consideration of cable corrosion and correlation is essential for lifetime safety evaluation of in-service cable-stayed bridges.     

旋挖成孔灌注桩施工质量控制技术探讨

根据重庆地区旋挖桩施工现状,分析了松散高填方建筑场地旋挖桩塌孔及孔底沉渣过厚等技术问题,并在工程调研和实践的基础上,提出了解决问题的措施,供同行参考。     

On repairable earthquake resisting archetypes with a view to resiliency objectives and assisted self‐centering

Performance‐based seismic design, as an alternative to conventional methods of approach, has served engineers and the public rather well during the last two decades. Neither approach guaranties catastrophic collapse prevention nor post‐earthquake realignment and repairs (PERR) due to major seismic events. As a result, most code‐compliant buildings can be regarded as relatively safe but practically disposable. The paper presents a new philosophy that leads to sustainable design of new structures and the upgrading of existing earthquake resisting moment frames. Repairability‐based design (RBD) relies on softening and control rather than strength and resistance to elevate seismic performance to economically viable, physical collapse prevention, damage control, and post‐earthquake realignment and repairs. The new approach was inspired by design led analysis (DLA), performance control (PC), and recent developments in rocking core‐moment frame design. DLA is a displacement based method of analysis with built‐in results. PC is the ability to design a structure in such a way as to expect predetermined modes of response at certain stages of loading, extents of damage, and drift ratios. This paper advocates higher performance objectives than current codes of practice do. Several demonstrative examples have been provided.     

Horizontal bracing to enhance progressive collapse resistance of steel moment frames

In this paper, the effect of horizontal bracing on enhancing the resistance of steel moment frames against progressive collapse is investigated. Previously designed 6 bay by 3 bay 18‐story steel frame prototype building with 6 m bay span (namely, unbraced frame), which was susceptible to progressive collapse, is retrofitted by four types of horizontal bracing systems on the perimeter of the topmost story and analyzed using 3D nonlinear dynamic method. Six different cross‐sections for each bracing system type are considered, and the capacity curves for each model are obtained. Three column removal circumstances, namely, Edge Short Column, First Edge Long Column, and Edge Long Column are considered in this paper. The results imply that horizontal bracing would increase the resistance of moment frames against progressive collapse. However, one of the bracing types in which axial compressive force is created in braces is not appropriate for retrofitting.     

Collapse safety margin-oriented seismic retrofit strategy for corroded reinforced concrete frames using fibre reinforced plastics

Considering residual service life, this paper presents a collapse safety margin-oriented seismic retrofit strategy for corroded reinforced concrete (RC) frames using fibre reinforced plastics (FRP). With the assumed uniform corrosion model, corrosion-induced initial damage combined with subsequent earthquake-induced damage is identified by the multi-mode-based global damage model developed previously. The collapse-level earthquake intensity determined by incremental dynamic analyses (IDA) with the damage model and the maximum considered earthquake (MCE)-level intensity considering residual service life are combined to generate the time-variant collapse safety margin assessment of corroded RC structures. Based on this assessment, the collapse safety margin-oriented FRP seismic retrofit strategy is proposed and demonstrated on a 4-storey frame. The damage model originally developed for earthquake scenarios has also exhibited its rationality for characterising corrosion-induced initial damage and its influence on coupled damage development with subsequent earthquake excitation. Seismic retrofitting with FRP composites should consider the effects of the corrosion development stage, target collapse safety margin and residual service life. FRP retrofits can cause decreases in the MCE-level collapse probability and increases in the collapse resistance of corroded RC structures. Retrofitting carried out at different times achieves different efficiencies and different time-variant collapse safety margins within the residual service life.