INTEGRATED PASSIVE-ACTIVE SYSTEM FOR SEISMIC PROTECTION OF A CABLE-STAYED BRIDGE

This paper presents an integrated passive-active (i.e. hybrid) system for seismic response control of a cable-stayed bridge. Since multiple control devices are operating, a hybrid control system could alleviate some of the restrictions and limitations that exist when each system is acting alone. Lead rubber bearings are used as passive control devices to reduce the earthquake-induced forces in the bridge and hydraulic actuators are used as active control devices to further reduce the bridge responses, especially deck displacements. In the proposed hybrid control system, a linear quadratic Gaussian control algorithm is adopted as a primary controller. In addition, a secondary bang-bang type (i.e. on-off type) controller according to the responses of lead rubber bearings is considered to increase the controller robustness. Numerical simulation results show that control performances of the integrated passive-active control system are superior to those of the passive control system and are slightly better than those of the fully active control system. Furthermore, it is verified that the hybrid control system with a bang-bang type controller is more robust for stiffness perturbation than the active controller with a μ-synthesis method, and there are no signs of instability in the over-all system whereas the active control system with linear quadratic Gaussian algorithm shows instabilities in the perturbed system. Therefore, the proposed hybrid protective system could effectively be used for seismically excited cable-stayed bridges.     

拱桥与我国古代力学

本文探讨了古代拱桥实物所体现的力学水平,并以拱桥源流为线索,结合有关文献和记载,分析了古代拱桥及相关力学的发展状况。结果表明,拱桥诸多方面符合近代力学原理,具有独特的计算方法,经历了一个春秋战国酝酿、秦汉产生、隋唐成熟、宋元发展完善、明清继承普及的过程。     

Structural Integrity of Stone Blocks From Charles Bridge in Prague

The Charles Bridge is the oldest, still-standing gothic bridge that crosses the Vltava River in Prague and up to now has belonged among the most sought-after historical monuments in the Czech Republic. The bridge has been repeatedly damaged due to floods and has been repaired several times. In the reconstructions, damaged sandstone blocks were substituted in facing. This experimental study focused on nonlinear ultrasonic spectroscopy for testing stone blocks that were extracted from the historical bridge structure. The objective of these experiments was verifying whether the methods can be applied to evaluating the internal structure of blocks, which are built-in in the structure in situ. Intact-structure blocks, blocks that had been repaired in the past, and damaged-structure blocks were measured. Two methods of nonlinear ultrasonic spectroscopy were applied—the method with single harmonic ultrasonic signal and with two harmonic ultrasonic signals. Measurement results of both applied methods proved resulting parameters correlation with block structure integrity quality.     

STRUT-AND-TIE COMPUTER MODELLING OF REINFORCED CONCRETE BRIDGE JOINT SYSTEMS

Nonlinear inelastic force-displacement response envelopes of large scale bridge tee-joints and multi-column bridge bents were established using strut-and-tie models (STMs) representing the entire structural system. The computer based STMs employed in the current study were formulated based on the force transfer mechanisms in the joint panel region reported in the literature, in conjunction with the formulation procedure for beam and column members that has been previously reported by the authors. Analysis was performed using the nonlinear analytical program Drain-2DX. Obtained analytical results, including response envelopes and sequences of structural failure, were found to correlate satisfactorily with those obtained from the experimental data.     

虞弘墓所谓“夫妇宴饮图”辨析

本文对虞弘墓图像中一幅学界一直认为是“夫妇宴饮图”的图像进行了辨析正名。作者列举了多件以“夫妇宴饮图”为主题的图像与虞弘墓这幅图像进行比对,通过男、女主人的排位原则考辨出虞墓图像的女主角不是虞弘夫人,又从其冠服特征、手持之物以及身旁二女伴的身份考定出她是一位天界神灵,即Daena女神。作者又进而指出,此幅图像的主题是表现墓主人灵魂进入天国后的美好情景。     

Restoration of the 1824 Wissekerke Iron Suspension Footbridge: Construction Details Revealed

The wrought iron suspension footbridge, built in 1824 at the Wissekerke Castle in Kruibeke (Belgium) is the oldest surviving chain footbridge in continental Europe. As the footbridge shifted from private to public use, the condition of the footbridge was surveyed and assessed. During restoration works, which started in the winter of 2011, new construction details were revealed. The original foundation was excavated giving insight into the applied-anchorage system of the suspension cable. The iron bridge was blast-cleaned, revealing not only its connections, but uncovering assembly and production stamps. These new findings not only broaden the insight in the construction of the 1824 Wissekerke footbridge, they also contribute to the overall knowledge of early construction in wrought iron.     

Evolution of Temperature and Moisture Fields in Charles Bridge in Prague: Computational Prediction and Measurements

Charles Bridge in Prague, founded in 1357, is one of the most prominent historical structures in Europe. It interconnects two Prague districts, the Lesser Town and the Old Town districts, separated by the Vltava River. In the past, the bridge underwent a variety of repairs and retrofits. Within the framework of the moderate repair carried into effect in 2007 to 2010, a measuring system was installed in the bridge, and the temperature and moisture content at selected gauge points have been continuously monitored for a period of 2 years. This article presents non-linear, fully coupled modeling of both fields utilizing a parallel version of the simple finite elements (SIFEL) computer code. Its cogency is validated against experimentally obtained data that serve as inputs for the second stage of a thermo-mechanical analysis—the detailed and mechanics-oriented simulations of the bridge as a whole.     

牺牲阳极法应用及其在钢筋混凝土文物保护中的应用研究

为研究牺牲阳极法在钢筋混凝土文物保护中的应用,首先对国内外关于牺牲阳极法的研究现状和应用实践进行归纳总结,主要从应用对象的转变、实践与研究并举的发展进程、应用层面的拓宽三个方面进行梳理分析;进而由发展的趋势转变提出牺牲阳极法在钢筋混凝土文物保护上的可行性,详述该法在钢筋混凝土文物保护中的应用机理与设计方法。最后以南京长江大桥为例,对牺牲阳极法应用于南京长江大桥双曲拱桥主拱圈耐久性加固工程进行了研究,在总结和回顾的基础上提出牺牲阳极法应用于文物保护中的新机遇。研究成果为牺牲阳极法在钢筋混凝土文物保护工程中的应用提供了一定的借鉴与指导。     

近代中原外向型经济的发展及其影响

长期以国内区域市场为主要贸易范围的中原地区,在进入近代以后,借助于传统水路和现代铁路,与沿海、沿江各通商口岸实施对接,从而逐步发展起了以沿海和国际市场的进出口贸易为导向的近代外向型经济。它不仅改变了中原经济发展的面貌,而且在中、西部地区近代经济的外向化过程中,也起到了不可或缺的桥梁作用。     

Predictive Tri-Linear Benchmark Curve for In-Plane Behavior of Adobe Walls

In the present study, numerical simulations are conducted to estimate the in-plane response of adobe walls subjected to pseudo-static cyclic loading based on the finite element code ABAQUS. The simplified micro-modeling approach is adopted and an interface model reported in ABAQUS material library is applied as material model for zero-thickness interface elements. The comparison between obtained results and field test data results in good agreement. Parametric studies are carried out to evaluate the effectiveness of independent parameters changes on response of adobe walls. It is noted that mechanical properties of joints and adobe units play an active role on in-plane behavior of walls. A tri-linear benchmark curve is proposed to predict the response of aforementioned walls. In this regard, a statistical study is performed to derive the predictive tri-linear benchmark curve. The regressive analysis on 59 numerical models resulted in proposing predictive models. Finally, by comparing tri-linear curves obtained from the regressive analysis, numerical analysis, and experimental study, appropriate accuracy of theoretical model can be found.