Numerical and experimental analysis of the vibration serviceability of the Bears’ Cage footbridge

The Bears’ Cage footbridge is a slender steel structure with a single span. Its dynamic behaviour is predicted based on a refined finite-element (FE) model and the vibration serviceability is assessed according to the current codes of practice. The assessment indicates a high susceptibility to human-induced vibrations with disturbing vibration levels even for sparse pedestrian densities. To validate the predicted behaviour of the structure, an extensive experimental study is performed including static deflection and dynamic vibration tests. The analysis shows that statically, the longitudinal movement of the supports on one side of the span can be considered unconstrained, indicating a behaviour of the sliding pot bearings as designed. Due to the footbridge’s arch-like shape, the longitudinal stiffness of the supports highly influences the natural frequency of the fundamental bending mode. The analysis shows that the longitudinal stiffness of sliding pot bearings and the structural inherent damping ratio of the fundamental mode significantly reduces once an initial friction level in the sliding pot bearings is overcome as the result of a significant movement at the supports. The vibration serviceability is reassessed based on the calibrated FE model and shows that even for high pedestrian densities, maximum vibration comfort is ensured.     

重载作用下索-桁架加固结构体系试验研究

溪洛渡±800千伏特高压直流输电工程建设过程中,需要通过公路运输大件设备,这些设备的重量已超过途经桥梁的极限承载力,需要进行临时加固。基于此,介绍了一种重载作用下的桥梁加固技术--索-桁架加固结构体系,该体系主要由预应力钢绞线和桁架组成,通过张拉钢绞线使桁架产生顶升力以抵消桥梁板自重,达到加固桥梁的目的。为了验证该体系的合理性以及加固效果,进行了足尺试验研究,模拟了重型车辆通过一跨桥梁的整个过程,考察了桥梁板加固前后结构响应的变化,研究了钢绞线穿过多个滑轮组后的预应力损失。试验结果表明,采用索-桁架加固结构体系可以部分抵消桥梁板自重,改善桥梁板内力分布,有效提升结构承载力和刚度,桥梁板在加固后以及加载时上下表面均未发生开裂|滑轮组作为转向装置可以有效传递钢绞线内力,穿过多个滑轮组后钢绞线内力损失不大。     

大型冷却塔表面脉动风压原型实测与分布准则

我国冷却塔规范风荷载条款仍源自20世纪80年代原型冷却塔（约90m高）实测资料,且仅规定了塔筒表面静态风压分布。事实上,超大型冷却塔（高度≥165m）风振问题与风荷载脉动作用关系更加密切,由此导致了冷却塔数学和物理试验模型雷诺数效应模拟准则的不完整性,难于准确再现冷却塔表面动态风荷载与来流条件、塔群组合状况等参数间的合理关系,已成为制约大型冷却塔抗风性能研究和结构设计的瓶颈。为此,采用全天候动态风压采集设备,对某电厂冷却塔（约166m高）进行通风筒表面动、静态风压长期现场观测,量化表面脉动压力与来流紊流度之间的影响关系,提出具有原创性的冷却塔超高雷诺数条件（Re≥6E7）脉动风压雷诺数效应模拟准则。     

钢管多支管构架柱节点承载力研究

以750kV输电塔架工程的复杂节点为背景,对其空间多支管柱节点承载力进行了试验研究和理论分析。试验采用2个足尺试件模型,在自平衡框架内完成,采用主动与被动加载相结合的方案。试验得到了节点的破坏模式、荷载-应变曲线及受力特性。在此基础上,利用虚功原理和圆环-母线梁模型建立了节点的承载力理论分析模型,给出了估算节点极限承载力的计算公式。研究结果表明：节点发生了主管凹曲变形的破坏,且未出现支管和焊缝的破坏;理论模型能够较准确反映节点局部屈服时塑性铰的发展,使节点复杂的受力状态得以简化,且理论分析方法考虑了空间支管的共同作用,所得计算结果及节点破坏特征与试验、有限元结果较接近,该理论模型具有一定的适用性。     

助燃剂对木垛火燃烧特性影响研究

蚁群算法是近几年优化领域中新出现的一种启发式仿生类并行智能进化系统,该算法采用分布式并 行计算和正反馈机制,易于与其他方法结合,目前已经在众多组合优化领域中得到广泛应用。在介绍基本蚁群 算法数学模型的基础上,列举了进入２１世纪以来部分具有代表性的蚁群算法改进模型及其应用情况,然后重点 从算法的模型改进、理论分析、并行实现、应用领域、硬件实现、智能融合等角度对蚁群算法在今后的研究方 向作了系统分析与展望。     

Review: Treatment and reuse of wastewater from the textile wet-processing industry: Review of emerging technologies

New ecolabels for textile products and tighter restrictions on wastewater discharges are forcing textile wet processors to reuse process water and chemicals. This challenge has prompted intensive research in new advanced treatment technologies, some of which currently making their way to full-scale installations. These comprise polishing treatments such as filtration, chemical oxidation and specialized flocculation techniques and pre-treatment steps including anaerobic digestion, fixed-film bioreactors, Fenton's reagent oxidation, electrolysis, or foam flotation. Though several of these new technologies are promising in terms of cost and performance, they all suffer limitations which require further research and/or need broader validation. A segment of the research deals with the separate handling of specific sub-streams such as dyebath effluents to which membrane filtration is sometimes applied. The main limitation of this approach is the treatment of the concentrate stream. The spectrum of available technologies may, in the future, be further broadened to include fungi/H₂O₂-driven oxidation, specialized bio-sorptive processes, solvent extraction, or photocatalysis. © 1998 SCI     

Full-scale field testing of precast Portland cement concrete panel airfield pavement repairs

A series of various sized Portland cement concrete (PCC) airfield repairs was performed using precast panels. The repairs received simulated C-17 aircraft traffic, and each repair was trafficked to failure. A heavy weight deflectometer was used to measure the panels' response to loading with increasing traffic applications. The results of traffic testing were used to evaluate the suitability of the precast panel repair technique for rapidly repairing PCC airfield pavements. Test results showed that the repair system was capable of supporting at least 5000 passes and possibly as many as 10,000 passes of C-17 traffic. Compared with other rapid airfield repair methods, the precast panel repair alternative may provide similar return-to-service timeliness and traffic performance at a slightly higher cost. Modifications to the system design and placement procedures are recommended to improve the field performance of the panels.     

激光测量水幕阻隔烟气全尺寸火灾实验设计与研究

通道建筑结构要求安装防火门进行防火分区以阻止火和烟气的蔓延，在难以安装防火分隔设施的场合提出以水幕代替防火门进行分区。为检测水幕对火灾烟气的阻隔情况，表现在烟气透过水幕后其浓度，温度和火焰辐射热流密度的变化，提出了整套大尺寸度全尺寸实验系统的设计，并构建了实验系统且进行了初步测试，测试结果表明，采用两套激光装置同时测量水幕两侧烟气可见性的实验系统是可行的；烟气能够透过水幕，但水幕对烟温有明显的阻隔作用。     

复合衬砌结构的预应力混凝土配比试验研究北大核心CSCD

为了解决高内压复合衬砌内衬混凝土浇筑易出现顶拱脱空、密集区浇筑不密实等施工难点,本文针对三种不同配合比预应力混凝土在双层钢绞线衬砌结构中的应用,开展洞外地面足尺模型试验研究。采用一种适用于监测顶拱脱空的装置以控制混凝土浇筑质量,对不同配合比的混凝土在双层预应力筋束衬砌结构中的浇筑效果进行对比分析。研究表明:将普通混凝土的骨料从二级配改为一级配,并采用合理的振捣工艺,可取得较好的浇筑效果;自密实混凝土可改善顶拱脱空和提高浇筑质量,但需控制材料收缩和徐变变形,并做好温控措施;混凝土在8~10天后温度趋于平缓,建议钢绞线张拉时混凝土养护时间不宜少于14天。     

U形肋正交异性组合桥面板力学性能

为验证桥面板在局部车轮荷载作用下的受力特性及桥面板在桥梁第二体系中的受力性能,提出新型U形肋正交异性组合桥面板系统,并区分其与常规桥面板的受力性能.设计制作了3个不同桥面板试件,其中包括1个混凝土桥面板,1个正交异性钢桥面板,1个带U形肋正交异性组合桥面板.通过静力试验测试了不同桥面板在荷载作用下负弯矩区混凝土开裂情况、桥面板不同部位的结构应变和变形等.试验结果表明:U形肋正交异性组合桥面板在车轮荷载作用下其局部应力水平显著低于正交异性钢桥面板,具有较强的抗疲劳性能;U形肋正交异性组合板在桥梁第二体系的承载能力分别是混凝土桥面板和钢桥面板的1.37倍和0.93倍.