田庄台辽河公路大桥控制爆破拆除技术分析

依据爆破设计建立完善的力学模型,分析了保证大桥爆破时应控制的关键环节,据此确定以采用水压爆破为主,辅以深孔爆破、浅孔爆破的多元精细爆破拆除工艺。分析了爆破振动波在水介质、淤泥介质及岩石介质的传播规律,结合潮汐因素选定爆破规模、最佳网路设计和起爆时间,并进行了实时监测检验和总结。     

Numerical Modeling of Abutment Scour with the Focus on the Incipient Motion on Sloping Beds

A three-dimensional computational fluid dynamics model is applied to predict local scour around an abutment in a rectangular laboratory flume. When modeling local scour, steep bed slopes up to the angle of repose occur. To predict the depth and the shape of the local scour correctly, the reduction of the critical shear stress due to the sloping bed must be taken into account. The focus of this study is to investigate different formulas for the threshold of noncohesive sediment motion on sloping beds. Some formulas only take the transversal angle (perpendicular to the flow direction) into account, but others also consider the longitudinal angle (streamwise direction). The numerical model solves the transient Reynolds-averaged Navier-Stokes equations in all three dimensions to compute the water flow. Sediment continuity in combination with an empirical formula is used to capture the bed load transport and the resulting bed changes. When the sloping bed exceeds the angle of repose, the bed slope is corrected with a sand-slide algorithm. The results from the numerical simulations are compared with data from physical experiments. The reduction of the bed shear stress on the sloping bed improves the results of the numerical simulation distinctly. The best results are obtained with the formulas that use both the transversal and the longitudinal angle for the reduction of the critical bed shear stress.     

Flexural Testing of Precast Bridge Deck Panel Connections

Precast deck panels are increasingly being utilized to reduce construction times and traffic delays as many departments of transportation (DOTs) emphasize accelerated bridge construction. Despite the short-term benefits, the connections between panels have a history of service failure. This research focused on the evaluation of the service and ultimate capacities of five precast deck panel connections. Full-scale tests were developed to determine the cracking and ultimate flexural strengths of two welded connections, a conventionally posttensioned connection, and two newly proposed, posttensioned, curved bolt connections. The conventionally posttensioned specimens were shown to perform well with the highest cracking loads and 0.42 times the theoretical capacity of a continuously reinforced concrete deck panel. The proposed curved bolt connections were shown to be a promising connection detail with approximately 0.5 times the theoretical capacity of a continuously reinforced panel. Data from the welded specimens showed that some welded connection types perform significantly better than others. The experimental results also compared closely with values calculated on the basis of finite-element modeling, which can be used for future analytical studies.     

Ultimate Capacity Destructive Testing and Finite-Element Analysis of Steel I-Girder Bridges

Current bridge design and rating techniques are based at the component level and thus cannot predict the ultimate capacity of bridges, which is a function of system-level interactions. While advances in computer technology have made it possible to conduct accurate system-level analyses, which can be used to design more efficient bridges and produce more accurate ratings of existing structures, the knowledge base surrounding system-level bridge behavior is still too small for these methods to be widely considered reliable. Thus, to advance system-level design and rating, a 1/5-scale slab-on-steel girder bridge was tested to ultimate capacity and then analytically modeled. The test demonstrated the significant reserve capacity of the steel girders, and the response of the specimen was governed by the degradation of the reinforced-concrete deck. To accurately capture the response of the specimen in an analytical model, the degradation of the deck and other key features of the specimen were modeled by using a dynamic analysis algorithm in a commercially available finite-element analysis program ABAQUS.     

基于量纲分析的宁波象山港大桥桥墩局部冲刷规律研究

针对宁波象山港大桥桥墩冲刷严重问题,为了剖析潮流径流共同作用下跨海大桥复式桥墩局部冲刷机理,科学预测桥墩局部冲刷规律,通过系统分析、评估、复核象山港大桥相关试验成果和现场实测数据,深入研究了象山湾内关键水文泥沙参数( 波浪、潮流、潮位、泥沙量、海底冲刷) 变化特征,利用主因子分析及量纲分析等手段,建立象山港大桥桥墩局部冲刷公式,并利用观测数据进行验证。研究表明,象山湾内各涨急落急流速变化不大,涨急和落急之间差别明显。涨急和落急时的代表垂线平均流速分别为－1 m /s 和 1. 14 m /s,且涨落急时刻对应的代表潮位分别为 1. 37 m 和 0. 54 m。针对象山港大桥桥墩特性分别建立三类桥墩局部冲刷公式,计算得到的预测值与观测值误差在±5%以内,说明所提出的预测公式具有较好的预测效果,能有效地揭示象山港大桥的冲刷规律。     

High-speed full adder based on minority function and bridge style for nanoscale

In this paper a new high-speed and high-performance Full Adder cell, which is implemented based on CMOS bridge style and minority function, is proposed. Several simulations conducted at nanoscale using different power supplies, load capacitors, frequencies and temperatures demonstrate the superiority of the proposed design in terms of delay and power-delay product (PDP) compared to the other cells. In addition the proposed structure improves the robustness and reduces sensitivity to the process variations of the other Bridge-Cap Full Adder cell already presented in the literature.     

Generalized bridge network performance analysis with correlation and time-variant reliability

A novel approach and framework for the analysis of bridge networks is presented. The goal of the analysis is to assess the life-cycle performance of the network and its time-variant reliability. The proposed approach combines three important features that determine its ability to estimate with accuracy and robustness the reliability of a network along its life-cycle.The first one is that the reliability of the individual bridges is modeled as time-variant, due to the deterioration of their structural components. The network performance analysis is repeated for several time instants, with the relative reliability of the bridges. Therefore, the network performance indicators are also time-variant. In this way, the proposed procedure can be used as a basic tool for maintenance planning at the network level.The second asset is that the proposed framework takes into account complex (i.e. “generalized”) network layouts, not necessarily describable using series, parallel or series-parallel models. In fact, when all the possible traffic flows in a network and all the possible trip origins and destinations are considered, it is not feasible, in general, to model the network with a simple scheme. In the present paper, techniques derived from transportation engineering for the traffic flow distribution and assignment are used.The third feature is that the proposed approach considers a correlation structure among the states (in/out of service) of the various bridges of the network. In fact, bridges associated with the same network are likely to share similar characteristics and external loads. Therefore, a correlation structure for the service state of individual bridges is estimated and implemented in the analysis.A case study involving a transportation network with fourteen bridges is presented as a numerical application.     

Temporal Development of Scour Holes around Submerged Stream Deflectors

Deflector structures used in many fish habitat rehabilitation schemes are frequently overtopped, yet few studies have examined the scour patterns created around submerged models. Furthermore, laboratory studies typically test smooth-surfaced structures, whereas those installed in natural rivers are generally made of logs or boulders. This study uses rough-surfaced paired deflectors to investigate the temporal evolution of scour for three overtopping ratios in identical approach flow conditions in a flume. Results show that maintaining identical discharge and raising the deflector height, which reduces the overtopping ratio (i.e., flow depth divided by structure height), generates increased depth and volume of scour next to the structures. The location of maximum depth and the rate of scouring with time is similar for the two highest deflectors (overtopping ratios of 1.22 and 1.83), but different for the lowest deflector model (overtopping ratio of 3.67). To improve the success rate of river restoration projects using in-stream structures, the overtopping ratio should be considered in equations that predict the scour depth evolution with time.     

苏通大桥5800t钢吊箱整体沉放技术

苏通大桥是我国在长江河口地区建设的世界首座跨径超千米的斜拉桥,主塔基础位于深水潮汐急流河段,采用钻孔灌注桩群桩基础,是规模最大的群桩基础。对于深水急流条件下的群桩基础,为承台提供施工条件的钢吊箱的高精度施工是一个关键难题。从沉放方案选择、结构方案设计、制作和安装、整体沉放工艺、同步性控制及定位等方面阐述了苏通大桥主塔基础5 800 t钢吊箱的整体沉放技术与工艺。其中,将钻孔桩施工平台与钢吊箱底板结合的结构方案和钢吊箱整体沉放工艺、同步性控制和定位技术具有明显的创新性。     

桥梁坍塌事故的原因分析及其预防措施

近年来全国桥梁事故频繁发生,造成了巨大的经济损失和社会负面影响。本文总结归纳了2007年以来,尤其是2011年全国公开报道的重大桥梁坍塌事故,并在此基础上分析讨论了导致桥梁坍塌的主要原因。然后,针对桥梁事故的主要原因提出了相应的预防措施,为后续桥梁建设提供指导,以提高桥梁工程建设的质量。