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1、精选优质文档-倾情为你奉上THE MAIN PROBLEMS OF DOMESTIC BRIDGE DESIGNINGNow, the countrys structural design process, such tendencies: more intensity considered in the design and durability consider less attention intensity limit to the use of state without limit state, and throughout the life cycle of the most i
2、mportant when it is precisely the use of performance; attention to the construction of the structure without attention to the maintenance of the structure. In fact, the current design of the bridge for more durability is a concern, as a concept, did not explicitly put forward the request of the use
3、of life, nor the durability of specialized design. These tendencies to a certain extent, led to the current project accidents, the use of poor performance, the short life of the adverse consequences of structural engineering with the increasing emphasis on international durability, safety, contrary
4、to the trend of applicability; does not conform to the structure dynamic and comprehensive economy requirements.Bridge safety, durability, the main reason for poor 1) Construction and management of low level More bridges at home and abroad destruction and the sudden collapse of the bridge has been e
5、ngineering more concerned about security issues. The general view is that the current project is barbaric incident management and construction caused by corruption. For the short term, such as the destruction and collapse of a sudden, mostly because of construction quality did not meet specification
6、s and design requirements, typical problems include inadequate and construction materials intensity of failure; also exist, such as individual bridge jerry serious management issues, but also on bridge safety of the fatal damage.And a large number of bridges in the far did not achieve the expected l
7、ife time, there has been affecting the normal use of disease and deterioration, especially in a number of bridges in use only a few years, or even just completed soon on the serious problem of insufficient durability, which and the low quality of construction is an important relationship, the typica
8、l problems of inadequate protection of reinforced and the current widespread in the construction site of the serious problem of cracking component. These construction, although short-term deficiencies of the bridge will not be the normal use of a clear impact, but the long-term durability of the str
9、ucture will have a very negative hazards.2) Design theory and structure of the system is not perfect enoughWhile acknowledging the existence of the problem, but it also, it is undeniable that bridge design fields, in particular on the bridge construction and use of the issue of safety there is still
10、 much improvement. Structural design first and foremost task is the choice of reasonable economic programmer, followed by the structural analysis and design of components and connections, and access to regulate the safety factor specified or reliability of indicators to ensure the safety of the stru
11、cture.Many designers often complacent with norms on the structural strength of the safety of the need, and ignore the structural system, structure, structure, structure of materials, structure maintenance, as well as from the structural durability of the design and construction process to make use o
12、f that often appear in the man-made wrong areas to strengthen and guarantee the safety of the structure. Some structural integrity and ductility inadequate redundancy small, but some of Schema and the uncertainty of the line, causing partial excessive force; some concrete strength grade too low to p
13、rotect slice through small diameter steel micromanage , a thin cross-section components of these structures have weakened the durability, it would seriously affect the safety of the structure. Many bridges, although the design specifications meet the requirements of the strength of only 5 to 10 year
14、s because of the durability of the problems affecting structural safety. Structural Durability shortage has become one of the most realistic security issues, from design to construction and materials, such as angle of measures to strengthen the durability of the structure.Of the environment and the
15、use of different conditions, different design of the structural system will target different aspects of the layout and structure requirements. Norms can not cover in detail the design staff should solve the various problems in the updated norms faster can also adapt to new understanding, new technol
16、ogies, new materials, rapid development of the structure of the new requirements. Therefore, reasonable and reliable addition to the structures is designed to meet the requirements of norms, and to design a structure to the correct understanding of nature, rich experience and accurate judgments.And
17、the need to improve efforts in the direction 1) Should pay more attention to the durability of structural problemsBridge in the construction and use of the process, will be subject to environmental, and the erosion of harmful chemical substances, and to bear vehicles, wind, earthquake, fatigue, over
18、loading, human factors, such as external role, and bridge materials used by the self-degradation of performance will continue , resulting in the structure of the different degrees of damage and deterioration. In the field of long-span bridges, and from the country since the 1980s, the construction o
19、f a large number of cable-stayed bridge, although so far there collapse or serious damage to the few examples, but has more bridges because of the durability of cable to the problem advance for cable, and this not only affects the use of increased economic losses.Needs to be pointed out is that many
20、 of these problems and did not conduct a reasonable durability of the design, which has also prompted renewed awareness of durability of the bridge. Diseases are a lot of examples of that, in addition to construction materials and the reasons for a decisive impact on the durability of the structure
21、from the structural factors (is design) flaws. From the country in the 1990s started to attach importance to the durability of the structure of the study, has also made quite a few successes. Most of these studies and statistics from the analysis of the material point of view, on how to structure an
22、d design from the perspective of how and the design and construction staff to be readily accepted and operation of the bridge approach to improving the durability has been little research. Moreover, for a long time, people have always been emphasis on the methods of calculation on the structure; it
23、ignores the details of the overall structure and processing concern. Design and durability of the structure of the structural design of a conventional nature of the difference between the current efforts will be needed on the durability of the qualitative analysis to the quantitative analysis of dev
24、elopment.2) Emphasis on the study of fatigue damageBridge structure to withstand the vehicle load and wind load are dynamic load will be in a cycle of change within the structure of the stress, not only will cause the vibration of the structure, but also from the structure of the accumulated fatigue
25、 damage. The bridge is not used by the material is uniform and continuous, in fact there are many tiny flaws in the role of cyclic loading, these deficiencies will be progressive development of micro, a merger of injury, and gradually formed in the material macro cracks. If the crack is not effectiv
26、e macro-control, is very likely to cause material, the structure of brittle fracture. Early fatigue damage is not always easy to be detected, but the consequences are often disastrous.Fatigue damage has been considered in the design of steel bridge is the core issue of fatigue caused by the steel st
27、ructure of steel crack more cases, many caused by fatigue fracture bridge collapse example. Over the past 20 years, fatigue injury research has entered the concrete structure, but by the use of corrosion of reinforced concrete structures dynamic performance and fatigue properties of need to be stren
28、gthened. On the fatigue damage of not only refers to the entire structure, the bridge structure often as a matter of fact some of the key parts of local fatigue failure of the entire structure and lead to failure, such as the cable-stayed bridge cables anchoring end of the fatigue damage.3) Pay full
29、 attention to the problem of overloading the bridgeThere are three main vehicle overloading: One is the early construction of the old bridge overage load carriers and the other is the passage of vehicular traffic bridge over the original design; the other is illegal overloading of vehicles. The firs
30、t two are the main reasons for the changes in the design load and the increase in the volume of traffic; users of the latter are illegal overloading of vehicles operating, the latter two phenomena of overloading in road transport in China is more common.On the one hand, overloading the bridge may tr
31、igger fatigue. Overloading bridge would increase the rate of fatigue stress injury aggravated, or even some structural damage caused by overloading accidents. On the other hand, due to overloading of the bridge caused internal damage can not be restored, the bridge will be made of the work under nor
32、mal load conditions change, which could endanger the safety of bridges and durability. For example, the concrete bridge has always been regarded as an adequate durability, but the overloading of the vehicle, cracking may occur; cracks even in the load will be able to divest closed, but the internal
33、structure of concrete has been damage, cracking component from the lower bend, Stiffness decline was in the normal use of load, should not have been cracking or structural cracks have become smaller cracks in excess of the norms to allow a larger cracks or deformation. These will be used for structu
34、ral performance and long-term durability has a negative impact, in addition to the Traffic Control departments should strengthen management, but also the need for overloading the consequences of research, analysis.4) Actively learn from foreign experience and results Domestic bridge design the main
35、problems is the use of the normal structure of poor performance (referring compared with the design expectations can be attributed to poor performance of the application, including the bridge too much vibration, linear irregularity, joints, diarrhea, excessive structural cracking and deformation, et
36、c.), durability and safety of the poor (including short life span, high maintenance costs, and more frequent accidents, etc.). While these issues have with the current domestic construction quality and management level lower, but to be fair, since this situation can not be resolved in the short term
37、, then as engineers we should address this issue in the premise, are fully taken into account stage of construction and management and materials technology, the use of appropriate security, the appropriate way to ensure that the design of a bridge to the use of the performance, this is a more proact
38、ive and effective means. Especially the durability of the bridge and safety of many problems with the structure or the use of material selection are unreasonable and improper handling of the structural details.In European countries (such as Germany, Denmark, etc.), attached great importance to the s
39、tructure of a performance-based design (PBD, Performance Based Design), which includes structural deformation, cracks, vibration, strong, handsome, durability, fatigue and so on. PBD study is to enable operators in the structure of the process, in addition to the guaranteed minimum security requirem
40、ents; the idea of the use of performance should be good (including life and durability, corrosion resistance, fatigue resistance, aesthetics, etc.). By their very nature, the European countries PBD theory, research in the use of structure in the course of performance out of service, the performance
41、by the weakening of the reasons for its occurrence and the mechanism of the law, to seek a new structural design concepts and methods.From the point of view of Europeans, PBD seems to be to the durability of the structure at the core of the comprehensive use of performance indicators to consider. Th
42、is is the domestic engineering should be based on the Enlightenment. At present the domestic design can be seen as static design, built only at the design definition of a structures ability and performance, and during the performance of operating time and the actual deterioration of the performance
43、of the lack of sufficient awareness and consideration; In other words, the economic point of view is to consider only the construction cost, the expense of operating and maintenance costs and service life should be the relative cost-effectiveness.Bridge safety and durability shortage has become an u
44、rgent need to address the problem, we should actively learn from successful foreign experiences and practices, in addition to strengthening the construction quality management, bridge design concepts and from the structure and tectonic perspective to the design of durability. At the same time need t
45、o study fatigue and overloading the durability of the bridge structure effects.国内桥梁设计存在的主要问题现在，国内的结构设计过程中，有这样的倾向：设计中考虑强度多而考虑耐久性少；重视强度极限状态而不重视使用极限状态，而结构在整个生命周期中最重要的却恰恰是使用时的性能表现；重视结构的建造而不重视结构的维护。实际上，目前的桥梁设计中，对于耐久性更多的只是作为一种概念受到关注，既没有明确提出使用年限的要求，也没有进行专门的耐久性设计。这些倾向在一定程度上导致了当前工程事故频发、结构使用性能差、使用寿命短的不良后果；也与国
46、际结构工程界日益重视耐久性、安全性、适用性的趋势相违背；也不符合结构动态和综合经济性的要求。 桥梁安全性、耐久性差的主要原因 1）施工和管理水平低 国内外多座桥梁的突然破坏与倒塌，已使工程界对桥梁安全性问题倍加关注。一般的看法认为当前的工程事故主要是野蛮施工和管理腐败所导致。对于短期内发生的诸如突然破坏与倒塌，多是由于施工质量没有达到规范和设计要求，典型的问题包括材料强度不足和施工工艺不合格等；也有个别桥梁存在诸如偷工减料、以次充好等严重的管理问题，更是对桥梁安全造成致命的损害。 而大量的桥梁在远没有达到预期使用寿命时，出现了影响正常使用的病害与劣化；特别是一些桥梁在只使用了几年、甚至刚建成不
47、久就出现严重的耐久性不足的问题，这也与施工质量低下有重要关系，典型的问题有钢筋保护层不足及目前广泛存在于施工现场的严重的构件开裂问题。这些施工上的缺陷虽然短期不会对桥梁的正常使用产生明显的影响，但却会对结构的长期耐久性产生非常不利的危害。 2）设计理论和结构构造体系不够完善 在承认施工存在问题的同时，也不可否认，在桥梁设计领域，特别是关于桥梁施工和使用期安全性的问题还有许多可以改进的地方。结构设计的首要任务是选择经济合理的结构方案，其次是结构分析与构件和连接的设计，并取用规范规定的安全系数或可靠性指标以保证结构的安全性。 许多设计人员往往只满足于规范对结构强度计算上的安全度需要，而忽视从结构体
48、系、结构构造、结构材料、结构维护、结构耐久性以及从设计、施工到使用全过程中经常出现的人为错误等方面去加强和保证结构的安全性。有的结构整体性和延性不足，冗余性小；有的计算图式和受力路线不明确，造成局部受力过大；有的混凝土强度等级过低、保护层厚度过小、钢筋直径过细、构件截面过薄；这些都削弱了结构耐久性，会严重影响结构的安全性。不少桥梁、虽然满足了设计规范的强度要求，仅用了510年就因为耐久性出了问题影响结构安全。结构耐久性不足已成为最现实的一个安全问题，设计时要从构造、材料等角度采取措施加强结构耐久性。 不同的环境和使用条件、不同的设计对象都会对结构体系提出不同的布局和构造等方面的要求。规范再详细
49、也不能包罗本应由设计人员解决的各种问题、规范更新得再快也适应不了新认识、新技术、新材料快速发展对结构提出的各种新的要求。因此，合理可靠的结构设计除了满足规范的要求外，还要求设计人员具有对结构本性的正确认识、丰富的经验和准确的判断。 需要改进和努力的方向 1）应该更加重视结构的耐久性问题 桥梁在建造和使用过程中，一定会受到环境、有害化学物质的侵蚀，并要承受车辆、风、地震、疲劳、超载、人为因素等外来作用，同时桥梁所采用材料的自身性能也会不断退化，从而导致结构各部分不同程度的损伤和劣化。在大跨桥梁领域，国内从上世纪80年代以来，修建了大量的斜拉桥；虽然迄今为止出现倒塌或严重损害的例子很少，但已经有多座桥梁因为拉索的耐久性问题而不得不提前换索，既影响了使用又增大了经济损失。 需要指出的是，很多这类问题与没有进行合理的耐久性设计有关，这也促使人们重新认识桥梁的耐久性问题。大量的病害实例也证明，除了施工和材料方面的原因，影响结构耐久性的决定性因素是来自构造上（也即设计上）的缺陷。 国内从上世纪90