1、 毕 业 设 计 英 文 翻 译 学 院： 建筑工程学院 专 业： 土木工程 学生姓名 : 学 号 : 设计题目 ： 近期美国在钢结构和钢筋混凝土结构 研究和设计方面的发展 指 导 教 师 : 专业负责人： 起迄日期 : 设计地点 : 发任务书日期 : 年 月 日 Recent Research and Design Developments in Steel and Composite Steel-concrete Structures in USA The paper will conclude with a look toward the future of structural ste
2、el research. 1. Research on steel bridges The American Association of State Transportation and Highway Officials (AASTHO) is the authority that promulgates design standards for bridges in the US. In 1994 it has issued a new design specification which is a Limit States Design standard that is based o
3、n the principles of reliability theory. A great deal of work went into the development of this code in the past decade, especially on calibration and on the probabilistic evaluation of the previous specification. The code is now being implemented in the design office, together with the introduction
4、of the Systeme Internationale units. Many questions remain open about the new method of design, and there are many new projects that deal with the reliability studies of the bridge as a system. One such current project is a study to develop probabilistic models, load factors, and rational load-combi
5、nation rules for the combined effects of live-load and wind； live-load and earthquake； live-load, wind and ship collision； and ship collision, wind, and scour. There are also many field measurements of bridge behavior, using modern tools of inspection and monitoring such as acoustic emission techniq
6、ues and other means of non-destructive evaluation. Such fieldwork necessitates parallel studies in the laboratory, and the evolution of ever more sophisticated high-technology data transmission methods. America has an aging steel bridge population and many problems arise from fatigue and corrosion.
7、Fatigue studies on full-scale components of the Williamsburg Bridge in New York have recently been completed at Lehigh University. A probabilistic AASTHO bridge evaluation regulation has been in effect since 1989, and it is employed to assess the future useful life of structures using rational metho
8、ds that include field observation and measurement together with probabilistic analysis. Such an activity also fosters additional research because many issues are still unresolved. One such area is the study of the shakedown of shear connectors in composite bridges. This work has been recently comple
9、ted at the University of Missouri. In addition to fatigue and corrosion, the major danger to bridges is the possibility of earthquake induced damage. This also has spawned many research projects on the repair and retrofit of steel superstructures and the supporting concrete piers. Many bridges in th
10、e country are being strengthened for earthquake resistance. One area that is receiving much research attention is the strengthening of concrete piers by jacketing them by sheets of high-performance reinforced plastic. The previously described research deals mainly with the behavior of existing struc
11、tures and the design of new bridges. However, there is also a vigorous activity on novel bridge systems. This research is centered on the application of high-performance steels for the design of innovative plate and box-girder bridges, such as corrugated webs, combinations of open and closed shapes,
12、 and longer spans for truss bridges. It should be mentioned here that, in addition to work on steel bridges, there is also very active research going on in the study of the behavior of prestressed concrete girders made from very high strength concrete. The performance and design of smaller bridges u
13、sing pultruded high-performance plastic composite members is also being studied extensively at present. New continuous bridge systems with steel concrete composite segments in both the positive moment and the negative moment regions are being considered. Several researchers have developed strong cap
14、abilities to model the three-dimensional non-linear behavior of individual plate girders, and many studies are being performed on the buckling and post-buckling characteristics of such structures.Companion experimental studies are also made,especially on members built from high-performance steels. A
15、 full-scale bridge of such steel has been designed, and will soon be constructed and then tested under traffic loading. Research efforts are also underway on the study of the fatigue of large expansion joint elements and on the fatigue of highway sign structures. The final subject to be mentioned is
16、 the resurgence of studies of composite steel concrete horizontally curved steel girder bridges. A just completed project at the University of Minnesota monitored the stresses and the deflections in a skewed and curved bridge during all phases of construction, starting from the fabrication yard to t
17、he completed bridge. Excellent correlation was found to exist between the measured stresses and deformations and the calculated values. The stresses and deflections during construction were found to be relatively small, that is, the construction process did not cause severe trauma to the system. The
18、 bridge has now been tested under service loading, using fully loaded gravel trucks, for two years, and it will continue to be studied for further years to measure changes in performance under service over time. A major testing project is being conducted at the Federal Highway Administration laborat
19、ory in Washington, DC, where a half-scale curved composite girder bridge is currently being tested to determine its limit states. The test-bridge was designed to act as its own test-frame, where various portions can be replaced after testing. Multiple flexure tests, shear tests, and tests under comb
20、ined bending and shear, are thus performed with realistic end-conditions and restraints. The experiments are also modeled by finite element analysis to check conformance between reality and prediction. Finally design standards will be evolved from the knowledge gained. This last project is the large
21、st bridge research project in the USA at the present time. From the discussion above it can be seen that even though there is no large expansion of the nations highway and railroad system, there is extensive work going on in bridge research. The major challenge facing both the researcher and the tra
22、nsportation engineer is the maintenance of a healthy but aging system, seeing to its gradual replacement while keeping it safe and serviceable. 2. Research on steel members and frames There are many research studies on the strength and behavior of steel building structures. The most important of the
23、se have to do with the behavior and design of steel structures under severe seismic events. This topic will be discussed later in this paper. The most significant trends of the non-seismic research are the following: Advanced methods of structural analysis and design are actively studied at many Uni
24、versities, notably at Cornell, Purdue, Stanford, and Georgia Tech Universities. Such analysis methods are meant to determine the load-deformation behavior of frames up to and beyond failure, including inelastic behavior, force redistribution, plastic hinge formation, second-order effects and frame i
25、nstability. When these methods are fully operational, the structure will not have to undergo a member check, because the finite element analysis of the frame automatically performs this job. In addition to the research on the best approaches to do this advanced analysis, there are also many studies on simplifications that can be easily utilized in the design office while still maintaining the advantages of a more complex analysis. The advanced analysis method is
