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土木工程外文译文.doc

xx科技学院学生毕业设计（论文）外 文 译 文学 院 建筑工程学院 专业班级 土木工程20xx级3班 学生姓名 xx 学 号 20xx442844 译 文 要 求1. 外文翻译必须使用签字笔，手工工整书写，或用a4纸打印。2. 所选的原文不少于10000印刷字符，其内容必须与课题或专业方向紧密相关，由指导教师提供，并注明详细出处。3. 外文翻译书文本后附原文（或复印件）。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 steel 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 on 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 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-combination 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 techniques 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. 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 methods 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 completed 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 the 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 structures 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, 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 using 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 capabilities 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 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 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 the 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 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 laboratory 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 combined 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 largest 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 transportation 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 these 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 universities, 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 instability. 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 well developed for in-plane behavior, but much work is yet to be done on the cases where bi-axial bending or lateraltorsional buckling must be considered. some successes have been achieved, but the research is far from complete. another aspect of the frame behavior work is the study of the frames with semirigid joints. the american institute of steel construction (aisc) has published design methods for office use. current research is concentrating on the behavior of such structures under seismic loading. it appears that it is possible to use such frames in some seismic situations, that is, frames under about 8 to 10 stories in height under moderate earthquake loads. the future of structures with semi-rigid frames looks very promising, mainly because of the efforts of researchers such as leon at georgia tech university, and many others. research on member behavior is concerned with studying the buckling and post buckling behavior of compact angle and wide-flange beam members by advanced commercial finite element programs. such research is going back to examine the assumptions made in the 1950s and 1960s when the plastic design compactness and bracing requirements were first formulated on a semi-empirical basis. the non-linear finite element computations permit the re-testing of the old experiments and the performing of new computer experiments to study new types of members and new types of steels. white of georgia tech is one of the pioneers in this work. some current research at the us military academy and at the university of minnesota by earls is discussed later in this report. the significance of this type of research is that the phenomena of extreme yielding and distortion can be efficiently examined in parameter studies performed on the computer. the computer results can be verified with old experiments, or a small number of new experiments. these studies show a good prospect fornew insights into old problems that heretofore were never fully solved.3. research on cold-formed steel structures next to seismic work, the most active part of research in the us is on cold-formed steel structures. the reason for this is that the supporting industry is expanding, especially in the area of individual family dwellings. as the cost of wood goes up, steel framed houses become more and more economical. the intellectual problems of thin-walled structures buckling in multiple modes under very large deformations have attracted some of the best minds in stability research. as a consequence, many new problems have been solved: complex member stiffening systems, stability and bracing of c and z beams, composite slabs, perforated columns, standing-seam roof systems, bracing and stability of beams with very complicated shapes, cold-formed members with steels of high yield stress-to-tensile strength ratio, and many other interesting applications. the american iron and steel institute (aisi) has issued a new expanded standard in 1996 that brought many of these research results into the hands of the designer.4. research on steel-concrete composite structures almost all structural steel bridges and buildings in the us are built with composite beams or girders. in contrast, very few columns are built as composite members. the area of composite column research is very active presently to fill up the gap of technical information on the behavior of such members. the subject of steel tubes filled with high-strength concrete is especially active. one of the aims of research performed by hajjar at the university of minnesota is to develop a fundamental understanding of the various interacting phenomena that occur in concrete-filled columns and beam-columns under monotonic and cyclic load. the other aim is to obtain a basic understanding of the behavior of connections of wide-flange beams to concrete filled tubes. other major research work concerns the behavior and design of built-up composite wide-flange bridge girders under both positive and negative bending. this work is performed by frank at the university of texas at austin and by white of georgia tech, and it involves extensive studies of the buckling and post-buckling of thin stiffened webs. already mentioned is the examination of the shakedown of composite bridges. the question to be answered is whether a composite bridge girder loses composite action under repeated cycles of loads which are greater than the elastic limit load and less than the plastic mechanism load. a new study has been initiated at the university of minnesota on the interaction between a semi-rigid steel frame system and a concrete shear wall connected by stud shear connectors.5. research on connections connection research continues to interest researchers because of the great variety of joint types. the majority of the connection work is currently related to the seismic problems that will be discussed in the next section of this paper. the most interest in non-seismic connections is the characterization of the monotonic moment-rotation behavior of various types of semi-rigid joints. 6. research on structures and connections subject to seismic forces the most compelling driving force for the present structural steel research effort in the us was the january 17, 1994 earthquake in northridge, california, north of los angeles. the major problem for steel structures was the extensive failure of prequalified welded rigid joints by brittle fracture. in over 150 buildings of one to 26 stories high there were over a thousand fractured joints. the buildings did not collapse, nor did they show any external signs of distress, and there were no human injuries or deaths. a typical joint is shown in fig. 2.2.1. in this connection the flanges of the beams are welded to the flanges of the column by full-penetration butt welds. the webs are bolted to the beams and welded to the columns. the characteristic features of this type of connection are the backing bars at the bottom of the beam flange, and the cope-holes left open to facilitate the field welding of the beam flanges. fractures occurred in the welds, in the beam flanges, and/or in the column flanges, sometimes penetrating into the webs. once the problem was discovered several large research projects were initiated at various university laboratories, such as the university of california at san diego, the university of washington in seattle, the university of texas at austin, lehigh university at bethlehem, pennsylvania, and at other places. the us government under the leadership of the federal emergency management agency (fema) instituted a major national research effort. the needed work was deemed so extensive that no single research agency could hope to cope with it. consequently three california groups formed a consortium which manages the work: (1) structural engineering association of california. (2) applied technology council. (3) california universities for research in earthquake engineering. the first letters in the name of each agency were combined to form the acronym sac, which is the name of the joint venture that manages the research. we shall read much from this agency as the results of the massive amounts of research performed under its aegis are being published in the next few years. the goals of the program are to develop reliable, practical and cost-effective guidelines for the identification and inspection of at-risk steel moment frame buildings, the repair or upgrading of damaged buildings, the design of new construction, and the rehabilitation of undamaged buildings. as can be seen, the scope far exceeds the narrow look at the connections only. the first phase of the research was completed at the end of 1996, and its main aim was to arrive at interim guidelines so that design work could proceed. it consisted of the following components: a state-of-the-art assessment of knowledge on steel connections. a survey of building damage. the evaluation of ground motion. detailed building analyses and case studies. a preliminary experimental program. professional training and quality assurance programs. publishing of the interim design guidelines. a number of reports were issued in this first phase of the work. a partial list of these is appended at the end of this paper. during the first phase of the sac project a series of full-scale connection tests under static and, occasionally, dynamic cyclic tests were performed. tests were of pre-northridge-type connections (that is, connections as they existed at the time of the earthquake), of repaired and upgraded details, and of new recommended connection details. a schematic view of the testing program is illustrated in fig. 2.2.2 some recommended strategies for new design are schematically shown in fig. 2.2.3. fig. 2.2.3 some recommended improvements in the interim guidelines the following possible causes, and their combinations, were found to have contributed to tile connection failures: inadequate workmanship in the field welds. insufficient notch-toughness of the weld metal. stress raisers caused by the backing bars. lack of complete fusion near the backing bar. weld bead sizes were too big. slag inclusion in the welds. while many of the failures can be directly attributed to the welding and the material of the joints, there are more serious questions relative to the structural system that had evolved over the years mainly based on economic considerations. the structural system used relatively few rigid-frames of heavy members that were designed to absorb the seismic forces for large parts of the structure. these few lateral-force resistant frames provide insufficient redundancy. more rigid-frames with smaller members could have provided a tougher and more ductile structural system. there is a question of size effect: test results from jo