4. To allow for the possibility that the resistances may be less than computed, and the load effects may be larger than computed, strength reduction factors, p, less than 1, and load factors, a, greater than 1, are introduced Rn≥aSn+aS2+ where R, stands for nominal resistance and S stands for load effects based on the specified loads 5. If y follows a standard statistical distribution, and if y and are known, the probability of failure can be calculated or obtained from statistical tables as a function of the type of distribution and the value of B. Thus if Y follows a normal distribution and B is 3. 5, then Y=3.5 oy and from tables of the normal distribution, Pr is 1/9091or1.1×10-4 6. The slope of the stress/strain line up to the yield point is called the modulus of elasticity E of the material and is a constant for the material E stress strain 8 This value of E for steel is 29x 106 psi 199.9 X10N/mm2), with a value of 30X 106 psi (206.8X10N/mm) being sometimes used for design 7. Timber, or wood, is a natural building material. It is available either as lumber, which is natural wood, or as glued laminated timber. This latter form is much stronger and conglue or adhesive. The laminations usually do not exceed 2 in. in thickness. Glued laminated beams are available in a variety of shapes. Both lumber and glued laminated timber are widely used in building construction 8. The use of materials in both tensile and compressive structures is extremely efficient since the entire cross section of each member is uniformly stressed. The strength of the members in a tensile structure is limited only by the basic material strength; thus, these are generally lightweight systems that are economical for spanning large distances. The cable-stayed bridge in Fig. 11. la is a suspension structure in which the primary structural components are totally in tension. Since the members in compressive structures have a propensity for buckling, the material stress is limited to a level which is lower than that for tensile members the arch is a common type of compressive structure, but under some conditions the intemal state of stress can include shear and bending moment. Nevertheless, compression is usually the dominant internal force. An example of an arch bridge is illustrated in Fig. 11.1b 9. A variety of cross-sectional geometries for the completed box structure are possible, with the
number of girders varying from two to six or more depending upon the plan geometry of the structure( Fig. 13. 2). Typical cross-sectional geometries are given in Fig. 13.3 for three two-box girder systems. Both single and double bearing arrangements and shallow and deep end-support diaphragms are illustrated. Typical spacing of the centreline of the box girders varies from 4.3 to 6.7 m, and the depth of the cast-in-place concrete deck varies from 190mm to 250mm. Thus, the ratio of dead load moment to live load moment for box girder structures will depend upon the depth of deck, the cross-section and the span arrangement chosen by the design engineer. 10. For conventional bored piles it is common practice to adopt values of K of 0.7, while for piles bored with a continuous nlight auger values of 0. 9(for sandy soils)down to 0.6 for silts and silty sands )are taken. In general, the roughness of the hole will ensure that the full soil friction is mobilized at the pile edge. However, potential loosening of the soil during the installation process may be allowed for by taking the friction anglesbetween and pr 11. The end-bearing pressure mobilized by a pile should, in principle, be comparable with that measured during a cone penetration test. However, effects of scale and of different rates of testing combine to yield variations in the ratio q/qe ranging from under 0.5 to over 2. Unless there is particular evidence to the contrary, for a given soil, the end-bearing pressure should be taken equal to that measured in a cone penetration test 12. Earthquake-resistant design is achieved with an accepted risk level. Thus, in practice, design of structures to withstand earthquakes of all potential magnitudes is neither practical nor economical. Within an accepted risk, however, design requires one or more of the following alternatives A. Design and detailing of structural members and beam-column joints for the prescribed earthquake loads given in the code B. Design of"shear wall"as earthquake load-carrying members C. Design of cross-bracing in structural frames. D, Use of the isolation concept
PART II Technica| English Writing科技英语写作 科技论文( Science Papers)是论述自然科学研究和技术成果的说理性文章。按其写作目 的,可分为学位论文( Thesis和学术论文( Research Papers)。这部分讲述并列举了如何撰写 学术论文,最后还给出了13篇1999年以来的博士论文摘要。它们既是很好的英文摘要的范 例,也代表了上木工程专业最新的发展方向。 Unit 5 Styles and Features of English Technical Writing 英文科技论文的写作格式与特点 学位论文的写作是非常严格的,分为前部、正文、后部三大部分。各部分所包含的内容 如下: FRONT前部 Front cover封面 Title Page(Subtitle)扉页 Authors Name, Author'' Address作者姓名,作者联系地址 Distribution List分发范围 Preface or Foreword序言/前言 Acknowledgements致谢 Abstract摘要 Keywords关键词 Table of Contents目录 List of illustrations( ables, Graphs)图表目录 MAIN TEXT正文 Introduction引言 Analysis and/or Experiment Methods and Procedure分析实验方法和过程
Results结果 Discussion讨论 Conclusions( Summary)结论 Recommendations建议 BACK后部 List of references参考文献 Appendixes附录 Tables表 Graphs图 nde素引 学术论文,是指期刊论文( Journal papers)和会议论文( Conference Papers),其写作格 式一般为: rtle标题 Author' s Name作者姓名 Author's Address作者联系地址 Abstract摘要 Keywords关键词 ntroduction引言 Analysis and/or Experiment Methods and Procedure分析/实验方法和过程 Resuits结果 Discussion讨论 Conclusions(Summary) yh Acknowledgments致谢 References参考文献 Appendixes附录 科技论文的标题要简明、朴实,统计资料显示:一般标题的平均词数为10。有的期刊 要求不超过20个词。摘要通常不超过200个词,要求简短扼要,引人入胜,而且要能独立使 用,使读者不读正文也能对论文的工作一目了然。一般概括如下内容:为什么从事这项研究? 完成了哪些工作?突出的成果:成果的意义。尽管摘要放在正文的前面,但它往往是在最后 写作;为方便文献检索,一般从论文中选取3~8个能表达主题内容的关键词排在摘要的左下 方。引言向读者解释论文的主题、目的和总纲,通过引言的初步介绍,可以引导读者明确地 领会该研究成果的研究背景、研究意义、采用的方法、简单了解研究中的发现。科技论文的 正文要求准确性、鲜明性、生动性。除了对材料、研究方法和研究过程的描述,还应包括讨 论、结论、建议等内容。结论比硏究结果和分析还要推进一步,要反映出该研究如何经过概 念、判断、推理的过程而形成总的观点,结论必须严密,不能有第二种解释,更不能杜撰。 在研究工作中得到的常规以外的帮助,应在文末予以致谢,用词要恰如其分。科技论文所列 举的参考文献反映了作者严肃的科学态度和研究工作的广泛依据。附录放在论文的最后,起 帮助读者阅读论文的作用
下面以一篇科技论文举例说明〈凼为本节旨在讲解写作,故这里略去了论文中的插图) A Simplified Optimization for vibration of Rectangular Plates with Cylindrical Voids 带空洞矩形板振动问题的简单优化解 Wu Xiuli and Jean-Pierre Bardet ABSTRACT Plae this paper proposes a simple method for calculating the natural frequencies of rectangular es with cylindrical voids that are arbitrarily positioned and illustrated its usefulness by optimizing the natural frequencies. The discontinuous variations in rigidity and mass density of plate that are induced by the voids are expressed by using the extended Dirac function. The free transverse vibration of the plate with cylindrical voids is obtained with the help of the Galerkin method. The natural frequency coefficients of the plate with voids are found to depend not only on the dimensions of the plate and the sizes as well as locations and dispositions of the voids, but alse on Poisson's ratio of plate material. It is pointed in the paper that voids locations and radii can be optimally designed to get the desired natural frequencies, e. g. the maximum or the minimum Furthermore, a very simple formula is extended to derive approximate values of the higher order natural frequencies for plates with cylindrical voids KEYWORDS Natural Frequencies; Cylindrical Voids; Rectangular Plate: Extended Dirac Function; INTRODUCTION Plates with voids are often used in civil engineering because they are light and structurally efficient. Many authors have discussed the analytical methods for static analysis of plates with voids, For example, ELliotto and Clark( 1982)investigated cylindrically voided concrete slab stiffness using the finite element method. Very few studies have been performed on the dynamic analysis of voided plate. Takabatake(1991)solved the dynamic response of elastic rectangular plates with arbitrarily disposed rectangular voids by means of the extended Dirac function, in which the modified variables are thickness and rigidity. He proposed some free and forced vibration I Professor, Civil En ing Department, Shijiazhuang Railway Institute, 050043,China 2 Professor, Civil Engineering Department, University of Southem California, Los Angeles