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Structural analysis, design and control by the Virtual Distortion Method
Book reviews ing design. At the end are some design questions to think about (only 27-far too few in my view) and a few items for further reading (30-again far too few and many rather out of date). The book represents an important step in the development of engineering design education in Britain. It is very readable and generally well-illustrated, though it must be mentioned that some of the drawings presuppose a good knowledge of technical drawing conventions or even a knowledge of what the object looks like in real life. Although the number and range of design examples is impressive I feel there is a bit too much revisiting old haunts. A book intending to enthuse people about design should have more examples of the sort of products a reader may aspire to design tomorrow. 1 recently met a sixth-former who had an extraordinary talent fbr designing structures but was not inspired by them-he preferred computers; if only he could have been e x p o ~ d to the exciting and challenging side of materials and structures for the future. While wave energy is covered, there could have been fewer bearings and pumps (yes, 1 know they are important) and more current engineering challenges-battery-powered cars, disc drive mechanisms, high performante yachts, replacement knee joints, gliders, mechanical hearts, high-speed trains, deployable space structures, car-assembly robots. "green' buildings, fibre-reinforced plastic bridges, photo-voltaic devices, and so on. However, for me, the examples present a unore fundamental difficulty. There are simply too many and the reason for their inclusion is not always clear; often the Ix)ok seems to be the design engineer's equivalent of a bird-watcher's notebook. All design aficionados are struck by clever ideas they have encountered, but this does not necessarily merit their inclusion in an introductory book. This is especially true when there are two rather important aspects of design that have been largely overlooked in the book. The first is some answers to the ultimate design question"How do you design a ...?" Far tc)o many of the examples focus on small, even minute, parts of large artefacts, yet nowhere is the big question addressed. Most design begins with a problem to solve; yet where is some mention of how to formalize the problem and create a brief and performance specification that a designer can then address. Despite Edward de Bono's many writings, rather too few engineering design courses and Ix~)ks address the blank-sheetof-paper stage of problems when basic assumptions may be challenged-even the very need for a product at all. Then there is the important question of levels of detail in design, and their hierarchy. As well as examples abstracted from much larger design problems, there is a need to I(~)k at one or two case studies from top to Ix)ttom-the brief, the project
335
economics and planning, early design ,schemes, design development, material selection and, most importantly of all, how the questions of costs and manufacture were addressed, from inception through to final production. It is vital for students to understand the link and feedback between an early product brief or outline design and the minute details of how it might be achieved. There is no point in starting to design a turbine blade if you don't know what sort of aircraft the engine is going to power, and what sort of flight plan it is likely to have; conversely, there is no point in proposing an aircraft performance without a knowledge of the limiting turbine temperatures and materials that are available from which to make suitable blades at an appropriate cost. There is also the issue of complexity. Engineering design addresses complex issues: to answer the question, 'How do you design a ...?" demands an understanding of the whole problem as well as the detail, and here I include environmental, aesthetic and political impact of the product. If British engineers are to gain the status of engineers in other countries, they need a deeper and broader education in "total' design than they presently get. Finally. a comment on the author's parallels between the manufactured and natural world. I agree it is interesting that man has learnt how to use materials, structures and systems in ways we discover, usually later, in the natural world. I also agree that the development, over time, of the design of guns or cars show changes for the better that resemble the steady evolution of species to suit specific conditions more effectively. But this does not seem to be a usefid parallel. I see no similarity in the mechanism or process by which design and evolution occur. As I understand it, evolution has no predetermined goal and it is the result of chance mutations, some of which give rise to species a little more effective than their ancestors, especially when the environment in which they live is different from before. Design and invention are neither of these. They are deliberate processes with an end in view and they only rarely benefit from happenstance or random events. They are based on quintessentially human characteristics such as our ability to conceive in the abstract and communicate such ideas to others who did not have the original idea. We could, no doubt, produce new machines by introducing random changes to existing ones but, actually, we are able to be much more efficient-we can foresee the effects of most changes by thinking and by manipulating mathematical models of our machine. Only in this way have we been able to achieve such rapid development, from beam engine to jet engine in less than 10 of man's generations, during which time man himself has evolved very little? This 367-page book is nevertheless a fascinating and enjoyable read and should
be compulsory reading for all engineering students. What I am not so sure about is whether they will see it so; sadly the question 'Will this be in the exam'?' seems to be becoming more and more the criteria for judging textbooks.
B. Addis
Structural analysis, design and control by the Virtual Distortion Method Jan Holnicki-Szulc and Jacek T. Gierlinski John Wiley & Sons Ltd., Chichester, UK (1995) ISBN 0471-95656-2 The Virtual Distortion Method (VDM) is a technique ba~d on the property that any local modification of sizing or material properties of a structure can be simulated by means of virtual distortions, and vice versa. Using this simple but versatile attribute the authors have developed over the last decade a host of methods for analysing efficiently nonlinear structures and reanalysing structures with modified sizing properties. This very original monograph is a compendium of the most striking applications of VDM in analysing and designing conventional and advanced structural systems. After reviewing the analysis of structures subjected to incompatible distortions in Chapter I the authors indicate in Chapters 2 and 3 how VDM can be put to use in the analysis of trusses and frames which present nonlinearities such as plasticity and vi.~oelasticity. Also studied are the progressive collap~ of structures, critical and postcritical structures and slackened structures. In Chapter 4, VDM is applied to mcxtelling structural modifications by means of applied virtual distortions. Finally Chapters 5 and 6 explore the design of passive control and active control of structures by m e a n s of VDM. Here the authors treat vibration mode shape suppression and active damping problems as well as the optimum location of actuators and sensors. The book is centred on the theoretical aspects of VDM; however, it delves and details many applications in the general field of structures. Of particular interest is the use of VDM in the optimal design context. The method often allows for considerable savings in the tedious reanalysis process in a wide spectrum of design paradigms. VDM is also applied to structural topology design both for discrete and continuous structures. Using applied virtual distortions the authors show, for instance, how they converge on Michelltype solutions, in the continuous case virtual distortions are used to emulate material properties of optimally stiffened material. This is applied to the layout design of fibres in optimal composite plates. In the chapter dedicated to the pass-
Book reviews
336 ive control of structures, VDM is used in improving the stress levels in structures by means of optimal prestressing in the elastic and in the plastic zones. Special attention is devoted to vibration suppression using both active and passive contrul. The variety of subjects treated is always refreshing: simulation of viscuous damping, strategies for aw)iding resonance, beams with controllable support stiffness, active track supports, active damping with controlled delamination and more. The book somehow lacks coherent editing and it could do with more worked-out examples. In similar vein, one deplores the absence of a chapter with a slow introduction to and overview of VDM including some illustrative examples. This would help in positioning VDM in the continually expanding scope of structural theory. Finally, an index would have been most welcome. These and other changes could be envisaged in subsequent editions. In conclusion, this interesting book will be most valuable for graduate students and researchers in structural analysis and design and for practicing engineers who are willing to leave beaten paths and explore new alleys. The authors have a remarkable knowledge of many aspects of current structural research themes. By applying VDM in these different fields the authors indirectly invite the interested reader to a guided tour of contemporary structural analysis and design. This may prove as valuable as mastering VDM.
M. B. Fuchs Elementary theory of structures
Yuan-Yu Hsieh and S. T. Mau Fourth edition, Prentice-Hall, Englewood Cliffs, NJ (1995) IBSN O- 13-301201-8 (hardback) Having reached a ff)urth edition since initial publication in 1970, this is clearly a book which has found favour with students of structural theory. With the increasing use of computer meth(xls in analysis, the bt~.)k has been progressively updated in content and style. Here is the fourth edition, large sections of the book are given over to computer-based methods using both flexibility and stiffness methods. The book commences with a well-written chapter on fundamental structural theory followed by a chapter on principles and applications of statics. At this stage there is an introduction to matrix methods applied to plane truss analysis, then to statically determinate rigid frames. There is a useful section on approximate methods based on assumed locations of points of contraflexure. Elastic deformation theory is introduced in Chapter 4 where the principles of virtual work are applied to truss analysis. Chapter 5 is devoted to the flexibility/force method and the matrix analysis of statically inde-
terminate trusses is formulated. The formal treatment of the Force meth(ul is in Chapter 6. The method of moment distribution is retained in Chapter 7 and includes the treatment of simple joint translation situations. It is questionable whether this method should have a place in a modern text book, however, the help it provides to students in visualizing structural behaviour is valuable and perhaps justifies the space occupied. Chapter 8 is on "slope-deflection" and is clearly a relic of earlier editions. A reasonably full treatment of the matrix displacement method is in the next chapter and this sbould subsume slope-deflection. The matrix method is well-developed and includes some material on stiffness modification, e.g. for pins in members. The treatment of influence lines in retained in Chapters 10 and I1 cover flexibility and stiffness computations for non-prismatic members. There are some useful Appendices on matrix equation solving, computer programs and energy principles. A floppy disk is included with the book and this contains five executable programs for beam, truss and frame analysis. The programs are limited in scope being for plane structures only and, in the case of plane frames, limited to 20 nodes and 20 members. This reviewer tested three of the programs and found them to be well explained and to give correct results for the reviewer's test structures. Each program is accompanied by a text file of explanations. As would be expected care is needed in the preparation and input of the data, this being interactive with limited facility for editing. This reviewer prefers a separate text file for data which is then read by the program and is easily displayed and edited. The book is liberally supplied with worked examples and end-of-chapter problems for solution. Answers are provided for a generous number of selected problems. The treatment of sign conventions is just adequate and more generalization would be preferred. For the sake of completeness, the analysis of the beam/column should have found a place in this book. This is a book which should continue to be appreciated by students in the earlier stages (perhaps years I and 2) of a degree in civil/structural engineering. It is not sufficiently advanced for final year studies. The provision of the suite of programs on disk will enhance the value of the book.
W. M. Jenkins Reinforced concrete: analysis and design
S. S. Ray Blackwell Science, Oxford, UK (1995) ISBN 0-632-03724-5 (hardback) This 543-page book deals with the design
of reinforced concrete buildings. Chapter I covers theory of reinforced concrete which surnmarizes the design equations given in the code BS 81 I0 and some others (e.g. W(x)d-Armer equations) with some derivations ahmg the way. While it is no doubt useful to have these equati,ons all in one place, it is doubtful if they contribute much to the understanding of the suhjecl. Chapter 2, design of reinforced concrete beams, is typical of the approach taken in the following chapters. The design process is laid out clearly in a series of steps: analysis, envelopes of forces, check for deemed to satisfy clauses, flexural steel design, shear steel, minimum ~teel requirements, serviceability clauses, crack width calculations. These steps are illustrated by detailed examples on rectangular and flanged beams both simply supported and continuous. The reviewer was intrigued b.,, the suggestion that only I()'~ redistribution of the moments should be done for continuous beams. The general approach has the great merit of bringing to the attention of the young designer all aspects t)f uhimate and serviceability designs and checks that need to be carried out in order to ensure safe designs, ltowever, fi,)r the student, it might all prove to be a bit t~x) much to take in one go. Chapter 3, design ()l reinforced concrete slabs, covers the design of one-way and tv, o-wa~, slabs using the same approach as in Chapter 2. This chapter has some useful charts on distribution of elastic moments m rectangular slabs ()f various support conditions and also charts to aid using the ~.ield linc method in design. Chapter 4 deals with design of reinforced concrete colunms: design of rectangular and circular columns under axial load and uni/biaxial moments. Tables are provided in Chapter 1 I to aid in design. Chapter 5, design of corbels and nibs, is an unusual topic not covered in standard text bc~ks and no doubt will be welcomed by designers. Chapter 6 covers design of pad foundations. This chapter treats in detail the design of variot.s types of pad foundations. Single column footings, footings connected by ground beam, multiple column pads are all dealt with. Included in this chapter is sufficient geote0hnical background to estimate allowable bearing capacity. Equations arc given for Lmaring pressure calculations for different cases of loading including cases where there is loss of contact over part of the footing. All the examples have a greater "practical" feel to them compared with the examples one finds in traditional text b(x)ks. Chapter 7: design of piled foundations, subjected to general loading, and pile caps are treated in this chapter. Both individual and group effects are dealt with in detail. Again like the chapter on the design of corbels and nibs, this is a topic not treated in any detail in textbc~)ks and will be v,'elcorned by designers. Chapter 8, design of walls, gi~es
335
economics and planning, early design ,schemes, design development, material selection and, most importantly of all, how the questions of costs and manufacture were addressed, from inception through to final production. It is vital for students to understand the link and feedback between an early product brief or outline design and the minute details of how it might be achieved. There is no point in starting to design a turbine blade if you don't know what sort of aircraft the engine is going to power, and what sort of flight plan it is likely to have; conversely, there is no point in proposing an aircraft performance without a knowledge of the limiting turbine temperatures and materials that are available from which to make suitable blades at an appropriate cost. There is also the issue of complexity. Engineering design addresses complex issues: to answer the question, 'How do you design a ...?" demands an understanding of the whole problem as well as the detail, and here I include environmental, aesthetic and political impact of the product. If British engineers are to gain the status of engineers in other countries, they need a deeper and broader education in "total' design than they presently get. Finally. a comment on the author's parallels between the manufactured and natural world. I agree it is interesting that man has learnt how to use materials, structures and systems in ways we discover, usually later, in the natural world. I also agree that the development, over time, of the design of guns or cars show changes for the better that resemble the steady evolution of species to suit specific conditions more effectively. But this does not seem to be a usefid parallel. I see no similarity in the mechanism or process by which design and evolution occur. As I understand it, evolution has no predetermined goal and it is the result of chance mutations, some of which give rise to species a little more effective than their ancestors, especially when the environment in which they live is different from before. Design and invention are neither of these. They are deliberate processes with an end in view and they only rarely benefit from happenstance or random events. They are based on quintessentially human characteristics such as our ability to conceive in the abstract and communicate such ideas to others who did not have the original idea. We could, no doubt, produce new machines by introducing random changes to existing ones but, actually, we are able to be much more efficient-we can foresee the effects of most changes by thinking and by manipulating mathematical models of our machine. Only in this way have we been able to achieve such rapid development, from beam engine to jet engine in less than 10 of man's generations, during which time man himself has evolved very little? This 367-page book is nevertheless a fascinating and enjoyable read and should
be compulsory reading for all engineering students. What I am not so sure about is whether they will see it so; sadly the question 'Will this be in the exam'?' seems to be becoming more and more the criteria for judging textbooks.
B. Addis
Structural analysis, design and control by the Virtual Distortion Method Jan Holnicki-Szulc and Jacek T. Gierlinski John Wiley & Sons Ltd., Chichester, UK (1995) ISBN 0471-95656-2 The Virtual Distortion Method (VDM) is a technique ba~d on the property that any local modification of sizing or material properties of a structure can be simulated by means of virtual distortions, and vice versa. Using this simple but versatile attribute the authors have developed over the last decade a host of methods for analysing efficiently nonlinear structures and reanalysing structures with modified sizing properties. This very original monograph is a compendium of the most striking applications of VDM in analysing and designing conventional and advanced structural systems. After reviewing the analysis of structures subjected to incompatible distortions in Chapter I the authors indicate in Chapters 2 and 3 how VDM can be put to use in the analysis of trusses and frames which present nonlinearities such as plasticity and vi.~oelasticity. Also studied are the progressive collap~ of structures, critical and postcritical structures and slackened structures. In Chapter 4, VDM is applied to mcxtelling structural modifications by means of applied virtual distortions. Finally Chapters 5 and 6 explore the design of passive control and active control of structures by m e a n s of VDM. Here the authors treat vibration mode shape suppression and active damping problems as well as the optimum location of actuators and sensors. The book is centred on the theoretical aspects of VDM; however, it delves and details many applications in the general field of structures. Of particular interest is the use of VDM in the optimal design context. The method often allows for considerable savings in the tedious reanalysis process in a wide spectrum of design paradigms. VDM is also applied to structural topology design both for discrete and continuous structures. Using applied virtual distortions the authors show, for instance, how they converge on Michelltype solutions, in the continuous case virtual distortions are used to emulate material properties of optimally stiffened material. This is applied to the layout design of fibres in optimal composite plates. In the chapter dedicated to the pass-
Book reviews
336 ive control of structures, VDM is used in improving the stress levels in structures by means of optimal prestressing in the elastic and in the plastic zones. Special attention is devoted to vibration suppression using both active and passive contrul. The variety of subjects treated is always refreshing: simulation of viscuous damping, strategies for aw)iding resonance, beams with controllable support stiffness, active track supports, active damping with controlled delamination and more. The book somehow lacks coherent editing and it could do with more worked-out examples. In similar vein, one deplores the absence of a chapter with a slow introduction to and overview of VDM including some illustrative examples. This would help in positioning VDM in the continually expanding scope of structural theory. Finally, an index would have been most welcome. These and other changes could be envisaged in subsequent editions. In conclusion, this interesting book will be most valuable for graduate students and researchers in structural analysis and design and for practicing engineers who are willing to leave beaten paths and explore new alleys. The authors have a remarkable knowledge of many aspects of current structural research themes. By applying VDM in these different fields the authors indirectly invite the interested reader to a guided tour of contemporary structural analysis and design. This may prove as valuable as mastering VDM.
M. B. Fuchs Elementary theory of structures
Yuan-Yu Hsieh and S. T. Mau Fourth edition, Prentice-Hall, Englewood Cliffs, NJ (1995) IBSN O- 13-301201-8 (hardback) Having reached a ff)urth edition since initial publication in 1970, this is clearly a book which has found favour with students of structural theory. With the increasing use of computer meth(xls in analysis, the bt~.)k has been progressively updated in content and style. Here is the fourth edition, large sections of the book are given over to computer-based methods using both flexibility and stiffness methods. The book commences with a well-written chapter on fundamental structural theory followed by a chapter on principles and applications of statics. At this stage there is an introduction to matrix methods applied to plane truss analysis, then to statically determinate rigid frames. There is a useful section on approximate methods based on assumed locations of points of contraflexure. Elastic deformation theory is introduced in Chapter 4 where the principles of virtual work are applied to truss analysis. Chapter 5 is devoted to the flexibility/force method and the matrix analysis of statically inde-
terminate trusses is formulated. The formal treatment of the Force meth(ul is in Chapter 6. The method of moment distribution is retained in Chapter 7 and includes the treatment of simple joint translation situations. It is questionable whether this method should have a place in a modern text book, however, the help it provides to students in visualizing structural behaviour is valuable and perhaps justifies the space occupied. Chapter 8 is on "slope-deflection" and is clearly a relic of earlier editions. A reasonably full treatment of the matrix displacement method is in the next chapter and this sbould subsume slope-deflection. The matrix method is well-developed and includes some material on stiffness modification, e.g. for pins in members. The treatment of influence lines in retained in Chapters 10 and I1 cover flexibility and stiffness computations for non-prismatic members. There are some useful Appendices on matrix equation solving, computer programs and energy principles. A floppy disk is included with the book and this contains five executable programs for beam, truss and frame analysis. The programs are limited in scope being for plane structures only and, in the case of plane frames, limited to 20 nodes and 20 members. This reviewer tested three of the programs and found them to be well explained and to give correct results for the reviewer's test structures. Each program is accompanied by a text file of explanations. As would be expected care is needed in the preparation and input of the data, this being interactive with limited facility for editing. This reviewer prefers a separate text file for data which is then read by the program and is easily displayed and edited. The book is liberally supplied with worked examples and end-of-chapter problems for solution. Answers are provided for a generous number of selected problems. The treatment of sign conventions is just adequate and more generalization would be preferred. For the sake of completeness, the analysis of the beam/column should have found a place in this book. This is a book which should continue to be appreciated by students in the earlier stages (perhaps years I and 2) of a degree in civil/structural engineering. It is not sufficiently advanced for final year studies. The provision of the suite of programs on disk will enhance the value of the book.
W. M. Jenkins Reinforced concrete: analysis and design
S. S. Ray Blackwell Science, Oxford, UK (1995) ISBN 0-632-03724-5 (hardback) This 543-page book deals with the design
of reinforced concrete buildings. Chapter I covers theory of reinforced concrete which surnmarizes the design equations given in the code BS 81 I0 and some others (e.g. W(x)d-Armer equations) with some derivations ahmg the way. While it is no doubt useful to have these equati,ons all in one place, it is doubtful if they contribute much to the understanding of the suhjecl. Chapter 2, design of reinforced concrete beams, is typical of the approach taken in the following chapters. The design process is laid out clearly in a series of steps: analysis, envelopes of forces, check for deemed to satisfy clauses, flexural steel design, shear steel, minimum ~teel requirements, serviceability clauses, crack width calculations. These steps are illustrated by detailed examples on rectangular and flanged beams both simply supported and continuous. The reviewer was intrigued b.,, the suggestion that only I()'~ redistribution of the moments should be done for continuous beams. The general approach has the great merit of bringing to the attention of the young designer all aspects t)f uhimate and serviceability designs and checks that need to be carried out in order to ensure safe designs, ltowever, fi,)r the student, it might all prove to be a bit t~x) much to take in one go. Chapter 3, design ()l reinforced concrete slabs, covers the design of one-way and tv, o-wa~, slabs using the same approach as in Chapter 2. This chapter has some useful charts on distribution of elastic moments m rectangular slabs ()f various support conditions and also charts to aid using the ~.ield linc method in design. Chapter 4 deals with design of reinforced concrete colunms: design of rectangular and circular columns under axial load and uni/biaxial moments. Tables are provided in Chapter 1 I to aid in design. Chapter 5, design of corbels and nibs, is an unusual topic not covered in standard text bc~ks and no doubt will be welcomed by designers. Chapter 6 covers design of pad foundations. This chapter treats in detail the design of variot.s types of pad foundations. Single column footings, footings connected by ground beam, multiple column pads are all dealt with. Included in this chapter is sufficient geote0hnical background to estimate allowable bearing capacity. Equations arc given for Lmaring pressure calculations for different cases of loading including cases where there is loss of contact over part of the footing. All the examples have a greater "practical" feel to them compared with the examples one finds in traditional text b(x)ks. Chapter 7: design of piled foundations, subjected to general loading, and pile caps are treated in this chapter. Both individual and group effects are dealt with in detail. Again like the chapter on the design of corbels and nibs, this is a topic not treated in any detail in textbc~)ks and will be v,'elcorned by designers. Chapter 8, design of walls, gi~es