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Is your structure suitably braced?
Book reviews
232 recognized throughout the world for each item mentioned. The bulk of the report is divided according to: (a) type of fastener and substrate-cast in place in fresh concrete, and postinstalled into hardened concrete or masonry; and (b) loading-mainly static but also cyclic, seismic, fatigue and impact. Performance criteria for all of these are examined under a brief (and possibly inadequate) section on environmental influences, viz. corrosion, acid rain, salt and u.v. exposure, fire, thermal, and wetting and drying. The report is clearly up to date-most of the 300 references are from the 1980s. It should be welcomed by the construction industry and fastener manufacturers as an authoritative document. Its cost of £75 will soon be recouped by savings made by the better selection of fasteners. The overall view is that the report will be treated as a user guide and is unlikely to be read as a text.
Kim S. Elliott Is your structure suitably braced? Ed. James M. Ricles Structural Stability Research Council, Lehigh University, Bethlehem, PA, 247 pages, ISBN 1-879749-55-6 This book is the report of the 1993 conference of SSRC held in April 1993 in Milwaukee. Twenty papers are included dealing with the bracing of beams, frames, and building systems by authors who have worked on significant problems in the field of instability. A paper by Kavanagh and Ellifritt reports theoretical and experimental evidence that for cold formed channels the American Iron and Steel Institute (AISI) specification for the design of cold formed steel members may underestimate the buckling-failure load for short spans where the warping stress results in another limit state intervening before the lateraltorsional buckling mode is reached. This means that for short spans (where it is often supposed that lateral bracing is less important) the failure load might be much less than its calculated design value. In a supplementary paper provided with the book, J.A. Yura gives a comprehensive survey of the theory and the practical methods of bracing horizontal beams with examples relating to parallel bridge girders. He also offers an abstract on the torsional bracing requirements for beams and columns. The question of what happens when a member is taken into its inelastic range before lateral buckling occurs is discussed in a paper by Ales and Yura. They show that Winter's 1958 model is appropriate for the two beams they tested and that the bracing equation for continuous bracing
can be used to determine the bracing required by discrete braces, They cast doubt on the 1964 Pincus rigid link model of two straight sections meeting in a plastic hinge, A paper by T.V. Galambos deals with the lateral bracing of light steel trussed beams designed to the Steel Joist Institute Specification (1992). He describes in detail the onerous lateral bracing requirements during handling and erection and that uplift due to wind on the light construction might threaten stability. A paper by Essa and Kennedy presents results for the form of construction in which alternate spans cantilever over supporting columns with a simply supported span connected to the ends of the cantilevers in the other bays. Their investigation followed the collapse of a parking roof with this form of construction in Burnaby, British Columbia. A computer finite element program and 31 full-scale tests draw attention to a number of bracing details especially that where the bottom (compression) flange of the cantilever passes over the column, both beam and column head need to be braced. A paper by Idriss et al. describes an interesting project where an existing road bridge is to be demolished. This is a twogirder nonredundant structure designated therefore as 'fracture critical'. To help in safely carrying out the demolition and to gain the maximum information from the best placement of transducers a computer program was developed to investigate the behaviour when a cut is made in one of the members to simulate a crack. The computer program indicates that when a girder cracks there is a re-arrangement of the load paths but a stable structure still results. A paper by Clarke and Bridge highlights the fact that manufacturing tolerances may seriously affect the failure load of columns. They consider the example of a column with a central brace and show that a very slight misplacement of this brace may result in unexpected failure since the failure load is very sensitive to slight asymmetry. Another paper by Plant and Via considers a similar topic. In the section concerned with building systems there is a paper by L.A. Lutz on bracing concepts for skylight and curtainwall framing of small aluminium alloy sections, which may be of 'unusual' extruded cross-section, and one by Kaehler and Fisher on bracing practices in metal building systems. There are papers by Biswas on when it is proper to consider a multistorey frame as adequately braced to support gravity loads, and by Helwig et al. on the bracing forces in diaphragms and cross-frames of bridge beams. A paper by Fisher and West contains a detailed discussion of American practice in the erection bracing of structural steel frames. A paper by Ono et al. discusses the buckling of knee joints in single-storey gabled frames of long span like wide factory shed buildings or school assembly halls. The authors show that
bracing for latticed members ought to be different from that for members made with solid webs. A paper by Abdelrazaq et al. is concerned with the diagonal megabracing which is a dramatic feature of the elevations of tall buildings like the John Hancock Center in Chicago. There is a paper by Judd on eccentric braced frames, and by A1-Mashary et al. on the effective bracing of trussed towers against secondary movements. There is also a paper by Tremblay and Stiemer on the design of friction bolted connections to resist severe earthquake ground motions without damage to the main structural members. The final paper is a brief review of the effect of bomb damage on the stability of columns at the World Trade Center. The book includes a panel discussion on questions raised by participants on the presentation of the papers. Engineers need to review their practice from time to time because of the effects which recent increases in the slenderness of construction might have on their structures and on their reputations if they neglect proper bracing. Buckling is a very dangerous form of premature failure because it is usually sudden and often complete. It will be seen that many topics about structural bracing and instability are considered in the book which will be a useful and interesting addition to the library of any thoughtful engineer wishing to do more than merely comply with the clauses of a design code.
Arthur Bolton Plastic hinge based methods for advanced analysis and design of steel frames: an assessment of the state-of-the art Editors: D.W. White and W.F. Chen, Structural Stability Research Council, Lehigh University, Bethlehem, PA, 1993, ISBN 1879749-53-X In June 1994 the Structural Stability Research Council - an organization formed originally to produce rules for the design of steel columns in the United States but subsequently expanded to take an interest in all forms of structural stability - held its 50th Anniversary Meeting and Technical Session at its spiritual home: Lehigh University, Bethlehem,Pennsylvania. Currently one of its most active task groups is that concerned with second-order inelastic analysis for frame design. Various special presentations and discussions have been organized by this group and the volume under review is the direct result of a workshop held at the 1992 SSRC meeting in which 47 representatives from 7 different countries participated. It comprises 13
232 recognized throughout the world for each item mentioned. The bulk of the report is divided according to: (a) type of fastener and substrate-cast in place in fresh concrete, and postinstalled into hardened concrete or masonry; and (b) loading-mainly static but also cyclic, seismic, fatigue and impact. Performance criteria for all of these are examined under a brief (and possibly inadequate) section on environmental influences, viz. corrosion, acid rain, salt and u.v. exposure, fire, thermal, and wetting and drying. The report is clearly up to date-most of the 300 references are from the 1980s. It should be welcomed by the construction industry and fastener manufacturers as an authoritative document. Its cost of £75 will soon be recouped by savings made by the better selection of fasteners. The overall view is that the report will be treated as a user guide and is unlikely to be read as a text.
Kim S. Elliott Is your structure suitably braced? Ed. James M. Ricles Structural Stability Research Council, Lehigh University, Bethlehem, PA, 247 pages, ISBN 1-879749-55-6 This book is the report of the 1993 conference of SSRC held in April 1993 in Milwaukee. Twenty papers are included dealing with the bracing of beams, frames, and building systems by authors who have worked on significant problems in the field of instability. A paper by Kavanagh and Ellifritt reports theoretical and experimental evidence that for cold formed channels the American Iron and Steel Institute (AISI) specification for the design of cold formed steel members may underestimate the buckling-failure load for short spans where the warping stress results in another limit state intervening before the lateraltorsional buckling mode is reached. This means that for short spans (where it is often supposed that lateral bracing is less important) the failure load might be much less than its calculated design value. In a supplementary paper provided with the book, J.A. Yura gives a comprehensive survey of the theory and the practical methods of bracing horizontal beams with examples relating to parallel bridge girders. He also offers an abstract on the torsional bracing requirements for beams and columns. The question of what happens when a member is taken into its inelastic range before lateral buckling occurs is discussed in a paper by Ales and Yura. They show that Winter's 1958 model is appropriate for the two beams they tested and that the bracing equation for continuous bracing
can be used to determine the bracing required by discrete braces, They cast doubt on the 1964 Pincus rigid link model of two straight sections meeting in a plastic hinge, A paper by T.V. Galambos deals with the lateral bracing of light steel trussed beams designed to the Steel Joist Institute Specification (1992). He describes in detail the onerous lateral bracing requirements during handling and erection and that uplift due to wind on the light construction might threaten stability. A paper by Essa and Kennedy presents results for the form of construction in which alternate spans cantilever over supporting columns with a simply supported span connected to the ends of the cantilevers in the other bays. Their investigation followed the collapse of a parking roof with this form of construction in Burnaby, British Columbia. A computer finite element program and 31 full-scale tests draw attention to a number of bracing details especially that where the bottom (compression) flange of the cantilever passes over the column, both beam and column head need to be braced. A paper by Idriss et al. describes an interesting project where an existing road bridge is to be demolished. This is a twogirder nonredundant structure designated therefore as 'fracture critical'. To help in safely carrying out the demolition and to gain the maximum information from the best placement of transducers a computer program was developed to investigate the behaviour when a cut is made in one of the members to simulate a crack. The computer program indicates that when a girder cracks there is a re-arrangement of the load paths but a stable structure still results. A paper by Clarke and Bridge highlights the fact that manufacturing tolerances may seriously affect the failure load of columns. They consider the example of a column with a central brace and show that a very slight misplacement of this brace may result in unexpected failure since the failure load is very sensitive to slight asymmetry. Another paper by Plant and Via considers a similar topic. In the section concerned with building systems there is a paper by L.A. Lutz on bracing concepts for skylight and curtainwall framing of small aluminium alloy sections, which may be of 'unusual' extruded cross-section, and one by Kaehler and Fisher on bracing practices in metal building systems. There are papers by Biswas on when it is proper to consider a multistorey frame as adequately braced to support gravity loads, and by Helwig et al. on the bracing forces in diaphragms and cross-frames of bridge beams. A paper by Fisher and West contains a detailed discussion of American practice in the erection bracing of structural steel frames. A paper by Ono et al. discusses the buckling of knee joints in single-storey gabled frames of long span like wide factory shed buildings or school assembly halls. The authors show that
bracing for latticed members ought to be different from that for members made with solid webs. A paper by Abdelrazaq et al. is concerned with the diagonal megabracing which is a dramatic feature of the elevations of tall buildings like the John Hancock Center in Chicago. There is a paper by Judd on eccentric braced frames, and by A1-Mashary et al. on the effective bracing of trussed towers against secondary movements. There is also a paper by Tremblay and Stiemer on the design of friction bolted connections to resist severe earthquake ground motions without damage to the main structural members. The final paper is a brief review of the effect of bomb damage on the stability of columns at the World Trade Center. The book includes a panel discussion on questions raised by participants on the presentation of the papers. Engineers need to review their practice from time to time because of the effects which recent increases in the slenderness of construction might have on their structures and on their reputations if they neglect proper bracing. Buckling is a very dangerous form of premature failure because it is usually sudden and often complete. It will be seen that many topics about structural bracing and instability are considered in the book which will be a useful and interesting addition to the library of any thoughtful engineer wishing to do more than merely comply with the clauses of a design code.
Arthur Bolton Plastic hinge based methods for advanced analysis and design of steel frames: an assessment of the state-of-the art Editors: D.W. White and W.F. Chen, Structural Stability Research Council, Lehigh University, Bethlehem, PA, 1993, ISBN 1879749-53-X In June 1994 the Structural Stability Research Council - an organization formed originally to produce rules for the design of steel columns in the United States but subsequently expanded to take an interest in all forms of structural stability - held its 50th Anniversary Meeting and Technical Session at its spiritual home: Lehigh University, Bethlehem,Pennsylvania. Currently one of its most active task groups is that concerned with second-order inelastic analysis for frame design. Various special presentations and discussions have been organized by this group and the volume under review is the direct result of a workshop held at the 1992 SSRC meeting in which 47 representatives from 7 different countries participated. It comprises 13