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Design of concrete structures: The use of model analysis
Book reviews
Canada. In the 75-storey Texas Commerce Tower, high strength concrete, with 52 MPa compressive strength specified for 28 days, was successfully used permitting an accelerated construction schedule, smaller column sizes, a more economical structural frame, and a greater stiffness for the composite structure as a whole. It is interesting to note that the concrete mix contained a Type C fly ash and a water-reducing admixture resulting in a water-cement ratio of 0.33. The concrete was pumped up to a height over 300m, and the 28 day strength averaged 56 MPa. The use of high strength concrete in the Seattle area, varying from 50 to 70 MPa 28 days strength in seven proiects is also reported. At the 76-storey Columbia Sea-First Centre, concrete of 67 MPa strength was used in three large composite columns. The concrete mix in this project also used a Class C fly ash, a water-reducing agent and a superplasticiser resulting in a final water-cement ratio of 0.25. The actual strength achieved averaged 77 MPa at 56 days, and 84 MPa at 180 days. That such high strength concretes can be readily obtained on site is confirmed again by the use of a 90 MPa silica fume concrete in the construction of an experimental column running through four subbasement elevations of a 26-storey high rise building. This concrete also had a water-cement ratio of 0.25 and a slump of 250mm after 45 minutes travel. Many papers discuss the implications of using high strength concrete in terms of temperature rise, thermal gradients, elastic modulus and shrinkage. They also emphasise the need for good quality control and co-operation among the engineer, contractor, materials supplier and the test laboratory. In using concrete strengths in excess of 40-45 MPa, it is important to ensure that existing design criteria and building codes are satisfied. This is important from a design point of view, and the second part of this volume contains eight papers which report the evaluation of existing design criteria for high strength concrete and ongoing research. Many of these papers show that high strength concrete needs, in many respects, to be treated as a material on its own, and there are many properties that need careful consideration at the design stage. The papers included in this section discuss high strength with normal and lightweight aggregates, and high strength steel fibre concrete. Several papers report tests on structural behaviour of members with high strength concrete---, flexural strength, shear strength, corbel behaviour, column behaviour and behaviour under uniaxial and biaxial compression. It is clear from all these papers that many provisions of current building codes are generally applicable to high strength concrete, but there are others that need to be re-examined and modified. The engineer's responsibility is to ensure structural safety and serviceability, with long term stability. The papers included in this volume should leave no one in doubt that it is possible to formulate concrete mixes of high strength and adequate workability, and that such strength can be readily produced on site, and used in construction with confidence and economy. One can only recommend this publication to
all practising engineers and hope that the experiences summarised here can be utilised to further benefits in the future.
Design of Concrete Structures: The Use of Model Analysis Edited by J. L. Clarke, F. K. Garas and G. S. T. Armer. Published by Elsevier Applied Science Publishers Limited, Crown House, Linton Road, Barking, Essex 1 G l l 8JU, England, 1985. ISBN 0 85334 387 X, Price £40.00, Xl + 380 pp. Many structures, both conventional and unconventional, pose severe problems to the engineer not only in analysis and design but also in construction and in the assessment of the performance of such structures. Several types of structures fail into this category - - such as multi-storey buildings subjected to impact or earthquake loading, nuclear containment vessels and offshore oil rigs. Model testing and analysis then becomes an inseparable part of the design and construction process, and helps the engineer in interpreting the response of these structures to complex loading conditions. The use of physical models has thus become an essential part of an engineer's knowledge and training. This volume provides an up to date report to enhance this experience on the modelling of concrete structures. The papers included in this publication represent the proceedings of an international seminar organised by the Institution of Structural Engineers and held at the Building Research Establishment in November 1984. There are 33 papers in the volume which have been divided into four broad sections - - recent developments in modelling techniques, reliability and accuracy of structural models, application of model results in design and analysis and interpretation of model test results. There is a wealth of information in these papers, much of which will be of great use to the practising engineer. In the section on recent developments in modelling techniques, eight papers are included. These discuss several new procedures for making model concrete and small diameter reinforcement. Two innovative methods deserve mention - - the use of coated aggregates to reduce the tensile strength of small aggregate concretes, and a device that rolls rather than knurls the small diameter reinforcement. The determination of the shear strength of slabs from microconcrete models still appears to need to be dealt with care, and suitable methods for extrapolating shear strength are yet to be established. The use of vinyls to model steel tanks is interesting, and the viability of these elastic models has been demonstrated The various improvements in modelling techniques suggested in these papers should help in extending and extrapolating model studies to design. Eight papers discuss the reliability and accuracy of structural models. The importance of 'size effects' is discussed in several papers. Size effects are closely related to the fracture behaviour of the model material, and to the development and propagation of cracks in concrete. Bond also remains a continuing problem in
137
Book r e v i e w s
influencing deformations and cracking, whilst in modelling dynamic effects, the strain rates are critical. The papers clearly emphasise again that concrete itself is a variable material and that the accuracy of the models should be discussed in relation to this variability. There are seven papers dealing with the interpretation and application of test results. A wide range of topics is covered in these papers - - punching shear in slabs, flat slab-edge column connections, buckling of reinforced concrete beams, design of pile caps and shear design of concrete slab bridges. These illustrate how models can provide insights into behaviour which could not only be helpful in design but also have considerable educational benefits. Models can be used to validate and develop theoretical analyses, and equally, they can be of use where no good theory is available. The last section of ten papers on analysis and interpretation of model test results contains a good set of interesting papers on a diverse set of topics. The areas covered in these papers include modelling bored and cast-in-situ piles to study shaft adhesion, model analysis for use in construction and repair of offshore structures, reinforced concrete beam-column subassemblages under reversed loading, and modelling of a reinforced concrete chimney. The results reported show ifq a convincing manner that models have an undeniable place in modern structural engineering. The aim of model testing is to improve design methodology, which in turn leads to better construction procedures resulting in structures with improved reliability, greater economy and good serviceability. The papers in this volume show convincingly that models can make positive and effective contributions to the art and science of structural engineering. Ultimately there is no substitute for physical understanding of structural behaw tour, and it is here that models have an undeniable role to play. This volume has a very distinct and invaluable contribution to make in this area.
Polymer Grid Fleinforcement Published by Thomas Telford Limited, Telford House, PO Box 101, 26-34 Old Street, London EC1P IJH, England, 1985.
ISBN 0 7277 0242 4, Price £28.00, 249 pp. Although polymeric materials have been around for many years, their use in civil engineering construction is relatively new. Such materials have been slow to catch on mainly because of the feeling amongst engineers that low modulus materials do not generally make effective reinforcing media nor can they be used as toad bearing structures. Apart from their low elastic modulus compared to metals, polymeric materials also exhibit etastoplastic behaviour and strain-rate dependency, both of which can influence the engineering properties of composites reinforced with such materials. However, the development of polymer geogrids of high tensile strength and manufactured from specially selected polyolefins to produce consistent and chemically inert engineering reinforcement materials has changed all that. Thanks to a co-operative research programme supported
138
by the Science and Engmeenng Research Council and Netlon Limited and involving the Universities of Xlottingham. Oxford, Sheffield and Strathcivae extenswe research and engineering data nave been developed ma; would ensure satisfactory and reliable performance of these grids ~n toad bearing aoplications. This publication is me result of this co-ordinated development study, and includes all the papers presented at me svmoos~um organ~sed n London in March 1984 Plastics [o reinforce soils asphalt pavements and concrete ~s me overall meme of me papers included n this proceedings volume. Thirtv-~nree papers combining research, design and applications, and divided m e seven groups, are included. The first four papers are devoted to the aeve~apmem of molecularly oriented polymer reinforcing gnds, their stress-strain-time behaviour tb,e imeracuon between soils and geogrids and the use of geogrid properties m design It ~s shown that onentm~on improves many properties not just strength and stiffness. ~t reduces the permeabHttv to gases, improves cnem~cal resistance, and makes tne material more stable with a much ~ower thermat coefficient of expansion and less permanent shrinkage The second and third grobps of papers are aevote(~ to reinstatement of slopes an{] tne reinforcement of embankments. Case histories from the UK USA and Canada confirm that layers of geogno reinforcement can De used not only to repair SI~D{ailures and landshdes Out also to reinforce steep embankments. Design cnteria and design charts were presented to show tnat eng~ neers can now use geognds for soil stabdisation and soil reinforcement with confidence adeouate factor of safety, cost effectweness and iong [erE', stabitit', The fourth group of oaDers numDenng five. aea~s w~th foundations for roads and ~oaded areas. An ncreasqa number of unpaveo roads and trafficked areas SUCh as parking lots and drilling pads are De{ng bullt using geognas but currently no oes~an metnods are available The mechanisms througn whiciq reinforcing meshes e~tner elastic or visco-e~astic contribute [o ~mprovea perfcrmance of an unpaved smJc~ure are still subject to debate but qeverthless " the I~gnt of 9resem, do,.
Canada. In the 75-storey Texas Commerce Tower, high strength concrete, with 52 MPa compressive strength specified for 28 days, was successfully used permitting an accelerated construction schedule, smaller column sizes, a more economical structural frame, and a greater stiffness for the composite structure as a whole. It is interesting to note that the concrete mix contained a Type C fly ash and a water-reducing admixture resulting in a water-cement ratio of 0.33. The concrete was pumped up to a height over 300m, and the 28 day strength averaged 56 MPa. The use of high strength concrete in the Seattle area, varying from 50 to 70 MPa 28 days strength in seven proiects is also reported. At the 76-storey Columbia Sea-First Centre, concrete of 67 MPa strength was used in three large composite columns. The concrete mix in this project also used a Class C fly ash, a water-reducing agent and a superplasticiser resulting in a final water-cement ratio of 0.25. The actual strength achieved averaged 77 MPa at 56 days, and 84 MPa at 180 days. That such high strength concretes can be readily obtained on site is confirmed again by the use of a 90 MPa silica fume concrete in the construction of an experimental column running through four subbasement elevations of a 26-storey high rise building. This concrete also had a water-cement ratio of 0.25 and a slump of 250mm after 45 minutes travel. Many papers discuss the implications of using high strength concrete in terms of temperature rise, thermal gradients, elastic modulus and shrinkage. They also emphasise the need for good quality control and co-operation among the engineer, contractor, materials supplier and the test laboratory. In using concrete strengths in excess of 40-45 MPa, it is important to ensure that existing design criteria and building codes are satisfied. This is important from a design point of view, and the second part of this volume contains eight papers which report the evaluation of existing design criteria for high strength concrete and ongoing research. Many of these papers show that high strength concrete needs, in many respects, to be treated as a material on its own, and there are many properties that need careful consideration at the design stage. The papers included in this section discuss high strength with normal and lightweight aggregates, and high strength steel fibre concrete. Several papers report tests on structural behaviour of members with high strength concrete---, flexural strength, shear strength, corbel behaviour, column behaviour and behaviour under uniaxial and biaxial compression. It is clear from all these papers that many provisions of current building codes are generally applicable to high strength concrete, but there are others that need to be re-examined and modified. The engineer's responsibility is to ensure structural safety and serviceability, with long term stability. The papers included in this volume should leave no one in doubt that it is possible to formulate concrete mixes of high strength and adequate workability, and that such strength can be readily produced on site, and used in construction with confidence and economy. One can only recommend this publication to
all practising engineers and hope that the experiences summarised here can be utilised to further benefits in the future.
Design of Concrete Structures: The Use of Model Analysis Edited by J. L. Clarke, F. K. Garas and G. S. T. Armer. Published by Elsevier Applied Science Publishers Limited, Crown House, Linton Road, Barking, Essex 1 G l l 8JU, England, 1985. ISBN 0 85334 387 X, Price £40.00, Xl + 380 pp. Many structures, both conventional and unconventional, pose severe problems to the engineer not only in analysis and design but also in construction and in the assessment of the performance of such structures. Several types of structures fail into this category - - such as multi-storey buildings subjected to impact or earthquake loading, nuclear containment vessels and offshore oil rigs. Model testing and analysis then becomes an inseparable part of the design and construction process, and helps the engineer in interpreting the response of these structures to complex loading conditions. The use of physical models has thus become an essential part of an engineer's knowledge and training. This volume provides an up to date report to enhance this experience on the modelling of concrete structures. The papers included in this publication represent the proceedings of an international seminar organised by the Institution of Structural Engineers and held at the Building Research Establishment in November 1984. There are 33 papers in the volume which have been divided into four broad sections - - recent developments in modelling techniques, reliability and accuracy of structural models, application of model results in design and analysis and interpretation of model test results. There is a wealth of information in these papers, much of which will be of great use to the practising engineer. In the section on recent developments in modelling techniques, eight papers are included. These discuss several new procedures for making model concrete and small diameter reinforcement. Two innovative methods deserve mention - - the use of coated aggregates to reduce the tensile strength of small aggregate concretes, and a device that rolls rather than knurls the small diameter reinforcement. The determination of the shear strength of slabs from microconcrete models still appears to need to be dealt with care, and suitable methods for extrapolating shear strength are yet to be established. The use of vinyls to model steel tanks is interesting, and the viability of these elastic models has been demonstrated The various improvements in modelling techniques suggested in these papers should help in extending and extrapolating model studies to design. Eight papers discuss the reliability and accuracy of structural models. The importance of 'size effects' is discussed in several papers. Size effects are closely related to the fracture behaviour of the model material, and to the development and propagation of cracks in concrete. Bond also remains a continuing problem in
137
Book r e v i e w s
influencing deformations and cracking, whilst in modelling dynamic effects, the strain rates are critical. The papers clearly emphasise again that concrete itself is a variable material and that the accuracy of the models should be discussed in relation to this variability. There are seven papers dealing with the interpretation and application of test results. A wide range of topics is covered in these papers - - punching shear in slabs, flat slab-edge column connections, buckling of reinforced concrete beams, design of pile caps and shear design of concrete slab bridges. These illustrate how models can provide insights into behaviour which could not only be helpful in design but also have considerable educational benefits. Models can be used to validate and develop theoretical analyses, and equally, they can be of use where no good theory is available. The last section of ten papers on analysis and interpretation of model test results contains a good set of interesting papers on a diverse set of topics. The areas covered in these papers include modelling bored and cast-in-situ piles to study shaft adhesion, model analysis for use in construction and repair of offshore structures, reinforced concrete beam-column subassemblages under reversed loading, and modelling of a reinforced concrete chimney. The results reported show ifq a convincing manner that models have an undeniable place in modern structural engineering. The aim of model testing is to improve design methodology, which in turn leads to better construction procedures resulting in structures with improved reliability, greater economy and good serviceability. The papers in this volume show convincingly that models can make positive and effective contributions to the art and science of structural engineering. Ultimately there is no substitute for physical understanding of structural behaw tour, and it is here that models have an undeniable role to play. This volume has a very distinct and invaluable contribution to make in this area.
Polymer Grid Fleinforcement Published by Thomas Telford Limited, Telford House, PO Box 101, 26-34 Old Street, London EC1P IJH, England, 1985.
ISBN 0 7277 0242 4, Price £28.00, 249 pp. Although polymeric materials have been around for many years, their use in civil engineering construction is relatively new. Such materials have been slow to catch on mainly because of the feeling amongst engineers that low modulus materials do not generally make effective reinforcing media nor can they be used as toad bearing structures. Apart from their low elastic modulus compared to metals, polymeric materials also exhibit etastoplastic behaviour and strain-rate dependency, both of which can influence the engineering properties of composites reinforced with such materials. However, the development of polymer geogrids of high tensile strength and manufactured from specially selected polyolefins to produce consistent and chemically inert engineering reinforcement materials has changed all that. Thanks to a co-operative research programme supported
138
by the Science and Engmeenng Research Council and Netlon Limited and involving the Universities of Xlottingham. Oxford, Sheffield and Strathcivae extenswe research and engineering data nave been developed ma; would ensure satisfactory and reliable performance of these grids ~n toad bearing aoplications. This publication is me result of this co-ordinated development study, and includes all the papers presented at me svmoos~um organ~sed n London in March 1984 Plastics [o reinforce soils asphalt pavements and concrete ~s me overall meme of me papers included n this proceedings volume. Thirtv-~nree papers combining research, design and applications, and divided m e seven groups, are included. The first four papers are devoted to the aeve~apmem of molecularly oriented polymer reinforcing gnds, their stress-strain-time behaviour tb,e imeracuon between soils and geogrids and the use of geogrid properties m design It ~s shown that onentm~on improves many properties not just strength and stiffness. ~t reduces the permeabHttv to gases, improves cnem~cal resistance, and makes tne material more stable with a much ~ower thermat coefficient of expansion and less permanent shrinkage The second and third grobps of papers are aevote(~ to reinstatement of slopes an{] tne reinforcement of embankments. Case histories from the UK USA and Canada confirm that layers of geogno reinforcement can De used not only to repair SI~D{ailures and landshdes Out also to reinforce steep embankments. Design cnteria and design charts were presented to show tnat eng~ neers can now use geognds for soil stabdisation and soil reinforcement with confidence adeouate factor of safety, cost effectweness and iong [erE', stabitit', The fourth group of oaDers numDenng five. aea~s w~th foundations for roads and ~oaded areas. An ncreasqa number of unpaveo roads and trafficked areas SUCh as parking lots and drilling pads are De{ng bullt using geognas but currently no oes~an metnods are available The mechanisms througn whiciq reinforcing meshes e~tner elastic or visco-e~astic contribute [o ~mprovea perfcrmance of an unpaved smJc~ure are still subject to debate but qeverthless " the I~gnt of 9resem, do,.