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Multi-storey Precast Concrete Framed Structures

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consequently, the trainee structural designer is rarely exposed to the virtues of using precast concrete in this way. Opportunities to study the basic concepts adopted in the design, manufacturing and site erection stages are not often made available to the vast majority of trainees. Even where precast concrete is accepted as a viable alternative form of construction to e.g. steelwork for medium to high-rise structures, or to insitu concrete for some of the more complex shaped buildings, or to masonry for low-rise work, it is often considered only at a late stage in the planning process. In these situations, precast concrete is then often restricted to the substitution of components carrying their own locally-induced stresses. 

The economic advantage of the precast components also carrying global stresses is lost in the urgency to commence construction. Indeed, precast component design has long been considered as having a secondary role to the main structural work. 

Only more recently have precast designers been challenged to validate the fundamental principles they are using, and to give clients conidence in precast concrete design solutions for entire structures. To meet ever-increasing building speciications, precast manufacturing companies have considerably reined the design of their product. 

They have formed highly effective product associations dealing with not only the marketing and manufacturing of the product, but also with technical matters. These include  common  design  solutions,  research  initiatives,  education,  uniied  design  approaches,  and, importantly, the encouragement of a wider appreciation of precast structures in the professional  design ofice. Even so, the structural and architectural complexity of some of the more recent precast frames has widened the gap between precast designers and the rest of the profession. 

The latter have limited sources for guidance on how the former are working. Satisfying codes of practice and the building regulations plays only a minor role in the total package; there is so much more, as this book shows. Nowadays, the use of precast reinforced and prestressed concrete for multi-storey framed buildings is widely regarded as an economic, structurally sound and architecturally versatile building method. 

Design concepts have evolved to satisfy a wide range of commercial and industrial building needs. ‘Precast concrete frames’ is a term which is now synonymous with high quality, strength, stability, durability and robustness.  Design  is  carried  out  to  the  highest  standard  of  exactness  within  the  concrete  industry and yet the knowhow, for the reasons given above, remains essentially within the precast industry itself. Precast concrete buildings do not behave in the same way as cast-in situ ones.

 The components which make up the completed precast structure are subjected to different forces and movements from the concrete in the monolithic structure. It is necessary to understand where these physical effects come from, where they go to, and how they are transferred through the structure. 

Consequently, this book aims to disseminate understanding of the disparate procedures involved in precast structural design, from drawing ofice practice to explaining the reasons for some of the more intricate operations performed by precast contractors on site. The principal focus is upon on skeletalframe type structures, the most extensively used form of precast structural concrete. They are deined as frameworks consisting essentially of beams, columns, slabs and a small number of shear walls.

 From the structural and architectural viewpoints, skeletal frames are the most demanding of all precast  structures.  They  contain  the  smallest  quantity  of  structural  concrete  per  unit  volume.  The precast components can be coordinated into the architectural façade, both internally and externally , to meet the social, economic and ecological demands that are now required. Ever greater accuracy, quality control, and on-site construction eficiency are being demanded and achieved.

 The construction  industry  is  turning  to  high-speciication  prefabricated  concrete  for  its  advancement,  using ‘factory engineered’ precasting techniques. The chapters in this book have been arranged so that different parts of the design process can be either isolated (for example in the cases of precast looring, or of connections), without the reader necessarily  referring  to  the  overall  frame  design,  or  read  sequentially  to  realise  the  entire  design. Chapters 1 to 3 present an overview of the subject in a non-technical way. Chapters 4 to 9 describe, in  detail,  the  design  procedures  that  would  be  carried  out  in  a  precast  manufacturing  company’s design ofice. Chapter 10 describes the relevant site construction methods. Numerous examples have been used to demonstrate the application of design rules, many of which are not code-dependent. There  are  many  aspects  to  the  design  of  precast  skeletal  frames  that  have  evolved  through  the natural development of precast frame design since the 1950s.

 One aim of this book is to update and coordinate this information for the future. Historically, the precast concrete industry considered many of  its  design  techniques  commercially  sensitive,  particularly  those  for  connector  design,  and  was consequently criticised by developers and consultants. More information is now freely available since the expiry of many patents of ideas. One of the main purposes of the irst edition was to bring together in  a  coherent  manner,  for  the  beneit  of  everyone,  the  widely  varied  design  methods  used  in  the industry.  The  second  edition  aims  to  extend  that  process  in  the  context  of  continually  developing technology and the introduction of Europe-wide design requirements embodied in the Eurocodes. It also demonstrates the trend towards greater, often fully serviced, spatial precast components. Precast concrete designs are not entirely code-dependent, but the primary recommendations are in  accordance  with  Eurocode  2  (BS  EN  1992-1-1)  and  its  predecessor  BS  8110. Where  the  design procedures from the two codes differ, they are explained. 

Where major differences occur, or accumulate in design examples, the text is presented in two parallel columns with the Eurocode version in the left column and the BS 8110 text in the right column. When minor textual differences occur for the application of the two codes, Eurocode 2 forms the basic text, with the alternative BS text within braces  or  curly  brackets  thus:  {to  BS  8110}.  It  may  help  the  reader  to  know  that  the  authors  have retained braces exclusively for this purpose, leaving the use of round brackets for the two contextually differentiable functions of parenthesis or mathematical grouping, and square brackets for references. The combination of a broad overview, background research, and detailed analysis, the references to  the  familiar  British  Standards  and  the  new  Eurocodes,  and  an  extensive  range  of  illustrations together combine to offer a valuable resource for both undergraduate and practising engineers in the ield of precast concrete .