1.1 REINFORCED CONCRETE STRUCTURES
Concrete is arguably the most important building material, playing a part in all building
structures. Its virtue is its versatility, i.e. its ability to be moulded to take up the shapes
required for the various structural forms. It is also very durable and fire resistant when
specification and construction procedures are correct.
Concrete can be used for all standard buildings both single storey and multi-storey and for
containment and retaining structures and bridges. Some of the common building structures are shown in Fig.1.1 and are as follows:
1. The single-storey portal supported on isolated footings;
2. The medium-rise framed structure which may be braced by shear walls or unbraced. The
building may be supported on isolated footings, strip foundations or a raft;
3. The tall multi-storey frame and core structure where the core and rigid frames together
resist wind loads. The building is usually supported on a raft which in turn may bear directly
on the ground or be carried on piles or caissons. These buildings usually include a basement.
Complete designs for types 1 and 2 are given. The analysis and design for type 3 is
discussed. The design of all building elements and isolated foundations is described.1.2
STRUCTURAL ELEMENTS AND FRAMES
The complete building structure can be broken down into the following elements:Beams horizontal members carrying lateral loadsSlabs horizontal plate elements carrying lateral loadsColumns vertical members carrying primarily axial load but generally subjected to axial
load and momentWalls vertical plate elements resisting vertical, lateral or in-plane loadsBases and foundations pads or strips supported directly on the ground that spread the loads from columns or walls so that they can be supported by the ground without excessive
settlement. Alternatively the bases may be supported on piles.
To learn about concrete design it is necessary to start by carrying out the design of separate
elements. However, it is important to recognize the function of the element in the complete
structure and that the complete structure or part of it needs to be analysed to obtain actions for design. The elements listed above are
Page 2illustrated in Fig.1.2 which shows typical cast-in-situ concrete building construction.
A cast-in-situ framed reinforced concrete building and the rigid frames and elements into
which it is idealized for analysis and design are shown in Fig.1.3. The design with regard to
this building will cover
1. one-way continuous slabs
2. transverse and longitudinal rigid frames
3. foundations
Various types of floor are considered, two of which are shown in Fig.1.4. A one-way floor
slab supported on primary reinforced concrete frames and secondary continuous flanged
beams is shown in Fig.1.4(a). In Fig.1.4(b) only primary reinforced concrete frames are
constructed and the slab spans two ways. Flat slab construction, where the slab is supported
by the columns without beams, is also described. Structural design for isolated pad, strip and
combined and piled foundations and retaining walls (Fig.1.5) is covered in this book.1.3
STRUCTURAL DESIGN
The first function in design is the planning carried out by the architect to determine the
arrangement and layout of the building to meet the client’s requirements. The structural
engineer then determines the best structural system or forms to bring the architect’s concept
into being. Construction in different materials and with different arrangements and systems
may require investigation to determine the most economical answer. Architect and engineer
should work together at this conceptual design stage.
Once the building form and structural arrangement have been finalized the design problem
consists of the following:
1. idealization of the structure into load bearing frames and elements for analysis and
design
2. estimation of loads
3. analysis to determine the maximum moments, thrusts and shears for design
4. design of sections and reinforcement arrangements for slabs, beams, columns and walls
using the results from 3
5. production of arrangement and detail drawings and bar schedules
1.4 DESIGN STANDARDS
In the UK, design is generally to limit state theory in accordance with BS8110:1997:Structural Use of Concrete Part 1: Code of Practice for Design and Construction
Page 3The design of sections for strength is according to plastic theory based on behaviour at
ultimate loads. Elastic analysis of sections is also covered because this is used in calculations
for deflections and crack width in accordance with BS 8110:1985: Structural Use of Concrete
Part 2: Code of Practice for Special CircumstancesThe loading on structures conforms to
BS 6399–1:1996 Loading for buildings. Code of Practice for Dead and Imposed LoadsBS 6399–2:1997 Loading for buildings. Code of Practice for Wind LoadsBS 6399–3:1988 Loading for buildings. Code of Practice for Imposed Roof LoadsThe codes set out the design loads, load combinations and partial factors of safety, material strengths, design procedures and sound construction practice. A thorough knowledge of the codes is one of the essential requirements of a designer. Thus it is important that copies of these codes are obtained and read in conjunction with the book. Generally, only those parts of clauses and tables are quoted which are relevant to the particular problem, and the reader should consult the full text.
Only the main codes involved have been mentioned above. Other codes, to which reference
is necessary, will be noted as required.
1.5 CALCULATIONS, DESIGN AIDS AND COMPUTING
Calculations form the major part of the design process. They are needed to determine the
loading on the elements and structure and to carry out the analysis and design of the elements.Design office calculations should be presented in accordance withHiggins, J.B and Rogers, B.R., 1999, Designed and detailed. British Cement Association.The need for orderly and concise presentation of calculations cannot be emphasized too strongly.
Design aids in the form of charts and tables are an important part of the designer’s equipment. These aids make exact design methods easier to apply, shorten design time and
lessen the possibility of making errors. Part 3 of BS 8110 consists of design charts for beams
and columns, and the construction of charts is set out in this book, together with
representative examples. Useful books areReynolds, C.E. and Steedman, J.C., 1988, Reinforced concrete designers handbook, (Spon Press).
Goodchild, C.H., 1997, Economic concrete frame elements, (Reinforced Concrete Council).The use of computers for the analysis and design of structures is standard practice.
Familiarity with the use of Spread Sheets is particularly useful. A useful reference isGoodchild, C.H. and Webster, R.M., 2000, Spreadsheets for concrete design to BS 8110
and EC2, (Reinforced concrete council).
Page 4In analysis exact and approximate manual methods are set out but computer analysis is used where appropriate. However, it is essential that students understand the design principles involved and are able to make manual design calculations before using computer programs.1.6 TWO CARRIAGE RETURNS DETAILINGThe general arrangement drawings give the overall layout and principal dimensions of the structure. The structural requirements for the individual elements are presented in the detail drawings. The output of the design calculations are sketches giving sizes of members and the sizes, arrangement, spacing and cut-off points for reinforcing bars at various sections of the structure. Detailing translates this information into a suitable pattern of reinforcement for the structure as a whole. Detailing is presented in accordance with theStandard Method of Detailing Structural Concrete. Institution of Structural Engineers,London, 1989.It is essential for the student to know the conventions for making reinforced concrete drawings such as scales, methods for specifying steel bars, links, fabric, cut-off points etc.
The main particulars for detailing are given for most of the worked exercises in the book. The bar schedule can be prepared on completion of the detail drawings. The form of the schedule and shape code for the bars are to conform to BS 8666:2000: Specification for Scheduling, Dimensioning, Bending and cutting of steel for Reinforcement for ConcreteIt is essential that the student carry out practical work in detailing and preparation of bar schedules prior to and/or during his design course in reinforced concrete. Computer detailing
suites are now in general use in design offices.
Page 5Fig 1.1 (a) Single storey portal; (b) medium-rise reinforced concrete framed building; (c) reinforced concrete frame and core structure.
Page 6Fig 1.2 (a) Part elevation of reinforced concrete building; (b) section AA, T-beam ; (c) section BB; (d) continuous slab; (e) wall; (f) column base
Page 7Fig 1.3 (a) Plan of roof and floor; (b) section CC, T-beam; (c) section DD, column; (d) side elevation,longitudinal frame; (e) section AA, transverse frame; (f) continuous one-way slab.
Page 8Fig.1.4 (a) One-way floor slab; (b) two-way floor slab.Fig.1.5 (a) Isolated base; (b) wall footing; (c) combined base; (d) piled foundation
