【正文】 r the use of lightweight aggregate concrete。 Part Supplementary rules for plain or lightly reinforced concrete structures。 Part Concrete foundations。 however the data given are limited to the following: IStructE EC2 (Concrete) Design Manual 3 – concrete up to characteristic cylinder strength of 50N/mm2 (cube strength 60 2N/mm ) – hightensile reinforcement with characteristic strength of 460 2N/mm – mildsteel reinforcement with characteristic strength of 250 2N/mm – prestressing tendons with 7wire lowrelaxation (Class 2) strands ? High ductility (Class H) has been assumed for: – all ribbed bars and grade 250 bars, and – ribbed wire welded fabric in wire sizes of 6mm or over ? Normal ductility (Class N) has been assumed for plain or indented wire welded fabric. For structures or elements outside this scope EC2 should be used. Contents of the Manual The Manual covers the following design stages: ? general principles that govern the design of the layout of the structure ? initial sizing of members ? estimating of quantities of reinforcement and prestressing tendons ? final design of members. IStructE EC2 (Concrete) Design Manual 4 2 General principles This section outlines the general principles that apply to both initial and final design of both reinforced and prestressed concrete building structures, and states the design parameters that govern all design stages. General One engineer should be responsible for the overall design, including stability, and should ensure the patibility of the design and details of parts and ponents even where some or all of the design and details of those parts and ponents are not made by the same engineer. The structure should be so arranged that it can transmit dead, wind and imposed loads in a direct manner to the foundations. The general arrangement should ensure a robust and stable structure that will not collapse progressively under the effects of misuse or accidental damage to any one element. The engineer should consider engineer site constraints, buildability2, maintainability and demissioning. The engineer should take account of his responsibilities as a ‘Designer’ under the Construction (Design amp。water where present Dead load kG Adverse Beneficial Imposed, windsnow load kQ 和 kW Adverse Beneficial Earth and water nE 1． Dead + imposed 2． Dead + wind 3． Dead + snow 4． Dead+imposed +wind+ snow — — — — — — ? ? ? ? The Table uses the simplified bination permitted in EC2. ?For pressures arising from an accidental head of water at ground level a partial factor of may be used. Material and design stresses Design stresses are given in the appropriate sections of the Manual. It should be noted that EC2 specifies concrete strength class by both the cylinder strength and cube strength (for example C25/30 is a concrete with cylinder strength of 25 and cube strength of 30 2N/mm at 28 days). Standard strength classes are C20/25, C25/30, C30/37, C35/45, C40/50, C45/55 and C50/60. All design equations which include concrete pressive strength use the characteristic 28 day cylinder strength, ckf . Partial factors for concrete are for ultimate limit state and for serviceability limit state. The strength properties of reinforcement are expressed in terms of the characteristic yield strength,ykf. Partial factors for reinforcement steel are for ultimate limit state and for serviceability limit state. IStructE EC2 (Concrete) Design Manual 9 4 Initial design – reinforced concrete Introduction In the initial stages of the design of building structures it is necessary, often at short notice,to produce alternative schemes that can be assessed for architectural and functional suitability and which can be pared for cost. They will usually be based on vague and limited information on matters affecting the structure such as imposed loads and nature of finishes, let alone firm dimensions, but it is nevertheless expected that viable schemes be produced on which reliable cost estimates can be based. It follows that initial design methods should be simple, quick, conservative and reliable. Lengthy analytical methods should be avoided. This section offers some advice on the general principles to be applied when preparing a scheme for a structure, followed by methods for sizing members of superstructures. Foundation design is best deferred to later stages when site investigation results can be evaluated. The aim should be to establish a structural scheme that is suitable for its purpose, sensibly economical, and not unduly sensitive to the various changes that are likely to be imposed as the overall design develops. Sizing of structural members should be based on the longest spans (slabs and beams) and largest areas of roof and/or floors carried (beams, columns, walls and foundations). The same sizes should be assumed for similar but less onerous cases – this saves design and costing time at this stage and is of actual benefit in producing visual and constructional repetition and hence, ultimately, cost benefits. Simple structural schemes are quick to design and easy to build. They may be plicated later by other members of the design team trying to achieve their optimum conditions, but a simple scheme provides a good ‘benchmark’ at the initial stage. Loads should be carried to the foundation by the shortest and most direct routes. In constructional terms, simplicity implies (among other matters) repetition。 for flat slabs restrict column spacings to 8m (e) adopt a minimum column size of