土木工程-外文翻譯-建筑結構(編輯修改稿)

　

【文章內容簡介】 ions are: (a) Characteristic dead load, kG : the weight of the structure plete with finishes, fixtures and fixed partitions (BS 4648 ) (b) Characteristic imposed load, kQ (BS6399， Parts1and 53 ) (c) Characteristic wind load, Wk (90% of the load derived from CP3, Chapter V, Part 62 )* (d) Nominal earth load, nE (BS 78004 ) (e) At the ultimate limit state the horizontal forces to be resisted at any level should be the greater of: (i) % of the characteristic dead load above that level, or (ii) 90% of the wind load derived from CP3, Chapter V, Part 62 , multiplied by the appropriate partial safety factor. The horizontal forces should be distributed between the strongpoints according to their stiffness. In using the above documents the following modifications should be noted: (f) The imposed floor loads of a building should be treated as one load to which the reduction factors given in BS 6399: Part 1: 51996 are applicable. (g) Snow drift loads obtained from BS 6399: Part 3: 51998 should be multiplied by and treated in a similar way to an imposed load and not as an accidental load. Limit states This Manual adopts the limitstate principle and the partial factor format of EC2. Ultimate limit state The design loads are obtained by multiplying the characteristic loads by the appropriate partial factor f?from Table . The ‘adverse’ and ‘beneficial’ factors should be used so as to produce the most onerous condition. Serviceability limit states IStructE EC2 (Concrete) Design Manual 8 Provided that span/effective depth ratios and bar diameter and spacing rules are observed it will not be necessary to check for serviceability limit states. Table Partial factors for loads γf at the ultimate limit state Load bination including earth 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。 avoidance of congested, awkward or structurally sensitive details and straightforward temporary works with minimal requirements for unorthodox sequencing to achieve the intended behaviour of the pleted structure. Standardized construction items will usually be cheaper and more readily available than purposemade items. Loads IStructE EC2 (Concrete) Design Manual 10 Loads should be based on BS 4648 ， BS6399： Parts1 and 53 andCP3： ChapterV： Part 62 Imposed loading should initially be taken as t