【正文】 when calculating the load carried by each strongpoint. These walls should generally be of reinforced concrete not less than 180mm thick to facilitate concreting, but they may be of 215mm brickwork or 190mm solid blockwork properly tied and pinned up to the framing for low to mediumrise buildings. Strongpoints should be effective throughout the full height of the building. If it is essential for strongpoints to be discontinuous at one level, provision must be made to transfer the forces to IStructE EC2 (Concrete) Design Manual 5 other vertical ponents. It is essential that floors be designed to act as horizontal diaphragms, particularly if precast units are used. Where a structure is divided by expansion joints each part should be structurally independent and designed to be stable and robust without relying on the stability of adjacent sections. Robustness All members of the structure should be effectively tied together in the longitudinal, transverse and vertical directions. A welldesigned and welldetailed castin situ structure will normally satisfy the detailed tying requirements set out in subsection . Elements whose failure would cause collapse of more than a limited part of the structure adjacent to them should be avoided. Where this is not possible, alternative load paths should be identified or the element in question strengthened. Movement joints Movement joints may need to be provided to minimize the effects of movements caused by, for example, shrinkage, temperature variations, creep and settlement. The effectiveness of movement joints depends on their location. Movement joints should divide the structure into a number of individual sections, and should pass through the whole structure above ground level in one plane. The structure should be framed on both sides of the joint. Some examples of positioning movement joints in plan are given in Fig. . Movement joints may also be required where there is a significant change in the type of foundation or the height of the structure. For reinforced concrete frame structures in UK conditions, movement joints at least 25mm wide should normally be provided at approximately 50m centres both longitudinally and transversely. In the top storey and for open buildings and exposed slabs additional joints should normally be provided to give approximately 25m spacing. Joint spacing in exposed parapets should be approximately 12m. Joints should be incorporated in the finishes and in the cladding at the movement joint locations. Fire resistance and durability For the required period of fire resistance (prescribed in the Building Regulations), the structure should: ? have adequate loadbearing capacity ? limit the temperature rise on the far face by sufficient insulation, and IStructE EC2 (Concrete) Design Manual 6 ? have sufficient integrity to prevent the formation of cracks that will allow the passage of fire and gases. Fig. Location of movement joints The design should take into account the likely deterioration of the structure and its ponents in their environment having due regard to the anticipated level of maintenance. The following interrelated factors should be considered: ? the required performance criteria ? the expected environmental conditions ? the position, properties and performance of materials ? the shape of members and detailing ? the quality of workmanship ? any protective measure ? the likely maintenance during the intended life. Concrete of appropriate quality with adequate cover to the reinforcement should be specified. The above requirements for durability and fire resistance may dictate sizes for members greater than those required for structural strength alone. IStructE EC2 (Concrete) Design Manual 7 3 Design principles – reinforced concrete Loading The loads to be used in calculations 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 ‘a(chǎn)dverse’ 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。