【正文】 hould be adopted: (a) provide stability against lateral forces and ensure braced construction by arranging suitable shear walls deployed symmetrically wherever possible (b) adopt a simple arrangement of slabs, beams and columns so that loads are carried to the foundations by the shortest and most direct routes (c) allow for movement joints (see subsection ) (d) choose an arrangement that will limit the span of slabs to 5m to 6m and beam spans to 8m to l0m on a regular grid。 Management) Stability Lateral stability in two orthogonal directions should be provided by a system of strongpoints within the structure so as to produce a braced nonsway structure, in which the columns will not be subject to significant sway moments. Strongpoints can generally be provided by the core walls enclosing the stairs, lifts and service ducts. Additional stiffness can be provided by shear walls formed from a gable end or from some other external or internal subdividing wall. The core and shear walls should preferably be distributed throughout the structure and so arranged that their bined shear centre is located approximately on the line of the resultant in plan of the applied overturning forces. Where this is not possible, the resulting twisting moments must be considered 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 ,