A breakaway wall is a wall that is not part of the structural support of the building, intended through its design and construction to collapse under specific lateral (wind and water) loading conditions without causing collapse, displacement, or other structural damage to the elevated portion of the building or supporting foundation system. Uses such as parking of vehicles, building access, or storage are permitted, as long as the walls of any enclosures are designed as "breakaway". In recognition of the desirability of using the sheltered space beneath elevated structures, NFIP regulations permit certain limited uses of enclosed space below the BFE. When the space below the lowest elevated floor is maintained free of solid obstructions as well, the potential for damage from waves or debris is further reduced. Stage 3: Calculate Design Strength of WallĮffective thickness is improved by the introduction of the stiffening piers and is the product of the actual thickness of the wall (102.5 mm) and the stiffening coefficient K obtained from BS 5628, Table 5 (see Table 5.1 Breakaway Walls Elevation of a structure on a properly designed foundation reduces the potential for water damage from flooding. For this example, we will select a wall/pier profile as shown in Figure 10.14 and check its suitability. The trial and error approach related to the objective of achieving a reasonable slenderness ratio will eventually lead to the designer becoming more familiar with the benefits gained from the introduction of stiffening piers. There are no simple and realistic guidelines that can be applied to the selection of the size and spacing of stiffening piers. The design load will be taken as the same as for Example 1: nw = 271.5 kN/m The best use is not being made of brickwork's natural compressive strength in this design and the pier-stiffened half-brick wall is an obvious alternative choice, as will be shown in this example. The design for Example 1 resulted in a 215 mm thick brick wall of extremely low strength merely to provide for the maximum permissible slenderness ratio. The design philosophy will be dealt with in more detail later in section 10.8.ĭesign the internal wall given for Example 1 as a half-brick wall adequately stiffened by the introduction of brick piers. The design philosophy for such an element would be based upon second moment of area and radius of gyration, rather than slender-ness ratio as traditionally calculated from effective thickness, and a diaphragm or fin wall profile is generally the most suitable geometric form. The most common occurrence of this situation would occur in an extremely high wall which is required to support heavy axial loading. It is considered, however, that if a 215 mm thick brick wall does not have an adequate slenderness ratio to withstand a particular loading condition, the design calls for the selection of a geometric shape best suited to provide the necessary second moment of area. The use of stiffening piers to increase the second moment of area of a wall section is, of course, not limited to half-brick walls and can be applied to any solid wall thickness as well as to cavity walls. The possibility of a half-brick wall buckling under axial loads can be significantly reduced by the introduction of piers placed at regular, specified centres and fully bonded into the wall itself.
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