Walls are defined as being vertical elements whose lengths are four times greater than their thicknesses. Their design does not differ significantly from the design of columns in that axial loads and moments about each axis are assessed and designed for.
Generally, the method of designing walls is as follows:
1. Determine design life.
2. Assess actions on the column.
3. Determine which combinations of actions apply.
4. Assess durability requirements and determine concrete strength.
5. Check cover requirements for appropriate fire resistance period.
6. Determine cover for fire, durability and bond.
7. Analyse structure for critical combination moments and axial forces.
8. Check slenderness and determine design moments.
9. Determine area of reinforcement required. 10. Check spacing of bars
<BS EN 1990 & NA Table NA 2.1> <BS EN 1991 (10 parts) & UK NAs>
<BS EN 1990 & NA Tables NA A1.1 & NA A1.2(B)> <BS 8500-1>
<Approved Document B BS 1992-1-2>
<BS EN 1992-1-1 Cl. 4.4.1> <BS EN 1992-1-1 Section 5>
<BS EN 1992-1-1 Section 6.1> <BS EN 1992-1-1 Sections 8 & 9>
Example 6.2 shows the design of a simple linear shear wall as typically used in medium rise buildings. Similar principals may be applied to walls that are shaped as C, L, T, Z and rectangles in-plan but issues of limiting flange dimensions and shear at corners need be addressed. The example shows only ULS design as, apart from minimum areas of steel to control cracking, SLS issues are generally non-critical in medium-rise structures. For shear walls in high-rise structures, reference should be made to specialist literature (ref to CIRIA R102 Design of shear wall buildings).
Wall 'A' is 200 mm thick and in addition to providing vertical support to 200 mm flat slabs at roof level and floors 1 to 3, it helps to provide lateral stability to the four storey office block. Assuming the stair itself provides no lateral stability, the wall is to be designed for the critical section at ground and first floor level using BS EN 1990 Exp. (6.10). The concrete is C30 / 37. The wall is supported on pad foundations and the ground floor is ground bearing.
The example is intended to show how a shear wall providing part of the lateral stability in one direction in a medium rise structure might be designed by hand.
Axial loads and first order moments are determined. The designs consider slenderness in order to determine design moments, MEd in the plane perpendicular to the wall. The effects of allowing for imperfections are also illustrated.
Paving 40 mm Waterproofing Insulation Suspended ceiling Services
Self-weight 200 mm slab Variable action
Ca rpet Raised floor Suspended ceiling Services
Self-weight 200 mm slab
Ground floor slab (ground bearing) Carpet Raised floor Services
Self-weight 200 mm slab Variable action kN / m2 3k Hk
150 waist @ 30
Tiles and bedding Variable
102 mm brickwork 50 mm insulation 100 mm blockwork Plaster
200 mm wall Plaster both sides
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