What is the unsupported length?

It is the unsupported length referred to in clauses 6.4.1 and 6.5.1 of the code, and it can be used to determine the minimum value for wall thickness.

This post was last edited by “The Moon in My Hometown is Round” on January 3, 2018, at 14:57. Expert explanation: The purpose of specifying the minimum thickness of shear walls is to ensure their out-of-plane stiffness and stability. The stability of a wall is strictly determined by formula D.0.1 in Appendix D of the High-rise Building Code. It can be seen that the stability of a wall depends on its thickness t, its height h (with the floor slabs acting as the upper and lower constraints, meaning the wall height is the distance between these constraints), the lateral constraints (reflected in the calculation length coefficient β), as well as the vertical loads acting on the top of the wall. In general structural design, the loads, floor heights, and lateral constraints are generally fixed; to ensure the stability of the walls, designers need to control the minimum wall thickness. When there is a shear wall intersecting it outside the plane of the wall, it can be regarded as a support for that shear wall, which helps to ensure its stiffness and stability outside the plane. Therefore, Clause 7.2.2 of the High-Code stipulates that the minimum wall thickness can be determined based on the floor height and the unsupported length. Under normal circumstances, it is recommended to determine this limit based on the floor height (that is, the distance bounded by the upper and lower floor slabs; generally, the spacing between floors is smaller than that of the wall sections). In some special cases, such as when a floor slab is missing or when large openings are created, resulting in a greater wall height, the effect of the lateral constraints on the wall can be taken into account; in such situations, the concept of unsupported length comes into play. It should be understood in this way: it refers to the length along the direction of the shear wall when there are no out-of-plane lateral supports, that is, the length up to the point where such lateral supports exist. The support can be a wing wall or an end column (the requirements for shear walls with wing walls or end columns shall comply with the provisions of Note 3 in Table 7.2.16 of the High-rise Building Code).