Integrating seismic resisting structure and architecture

Readers may wonder if architecture in seismic zones might be bland and boring given its potential to be dominated by structural requirements (Fig. 6.2). As illustrated above, the size of seismic resisting structure can be large when compared to that required to withstand gravity and wind forces. Also, readers will remember recommendations from the previous chapter, such as wherever possible seismic resisting structures are symmetrical and regular and that moment frame column dimensions are larger than those of the beams. Surely the antithesis of exciting architecture!

All walls 4.0 x 0.5 m lever arm lever arm

(b)

(f)

x

(c)

(g)

_

lever

arm

▲ 6.3 Ground floor plans showing different shear wall layout options that provide symmetrical resistance for x direction seismic forces (Y direction and gravity structure not drawn).

▲ 6.3 Ground floor plans showing different shear wall layout options that provide symmetrical resistance for x direction seismic forces (Y direction and gravity structure not drawn).

The intention of this section is to explain that, although special requirements of seismic structure must be met and might constrain some architectural intentions, these requirements may not be nearly as severe as first thought. Any negative influences may often be avoided by timely and creative structural configuration.

For example, consider the recommendation of structural symmetry. Fig. 6.3 shows the ground floor plan of the four-storey building discussed in Fig. 6.1. Two or three shear walls provide resistance against x direction forces. Even though each structure is perfectly symmetrical with respect to those forces some shear wall layouts do not appear symmetrical especially when considering forces acting in the y direction. This is because shear walls resist forces only parallel to their lengths. Of the four options suggested for a two-wall layout, all are equally effective although the lesser lever arm of option (d) reduces resistance against any in-plan torsion that may occur. All four three-wall options are equally satisfactory from both the perspective of x direction forces and torsion.

A similarly diverse structural layout is possible if, for example, the shear walls are replaced by one-bay or multi-bay moment frames. There are so many possible layouts, each of which can contribute in some way to a more expressive and compelling architecture. In Fig. 6.4, one-way frames in the x and y directions might both form and articulate circulation or assist in architectural form making. Figure 6.5 presents one possible layout for structure that is also symmetrical in both orthogonal directions. Over half the length of the perimeter walls y y x x

One-way moment frame resists x direction force

Gravity only columns

One-way moment frame resists y direction force

Circulation route

Plan

One-way moment frame resists x direction force

Gravity only columns

One-way moment frame resists y direction force

Circulation route

Plan

▲ 6.4 The creation of circulation routes using one-way frames whose structurally symmetrical layout does not cause torsion.

Shear wall

Plan

▲ 6.5 Ground floor plan showing seismic resisting structure placed symmetrically for x and y directions (gravity structure not shown).

y x as well as the floor plan is free of seismic resisting structure and hence suspended floors require minimally dimensioned gravity-only columns for support in those areas.

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