Introduction

This chapter addresses how the previously discussed horizontal and vertical seismic resisting systems are brought together in the making of architecture. While the integration of structure with architecture in general is a challenge that architects face, the task of integrating seismic resisting structure is even more formidable due to the relatively large structural footprints required to resist seismic forces; at least, in regions of medium to high seismicity.

In order to appreciate the amount of seismic resisting structure that is sometimes required, consider a four- and an eight-storey office building in Wellington, New Zealand, founded on soft soils. The building materials are heavy; precast concrete slabs overlaid with topping concrete and with some concrete masonry interior and exterior walls. Figure 6.1 shows the structural footprints for the minimum vertical structure to support firstly, gravity forces, and then secondly, seismic forces.1 For both buildings, the cross-sectional area of shear walls at ground floor level is approximately four times that of the gravity-only columns. If perimeter moment frames resist seismic forces in both directions their structural footprint to is up to three times larger than the gravity-only structural footprints. When the perimeter gravity-only columns are increased in size so seismic forces are resisted by two moment frames in each direction, then column dimensions increase by a factor of approximately between two and three. If wind force is the only horizontal force the shear walls are designed for, their cross-sectional areas reduce to less than one half the area required for seismic resisting shear walls.

The above example, set in an area of high seismicity and on soft soil -both of which lead to large design forces - illustrates how seismic resisting structure can significantly impact upon the structural footprint of a building. Seismic structure may profoundly affect an architect's

350 x 350 mm columns

350 x 350 mm columns

20 m

Gravity force structure

20 m

Shear walls only

1050 x 630 mm columns

1050 x 630 mm columns

Moment frames (one direction only)

20 m

Gravity force structure

Shear walls only

Moment frames (one direction only)

500 x 500 mm columns

Four storeys 8.0 x 0.45 m shear walls

500 x 500 mm columns

Gravity force structure

Four storeys 8.0 x 0.45 m shear walls

Shear walls only

"y

Eight storeys

1300 x 800 mm columns r m

Gravity force structure

Moment frames (one direction only)

Shear walls only

"y

Eight storeys

▲ 6.1 Ground floor plans of a four and an eight-storey building showing the structural footprints first for gravity forces only, and then for seismic forces where resisted by shear walls and moment frames (drawn to scale).

▲ 6.2 The eight-storey moment frame building of Fig. 6.1 illustrating seismic resisting structure only. Although well-configured for seismic resistance it is architecturally bland.

1300 square columns at corners

1300x800 columns

▲ 6.2 The eight-storey moment frame building of Fig. 6.1 illustrating seismic resisting structure only. Although well-configured for seismic resistance it is architecturally bland.

ability to resolve both the design program and design concept satisfactorily. This chapter considers how such possibly dominant vertical structure is integrated with the architectural design and with other structural and non-structural aspects of a building.

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