Proper selection of a structure

  • The choice of the basic plan shape and configuration of a superstructure to withstand earthquake ground shaking is the most critical. Building structures have several types and configurations but here is no universal ideal configuration for any particular type of building. However, the following guiding principles will help the designer in selecting an adequate building configuration, structural layout, structural system, structural material and the non-structural components.
  • The superstructure and non-structural components of building should be light and avoid unnecessary masses. Smaller masses will have smaller earthquake forces (inertia forces).
  • The building and its structures should be simple, symmetric and regular in plan and elevation to prevent significant torsional forces, avoiding large height-width ratio and large plan area.
  • Superstructure should have relatively shorter spans than non-seismic structure and avoid use of long cantilevers.
  • The non-structural should either be well separated so that they will not interact with the rest of the structure, or they should be integrated with the structure. On the latter case, it is desirable that the structure should have sufficient lateral stiffness to avoid significant damage under minor and moderate earthquake shaking and toughness with stable hysteric behavior (that is, stability of strength, stiffness and deformability) under the repeated reversal of deformations which could be induced by severe earthquake ground motion. The stiffer the structure, the less sensitive it will be to the effects of the interacting non-structural components, and the tougher is, the less sensitive it will be to effect of sudden failure of the interacting non-structural elements.
  • Some building components (architectural, mechanical and electrical) can become very responsive during the earthquake shaking of the building foundation. The effects of the interaction can be grouped into two categories; first the effect of the response of the structural system on the non-structural components; and second the effect of the non-structural components on the response of the structural system. The more flexible the basic structural system the worse the effects of the non-structural components will be.
  • Superstructure should be detailed so that the inelastic deformations can be constrained (controlled) to develop in desired regions and according to a desirable hierarchy.
  • Superstructure should have the largest possible number of defense lines. It should be composed of different tough structural subsystems which interact or are interconnected by very tough structural elements (structural fuses) whose inelastic behavior would permit the whole structure to find its way out from critical stage of dynamic response.
  • A structure should have the largest possible number of internal and external redundancies. Further, it should have sufficient ductility, toughness and stable hysteric behavior under repeated cycles of deformation reversals. To achieve this it is necessary to proportion (size) and detail its members, connections and supports so that all the inelastic deformations are constrained (controlled) to develop in desired regions and according to a desirable hierarchy, and are dispersed in a sufficiently large number of regions over the plan and height of the whole structure.
  • Superstructure should be provided with balanced stiffness and strength between its members, connections and supports. Collapse and severe damage of buildings due to lack of good connections is common.
  • The stiffness and strength of the entire building should be compatible with the stiffness and strength of the soil foundation.

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