In the field of Earthquake Engineering, many advancements are being made and engineers are investigating new techniques to minimize the risk of loss of human life and property. Various researches have been made for improving building performance under earthquake. Building codes also provides guide lines and provision based on historic records of structural behavior. While the research on earthquake resistant buildings will continue to make improvements, here is the brief overview of techniques to build earthquake resistant structures
Increase Structure Stiffness
This is the traditional and most commonly used techniques in which stiffer or heavy size members are used to resist the lateral force acting on structure. ACI code give provision of minimum width of member as 0.3h or 10” for special seismic structure.
Building Geometry and Regularity
A regular and symmetrical structure performs better than irregular and unsymmetrical structure. Structures with irregular geometry can be converted into structure of regular geometry by providing seismic joints/ expansion joint. Structural symmetry can be achieved by providing symmetry in framing, columns and shear wall locations. Stiffer columns should be provided at parking levels to avoid soft story effect.
Structural performance can be improved by proper reinforcement detailing, lap lengths, bends, hoops and stirrups spacing. Structure with ductile beam-column junctions behave better under lateral loading. ACI code gives minimum provision for detailing in moderate and high seismic zone.
Lateral Force Resisting System
We can design our structure by adopting different framing and lateral force resisting system. Three basic systems are Moment Resisting Frame System, Building Frame System and Dual System. Moment Resisting Frame System is designed to resist all the seismic forces acting on structure. They are further classifying into ordinary, intermediate and special system depends on earthquake zone of the structure. Building Frame systems are designed for gravity loads only. Shear wall are added to resist all lateral loading acting on structures. Dual system have shear wall along with moment resisting framing. Both contribute their part when an earthquake force acts on structure.
Reinforcing Non-Structural Elements
In most of the earthquake we observe, severe loss is due to collapse of block masonry partition walls. This can be avoided by providing hollow block reinforced wall specifically for high rises structure or structure will greater story heights. Similarly proper detailing of openings for doors, windows and elevators etc. help to minimize the risk.
Base Isolated Structure
The concept of base isolation is explained through an example of the building resting on friction-less rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply the building does not experience earthquake. The flexible pads are called base-isolators, whereas the structure protected by means of these devices are called base-isolated buildings.
Energy Damping Devices
The isolators are often designed, to absorb energy and thus add damping to the system. This help in further reducing the seismic response of the building. These energy damping devices absorbs 10%-20% of energy at 100% shear strain level. Few common types of damping devices available in market are:
- High Damping Rubber Bearings (HDRBs)
- Lead Rubber Bearings (LRBs)