Earthquake Resistant Buildings: Precautions & Planning in Design of Structures
Earthquakes can strike at any time. It may cause a huge destruction if necessary precautions & resistance of a structure is not provided. We can decrease the affects earthquake if precautions can be taken for resistance of structures. Otherwise, buildings or structures will be damaged greatly. There are some tests to be done to ensure earthquake resistance.
Earthquake Resistance Precautions For New Structures or Buildings
- First do the soil test. Structures will be constructed after testing the soils compaction tendency.
- Design of the structures or buildings should be made by professional engineer.
- Use rods according to the foundation type. The rod must provide necessary earthquake resistance to the building or structure.
- Maintain the quality of cement, rod and sand.
- Provide necessary rod in the joint of foundation and grade beam.
- The tail of a bond in the column rod will be 135 degree and the distance between the bonds will be less. This helps to provide extra earthquake resistance to the structures or buildings.
- Check column and slab design requirements by the authority.
- For earthquake resistance purposes, there will be no connection in the intersection of beam column.
- In multistory building, necessary concrete wall space should be provided.
- Constructing a new building, about 0.2 – 0.5$ per square feet will cost to provide sufficient earthquake resistance.
Earthquake Resistance Precautions For Old Structures or Buildings
- Columns of the structures or buildings need to be made strong to provide needed resistance. Column size can be increased from the foundation necessarily.
- Bracing can be used to strengthen the walls to resist earthquake.
- Horizontal bracing can be provided if necessary.
- Do soil test again if needed.
- Earthquake may harm lintels of a structure. In this case give additional lintels.
- Repairing an old building, about 1 – 1.5$ per square feet will cost for earthquake resistance system. Providing earthquake resistance system to an old structure is more costly than to a new one.
Earthquake Resistant Design Philosophy
The general philosophy of earthquake resistant building design is that:
(a) For minor earthquakes – there should be no damage
(b) For moderate earthquakes – there may be minor, repairable, structural damage and some non‐structural damage
(c) For major earthquakes ‐ there may be major, unrepairable, structural and non‐structural damage but without collapse of the building.
What civil engineers do is to make a structure earthquake resistant. In terms of objective (c), though the building can be designed to remain in the elastic range of material behavior, by international consensus it is agreed that allowing unrepairable damage is most economical for the majority of structures. This approach is called design by hysteretic damping. The objective is to allow the structure to enter the inelastic range at certain points, and maximize the energy absorbed by plastic flow. To achieve this, any type of possible brittle failure (e.g. shear failure, bond failure, slip, etc) must be suppressed as much as possible. This approach is therefore based on the need for ductility in the structural system chosen to resist the earthquake. Some systems (materials plus geometric configuration) are naturally more ductile than others. Each system has a ductility capacity. This capacity is determined, in the case of reinforced concrete and reinforced masonry, by the arrangement of the reinforcement. In the case of structural steel the ductility capacity is determined by the arrangement of the connections, and selection of the section types. Since the ductility demand on the structure is typically not calculated, it is important that the detailing be consistent with the response modification factor used to determine the base shear. Other approaches to earthquake resistant include base isolation, and the use of supplemental damping devices.
In terms of objectives (a) and (b), under more frequent but less severe earthquakes, excessive damage to the secondary elements such as partitions, is controlled by specifying limits on the horizontal displacement of the floors, called the inter‐storey drift – the ratio of the story’s inelastic lateral displacement to the story height. Controlling the lateral displacement is also needed to minimize instability due to the P‐Δ effect.