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Earthquakes cause distress in structural components of lateral and gravity load-resisting systems (beams, columns, load-bearing walls, and shear walls) as well as horizontal diaphragms (slabs and roofs).
Once the structure is damaged, the structure is demolished or repaired depending on the severity of the damage. The structure affected by the earthquake may suffer both non-structural and structural damages.
In this article, we shall discuss how to repair non-structural and structural damages caused due to earthquakes.
1. Non-Structural/Architectural Repairs
Non-structural and architectural components get easily dislocated/affected during earthquakes. Non-structural repairs cover the damages to civil and electrical items, including the services in the building. Repairs to non-structural components are taken up after the structural repairs are carried out. It involves the following:
- Patching up of defects such as fall of plaster and cracks.
- Repair of doors, windows, replacement of glass panes.
- Checking and repairing electric conduits/wiring.
- Checking and repairing gas pipes, water pipes, and plumbing services.
- Rebuilding non-structural walls, smoke chimneys, parapet walls, etc.
- Replastering of walls as required.
- Rearranging disturbed roofing tiles.
- Relaying cracked flooring at ground level.
- Redecoration – painting, whitewashing, etc.
The above repairs to non-structural components do not restore the original structural strength of structural components in the building. If only non-structural repairs are carried out, and the required structural repairs are neglected, there may be severe implications on the safety of the building.
2. Structural Repairs
2.1 Damage Assessment
Before taking up the structural repairs and strengthening measures, it is necessary to conduct a detailed damage assessment to determine:
- The structural condition of the building to decide whether a structure is amendable for repair; whether a continued occupation is permitted; to decide the structure as a whole or a part requires demolition if considered dangerous;
- If the structure is considered amendable for repair, a detailed damage assessment (distress location, mapping of the crack pattern, crushed concrete, reinforcement bending/yielding, etc.) shall be carried out for each structural component.
- Non-destructive testing techniques could be employed to determine the residual strength of the members.
- Work out the details of the temporary supporting arrangement of the distressed members so that the structure does not undergo further distress due to gravity loads.
2.2 Repair of Structural components
After a successful damage assessment of individual structural elements, appropriate repair methods are to be carried out component-wise depending upon the extent of the damage.
The repair may consist of the following:
- Removal of the portions of cracked masonry walls and piers and rebuilding them with richer mortar. Use of non-shrinking mortar will be preferable.
- Addition of reinforcing mesh on both faces of the cracked wall, fixing it to the wall with the use of spikes or bolts, and covering it with cement mortar or micro-concrete.
- Injecting cement or epoxy-like material, which is strong in tension, into the cracks in walls.
- The cracked reinforced cement elements may be repaired by epoxy grouting and could be strengthened by epoxy or polymer mortar applications like shotcreting, jacketing, etc.
2.3 Seismic Strengthening
The main purpose of seismic strengthening is to enhance the seismic resistance of an earthquake-damaged building to make it safer for similar future occurrences.
This work may involve some of the following actions:
- Increasing the lateral strength in one or both directions by increasing column and wall areas or the number of walls and columns.
- Imparting integrity to the structure by providing a proper connection between its resisting elements so that inertia forces generated by the building's vibration can be transmitted to the members that can resist them. Specific vital aspects are the connections between roofs or floors and walls, between intersecting walls, and between walls and foundations.
- Eliminating features that are sources of weakness or that produce stress levels in some members. Asymmetrical plan distribution of resisting members, abrupt changes of stiffness from one floor to the other, the concentration of large masses, and large openings in walls without a proper peripheral reinforcement are examples of defects of this kind.
- Avoiding the possibility of brittle modes of failure by proper reinforcement and connection of resisting members.
The causes for casualty during earthquakes are:
1. Urbanization is rapidly increasing, and due to an increase in land cost, many multi-storied buildings are being constructed.
2. Code is not mandatory.
3. Municipal by-laws govern construction as such.
4. Seismic provisions are not incorporated.
5. Non-enforcement of elaborated checks proper ways.
6. No checks even for a simple ordinary design.
It is the process of reconstruction and renewal of structural concrete elements like columns, beams, slabs, walls, etc. Retrofitting involves determining the origin of distress, removing damaging materials, and selecting suitable repair material and repair techniques.
The purpose of retrofitting is to regain the load-carrying capacity of the damaged member and increase its life span or increase the ultimate load-carrying capacity when an increase in the imposed load is expected due to variations in the function of the building.