Seismic retrofitting is the process of modifying an existing structure so that it can be more resistant towards ground motion, seismic activity or failure of soil because of earthquakes. Today, a better understanding of structure’s seismic demand and the recent incidents of large earthquakes in the urban areas has made seismic retrofit a common practice all over the world.
Nowadays, people prefer going to shopping malls or shopping complexes to buy different products. That’s why a large number of shopping malls are running successfully in most parts of the world. These shopping malls give you the pleasure of buying many things from a single place though they are a reason of mass destruction in case of any natural disasters, like an earthquake.
The shopping malls in the regions where earthquakes are experienced frequently require seismic retrofit the most. When earthquakes occur, the strengthened concrete beams situated at different places in the shopping mall can get cracks. In such a situation, an immediate action by the construction management department of the mall should contact a general contractor for studying the problems in the disturbed beams. Since numerous people visit the shopping mall every day, it becomes even more essential to act immediately in such a condition. The procedure of seismically retrofitting a shopping mall is mentioned below.
Retrofitting of a Shopping Mall
Shopping malls are buildings with many stories and have moment-resisting frames consisting of columns and RC beams. These frames are made to carry the load of the whole building easily but in case of any seismic activity, certain deficiencies occur.
Depending on the damage or requirement, several retrofitting techniques can be used in a shopping mall. They are as follows:
1. Addition of Fresh Shear Walls
These are usually used for the retrofitting of solid and strong buildings with concrete frames. The additional elements are mostly placed in the building’s exterior. New shear walls are not the first choice of the structure’s interior.
2. Addition of Steel Bracings
When the requirement of a shopping mall is a large opening, an addition of steel bracing is the most effective solution. The steel bracings, when used in the shopping mall, have many advantages, including the following:
- Higher stiffness and strength
- It allows the natural light to easily enter the structure
- Steel bracing minimizes the foundation cost which means less efforts
- A steel bracing with very less weight is set on the pre-existing structure
This is one of the most famous methods to strengthen the columns of the shopping mall. Jacketing is used to fulfill different purposes, such as increasing the concrete confinement, the shear strength as well as the flexural strength of the structure. There are three types of jackets – the steel jacket, the reinforced concrete jacket, and the FRPC (Fibre Reinforced Polymer Composite) jacket.
4. Seismic Isolation (or Base Isolation)
When the superstructure is isolated from the base (foundation), it is called the base isolation. This is one of the strongest tools for the dormant structural vibration controlling technique. Base isolation has both advantages as well as disadvantages.
Base Isolation’s Advantages
- The main advantage is that the building is isolated from the ground motion. This means that there will be less seismic loads and therefore the structure will suffer less damage. The superstructure will undergo minimum repairs.
- During construction, the building will remain serviceable.
- The existing superstructure will not involve any major intrusion.
Base Isolation’s Disadvantages
- This technique is quite expensive.
- Other retrofitting techniques can be partially applied but this technique can’t be applied fractionally.
- The implementation of this technique in an efficient way is a big challenge.
5. The Technique of Mass Reduction
If the shopping mall has many storeys, one or more than one storey can be removed for an effective seismically retrofit. This way, the mass will be removed and it will ultimately result in an increase of the strength.
6. The Technique of Wall Thickening
The pre-existing walls of the shopping mall are given an additional thickness. This thickness is increased by adding concrete, bricks, and steel arranged at different areas. As a result, the wall’s weight increases and a lot more weight is borne by it both vertically and horizontally. Moreover, the designing of wall bears some special conditions and the transverse loads prevent it from sudden failure.
Some Important Things to Consider
· Condition Assessment is Important, so is the Seismic Evaluation
Before going for a seismic retrofit, you should first identify the conditions and then detect the deficiencies of the building. With condition assessment, you will be able to find the real condition of the shopping mall which will possibly be different from the construction documents. Seismic evaluation is beneficial in finding out the defects of the shopping mall. Retrofit strategies are usually chosen based on the defects and condition of the mall.
· Selecting a Retrofit Tactic
When the shopping mall is severely damaged, you should go for the global retrofit tactic to stiffen and strengthen the structure. Since every retrofit tactic has both merits and demerits that vary according to the project, it becomes essential to select a retrofit strategy after carefully considering the constructability and cost. A retrofit tactic should be properly designed. While inspecting the shopping mall, you should see that any adjustment in the load path should be sensibly detected and if there is any overstressed member, it should be identified.
· Construction Quality
The aim of seismic retrofit is to overcome the defects in the existing building. Thus, the construction quality of a positive retrofit scheme can’t be ruled out. Any kind of patchwork in such condition would be a fruitless effort.
From the above discussion, it can be said that seismic retrofitting is an acceptable technique for the protection of various kinds of structures. It has gained popularity in recent years and today, it is one of the most reliable technologies. The prime challenge is to gain a desired level of performance at the minimum cost. Only the renowned commercial construction companies or commercial general contractors can help you achieve this.