Retrofitting of reinforced concrete frames using steel bracings

Published on 16 Apr 2022. Written by Nidhi Tiwari

Earthquakes are in no doubt that it is one of the biggest threats to any building that stand high. Various methods are applied to reduce this threat on a building and Steel braced frame is one of such measures which is used to resist earthquakes in multi storied buildings.

The existing concrete buildings lack resistance to earthquakes and they have a great chance of failure under seismic activities. These buildings thus need retrofitting to improve their resistive power when concrete buildings are not capable enough to resist the damage caused due to earthquakes.

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SLNOTE
Bracing system is used in such cases as they act by reducing the bending moments and shear forces in the columns of the structure and the lateral load on the structure are transferred to the foundation by axial action. Besides, they also improve the displacement capacity of the structure along with the stiffness and strength capacity. Steel bracings are frequently used as they are not much costly, are easy to construct and have enough flexibility for their design according to requirement.

Objective:

The main objectives of this project are to evaluate the effect of seismic loads on braced and unbraced structures, to compare certain parameters for various types of bracings, and to come to the best result that should be used to reduce to serve the purpose efficiently.

Project Implementation:

For retrofit a structure for enhancing its seismic performance, the seismic adequacy of the building needs to be evaluated. You can do this using the ETABS software. If the building lacks much in seismic adequacy, the building either has to be retrofitted or to be replaced.

In this project, you will analyse the performance of a Reinforced concrete building that has been retrofitted with steel bracing to improve its performance and see if the retrofitting is enough to improve the life of the structure.

SLLATEST
For this, the bracing has to provided and the analysis of the building needs to be done for a particular seismic zone in accordance with IS 1893-2002 using ETABS software. The model has to be prepared on ETABS and to be retrofitted with various types of steel bracings.

The various steel bracings for which the model has to be analyzed include majorly:

• Diagonal bracing
• V type bracing
• Inverted V type bracing
• Combined V type bracing
• X type bracing
• K type bracing

This can be done for buildings of various heights.

The various parameters which you need to specify for making the model are:

• Type of the building
• Type of frame
• Storey height
• Beam Size
• Column size
• Slab thickness
• Loads acting on the building
• Yield strength of the steel that you use
• Method of analysis, etc.

Once you specify these factors, you can very easily make a model of the building on ETABS and can change various parameters as and when required for a detailed analysis.

After you have done designing the model and retrofitting them with bracings, you can record various parameters for each case like-

1. Lateral Displacement
2. Story Drift
3. Axial Force
4. Base Shear

Once you are done studying these parameters for each type of bracing, analyse the recorded results in comparison with each other along with a unbraced structure.

Conclusion:

After this analyse, you will know the extent to which bracings enhance the seismic behavior of a building. The study will tell you which type of bracing gives a maximum reduction in lateral displacement, story drift, base shear, etc. Thus, you will also know which type of bracing is the best for a building of a given height.

SLDYK
Kit required to develop Retrofitting of reinforced concrete frames using steel bracings:

• ETABS

Technologies you will learn by working on Retrofitting of reinforced concrete frames using steel bracings:

• Civil Engineering
• ETABS

Any Questions?