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What are the basic parameters considered for seismic analysis in building design and structural engineering | civil engineering
Seismic load is also called as earth quake load which acts perpendicular to the gravitational force. The forces of seismic conditions generally seen in X direction and Y direction of the building structure. In order to prevent the damages that caused due to seismic or earth quake loading condition it is important for structural engineering to consider various basic parameters as per the standards provided by the various code provisions all over the world. As per the Indian standard system the seismic analysis of the structures like buildings, water tanks, towers etc are considered as per the IS 1893:2016 code standards. In this article you can able to learn what are the basic parameters considered for seismic analysis as per the IS 1893 code provisions in designing process.
Types of basic parameters used in building design
As per the design considerations the major factors are classified in to following 4 types
- Type of Seismic zone
- Type of soil condition
- Damping ratio
- Response reduction factor
Type of seismic zone
As per the various consideration for different areas the seismic zones as per IS 1893 code provisions classified in to four types they are Zone II, Zone III, Zone IV and Zone V. The Zone II seismic condition is called as low seismic zone, Zone III is called as medium seismic zone, Zone IV is called as high seismic zone and finally the Zone V is called as sever condition. The amount of the seismic load depends upon the seismic coefficient factor Z values. As per the code IS 1893 standard the zone II has 0.10 value, zone III has 0.16 value, zone IV has 0.24 value and Zone V has 0.36 value. The various seismic zones for main cities in Indian condition is shown in the appendix page of the IS 1893 code.
Basically the structure which is exists in the Zone V condition has more damage rate than other type of zones namely zone II, zone III and zone IV condition. In order to reduce the damage rate it is important to consider the earth quake resistant designing concepts. The types of retrofitting are explained in my previous blog read complete concept with below specified link.
What is retrofitting and types of retrofitting used in the building design.
Type of soil condition
Soil condition is the second major factor we need to consider as per the seismic analysis. The major soil types conditions are classified in to three types depending upon the compressive strength and shear strength of the existed soil. They are comes under the loose soil condition, medium soil condition and rock soil condition. Basically the major constructions are preferred in the medium soil conditions as per the standards. As we know if the building structure is designed in loose soil condition the deflections and deformation values are more due to the effect of the less compressive strength and shear strength values. In order to design earth quake resistant building models we will initially convert the soil condition to medium or rock type depending upon the requirements.
Damping ratio
The damping ratio is the percentage of damping which is assumed for the building structure generally the maximum of 5% damping is considered for the structural design considerations. There are two types of damping are considered frequently related to the viscous damping and hysteretic damping. The viscous damping is occurred in building due to the effect of various mechanisms like cracks, non structural elements and soil interactions etc. The hysteretic damping in the structures basically observed due to presents of the internal vibrations and internal cracks in structural components. Sometimes the damping ratio of 2% or 3% are considered under certain limitations and conditions as per the seismic design consideration.
Response reduction factor
The response reduction factor is the last and very most important factor to be considered in structural design. For the general building cases the factor of response reduction is taken as 5 value and for the different structural elements the response reduction factor values are shown in the below table
| S. No | Structure type | Response reduction factor |
| 1 | Ductile shear wall with OMRF |
4.5 |
| 2 | Ductile shear wall |
4 |
| 3 | Load bearing masonry wall building-reinforced |
2.5 |
| 4 | Load bearing masonry wall building-un reinforced |
1.5 |
| 5 | Ordinary RC moment resistant Frame(OMRF) |
3 |
| 6 | Ordinary reinforced concrete shear walls |
3 |
| 7 | Ordinary shear wall with OMRF |
3 |
| 8 | Ordinary shear wall with SMRF |
3 |
| 9 | Special RC moment resisting frame |
5 |
| 10 | Steel frame with concentric braces |
4 |
| 11 | Steel frame with eccentric braces |
5 |
| 12 | Steel moment resisting frame design as per SP:6 | 5 |
In general condition if the value of structure type is not gives use Special RC moment resisting frame with 5 value.
The complete concepts of basic parameters of in seismic analysis is completely explained in my YouTube channel see video below.
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The above explained concepts are related to what are the basic parameters considered for seismic analysis. As per the code standards the basic parameters are classified in to four types related to type of Seismic zone, type of soil condition, damping ratio, response reduction factor. These factors helps in designing the earth quake resistant design as per IS 1893 standards.
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