Seismic load (Earthquake) and Wind loads have a history of causing severe structural and non-structural damages. Therefore, from design stage, it is important to fortify structure, so as to minimize these damages. A structure must possess adequate strength to resist vertical loads, along with stiffness to resist the effect of lateral loads. No building can survive a major earthquake. Albeit, all types of structures, low rise and high rise, can be made to withstand lateral loads by taking certain precautions.
In structural engineering, earthquake resistant design involves providing a structure with adequate features to withstand seismic loads and wind loads. The use of shear walls as an earthquake resistant design is becoming dominant in seismic zones.
For a structural engineer, the number one priority, when designing a building, is safety. Designing walls to resist lateral loads is part of ensuring safety of a structure. Shear walls are installed in a structure to improve the structure’s resistance to lateral loads. Studies has shown that, They offer good resistance to wind load and seismic load. The vulnerability of a structure towards lateral loads is directly proportional to the height of the structure. In other words, the vulnerability of a structure to lateral loads increases as the height of the structure increases. However, all types of buildings in seismic zones require proper care to ensure safety.
Generally, They are structural members, which its proper positioning at different locations in a building, from top level to foundation level, will ensure the building resists lateral loads. They can be constructed using various materials such as reinforced concrete, timber and reinforced masonry. However, in the united states, the use of Cross laminated timber (CLT) to construct walls and floors is becoming rampant. (Journal of Structural Engineering – Volume 143 Issue 12 – December 2017)
BEHAVIOUR OF SHEAR WALLS TOWARDS LATERAL LOADS
Shear walls offer resistance to wind load and seismic load by transferring all the forces to the foundation.
Under most building codes, exterior walls must be shear walls. Additionally, interior walls must be shear walls if the size of the structure is large. Notwithstanding, studies has shown that internal shear walls are more efficient than exterior shear walls.
Shear wall contains openings because of the structure’s functional needs like doors and windows. Openings in a shear wall can cause reduction in the ability of the shear wall. A research renowned structural engineer on the behavior of shear walls with openings under seismic load shows that the size of openings and location of the shear wall in a structure affects the stiffness and seismic responses of a structure. Also, the research records that, as the size of the opening increases, the deflection and bottom stresses increase.
DISTRIBUTION OF SHEAR WALLS
The distribution and shape of shear walls are essential to achieve maximum end result. Designing a shear wall for only one direction is not enough. This type of design ensures lateral load resisting in that direction alone.
It is important to note that position and length of shear walls does not have any noteworthy effect in low rise buildings. However, for high rise buildings, the position and length of shear wall is very important. (International Journal of Engineering Trends and Technology (IJETT) – Volume 37 Number 7 – July 2016)
Recent studies show that, positioning shear walls at corners, core or a combination of both results in a good lateral load resisting performance. For medium buildings, shear walls at cores are a good option. But for high rise buildings, longer shear walls towards periphery is better.
Shear walls are very prominent in resisting lateral forces. Structural engineering firms must take into consideration the best position, size of opening and length of shear wall, for a structure, that offers the least displacement.
They provide the stiffness and strength of a building and resists lateral forces by transferring all the forces, caused by the lateral load, to the foundation of the building. They can be used as lateral load resisting systems and also retrofitting of structures. The positioning of shear walls in advantageous positions in the building, can form an efficient lateral force resisting system by reducing lateral displacements under wind loads and seismic loads.
Therefore, it is important for a structural engineer to determine the effective, efficient and ideal length of shear wall, and position of shear wall.