Generalize Recommendation To Design Earthquake Resistant Structure
In earthquake prone areas, structural design philosophy includes one consideration of performing structure as single unit i.e. it is agitated in unison under ground motion generated by earthquake vibration. It should keep in mind that both in design and construction this compact performance is expected.
We will discuss how to calculate performance of elements of structural form with stiffening shear wall both in approximate (manual method) and using software like STAAD. Pro and ETABS. The localized amplification of earthquake force due to different soil condition with layer effect will also be discussed in this blog.
We will discuss how to calculate performance of elements of structural form with stiffening shear wall both in approximate (manual method) and using software like STAAD. Pro and ETABS. The localized amplification of earthquake force due to different soil condition with layer effect will also be discussed in this blog.
We are emphasizing over construction process with designing as some assumption are taken in design office which should be satisfied in construction phase rightly. As most of the forming system and shear walls consist of different concrete member and we can imagine the importance of supervising concreting work by qualified officials.
Many structures in the world, failed due to poor construction process not by design fault.
The recommendations for designing earthquake resistant structure are provided below:
a. Selection of construction materials should be as per specifications (obviously good quality). The specification may of ASTM, BS, IS or any other local or regional code that accounts earthquake impact on structures and its elements.
b. Regarding foundation design, the structure should be on solid rock rather than loose materials. In case of solid rock the shear wave velocity is more than looser one and reflection and refraction of different types of earthquake waves between interface of two layer also effect seismic performance of foundation i.e. structure over it.
We discussed about different types of waves associated with earthquake agitation including their speed and arrival time and their capability to impact on a structure.
It is worth mentioning that a loose soil profile generally gets compacted under earthquake motion and definitely settlement also accompanied.
In case of loose sand with necessary moisture content, the soil may be subjected to liquefaction. We have published numerous posts about liquefaction and evaluation of liquefaction impact under different code.
c. The foundation should be rested on above mentioned soil and generally expected to have uniform depth. The details of the requirements for uniform depth will be discussed soon.
d. In designing an earthquake resistant building, it is focused on the simplification in both architectural plan and placing of different structural elements like (columns, beams, shear wall, pier etc.). Regarding foundation a square shape provides more stability than other geometric shapes.
e. Opening as windows and doors are arrived inherently in both structural wall (shear wall) and non-structural walls. Opening in shear wall require some connections between both side (beams) which is called coupling beam. Coupling beam is a heavily reinforced member; depending on stiffness of it, two walls may perform as either composite or individual shear wall. We will learn about the design of coupling beam both manually and ETABS in our upcoming posts.
Whatever may be location of openings, it is expected to limit number of opening as less as possible. Few opening produce continuous nature of wall. The more discontinuity the more instability will accompanied.
f. A better performance is observed when openings (windows and doors) are not provided in identical vertical rows. It is expected to arrange in diagonals if practical.
g. Less non-structural elements should be included in structure say infill brick wall, low height or full height partitions, may be of aluminum or other materials. Reinforced cement concrete, steel structural elements are expected.
h. Floors and roofs provides some lateral stiffness to the structures and reinforced concrete monolithic roof provides additional stiffness (lateral) to structures preferably flat (nor pitched).
i. Height of structure should be, if possible, kept uniform; the goal behind this is also stability.
j. Some types of extra projections, if possible, should be ignored in both structural detailing and architectural plans.
Some examples of extra projections are:
• Chimney
• Domes
• Arches
• Cantilevers
k. During earthquake it is expected to behave, different parts of structure, as single unit. To achieve these, all parts of structure should be tied properly; special attention should be paid to corners and edges.