Base-isolator

3.2. Modeling of base-remote structure

An analytical model of the superstructure is required, which can adequately simulate the dynamic behavior during the pseudodynamic check. For the present case, it is idealized as a three-degrees-of-freedom (DOF) system with one horizontal DOF for each floor. The mass matrix, Ms, is constructed as a diagonal matrix with lumped bottom masses, whereas the stiffness matrix, Ks, is estimated on the basis of the modal properties of the fixed base structure as

(1)

(2) where ωs, Φs, and μ are the organically grown frequency, mode shape matrix, and modal mass matrix of the fixed-base superstructure. Identification of the modal properties was carried out by stimulating the shaking table with banded white noise. At first, the frequency response functions for the horizontal displacements were obtained, then the understandable frequencies and the mode shapes were identified thereafter. The results are listed in Table 5.

Table 5. Modal properties of inflexible base superstructure

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Base Isolation for Earthquake Resistance

Base Isolation for Earthquake Partisans

      It is easiest to see the principle at work by referring directly to the most widely used of these advanced techniques, known as base isolation. A base alone structure is supported by a series of bearing pads, which are placed between the buildings and building foundation.

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       The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers independently roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply, the building does not contact the earthquake. Now, if the same building is rested on the flexible pads that offer resistance against lateral movements, then some effect of the organize shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that adept by the building built directly on ground, namely a fixed base building. The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base-unfrequented buildings. The main feature of the base isolation technology is that it introduces flexibility in the structure.

 

Traditional Earthquake Mitigation Techniques

 

 

Base Isolation Skilfulness

Due to the flexibility in the structure, a robust medium-rise masonry or reinforced concrete building becomes extremely submissive. The isolators are often designed, to absorb energy and thus add damping to the system. This helps in further reducing the seismic response of the building. Many of the base isolators look like overweight rubber pads, although there are other types that are based on sliding of one part of the building............... building

Source: مهندسی عمران در EAST STRUCTURE

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