Loading...

Isolation System for Mitigation of Horizontal Seismic Waves Effects

Sarraf, Sadyar | 2018

535 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 51240 (53)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Dolatshahi, Kiarash; Rafiee Dehkharghani, Reza
  7. Abstract:
  8. Earthquakes cause considerable damages and human and financial losses all around the world. Without doubt, the most important earthquake injuries are those that arise as a result of building failure in an earthquake. Conventional design codes provided a minimum level of protection against strong ground shaking to mitigate earthquake effects on structure by utilizing structural elements such as shear walls, braced frames, etc. Although, these provisions guarantee only that the building will not collapse, but it does not protect the buildings from structural damage. This method considers strengthening of structural lateral resistance system to verify earthquake forces. However, new methods intend to prevent transmission of earthquake to part of or whole structure using tools and instruments, which reduce transmitted force to structure by utilizing quake-attenuating. Quake-attenuating are devices, which absorb earthquake energy and amplify ground motion frequency to the others; thus, structure experiences less force or energy during excitations. Quake-attenuating are divided into two main groups of dampers and isolators. Damper refers to structural members which are installed and used in the structure as structural elements. Damper reduces the effects of ground shaking by absorbing the transmitted earthquake energy from ground to structure during occurrence of an earthquake. Isolators are those parts of structure which act as a counter between earthquake and building and soothe passing earthquake intensity through itself; therefore, by decreasing earthquake intensity, buildings experience less earthquake forces. Available dampers and isolators do not have the ability of widely being used in building industry, especially in the developing countries, because of high cost of installation and initiation and requirement of higher expertise. Due to these limitations, there is a need to introduce and use low-cost approaches for mitigating the effects of earthquake loading. Therefore, nowadays civil engineering suffers from the lack of such quake-attenuating systems to be able to respond simply but applicable mechanism at the same time for almost all types of structure; based on what expressed, this proposal suggests utilizing geo-composite material placed between structure and ground base with flexible and sliding characteristic for decoupling the motion of the structure from ground motion Choosing this proposal research is a step forward in this direction since by selecting the damping feature, it tries to relocate new isolation system from structural element location into underground position that not only can solve the defects of other mentioned method defeats but also it reduces super structural demands by changing stress level of material from steel to soil. This new idea is evaluated by considering a 2D plane strain modeling assuming a model with 50m width to 30m depth model dimensions. Evaluation of model is considered for two types of isolated ground and pure soil to be compared with each other to find advantages and disadvantage of this new system. For isolated model a layer of Isolation material made from mixture of Rubber Soil Mixture, which is known as RSM, is considered and located under superstructure foundation location. Because of RSM material sensitivity to plastic nonlinear behavior, an especial advance constitutive modeling of Manzari-Dafalias (2004), which is known as the latest achievement over this field, is utilized; therefore, theory of this modeling is discussed forward and relative parameters are introduced inside. This model is imposed by seven earthquake records which are selected in accordance to FEMA-440a and FEMA-P695 and are applied as uniform base displacement excitation for this model; furthermore, all these records are scaled by peak ground acceleration (PGA) to 0.35g for each earthquake. Numerical evaluation of this research is performed by open source software framework of OpenSees which is known as one of the most powerful and popular application over the fields of soil, structure and soil-structure interaction consideration. Horizontal assessment of this system is also offered to prove both its ability and satisfaction needs of literature over this issue. Horizontal evaluation proved that this isolation system does not allow the super points to suffer more than 0.35g acceleration even for excitations which make more than 0.7g acceleration over pure soil analysis, while it is revealed that vertical outcomes of isolation system is doubled compare to pure soil; indeed, isolated ground experiences 1.2g acceleration in worst cases whereas the peak acceleration for pure soil is 0.78g; reasons of this phenomena are described and discussed. Final results of this report are performed in the form of spectral acceleration to find a better comparison between pure soil and isolated ground response, mean value plus one standard deviation (μ+σ) curve with 84.1% consideration of spectral responses are chosen
  9. Keywords:
  10. Vibration Isolators ; Seismic Analysis ; Earthquake Isolation ; Horizontal Waves

 Digital Object List

 Bookmark

No TOC