Abstract
In this study, the linear and nonlinear seismic behavior of a 2D ten story steel model frame is investigated in four cases: Without Isolation (WI), Base Isolation (BI), Roof Isolation (RI) and Two Top Floor Isolation (2TFI). Friction Pendulum System (FPS) is used for base and top floor isolations. First, the selected model without any isolation was used as a base for comparison of the seismic behavior of models. For dynamic analysis two types of base acceleration was used namely: 1- 1979 El Centro earthquake, 2- A newly proposed base acceleration similar to displacement oscillation proposed in FEMA 461 code. In the two cases, the maximum equivalent standard acceleration at DBE level spectrum with duration of 8 seconds was used. For the WI frame Nonlinear Statical Analysis (Pushover or POA) was used by applying UBC-97 loading code. The concluding result shows that in linear and nonlinear ranges BI frame shows comparatively superior seismic behavior for MCE and DBE earthquake levels. Results of POA of WI frame according to UBC-97 code shows better behavior than that of dynamical analysis. RI frame in nonlinear range shows better behavior than WI frame using POA. Two Top Floor Isolation frame shows better behavior both in linear and nonlinear ranges compared to both RI and WI frames. The details of the behavior of all frames are shown in various diagrams.
Highlights
During recent decade, the design and development of Base Isolation and Top Floor Isolation in seismic design of building have been subjected of various studies where successful applications of the isolation concept in various developed country are reported in references [1,2]
The purpose of this study is to investigate three issues: 1. Comparison of seismic behavior using conventional linear analysis for four types of frames namely: Base Isolation (BI), Roof Isolation (RI), Two Top Floor Isolation (2TFI) and Without Isolation (WI) of a ten story 2D steel frame used as model frame structure
The second objective of this paper is to compare the seismic behavior of model structure under non-linear static and dynamic analyses to find out more realistic behavior of the isolated frames (BI, RI and 2TFI) vs. WI frame under given loading conditions in particular from point of performance based design for low-rise, conventional, regular and fixed base structures
Summary
The design and development of Base Isolation and Top Floor Isolation in seismic design of building have been subjected of various studies where successful applications of the isolation concept in various developed country are reported in references [1,2]. During recent years the method of IDA, which employs gradually increasing acceleration amplitude in sequential THA is being used in seismic analysis of important structures [7] It uses a large number of different time history accelerations (In some cases about 40 accelerograms) to obtain more reliable structural responses due to increasing levels of severity of earthquakes. 3- In this paper NDA in the form of step by step increasing amplitude of accelerograms are used to obtain dynamic results in the form P-Δ curves similar to POA method in the NSA approach for all model frames For this purpose, two accelerograms are selected namely 1979 El Centro earthquake and innovative accelerogram which is called FEMA 461-AA. It is hoped that this new approximate dynamic analysis (PUA method) can have the ability to compete with POA method and can be used for approximate nonlinear dynamic seismic analysis of conventional structures
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