Fiber Based Pushover Analysis of Reinforced Concrete Frame (A case study on the structural performance assessment of existing School Building in Addis Ababa city)
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Date
2011-02
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Addis Ababa University
Abstract
There is a significant variation in seismic zoning adopted in Ethiopia for urban areas between the seismic building code (EBCS-8:1995) and those reported in other research publications. Adopting a conservative value is, therefore, crucial for particularly in places such as Ethiopia where quality control in the construction industry is not at adequate level yet and reinforcement detailing in practice may not complying with the codes. This paper deals with structural performance assessment of a G+4 ribbed slab School Building (Reinforced Concrete Frame) as a case study located in Addis Ababa City, Ethiopia where proposed peak ground acceleration value by RADIUS 1999 project and others is more than twice as of EBCS-8:1995 (RADIUS 1999 project). Two verification problems: rectangular reinforced concrete column at element level and six story four bay regular reinforced concrete planar frame have been taken to check the reliability of fiber beam column model and the validation of software outputs through the performance assessment of reinforced concrete buildings using conventional pushover analysis. Material nonlinearity behavior was included through Mander’s confined concrete compression model with tension stiffening effect; and bilinear steel reinforcement model with some strain-hardening effect. There is some variation between capacity curves from Response2000 and SAP2000 with the experiment result at element level while the result from Seismostruct is acceptably similar. Furthermore, Seismostruct (for both uniform and triangular lateral load patterns) give nearly similar result with the reference capacity curves for the frame while the capacity curves from SAP2000 V14 (not licensed) are not comparable. Pushover curve results of SAP2000 V14 and the research application software Seismostruct revealed that they are not comparable. Therefore, the structural performance assessment was done based on Seismostruct results. The results show that capacity of the case study building is below the force demand for PGA of 0.1g and 0.05g for all soil class and soil class C respectively at life safety structural performance level set by ATC-40. The building complies with inter-story and roof displacement requirements for demand of 0.05g. Since it is possible only to capture flexural failures in fiber model, premature failure (e.g. shear) was checked before criterion are reached. Keywords: Buildings, earthquakes, performance, life safety, safety factor, seismic codes, material model, tension stiffening model, fiber elements, capacity curve, Peak Ground Acceleration.
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Keywords
Buildings; earthquakes; performance; life safety; safety factor; seismic codes; material model; tension stiffening model; fiber elements; capacity curve; Peak Ground Acceleration.