Abstract: This work presents an assessment of the behavior of infilled frames with different configurations of openings under lateral load. It is now widely recognized that masonry infill panels, used in reinforced concrete (RC) frame structures, significantly enhance both the stiffness and the strength of the surrounding frame but most designs do not consider the shear strength response of the walls and the contribution of the infill panel openings in the reduction of the shear strength of the infill especially in critical cases of dynamic load. Their contribution is often not taken into account because of the lack of knowledge of the composite behavior of the surrounding frame and the infill panel. Currently, Seismic Design Guidelines such as (EC8 – Part 3, FEMA – 440, ASCE 41-06) contain provisions for the calculation of the stiffness of solid infilled frames mainly by modeling infill walls as "diagonal struts." However, such provisions are not provided for infilled frames with different configurations and sizes of openings. A finite element program that utilized the constant strain plane rectangular element for the analysis was developed and used to model one-storey one-bay reinforced Concrete infill frame with different configurations and size of opening ranging from 0 to100% and the performance of reinforced concrete frames under lateral loading were observed. The values obtained for deflection (Δ) against applied lateral force was obtained and used to calculate the shear stiffness (K) and hence the stiffness reduction factors (λ) for varying configurations and size of openings. The results were validated by modeling the same set of structural models with STAAD.ProV8i, which is standard commercial software for FE analysis. Results from this work showed that the developed FE based program compared favorably with the results from STAAD.ProV8i program. The basic specifics drawn from the results is that the estimated stiffness reduction factors to account for varying configurations and sizes of opening vary from a value of 1.0 for the complete rigid frame (β = 0) to a value of about 0.45 for the bare frame (β = 1.0).
Title: Development of Stiffness Reduction Factors for Modelling of Infilled Frames, Case of Varying Configuration of Opening Size
Author: T.C. Nwofor, M.E. Ephraim
International Journal of Civil and Structural Engineering Research
ISSN 2348-7607 (Online)
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