Browsing by Author "Sasmal, Saptarshi"

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    Performance evaluation and strengthening of deficient beam-column sub-assemblages under cyclic loading
    (2009) Sasmal, Saptarshi; Novák, Balthasar (Prof. Dr.-Ing. )
    Evidence from the previous earthquakes has posed a serious question on the performance of reinforced concrete (RC) structures, both existing and newly built, under seismic loading. In the present study, exterior beam-column sub-assemblage which is proved to be one of the most critical components of an RC structure has been chosen for investigation. European Codes and Indian Standards of practice for seismic design have been considered for designing and detailing the sub-assemblages of a most regular and conventional RC structure. Different specimens represented the existing condition of buildings designed according to the available knowledge and prevailing guidelines at different times. The experimental investigations under repeated cyclic loading have shown that "GLD" specimen can hardly withstand any reverse loading due to insufficient reinforcement, inadequate bonding and poor detailing. Among the "NonDuctile" specimens, Indian Standard based specimen exhibited better performance (strength deterioration, stiffness degradation and energy dissipation) over the Eurocode based specimen, even though in both cases energy dissipation was mainly through the damage in joint region which is extremely unwanted. The strength hierarchy of all the specimens has been developed based on the results obtained from experimental and analytical studies for identification and quantification of required improvements of deficient sub-assemblages towards "Ductile" ones. After the experimental investigations, severely damaged specimens were further studied for adequate retrofitting to ensure their re-usability in post-earthquake scenario. An effective, simple and economical retrofitting scheme has been proposed here by judiciously using GFRP in members beyond the joint and steel plate in the joint region holding by through-through bolts. Surface treatment and epoxy injection were carried out to re-install concrete integrity and bond. From the experimental investigation, it has have noted that the retrofitted "NonDuctile" and "Ductile" specimens could be able to regain, if not better, their original seismic performance. Deformation capacity of the retrofitted "NonDuctile" specimen was also considerably increased with respect to undamaged ones. Further, in both retrofitted specimens, strength deterioration with increase in displacement demand was extremely low. Thus, the retrofitting schemes as proposed in this study could effectively be implemented for damaged "NonDuctile" or "Ductile" sub-assemblages for their further usage. Three different schemes have been proposed in this study for upgradation of poorly designed "GLD" structures which are present in massive quantity throughout the world. The schemes have been developed by using hybrid FRP-steel plate system. Using the analytical formulation, a detailed study has been carried out on improvement of strength and ductility due to application of external reinforcement and confinement. CFRP fabric and CFRP laminate were used for flexural strengthening, GFRP wrap was used for confinement of beam and column sections and steel plate-bolt system was adopted for confinement and shear strength enhancement of the joint. From the cyclic load test as adopted for original "GLD" specimen, it has been observed that the seismic performance of the upgraded specimens can be considerably improved by using these schemes. For example, double the energy dissipation was achieved at same drift ratio and final energy dissipation was 5 times more than that obtained from original "GLD" specimen. Most importantly, the plastic hinge shifted in the beam away the joint and in last upgraded specimen where only D-region upgradation was carried out, it could even form a spread plastic hinge in the beam, which ensures large and consistent dissipation of energy with increase in drift demand. Finally, non-linear Finite Element analysis using software ATENA has been carried out on "GLD", "NonDuctile" and upgraded specimens. Material and geometrical models have suitably been incorporated in the numerical analyses. The results obtained from numerical analyses are in good agreement with that from experimental investigations. A comparative study on energy dissipation obtained from both numerical and experimental studies has been carried out and correlated for practical use. Influence of axial load in column has also been explored. Further, a parametric study has also been conducted to investigate the effects of amount of bending FRP, number of wrapping layers, bond behaviour and role of individual upgradation components on the overall performance of the upgraded specimens which would offer the scope for any further modifications on the proposed schemes. The study as a whole would provide the promising aspects on strengthening of deficient structural components and encourage for further research.