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Existing gravity load designed (GLD) structures are vulnerable to seismic event due to their inherent weaknesses. The present study, focuses on the development of non-invasive and feasible strategies for seismic upgradation of these non-seismically designed structures. Three novel schemes, namely (i) single haunch upgradation scheme (U1), (ii) straight bar upgradation scheme (U2) and (iii) simple angle upgradation scheme (U3) are proposed for seismic upgradation of GLD specimens. The efficacy and effectiveness of these upgradation schemes are evaluated by conducting the reverse cyclic load tests on control and upgraded GLD exterior beam-column sub-assemblages. The performance of the upgraded specimens is compared with that of the control GLD beam-column sub-assemblage, in terms of load–displacement hystereses, energy dissipation capacities and global strength degradation behaviour. Tremendous improvement in the energy dissipation capacity to the tune of 2.63, 2.83 and 1.54 times the energy dissipated by the control GLD specimen is observed in single haunch upgraded specimens, straight bar upgraded specimen and simple angle upgraded specimen respectively. The specimen with single haunch upgradation performed much better compared to the GLD specimens upgraded with the other two schemes, by preventing the brittle anchorage failure, delaying the joint shear damage and redirecting the damage partially towards the beam.
In the present work, studies are carried out on experimental modal analysis of reinforced concrete structural members for damage assessment using linear and nonlinear vibration characteristics at different levels of damage. Parameters such as support conditions, type and level of excitation etc. are found to have prominent influence on vibration characteristics. Experimental investigations have been carried out to estimate the influence of these parameters on the vibration characteristics of reinforced concrete structures. Based on the investigations using different excitation mechanisms, it is noted that resolution of modal responses in the case of burst random is much better when compared to true random excitation. The excitation type and force levels are found to have considerable influence on vibration characteristics. It is opined that judicious selection in using the type of excitation, level of excitation force plays important role especially when evaluating the vibration characteristics of reinforced concrete structures for damage assessment.
Content available remote Dynamic behaviour of bridge decks curved in plan
In this paper, a detailed study has initially been carried out, using SAP2000, to evaluate the adequacy of a griIIage model in refleeting the vibration characteristics of a curved bridge in comparison with the finite element model since the griIIage model is widely used by professional engineers due to its simplicity in modeIIing and interpretation. From this study, it has been noted that the grillage model is not capable of retleeting the dynamic characteristics accurately. In view of this, a finite element formulation and a computer program have been developed using eight noded isoparametric curved quadratic shell finite elements to assess the influence of different parameters, viz., curvature, aspect ratio, on the dynamic response of bridges curved in plan. However, the question of whether or not the deck slab curved in plan should be assumed to be rigid in its pIane during vibration, is yet to be answered. Therefore, the effect of curvature on in-plan deck tlexibility during in-pIane vibration of bridge decks curved in plan is also studied. The parametric study carried out in this investigation to establish the relationship between the structural behaviour of curved bridge deck with that of straight bridge would prove to be very useful for bridge engineers to readily assess the behaviour of bridge decks curved in plan, based on the responses for a straight bridge deck.
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