Balthasar Novák

Seismic performance evaluation of exterior beam-column sub-assemblages designed according to different codal recommendations

In the present study, seismic performance of exterior beam-column sub-assemblages is evaluated by considering different stages of Eurocode (EC) and Indian Standard (IS) provisions for design of the reinforced concrete structures. The study has brought out the implications of the differences in the guidelines on seismic performance. It is found that the gravity load designed (GLD) structure is vulnerable to even medium intensity earthquake. Among the seismically designed specimens without ductile detailing, the one which was designed as per IS exhibits better performance compared to that designed according to the EC with 10% more energy dissipation under large drift ratio. Among the seismically designed and ductile detailed specimens, the one designed as per EC provisions for medium ductility could not perform as good as that designed as per ductile provisions from IS (25% less energy dissipation). Stiffness degradation of the specimens is also found to be a crucial parameter and varies considerably among the specimens. Therefore, earthquake design and ductile detailing provisions of different standards and their progressive improvements have considerable influence on seismic performance of reinforced concrete structures.

Seismic retrofitting of damaged exterior beam–column joints using fibre reinforced plastic composite–steel plate combined technique

A conventional gravity load design philosophy for reinforced concrete (RC) structures has been slowly replaced by seismic design since the 1970s. But, till recently, capacity design and ductile detailing were not strictly implemented in practice in many developing countries which are prone to seismic hazard. In the present study, performance of exterior beam–column joints designed based on ductile and non-ductile philosophy has been studied under cyclic load. It is found that although the incorporation of ductile detailing has considerably improved the seismic behaviour of the structural component, it could not assure the damage propagation in a safe zone. Moreover, in both specimens, the main damage has been concentrated in the joint zone irrespective of ductile detailing. Further, the damaged specimens were adequately repaired and suitably retrofitted using fibre reinforced plastic and steel plate and tested again under the same cyclic load. The retrofitted ‘NonDuctile’ specimen, as proposed in this study, could not only be able to regain its original performance (in terms of strength deterioration, stiffness degradation, energy dissipation), but has also shown improved performance in comparison to the original ones which is ideally desirable as well. Further, the retrofitted ‘Ductile’ specimen has shown a promising aspect of the proposed retrofitting strategy for seismically damaged components.

Dynamic performance evaluation of straight and curved cable-stayed bridges

Cable-stayed bridges with straight and curved deck geometry are studied for their free vibration response. A study on cable-stayed bridges with a single pylon with equal side spans is presented in this paper. 3-D geometries of cable-stayed bridges with spans 120-240 m, A-shaped and H-shaped pylon are numerically investigated using FEM software ANSYS. Further response of straight bridges under El Centro earthquake loading is presented using dynamic time history analysis and the results are studied for different geometries. The effect of induced curvature in decks introduces coupling of different modes even at their initial phases whereas the modes are quite distinct in straight bridges. Under El Centro load time history bending stress, shear stress distribution in decks is studied for different geometries of straight bridges which gives the typical behavior pattern of load sharing among the components of the cable-stayed bridge.