SEISMIC EVALUATION OF BLOCK MASONRY INTERLINKED WITH VISCOELASTIC LINK ELEMENTS

Abstract

The inter-linked block masonry system with visco-elastic link elements is a new alternative technique for the construction of earthquake resistant low cost unreinforced masonry houses which is originally developed in the Department of Earthquake Engineering, IIT Roorkee. This technology works on the principle of frictional as well as visco-elastic damping. Frictional damping is achieved through concrete block surface in contact with each other and the visco-elastic damping is achieved through visco-elastic shear links provided in vertical and horizontal directions. The visco-elastic link elements are to be prepared from Neoprene Rubber and Styrene-butadiene Rubber i.e "ply" part of used/discarded radial rubber tires of passenger cars available in abundance in "kabari" or scrap market in India. In the proposed technology, each block is restrained against translational and rotational movements by providing the visco-elastic link elements. In case of severe earthquakes, as the slotted blocks force to move in any possible directions, the provided visco-elastic link elements start to deform and dissipate the energy keeping the entire structure in elastic condition. This concept of inter-linked block masonry is verified after constructing and testing a full scale single storey model on the Shake Table Test facility at the Department of Earthquake Engineering, IIT Roorkee in simulated earthquake motions as per IS: 1893 (Part 1):2002 under Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) corresponding to most severe Zone V of India. The shake table test results indicate that there is 65% reduction in peak acceleration response at the roof level as compared to the base level under MCE. It is also observed that the inter-linked block masonry model is able to dissipate more than 60% of input energy even at the excited frequencies in the range of predominant frequency of the model. The models are further tested in Shock (Impulse) Table facility of the Department of Earthquake Engineering, IIT Roorkee. Shock table test results also reveal that there is drastic reduction in the peak ground acceleration at roof level as compared to base level. Nearly 70 to 80% energy is dissipated along the height of the structural models. However in conventional unreinforced/reinforced masonry system there is amplification of acceleration along the height of model and the energy is dissipated only through the cracks developed in the model. After successful testing of single storey model under both types of test, a two storey model is further tested in Shock Table Test facility. The tested system has withstood against severe shaking without any distress and is found fit for immediate occupation even after the test. The stable hysteresis behavior of the inter-linked block masonry models obtained from the cyclic testing also clearly manifests that its energy absorbing capacity without depicting any significant pinching effect is significantly higher than the conventional iv masonry building. Moreover, the seismic performance of the interlinked model will further improve as the load/storey on the model increases since friction and viscous damping properties are proportional to the weight of the model. The concept of block masonry with visco-elastic link is completely successful since the energy is completely released through friction damping arising from the rigid surfaces of blocks in contact. This sliding friction can be effectively used as a damping mechanism for the dissipation of energy and sometimes may be very effective where other mechanism may not be effective or desirable. The main advantage of friction damping is that it offers uniform dissipation across the entire frequency range much unlike the base isolation and viscous dampers. Moreover, in the event of earthquakes that feature an uncharacteristically large amount of energy in long period range such as Nepal Earthquake, 2015, the conceptualized system is the only promising approach in which the use of dry friction/metal yielding is a means to dissipate vibration energy. Similarly, the visco-elastic link elements not only restrict the translational and rotational movement of each block under normal loading conditions, but the same are also able to dissipate the energy through viscous damping by yielding in case of severe earthquake conditions. Therefore, the conceptualized system is an alternative technique to construct earthquake resistant housing based on the concept of energy dissipation/damping. Practically, the damping based vibration control is a much more viable, efficient, preferred solution at low-cost as compared to conventional earthquake resistant measures based on ductility. Thus the introduction of inter-linked block masonry system with visco-elastic link is a promising, new generation system in medium to high seismic zones.