Climate change is one of the biggest challenges the world is facing nowadays, and due to the extreme weather events and natural hazards, the threat to the infrastructure assets keeps increasing. Hence, with the continuous efforts to reduce the climate change, we also need to prepare our infrastructure for the natural hazards that we can’t avoid.
The requirements for the seismic design of tall buildings have become much stricter nowadays because any damage to the structure will have a huge impact on the economy and to the lives of people. Hence, it is necessary to develop the earthquake resilient structures which can rapidly restore the function of a city and efficiently reduce the economic losses. Working on a whole structure level to be resilient is more important nowadays rather than working on specific structural components. The primary focus of the green and sustainable projects around the world is on water, energy, and materials. When we want the buildings to have self-righting capability during an event like the earthquake, they are known as resilient in nature, i.e. they will have minimum damage during any natural disaster keeping in mind the safety of the people. In this study, we would like to develop and analyze a rocking frame resilient structure which restores its original position with the help of unbonded post-tensioned prestressing tendons.
The efficiency of the material and the construction speed of the precast concrete members made them popular throughout the world. But because of the poor performance of the inelastic construction joints during the earthquakes, precast concrete lost its effectiveness in the lateral load resisting systems. Initially, the use of prestressing tendons in seismic force resisting systems was banned by ACI 318. In 1982, NIST started the research on the use of prestressing tendons in seismic force resisting systems. To expand the research further in this field, the PRESSS Project (Precast Seismic Structural Systems) was initiated in 1990 and after that, the use of prestressing tendons was permitted by ACI 318 in seismic force resisting systems.
Housner (1963) proposed the concept of rocking structures, and since then there have been a lot of research on this topic. Precast and Prestressed concrete beam to column connections for rocking behavior was proposed by Priestley and Tao (1993). Stanton et al. (1997) later came up with the Hybrid Reinforced Precast Frame especially designed for the seismic regions. Since then, the precast hybrid moment frame has undergone a lot of testing for its behavior under earthquake loading conditions. The hybrid moment frame structure was erected and tested in 1999 at University of California, San Diego under the PRESSS Project. According to its report in PCI Journal (1999), researchers found no significant strength loss in the direction of the frame and achieved up to 4.5 percent of drift levels. Stanton and Nakaki (2002) claimed in their PRESSS Project report, that the frame system offers a unique characteristic of zero residual drift in the structure.
Apart from RC frames, steel rocking frames with self-centering spine systems that employ controlled rocking, also offer a great solution for structures to resist large earthquake ground motions. Ricles et. al (2002) developed a steel column-beam rocking joint with the help of unbonded post-tensioning steel tendons. Further, Deierlein et. al (2011) proposed a steel rocking frame structure with vertical post-tensioning tendons and employed the structural fuses to absorb the seismic forces. They performed an extensive study to develop a controlled steel braced rocking frame with experiment and testing of large-scale specimens at the University of Illinois and E-Defense shaking table facility at Japan. Rocking frames, being a topic of extensive research can be designed with various self-centering configurations, which were illustrated by Eatherton et. al (2012).
Most recently, a controlled rocking reinforced concrete frame (CR-RCF) has been developed by Lu et. al (2013) and later (2015), performed the push-over analysis for the seismic performance of the structure. They also proposed that inter-story dampers may be installed to improve the seismic response by effectively controlling the displacement of the structure. Further, to investigate the seismic performance of CR-RCF, a dynamic elastic-plastic time history analysis was performed using the FEA model in ABAQUS by Lu et. al (2017). According to their study, the removable dampers yield to dissipate the earthquake energy but the main members remain elastic satisfying the objective of the study being a damage-free structure.
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