DYNAMIC BEHAVIOR OF PRIMARY STRUCTURES ATTACHED WITH FLEXIBLY CONNECTED SECONDARY SYSTEMS

S.P.Challagulla, Chandu Parimi

Abstract: Researchers have studied the seismic behavior of the secondary systems (SS) or nonstructural elements (NSEs)attached to the main structural system or primary structure (PS)during seismic events and their protection during such type of events. An adverse effect on the dynamics of main structural system due to NSEs during seismic events is observed. These studies considered NSEs that are rigidly connected like masonry in-fills, claddings and term them as stiffening NSEs. NSEs which are not rigidly connected to the main structural system are called as flexible NSEs. During seismic events, NSEs which are rigidly connected to the main structure act integral to the main structure. These NSEs do not vibrate independent of the main structure. Whereas, flexibly connected NSEs vibrate relative to their point of attachments. In cases where the frequency of vibration of NSEs matches the natural frequency of the structure, it will result in resonance. This paper proposes and analyzes the effects of secondary systems which are not rigidly attached to the main structure on the dynamic behavior of the primary structure. Such secondary systems tend to change the dynamic behavior of primary structures especially when their mass is comparable to the primary structure. Designers tend to either completely ignore this effect or conservatively add the complete mass of the secondary system in the seismic analysis. This paper attempts to quantify this effect so that the seismic design of the primary structure can be more economical and accurate. In this paper free, undamped vibrations of a SDOF system attached with secondary system are analyzed. Damping is also considered in some problems for the former case. This paper concludes that secondary systems have a significant effect on the dynamics of the primary structure from the preliminary work conducted. This paper also presents the response time history plots of the primary structure with and without considering the effect of secondary system and inertial forces vs. time plots of the primary structure.

Keywords: Dynamic Behavior, Primary Structure, Nonstructural Elements (NSEs), Stiffening NSEs, Flexible NSEs.

DOI: https://doi.org/10.15623/ijret.2016.0532021