Seismic stressing state evolution features of a FRP-BF structure revealed by modelling tested strain data

Abstract

Researchers have been pursuing the accurate prediction of structural seismic capacity applying various theories and methods. Recently, structural stressing state theory explores a new way to assess structural anti-seismic capacity accurately. In this study, the new theory combining the modeling method in thermodynamic system is applied to investigate the dynamic strain data recorded in the shaking table test of a 1/5-scale four-story bottom frame model reinforced by fiber-reinforced polymer (FRP-BF structure), in order to reveal its definite stressing state features. The dynamic strain data at individual levels of white noise loading are modeled as state variables similar to a set of observations of the thermodynamic system. For the columns with fewer strain samples, the stressing state mode and its characteristic parameter curves are built based on the similarity between dynamic strain values. For the walls with more strain samples, the stressing state mode and characteristic parameter are derived by the differences of the accumulated state variables. Then, integrating the modes and characteristic parameters for columns and walls can obtain the stressing state mode and characteristic parameter of the FRP-BF structure. Further, the definite phase transition points are revealed by applying the clustering analysis criterion to detect the evolution curves of the characteristic parameters and to verify the evolution curves of the stressing state modes. The characteristic points define the elastoplastic branch point and the failure starting point of the FRP-BF structure. Both characteristic points surely exist in the tested strain data of structural seismic working process as the specific embodiment of the natural law from quantitative change to qualitative change of a system. Thus, the elastoplastic branch point and the failure starting point provide the new reference to the design and safety estimation of the FRP-BF structures.