As a qualitative health monitoring method, the electromechanical impedance technique
(EMI) has been widely studied. Due to the complexities of the damaged structures and the
difficulties in high-frequency analysis, further information about the nature of damage
cannot be obtained using EMI in its conventional non-model-based way. Thus, in this
paper, a hybrid technology combining the EMI technique and reverberation matrix
method (RMM) is proposed to quantitatively correlate damage in beam structures
with high-frequency signatures for structural health monitoring. Timoshenko
beam theory is employed to study the dynamics of beam-like structures bonded
with multiple pairs of PZT patches. A piecewise, homogeneous beam model is
introduced to approximate the nonhomogeneous beam in which inhomogeneity is
introduced because damages of an originally uniform beam can be modeled by different
cross-sectional properties. Here, only one-dimensional axial vibration of PZT
wafers is considered. A shear lag model is adopted to simulate the interfacial
bonding between PZT patches and the host beam. An analytical expression of
impedance (or admittance) related to the response of the coupled model of the
PZT patch-bonding layer–host beam system is derived and then investigated by
comparing with other theories. Finally, covariance, a kind of non-parametric damage
index, is also employed to identify the damage severity, propagation and location.
A prestress force identification method for externally prestressed concrete uniform beam based on the frequency equation and the measured frequencies is developed. For the purpose of the prestress force identification accuracy, we first look for the appropriate method to solve the free vibration equation of externally prestressed concrete beam and then combine the measured frequencies with frequency equation to identify the prestress force. To obtain the exact solution of the free vibration equation of multispan externally prestressed concrete beam, an analytical model of externally prestressed concrete beam is set up based on the Bernoulli-Euler beam theory and the function relation between prestress variation and vibration displacement is built. The multispan externally prestressed concrete beam is taken as the multiple single-span beams which must meet the bending moment and rotation angle boundary conditions, the free vibration equation is solved using sublevel simultaneous method and the semi-analytical solution of the free vibration equation which considered the influence of prestress on section rigidity and beam length is obtained. Taking simply supported concrete beam and two-span concrete beam with external tendons as examples, frequency function curves are obtained with the measured frequencies into it and the prestress force can be identified using the abscissa of the crosspoint of frequency functions. Identification value of the prestress force is in good agreement with the test results. The method can accurately identify prestress force of externally prestressed concrete beam and trace the trend of effective prestress force.
In 2003, an 8-storey reinforced concrete (RC) frame-supported masonry structure, located in Hengyang City, China, underwent a severe fire-induced collapse accident. Information on the structure and the fire scenario is presented. It includes the design data, the site observation record of the fire incident, and the laboratory material test results. Preliminary investigation reveals that about 45.9% of the bottom storey of the RC frame experienced temperatures in excess of 800°C, and its central area reached 1300°C. Such a severe fire load, of fairly high temperature and large area, is thought to be the primary cause of the progressive collapse of the entire building structure. To better understand the collapse mechanism, this study presents a coupled thermo-mechanical numerical simulation of the building collapse. The actual collapse area is well reproduced by the proposed numerical model. The simulation further demonstrates that the initial damage happened to two interior columns exposed to temperature of 1300°C. Such damage was also attributable to the large gravity load they carried, and the complicated nature of the local structural arrangements. The adjacent structural members were subsequently damaged, because they were also weakened by the fire, and were over-loaded by the redistributed load. Failure of the two interior columns and adjacent area eventually triggered a progressive collapse. Further, the effect of some critical factors on the collapse mechanism is discussed. On the basis of this numerical case study, practical design considerations on the key structural components, the fire compartments, and the structural robustness are given for the prevention of the fire-induced progressive collapse of RC frame structures.
The paper presents an experimental investigation on the shear strength of self-piercing rivet connections used in thin-walled steel structures. The test program included specimen variations in the number of rivets in each connection, rivet spacing, end distance, and steel sheet thickness. According to the experimental results, the curve of load-slip, peak load, and failure mechanism for all specimens were analyzed. Parameters of riveting in terms of end distance, spacing, arrangement, length, and thickness difference between connection components were studied on their effects for shearing performances of self-piercing rivet connections. A design method based on the model of transmission dynamics of infectious diseases was proposed for calculating the shear strength of the rivet connections. The strength reduction due to the effect of group rivets was considered in the new method.ii
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.