Yoshikazu Kitagawa

Pseudoelastic behavior of shape memory alloy wire and its application to seismic resistance member for building

In this paper, a new type of the seismic resisting members with the shape memory alloys (SMA) wire, such as brace and exposed-type column base, were proposed as a hysteretic damper for building structures. Pulsating tension loading tests were performed with constant, increasing and decreasing strain amplitude to investigate restoring force characteristics of the wire. Then, the metallo-thermomechanics model with internal variable was introduced. Using the numerical model, the restoring force characteristics of the wire under high speed loading, such as a seismic loading, were predicted. The results showed that the phenomena should be treated in the numerical model with transformation. Furthermore, these results are used to discuss the applicability and availability of the SMA wire for the seismic resisting members.

Experimental study on enhancement of self-restoration of concrete beams using SMA wire

Shape Memory Alloys (SMA) exhibit stable superelasticity between a reverse transformation finish temperature (Af) and approximately 30°C above Af, and therefore can sufficiently work as a superelastic material for structural use in building under the temperature in a construction environment. In order to verify the potential self-restoration capacity of mortar beams containing superelastic SMA reinforcements, static loading tests were conducted, and the results were then compared with those for a beam containing steel wires. The comparison indicates that (1) after maximum deflection, the mortar beam with SMA can return to an about one-tenth deflection compared with the maximum, (2) the range of deflection of the mortar beam with SMA is more than seven times that of the beam with steel, and (3) wide single crack can occur at the critical section due to a weaker bond force between SMA and mortar.

Application of SMA rod to exposed-type column base in smart structural system

A seismic-resistant member with a shape memory alloy (SMA) rod was used in an exposed-type column base as a passive damper for building structures. Horizontal and vertical loading tests on the column base with SMA anchorage were done with increasing drift amplitude to investigate the restoring force characteristics of the column base. The results showed that (1) use of an SMA rod prevents deterioration of the restoring force characteristics, (2) use of an appropriate SMA material and a moderate-size rod can yield large deformation capacity and good restoring force characteristics, and (3) after a large drift in the building frame, SMA anchorage enables the original shape and resisting performance to recover with unloading.

Structural Damage Detection by Using Modal Data and Wave Propagation

Demand for monitoring systems applied to structures for quality assurance and for evaluating seismic risk is stronger than ever. Here, a monitoring systems to assess structural integrity was developed in which the damage-detection strategy uses two newly developed methods to first identify the damage sites globally (i.e., detect whether the damage occurred or not, and detect the story level) and to then evaluate the damage sites locally. One method identifies the sites and extent of damage globally by using an improved MDLAC (Multiple Damage Location Assurance Criterion) method by using modal data (i.e., frequency and mode shape), and the other identifies the damage sites locally by using wave propagation. Results showed that these two methods are practical and effective in assessing structural integrity of a structure for seismic safety.Copyright

Structural Assessment System for Damage and Degradation: Two-Stage Damage Identification Based on Neural Networks and Improved MDLAC Method

A “smart” structure has many functions, including monitoring, repairing, shape formation, and learning. Recently, interest in applying a monitoring system to structures for quality assurance and for evaluating seismic risk has been strong. Monitoring system is useful to diagnose the structural condition, and detect structural damage and degradation. In this study, we developed a monitoring system to assess the structural integrity. This system includes a diagnostic system for structural damage and degradation based on neural networks and improved MDLAC method, say, to detect the damage sites globally by applying neural networks and then to narrow the damage sites by using improved MDLAC method. To validate this system, we then use the 5-story structure in which the beams are fixed at both ends in order to confirm the performance of our proposal damage detection methods. As a result, it is pointed out that there are some possibilities to confirm the diagnostic system by utilizing these two methods.Copyright

Characteristics of piezoelectric damper in smart structural system

Characteristics of piezoelectric dampers built with piezoelectric materials were investigated as part of a smart structural system for buildings. Piezoelectric materials can be applied not only to the sensors and the actuators, but also to the dampers. Here, first the damping mechanism and the complex stiffness for a piezoelectric damper were derived from the piezoelectric equations. Then, based on the complex stiffness and Biggss formula, an equation used to evaluate the damping performance for building structures with piezoelectric dampers was derived. Finally, to determine the applicability and availability of piezoelectric dampers, the habitability of a building with piezoelectric dampers to strong wind was investigated for a high-rise steel apartment building. The results show that piezoelectric dampers enable high-rise apartments of practical dimensions to satisfy H-2 grade habitability.