Radio Frequency IDentification (RFID) tag is a promising device for the management of products at a very low cost.
Huge number of such low-cost sensors can be installed to the structure beforehand, after a disaster we can access to
these sensors wirelessly and very easily. In this system, an electrically conductive paint or printed sheet is applied to a
part of structure in which crack will occur. Copper wire is connected to the attachment on the structure and a RFID tag.
When a crack occurs, the paint or printed sheet is broken, resulting in an increase in resistance. Crack width can be
estimated by the ability of an RFID transmitter to communicate with the tag. By bending tests of concrete specimens,
the relationships between concrete crack width and conductivity of the materials are examined. It is shown that the level
of concrete crack width can be related to the ability of the paint or printed sheet to conduct electricity or not. This
printed sheet is also applied for steel crack. By fatigue test of steel specimen with a notch, very small steel crack can be
detected by this sensor.
Target building is an 8-story steel encased reinforced concrete building which was constructed in 1998. In this structural health monitoring system, strong motion observation data is used and accelerometers were installed just after the completion of construction at 1st story, 2nd story, 5th story and 8th story. By use of system identification using ARX model, natural frequency, damping ratio and participation function are calculated, and concentrated equivalent story stiffness can be also determined by using Moore and Penrose generalized inverse matrix. From the identification results, natural frequency and concentrated equivalent story stiffness tend to decrease by the aging. Especially, just after the completion of construction and after a large earthquake, changes of natural frequency and concentrated equivalent story stiffness are very remarkable. From the point of amplitude dependence, natural frequency and concentrated equivalent story stiffness tend to change more by equivalent velocity of input energy than by peak ground acceleration. Analytical frame model is constructed from the structural design documents and concentrated equivalent story load-displacement relationships are obtained by carrying out push-over analysis. By the comparison between analytical and identified concentrated equivalent story stiffness, the structural conditions is estimated. From the identification results, a model using stick-slip elements is proposed. Natural frequency and story stiffness described by this model are consistent with identified results.
We carry out shaking table test using a three-story large-scale steel structure with cementitious devices to detect and estimate damages. The test frame floor height is 1.8m, total height is 5.4m, floor plan is 4mx3m. Shaking table test is carried out at large-scale earthquake simulator facility of the National Research Institute for Earth Science and Disaster Prevention. Cementitious devices are installed in the center frame of tested structure and devices are actually damaged during the shaking. Two types of identification are tried. One is identification using the data under excitation and the other is identification using the data of before and after of the excitation. In both cases, we use identification method by ARX model. From identified results, natural frequency decreases, damping ratio increases and story stiffness decreases as experienced amplitude increases or input amplitude increases. A model using stick-slip elements is proposed. Natural frequency, damping ratio and story stiffness described by this model are consistent with experimental results. The fitting of the experimental result based on this model is carried out, and skeleton curve got from structural design and fitting result are corresponded well. Damage evaluation method using this fitting results and skeleton curve is proposed.
KEYWORDS: Ferroelectric polymers, Sensors, Actuators, Control systems, Control systems design, Ferroelectric materials, Interference (communication), Passive isolation, Polymers, Digital filtering
Induced strain actuator (ISA) can change their own shapes according to external electric/magnetic fields, and vice versa. Recently these materials have been widely used for the small/precision. The objectives in this study are to develop smart members for building and to realize the smart, comfortable and safe structures. The research items are 1) Semi-active isolation of structures using piezoelectric actuator, 2) Using ISA as sensor materials and 3) Improvement of Acoustic Environment. Semi-active base isolation system with controllable friction damper using piezoelectric actuators is proposed. Simulation study was carried out, and by semi-active isolation, it could be realized to reduce response displacement of the structure to 50% of values of the passive isolation. ISA materials can act as sensors because they cause change of electric or magnetic fields under deformation. PVDF sensors are suitable for membrane structures. We evaluate performance of PVDF sensors for membrane structures by experiment. Polymer based ISA films or distributed ISA devices can control vibration mode of plane members. Applications to music halls or dwelling partition walls are expected. Results of experimental studies of noise control are discussed.
This paper presents damage detection tests of five-story steel frame with simulated damages. We discuss pre-analytical study and results of experiments. Fiber brag grating (FBG) sensors, accelerometers, strain gauges and laser displacement meters are installed in this test frame. We assume damages by removing studs from only one story, loosening bolts of beams, cutting part of beams and extracting braces from only one story. From the results of pre-analytical study, we can estimate which story is damaged from the change of natural period and mode shape to some extent. We applied flexibility method which is one of a damage identification methods using modal properties. We also apply flexibility method to results of experiments. In some cases we can estimate which story is damaged, and in other cases we cannot. We also applied a method using multiple natural frequency shifts. Making use of the change in five natural frequencies due to damage, the location of damaged stories can be pinpointed. In both methods, we cannot identify damaged story in some cases. Some methods other than methods using modal properties have to be tried to apply in such cases.
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