Estimation Method of Maximum Inter-Story Drift Angle of Wood-Frame House using Two Accelerometers

In April 2016, Kumamoto earthquake occurred in Japan and many wooden houses collapsed and many lives were lost because of the second and larger main shock. As a result, the need for Structural Health Monitoring (SHM) for wooden houses is receiving increased attention. In the SHM system, maximum inter-story drift angle is considered as the damage index. We assume that the first story of a wooden house will be damaged so that we need only to focus on the response of this first story. Hence, we install accelerometers on the ground floor and the second floor. In order to estimate the inter-story drift angle, we need to integrate the acceleration records twice. The simple double integration will result in erroneous results. Thus, in this paper, we propose the most appropriate integration method to estimate the maximum story drift angle with high accuracy using two accelerometers.

Numerical Simulation on Micro-damage Detection In CFRP Composites Based on Nonlinear Ultrasonic Guided Waves

Micro-damages such as pores, closed delamination/debonding and fiber/matrix cracks in carbon fiber reinforced plastics (CFRP) are vital factors towards the performance of composite structures, which could collapse if defects are not detected in advance. Nonlinear ultrasonic technologies, especially ones involving guided waves, have drawn increasing attention for their better sensitivity to early damages than linear acoustic ones. The combination of nonlinear acoustics and guided waves technique can promisingly provide considerable accuracy and efficiency for damage assessment and materials characterization. Herein, numerical simulations in terms of finite element method are conducted to investigate the feasibility of micro-damage detection in multi-layered CFRP plates using the second harmonic generation (SHG) of asymmetric Lamb guided wave mode. Contact acoustic nonlinearity (CAN) is introduced into the constitutive model of micro-damages in composites, which leads to the distinct SHG compared with material nonlinearity. The results suggest that the generated second order harmonics due to CAN could be received and adopted for early damage evaluation without matching the phase of the primary waves.

Seismic Fragility Analysis of Mid-Story Isolation Buildings

Seismic fragility analysis is essential for seismic risk assessment of structures. This study focuses on the damage probability assessment of the mid-story isolation buildings with different locations of the isolation system. To this end, the performance-based fragility analysis method of the mid-story isolation system is proposed, adopting the maximum story drifts of structures above and below the isolation layer and displacement of the isolation layer as performance indicators. Then, the entire process of the mid-story isolation system, from the initial elastic state to the elastic-plastic state, then to the limit state, is simulated on the basis of the incremental dynamic analysis method. Seismic fragility curves are obtained for mid-story isolation buildings with different locations of the isolation layer, each with fragility curves for near-field and far-field ground motions, respectively. The results indicate that the seismic fragility probability subjected to the near-field ground motions is much greater than those subjected to the far-field ground motions. In addition, with the increase of the location of the isolation layer, the dominant components for the failure of mid-story isolated structures change from superstructure and isolation system to substructure and isolation system.

Innovation and Practice of Cable-Pylon Anchorage Zone Using Group Aggregated Anchor System

With the development of the cable-stayed bridge, the anchorage form on pylon of cable-stayed has been improved and innovated continuously, and the anchorage methods such as circumferential prestressed anchorage, steel anchor beam and steel anchor box have been gradually formed and developed, which further increases the span of cable-stayed bridge and meets the social needs of economic development and environmental integration. The group aggregated anchorage system between cable and pylon is a kind of anchorage form outside the pylon, which has the characteristics of clear force transmission, simple structure and high construction efficiency. It has been successfully applied in Chizhou Yangtze River Bridge for the first time. The main span of Chizhou Yangtze River Bridge is 828m, and the cable-stayed bridge with spatial cable plane of two towers is constructed. Six steel beams are deployed between tower legs to anchor 54 pairs of cables respectively. The steel beams and the concrete tower columns are effectively connected by prestressed anchors, shear nails and short steel bars, which could transfer the cable force to the tower column reliably. This kind of anchoring system has clear force transmission, which could reduce the tensile stress of concrete tower column and the risk of concrete cracking. Meanwhile, the steel beam could be constructed by the engineering manufacture and the field installation, which could reduce the working time at height, further the construction quality and safety could be controlled. Based on the construction of Chizhou Yangtze River Bridge, this paper mainly introduces the proposal, construction, key construction technology and engineering application effect of group aggregated anchorage system. The engineering practice proves that this new type of anchorage could not only meet the basic requirements of the intrinsic safety of the bridge, but integrate with the regional culture to create the beauty of natural harmony as well.

Structural Health Monitoring (SHM) of Space Structures

Recent years have seen an increased interest in exploring outer space for space tourism or for unmanned or manned planetary explorations. The captivated interests among various stakeholders to employ advanced technologies to meet the requirements of these missions have necessitated the use of newly developed asset monitoring systems to ensure robustness and mission reliability. Although, Non-Destructive Testing (NDT) methods provide sufficient information about the state of the structure at the time of inspection, the need for continuously monitoring the health of the structure throughout the mission has asserted the use of Structure Health Monitoring (SHM) technologies to increase the levels of safety and thereby, reducing the overall mission costs. However, since the implementation of SHM technologies for space missions can be affected by several factors including, environmental conditions, measurement reliability and unavailability of adequate standards, additional considerations on its employability must be reconsidered. This article demonstrates a structured approach to compare the capabilities of some of the most promising SHM technologies in consideration of these influential factors. Additionally, remarks on the feasibility of employing these SHM technologies and the role they could play in such critical missions would be elaborated.

Magnetic Pre-Loading for a Tonpilz-Type Acoustic Projector

This paper describes a new magnet-based method for applying a compressive pre-load to the piezoceramic elements of a Tonpilz-type acoustic projector, with the advantage of lower damping due to mechanical friction and a greater range of unhampered resonant motion since no plate spring is required. The Tonpilz-type acoustic projector can be applied to structural health monitoring studies involving air coupled ultrasound. Acoustic model predictions and the measured behaviour of a relaxor ferroelectric single crystal (RFSC) based prototype device, operating in air, are presented and show good correlation. With a 5 V drive, at 9420 Hz resonance, the prototype device generates a sound pressure level of 113 dB measured at an axial distance of 5 mm. The maximum peak tip displacement of the device’s head mass is predicted to be 0.7 µm at resonance. This is well within the 2 µm displacement produced by the 90 N magnetic pre-load, thus protecting the RFSC ceramic element from damaging tensile stress.

Estimation of Maximum Drift of MDOF Shear Structures Using Only One Accelerometer

This paper presents a new method to estimate maximum drifts, relative displacements between adjacent floors, of all stories of multi-degree-of-freedom (MDOF) shear structures using only one floor’s absolute acceleration time history response under the ground excitation. The absolute acceleration and relative displacement are formulated in modal coordinates and the state-space expression is derived. Then the numerical simulation for a three-story structure was conducted to verify the performance of the state-space equation. The comparison of the estimated state and input with actual values is made and shows the good agreement. In addition, the relative displacement time histories of all floors were obtained, and the errors of maximum displacements and inter-story drifts were analyzed. The robustness against environmental noise was also investigated by numerical simulations as well. The results of simulations indicate the estimation is satisfactory, and very robust against the environmental disturbance.

Improving the Drive-by Bridge Inspection Performance by Vehicle Parameter Optimization

Recently, there has been an increasing emphasis in the Indirect bridge health monitoring method employing passing vehicles, which is regarded as one of the most effective approaches in bridge damage screening. However, few researches have been conducted on the Drive-by bridge inspection method using vehicle displacement profile as damage indicator due to the challenges in displacement measurement and result accuracy. This paper proposes an optimization approach of designing the optimum vehicle parameters to improve the performance of vehicle displacement-based Drive-by bridge damage inspection. A generalized Vehicle-Bridge Interaction (VBI) system is built in MATLAB, where the bridge is modelled as a simply supported beam with 10 elements and the passing vehicle is represented as a simplified quarter car. Employing the Monte Carlo methods, the optimum parameters are determined by numerous simulations processed under diverse damage scenarios. Results show that by employing the optimal vehicle parameters, the bridge damages can be detected effectively and accurately for general damage scenarios based on the vehicle displacement profile. The proposed optimization method can contribute to the wide application of vehicle displacement-based Drive-by bridge damage inspection, providing merits in simplicity and visualization.

Optimal Waiting Position of a Home Robot for Risk Communication Considering Behavior Patterns of an Occupant

The risk communication in a home between a home robot and an occupant must be smooth in a way that the home robot does not disturb the occupant lives. In this paper, we propose a new method to determine the optimal waiting position considering the personal space and the obstacles such as furniture and the occupant’s walking patterns. It is shown that the distance to the wall from the occupant in the direction of the home robot and the standing or sitting posture affect most on the personal space. Furthermore, this personal space is dependent on each individual preference. The performance of the proposed method is much more feasible compared with those obtained in our previous approach.

A 3D Printed, Constriction-Resistive Sensor for the Detection of Ultrasonic Waves

Ultrasonic waves, either bulk waves or guided waves, are commonly used for non-destructive evaluation, for example in structural health monitoring. Traditional sensors for detecting ultrasonic waves include metallic strain gauges and piezoelectric ceramics. Recently piezoresistive nanocomposites have emerged as a promising sensor with high sensing range. In this paper, a constriction-resistive based sensor made from a graphene reinforced PLA filament is developed using a fused deposition modelling 3D printing approach as a novel type of ultrasonic sensor for structural health monitoring purposes. The sensor is made of very low-cost and recyclable thermoplastic material, which is lightweight and can be either directly printed onto the surface of various engineering structures, or embedded into the interior of a structure via fused filament fabrication 3D printing. These characteristics make this sensor a promising candidate compared to the traditional sensors in detecting ultrasonic waves for structural health monitoring. The printed sensors can detect ultrasonic signals with frequencies around 200 kHz, with good signal-to-noise ratio and sensitivity. When deployed between two adjacent printed tracks , and exploiting a novel kissing-bond mechanism, the sensor is capable of detecting ultrasonic waves. Several confirmatory experiments were carried out on this printed sensor to validate the capability of the printed sensor for structural health monitoring.