Wensong Zhou

Structural Health Monitoring System for the Shandong Binzhou Yellow River Highway Bridge

The Binzhou Yellow River Highway Bridge is a cable-stayed bridge in China. A structural health monitoring system was implemented on this bridge during its construction for monitoring its structural health status and assessing its safety for long-term service. This paper describes the design, implementation and functions of this system, and presents the measured responses of the bridge subjected to moving vehicle loads. The system includes a sensor module, a data acquisition module, a wired and wireless data transmit module, a structural analysis module, a database module, and a warning module. It is integrated by using LabVIEW software and can be remotely operated via Internet. After two years of service, the system operates well and confirms the current reliability of the bridge.

Sparse representation for Lamb-wave-based damage detection using a dictionary algorithm

&NA; Lamb waves are being investigated extensively for structural health monitoring (SHM) because of their characteristics of traveling long distances with little attenuation and sensitivity to minor local damage in structures. However, Lamb waves are dispersive, which results in the complex overlap of waveforms in the damage detection applications of the SHM community. This paper proposes a sparse representation strategy based on an Symbol‐norm optimization algorithm for guided‐Lamb‐wave‐based inspections. A comprehensive dictionary is designed containing various waveforms under diverse conditions so that the received waveform can be decomposed into a spatial domain for the identification of damage location. Furthermore, the Symbol‐norm optimization algorithm is employed to pursue the sparse solution related to the physical damage location. The functionality of the created dictionary is validated by both metal beam and composite wind turbine experiments. The results indicate a great potential for the proposed sparse representation using a dictionary algorithm, which provides an effective alternative approach for damage detection. Symbol. No caption available.

Study on Electromechanical Behavior of Unidirectional Carbon Fibre Sheet without Epoxy Resin Matrix

The relationship between stress, strain and electrical resistance of carbon fibre sheet without an epoxy resin matrix has been studied. Carbon fibre sheet specimens were tested under a tensile loading condition to investigate their self-diagnostic properties, that is, the ability of the specimens to sense the strain themselves. The experimental results indicate that the electrical resistance of carbon fibre sheet changes linearly with applied strain, such that carbon fibre sheet can act as a sensor to measure strain. A parallel circuit is employed to model the electrical behavior of carbon fibre sheet. The Weibull distribution model for fibre strength is made use of to calculate change in electrical resistance as fibres break. The ratio of broken fibres not making contact with neighbouring fibres, to all broken fibres in total is identified by fitting the test data. The results calculated using the parallel circuit model agree well with the test results.

Damage Detection for SMC Benchmark Problem: A Subspace-Based Approach

A full-scale bridge benchmark problem was issued by the Center of Structural Monitoring and Control at the Harbin Institute of Technology. The data used in this problem were collected by an in situ structural health monitoring system implemented into a full-scale cable-stayed bridge before and after the bridge was damaged, which is very rare in structural health monitoring field. This benchmark problem will help to verify and/or make comparison of the condition assessment and the damage detection methods, which are usually validated by numerical simulation and/or laboratory testing of small-scale structures with assumed deterioration models and artificial damage. With respect to damage detection of girder, one of the benchmark problems, using the monitored and field testing acceleration data, this paper describes a damage detection method, based on a residual generated from a subspace-based covariance-driven identification method, to detect the damage, and give relative quantitative damage indexes. This method was applied on both two parts of the given benchmark problem, and then detailed discussions and results on this problem are reported in this paper.

A benchmark problem for structural health monitoring based on a real bridge structure

A benchmark study is a valid way to make comparison of kinds of Structural Health Monitoring technologies, for example modal identification, finite element model updating, damage identification and so on. Several successful benchmark SHM problems were developed by IASC-ASCE SHM Task Group and the encouraging analytical studies results were obtained. But this benchmark study is based on a steel-frame scale-model structure built in the laboratory. Due to the striking difference in structure’s properties, SHM system and so on between the structure in the laboratory and the real structure, many SHM technologies developed in the laboratory is not applicable to the real structure. Thus a new benchmark study based on a real structure is developed in this paper. The first and the second phase of a benchmark problem based on SHM system for Binzhou Yellow River Highway Bridge have been detailed and the criterion of benchmark problem are given simultaneously.

Seismic Damage Detection for a Masonry Building Using Aftershock Monitoring Data

The problem of detecting structural damage by exploiting vibration signal measurements produced from earthquake excitation is addressed in this work. Following the Wenchuan earthquake of 12 May 2008, a residential masonry building was selected for instrumentation with accelerometers by the Harbin Institute of Technology. This building had been damaged in the Wenchuan earthquake. It represents a rare case of an instrumented building that has been previously damaged, thus serving as a full-scale benchmark model to evaluate structural identification and damage detection methods. More than 20 earthquakes were recorded by the system after the building was instrumented. For detecting the structural damage, a vibration-based damage detection algorithm for structures under earthquake excitation is introduced in this paper. This method is based on a residual associated with subspace-based modal identification, with global χ2-tests built on this residual. This method makes effective use of non-stationary and limited duration earthquake excitation, handles the uncertainties, and further detects the structural damage. The results obtained from these structural responses and earthquake excitations are reported using both identification and damage detection methods.

Acoustic emission monitoring of concrete columns and beams strengthened with fiber reinforced polymer sheets

Acoustic emission (AE) technique is an effective method in the nondestructive testing (NDT) field of civil engineering. During the last two decades, Fiber reinforced polymer (FRP) has been widely used in repairing and strengthening concrete structures. The damage state of FRP strengthened concrete structures has become an important issue during the service period of the structure and it is a meaningful work to use AE technique as a nondestructive method to assess its damage state. The present study reports AE monitoring results of axial compression tests carried on basalt fiber reinforced polymer (BFRP) confined concrete columns and three-point-bending tests carried on BFRP reinforced concrete beams. AE parameters analysis was firstly utilized to give preliminary results of the concrete fracture process of these specimens. It was found that cumulative AE events can reflect the fracture development trend of both BFRP confined concrete columns and BFRP strengthened concrete beams and AE events had an abrupt increase at the point of BFRP breakage. Then the fracture process of BFRP confined concrete columns and BFRP strengthened concrete beams was studied through RA value-average frequency analysis. The RA value-average frequency tendencies of BFRP confined concrete were found different from that of BFRP strengthened concrete beams. The variation tendency of concrete crack patterns during the loading process was revealed.

Study on variability of modal parameters of concrete structure : humidity and moisture effect

The complex external environment for civil engineering structures results in the structural vibration properties varying with external conditions, such as humidity and temperature. For the vibration-based structural health monitoring techniques, for example damage identification, modal updating etc., above characteristics will result in the vibration-based techniques invalid. Other researchers have reported that modal frequencies varied significantly due to temperature change, but the humidity affect structural vibration properties in another manner. This paper discusses the variation of frequencies and mode shapes with respect to humidity and temperature changes for concrete structures, for which the changing of moisture will affect the density of materials, and the changing of temperature will affect the stiffness of structures. This paper models these two factors with finite element model approach based on the theoretical analysis, and numerical results obtained on the FE model of a concrete bridge deck are reported.

In-plane shear piezoelectric wafer active sensor phased arrays for structural health monitoring

This paper proposes a new way for guided wave structural health monitoring using in-plane shear (d36 type) piezoelectric wafer active sensors phased arrays. Conventional piezoelectric wafer active sensors phased arrays based on inducing into specific Lamb wave modes (d31 type) has already widely used for health monitoring of the thin-wall structures. Rather than Lamb wave modes, the in-plane shear piezoelectric wafer active sensors phased arrays induces in-plane shear horizontal (SH) guided waves. The SH guided waves are distinct with the Lamb waves with simple waveform and less additional converted wave modes and the zero symmetric mode (SH0) is non-dispersive. In this paper, the advantage of the shear horizontal wave and the in-plane shear piezoelectric wafers capability to generate SH waves is first reviewed. Then finite element analysis of a 4-in-plane shear wafer active sensors phased array embedded on a rectangular aluminium plate is performed. In addition, numerical simulations with respect to creaks with different sizes as well as locations are implemented by the in-plane shear wafer active sensors phased array. For comparison purposes, the same numerical simulations using the conventional piezoelectric wafer active sensors phased arrays are also employed at the same time. Results indicate that the in-plane shear (d36 type) piezoelectric wafer active sensors phased arrays has the potential to identify damage location and assess damage severity in structural health monitoring.

The study of damage identification based on compressive sampling

This paper proposes a novel and effective method to identify the damage in the 2-D beam via Lamb wave. Two problems in the structural damage identification: damage location and damage severity are solved based on the theory of compressive sampling (CS) which indicates that sparse or compressible signals can be reconstructed using just a few measurements. Because of the sparsity nature of the damage, a database of damage features is established via a sparse representation for damage identification and assessing. Specifically, this proposed method consists of two steps: damage database establishing and feature matching. In the first step, the features database of both the healthy structure and the damaged structure are represented by the Lamb wave which propagates in the 2-D beam. Then in the matching step, expressing the test modal feature as a linear combination of the bases of the over-complete reference feature database which is constructed by concatenating all modal features of all candidate damage locations builds a highly underdetermined linear system of equations with an underlying sparse representation, which can be correctly recovered by ℓ1-minimization based on CS theory; the non-zero entry in the recovered sparse representation directly identifies the damage location and severity. In addition, numerical simulation is conducted to verify the method. This method of identifying damage location and assessing damage severity, using limited Lamb wave features, obtains good result.