Damage identification of steel beams using local and global methods

Structural condition monitoring methods can be generally classified as local and global. While the global method needs only a small number of sensors to measure the low-frequency structural vibration properties, the acquired information is often not sufficiently sensitive to minor damages in a structure. Local methods, on the other hand, could be very sensitive to minor damages but their detection range is usually small. To overcome the drawbacks and take advantage of both methods, an integrated condition monitoring system has been recently developed for structural damage detection, which combines guided wave and structural vibration tests. This study aims at finding a viable damage identification method for steel structures by using this system. First, a spectral element modelling method is developed, which can simulate both wave propagation and structural vibration properties. Then the model is used in updating analysis to identify crack damage. Extensive numerical simulations and model updating works are conducted. The experimental and numerical results suggest that simply combining the objective functions cannot provide better structural damage identification. A two-stage damage identification scheme is more suitable for identifying damage in steel beams.

Spectral element model updating for damage identification using clonal selection algorithm

A spectral element model updating procedure is presented to identify damage in a structure using Guided wave propagation results. Two damage spectral elements (DSE1 and DSE2) are developed to model the local (cracks in reinforcement bar) and global (debonding between reinforcement bar and concrete) damage in one-dimensional homogeneous and composite waveguide, respectively. Transfer matrix method is adopted to assemble the stiffness matrix of multiple spectral elements. In order to solve the inverse problem, clonal selection algorithm is used for the optimization calculations. Two displacement-based functions and two frequency-based functions are used as objective functions in this study. Numerical simulations of wave propagation in a bare steel bar and in a reinforcement bar without and with various assumed damage scenarios are carried out. Numerically simulated data are then used to identify local and global damage of the steel rebar and the concrete-steel interface using the proposed method. Results show that local damage is easy to be identified by using any considered objective function with the proposed method while only using the wavelet energy-based objective function gives reliable identification of global damage. The method is then extended to identify multiple damages in a structure. To further verify the proposed method, experiments of wave propagation in a rectangular steel bar before and after damage are conducted. The proposed method is used to update the structural model for damage identification. The results demonstrate the capability of the proposed method in identifying cracks in steel bars based on measured wave propagation data.

Data mining techniques for the assessment of factors contributing to the damage of residential houses in Australia

This paper reports on the preparation and management processes of inconsistent data on damage on residential houses in Victoria, Australia. There are no existing specific and fully relevant databases readily available except for the incomplete paper-based and electronic-based reports. Therefore, the extracting of information from the reports is complicated and time consuming in order to extract and include all the necessary information needed for analysis of damage on residential houses founded on expansive soils. Data mining is adopted to develop a database. Statistical methods and Artificial Intelligence methods are used to quantify the quality of data. The paper concludes that the development of such database could enable BHC to evaluate the usefulness of the reports prepared on the reported damage properties for further analysis.

Bansuri flute stinger INDIA

A short composition featuring an Indian bansuri flute, percussion and a soft synth pad.

Damage identification of civil infrastructure in the time domain using FEM calibrated ARMAX model

Due to environmental loads, mechanical damages, structural aging and human factors, civil infrastructure inevitably deteriorate during their service lives. Since their damage may claim human lives and cause significant economic losses, how to identify damages and assess structural conditions timely and accurately has drawn increasingly more attentions from structural engineering community worldwide. In this study, a fast and sensitive time domain damage identification method will be developed. First, a high quality finite element model is built and the structural responses are simulated under different damage scenarios. Based on the simulated data, an Auto Regressive Moving Average Exogenous (ARMAX) model is then developed and calibrated. The calibrated ARMAX model can be used to identify damage in different scenarios through model updating process using clonal selection algorithm (CSA). The identification results demonstrate the performance of the proposed methodology, which has the potential to be used for damage identification in practices.

Two maximal isometric contractions attenuate the magnitude of eccentric exercise-induced muscle damage

This study investigated whether maximal voluntary isometric contractions (MVC-ISO) would attenuate the magnitude of eccentric exercise-induced muscle damage. Young untrained men were placed into one of the two experimental groups or one control group (n = 13 per group). Subjects in the experimental groups performed either two or 10 MVC-ISO of the elbow flexors at a long muscle length (20° flexion) 2 days prior to 30 maximal isokinetic eccentric contractions of the elbow flexors. Subjects in the control group performed the eccentric contractions without MVC-ISO. No significant changes in maximal voluntary concentric contraction peak torque, peak torque angle, range of motion, upper arm circumference, plasma creatine kinase (CK) activity and myoglobin concentration, muscle soreness, and ultrasound echo intensity were evident after MVC-ISO. Changes in the variables following eccentric contractions were smaller (P < 0.05) for the 2 MVC-ISO group (e.g., peak torque loss at 5 days after exercise, 23% ± 3%; peak CK activity, 1964 ± 452 IU·L^–1; peak muscle soreness, 46 ± 4 mm) or the 10 MVC-ISO group (13% ± 3%, 877 ± 198 IU·L^–1, 30 ± 4 mm) compared with the control (34% ± 4%, 6192 ± 1747 IU·L^–1, 66 ± 5 mm). The 10 MVC-ISO group showed smaller (P < 0.05) changes in all variables following eccentric contractions compared with the 2 MVC-ISO group. Therefore, two MVC-ISO conferred potent protective effects against muscle damage, whereas greater protective effect was induced by 10 MVC-ISO, which can be used as a strategy to minimize muscle damage.

Guided wave based methods for damage detection : experimental study on concrete joint

Since Guided wave (GW) is sensitive to small damage and can propagate a relatively longer distance with relatively less attenuation, GW-based method has been found as an effective and efficient way to detect incipient damages. In this study, a full-scale concrete joint was constructed to further verify the effectiveness of GW-based method on real civil structures. GW tests were conducted in three stages, including baseline, serviceability and damage conditions. The waves are excited by one actuator and received by several sensors, which are made up of independent piezoelectric elements. Experimental results show that the mehod is promising for damage identification in practices.

Static and dynamic tests for damage identification of a slab-girder structure

Slab-girder bridges are widely used in Australia. The shear connection between reinforced concrete slab and steel girder plays an important role in composite action. In order to test the suitability and efficiency of various vibration-based damage identification methods to assess the integrity of the structure, a scaled composite bridge model was constructed in the laboratory. Some removable shear connectors were specially designed and fabricated to link the beam and slab that were cast separately. In this test, two static loads were acted in the 1/3 points of the structure. In the first stage, dynamic test was conducted under different damage scenarios, where a number of shear connectors were removed step by step. In the second stage, the static load is increased gradually until concrete slab cracked. Static tests were conducted continuously to monitor the deflection and loading on the beam. Dynamic test was carried out before and after concrete cracking. Both static and dynamic results can be used to identify damage in the structure.

Damage identification of slab–girder structures: experimental studies

Slab–girder structures composed of steel girder and reinforced concrete slab are widely used in buildings and bridges in the world. Their advantages are largely based on the composite action through the shear connection between slab and girder. In order to assess the integrity of this kind of structures, numerous vibration-based damage identification methods have been proposed. In this study, a scaled composite slab–girder model was constructed in the laboratory. Some removable shear connectors were specially designed and fabricated to connect the girder and slab that were cast separately. Then, a two-stage experiment including both static and vibration tests was performed. In the first stage, vibration tests were conducted under different damage scenarios, where a certain number of shear connectors at certain locations were removed step by step. In the second stage, two sets of hydraulic loading equipment were used to apply four-point static loads in the test. The loads are increased gradually until concrete slab cracked. The loading histories as well as deflections at different points of the beam are recorded. Vibration test was carried out before and after concrete cracking. Experimental results show that the changes of mode shapes and relative displacement between slab and girder may be two promising parameters for damage identification of slab–girder structures.