Key Engineering Materials Vols. 569-570

Abstract: Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. The structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.

Abstract: In analyzing the vehicle-inducedvibrations of short- to medium-span bridge, this study adopts the conventionalmultivariate autoregressive (MAR) model along with a stabilization diagram (SD) that is introduced to resolve the difficulty indeciding the optimal model order and to reduce the variation of identifiedcharacteristics. Such a combined identification technique is applied to identify dynamic characteristics of a simple steel highway viaduct in Osaka, Japan, with three pavement andparapet conditions. Two issues are investigated through the field experiment: firstly, the accuracy and precision of the present technique is verified, especially in the frequencyidentification; and secondly, the vehicle-bridge interactions (VBI) issues areinvestigated. The bridge frequencies vary due to differentpavement and parapet conditions, but no obvious variation in the mode shapes is observed. Observations also demonstrate that the correlations betweenvehicle and bridge responses are not strong enough to guarantee the successfulidentification of bridge parameters from the raw vehicle responses. Somefurther data processing techniques should be applied to realize the indirect identification of bridge’s dynamic characteristics utilizingvehicle vibrations.n analyzing the vehicle-induced vibrations of short-to medium-span bridge, this study adopts the conventional multivariate autoregressive (MAR) model along with a stabilization diagram (SD) that is introduced to resolve the difficulty in deciding the optimal model order and to reduce the variation of identified characteristics. Such a combined identification technique is applied to identify dynamic characteristics of a simple steel highway viaduct in Osaka, Japan, with three pavement and parapet conditions. Two issues are investigated through the field experiment: firstly, the accuracy and precision of the present technique is verified, especially in the frequency identification; and secondly, the vehicle-bridge interactions (VBI) issues are investigated. The bridge frequencies vary due to different pavement and parapet conditions, but no obvious variation in the mode shapes is observed. Observations also demonstrate that the correlations between vehicle and bridge responses are not strong enough to guarantee the successful identification of bridge parameters from the raw vehicle responses. Some further data processing techniques should be applied to realize the indirect identification of bridges dynamic characteristics utilizing vehicle vibrations.

Abstract: Ground penetrating radar (GPR) and active thermography are well known non-destructive testing (NDT) methods for structural visualization and defect detection in concrete. However, for both methods, the probability of detection is strongly depth-dependent and each method suffers from an almost blind region at a specific depth. In this study we propose the use of unsupervised clustering techniques for the fusion of GPR and thermographic phase contrast data to enhance defect visualization in concrete. The evaluation was carried out on the basis of experimental data acquired on laboratory concrete test specimens, which contain inbuilt anomalies varying in shape, material and position. To achieve an optimal fusion of radar depth slices and thermographic phase contrast images along the depth axis, we derive sensitivity curves for both NDT methods and use the probability mass information to further improve the fusion results. Results show that the fuzzy c-means algorithm may contribute to an enhanced detection probability of defects below high density reinforcement. For defects with a concrete cover from 1.5 to 2 cm, the use of weighted clustering is particularly suggested. In general, complex defect types and shapes could be better resolved by using the Gustafson-Kessel algorithm or noise clustering. In addition, we demonstrate the application of the Dempster-Shafer theory to quantitatively evaluate the effectiveness of fused data on the basis of joint mass probability.

Abstract: Weigh-In-Motion (WIM) and Bridge Weigh-In-Motion (B-WIM) are systems that allow obtaining the axle weights of road vehicles in motion, at normal traffic speeds. While WIM employs sensors embedded in the road pavement, B-WIM use the strain recordings of a bridge to infer the traversing vehicle axle weights. Both systems have been heavily improved over the past decades, and commercial versions are currently in operation. The two main applications of these systems are: (1) to assess the traffic loading on the infrastructure, and (2) to enforce the maximum weight limits. This paper suggests a novel application of these two systems to identify changes in bridge stiffness. It requires the bridge to be instrumented with a B-WIM system and a WIM system nearby. The principle is to use both systems to evaluate the gross weight of vehicles passing over the bridge and correlate their predictions. Changes in correlation of the predicted axle weights over time will indicate either structural damage or faulty sensor. A finite element model of a coupled vehicle-bridge system with different damage scenarios is used to test the approach numerically. Vehicle mechanical properties and speeds are randomly sampled within a Monte Carlo simulation. Results show how correlation changes as damage increases and how this correlation can be employed as a damage indicator.

Abstract: In the present paper we have evaluated the seismic response of a Reinforced Concrete (RC) existing building located in an area classified as high seismicity zone and designed, in the past, only for gravitational loads. We have compared traditional and innovative steel braces for the seismic retrofitting by using a Displacement Based Approach. The innovative steel braces allow a significant improvement of the seismic behavior of the building by providing a better dissipation of the seismic input energy in the structure and thus ensuring a better performance of the RC structure in the elastoplastic range. Unlike the traditional retrofitting, the innovative strategy allows to significantly reduce the plasticization of the structural frame at the ultimate limit state, in order to minimize the post-seismic actions on the structure.

Abstract: Previous work by the authors have shown that the acceleration response of a damaged beam subject to a constant moving load can be assumed to be made up of three components: ‘dynamic’, ‘static’ and ‘damage’. Therefore, appropriate filtering of the acceleration signal can be used to highlight the ‘damage’ component and quantify its severity. This paper builds on these findings to examine if the same approach can be used to identify damage in the more realistic case of a bridge loaded by a sprung vehicle travelling on a road profile. The consideration of a road profile has the effect of exciting the vehicle modes of vibration which will corrupt the spectrum of bridge accelerations with road/vehicle frequencies. Some of these vehicle frequencies may be lower than the first frequency of the bridge and close to the frequency of the ‘damage’ component. In the latter, the vehicle frequencies are difficult to remove without also filtering part of the ‘damage’ component out. As a result, the approach is shown to perform best for low vehicle speeds.

Abstract: Port infrastructure is vulnerable to the corrosive marine environment leading to deterioration, loss of functionality, delays in shipping, major maintenance, remediation and, in the worst cases, loss of structural integrity and consequent replacement of the asset. Despite this, asset managers are unable to adequately plan for the prevention and minimisation of maintenance due to a lack of reliable predictive tools, that simulate the deterioration and a lack of a lifecycle model incorporating protection/maintenance options. This paper reports on a project to develop such a tool to facilitate the probabilistic modelling of the deterioration of reinforced concrete elements from construction through onset of corrosion to subsequent cracking and spalling. The Australian government funded project is in collaboration with several port authorities. The study has narrowed the key factors that have the most impact on the estimation of corrosion initiation and damage propagation allowing better definition of what data should be collected, how much and levels of accuracy required to ensure that predictive outputs obtained are as ‘robust’ as possible.

Abstract: This paper investigates the use of Moving Force Identification as a method of bridge damage detection. It identifies changes in the predicted axle force histories that occur as a result of loss in bridge element stiffness, i.e. as a result of bridge damage. A 2-dimensional Vehicle-Bridge Interaction model is used in numerical simulations to assess the effectiveness of the method in detecting changes in stiffness. Fleets of similar vehicles are simulated and the mean force pattern is used as the damage indicator. Results show that the method is more sensitive to damage than direct measurements of displacement. The paper also explores the use of the force history as an indicator of damage location.

Abstract: Fiber optic sensors become very popular for structural testing and monitoring in civil engineering nowadays, due to its advantage of high resolution and environment durability. In this paper, long-gauge fiber optic bragg grating sensors will be introduced. Structural damage detection stratagem using the micro-strain mode will be studied. Then its application to a structural testing and monitoring for a real long span truss bridge will be discussed in detail. In the testing, 23 long-gauge fiber optic bragg grating sensors were deployed on the mid span of the bridge. Testing were made under conditions either there is train on the bridge or no train on it. Corresponding dynamic characteristics were analyzed and discussed. Results of the testing show that long-gauge fiber optic sensors can work well for structural testing and also damage detection for truss bridges.

Abstract: This paper describes the design of a system to monitor floor vibrations in an office building and an analysis of several months worth of collected data. Floors of modern office buildings are prone to occupant-induced vibrations. The contributing factors include long spans, slender and flexible designs, use of lightweight materials and low damping. As a result, resonant frequencies often fall in the range easily excited by normal footfall loading, creating potential serviceability problems due to undesirable levels of vibrations. This study investigates in-situ performance of a non-composite timber-concrete floor located in a recently constructed innovative multi-storey office building. The floor monitoring system consists of several displacement transducers to measure long-term deformations due to timber and concrete creep and three accelerometers to measure responses to walking forces, the latter being the focus of this paper. Floor response is typically complex and multimodal and the optimal accelerometer locations were decided with the help of the effective independence-driving point residue (EfI-DPR) technique. A novel approach to the EfI-DPR method proposed here uses a combinatorial search algorithm that increases the chances of obtaining the globally optimal solution. Several months worth of data collected by the monitoring system were analyzed using available industry guidelines, including ISO2631-1:1997(E), ISO10137:2007(E) and SCI Publication P354. This enabled the evaluation of the floor performance under real operating conditions.