Jun Deng

Damage detection with streamlined structural health monitoring data.

The huge amounts of sensor data generated by large scale sensor networks in on-line structural health monitoring (SHM) systems often overwhelms the systems’ capacity for data transmission and analysis. This paper presents a new concept for an integrated SHM system in which a streamlined data flow is used as a unifying thread to integrate the individual components of on-line SHM systems. Such an integrated SHM system has a few desirable functionalities including embedded sensor data compression, interactive sensor data retrieval, and structural knowledge discovery, which aim to enhance the reliability, efficiency, and robustness of on-line SHM systems. Adoption of this new concept will enable the design of an on-line SHM system with more uniform data generation and data handling capacity for its subsystems. To examine this concept in the context of vibration-based SHM systems, real sensor data from an on-line SHM system comprising a scaled steel bridge structure and an on-line data acquisition system with remote data access was used in this study. Vibration test results clearly demonstrated the prominent performance characteristics of the proposed integrated SHM system including rapid data access, interactive data retrieval and knowledge discovery of structural conditions on a global level.

Numerical study on notched steel plate with center hole strengthened by CFRP

Abstract Steel members could be damaged and fail to fulfill the requirements of safety after long-term service. Carbon fiber reinforced polymer (CFRP) strengthening turns out to be an excellent method for prolonging its service life. The strengthening technique has been extensively studied in recent decades, however, few researchers concerned about the simulation of steel plates with center hole strengthened by CFRP. Therefore, its mechanical performance was investigated numerically in this study. The numerical results were compared with the experimental results and an acceptable agreement was reached, which verified the validity of the numerical model. A parametric study was conducted, in which the interfacial stress distribution change with CFRP elastic modulus, thickness and strengthening form was analyzed. For fully covered CFRP strengthening, increasing of elastic modulus and thickness of CFRP plates can enhance the stiffness of steel plates, however, it has insignificant effect on debonding load and obvious decrease on ultimate load. While the partially covered CFRP bonding strengthening can also upgrade the stiffness with CFRP elastic modulus and thickness, the effect to both of debonding load and ultimate load is minimal.

Condition Evaluation of Existing Long-Span Bridges Using Fuzzy Based Analytic Hierarchy Process

The existing long-span bridges deteriorate with time due to fatigue, overloading, corrosion and environmental effects. To date, condition evaluation of the existing long-span bridges is important to carrying out the activities related to maintenance, rehabilitation and replacement of bridges. In this paper, a methodology was developed to evaluate the condition of the existing long-span bridges. The analytic hierarchy process was combined with the fuzzy synthesis. A procedure is given for condition rating of the existing long-span bridges as well. A bridge as the example is evaluated by this method and the results show that the damage of the bridge is marginal, which is same as the conclusion obtained from the traditional methods.

Main Crack Propagation Behaviour of RC Beams Strengthened with CFRP under Fatigue Load

The fatigue performance and durability of the reinforced concrete (RC) beams strengthened with fibre reinforced polymer (FRP) laminates is an advanced research topic in civil engineering. The crack propagation life is the dominant part of the whole fatigue life of the cracked RC members strengthened with FRP laminates under cyclic loads. In this paper, a theoretical and experimental study was conducted to investigate the rule of the fatigue crack propagation of the RC beams strengthened with carbon FRP (CFRP) under constant cyclic bending load. A total of 5 RC beams with sizes 1850×100×200mm strengthened with CFRP were tested. The results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation (Phase I), stable propagation and then rest (Phase II) and unstable propagation (Phase III). In accordance with Paris-Erdogan Law, a semi-empirical equation was developed to predict the crack propagation rate. The empirical coefficients of the equation were obtained from the fatigue test results. To validate this equation, the predicted fatigue life of crack propagation calculated by it is compared with the data obtained from tests. It shows the agreement is good.

Test Methods for Mechanical Properties of Structural Adhesives

One of the greatest drawbacks to predicting the behaviour of bonded joints has been the lack of reliable data on the mechanical properties of adhesives. In this study, methods for determining mechanical properties of structural adhesive were discussed. The Young’s modulus, Poisson’s ratio and tensile strength of the adhesive were tested by dogbone specimens (bulk form) and butt joint specimens (in situ form). The shear modulus and shear strength were test by V-notched specimens (bulk form) and thick adherend lap-shear (TALS) joint specimens (in situ form). The test results show that the elastic modulus provided by the manufacturer is too low, the dogbone specimen is better than the butt joint specimen to test the tensile strength and elastic modulus and the TALS joint specimen is better than the V-notched specimen to test the shear strength.

Fibre Reinforced Polymer Composites for Structural Applications in Construction

In recent years, advanced fibre reinforced polymer (FRP) composites have become increasingly popular following the rapid growth in structural applications in construction around the world. These high-performance materials have been utilized in construction both for new structures and for strengthening/rehabilitation of existing buildings and bridges. Despite their widespread use, their full potential has still not been realized because of a number of fundamental concerns including high material costs, durability issues, bonding integrity, long-term interaction between loading and damage, and so forth.This special issue is aimed at providing a platform for the dissemination and discussion of recent research and achievements which address the issues on this topic from the theoretical and practical viewpoints. A total of 13 original research papers were published in this special issue. These papers deal with materials and products, bond behavior, strengthening of concrete structures, and durability. Six papers focus on the mechanical and durability performances of FRP materials and products including BFRP bars, GFRP bars, steel-FRP bars, BFRPmesh, GFRP sheets, and basalt particle-filled SMC composites. Three papers report investigations on bond behavior of both FRP-concrete and FRP-steel after environmental exposure. Two more papers deal with prestressing systems designed to strengthen reinforced concrete beams and concrete-filled steel tubes and especially the prestress loss and bearing capacity. Theoretical and experimental studies on the durability behavior of FRP strengthened reinforced concrete beams subjected to fatigue loading and hygrothermal environment are reported in two papers as well. These recent theoretical and experimental investigations that have been disseminated in this special issue address some critical fundamental issues, especially the long-term performance of both the FRP materials and strengthened structures. We expect that this special issue will be of interest to both researchers and engineers and contribute toward the developments in FRP applications in construction.

Effects of Locations of Adhesive Hollows on Interfacial Stress

Fiber Reinforced Polymer (FRP) has been effectively used for strengthening concrete beams. In this study, nonlinear finite element (FE) model of the beam strengthened with CFRP is established to analyze the debonding failure caused by the adhesive hollow defects. The constitutive relationship of the adhesive layer in the FE models is similar to Monti’s bi-linear mode. Three different locations of the hollows are considered in the FE models. The principal stresses in the concrete, the debonding stresses in the adhesive and the stress in CFRP are calculated. The results show that the effect of the locations of the hollow is marginal on the principal stresses in the concrete. When the hollow appears close to the interfacial end, the debonding stresses in the adhesive and the shear stress in the CFRP are significant, which easily causes the debonding failure.

Effect of Crack on Interfacial Stresses of RC Beam Strengthened with CFRP

External bonding of fiber reinforced polymer (FRP) plates or sheets, because of their advantages, such as high strength to weight ratio and good resistance to corrosion, has become a popular technique for the strengthening and upgrading of structurally inadequate or damaged reinforced concrete (RC) structures. Interface debonding failure is one of the most common failure modes of the FRP strengthened RC structures. In this paper, the damaged concrete constitutive model is established and the effects of crack on the interfacial stresses of RC beam strengthened with CFRP are investigated. Longitudinal stress in the CFRP, shear stress in the adhesive layer and the first principal stress in the concrete at the crack tips of the retrofitted RC beams with cracks at different locations are analyzed. The results show that when cracks locate at the loading position, the longitudinal stress in the CFRP is the largest and the tensile failure of the CFRP is the most likely occurred.

Risk Consequence Assessment of Existing Bridges Using Fuzzy Based Analytic Hierarchy Process

The assessment of the risk probability and risk consequence of existing long-span bridges has become a focus in both research and engineering applications. In this paper, a process to assess the risk consequence of existing long-span bridges is developed. The analytic hierarchy process was combined with the fuzzy synthesis. In accordance with the features of existing long-span bridges, risk consequences are classified and the model of the risk consequence is simulated. A bridge as the example is evaluated by this process and the results show that the risk consequence of the bridge is negligible. Combining the risk probability and risk consequence gives the comprehensive risk of this bridge is negligible.

Nonlinear Numerical Optimization Design Applied to Wall-Thickness of Welding T Shaped Connecting HDPE Tube

There are two reasons to enlarge the thickness of welding HDPE tri-branch tube. Firstly, welding weakens the HDPE material properties. Secondly, stress concentration occurs at the joint of tri-branch tube. The material properties of HDPE and the tensile strength of welding HDPE were tested. Based on the test results, the wall-thickness of HDPE tri-branch tube was investigated by numerical optimization design with particle swarm optimization (PSO). Two material constitutive models of elasto-palstic and Ramberg-Osgood for HDPE are adopted in FEM. Some valuable conclusions of pipeline design are concluded by the distribution of stress contour curves and optimization curves of welding joint of HDPE tri-branch tube.