Papers by Author: Jin Ping Ou

Abstract: Prestress strands are the key parts of the prestressed structure, and the stress of the prestressed strands is one of the important indicators to assess prestress component security. Unfortunately, up to date, there are no qualified techniques to handle this issue due to that it is too hard for sensors to survive the harsh construction environments and the time-dependent service life of prestressed structures. In this paper, a novel smart steel strand based on the technique of GFRP-FBG rebar was introduced, and its sensing principle has also been given in details. The novel smart steel strand has been tested by serious experiments to research its mechanical and sensing properties. The monitoring results show that the mechanical properties of the smart strands are similar to ordinary strands, and its sensing properties include that distinguish-ability is less than 0.466% F•S, hysteresis less than 2.15% F•S, repeatability less than 1.32% F•S, linearity less than 0.86% F•S, and overall accuracy less than 2.67% F•S. Such kind of GFRP-FBG smart steel strand can be used for both structural and functional materials and applied in practical prestressed structure.

Abstract: The concept of the fiber reinforced polymer (FRP)-concrete composite design was exploited in a new type of bridge superstructure. The proposed FRP-concrete composite bridge superstructure is intended to have durable, structurally sound, and cost effective composite system that will take full advantage of the inherent and complementary properties of FRP material and concrete. As a trial case, a prototype bridge superstructure was designed as a simply supported single-span one-lane bridge with a span length of 10 m. The bridge superstructure consists of two bridge decks and each bridge deck is comprised of four FRP box sections combined with a thin layer of concrete in the compression zone. A test specimen, fabricated as a one-third scale model of the prototype bridge superstructure, was subjected to four-points loading to simulate the two heaviest axles of the Chinese design truck load. The test results indicate that the proposed bridge model meets the stiffness requirement and has significant reserve strength.

Abstract: This paper presents the analysis of strain time histories measured by structural health monitoring system. The main objective of this study is to prepare data for reliability estimation of main components as well as the entire structural system. The strain and corresponding temperature data is collected at the following stages: closure segment reconstruction stage and operating stage. The strain monitoring of the closure segment during the reconstruction stage provided valuable information on early-life strain development and reference characteristics for events such as post tensioning and temperature change. These lessons learnt from the reconstruction monitoring can be used for understanding subsequent bridge behavior, including damage detection and reference points of subsequent monitoring. Specially, the loading test results reveal the effectiveness and correctness of the strain acquiring system and provide evidence for reliable long-tem monitoring. Strain and temperature data have been recorded at sampling frequency of 62.5Hz since loading test, which would provide information linear stress-strain relationships. The long-term creep and shrinkage model were provided by Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culverts (JTG D62-2004). Through the statistical analysis of the online strain response, the probability model of long-term performance under environmental and random traffic loading are obtained which gives the potential of its application of reliability based assessment on cable stayed bridges where they evaluated the reliability of elements such as cables and stiffening girder.

Abstract: Acoustic emission (AE) test monitoring is an effective non-destructive technique. In the paper, a new damage assessing method which is damage acuteness index for AE signal of PZT patches based on fractal theory was proposed. The damage index was deduced by the character of signal analysed by fractal theory. It is deduced that both the curve length and the fractal dimension (FD) of signal are related with damage development. The AE test of Pseudo-static experiment of a concrete-filled GFRP tubes (CFFT) was performed for validation. The results show that the damage acuteness index can assess damage development process effectively. So the damage acuteness index is a promising method to apply in AE test monitoring.

Abstract: Based on the research achievements of the mechanical properties of concrete at uniaxial compression and steel at uniaxial tension after exposed to high temperatures, the axisymmetric- triaxial-compressive stress-strain relationships of concrete and multiaxial stress-strain relationships of steel after exposed to high temperatures was suggested. Based on continuum mechanics, the mechanical model of concentric cylinders of circular steel tube with concrete core of entire section loaded after exposed to high temperature was determined. By applying Elasto-Plastic Analysis Method, theoretical calculation formulas for composite elastic modulus and composite stress-strain relationships of concrete-filled circular steel tubular (CFST) stub columns were proposed and a FORTRAN program was developed and the load-axial strain relationships of CFST stub columns after exposed to high temperatures were analyzed. The analysis results were in reasonable agreement with the experiment ones from references.

Abstract: Shape memory alloy (SMA) has many potential applications as an actuator in smart material systems due to its abilities of shape memory, pseudo-elasticity, high damping and wear resistant. In this paper, a smart concrete beam has been developed by taking advantage of the shape memory effect of SMA and the characteristic of applying large forces on the resisting member in the transformation of SMA on heating. Deformation behavior and influence of factors on the deformation behavior of SAM smart concrete beam were investigated experimentally. Actuation mechanics of SMA was analyzed. Experimental results show that SMA wires significantly increase structural survivability and allow structural to recover from residual deformation by damaged earthquake and typhoon, and the crack almost closes completely after electrically heating the SMA wires. The number or areas of SMA wires has no influence on the tendency of deformation during loading and the tendency of reversion by heating. An increasing of the initial pre-strain of SMA wire can significantly improve the capacity of self-restoration of SMA concrete beams, but the steel main bars play a very negative role in reducing residual deformation.

Abstract: Smart concrete technology provides a new alternative way for health monitoring of reinforced concrete structures. In this paper, the piezoresistivity of two kinds of smart concrete filled with carbon black or carbon fiber was studied, and two types of embedded sensors were fabricated using the smart concrete with favorable piezoresistivity. The sensing performance, the measuring methods and the response to environmental temperature and humidity of embedded sensors were investigated. A compensation circuit was incorporated to reduce the effect of temperature and humidity on the output of embedded sensors. The sensors were embedded in concrete beams and columns to monitor the structural compressive strain under field conditions. Experimental results indicate that the embedded sensors fabricated using smart concrete filled with carbon black or carbon fiber feature favorable sensing performance (gauge factors are 55.28 and 138 respectively). The self-sensing concrete components embedded with these sensors can realize the monitoring of their local compressive strain. It therefore can be concluded that the prepared smart concrete and the developed embedded sensors have great potential to be used for health monitoring and damage assessment of concrete structures.

Abstract: A uniaxial experimental set-up was developed to evaluate the self-induced stresses, visco-elastic strains and cracking potential of concrete from the time of its placement. The totally restrained condition is achieved by keeping the length change within a threshold of 3μm. The temperature rise of the specimens can be controlled within 1.5
, by which the deformation because of temperature change due to cement hydration could be prevented. The tensile force required to compensate the shrinkage could be monitored and elastic strain and tensile creep can be calibrated without an obvious interference of temperature deformation. The preliminary results testified the workability of the system.

Abstract: Cement mortar of high damping ability has been maded by using styrene-acrylate emulsion as an admixture. The addition of styrene-acrylate emulsion causes the loss tangent of plain cement mortar to increase at all temperature (-30-30 °C) and frequencies (0.1-2.0 Hz), and the loss tangent increase is particularly large at 15-30 °C, even up to 0.25 at 30 °C and 0.5Hz due to the glass temperature of styrene-acrylate emulsion, although the storage modulus of cement mortar with this admixture decreases at all temperatures and frequencies, however, for the loss modulus, which serves as an comprehensive figure-of-merit for the vibration reduction ability, styrene-acrylate emulsion may dramatically increase it. The X-ray diffraction (XRD) and infrared (IR) spectrum analysis have provided evidence that styrene-acrylate decelerates the hydration of cement paste.