Key Engineering Materials Vols. 525-526

Abstract: Thinner and lighter members can be designed by utilizing the high stiffness and toughness, and high compressive strength of Ultra High Performance Concrete (UHPC), which reaches up to 180MPa. This high strength and ductile tensile behavior of UHPC makes it possible to design the web of the UHPC I Girder without conventional shear stirrups, which makes the UHPC I girder slender, light and economical. However, establishing shear design procedure for UHPC I girders without stirrups requires additional theoretical and experimental studies. This paper investigated shear behavior of UHPC I girder without shear stirrups. The test results show, in spite of no shear stirrups, test specimens have high ductility due to the bridging action of steel fibers against crack opening. UHPC I girders without shear stirrups tested show gradual increase of strength after initial cracking instead of brittle loss of strength as expected from the ordinary reinforced concrete I girders without stirrups. The decrease of the shear span-depth ratio increase the shear strength of the UHPC I girder without stirrups.

Abstract: In the application of Ultra High Performance Concrete (UHPC) to PSC girders by using the post-tensioning system, the high strength and ductility of UHPC in tension can be exploited to substitute the confined reinforcing bars which control the rupture around the anchorage device. The exploitation of such properties is expected to simplify the reinforcing details around the anchorage zone. Taking advantage of UHPC can downsize a cross section with the attributes of high compression and tensile strength. This paper reports the local behavior of UHPC anchor block under compression. Test specimens were made based on mix proportion of K-UHPC (KICT-Ultra High Performance Concrete) developed by the Korea Institute of Construction Technology (KICT). The performance of the anchor block was evaluated according to ETAG-013 (European Technical Agreement Guide No.13) of EOTA (European Organization for Technical Approvals). As the results of the experiment, it is found that the details and reinforcement of UHPC anchorage zone can be simplified with the interconnection effect and the high intensity of the matrix itself.

Abstract: A number of small mass and large mass impacts on a sensorised aircraft stiffened panel were numerically simulated. Sensor signals and the contact force history were recorded during each impact. A significant difference was noticed between the small mass and large mass impacts with respect to the contact force. To distinguish between these two types of impacts, the Fast Fourier Transform was performed on the sensor signals and a categorisation criterion was defined. Finally, two separate Artificial Neural Networks were trained to approximate the peak contact force for each type of impact. It was found that the performance of these ANNs were better than a single ANN trained for both small and large mass impacts.

Abstract: Numerical modelling of EMI for damage detection has been presented in this paper. The PZT model is validated against the published experimental result for free disk and tied to the structure. The numerical modelling of the PZT patch will result in the admittance measure of the structure. The imaginary part of the admittance measure is used for developing a self-diagnostic sensor system. The real part of the admittance measure was used to develop a damage detection algorithm. Damage detection using EMI method was successfully applied to a simple composite disk and a stiffened panel. The EMI method is suitable for short range damage detection in structural parts with limited or no access.

Abstract: Considering the background of vibration engineering of lining structure of subway tunnel with primary defects under moving train loading, and according to the measured information of a dynamic loading spectrum of subway in Beijing, dynamic response of the lining structure with differently primary defects caused by neighboring tunnel construction has been investigated for different cases including one-way and two-way trains in this paper. The results show that the curves of dynamic time history analysis are similar with each other for displacement and stress under different cases with differently primary defects. The peak value of displacement and stress under the case of two-way train is much larger than that under the case of one-way train, and the structure primarily depends on tensile strength of concrete in safety. Under the case of one-way train with primary defects would there be no defect by vibration loads.

Abstract: For a practical engineering in which the tunnel of Subway Line No.7 between Guangqumen outside Station and Shuangjing station is down through Shuangjing Station of existed Subway Line No.10, numerical simulations of construction process of the tunnel have been investigated by FLAC 3D software and compared with site monitoring data. The sedimentation curves of the earth's surface along the cross-sectional and longitudinal direction are obtained, which show that all results including numerical simulation and site monitoring are accord with the data from the Peck formula. At the same time according to numerical computation, some relations between width and depth of excavating a tunnel are discussed. All these have important significant to theoretical research and engineer practice of subway construction.

Abstract: A SMART Platform is developed based on sensor readings for Structural Health Monitoring of a stiffened composite panel. The platforms main function is divided into three categories: Passive sensing, Active sensing and Optimal sensor positioning. The platform has self-diagnostic capabilities, i.e. prior to its application the health of the sensors and their connection will be checked to avoid any false alarm. Passive sensing results in impact location and force magnitude detection. Active sensing is performed for damage detection. It results in detecting the damage location and severity. Finally the optimal sensor location can be provided given the number of sensors and probability of detection value. This platform is the first step in applying the developed SHM methodologies to real size structures in service load conditions.

Abstract: Microstructures in the weld heat affected zone (HAZ) can cause a decrease in fracture toughness, and evaluating the effect of microstructures on fracture toughness is helpful in understanding the cause of the fracture toughness decrease. In this study, micro-sized tensile specimens were sampled from base metal and HAZ, and the mechanical properties and fracture behaviours of different steel microstructures were directly investigated by micro-sized mechanical testing.

Abstract: Ceramic refractory materials initially contain a multitude of defects such as voids, microcracks, grain boundaries etc. Particularly being exposed to high temperatures above 1000 °C the macroscopic properties such as effective compliance, strength and lifetime are essentially determined by microscopic features of the material. The deformation process and failure mechanisms are going along with the creation of new microdefects as well as the growth and coalescence of cracks. A brittle material damage model for dynamic thermomechanical loading conditions is presented in this paper. Representative volume elements (RVE) include microcrack initiation and growth. The material laws are formulated on the continuum level using appropriate homogenisation methods. To demonstrate the potential of the numerical tools, two examples are presented which are taken from applications. Based on experiments, cyclic thermal shock tests at refractory plates are simulated by FEM. To quantify the thermal shock resistance of ceramics, experiments suggested by Hasselman are simulated numerically supplying a critical temperature slope.

Abstract: This study is related to the FRP-concrete composite bridge deck for cable-stayed bridges developed by the Korea Institute of Construction Technology since 2007. This deck disposes a FRP panel at the bottom and is orthotropic owing to its fabrication through pultrusion process. In the cable-stayed bridge applying precast deck, support conditions occur at the cross beam and edge girder. Therefore, need is to verify the performances in the longitudinal and transverse directions when applying the orthotropic deck to cable-stayed bridges. Accordingly, specimens enabling to verify the performance in each direction are fabricated and subject to structural performance test. Based on the test results, the serviceability and applicability of the FRP-concrete composite deck to cable-stayed bridges are evaluated.