Papers by Keyword: Cyclic

Abstract: Fiber Reinforced Cementitious Matrix (FRCM) composite materials represent one of the most interesting retrofitting methods for improving the out-of-plane flexural capacity of masonry walls. Despite their use is becoming more and more widespread, the actual knowledge about the out-of-plane behavior of FRCM-strengthened masonry panels needs further improvements, analyzing in particular the effectiveness of the reinforcement under cyclic loads. In this framework, an innovative experimental set-up, capable of applying a vertical axial load and cyclic out-of-plane horizontal forces on full-scale masonry panels, was used for testing walls retrofitted with glass, aramid-glass, basalt and steel fabrics. The presented experimental study is focused on the analysis of the effectiveness of the different FRCM systems, analyzing in detail failure modes, maximum capacity and the potential performance degradation of the strengthened panels under cyclic actions, providing also a useful comparison with the corresponding monotonic results.

Abstract: The introduction of wide range of novel raw materials and composites are tuning exceptionally the construction industry on its head. The recent research trends majorly intensified on hybrid concept using the varied materials collectively. This study primarily aims at experimentally investigating the response of concrete exterior beam column joint with Hybrid Reinforcement Technique (HRT) for reverse cyclic load conditions. The on-site fabricated, Hand Layup Carbon Fibre Reinforced Polymer (CFRP-HL) stirrups and the conventional steel main reinforcements form a hybrid reinforcement system in this study. The on-site constructed CFRP-HL reinforcement serves as a substitute for pre-fabricated CFRP rebars which has limitations and inflexibility in adapting the construction alterations. In total six types of specimens, a couple of test specimens are strengthened with HRT and another with external bond CFRP fibre wrap. In the remaining three specimens, one with non-conventional steel detailing and a couple of conventional joints that are designed according to IS 456:2000 and IS 13920:1993 respectively. In addition, the influence of varied spacing of stirrups in specimens is studied separately. Further, the test results on overall strength, stiffness, load deflection characteristics, dissipated energy and ductility of test specimens is evaluated and discussed. The use of CFRP-HL with steel as hybrid combination enables to comprehend the benefit from their distinctive characteristics. This proposal strongly improves the greater flexibility of using CFRP-HL in field as needed.

Abstract: The geosynthetic materials are extensively used in a wide range of applications in civil engineering. In this study, a nonwoven high strength geotextile which is generally utilized as a reinforcing material for earth structures and a ultrahigh molecular weight polyethylene (UHMWPE) geomembrane (generally used to seal the inner face of toxic liquid tanks against leakage) are used together beneath structures for seismic isolation purposes. The dynamic interface properties of the surface formed between these two materials have been tested on small scale models by shaking table tests. The results were impressive such that the accelerations transferred to the superstructure were significantly reduced. Also, it was observed that the materials used during the research had almost no abrasion at the end of a series of experiments which revealed that the tested materials could be used for repetitive dynamic loadings.

Abstract: The steam generators at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK are potentially life-limiting components. Enhancing the capability to monitor the steam generators has been identified as having the potential to provide key evidence in justifying the extension of the generating lifetime of the stations. It has been proposed to install new temperature measuring instrumentation to monitor reactor gas temperature and to provide additional data regarding steam generator operating conditions. The modification will be to introduce thermocouples to the bore of an intact steam generator tube to facilitate temperature measurement at or near to the locations of interest. The modified steam generator tube will be sealed at the feed header upstand. Between the upper surface of the superheater header tubeplate and the wall of the superheater header, the thermocouple bundle and sheath will be contained within a rigid stainless steel guide tube. The guide tube will be attached at both ends by welds, each forming a pressure boundary. At the tubeplate a weld will separate the bore of the sealed guide tube from the steam space within the superheater header; a weld between the guide tube and the superheater header will separate the steam space within the superheater header from atmosphere outside the header. In order to obtain a better design, three 3-dimentional finite element models have been created using ABAQUS. A series of cyclic pressure, and start-up and shutdown thermal transient stress analyses have been carried out to provide stress values for structural integrity assessments to be conducted using ASME III, Subsection NH and R5.

Abstract: The optical fiber has been extensively used as a sensor in some special fields. Because the optical fiber exists crackles itself and also produce the micro-crack as well as local damage, the fatigue behavior of the optical fiber become the main problem we care about. This paper presents the experimental study on the fatigue performance of bare fiber under static, dynamic and cyclic load. The corresponding fatigue life index (Stress corrosion index) n can be obtained, which are 17.14, 11.83 and 5.88, respectively. The experiment data reveal that fatigue life index is related to loading mode and is treated as the indicator of crack propagation resistance of materials. Because dynamic and cyclic loads can induce additional damage, the fatigue life declines dramatically under the same stress levels.

Abstract: The current theory of elasticity persisted in the standpoint that normal stress exists in pure bending and shearing stress exists in pure torsion, which has been negated by the non-zero point force moment elasticity theory .The mentioned new theory proved that bending point moment exists in pure bending and torsional point moment exists in pure torsion, which debunk the current theory of elasticity that the limit moment acting on the unit area is zero. As a consequence, the causation of fatigue should be revised as point moment instead of stress. By using theory of stress and the new theory to analyze fatigue of non-slender rod, safety factor worked out by the former one is much bigger, which suggests that theory of stress cannot ensure safety. Undoubtedly, that is the fundamental causation of frequent occurrence of fatigue rupture. Thus, the new theory is of great significance in the prevention of unexpected fatigue rupture in the field of aerospace, navigation, transportation and mechanical engineering, etc.

Abstract: Aim of this article is in presentation of results of static and cyclic tests of round timber bolted joints with inserted steel plates. At first, timber specimens were tested without reinforcement. Based on static tests results, mechanical reinforcement methods were proposed and tested: using modified washers and boost with screws. Rate of improvement in tensile strength was established for used reinforcement method. Static tests in tension were carried out on pressure machine EU 100 in laboratory of the Faculty of Civil Engineering VŠB-TU Ostrava. Round timber joints multi cyclical dynamic (fatigue) tests in tension were made in laboratory of ITAM AS CR Prague and in TRI Žilina.

Abstract: A generic heat generation equation with the heat transfer has been developed for pure mechanical loading. Frequency dependent temperature field can be obtained on a specimen subjected to pure mechanical, cyclic or non-cyclic loading. Results have been compared with the literature and a good agreement has been found with the experimental results. Applications and effectiveness of the equation is highlighted in predicting the fatigue damage in case of high cyclic or vibration fatigue.

Abstract: The paper focuses on the development of a cyclic plasticity model based on the fuzzy set theory, which is implemented as a computational tool in order to simplify the computer programming of the constitutive driver. The constitutive model is a rate independent elasto-plastic model which is capable of describing repeated load cycles, dilatancy, material memory, and critical state soil mechanics features. Also, with the aid of membership function, the validity of the constitutive model is enhanced by comparing the theoretical output with a set of experimental data obtained from a variety of cyclic triaxial tests of loose sand.

Abstract: To explore the deposition mechanism of check dam and provide the basis for layout of dam system, with tracing technology of caesium-137 and local rainfall data, the siltation time of each cyclic in the profile of south ditch check dam are confirmed based on the rule of heavy rain on large sand. Then regression analysis of sediment volume with the four indexes of erosive rainfall (R, I30, P and I) are made, the results show the first three indicators are main factors causing soil erosion. Furthermore, the model predicting sediment yield of the watershed is made by multiple regression analysis of sediment deposition with the three main factors. Finally, the neural network of RBF and BP are respectively applied regarding the three main indexes as input vectors to predict siltation and fit with actual value to testify what the model built is right.