Home About us Contact
|
Home About us Contact | ||
|
|
||
Loading Tests (loading + test)
Selected AbstractsDamaging properties of ground motions and prediction of maximum response of structures based on momentary energy responseEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2002Norio Hori Abstract Dynamic damaging potential of ground motions must be evaluated by the response behaviour of structures, and it is necessary to indicate what properties of ground motions are most appropriate for evaluation. For that purpose, the behaviour of energy input process and hysteretic energy dissipation are investigated in this study. It is found that the momentary input energy that is an index for the intensity of input energy is related to the characteristics of earthquakes such as cyclic or impulsive, and to the response displacement of structures immediately. On the basis of these results, a procedure is proposed to predict inelastic response displacement of structures by corresponding earthquake input energy to structural dissipated damping and hysteretic energy. In this procedure the earthquake response of structures is recognized as an input and dissipation process of energy, and therefore structural properties and damaging properties of ground motions can be taken into account more generally. Lastly, the studies of the pseudodynamic loading test of reinforced concrete structure specimens subjected to ground motions with different time duration are shown. The purpose of this test is to estimate the damaging properties of ground motions and the accuracy of the proposed prediction procedure. Copyright © 2002 John Wiley & Sons, Ltd. [source] Relations between load and settlement of circular foundations on or in a dense sand expressed by a function of diameter and depthINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2005Hiroaki Nagaoka Abstract When load acts on a circular foundation on or in a dense sand, average contact pressure on the lower surface of the foundation is q and settlement of the foundation is s. Diameter and depth of the foundation are B and Df. When the sand, B and Df are given, we can know the relation between q and s/B by, e.g. a loading test, i.e. the relation is determined by B and Df for the sand. Using the results of numerical analyses, we express a relation between q and s/B up to s=0.1B by functions of a single variable which is a linear combination of B and Df. Consequently when two foundations have different B's and different Df's but have the same value of the variable, the relations are the same. Then we examine whether the functions can express the results of eleven tests of model foundations of wide range of B and/or Df. In all the tests, the relations are expressed with sufficient accuracy. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Beneficial Effect of Propolis on Fat Accumulation and Lipid Metabolism in Rats Fed a High-Fat DietJOURNAL OF FOOD SCIENCE, Issue 5 2009I. Ichi ABSTRACT:, This study examined whether propolis, which had many biological activities, affected body fat and lipid metabolism. Four-week-old Wistar rats were fed a control or propolis diet for 8 wk. The control group was fed a high-fat diet, the low and the high group were fed a high-fat diet supplemented with 0.5% (w/w) and 0.05% (w/w) propolis, respectively. The weight of total white adipose tissue of the high group was lower than that of the control group. The level of PPAR, protein in the adipose tissues of the high group was significantly lower than that of the control group. In plasma and the liver, the high group showed a significantly reduced level of cholesterol and triglyceride compared to the control group. The liver PPAR, protein level of the high group was significantly higher than that of the control group. The liver HMG-CoA reductase protein in the high group was also significantly lower than that in the control group. Results from rats on an olive oil loading test were used to investigate whether propolis inhibited triglyceride absorption. The serum triglyceride level of the group, which received propolis corresponding to the daily dose of the high group, was significantly lower than that of the control group. It is possible that the administration of propolis improves the accumulation of body fat and dyslipidemia via the change of the expression of proteins involved in adipose depot and lipid metabolism. [source] Bonding strength between a hard chairside reline resin and a denture base material as influenced by surface treatmentJOURNAL OF ORAL REHABILITATION, Issue 12 2001C. R. Leles Direct relining of dentures made with hard chairside reline resins is faster than laboratory-processed reline systems and the patient is not without the prosthesis for the time necessary to perform the laboratory procedures. However, a weak bond between the autopolymerizing acrylic reline resins and the denture base material has been observed. This study evaluated the effect of six different surface treatments on the bond strength between a hard chairside reline acrylic resin and a heat-cured acrylic resin. Specimens of the heat-cured acrylic resin were divided into seven groups. One of these groups remained intact. In the other groups, a 10-mm square section was removed from the centre of each specimen. The bonding surfaces were then treated with (i) methyl methacrylate monomer, (ii) isobutyl methacrylate monomer, (iii) chloroform, (iv) acetone, (v) experimental adhesive and (vi) no surface treatment , control group. Kooliner acrylic resin was packed into the square sections and polymerized. The bonding strength was evaluated by a three-point loading test. The results were submitted to one-way analysis of variance (ANOVA) followed by a Tukey multiple range test at a 5% level of significance. No significant difference was found between the surface treatment with Lucitone 550 monomer or chloroform, but both were stronger than the majority of the other groups. The bond strength provided by all the surface treatments was lower than that of the intact heat-cured resin. [source] PREDICTION OF MECHANICAL PROPERTIES OF CUMIN SEED USING ARTIFICIAL NEURAL NETWORKSJOURNAL OF TEXTURE STUDIES, Issue 1 2010M.H. SAIEDIRAD ABSTRACT In this paper, two artificial neural networks (ANNs) are applied to acquire the relationship between the mechanical properties and moisture content of cumin seed, using the data of quasi-static loading test. In establishing these relationship, the moisture content, seed size, loading rate and seed orientation were taken as the inputs of both models. The force and energy required for fracturing of cumin seed, under quasi-static loading were taken as the outputs of two models. The activation function in the output layer of models obeyed a linear output, whereas the activation function in the hidden layers were in the form of a sigmoid function. Adjusting ANN parameters such as learning rate and number of neurons and hidden layers affected the accuracy of force and energy prediction. Comparison of the predicted and experimented data showed that the ANN models used to predict the relationships of mechanical properties of cumin seed have a good learning precision and good generalization, because the root mean square errors of the predicated data by ANNs were rather low (4.6 and 7.7% for the force and energy, respectively). PRACTICAL APPLICATIONS Cumin seed is generally used as a food additive in the form of powder for imparting flavor to different food preparations and for a variety of medicinal properties. Physical properties of cumin seeds are essential for the design of equipment for handling, harvesting, aeration, drying, storing, grinding and processing. For powder preparation especially the fracture behavior of the seeds are essential. These properties are affected by numerous factors such as size, form and moisture content of the grain and deformation speed. A neural network model was developed that can be used to predict the relationships of mechanical properties. Artificial neural network models are powerful empirical models approach, which can be compared with mathematical models. [source] Health Monitoring of Rehabilitated Concrete Bridges Using Distributed Optical Fiber SensingCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2006Wei Zhang As newly developed techniques, distributed optical fiber sensing (DOFS) have gradually played a prominent role in structural health monitoring for the last decade. This article focuses on the employment of two types of DOFS, namely fiber Bragg grating (FBG) and Brillouin optical time domain reflectometry (BOTDR), into an integrated HMS for rehabilitated RC girder bridges by means of a series of static and dynamic loading tests to a simply supported RC T-beam strengthened by externally post-tensioned aramid fiber reinforced polymer (AFRP) tendons. Before the loading tests, a calibration test for FBG and another one for BOTDR were implemented to, respectively, obtain good linearity for both of them. Monitoring data were collected in real time during the process of external strengthening, static loading, and dynamic loading, respectively, all of which well identified the relevant structural state. The beam was finally vibrated for 2 million cycles and then loaded monotonously to failure. Based on the bending strength of externally prestressed members, ultimate values for the test specimen were numerically computed via a newly developed simplified model, which satisfactorily predicted the ultimate structural state of the beam. And then the alert values were adopted to compare with the monitoring results for safety alarm. The investigation results show a great deal of applicability for the integrated SHM by using both DOFS in rehabilitated concrete bridges strengthened by external prestressing. [source] A mechanical model for elastomeric seismic isolation bearings including the influence of axial loadEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2009Sachie Yamamoto Abstract For the purpose of predicting the large-displacement response of seismically isolated buildings, an analytical model for elastomeric isolation bearings is proposed. The model comprises shear and axial springs and a series of axial springs at the top and bottom boundaries. The properties of elastomeric bearings vary with the imposed vertical load. At large shear deformations, elastomeric bearings exhibit stiffening behavior under low axial stress and buckling under high axial stress. These properties depend on the interaction between the shear and axial forces. The proposed model includes interaction between shear and axial forces, nonlinear hysteresis, and dependence on axial stress. To confirm the validity of the model, analyses are performed for actual static loading tests of lead,rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Seismic response analyses with the new model are also conducted to demonstrate the behavior of isolated buildings under severe earthquake excitations. The results obtained from the analyses with the new model differ in some cases from those given by existing models. Copyright © 2008 John Wiley & Sons, Ltd. [source] Cyclic behavior of laterally loaded concrete piles embedded into cohesive soilEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2008Rabin Tuladhar Abstract Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full-scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300,mm and a thickness of 60,mm. The test piles were 26,m long. Three-dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load-carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil. Copyright © 2007 John Wiley & Sons, Ltd. [source] Cyclic tests on steel and concrete-filled tube frames with Slit WallsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2007Toko Hitaka Abstract Cyclic loading tests were performed on three one-storey steel frames and four three-storey concrete-filled tube (CFT) moment frames reinforced with a new type of earthquake-resisting element consisting of a steel plate shear wall with vertical slits. In this shear wall system, the steel plate segments between the slits behave as a series of flexural links, which provide fairly ductile response without the need for heavy stiffening of the wall. The steel shear walls and the moment frames behaved in a ductile manner up to more than 4% drift without abrupt strength degradation or loss of axial resistance. Results of these tests and complementary analysis provide a basis for an equivalent brace model to be employed in commercially available frame analysis programs. Test and analytical results suggest that the horizontal force is carried by the bolts in the middle portion of the wall,frame connection, while the vertical forces coupled with the moment in the connection are resisted by the bolts in the edge portion of the connection, for which the friction bolts in the connection should be designed. When sufficient transverse stiffening is provided, full plastic strength and non-degrading hysteretic behaviour can be achieved for this new type of shear wall. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of displacement coefficient method and capacity spectrum method with experimental results of RC columnsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2004Yu-Yuan Lin Abstract For the performance-based seismic design of buildings, both the displacement coefficient method used by FEMA-273 and the capacity spectrum method adopted by ATC-40 are non-linear static procedures. The pushover curves of structures need to be established during processing of these two methods. They are applied to evaluation and rehabilitation of existing structures. This paper is concerned with experimental studies on the accuracy of both methods. Through carrying out the pseudo-dynamic tests, cyclic loading tests and pushover tests on three reinforced concrete (RC) columns, the maximum inelastic deformation demands (target displacements) determined by the coefficient method of FEMA-273 and the capacity spectrum method of ATC-40 are compared. In addition, a modified capacity spectrum method which is based on the use of inelastic design response spectra is also included in this study. It is shown from the test specimens that the coefficient method overestimates the peak test displacements with an average error of +28% while the capacity spectrum method underestimates them with an average error of -20%. If the Kowalsky hysteretic damping model is used in the capacity spectrum method instead of the original damping model, the average errors become -11% by ignoring the effect of stiffness degrading and -1.2% by slightly including the effect of stiffness degrading. Furthermore, if the Newmark,Hall inelastic design spectrum is implemented in the capacity spectrum method instead of the elastic design spectrum, the average error decreases to -6.6% which undervalues, but is close to, the experimental results. Copyright © 2003 John Wiley & Sons, Ltd. [source] A mathematical hysteretic model for elastomeric isolation bearingsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2002J. S. Hwang Abstract An analytical model for high damping elastomeric isolation bearings is presented in this paper. The model is used to describe mathematically the damping force and restoring force of the rubber material and bearing. Ten parameters to be identified from cyclic loading tests are included in the model. The sensitivity of the ten parameters in affecting the model is examined. These ten parameters are functions of a number of influence factors on the elastomer such as the rubber compound, Mullins effect, scragging effect, frequency, temperature and axial load. In this study, however, only the Mullins effect, scragging effect, frequency and temperature are investigated. Both material tests and shaking table tests were performed to validate the proposed model. Based on the comparison between the experimental and the analytical results, it is found that the proposed analytical model is capable of predicting the shear force,displacement hysteresis very accurately for both rubber material and bearing under cyclic loading reversals. The seismic response time histories of the bearing can also be captured, using the proposed analytical model, with a practically acceptable precision. Copyright © 2002 John Wiley & Sons, Ltd. [source] Variable amplitude loading in the very high-cycle fatigue regimeFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8-9 2002S. E. STANZL-TSCHEGG ABSTRACT Ultrasonic fatigue testing is appropriate to perform random loading tests in the regime of very high numbers of cycles. It has been shown that neither an endurance limit nor a threshold stress intensity exists under loading with randomly varying amplitudes even for materials that do show these limits under constant amplitude loading conditions. The technical features of the ultrasonic testing technique in order to perform random fatigue tests are shortly described. Endurance tests were performed on smooth specimens of AlSi7Mg (A356.0) aluminium alloy and on notched AISI 4142 and C45 steel specimens. The previous studies of crack propagation and threshold behaviour on AISI 420 ferritic chromium steel and GGG 100-B cast iron are included. Experimental results on lifetime and fatigue crack growth measurements under randomly varying amplitudes, as well as lifetime predictions, based on constant amplitude measurements and damage accumulation calculations are reported. [source] Sensing of Damage Mechanisms in Fiber-Reinforced Composites under Cyclic Loading using Carbon NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Limin Gao Abstract The expanded use of advanced fiber-reinforced composites in structural applications has brought attention to the need to monitor the health of these structures. It has been established that adding carbon nanotubes to fiber-reinforced composites is a promising way to detect the formation of microscale damage. Because carbon nanotubes are three orders of magnitude smaller than traditional advanced fibers, it is possible for nanotubes to form an electrically conductive network in the polymer matrix surrounding the fibers. In this work, multi-walled carbon nanotubes are dispersed into epoxy and infused into a glass-fiber preform to form a network of in situ sensors. The resistance of the cross-ply composite is measured in real-time during incremental cyclic tensile loading tests to evaluate the damage evolution and failure mechanisms in the composite. Edge replication is conducted to evaluate the crack density after each cycle, and optical microscopy is utilized to study the crack mode and growth. The evolution of damage can be clearly identified through the damaged resistance parameter. Through analyzing the damaged resistance response curves with measurements of transverse crack density and strain, the transition between different failure modes can be identified. It is demonstrated that the integration of an electrically conducting network of carbon nanotubes in a glass fiber composite adds unique damage-sensing functionality that can be utilized to track the nature and extent of microstructural damage in fiber composites. [source] A note on formulas for localized failure of frictional materials in compression and biaxial loading modesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2001Matthias Lambrecht Abstract The paper investigates aspects of the localization analysis of frictional materials. We derive closed formulas and diagrams for the inclination angle of critical discontinuity surfaces which develop in homogeneous compression and biaxial loading tests. The localization analysis is based on a Drucker,Prager-type elastoplastic hardening model for non-associated plastic flow at small strains, which we represent in spectral form. For this type of constitutive model, general analytical formulas for the so-called critical hardening modulus and the inclination angle of critical discontinuity surfaces are derived for the plane strain case. The subsequent treatment then specializes these formulas for the analysis of compression and biaxial loading modes. The key contribution here is a detailed analysis of plane strain deformation modes where the localized failure occurs after subsequent plastic flow. The derived formulas and diagrams can be applied to the checking of an accompanying localization analysis of frictional materials in finite-element computations. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||||||||