Applied Mechanics and Materials Vols. 744-746

Abstract: In this paper, a free vibration analysis of two types of conical springs is presented by using ANSYS software. The APDL programming is employed for the finite element modeling. Two types of conical springs, such as constant pitch and constant pitch angle, which are not distinguished in previous researches, are investigated. The results suggest that the two types of conical springs should be distinguishable in the dynamic applications.

Abstract: This paper presents the results of an experimental study on the influence of concrete age on the compressive behavior of fiber reinforced polymer (FRP)-confined normal-strength (NSC) and high-strength concrete (HSC). The first part of the paper presents the results of 18 FRP-confined and 18 unconfined concrete specimens tested at 7 and 28 days. To extend the investigation with specimens with concrete ages up to 900 days, existing test results of FRP-confined concrete was assembled from the literature. Based on observations from both short-and long-term influences of concrete age on compressive behavior of FRP-confined concrete, a number of important findings were drawn and are presented in the second part of the paper. It was observed that, at a same level of FRP confinement and unconfined concrete strength, the stress-strain behavior of FRP-confined concrete changes with concrete age. This difference is particularly pronounced at the transition zone of the stress-strain curves. It is found that, in the short-term, the ultimate condition of FRP-confined concrete is not significantly affected by the age of concrete. However, in the long-term, slight decreases in the compressive strength and the ultimate axial strain are observed with an increase in concrete age.

Abstract: The compressive strengths of the concrete cubes added fly ash were increased 53.2%, the density was almost unchanged, but the water absorption was decreased 30%. The concrete permeability coefficient and chloride diffusion coefficient added fly ash were lower than the common concrete at all ages. The concrete specimens corrosion potential added fly ash were higher than-300mV, while common concrete almost were lower than-500mV. Corrosion probability was small and there was no crack and corrosion pot on the surface of the specimens until 82 times cycles in wet-dry chlorides solution. Fly ash in concrete has obvious act for improving concrete behavior in protecting the embedded steel in corrosion.

Abstract: This paper presents an experimental investigation on the influence of prestress on axial compressive behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs). A total of 12 aramid FRP- (AFRP) confined high-strength concrete (HSC) specimens with circular cross-sections were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and their unconfined concrete strengths were approximately 100 to 110 MPa. The influence of FRP prestress was examined by applying 3 different levels of lateral prestress ranging from 4.29 to 7.27 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of non-prestressed specimens. On the other hand, the influence of prestress on axial strain was found to be minimal, with prestressed specimens displaying a slight decrease in ultimate strain, compared to their non-prestressed counterparts. The results also indicate that prestressing the AFRP shell prevents the sudden drop in strength, typically observed in FRP-confined HSC specimens, that initiates at the transition point which connects the first and second branches of the stress-strain curves.

Abstract: For the low power wind turbine, the tower and the generator unit is easy to produce resonance, which will result in bigger amplitude. In this paper, as an example, the authors establish a finite element model for modal analysis by a 55kw direct-drive permanent-magnet generator, to confirm its inherent frequency and vibration mode. Horizontal amplitude on the top of the tower can be received under different external excitation frequency. The results correspond to the codes very well and can provide effective reference data for the design of the wind turbine tower.

Abstract: In order to determine the cement grouting compactness, a new method is proposed for echo signals processing. A model containing four different defects is constructed and simulated using finite element method (FEM). The collected impact-echo signals are processed by systemic de-convolution. It is found that the surface depth of the defect is directly related to the beginning time of the head wave after de-convolution. Using this method, the defect position and dimension can be obtained.

Abstract: According to the element-length errors inevitably existing in the real cable-bar tensile structures, numerical analysis on the element-length error sensitivity was firstly carried out with the help of ANSYS software, where the element length change was simulated by imposing the temperature affection. Then a cable-bar tensile structure model with the diameter of 5.0m was designed and fabricated. The element-length errors were simulated by adjusting the element length and each member in one unit was elongated 3mm respectively to explore the error sensitivity of each kind of element. The numerical analysis and experimental results indicated that different element has different error sensitivity. The error sensitivity of the hoop cables was the most sensitive, the ridge cables and diagonal cables were lower and the struts were the lowest. The experimental results performed almost consistent with the analytical results, which indicated that the proposed error sensitivity analysis method is accurate and the design of the model is effective.

Abstract: This paper deals with the numerical analysis of damage to a precast reinforced concrete structural system caused by the effects of temperature changes. Specifically, the analysis aims to examine the failures in the contact place between the TT panel of the roof structure and the girder. A computer model was created based on the actual construction of the occurring disorders. Temperature changes, which act on the structure, were identified by measurements taken over a long period. The structure was modeled using GiD 11 software and calculated using the ATENA WIN program. The results of the numerical analysis and the manifestations of damage to the actual construction were mutually compared.

Abstract: Carbon Fiber Reinforced Plastic (CFRP) has been widely used in large-scale concrete infrastructure’s reinforcement and renovation because of its low weight and high strength, which promotes CFRP application in the field of civil engineering. This paper two aged beams reinforced by CFRP sheet was loaded to failure in four-point bending by laboratory experiment. Then the numerical model was built to simulate the destruction process and compared with test results. Based on the studying of this paper, the changing law of beam’s stress, ultimate bearing capacity growth, failure mode and cracking propagation was investigated during the loading process. The research has guiding significance for the design and construction of concrete structures reinforced by CFRP laminates.

Abstract: This paper analyzed the mechanical properties of the web opening nodes on the steel frame which considered the combined effects, with the finite element analysis software ABAQUS . When the structure with the web openings withstood static loads,formation process of plastic hinge was also analyzed. By applying a load-displacement curve at the endpoint of the main beam, the impact of the flange thickness ratio on the seismic performance was researched. The results showed that reducing the flange thickness will decrease the structural capacity, while the improvement of hysteretic performance was not significant. However, reducing the flange thickness and increasing width of the flange at the same time would not only increase the structural capacity, but also improve the hysteretic behavior and the seismic performance of the structure.