Key Engineering Materials Vols. 385-387

Abstract: A structural steel should satisfy various properties under varied conditions. Fatigue strength is one of them. When structural steels are used in the form of welded joints, fatigue strength is one of the key characteristics that should be considered. In this study, comprehensive fatigue tests of a structural steel with yielding strength of about 350 MPa and tensile strength of about 520 MPa were carried out. First, a lot of specimens: parent material plates, butt welded specimens with reinforcement removed, as-welded plates, plates with weld toe ground, load-carrying cruciform, non load-carrying cruciform, plates with transverse fillet welded rib, etc were prepared and tested. S-N curves for the above specimens were compared and analyzed. Secondly, some life-size rectangular beams were fabricated by welding and tested. It is found that annealing is detrimental to fatigue strength rather than beneficial. The experimental data and results may be used usefully by engineers.

Abstract: Flexible pavement plays an important role in the primary concrete bridges at present. However, climate environment, to which pavement is exposed, significantly impact pavement stability and long-term performance. Especially, low temperature cracking of asphalt pavement in cold region is a common existing problem. In order to improve the pavement’s crack resistance it is necessary to predict the temperature stress distribution within the asphalt layers. A two-dimensional finite element model of a concrete bridge in thermal and thermal-structural couple analysis is developed to predict temperature and temperature stress variation of asphalt layers in cold region. The temperature stress variation is analyzed at seasonal temperature, different cooling rate and the different thickness of asphalt layers. The model considers a set of primary thermal environmental conditions. Ultimately, the model is aimed at providing pavement engineers with an efficient computational tool that attempts to increase the prediction accuracy of temperature in asphaltic pavement of cold region for more reliable pavement design.

Abstract: A crack in the tooth root is the least desirable damage of gear units, which often leads to failure of gear unit operation. A possible damage can be identified by monitoring vibrations. The influences that a crack in the tooth root of a single-stage gear unit has upon vibrations are dealt with. Changes in tooth stiffness are much more expressed in relation to a fatigue crack in the tooth root, whereas in relation to other faults, changes of other dynamic parameters are more expressed. Signal analysis has been performed in relation to a non-stationary signal, by means of the Time Frequency Analysis tool, such as Wavelets. Typical scalogram patterns resulting from reactions to faults or damages indicate the presence of faults or damages with a very high degree of reliability.

Abstract: The purpose of this research is to evaluate the effectiveness of nitrate as a corrosion inhibitor in mortar containing chloride. In the experiment, test specimens of mortar to which chloride and nitrite had been added, were subjected to accelerated corrosion by means of repeated drying and wetting on condition of high temperature. This study concerns the assessment of the inhibition effect of nitrite-based corrosion inhibitor using a polarization method and its influence on the chloride transport, compressive strength and setting time of concrete. From the results of the experiments, it was confirmed that the lithium, calcium nitrite corrosion inhibitor and new corrosion inhibitor over dosage 0.6 (NO2-/Cl-) molar ratio is very effective in protecting reinforcement from corrosion in mortar in which chloride ions have contained.

Abstract: A significant amount of research has been conducted on the buckling behavior of delaminated composite laminates. However, none of the investigations has been focused on establishing similarity and scaling laws for buckling response of composite laminated with delamination. The main objective of this study is to demonstrate the applicability of similitude theory in designing scaled down models for predicting the buckling behavior of delaminated laminated beam subjected to uni-axial compression. The results presented herein indicate that, for buckling response of delaminated beam-plates, based on structural similitude, a set of scaling laws can be found which use to develop design rules for small scale models. For models with the same material properties and stacking sequence as prototype, distorted models with different number of delaminations, delamination length and depth than those of the prototype can predict the behavior of the prototypes with good accuracy.

Abstract: Examination about sticking intensity security way of normal temperature metal spraying covering is required compulsorily accordingly with quantitative assessment about steel plate's surface roughness to secure adhesive power of steel materials and metal membrane stably at application of way method of construction by normal temperature metal spraying. In case of metal spraying, Sticking strength of metal spraying way finish is influenced greatly, and it is judged that is desirable that manages Sm/Rz by 6 lows to secure more than sticking intensity 20kgf/cm2 by Sm/Rz that evaluate that is rough of nature surface. The purpose of this study was to analyze an adhesion strength of metal spraying finish layer with the surface conditions of steel plate. For the purpose the experimental factors such as anticorrosive finish method and surface treatment method were selected.

Abstract: A new technique, Analytical Trial Function Method (ATFM), is proposed to formulate new finite element models for analysis of plane crack/notch problems. A new analytical finite element, named ATFM-CN, is successfully constructed. Furthermore, in order to determine the eigenvalues of the crack/notch problems, which utilized in above analytical trial functions, a modified sub-region accelerated Müller method is also suggested. Numerical examples show the present approach exhibits excellent performance in the analysis of stress-singularity problems.

Abstract: Due to the uncertainty of variables in durability model, the probabilistic approach is increasing. Monte Carlo Simulation (MCS) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (FOSM), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict similar reliability indexes and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to failure probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the possibility of corrosion initiation in harbor concrete structures.

Abstract: Life span of structures made with concrete was shortened by carbonation. This phenomenon makes pH in concrete lower. If pH value in concrete become below 10, rebar in concrete begin to be corroded. This pH value was effected by quantity of Ca(OH)2 that depends on cement types, hydration reaction and carbonation time. In this study, pH value and quantity of Ca(OH)2 in mortar which has blast furnace slag were tested according to hydration and carbonation time. As a test result, the more cement has blast furnace slag (BFS) and the longer carbonation time last, the lower pH value in mortar has. And using this quantitative analysis result of pH and Ca(OH)2, it may be used effectively when service life considering carbonation is predicted using FEMA.

Abstract: Autogenous shrinkage is the term for the bulk deformation of a closed, isothermal, cement-based material system not subjected to external forces. It is associated with the internal volume reduction of cement/water mixture in the course of the hydration process. However, addition of blended components to cement, especially such as fly ash or silica fume, for the high-performance concrete will lead to a densification of the microstructure. The autogenous shrinkage deformation will increase and the following autogenous shrinkage crack will do harm to durability of concrete structure. In this paper, numerical simulation is suggested to predict autogenous shrinkage of high performance cement paste. The simulation is originated from a multicomponent hydration model. The numerical program considers the influence of water to cement ratio, curing temperature, particle size distribution, cement mineral components on hydration process and autogenous shrinkage. The prediction result agrees well with experiment result.