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Volume 31, Number 1, January10 2009
Abstract
An experimental investigation was conducted to evaluate the performance of mortars with and without Metakaolin (MK) exposed to elevated temperatures 200oC, 400oC, 600oC and 800oC for two hours. The binder to sand ratio was kept constant (1:5.23). The ordinary Portland cement (OPC) was replaced with MK at 0%, 5%, 10% 20% and 30%. All mixtures were designed to have a flow of 94 ?5%. The compressive strength of mortars before and after exposure to elevated temperature was determined. The formation of various decomposition phases were identified using X-ray diffractometry (XRD) and differential thermal analysis (DTA). The microstructure of the mortars was examined using scanning electron microscope (SEM). Test results indicated that MK improves the compressive strength before and after exposure to elevated temperature and that the 20% cement replacement of MK is the optimum percentage.
Key Words
elevated temperature resistance; metakaolin; mortar; microstructure; blended cement.
Address
M. S. Morsy, A. M. Rashad and H. A. El-Nouhy: Housing & Building National Research Center, 87 El-Tahrir St., Dokki, Giza 11511, P.O. Box: 1770 Cairo, Egypt
Abstract
In China, the oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the
design, construction, utilization, maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform under the extreme ice load. In this study, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death and injury as well as discounting cost over time are considered. An efficient approximate method of the global reliability analysis for the offshore platforms is provided, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. The proposed life-cycle optimum design formula are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared to the conventional design.
Key Words
life-cycle cost; cost-effective design; global reliability; optimal design; offshore platform; ice load.
Address
Gang Li, Da-yong Zhang and Qian-jin Yue: State Key Laboratory of Structural Analysis of Industrial Equipment, Dalian University of Tech, Dalian, 116023, China
Abstract
Local failure of a primary structural component induced by direct air-blast loading may be itself a critical damage and lead to the partial or full collapse of the building. As an extensive research to
mitigate blast-induced hazards in steel frame structure, a state-of-art analytical approach or high-fidelity computational nonlinear continuum modeling using computational fluid dynamics was described in this paper. The capability of the approach to produce reasonable blast pressures on a steel wide-flange section column was first evaluated. Parametric studies were conducted to observe the effects of section sizes and boundary conditions on behavior and failure of columns in steel frame structures. This study shows that the analytical approach is reasonable and effective to understand the nature of blast wave and complex interaction between blast loading and steel column behavior.
Key Words
computational fluid-dynamics; fluid-structure interaction; blast load; steel column.
Address
Kyungkoo Lee: Dept. of Architectural Engineering, Seoul National University, Seoul 151-742, Korea
Taejin Kim and Jinkoo Kim: Dept. of Architectural Engineering, Sungkyunkwan University, Suwon 440-746, Korea
Abstract
Vibration is an undesirable phenomenon in a dynamic system like lightly damped aerospace structures and active vibration control has gradually been employed to suppress vibration. The objective of the current investigation is to introduce an active torsional magneto-rheological (MR) fluid based damper for vibration control of a typical nose landing gear. They offer the adaptability of active control devices
without requiring the associated large power sources. A torsional damper is designed and developed based on Bingham plastic shear flow model. The numerical analysis is carried out to estimate the damping
coefficient and damping force. The designed damper is fabricated and an experimental setup is also established to characterize the damper and these results are compared with the analytical results. A typical FE model of Nose landing gear is developed to study the effectiveness of the damper. Open loop response analysis has been carried out and response levels are monitored at the piston tip of a nose landing gear for various loading conditions without damper and with MR-damper as semi-active device. The closedloop full state feedback control scheme by the pole-placement technique is also applied to control the landing gear instability of an aircraft.
Key Words
MR fluid; torsional damper; nose landing gear; full state feedback; pole placement.
Address
Sateesh B. and Dipak K. Maiti: Dept. of Aerospace Engineering, Indian Institute of Technology, Kharagpur-721302, India
Abstract
Power signals resulting from spindle and feed motor, present a rich content of physical information, the appropriate analysis of which can lead to the clear identification of the nature of the tool wear. The partial least-squares regression (PLSR) method has been established as the tool wear analysis method for this purpose. Firstly, the results of the application of widely used techniques are given and their limitations of prior methods are delineated. Secondly, the application of PLSR is proposed. The singular value theory is used to noise reduction. According to grey relational degree analysis, sample
variable is filtered as part sample variable and all sample variables as independent variables for modelling, and the tool wear is taken as dependent variable, thus PLSR model is built up through adapting to several experimental data of tool wear in different milling process. Finally, the prediction value of tool wear is compare with actual value, in order to test whether the model of the tool wear can adopt to new measuring data on the independent variable. In the new different cutting process, milling tool wear was predicted by the methods of PLSR and MLR (Multivariate Linear Regression) as well as BPNN (BP Neural Network) at the same time. Experimental results show that the methods can meet the needs of the engineering and PLSR is more suitable for monitoring tool wear.
Key Words
partial least-squares regression; singular value decomposition; tool wear; cutting experiment.
Address
Xu Chuangwen
School of Mechanical Engineering, Xi?an Jiaotong University, Xi?an, Shanxi, China
Department of Mechanical Engineering, Lanzhou Polytechnic College, Lanzhou, Gansu, China
Chen Hualing
School of Mechanical Engineering, Xi?an Jiaotong University, Xi?an, Shanxi, China
Abstract
It is known that retaining walls were severely damaged as well in the most recent earthquakes having occurred in the countries in the active seismic belts of the world. This damage can be ascribed to
the calculation methods used for the designs of retaining walls in the event of their constructions and employment having been accurately carried out. Generally simplified pseudo-static methods are used in
the analysis of retaining walls with analytical methods and soil-structure interaction are not considered. In view of these circumstances, in this article by taking soil interaction into consideration, linear and nonlinear behaviours of retaining walls are analyzed with the assistance of LUSAS which is one of the structural analysis programs. This investigations are carried out per LUSAS which employs the finite element method as to the Erzincan (1992) Earthquake North-South component and the obtained findings are compared with the ones obtained from the method suggested in Eurocode-8, which is still effective today, and Mononobe-Okabe method. Not only do the obtained results indicate the distribution and magnitude of soil pressures are depend on the filling soil but on the foundation soil as well and nonlinear effects should be considered in designs of these walls.
Key Words
retaining walls; foundation soil properties; analytical and numerical methods; linear and nonlinear behaviours.
Address
Senol Gursoy and Ahmet Durmus: Karadeniz Technical University, Department of Civil Engineering, Gumuhane, Turkey
Karadeniz Technical University, Department of Civil Engineering, Trabzon, Turkey
Abstract
In this study seismic analyses of steel structures were carried out to examine the effect of ground motion characteristics and structural properties on energy demands using 100 earthquake ground
motions recorded in different soil conditions, and the results were compared with those of previous works. Analysis results show that ductility ratios and the site conditions have significant influence on input energy. The ratio of hysteretic to input energy is considerably influenced by the ductility ratio and the strong motion duration. It is also observed that as the predominant periods of the input energy spectra are significantly larger than those of acceleration response spectra used in the strength design, the strength demand on a structure designed based on energy should be checked especially in short period structures. For that reason framed structures with buckling-restrained-braces (BRBs) were designed in such a way that all the input energy was dissipated by the hysteretic energy of the BRBs, and the results were compared with those designed by conventional strength-based design procedure.
Key Words
input energy; hysteretic energy; energy-based seismic design; strength-based design.
Address
Hyunhoon Choi and Jinkoo Kim: Dept. of Architectural Engineering, Sungkyunkwan University, Suwon, Korea
Abstract
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Key Words
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Address
Christian N. Della and Dong Wei Shu:
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
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Editor-in-Chief
Structural Mechanics
