Far-field radar NDT technique for detecting GFRP debonding from concrete

A radar nondestructive testing (NDT) technique using an airborne horn antenna operating in the far-field condition is developed for detecting damages such as debonding and concrete cracking in glass fiber reinforced polymer (GFRP)-wrapped concrete columns. The far-field airborne radar (FAR) NDT technique is advantageous for distant measurement in practical applications where contact/near-contact measurement becomes an issue. In this technique the radar antenna operates in inverse synthetic aperture radar (ISAR) mode. Laboratory measurements at the frequency range 8–18 GHz are made on artificially damaged GFRP–concrete specimens for a preliminary validation of this technique. Collected frequency–angle measurements are further processed by the fast backprojection algorithm to render range–cross-range imagery for damage detection. From the reported measurements and imaging results the proposed FAR NDT technique is conceptually validated; the potential of this technique is shown in identifying defects and debonding in the GFRP–concrete interface regions of the concrete columns wrapped with these composite materials.     

Polystyrene functionalized carbazole and electrochromic device application

Polystyrene (PS) functionalized carbazole macromonomer was synthesized and polymerized by electrochemical oxidative polymerization on the ITO-glass surface. The structure of the macromonomer was elucidated by ¹H NMR, FT-IR, UV–Vis and cyclic voltammetry (CV). The spectro-electrochemical and electrochromic properties of the polymer film were investigated. Also the greenish blue colored film converted to dark blue color by the applying potential. Polystyrene-carbazole/polyethylenedioxythiophene (PS-Carb/PEDOT) electrochromic device was assembled in sandwich configuration: ITO-coated glass/anodically coloring polymer (PS-Carb)//gel electrolyte//cathodically coloring polymer (PEDOT)/ITO-coated glass. According to kinetic studies of this device, the optical contrast ΔT% at 640 nm between −1.0 and +2.0 V with a residence time of 10 s was found to be 38% and switching time was measured as 1.1 s.     

Competitive analysis of the Turkish brick industry—a case study for developing countries

The aim of this article was to examine the factors affecting the competition in brick industries in developing countries. Turkish brick industry was analysed as a case study within the frame of Porter's five forces model.     

Industry financial ratios—application of factor analysis in Turkish construction industry

Turkish economy has been hit by various economical crises between the years 1998 and 2001 and the economic stagnation still continues. Past experiences in various countries show that it is vitally important to encourage construction activities in order to get out of stagnation, as construction output directly affects about 200 other sectors and industry financial ratio analysis is a means to provide a basis for the governments to undertake corrective action. However, there are over 50 financial ratios that can be used during analysis and some are more important than the others for different industries. Previous research has shown that there are about 25 factors that are important for the construction companies. This, in turn, requires elimination of unrelated data. Factor analysis is a data reduction and classification technique, which can be applied in financial analysis. Factor analysis was thus applied to the financial data collected from Turkish construction companies for a 5-year period in order to determine the financial indicators that can be used to analyse the financial trend of the industry. Five independent factors, i.e. liquidity, capital structure and profitability, activity efficiency, profit margin and growth, and assets structure were identified to be sensitive to the economical changes in the country. The results of the factor-based analysis can be used both by the government to analyse the changes in the industry with respect to time and by the construction companies to analyse their financial state with respect to their rivals.     

Integrating renewable sources of energy into an existing combined heat and power system

In recent years, renewable energy sources have played an increasingly important role in potential energy production. The integration of renewables into energy production plants has therefore become a major challenge for many organizations. This study concerns the modernization of a small power plant in a large hospital. The design criteria include the possibility of utilizing renewable energy sources and providing a potential increase in heat production (with additional heat being supplied to a nearby university campus). The existing boiler conditions (i.e. controls, efficiency, etc.) are unable to satisfy the desired requirements and therefore require an extensive retrofit.     

Poly(methyl methacrylate)/clay nanocomposites by photoinitiated free radical polymerization using intercalated monomer

A series of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposite were prepared by successfully dispersing the inorganic nanolayers of MMT clay in an organic PMMA matrix via in situ photoinitiated free radical polymerization. Methyl methacrylate monomer was first intercalated into the interlayer regions of organophilic clay hosts by “click” chemistry followed by a typical photoinitiated free radical polymerization. The intercalated monomer was characterized by FT-IR spectroscopy, elemental analysis and thermogravimetric analysis methods. The intercalation ability of the modified monomer and exfoliated nanocomposite structure were confirmed by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Thermal stability of PMMA/MMT nanocomposites was also studied by both differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Properties of sol-gel derived strontium barium niobate ceramics and the effect of V2O5 additive

Strontium barium niobate, Sr _x Ba_1–x Nb₂O₆, (SBN) ceramics with a range of Sr/Ba ratios were fabricated using a solution chemistry approach with alkoxides dissolved in acetic acid. Powders obtained from dried gels were calcined at 800°C for three hours, a heat treatment that produced fully crystalline powders. After preparing bulk ceramics from these powders by sintering at 1200°C for 1–24 hours, the tetragonal tungsten bronze (TTB) phase was present in all compositions between 0 x 1, although not predicted by the phase diagram for BaNb₂O₆and SrNb₂O₆. Vanadium pentoxide (V₂O₅) additions increased the densification, the amount of tungsten bronze phase, and the dielectric constant for all compositions except for Sr_0.65Ba_0.35Nb₂O₆(SBN65) ceramics.     

Research on modeling shear transfer in reinforced concrete nuclear structures

This paper provides an overview of research in modeling the mechanisms of shear transfer in reinforced concrete nuclear structures. Bases for the development of analytical models are discussed. Preliminary analysis results are presented for the wall specimens to study the behavior of a containment wall portion under biaxial tension and tangential shear loading. Further research needs and interests are suggested for improved analysis capabilities and design.     

Nonlinear analysis of reinforced concrete structures

For the prediction of yield and failure of concrete under combined stress, a generalization of the Mohr-Coulomb behavior is made in terms of the principal stress invariants. The generalized yield and failure criteria are developed to account for the two major sources of nonlinearity: the progressive cracking of concrete in tension, and the nonlinear response of concrete under multiaxial compression. Using these criteria, incremental stress-strain relationships are established in suitable form for the nonlinear finite element analysis.For the analysis of reinforced concrete members by finite elements, a method is introduced by which the effect of reinforcement is directly included. With this approach, the stress-strain laws for the constituent materials of reinforced concrete are uncoupled permitting efficient and convenient implementation of a finite element program. The applicability of the method is shown on sample reinforced concrete analysis problems.     

Equivalent Formulations of Inventory Control Problems

A general multi-item periodic-review inventory control problem is formulated in several ways, each reflecting a different point of view of the decision maker. These formulations are evaluated with respect to implementation criteria of: (i) technical difficulty in obtaining an optimal solution from the model, (ii) estimation effort required to find the values of the parameters in the model, (iii) effort needed to maintain the model continuously updated during the inventory management process. The most promising one is then compared with the conventional formulation, where the objective function is expressed as the sum of expected inventory holding and shortage costs. It is shown that both formulations lead to the same optimal solution under a certain budgetary constraint. This result offers an instrument for implementation improvements in inventory control systems.