Condition evaluation of existing reinforced concrete bridges using fuzzy based analytic hierarchy approach

There is an urgent need for a systematic methodology for condition assessment of the bridges because the old bridges of most of the countries are inadequate to carry current-day traffic and satisfy the present codal provisions and even in newer bridges, deterioration caused by unforeseen service condition and deferred maintenance is of great concern. In view of this, an attempt has been made in this study to develop a systematic procedure and formulations for condition evaluation of existing bridges using Analytic Hierarchy Process in a fuzzy environment. Analytic Hierarchy Process (AHP) is an efficient decision making tool for complicated problems with multiple evaluation criteria and uncertainty. Fuzzy logic approach has been used to take care of the uncertainties and imprecision in the bridge inspector’s observations. In this paper, first, a methodology has been proposed for condition ranking of number of reinforced concrete (RC) bridges. Then, based on the results obtained from prioritization, rating of the most deserved bridge has been carried out using MADM based fuzzy logic. Computer programs have been developed based on the formulations presented in this paper for evaluating condition of existing bridges and the details are presented in the paper. The methodology and its application are demonstrated through a case study. This methodology would certainly help the engineers and policy makers concerned with bridge management to overcome the problem related to prioritization and decision on funding related to rehabilitation of bridges.     

Purification and Characterization of β-Glucosidase from Aspergillus niger

Aspergillus niger, an isolate of soil contaminated with effluents from cotton ginning mill was grown in Czapek-Dox medium containing sawdust, Triton-X 100 and urea for production of an extracellular β-glucosidase. β-Glucosidase enzyme was purified (86-fold) from culture filtrate of A. niger by employing ammonium sulphate precipitation and gel filtration on sephadex G-75. The molecular mass of the purified enzyme was estimated to be 95 kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The enzyme had an optimal activity on p-nitrophenyl β-D-glucopyranoside at 50°C and pH 5.0. The K_m and V_max of the enzyme on p-nitrophenyl β-D-glucopyranoside at 50°C and pH 5 were 8.0 mM and 166 µmol/min/mg of protein, respectively. The enzyme could hydrolyze cellobiose and lactose but not sucrose. Heavy metals like Hg²⁺, Al³⁺, and Ag⁺ inhibited the activity, whereas Zn²⁺ and detergents such as Triton-X 100 and Tween-80 increased the activity at 0.01%. The enzyme activity increased in the presence of methanol and ethanol.     

Biological phenol removal using immobilized cells in a pulsed plate bioreactor: effect of dilution rate and influent phenol concentration

The continuous aerobic biodegradation of phenol in synthetic wastewater was carried out using Nocardia hydrocarbonoxydans immobilized over glass beads packed between the plates in a pulsed plate bioreactor at a frequency of pulsation of 0.5s(-1) and amplitude of 4.7 cm. The influence of dilution rate and influent phenol concentration on start up and steady state performance of the bioreactor was studied. The time taken to reach steady state has increased with increase in dilution rate and influent phenol concentration. It was found that, as the dilution rate is increased, the percentage degradation has decreased. Steady state percentage degradation was also reduced with increased influent phenol concentration. Almost 100% degradation of 300 and 500 ppm influent phenol could be achieved at a dilution rate of 0.4094 h(-1) and more than 99% degradation could be achieved with higher dilution rates. At a higher dilution rate of 1.0235 h(-1) and at concentrations of 800 and 900 ppm the percentage degradation has reduced to around 94% and 93%, respectively. The attached biomass dry weight, biofilm thickness and biofilm density at steady state were influenced by influent phenol concentration and dilution rate.     

Seismic retrofitting of nonductile beam-column sub-assemblage using FRP wrapping and steel plate jacketing

The paper discusses the aspects of repair and retrofitting technique adopted for a damaged reinforced concrete beam-column joint specimen under cyclic loading. A specimen designed based on Indian Standard specifications with consideration of seismic load but without adopting ductile detailing (NonDuctile) was investigated under reverse cyclic loading. Then, the damaged nonductile specimen was repaired with epoxy mortar and grouted using low viscous polymer, and retrofitted using fiber reinforced plastic (FRP) wrapping in beam and column components and steel plate jacketing in joint region. The experimental results showed that the retrofitted specimen not only regained its original strength and stiffness but also has overcome the deficiencies of nonductile detailing. The present study shows that a proper repair and adequate retrofitting technique can be used for strengthening and improvement of damaged regions in reinforced concrete structures.     

Determination of boron in uranium-aluminum-silicon alloy by spectrophotometry and estimation of expanded uncertainty in measurement

Quantification of boron in diverse materials of relevance in nuclear technology is essential in view of its high thermal neutron absorption cross section. A simple and sensitive method has been developed for the determination of boron in uranium-aluminum-silicon alloy, based on leaching of boron with 6 M HCl and H₂O₂, its selective separation by solvent extraction with 2-ethyl hexane 1,3-diol and quantification by spectrophotometry using curcumin. The method has been evaluated by standard addition method and validated by inductively coupled plasma-atomic emission spectroscopy. Relative standard deviation and absolute detection limit of the method are 3.0% (at 1σ level) and 12 ng, respectively. All possible sources of uncertainties in the methodology have been individually assessed, following the International Organization for Standardization guidelines. The combined uncertainty is calculated employing uncertainty propagation formulae. The expanded uncertainty in the measurement at 95% confidence level (coverage factor 2) is 8.840%.     

Fuzzy Logic Based Condition Rating of Existing Reinforced Concrete Bridges

Fuzzy logic is a means for modeling the uncertainty involved in describing an event/result using natural language. The fuzzy logic approach would be particularly useful for remedying the uncertainties and imprecision in bridge inspectors’ observations. This study explores the possibilities of using fuzzy mathematics for condition assessment and rating of bridges, developing a systematic procedure and formulations for rating existing bridges using fuzzy mathematics. Computer programs developed from formulations presented in this paper are used for evaluating the rating of existing bridges, and the details are presented in the paper. In this approach, the entire bridge has been divided into three major components—deck, superstructure, and substructure—each of which is further subdivided into a number of elements. Using fuzzy mathematics in combination with an eigenvector-based priority setting approach, the resultant rating set for the bridge has been evaluated based on the specified ratings and importance factors for all the elements of the bridge. Then the defuzzified value of the resultant rating fuzzy set becomes the rating value for the bridge as a whole. It is argued that the methodology presented in this paper would help the decision makers/bridge inspectors immensely.     

Seismic performance evaluation of GLD beam–column sub-assemblages of three different scenarios

Gravity load designed (GLD) structures exhibit poor seismic performance due to inadequate reinforcement to cater for the seismic forces, lack of confinement, poor joint strength, improper anchorage, presence of weak column and strong beams. These structures are also susceptible to environmental impact leading to corrosion of reinforcement which would further degrade their seismic performance. In RC structures, beam–column joints are crucial members and dissipate the seismic energy imparted to the structure. Hence in this study, two typical cases of GLD (i) uncorroded GLD and (ii) corrosion affected GLD (corroded) exterior beam–column sub-assemblages subjected to reverse cyclic loading are investigated and compared. Reinforcement corrosion of one of the GLD specimens is accelerated by the impressed current technique. Based on the investigation on uncorroded GLD and corrosion affected GLD beam–column specimens, it is noted that the corrosion has significant effect on the seismic performance in terms of loss of energy dissipation, strength- and stiffness- degradation. To improve the seismic performance of uncorroded GLD specimens, a low invasive single steel haunch upgradation scheme (SHUS) is proposed in this study. The maximum load carried by steel haunch upgraded GLD specimen is about 30% higher than that of GLD specimen. Hence, it is noted that by implementing the proposed upgradation scheme for GLD beam–column sub-assemblage, remarkable improvement in the seismic response can be achieved. The present study provides insight into the behaviour of steel haunch upgraded GLD specimen and would also pave the way for formulating seismic upgradation of even corroded GLD beam–column sub-assemblage.     

Modeling server-unreliability in closed queuing-networks

A method is presented to model server unreliability in closed queuing networks. Breakdowns and repairs of servers, assumed to be time-dependent, are modeled using virtual customers and virtual servers in the system. The problem is thus converted into a closed queue with all reliable servers and preemptive resume priority centers. Several recent preemptive priority approximations and an approximation of the one proposed are used in the analysis. This method has approximately the same computational requirements as that of mean-value analysis for a network of identical dimensions and is therefore very efficient     

Structure-Property Correlation of AA2014 Friction Stir Welds: Role of Tool Pin Profile

The influence of rapid plastic deformation in the generation of welding heat during friction stir welding (FSW), supplementing the frictional heat generation by the tool shoulder, forms the thrust of the present investigation. Several researchers have highlighted the role of tool shoulder in the generation of frictional heat and suggested that the tool-material interface friction as the sole mechanism for heating. The configuration of tool pin profile is seldom studied for its contribution to welding heat through rapid plastic deformation at high strain rates (10³/s), especially while welding thick plates. An attempt has been made to understand the dependence of deformation heat generation with different tool pin profiles in welding 5 mm thick AA2014-T6 aluminum alloy, maintaining the same swept volume during the tool rotation. An attempt has also been made to correlate the influence of process response variables such as force and torque acting on the tool pin. To quantify the physical influence of tool pin profile, temperature measurements were made in the region adjacent to the rotating pin, close to nugget in the thermo-mechanically affected zone (TMAZ). It has been observed that the temperature rises at a relatively rapid rate in the case of hexagonal tool pin compared to the welds produced employing other tool pin profiles. It is observed that during FSW, extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the mechanical properties of the joint. The present study is also aimed at understanding the influence of tool profile on the microstructural changes and the associated mechanical properties. Transverse tensile samples failed at the nugget/TMAZ boundary due to localized softening. Hexagonal tool pin profile welds have shown higher tensile strength, low TMAZ width, and high nugget hardness compared to other tool pin profile welds.