Analysis of self supported steel chimney as per indian standard

Most of the industrial steel chimneys are tall structures with circular cross-sections. Such slender, lightly damped structures are prone to wind-exited vibration. Geometry of a self supporting steel chimney plays an important role in its structural behaviour under lateral dynamic loading. This is because geometry is primarily responsible for the stiffness parameters of the chimney. However, basic dimensions of industrial self supporting steel chimney, such as height, diameter at exit, etc., are generally derived from the associated environmental conditions. To ensure a desired failure mode design code (IS-6533: 1989 Part 2) imposes several criteria on the geometry (top-to-base diameter ratio and height-to-base diameter ratio) of steel chimneys. The objective of the present study is to justify the code criteria with regard to basic dimensions of industrial steel chimney. A total of 66 numbers self supporting steel flared unlined chimneys with different top-to-base diameter ratio and height-to-base diameter ratio were considered for this study. The thickness of the chimney was kept constant for all the cases. Maximum bending moment and stress for all the chimneys were calculated for dynamic wind load as per the procedure given in IS 6533: 1989 (Part 2) using MathCAD software. Also the results were verified with the finite element analysis using commercial software ANSYS. Basic wind speed of 210 km/h which corresponds to costal Orissa area is considered for these calculations. Maximum base moments and associated steel stresses were plotted as a function of top-to-base diameter ratio and height-to-base diameter ratio. The results obtained from this analysis do not agree with the code criteria

Studies on Concrete Made of Recycled Materials for Sustainability

Construction industry uses Portland cement which is known to be a heavy contributor to the CO2 emissions and environmental damage. Incorporation of industrial wastes like demolished old concrete, silica fume (SF) and fly ash (FA) as supplementary cementing materials (SCMs) could result in a substantial reduction of the overall CO2 footprint of the final concrete product. However, use of these supplementary materials in construction industry especially in the making of concrete is highly challenging. Significant research efforts are required to study the engineering properties of concrete incorporating such industrial wastes. Present research is an effort to study the properties of concrete incorporating industrial wastes such as demolished concrete, SF and FA. Recycled coarse aggregate (RCA) concrete construction technique can be called as ‘green concrete’, as it minimizes the environmental hazard of the concrete waste disposal. Indian standard recommends target mean compressive strength of the conventional concrete in terms of water cement ratio (w/c). The behaviour of RCA concrete, prepared from two samples of parent concrete having different age groups, is investigated, to propose the relationship of compressive strength with water cement ratios, in the present study. Number of recycling may influence the mechanical properties of RCA concrete. The influence of age and number of recycling on the properties such as capillary water absorption, drying shrinkage strain, air content, flexural strength and tensile splitting strength of the RCA concrete are examined. While the compressive strength reduces with number of recycling gradually, the capillary water absorption increases abruptly, which leads to the conclusion that further recycling may not be advisable. Previous studies show that the properties of RCA concrete are inferior in quality compared to NCA concrete. The improvement of properties of RCA concrete with the addition of two ureolytic-type bacteria, Bacillus subtilis and Bacillus sphaericus to enhance the properties of RCA concrete. The experimental investigations are carried out to evaluate the improvement of the compressive strength, capillary water absorption and drying shrinkage of RCA concrete incorporating bacteria. The compressive strengths of RCA concrete are found to be increased by about 20% and 35% at the cell concentrations of 106 cells/ml for the two bacteria. The capillary water absorption as well as drying shrinkage of RCA are reduced when bacteria is incorporated. The improvement of RCA concrete is confirmed to be due to the bacterial mineral precipitation as observed from the microstructure studies such as EDX, SEM and XRD. The mechanical properties, such as compressive, flexural and tensile splitting strength, of SF concrete considering the 10% additional quantity of cement as recommended by International codes, by partial replacement of slag cement on low to medium strength concrete, have not been investigated so far. The present study investigates the mechanical properties of medium strength SF concrete made as per this construction practice by partial replacement of slag cement. Effect of SF on compressive, flexural and tensile splitting strength of hardened concrete is examined. Seven concrete mixes are prepared using Portland slag cement (PSC) partially replaced with SF ranging from 0 to 30%. The mix proportions were obtained as per Indian standard IS: 10262-2009 with 10% extra cement when SF is used as per the above the construction practice. Optimum dosages of SF for maximum values of compressive strength, tensile splitting strength and flexural strength at 28 days are determined. Results of the present study are compared with similar results available in literature associated with Portland cement. Relationships, in the form of simplified equations, between compressive, tensile splitting and flexural strengths of SF concrete are proposed. Several studies related to sustainable concrete construction have encouraged the usage of industrial waste products such as SF and FA. Design of structures, made using such SF and FA concrete, for an acceptable level of safety, requires the probabilistic descriptions of its mechanical properties. For this purpose, an extensive experimental programme was carried out on compressive strength, flexural strength and tensile splitting strength properties of SF and FA concrete. The probability distribution models are proposed based on the three goodness-of-fit tests such as Kolmogorov-Sminrov, Chi-square and log-likelihood tests. The proposed probability distributions are used to study performance of typical buildings made of SF and FA concrete through seismic fragility curves and reliability indices

Seismic safety assessment of buildings with fly-ash concrete

Sustainable concrete construction has encouraged the utilization of industrial wastes [fly ash (FA), silica fume, ground granulated blast furnace slag, metakaolin, and so forth] as a composite cementitious material due to its high pozzolanic activity. Among them, fly-ash concrete is gaining high popularity in the construction industry due to its many benefits to concrete structures, including increased structural performance. To estimate the seismic performance of FA concrete buildings, a probabilistic study was performed to determine its mechanical parameters at various performance limit states. Weibull, normal, log-normal, and gamma distribution probability distribution models were considered for three goodness-of-fit tests: the Kolmogorov–Smirnov (KS), chi-square (CS), and log-likelihood (LK) tests. Among them, the lognormal distribution was found to be the closest distribution describing the variations in the mechanical properties of FA concrete compared with other distributions. It was observed that 20%–40% partial replacement of FA with cement improves the performance of structures with enhanced structural safety at economical cost

Variability of silica fume concrete and its effect on seismic safety of reinforced concrete buildings

Design of structures made using silica fume (SF) concrete to an acceptable level of safety requires the probabilistic evaluation of its mechanical properties. An extensive experimental program was carried out on compressive strength, flexural strength, and tensile splitting strength of SF concrete. Seven concrete mixes with different proportions of SF were designed to produce 490 concrete samples. The probabilistic models to describe the variability of the mechanical properties of SF concrete were proposed. Two-parameter probability models such as Weibull, normal, lognormal, and gamma distribution were considered for the representation of variability. The probability distribution models were selected based on goodness-of-fit tests such as the Kolmogorov-Sminrov (KS), chi-square (CS), and log-likelihood (LK) tests. The results obtained from the models are useful for description of the variability of selected mechanical properties of SF-incorporated concrete. This study proposes the lognormal distribution function as the distribution model that most closely describes the variations of different mechanical properties of SF concrete from a practical point of view. Further, the performance of typically selected buildings using SF concrete was evaluated through fragility curves and reliability indices incorporating the proposed probability distributions and variability of compressive strength property. It was found that 15%-25% of partial replacement of cement with SF may yield better performance of the frames