Strut-tie method of design and possible serviceability problems: an exploration by NLFE

The strut and tie method presents a rational and consistent approach to the design of all parts in a reinforced concrete structure. With this approach, the load carrying mechanism of the structure is represented by approximating the compressive stress fields as struts, and tensile stress fields as ties. The stress in the struts and ties should not exceed the allowable compressive strength of the concrete or yield strength of the steel respectively. In the design of structures by this method there are two important issues to be addressed. The first issue is that of the visualization of an appropriate strut-tie model for a given structural system. In many structures there may be various load paths available and hence no unique strut-tie model exists. The second issue is that of validity of chosen models in relation to the serviceability and ultimate load characteristics of the resulting structure. It is important that the ductility of the structure should be maintained by insuring that crushing of concrete prior to yielding of steel is avoided at design loads. Since the strut and tie method involves a redistribution of the stresses from the elastic pattern, it is necessary to determine the extent to which that re-distribution can be allowed for, while preserving the required performance from the structure. In this work, visualization of strut-tie models was carried out using elastic finite element analysis. The resulting stress fields were used to design structures which were analysed using an in-house non-linear finite element program and also physically tested in the laboratory

Mechanical behavior of fiber reinforced SiC/RBSN ceramic matrix composites: Theory and experiment

The mechanical behavior of continuous fiber reinforced SiC/RBSN (Reaction Bonded Silicon Nitride) composites with various fiber contents is evaluated. Both catastrophic and noncatastrophic failures are observed in tensile specimens. Damage and failure mechanisms are identified via in-situ monitoring using NDE (nondestructive evaluation) techniques through the loading history. Effects of fiber/matrix interface debonding (splitting) parallel to fibers are discussed. Statistical failure behavior of fibers is also observed, especially when the interface is weak. Micromechanical models incorporating residual stresses to calculate the critical matrix cracking strength, ultimate strength, and work of pull-out are reviewed and used to predict composite response. For selected test problems, experimental measurements are compared to analytical predictions

Effect of Tyre Pyrolysis Oil (TPO) Blends on Performance of Single Cylinder Diesel Engine

Increasing industrialization and motorization led to a significant rise in demand of petroleum products. As these are the non-renewable resources, it will be troublesome to predict the availability of these resources in the future, resulting in uncertainty in its supply and price and is impacting growing economies like India importing 80% of the total demand of the petroleum products. Many attempts have been made by different researchers to find out alternate fuels for Internal Combustion engines. Many alternate fuels like Biodiesel, LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas) and Alcohol are being used nowadays by different vehicles. In this context pyrolysis of scrap tyres can be used effectively to produce oil, thereby solving the problem of waste tyre disposal. In the present study, Experimental investigations were carried out to evaluate the performance and emission characteristics of a single cylinder diesel engine fueled by TPO10, TPO15, and TPO20 at a crank angle 260 before TDC (Top Dead Centre) and injection pressure of 200 bar keeping the blend quality by controlling the density and viscosity of tyre pyrolysis oil within permissible limit of euro IV diesel requirement. The performance and emission results were analyzed and compared with that of diesel fuel operation. The results of investigations indicate that the brake thermal efficiency of the TPO - DF blend decreases by 6 to 10%. CO emissions are slightly higher but well within permissible limit of euro IV emission standards. HC emissions are higher by about 25 to 35% at partial load whereas smoke opacity is lower by about 3% to 21% as compared to diesel fuel