Mechanical Properties and Energy Dissipation of Sandstone under Cyclic Loading-Unloading

For the bearing rock in geotechnical engineering, it is frequently affected by external loads. This paper adopted different upper limits of stress to carry out cyclic loading-unloading on the sandstone specimens to make them in different damage degrees and analyzed the mechanical mechanism of the damaged sandstone under different stresses. Then, the strength change and energy evolution of sandstone with different damage degrees were analyzed, and the damage of the loaded sandstone was quantitatively characterized. The experimental results showed that the strength and plastic deformation of sandstone after cyclic loading-unloading with different upper-stress limits gradually decreased with the increase of the upper-stress limit. In the loading-unloading stages of cyclic loading-unloading, the elastic modulus increased with the increase of the upper-stress limit. In general, as the number of cycles increased, the total strain energy density and elastic deformation energy density gradually increased, and as the upper-stress limit increased, both of them also increased. The damage factor of sandstone after cyclic loading-unloading, which was characterized by dissipated energy, increased in an S-shape with the increase of the upper-stress limit, and the growth rate first increased and then decreased.

ON THE VARYING BRACHISTOCHRONE SHAPE WITH ALLOWANCE FOR CHUTE LOADING LIMITATION

first time. Here, the dynamic equations for the motion of the material body rolling down the chute are formulated neglecting the friction forces. It is shown that if the stress limit for the chute material is taken into account, the shape of the chute varies greatly as a function of the parameter. Four possible cases are analyzed when the parameter is: equal to zero, more than unity, less than unity, and equal to unity. It is found that if the parameter is more than unity, the chute shape represents almost horizontal and vertical segments of a trajectory, which is clear from a physical point of view, since for this type of the trajectory the chute is least affected by the body moving along. If the parameter is equal to unity, the chute takes a specific loop-like shape. If the parameter is equal to zero, the system of equations describes a classical brachistochrone. The solution to the problem is applicable in practice for predicting the shape of the chute withstanding high loads when the stress limit for the material is known.

Evaluating the thermal effect on the rheological properties of waste vegetable oil biodiesel modified bentonite drilling muds using Vipulanandan model

In this investigation, the effects of the temperature on the flow characteristics of waste vegetable oil biodiesel modified bentonite drilling mud were quantified. The biodiesel contents in the drilling muds are varied from 0 to 9% of the volume of the water in order to reduce the yield point and upper shear stress limit produced by the mud during drilling activities under simulated thermal condition ranging from 28°C to 180°C. The results revealed that the bentonite drilling mud loaded with 6 vol.% waste vegetable oil biodiesel demonstrates fairly favorable rheological properties compared to others when exposed to similar heat treatment. Moreover, the rheological behavior of biodiesel-free bentonite mud and samples loaded with biodiesel were quantified using the Vipulanandan model and compared with others existing models used in the industry such as: Bingham plastic model and Herschel-Bulkley model. It was observed that the Vipulanandan model predicts satisfactorily the shear thinning relationship between the shear stress and shear strain rate of the modified bentonite drilling muds. Furthermore, by using the Vipulanandan model, the maximum shear stress values for 0%, 3%, 6% and 9% biodiesel content at 28°C are found to be 63.67 Pa, 84.54 Pa, 84.64 Pa and 85.02 Pa, respectively. When exposed to heat treatment at 180°C, the maximum shear stress values recorded for 0%, 3%, 6% and 9% are 53.18 Pa, 67.39 Pa, 64.52 Pa and 72.70 Pa, respectively, which represent a reduction of 14% to 16% in the upper shear stress limit.

Retrofitting and Rehabilitation of Damage Footbridge Over Yamuna River

Every Structure has a certain predefined age with which it has to withstand, and after that, it requires the rehabilitation/repairing to avoid any damage or collapse. The footbridge over Yamuna River in Delhi, India was constructed in 1960 adjacent to Wazirabad barrage, and this is a very important link to East Delhi and West Delhi. Due to heavy traffic plying on this footbridge, in due course of time, the signs of deterioration were visible in the bridge expansion joint assemblies in the deck slab and cantilever portion of footpath slab. There were many potholes also developed in the wearing course. It was also dilapidation observed in many portions of the footpath, and some portion of the footpath slab were collapsed. The cantilever portion of the footbridge was retrofitted with steel jacketing fixing in the main longitudinal girder of the bridge. In this study analysis of the cantilever footbridge slab retrofitted by a steel jacket was carried out to check the deflection and stress limit of the bridge and it is found that the bridge is safe and now Bridge is open for traffic