Experimental and theoretical studies on the torque required to install screw anchors in sand are presented. Tests were conducted on five models of screw anchors with different geometry to study the effect of the shape of the screw element on the performance of the anchor during installation. Anchors were installed into prepared layers of dense, medium, and loose sand. An experimental setup was instrumented to allow the measurement of the total pullout load, the upward displacement, the sand surface deflection, installation torque value, and the stress development in the sand layer during all phases of the testing procedure. Special tests were conducted on coloured-layered sand to examine the effect of the installation procedure on the sand deposit and to define the sand wedge involved in resisting the installation of the screw anchor. Based on the results of the experimental investigation, the factors affecting the value of the installation torque were identified. A theoretical model was developed, from which the required installation torque value can be predicted. A torque factor was established in terms of the parameters affecting the torque value, and a correlation between this factor and the uplift capacity factor was proposed. From this correlation, the uplift capacity of a screw anchor can be determined from the measured installation torque value. A comparison between theoretical and experimental results showed good agreement. Also, reasonable agreement was observed when the present theoretical results were compared with the available field results from other investigations. Key words: anchorages, anchors, bearing capacity, helical anchors, models, sand, screw anchors, screw helical anchors, soil mechanics, torque, uplift capacity.
Waste rubber tires that cannot be processed for useful applications are numbered in the millions around the world. The build up of old rubber tires in landfills is commonly considered a major threat to the environment, and it is unquestionably a burden on landfill space. This research project was an investigation into the possibility of using fine rubber particles in concrete mixtures. The experimental testing program was designed to study the effect of the addition of crumb rubber, as replacement of a portion of fine aggregates (sand), on the strength of concrete. Rubber was added to concrete in quantities of 5%, 10%, and 15% by volume of the mixture. Three different water/cement ratios were used: 0.47, 0.54, and 0.61. A total of 180 concrete cubes were made. The cubes were tested in compression at 1, 7, 14, 21, and 28 d with the load continuously and automatically measured until failure. The load values were used to calculate compressive stress as related to different rubber contents and water/cement ratios. Compression test results were used to develop several plots relating rubber content and water/cement ratio to compressive stress of concrete. Test results gathered in this research project indicated that the addition of crumb rubber to concrete results in a reduced strength as compared with that of conventional concrete. Based on the experimental results, correlations have been developed to estimate the reduction in concrete strength as a function of the rubber content in the mix.Key words: compressive strength, concrete, crumb rubber, rubberized concrete.
An investigation into the performance of single vertical screw anchors installed in sands is presented. Models were developed employing the limit equilibrium method of analysis to predict the uplift capacity of anchors installed into shallow, transition, and deep depths. An experimentally observed log-spiral rupture surface was used in the theoretical analysis. Shear stresses were calculated on the surface of rupture using Kötter's differential equation. Weight and shear factors for shallow and deep anchors are established to simplify the calculation of the uplift capacity from the theories developed. These factors are presented in simple graphs as functions of the angle of shearing resistance of the sand and the relative depth ratio of the anchor. The effect of sand overconsolidation resulting from the application of mechanical compaction was introduced by incorporating the overconsolidation ratio in the uplift capacity calculations. Comparisons between the theoretical values and the experimental results of the present investigation as well as field results reported in the literature showed good agreement. Key words : anchors, failure mechanism, limit equilibrium, overconsolidation ratio, theoretical analysis, uplift capacity.
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