Investigation on the Behavior of Conical Shell Foundations Composed of Reactive Powder Concrete Embedded on Sandy Soil

Abstract

Many forms of shells are available for use as foundations. Then frustum of a cone in the upright position can serve as footing for columns or raft for structure such as chimneys. Reactive Powder Concrete (RPC) is an ultra-high strength, low porosity material with high cement and silica fume contents and steel fibers. RPC uses low water-binder ratios and new generation superplasticizers with eliminating the coarse aggregates, all optimized particle size less than 600 micrometers. RPC can be readily used in a wide variety of structural applications, including situations where the concrete is required to carry substantial tensile stresses due to shear and bursting forces. The present study is devoted to study the behavior of RPC shell foundations. A complete load-frame assembly was designed and fabricated for experimental work. Five values of steel fiber volume fractions of 0, 0.5%, 1.0%, 1.5%, and 2.0% were used in casting the shells in order to study the effect of steel fiber content on the shear strength. Three percentages of silica fume were used to obtain different grades of concrete to study the effect of concrete compressive strength on the shear strength. The percentages of silica fume are 5%, 10% and 15% by mass of cementations materials. Results of loading tests conducted on wire – reinforced small – concrete models of conical foundations under loads established substantially high values of load factors involved in the traditional design of the conical foundations by membrane theory. The inclusion of steel fibers in RPC footings results in enhanced stiffness, reduced crack width and reduced rate of crack propagation. At failure, the RPC footings behave in a ductile manner as compared with the nonfibrous footing and most of the steel fibers pulled out of the cement matrix. The inclusion of steel fibers in RPC footings results in a significant enhanced ductility and absorbed energy. For RPC footings with the same steel fiber content, the footings with ring beam have stiffness greater than footings without ring beam. The failure of the conical shell footing is found to start with tension to extend upwards along the generator with its width decreasing with edge. As the applied load increases, the value of circumferential tension increases bending in the radial vertical plane increase near the pedestal base at top where there is complete fixity.