Mechanical properties of precast reinforced concrete slab tracks on non-ballasted foundations

AbstractThis article deals with the mechanical properties of steel-reinforced concrete precast slab tracks on non-ballasted elasto-plastic foundations. To work out the spanning behavior of slab tracks, a FEM analysis was executed for discrete and continuous systems. At first, full-size slabs without foundation including solid and hollow-core specimens (with 30% weight reduction) were tested under centric static (monotonic) line loads, and load–deflection curves were extracted. Then, FEM results for zero foundation stiffness were verified with those of experiments, which were in good agreement. Original results include the effects of several parameters on the cracking load, ultimate load, and energy absorption of slabs placed on elasto-plastic foundations including the slab width, concrete tensile strength and load factor. Analyses revealed that mechanical properties in hollow-core sections are not so different from those in solid ones, and thus hollow-core sections are more efficient because of significant weight reduction

Effects of pozzolans together with steel and polypropylene fibers on mechanical properties of RCC pavements

Effects of pozzolans and fibers on mechanical properties of RCC are addressed. The mechanical properties were evaluated using optimum moisture with different amounts of pozzolans, steel and polypropylene fibers. Using pozzolans, maximum increase in compressive strength was observed to occur between 28 and 90 days of age, rupture modulus was found to decrease; but toughness indices did not change considerably. The influence of steel fibers on compressive strength was often more significant than that of PP fibers; but neither steel nor PP fibers did contribute to increase in the rupture modulus independently from pozzolans. Also, the toughness indices increased when steel fibers were used. © 2011 Elsevier Ltd. All rights reserved

Life-cycle cost optimization of prestressed simple-span concrete bridges with simple and spliced girders

In this paper, determination of the design variable optimum values of simple and spliced pre-tensioned girders in bridges is addressed by considering the life cycle cost of the whole structure. To this end, a program called OBPG is written with FORTRAN, consisting of the analysis, design and optimization subroutines based on the feasible direction method. AASHTO principles are used, assuming initial values for the design variables such as the dimensions of the girders and the deck, and the strands number. Then, using the analysis outcomes and considering the design criteria, the total cost of the structure, including that of the girders and slabs concreting, pre-tensioning cables performance, reinforcement and frameworks, are minimized as functions of the design variables. Although the initial optimization cost using life cycle cost is slightly more than that using the initial cost, optimization of the life cycle cost proves to be more economical. Ultimately, a program capable of analyzing simple and spliced pre-tensioned bridge girders is developed which calculates the life cycle and gives an optimum design. © Shiraz University