Abstract: The objective of this research is to investigate the
advantages of using large-diameter 0.7 inch prestressing strands in
pretention applications. The advantages of large-diameter strands are
mainly beneficial in the heavy construction applications. Bridges and
tunnels are subjected to a higher daily traffic with an exponential
increase in trucks ultimate weight, which raise the demand for higher
structural capacity of bridges and tunnels. In this research, precast
prestressed I-girders were considered as a case study. Flexure
capacities of girders fabricated using 0.7 inch strands and different
concrete strengths were calculated and compared to capacities of 0.6
inch strands girders fabricated using equivalent concrete strength.
The effect of bridge deck concrete strength on composite deck-girder
section capacity was investigated due to its possible effect on final
section capacity. Finally, a comparison was made to compare the
bridge cross-section of girders designed using regular 0.6 inch strands
and the large-diameter 0.7 inch. The research findings showed that
structural advantages of 0.7 inch strands allow for using fewer bridge
girders, reduced material quantity, and light-weight members. The
structural advantages of 0.7 inch strands are maximized when high
strength concrete (HSC) are used in girder fabrication, and concrete
of minimum 5ksi compressive strength is used in pouring bridge
decks. The use of 0.7 inch strands in bridge industry can partially
contribute to the improvement of bridge conditions, minimize
construction cost, and reduce the construction duration of the project.
Abstract: The National Bridge Inventory (NBI) includes more
than 600,000 bridges within the United States of America.
Prestressed concrete girder bridges represent one of the most widely
used bridge systems. The majority of these girder bridges were
constructed using 0.5 and 0.6 inch diameter strands. The main
impediments to using larger strand diameters are: 1) lack of prestress
bed capacities, 2) lack of structural knowledge regarding the transfer
and development length of larger strands, and 3) the possibility of
developing wider end zone cracks upon strand release.
This paper presents a study about using 0.7 inch strands in girder
fabrication. Transfer and development length were evaluated, and
girders were fabricated using 0.7 inch strands at different spacings.
Results showed that 0.7 inch strands can be used at 2.0 inch spacing
without violating the AASHTO LRFD Specifications, while attaining
superior performance in shear and flexure.
Abstract: The main objective of this paper is to determine the
isolated effect of silica fume on tensile, compressive and flexure strengths on high strength lightweight concrete. Many experiments
were carried out by replacing cement with different percentages of silica fume at different constant water-binder ratio keeping other mix
design variables constant. The silica fume was replaced by 0%, 5%,
10%, 15%, 20% and 25% for a water-binder ratios ranging from 0.26
to 0.42. For all mixes, split tensile, compressive and flexure strengths
were determined at 28 days. The results showed that the tensile, compressive and flexure strengths increased with silica fume incorporation but the optimum replacement percentage is not
constant because it depends on the water–cementitious material (w/cm) ratio of the mix. Based on the results, a relationship between
split tensile, compressive and flexure strengths of silica fume concrete was developed using statistical methods.
Abstract: In order to calculate the flexural strength of
normal-strength concrete (NSC) beams, the nonlinear actual concrete
stress distribution within the compression zone is normally replaced
by an equivalent rectangular stress block, with two coefficients of α
and β to regulate the intensity and depth of the equivalent stress
respectively. For NSC beams design, α and β are usually assumed
constant as 0.85 and 0.80 in reinforced concrete (RC) codes. From an
earlier investigation of the authors, α is not a constant but significantly
affected by flexural strain gradient, and increases with the increasing
of strain gradient till a maximum value. It indicates that larger
concrete stress can be developed in flexure than that stipulated by
design codes. As an extension and application of the authors- previous
study, the modified equivalent concrete stress block is used here to
produce a series of design charts showing the maximum design limits
of flexural strength and ductility of singly- and doubly- NSC beams,
through which both strength and ductility design limits are improved
by taking into account strain gradient effect.
Abstract: This article presents the analysis of experimental values regarding cracking pattern, specific strains and deformability for reinforced high strength concrete beams. The beams have the concrete class C80/95 and a longitudinal reinforcement ratio of 2.01%, respectively 3.39%. The elements were subjected to flexure under static short-term and long-term loading. The experimental values are compared with calculation values using the design relationships according to Eurocode 2.
Abstract: This paper in essence presents comparative
experimental data on the mechanical performance of steel and
synthetic fibre-reinforced concrete under compression, tensile split
and flexure. URW1050 steel fibre and HPP45 synthetic fibre, both
with the same concrete design mix, have been used to make cube
specimens for a compression test, cylinders for a tensile split test and
beam specimens for a flexural test. The experimental data
demonstrated steel fibre reinforced concrete to be stronger in flexure
at early stages, whilst both fibre reinforced concrete types displayed
comparatively the same performance in compression, tensile splitting
and 28-day flexural strength. In terms of post-crack controlHPP45
was preferable.