International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-5 of 476 Abstracts search results

Document:

17-352

Author(s):

Vasileios Papadopoulos, Juan Murcia-Delso, and P. Benson Shing

Publication:

Structural Journal

Volume:

115

Issue:

5

Abstract:

This paper presents results of an investigation on the development of headed bars extending from a column into the slab of a reinforced concrete slab bridge. Three full-scale slab-column specimens were tested under quasi-static cyclic lateral loading to determine the minimum embedment length required for the headed bars to develop their full tensile capacity, and the reinforcement details needed in the slab-column joint region to prevent premature anchorage failure, when a plastic hinge forms at the top of the column. The experimental results showed that for 5000 psi (34.5 MPa) concrete and Grade 60 steel, a development length equal to 11 times the bar diameter is adequate for headed bars in slab-column joints designed according to Caltrans specifications with a minimum of 2 in. (50.8 mm) of clear concrete cover. Specimens with shorter embedment lengths were able to develop the moment capacity of the columns and showed significant ductility, but exhibited moderate to severe punching cracks in the cover concrete of the slabs. Finite element analyses of slab-column assemblies showed that punching damage can be eliminated by increasing the concrete cover above the bar heads.

Date:

September 1, 2018

DOI:

10.14359/51702247


Document:

16-348

Author(s):

Caitlin M. Tibbetts, Michael C. Perry, Christopher C. Ferraro, and H. R. (Trey) Hamilton

Publication:

Structural Journal

Volume:

115

Issue:

4

Abstract:

The structural design of concrete is typically based on service limit states and uses the modulus of elasticity as a design parameter. However, the modulus of elasticity of concrete used for the design of structures is typically determined indirectly using specified compressive strength. This research investigated the differences between the physical and empirically based relationships of the modulus of elasticity and compressive strength of concrete. Concrete incorporating various types of coarse aggregate was evaluated with particular emphasis on limestone from Florida formations, better known as limerock. The goal of this research was to establish the accuracy of coarse aggregate correction factors used for predicting the modulus of elasticity of concrete. It was found that a value of 1.0, rather than 0.9, was appropriate for the correction factor for Florida limerock; the current structural design guidelines used by the Florida Department of Transportation have revised the specifications to reflect this finding.

Date:

July 1, 2018

DOI:

10.14359/51701914


Document:

16-372

Author(s):

Jun Ki Lee

Publication:

Structural Journal

Volume:

115

Issue:

3

Abstract:

This study investigates the transfer length of 0.6 in. (15.4 mm) Grade 350 (2400 MPa) strand in 11.6 ksi (80 MPa) pretensioned concrete members. The test specimens were fabricated considering an accelerated construction scheme including gradual releasing and strand debonding, along with steam curing to achieve three initial concrete compressive strengths (fci′) of 5.8, 8.7, and 11.6 ksi (40, 60, and 80 MPa). At the release, the longitudinal strain profiles of both strand and concrete were measured using a series of electrical resistance strain gauges (ERSGs) to determine the transfer length. The strain profiles of the strands were in good agreement to those of the concrete and clearly presented the prestress bond transfer from the strand to the concrete. The experimental results indicate that the transfer length of high-strength concrete pretensioned members with Grade 350 strands is well-correlated to the initial compressive strength of concrete (fci′). Also, the transfer length is conservatively predicted using the design provisions in the ACI 318 and AASHTO specifications.

Date:

May 1, 2018

DOI:

10.14359/51701295


Document:

16-098

Author(s):

Jacob D. Henschen, Daniel I. Castaneda, and David A. Lange

Publication:

Materials Journal

Volume:

115

Issue:

3

Abstract:

Industry guidelines recommend that formwork be designed to withstand full hydrostatic pressures when using self-consolidating concrete (SCC) and highly flowable concrete. However, full hydrostatic pressures are seldom observed during SCC pours, meaning that it is possible to safely relax formwork design specifications. Numerous researchers have developed models that incorporate lab-tested material values to predict formwork pressure, but these models are affected by changing concrete mixture design, air temperature, humidity, and other factors that cannot be accounted for quickly. A simple field test method and model is presented in this study that predicts the formwork pressure using a calibrated behavior, which we call a “pressure decay signature.” The simple formwork pressure model is shown to agree well with experimentally measured values during the construction of two tall-walls, suggesting that this method and model can contribute to increased cost efficiency of SCC construction while maintaining safe practices.

Date:

May 1, 2018

DOI:

10.14359/51702183


Document:

16-413

Author(s):

Yail J. Kim, Jae-Yoon Kang, Jong-Sup Park, and Woo-Tai Jung

Publication:

Structural Journal

Volume:

115

Issue:

2

Abstract:

This paper presents an analytical investigation into the performance of a reinforced concrete bridge girder strengthened with post-tensioned near-surface-mounted (NSM) carbon fiberreinforced polymer (CFRP) strips in a corrosion-overload multihazard environment. Stochastic models are formulated to examine the service- and strength-level responses, functional requirements such as deformability and vulnerability, and time-dependent reliability of the strengthened girder. In conjunction with environmental data recorded for 30 years, four service zones specified in the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications are employed to generate practical research outcomes. Chloride-induced diffusion becomes more active in summer compared with other seasons. As such, stresses in the girders’ steel reinforcement increase with the progression of corrosion; however, the increase does not cause a fatigue concern. A marginal increase in CFRP stress is noticed, spanning a 100-year service period. The deformability of the strengthened girder is acceptable within a reduction range of up to 20%. The multi-hazard distress augments the vulnerability of the girder and, accordingly, affects the long-term reliability, which should be taken into consideration when implementing the NSM CFRP technology.

Date:

March 1, 2018

DOI:

10.14359/51701118


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