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International Concrete Abstracts Portal

Showing 1-5 of 473 Abstracts search results

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:

16-413

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


Document:

17-054

Author(s):

Yail J. Kim and Raymon W. Nickle

Publication:

Structural Journal

Volume:

115

Issue:

1

Abstract:

This paper presents the flexural characteristics of highway bridge girders prestressed with fiber-reinforced polymer (FRP) tendons. Of interest are the technical challenges identified by ACI Subcommittee 440-I (FRP-Prestressed Concrete): long-term multipliers, deformability, and minimum reinforcement. Aramid and carbon FRP (AFRP and CFRP, respectively) composites are used to prestress concrete girders. Based on analytical models, new design expressions are proposed for the aforementioned items, followed by an assessment using laboratory test data and full-scale benchmark bridges. The long-term multipliers calibrated per reliability theory are mostly different from the empirical multipliers adopted in ACI 440.4R-04. The girders prestressed with AFRP/CFRP sufficiently deform in flexure, even though their moment-curvature responses are not comparable with those of steel-prestressed girders. The new deformability index specifies design requirements for AFRP/CFRP-prestressed members with either compression-controlled or tensioned-controlled sections. The importance of a potential change in FRP modulus during the service life of prestressed concrete girders is examined. A factored ultimate-tocracking moment ratio of ϕMn/Mcr = 1.2 is suggested for girders prestressed with AFRP/CFRP, which aligns with the articles of existing design manuals and specifications dedicated to prestressed concrete.

Date:

January 1, 2018

DOI:

10.14359/51700988


Document:

16-309

Author(s):

J. Salazar, H. Yousefpour, R. Alirezaei Abyaneh, H. Kim, A. Katz, T. Hrynyk, and O. Bayrak

Publication:

Structural Journal

Volume:

115

Issue:

1

Abstract:

This paper presents an experimental study on transfer length, end-region cracking, and transverse end-region stresses in pretensioned concrete I-girders fabricated using 0.7 in. (17.8 mm) diameter strands on a 2 x 2 in. (51 x 51 mm) grid. The full-scale specimens consisted of two Tx46 and two Tx70 girders that were fabricated in a controlled laboratory environment using different strand patterns and concrete release strengths. The detailing for mild-steel reinforcement was done according to the current practice in Texas for girders with smaller-diameter strands. The measured 24-hour transfer lengths from the specimens exceeded estimates by both AASHTO LRFD and ACI 318-14 provisions. The observed crack widths in the specimens within 28 days after prestress transfer were generally limited to 0.007 in. (0.18 mm), indicating satisfactory performance for exposure to deicing chemicals according to ACI 224R guidelines. However, noticeably greater transverse forces were observed in the end regions of the specimens compared to the resistance required by AASHTO LRFD specifications.

Date:

January 1, 2018

DOI:

10.14359/51700783


Document:

16-222

Author(s):

G. A. Martinez, K. S. Beiter, A. R. Ghiami Azad, G. E. Polo, R. L. Shinn, T. D. Hrynyk, and O. Bayrak

Publication:

Structural Journal

Volume:

114

Issue:

6

Abstract:

The seventh edition of the AASHTO LRFD Bridge Design Specifications (2016 interim) includes revised provisions for the design of deep beams using the strut-and-tie method. The validity and accuracy of these provisions as applied to simply supported deep beams loaded in a manner that generates an inflection point between the supports was investigated in this research. As part of a course-related laboratory investigation, graduate students at the University of Texas at Austin used these provisions to design two reduced-scale deep beams. The specimens were subsequently constructed and tested. The experimental behaviors of the specimens including governing failure modes, load-displacement curves, and their ultimate capacities were investigated and compared with estimates developed from the strutand-tie method. The results obtained validated the suitability of the revised provisions for the design of deep beams with inflection points located between supports. Additionally, the students developed pre-test estimates for the behaviors and strengths of the two deep beam specimens using the finite element software program VecTor2. While there was some variation among the computed responses, the blind predictions accurately captured governing failure modes and provided reasonable capacity estimates.

Date:

November 1, 2017

DOI:

10.14359/51689504


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