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Showing 1-10 of 160 Abstracts search results

Document: 

17-426

Date: 

November 1, 2018

Author(s):

Yail J. Kim and Ahmed Ibraheem

Publication:

Structural Journal

Volume:

115

Issue:

6

Abstract:

This paper presents the efficacy of functional periodicity on controlling the occurrence of interfacial failure in concrete members strengthened with carbon fiber-reinforced polymer (CFRP) sheets. The hypothesis tested is that periodically placed stress reducers preserve the integrity of the CFRP-concrete interface by interrupting the progression of mechanical damage, unlike conventional debonding control methods based on a prescribed strain limit. To substantiate this novel debonding-control concept, an experimental program was conducted with three types of stress reducers: epoxy-filled grooves (PG), discrete U-wraps (PU), and silylmodified polymer (SMP) strips (PS). The load-carrying capacity of the PG and PU specimens is enhanced over 60% relative to the capacity of plain-bond control specimens (COT). The periodic configurations of these specimens (the number of grooves and U-wraps) influence the degree of the capacity increase and failure modes by distributing interfacial stresses. Although the capacity of the PS specimens is similar to that of the control, the permanent elastic nature of SMP improves the energy dissipation of the interface, which indicates the potential of the SMP-epoxy hybrid bond for seismic strengthening in tandem with other debonding-control methods. The groove and U-wrap near the loaded end dissipate interfacial fracture energy and impede stress progression. Statistical inference alongside a probability-based assessment corroborates that the individual debonding-control methods and their configurations affect the performance of the CFRP-concrete interface.

DOI:

10.14359/51702417


Document: 

17-113

Date: 

September 1, 2018

Author(s):

A. Macanovskis, A. Lukasenoks, A. Krasnikovs, R. Stonys, and V. Lusis

Publication:

Materials Journal

Volume:

115

Issue:

5

Abstract:

Concrete beams reinforced by short composite macrofibers uniformly distributed in their volume were tested mechanically in bending. The short composite macrofibers were a few centimeters long and less than 2.5 mm (0.01 in.) in diameter. Macrofibers were manufactured impregnating glass or carbon-fiber tows by epoxy resin, forming unidirectionally oriented composite material rods later cut in short pieces. Such fibers were designated in the framework of the paper as macrofibers. The length-to-diameter ratios L/d of the glass and carbon macrofibers were equal to 22.9 and 28.2, respectively. The beams were loaded until the opening of the macrocrack reached 5 mm (0.02 in.). The macrofibers bridging the crack were pulled out during opening of the crack. Low-, medium-, and high-strength concretes in the range of 40 to 120 MPa (5800 to 17,405 psi) were used in the experiments. Pullout tests with single fibers were carried out. The volume fraction of the fibers in concrete was 1.5%. Two types of fiber-reinforced concrete beams with glass and carbon fibers were manufactured and tested, and the data obtained were compared with experimental results for steel fiber-reinforced concrete beams. The potential of the composite fibers was analyzed.

DOI:

10.14359/51702343


Document: 

17-024

Date: 

July 1, 2018

Author(s):

Zuhair Al-Jaberi, John J. Myers, and Mohamed A. ElGawady

Publication:

Structural Journal

Volume:

115

Issue:

4

Abstract:

Eighteen reinforced masonry walls were built as a part of this study. These reinforced walls were strengthened with carbon fiber reinforced polymer (FRP) bars and strips and glass FRP bars using a near-surface-mounted (NSM) technique; different mild steel reinforcement ratios (ρ) were used. These simply supported walls were tested under an out-of-plane cyclic load that was applied along two line loads. Various parameters were investigated, including those related to FRP (type and amount), bond pattern (stack and running), mortar pattern (face shell bedding and fully bedding), embedding material (epoxy and cementitious paste), amount of internal steel reinforcement, existence of compression FRP bars, and groove size. The ultimate load, deflection at ultimate load, and mode of failure were investigated in this study. The test results indicated a significant increase in stiffness and flexural capacity of out-of-plane reinforced walls strengthened with FRP compared to the unstrengthened reinforced walls. Different modes of failure occurred in the strengthened reinforced walls, including flexure-shear failure through the concrete block, as well as debonding of FRP reinforcement from the masonry substrate. Furthermore, a simple analytical model for computing the moment capacity of strengthened reinforced masonry walls is proposed and compared with the experimental results.

DOI:

10.14359/51702227


Document: 

16-440

Date: 

July 1, 2018

Author(s):

Mostfa Al Azzawi, Philip Hopkins, Joseph Ross, Gray Mullins, and Rajan Sen

Publication:

Structural Journal

Volume:

115

Issue:

4

Abstract:

Two full-scale concrete masonry walls were repaired with three horizontally aligned 20 in. (508 mm) wide unidirectional carbon fiber sheets using different commercially available epoxies. Twenty years later, the carbon fiber-reinforced polymer concrete masonry unit (CFRP-CMU) bond was determined through selective pulloff tests that were preceded by detailed nondestructive evaluation. Results showed that despite superficial damage to the top epoxy coating and debonding along masonry joints, the residual CFRP-CMU bond for the wall surface was largely unaffected by prolonged exposure to Florida’s harsh environment. Therein, over 90% of the failures were in the concrete substrate. Although bond was poorer at mortar joints because the CFRP was well bonded to the masonry surface, its impact on structural performance of the repair was expected to be minimal. Overall, the repairs proved to be durable with both epoxy systems performing well.

DOI:

10.14359/51702226


Document: 

17-003

Date: 

November 1, 2017

Author(s):

Ruohong Zhao, Christopher Y. Tuan, Daobo Fan, An Xu, and Bao Luo

Publication:

Materials Journal

Volume:

114

Issue:

6

Abstract:

An innovative conductive composite, ionically conductive mortar, is developed in this study. The directional migration of ions under external voltage makes the mortar conductive. The electrical resistance of the mortar causes the mortar to generate heat, which is used for deicing. To ensure conductivity, the number of free ions and the moisture content in the mortar must stay relatively high. The specimens were soaked in electrolyte solutions for 96 hours to saturation and coated with epoxy resin. Subsequent electrical heating tests showed that the specimens could achieve a heating rate of 19.7°C (35.5°F) in 120 minutes under 30 V AC. This heating performance would improve with increasing applied voltage.

DOI:

10.14359/51700897


Document: 

16-429

Date: 

September 1, 2017

Author(s):

Ruo-Yang Wu and Chris P. Pantelides

Publication:

Structural Journal

Volume:

114

Issue:

5

Abstract:

Experimental results are presented regarding the seismic repair of reinforced concrete bridge columns using a carbon fiber-reinforced polymer (CFRP) shell and epoxy-anchored headed steel bars. The CFRP shell, consisting of unidirectional laminates in the hoop and vertical direction, encloses the headed bars and is filled with non-shrink concrete to relocate the column plastic hinge. Two columns designed to current standards—one in a cap beam-to-column connection and the other in a footing-to-column connection—were damaged under cyclic forces. Damage included longitudinal bar fracture and buckling across multiple spiral hoops; concrete damage in the plastic hinge region included cracking and spalling of the column core concrete. Finite element analysis was used to design the CFRP shell and the headed bars were designed for the increased flexural demand on the repaired section. The seismic repair was rapid, required minimal intervention, and successfully relocated the plastic hinge and restored strength and displacement capacity.

DOI:

10.14359/51700789


Document: 

16-185

Date: 

July 1, 2017

Author(s):

Vahab Toufigh, Mostafa Jafarian Abyaneh, and Khashayar Jafari

Publication:

Materials Journal

Volume:

114

Issue:

4

Abstract:

In this investigation, polymer concrete (PC) with three different epoxy resin contents, ordinary cement concrete (OCC), lightweight concrete (LWC), and lime-mortar soil (LMS) have been studied under uniaxial and triaxial compression tests to determine their mechanical behavior by measuring axial stress-strain and volumetric strain versus axial strain curves. According to the results, PC showed higher strength, ductility, and energy absorption than that of OCC and LWC. Then, nonlinear finite element analysis (NFEA) was implemented to predict the experimental results using hierarchical single-surface (HISS) failure criterion and disturbed state concept (DSC) to capture the elastoplastic behavior of concrete materials including volumetric strain. Moreover, the pattern of failure was estimated using ultimate disturbance values obtained from the model, followed by comparison with the experimental and Mohr-Coulomb failure patterns. The proposed model is applicable to a variety of materials with different behavior, and its prediction is in good accordance with experimental results.

DOI:

10.14359/51689716


Document: 

15-441

Date: 

May 1, 2017

Author(s):

Rahulreddy Chennareddy and Mahmoud M. Reda Taha

Publication:

Structural Journal

Volume:

114

Issue:

3

Abstract:

Flexural strengthening of reinforced concrete (RC) beams using near-surface-mounted (NSM) fiber-reinforced polymers (FRP) and U-wrap FRP shear strengthening are two well-established methods. There is a fair chance that the two aforementioned techniques might be mixed in strengthening of RC beams. This research examines the behavior of RC beams strengthened using NSM and U-wrap FRP strengthening. The NSM-FRP flexural strengthening technique is strongly dependent on the performance of bond between the NSM-FRP bar and the surrounding epoxy. Tension rupture of the NSM-FRP bar is highly unlikely, even when a full development length is provided. However, when U-wrap FRP is considered, confinement has shown to improve the bond strength of NSM-FRP bars and marginally increase the flexural capacity of strengthened RC beams. However, the improvement in the bond strength of NSM-FRP bars results in changing the NSM-FRP debonding to an abrupt failure caused by NSM-FRP bar rupture. Special care should be taken in designing RC strengthening combining NSM and U-wrap FRP strengthening.

DOI:

10.14359/51689443


Document: 

15-173

Date: 

May 1, 2016

Author(s):

Joel E. Parks, Dylan N. Brown, M. J. Ameli, and Chris P. Pantelides

Publication:

Structural Journal

Volume:

113

Issue:

3

Abstract:

A repair technique for severely damaged precast reinforced concrete (RC) bridge columns with grouted splice sleeve (GSS) connections has been developed that uses a carbon fiber-reinforced polymer (CFRP) shell and epoxy-anchored headed bars to relocate the column plastic hinge. Four original specimens were built using an accelerated bridge construction (ABC) technique with two different GSS systems and were tested to failure using cyclic quasi-static loads. One GSS system was used to connect an RC bridge pier cap to a column and the second GSS system was used to connect an RC footing to a column. Failure of the four original specimens occurred at drift ratios between 5.6 and 8.0% with longitudinal bar fracture or pullout from the GSS connections. The repair method successfully relocated the plastic hinge to the original column section adjacent to the repair and was capable of restoring the diminished load and displacement capacity. The method is a viable and cost-effective technique for rapid seismic repair of severely damaged precast bridge assemblies.

DOI:

10.14359/51688756


Document: 

14-410

Date: 

May 1, 2016

Author(s):

Joseph Jones and Julio A. Ramirez

Publication:

Structural Journal

Volume:

113

Issue:

3

Abstract:

This paper describes an examination of the development of tension lap splices in high-strength concrete and the applicability of the restriction in the ACI 318 code where the values of √fc′ used to calculate development length shall not exceed 100 psi. The focus is on the development of splices with Grade 60 epoxy-coated and uncoated bars in normal weight concrete. A summary of the behavior of bond is presented to provide context for the study. It is followed by a literature review to analyze the relevant previous experimental work in this area. Based on the analysis of those data, a modification to the current code limitation is proposed. The main conclusion of this paper is that the limit of 100 psi (0.689 MPa) on the square root of the specified compressive strength in Section 12.1.2 of ACI 318-11 (Section 25.4.1.4 of 318-14) may be extended to 120 psi (0.827 MPa) based on the analysis of available data without significant modifications to the current provisions for concrete strengths up to 16,000 psi (110 MPa).

DOI:

10.14359/51688620


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