International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-10 of 293 Abstracts search results

Document: 

18-153

Date: 

March 1, 2019

Author(s):

Usama Ebead, Ahmed El Refai, Kshitij Shrestha, and Antonio Nanni

Publication:

Structural Journal

Volume:

116

Issue:

2

Abstract:

The structural performance of reinforced concrete (RC) beams strengthened with fabric-reinforced cementitious matrix (FRCM) was investigated. Fourteen unstrengthened and strengthened beams were tested in flexure under four-point load configuration. Test parameters included the internal reinforcement ratios (0.5% representing flexure-deficient beams and 0.72 or 1.27% representing typical under-reinforced beams), the type of FRCM fabric (carbon and polyparaphenylene benzobisoxazole [PBO]), the number of fabric plies (one and two plies), and the strengthening scheme (straight at soffit or U-wrap). Test results revealed that the gain in flexural strength was inversely proportional to the internal reinforcement ratio of the beams regardless of the fabric type, scheme, or number of plies used. U-wrap strengthening scheme provided an inherent anchorage that limited the premature delamination of the fabric, which was a common mode of failure in the soffit-strengthening scheme. Beams strengthened with U-wrap single-ply of carbon- and PBO-FRCM showed an average gain in strength of 70% and 51%, respectively, compared to 28% and 20% for their counterparts strengthened with the soffit scheme. Moreover, the use of U-wrap double-ply of PBO fabric resulted in an average gain in strength of 72%. The theoretical formulations of ACI 549 satisfactorily predicted the load-carrying capacities of the soffit and U-wrap strengthened beams with an average ratio of Pu/Pu Th of 1.07 and a standard deviation of 11%.

DOI:

10.14359/51713292


Document: 

18-058

Date: 

March 1, 2019

Author(s):

Jonathan P. Rivera and Andrew S. Whittaker

Publication:

Structural Journal

Volume:

116

Issue:

2

Abstract:

FEMA P-58 provides engineers with second-generation tools for performance-based seismic assessment of buildings. Central to the loss calculations enabled by FEMA P-58 are fragility functions, which plot the probability of exceeding a user-specified damage state (linked to a repair measure) as a function of a demand parameter. Gulec and Whittaker developed the fragility functions for shear-critical reinforced concrete walls that are part of the FEMA P-58 documentation. In past experimental programs, damage was often reported at displacements greater than that of peak shear strength and damage data at zero lateral loading, mimicking the post-earthquake condition, was not provided. This paper updates the fragility functions developed by Gulec and Whittaker using damage documented at zero lateral loading, which is the starting point for repair. The fragility functions use peak transient displacement as the demand parameter because it is output from seismic analysis of a numerical model.

DOI:

10.14359/51711139


Document: 

18-021

Date: 

January 1, 2019

Author(s):

Youngjae Choi and Shih-Ho Chao

Publication:

Structural Journal

Volume:

116

Issue:

1

Abstract:

This paper presents an experimental study on the seismic performance of reinforced concrete (RC) perimeter interior special moment frames (SMFs) that use high-performance fiber-reinforced concrete (HPFRC) in joint and beam plastic hinge regions. This research evaluates the feasibility of using both HPFRC joint and beams as major sources of energy dissipation in an effort to reduce overall damage and repair cost after earthquakes and to provide ease of construction for beam-column connections. A balanced damage concept was used so the energy dissipation was shared by the joint and beam plastic hinges, thereby preventing severe damage from occurring to the beams. This concept together with the mechanical properties provided by HPFRC, including high shear and bond strength, reduce the need of placing a large number of transverse reinforcement in the joint and beam plastic hinge regions. A full-scale HPFRC slab-beam-column (SBC) subassemblage designed with this concept was tested under large displacement reversals. This specimen used a small amount of transverse reinforcement (approximately 20% of that used in a typical RC joint) in the joint and no transverse reinforcement in the beam plastic hinge regions, thus significantly enhancing the constructability. A counterpart conventional RC specimen compliant with ACI 318-14 was tested under the same loading protocol. Both specimens showed stable hysteretic responses up to 3.5% column drift ratio without significant strength degradation, which meets the collapse prevention structural performance according to the criteria given in ACI 374. Experimental results show that the damage in the HPFRC specimen was distributed in both joint and beam ends, whereas the conventional RC specimen had severe damage concentrated in the beam plastic hinging regions. This research proves the feasibility of using ductile HPFRC joint to dissipate seismic energy, thereby balancing the damage between the joint and beams.

DOI:

10.14359/51710875


Document: 

17-181

Date: 

November 1, 2018

Author(s):

A. C. Altunısık, O. S. Karahasan, A. F. Genç, F. Y. Okur, M. Günaydın, E. Kalkan, and S. Adanur

Publication:

Structural Journal

Volume:

115

Issue:

6

Abstract:

The aim of this paper was to determine the effect of fiber-reinforced polymer (FRP) strengthening on the dynamic characteristics of reinforced concrete (RC) frames using ambient vibration-based automated model updating procedure. Four different structural conditions were examined: undamaged, damaged, “repaired with injections”; and “strengthened with FRP composites”. Ambient vibration tests were conducted to extract the experimental dynamic characteristics using enhanced frequency domain decomposition (EFDD) and stochastic subspace identification (SSI) methods. To validate the experimental results, an initial finite element (FE) model was constructed and numerical dynamic characteristics obtained. To eliminate the differences between initial FE and experimental results, global and sensitivity-based automated model updating procedures were applied to account for various uncertain parameters. The maximum differences were reduced from 38.38% to 4.14% and 0.21% with global and automated model updating. The updated FE model was used as the initial model for the damaged condition. This procedure was followed for each structural condition in turn to demonstrate the effect of FRP strengthening.

DOI:

10.14359/51706894


Document: 

16-129

Date: 

November 1, 2018

Author(s):

Katelyn S. Low, Gloriana Arrieta Martinez, David M. Wald, and Oguzhan Bayrak

Publication:

Structural Journal

Volume:

115

Issue:

6

Abstract:

As concrete infrastructure ages or is repurposed, there is an increasing need for efficient retrofit solutions. A possible retrofit technique to increase the capacity of members with deficient tension lap splices is to use post-installed, undercut anchors. The anchors can provide active confinement in the splice region. This solution requires access to only one face of the reinforced concrete element being repaired, greatly facilitating its implementation in existing structures. To evaluate this retrofit solution, four large-scale tests on beam specimens were completed at the University of Texas at Austin. One specimen contained the full tension lap splice length required by ACI 318-71 provisions and served as a control specimen. The other three specimens contained half of that tension lap splice length. One of the latter specimens was tested without a retrofit to determine baseline behavior while the other two were retrofitted. Results from these tests indicated that post-installed anchors could enhance the strength of members with deficient lap splices up to half the specified length.

DOI:

10.14359/51702378


Document: 

17-480

Date: 

September 1, 2018

Author(s):

Yao Luan, Osamu Sanada, and Hiroshi Mutsuyoshi

Publication:

Materials Journal

Volume:

115

Issue:

5

Abstract:

The durability of concrete structures is increasingly being compromised by corrosion of the steel reinforcement resulting from chloride attack. Although mortar containing a nitrite compound is often used in repair work to inhibit corrosion, a harmless and more economical material is sought. The authors investigated adding an ion-exchange resin (IER) to mortar as a possible way to remove chloride from old concrete. IERs, which are widely used in water purification, are capable of exchanging chloride ions in aqueous condition. The anion exchange capacity of an IER in cement solution is experimentally investigated. Then, two chloride diffusion experiments, one involving immersion and drying cycles and the other inverse diffusion from a mortar substrate, are carried out with IER mortar. Chloride profiles are determined by titration and the chlorine distribution is visualized. The results confirm that the IER accelerates chloride diffusion in the mortar as a result of its ability to exchange chloride ions.

DOI:

10.14359/51706845


Document: 

17-196

Date: 

September 1, 2018

Author(s):

D. G. Mapa, A. Markandeya, A. Sedaghat, N. Shanahan, H. DeFord, K. A. Riding, and A. Zayed

Publication:

Materials Journal

Volume:

115

Issue:

5

Abstract:

Jointed plain concrete pavement (JPCP) replacement slabs can experience early-age cracking from early-age volume change. These slabs are often made of high-early-strength (HES) concrete characterized by high cement content and low water-cement ratio (w/c), which can result in large temperature rise and high levels of autogenous shrinkage, and ultimately an elevated cracking potential. This study investigated the effects of reduced paste content and base restraint minimization on reducing concrete early-age cracking potential. The effect of each of these measures was evaluated in place by measuring the stress and temperature development in concrete test slabs instrumented with concrete stressmeters and thermocouples. Calorimetry studies and mechanical properties testing were used with modeling software to assess field trends. The findings indicated that it is possible to achieve higher strengths and lower stresses with low-paste mixtures. Changes in concrete stress during the first 24 hours after placement, due to moisture loss to the base, were seen in slabs with polyethylene sheet or geotextile fabric underneath the slab.

DOI:

10.14359/51702241


Document: 

17-275

Date: 

July 1, 2018

Author(s):

Haider M. Al-Jelawy, Kevin R. Mackie, and Zachary B. Haber

Publication:

Structural Journal

Volume:

115

Issue:

4

Abstract:

Accelerated bridge construction (ABC) is being increasingly used in new bridge construction and repair. For bridge substructure elements, ABC typically requires connections, such as mechanical couplers, between prefabricated elements where moment demands are largest. Grouted sleeves (GSs) offer good construction tolerances and load transfer between precast concrete elements. Therefore, they have gained interest for use in ABC in seismic regions. Large-scale precast column models using GS splices were designed and tested using a shifted plastic hinge (SPH) concept to minimize the damage in the footing and retain the column ductility. The testing matrix considered aspect ratio, moment gradient, and splicing details. Results showed that SPH can be used for flexural and flexural-shear columns; plastic hinging formed above the sleeve region and footing dowels remained elastic to minimize footing damage. Each precast column exhibited good ductility and energy dissipation, and formed slightly shorter SPH length compared with conventional columns.

DOI:

10.14359/51702233


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: 

17-246

Date: 

May 1, 2018

Author(s):

P. Kathirvel, S.-J. Kwon, H.-S. Lee, S. Karthick, and V. Saraswathy

Publication:

Materials Journal

Volume:

115

Issue:

3

Abstract:

In the present investigation, a feasibility study was made for the first time by using graphite ore tailings (GOTS) as a replacement material for river sand in making mortar and concrete. As-received GOTS and treated GOTS (T-GOTS) at 1000°C (1832°F) were replaced with river sand and various percentages of replacement ranging from 10 to 100%, and their strength evaluation, were done by conducting compression and split tensile tests in mortar and concrete. Bond strength was evaluated using a pullout test and the permeability characteristic was assessed by water absorption and effective porosity tests. The quality of the concrete was assessed by electrical resistivity and ultrasonic pulse velocity measurements. The corrosion resistance evaluation was done by half-cell potential measurement, alternating current impedance or electrochemical impedance spectra, and potentio-dynamic polarization studies. From the studies, it is observed that river sand may be replaced with 40% T-GOTS and be effectively used for structural repair applications.

DOI:

10.14359/51702191


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