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Special Issue "Selected Papers from "SMAR 2013""

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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (30 November 2013)

Special Issue Editors

Guest Editor
Prof. Dr. Masoud Motavalli (Website)

Empa, Structural Engineering Research Laboratory, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Phone: +41 58 765 4116
Interests: application of advanced materials (such as fiber-reinforced polymer composites and shape memory alloys in civil engineering); structural rehabilitation and repair; seismic retrofitting; large and full scale laboratory and field experiments
Guest Editor
Prof. Dr. Alper Ilki (Website)

Structural and Earthquake Engineering Laboratory, Civil Engineering Faculty, Istanbul Technical University, 34469 Maslak Istanbul, Turkey
Phone: + 90 212 285 3838 (office)
Fax: + 90 212 285 3838
Interests: structural engineering; reinforced concrete structures; masonry structures; seismic retrofit with advanced materials; seismic performance assessment

Special Issue Information

Dear Colleagues,

This is a special issue for the extended versions of the best papers of the SMAR2013 conference (www.smar-2013.org) in the field of rehabilitation of civil structures using FRP composites. The topics are included but not limited to:

  • External strengthening of concrete, timber and steel structures using FRP composites
  • Strengthening of masonry and historic structures using FRP composites
  • Confinement of concrete columns using FRP composites
  • Near surface mounting reinforcement using FRP composites
  • Seismic Retrofitting using FRP composites
  • Durability issues of FRP strengthened structures as related to harsh environments
  • Fire protection systems for FRP strengthened structures
  • Practical applications and case studies.


Prof. Dr. Masoud Motavalli
Prof. Dr. Alper Ilki
Guest Editors

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs).


Keywords

  • FRP composites
  • external strengthening
  • structural rehabilitation
  • durability
  • fire protection systems
  • NSMR using FRP
  • seismic retrofitting

Published Papers (15 papers)

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Research

Jump to: Review

Open AccessArticle Cost and Ductility Effectiveness of Concrete Columns Strengthened with CFRP and SFRP Sheets
Polymers 2014, 6(5), 1381-1402; doi:10.3390/polym6051381
Received: 26 December 2013 / Revised: 19 April 2014 / Accepted: 4 May 2014 / Published: 13 May 2014
Cited by 2 | PDF Full-text (445 KB) | HTML Full-text | XML Full-text
Abstract
Recently, steel fibre reinforced polymers (SFRP) sheets have been introduced for the repair and rehabilitation of concrete structures. Few researchers studied the behaviour of the concrete columns wrapped with SFRP sheets; however, several critical parameters such as the cost and ductility effectiveness [...] Read more.
Recently, steel fibre reinforced polymers (SFRP) sheets have been introduced for the repair and rehabilitation of concrete structures. Few researchers studied the behaviour of the concrete columns wrapped with SFRP sheets; however, several critical parameters such as the cost and ductility effectiveness of the SFRP wrapped concrete columns have been lightly addressed. Thus, the main objective of this paper is to study the cost and ductility effectiveness of SFRP wrapped concrete columns and compare the results with the conventionally used carbon FRP (CFRP) wrapped concrete columns. In addition, an analytical procedure to predict the cost effectiveness of SFRP wrapped concrete columns is also suggested, from which, a parametric study was conducted. The parametric study investigated the effect of the concrete strength, the number of SFRP layers, and the size and slenderness effects on the cost effectiveness of the concrete columns wrapped with SFRP sheets. The results from the cost and ductility effectiveness study indicated that the SFRP wrapped concrete columns showed enhanced performance over the CFRP wrapped concrete columns. The suggested analytical procedure proved to be a reliable and accurate method to predict the cost effectiveness parameter of SFRP wrapped concrete columns. The parametric study showed the significant impact of the investigated parameters on the cost effectiveness of concrete columns wrapped with SFRP sheets. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Simplified Modeling of Rectangular Concrete Cross-Sections Confined by External FRP Wrapping
Polymers 2014, 6(4), 1187-1206; doi:10.3390/polym6041187
Received: 2 December 2013 / Revised: 10 February 2014 / Accepted: 8 April 2014 / Published: 17 April 2014
Cited by 6 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes [...] Read more.
The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes for reinforced concrete (RC) columns are considered herein, namely square and rectangular. The simplified model is derived from a more refined iterative confinement model proposed by the same authors to evaluate the entire stress-strain relationship of confined concrete. Based on a detailed analysis of the stress state through Mohr’s circle, a simplified closed form solution is proposed to account for the non-uniformly confined concrete performance exhibited in non-axisymmetric sections. The non-uniform confining stress field exhibited in such cross-sections is explicitly considered by means of the mean value integral of the pointwise variable stress state over the cross-section. The key aspect of the proposed methodology is the evaluation of the effective equivalent pressure to be inserted in any triaxial confinement model, to account for the peculiarities of square and rectangular cross-sections. Experimental data, available in the literature and representative of a wide stock of applications, were compared to the results of the theoretical simplified model to validate the proposed approach, and satisfactory results were found. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Finite Element Analysis for Fatigue Damage Reduction in Metallic Riveted Bridges Using Pre-Stressed CFRP Plates
Polymers 2014, 6(4), 1096-1118; doi:10.3390/polym6041096
Received: 24 December 2013 / Revised: 6 March 2014 / Accepted: 26 March 2014 / Published: 11 April 2014
Cited by 8 | PDF Full-text (1679 KB) | HTML Full-text | XML Full-text
Abstract
Many old riveted steel bridges remain operational and require retrofit to accommodate ever increasing demands. Complicating retrofit efforts, riveted steel bridges are often considered historical structures where structural modifications that affect the original construction are to be avoided. The presence of rivets [...] Read more.
Many old riveted steel bridges remain operational and require retrofit to accommodate ever increasing demands. Complicating retrofit efforts, riveted steel bridges are often considered historical structures where structural modifications that affect the original construction are to be avoided. The presence of rivets along with preservation requirements often prevent the use of traditional retrofit methods, such as bonding of fiber reinforced composites, or the addition of supplementary steel elements. In this paper, an un-bonded post-tensioning retrofit method is numerically investigated using existing railway riveted bridge geometry in Switzerland. The finite element (FE) model consists of a global dynamic model for the whole bridge and a more refined sub-model for a riveted joint. The FE model results include dynamic effects from axle loads and are compared with field measurements. Pre-stressed un-bonded carbon fiber reinforced plastic (CFRP) plates will be considered for the strengthening elements. Fatigue critical regions of the bridge are identified, and the effects of the un-bonded post-tensioning method with different pre-stress levels on fatigue susceptibility are explored. With an applied 40% CFRP pre-stress, fatigue damage reductions of more than 87% and 85% are achieved at the longitudinal-to-cross beam connections and cross-beam bottom flanges, respectively. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Nonlinear Progressive Damage Analysis of Notched or Bolted Fibre-Reinforced Polymer (FRP) Laminates Based on a Three-Dimensional Strain Failure Criterion
Polymers 2014, 6(4), 949-976; doi:10.3390/polym6040949
Received: 2 January 2014 / Revised: 19 March 2014 / Accepted: 21 March 2014 / Published: 31 March 2014
Cited by 3 | PDF Full-text (2999 KB) | HTML Full-text | XML Full-text
Abstract
Notching and bolting are commonly utilised in connecting fibre-reinforced polymer (FRP) laminates. These mechanical methods are usually superior to other connections, particularly when joining thick composite laminates. Stress distributions, damage modes and ultimate strengths in notched or bolted FRP laminate designs are [...] Read more.
Notching and bolting are commonly utilised in connecting fibre-reinforced polymer (FRP) laminates. These mechanical methods are usually superior to other connections, particularly when joining thick composite laminates. Stress distributions, damage modes and ultimate strengths in notched or bolted FRP laminate designs are of particular interest to the industrial community. To predict the ultimate strengths and the failure processes of notched or bolted composite laminates, nonlinear progressive damage analyses (PDA) based on the finite element method (FEM) at the meso-scale level are performed in this paper. A three-dimensional strength criterion in terms of strains, which can distinguish different damage modes, was developed and adopted in the analysis model to detect damage initiation in the laminates. Different material degradation methods and the influence of cohesive layers were discussed and compared with results of verification experiments. The results showed that the analysis model that used the succinct strength criterion proposed in this paper could properly predict the damage initiation and the ultimate strengths of notched or bolted FRP laminates. The errors between the numerical results and experimental data were small. The material degradation method with continuum damage mechanics (CDM)-based exponential damage factors using the damage index as the independent variable achieved greater accuracy and convergence than the method with CDM-based exponential damage factors using the square index as the independent variable or than the method with constant damage factors. Adding cohesive layers in the model had negligible influence on the final results, largely because the succinct analysis model proposed in this paper is sufficiently accurate in cases of small delamination. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Behavior of FRP Bars-Reinforced Concrete Slabs under Temperature and Sustained Load Effects
Polymers 2014, 6(3), 873-889; doi:10.3390/polym6030873
Received: 28 November 2013 / Revised: 10 March 2014 / Accepted: 12 March 2014 / Published: 18 March 2014
Cited by 2 | PDF Full-text (970 KB) | HTML Full-text | XML Full-text
Abstract
The large temperature variation has a harmful effect on concrete structures reinforced with fiber reinforced polymer (FRP) bars. This is due to the significant difference between transverse coefficient of thermal expansion of these bars and that of the hardened concrete. This difference [...] Read more.
The large temperature variation has a harmful effect on concrete structures reinforced with fiber reinforced polymer (FRP) bars. This is due to the significant difference between transverse coefficient of thermal expansion of these bars and that of the hardened concrete. This difference generates a radial pressure at the FRP bar/concrete interface, and may cause splitting cracks within concrete. This paper presents results of an experimental and analytical study carried out on FRP-reinforced concrete slabs subjected, simultaneously, to thermal and mechanical loads. The analytical model based on the theory of linear elasticity consists to evaluate combined effects of thermal and mechanical loads on the transverse expansion of FRP bars. Parameters studied in this investigation are the concrete cover thickness, FRP bar diameter, and the temperature variation. The thermal cycles were varied from −30 to +60 °C. Comparisons between analytical and experimental results show that transverse strains predicted from the proposed model are in good correlation with experimental results. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle RC Beams Strengthened with Mechanically Fastened Composites: Experimental Results and Numerical Modeling
Polymers 2014, 6(3), 613-633; doi:10.3390/polym6030613
Received: 18 December 2013 / Revised: 17 February 2014 / Accepted: 19 February 2014 / Published: 5 March 2014
Cited by 3 | PDF Full-text (1464 KB) | HTML Full-text | XML Full-text
Abstract
The use of mechanically-fastened fiber-reinforced polymer (MF-FRP) systems has recently emerged as a competitive solution for the flexural strengthening of reinforced concrete (RC) beams and slabs. An overview of the experimental research has proven the effectiveness and the potentiality of the MF-FRP [...] Read more.
The use of mechanically-fastened fiber-reinforced polymer (MF-FRP) systems has recently emerged as a competitive solution for the flexural strengthening of reinforced concrete (RC) beams and slabs. An overview of the experimental research has proven the effectiveness and the potentiality of the MF-FRP technique which is particularly suitable for emergency repairs or when the speed of installation and immediacy of use are imperative. A finite-element (FE) model has been recently developed by the authors with the aim to simulate the behavior of RC beams strengthened in bending by MF-FRP laminates; such a model has also been validated by using a wide experimental database collected from the literature. By following the previous study, the FE model and the assembled database are considered herein with the aim of better exploring the influence of some specific aspects on the structural response of MF-FRP strengthened members, such as the bearing stress-slip relationship assumed for the FRP-concrete interface, the stress-strain law considered for reinforcing steel rebars and the cracking process in RC members resulting in the well-known tension stiffening effect. The considerations drawn from this study will be useful to researchers for the calibration of criteria and design rules for strengthening RC beams through MF-FRP laminates. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Nonlinear Analyses of Adobe Masonry Walls Reinforced with Fiberglass Mesh
Polymers 2014, 6(2), 464-478; doi:10.3390/polym6020464
Received: 5 December 2013 / Revised: 30 January 2014 / Accepted: 10 February 2014 / Published: 17 February 2014
Cited by 6 | PDF Full-text (2389 KB) | HTML Full-text | XML Full-text
Abstract
Adobe constructions were widespread in the ancient world, and earth was one of the most used construction materials in ancient times. Therefore, the preservation of adobe structures, especially against seismic events, is nowadays an important structural issue. Previous experimental tests have shown [...] Read more.
Adobe constructions were widespread in the ancient world, and earth was one of the most used construction materials in ancient times. Therefore, the preservation of adobe structures, especially against seismic events, is nowadays an important structural issue. Previous experimental tests have shown that the ratio between mortar and brick mechanical properties (i.e., strength, stiffness and elastic modulus) influences the global response of the walls in terms of strength and ductility. Accurate analyses are presented in both the case of unreinforced and reinforced with fiberglass mesh when varying the mechanical properties of the materials composing the adobe masonry structure. The main issues and variability in the behavior of seismic resisting walls when varying the mechanical properties are herein highlighted. The aim of the overall research activity is to improve the knowledge about the structural behavior of adobe structural members unreinforced and reinforced with fiberglass mesh inside horizontal mortar joints. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle CFRP-Strengthening and Long-Term Performance of Fatigue Critical Welds of a Steel Box Girder
Polymers 2014, 6(2), 443-463; doi:10.3390/polym6020443
Received: 29 November 2013 / Accepted: 28 January 2014 / Published: 11 February 2014
Cited by 4 | PDF Full-text (1906 KB) | HTML Full-text | XML Full-text
Abstract
Empa’s research efforts in the 1990s provided evidence that a considerable increase of the fatigue strength of welded aluminum beams can be achieved by externally bonding pultruded carbon fiber reinforced polymer (CFRP) laminates using rubber-toughened epoxies over the fatigue-weak welding zone on [...] Read more.
Empa’s research efforts in the 1990s provided evidence that a considerable increase of the fatigue strength of welded aluminum beams can be achieved by externally bonding pultruded carbon fiber reinforced polymer (CFRP) laminates using rubber-toughened epoxies over the fatigue-weak welding zone on their tensile flange. The reinforcing effect obtained is determined by the stiffness of the unidirectional CFRP laminate which has twice the elastic modulus of aluminum. One can therefore easily follow that an unstressed CFRP laminate reinforcement of welded beams made of steel will not lead to a substantial increase in fatigue strength of the steel structure. This consideration led to the idea of prestressing an external reinforcement of the welded zone. The present investigation describes experimental studies to identify the adhesive system suitable for achieving high creep and fatigue strength of the prestressed CFRP patch. Experimental results (Wöhler-fields) of shear-lap-specimens and welded steel beams reinforced with prestressed CFRP laminates are presented. The paper concludes by presenting a field application, the reinforcement of a steel pendulum by adhesively bonded prestressed CFRP laminates to the tensile flanges of the welded box girder. Inspections carried out periodically on this structure revealed neither prestress losses nor crack initiation after nine years of service. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Numerical Study of FRP Reinforced Concrete Slabs at Elevated Temperature
Polymers 2014, 6(2), 408-422; doi:10.3390/polym6020408
Received: 2 January 2014 / Revised: 6 February 2014 / Accepted: 7 February 2014 / Published: 10 February 2014
PDF Full-text (315 KB) | HTML Full-text | XML Full-text
Abstract
One-way glass fibre reinforced polymer (GFRP) reinforced concrete slabs at elevated temperatures are investigated through numerical modeling. Serviceability and strength requirements of ACI-440.1R are considered for the design of the slabs. Diagrams to determine fire endurance of slabs by employing “strength domain” [...] Read more.
One-way glass fibre reinforced polymer (GFRP) reinforced concrete slabs at elevated temperatures are investigated through numerical modeling. Serviceability and strength requirements of ACI-440.1R are considered for the design of the slabs. Diagrams to determine fire endurance of slabs by employing “strength domain” failure criterion are presented. Comparisons between the existing “temperature domain” method with the more representative “strength domain” method show that the “temperature domain” method is conservative. Additionally, a method to increase the fire endurance of slabs by placing FRP reinforcement in two layers is investigated numerically. The amount of fire endurance gained by placing FRP in two layers increases as the thickness of slab increases. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle A Unified Theoretical Model for the Monotonic and Cyclic Response of FRP Strips Glued to Concrete
Polymers 2014, 6(2), 370-381; doi:10.3390/polym6020370
Received: 30 November 2013 / Revised: 20 January 2014 / Accepted: 27 January 2014 / Published: 3 February 2014
Cited by 9 | PDF Full-text (551 KB) | HTML Full-text | XML Full-text
Abstract
The mechanical behavior of the adhesive interface between the fiber-reinforced polymer (FRP) strip and the concrete substrate often controls the response of FRP-strengthened reinforced concrete (RC) members. Plenty of studies devoted to understanding the mechanical behavior of FRP strips glued to concrete [...] Read more.
The mechanical behavior of the adhesive interface between the fiber-reinforced polymer (FRP) strip and the concrete substrate often controls the response of FRP-strengthened reinforced concrete (RC) members. Plenty of studies devoted to understanding the mechanical behavior of FRP strips glued to concrete are currently available in the scientific literature. However, they are mainly focused on the response under monotonic actions, which is certainly relevant in a wide class of practical applications. Conversely, few contributions are currently available to better understand the response of FRP-to-concrete interfaces under cyclic actions, such as those deriving from either seismic excitations or traffic loads. This paper presents a unified numerical approach to simulate both monotonic and cyclic behavior of FRP plates glued on quasi-brittle substrates like those made of concrete. Particularly, a damage-based approach is proposed to simulate the fracture behavior of FRP-to-concrete joints under loading/unloading cycling tests. The model is formulated within the general framework of Fracture Mechanics and is based on assuming that fracture at the FRP-to-concrete interface develops in (pure shear) mode II, as widely accepted in similar problems. Two alternative expressions of the bond-slip behavior are herein considered and their preliminary validation is finally proposed. The proposed results highlight the difference between the monotonic and the cyclic response; particularly, they show that the latter is characterized by a significantly lower force and displacement capacity. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Retrofitting Masonry Walls with Carbon Mesh
Polymers 2014, 6(2), 280-299; doi:10.3390/polym6020280
Received: 2 December 2013 / Revised: 21 January 2014 / Accepted: 22 January 2014 / Published: 27 January 2014
Cited by 3 | PDF Full-text (3641 KB) | HTML Full-text | XML Full-text
Abstract
Static-cyclic shear load tests and tensile tests on retrofitted masonry walls were conducted at UAS Fribourg for an evaluation of the newly developed retrofitting system, the S&P ARMO-System. This retrofitting system consists of a composite of carbon mesh embedded in a specially [...] Read more.
Static-cyclic shear load tests and tensile tests on retrofitted masonry walls were conducted at UAS Fribourg for an evaluation of the newly developed retrofitting system, the S&P ARMO-System. This retrofitting system consists of a composite of carbon mesh embedded in a specially adapted high quality spray mortar. It can be applied with established construction techniques using traditional construction materials. The experimental study has shown that masonry walls reinforced by this retrofitting system reach a similar strength and a higher ductility than retrofits by means of bonded carbon fiber reinforced polymer sheets. Hence, the retrofitting system using carbon fiber meshes embedded in a high quality mortar constitutes a good option for static or seismic retrofits or reinforcements for masonry walls. However, the experimental studies also revealed that the mechanical anchorage of carbon mesh may be delicate depending on its design. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Prestressed CFRP Strips with Gradient Anchorage for Structural Concrete Retrofitting: Experiments and Numerical Modeling
Polymers 2014, 6(1), 114-131; doi:10.3390/polym6010114
Received: 29 November 2013 / Revised: 23 December 2013 / Accepted: 24 December 2013 / Published: 6 January 2014
Cited by 12 | PDF Full-text (1881 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a study on the load carrying capacity of reinforced concrete (RC) beams strengthened with externally bonded (EB) carbon fiber reinforced polymer (CFRP) strips prestressed up to 0.6% in strain. At the strip ends, the innovative gradient anchorage is used [...] Read more.
This paper presents a study on the load carrying capacity of reinforced concrete (RC) beams strengthened with externally bonded (EB) carbon fiber reinforced polymer (CFRP) strips prestressed up to 0.6% in strain. At the strip ends, the innovative gradient anchorage is used instead of conventional mechanical fasteners. This method, based on the epoxy resin’s ability to rapidly cure under high temperatures, foresees a sector-wise heating followed by a gradual decrease of the initial prestress force towards the strip ends. The experimental investigation shows a promising structural behavior, resulting in high strip tensile strains, eventually almost reaching tensile failure of the composite strip. Additionally, ductility when considering deflection at steel yielding and at ultimate load is satisfying, too. From a practical point of view, it is demonstrated that premature strip grinding in the anchorage zone is not beneficial. In addition, a non-commercial 1D finite element code has been enlarged to an EB reinforcement with prestressed composite strips. A bilinear bond stress-slip relation obtained in earlier investigations is introduced as an additional failure criterion to the code. The numerical code is able to almost perfectly predict the overall structural behavior. Furthermore, the calculations are used for comparison purposes between an initially unstressed and a prestressed externally bonded composite reinforcement. The increase in cracking and yielding load, as well as differences in structural stiffness are apparent. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Epoxy Enhanced by Recycled Milled Carbon Fibres in Adhesively-Bonded CFRP for Structural Strengthening
Polymers 2014, 6(1), 76-92; doi:10.3390/polym6010076
Received: 27 November 2013 / Revised: 18 December 2013 / Accepted: 19 December 2013 / Published: 31 December 2013
Cited by 1 | PDF Full-text (4434 KB) | HTML Full-text | XML Full-text
Abstract
This paper investigates the mechanical performance and electrical resistivity of a structural adhesive epoxy enhanced using milled carbon fibre (MCF) as well as the bond performance of carbon fibre reinforced polymers (CFRP) and steel adhesively bonded joints using the enhanced epoxy. The [...] Read more.
This paper investigates the mechanical performance and electrical resistivity of a structural adhesive epoxy enhanced using milled carbon fibre (MCF) as well as the bond performance of carbon fibre reinforced polymers (CFRP) and steel adhesively bonded joints using the enhanced epoxy. The epoxy was enhanced using such MCFs with different weight ratios of 1.5%, 3% and 5%. Tensile experiments were performed on the original and enhanced epoxy specimens according to ASTM D638. More ductile process failure was found for the epoxy after modification and significant improvements of E-modulus and tensile strength were evidenced when the MCF weight ratio was larger than 1.5%. Scanning electron microscopy (SEM) revealed that the failure mechanism of short MCFs pulled out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy. The electrical resistivity of the epoxy with MCF weight ratio of 5% was reduced by at least four orders of magnitude compared to the original epoxy, due to the conductive network formed by MCFs. Steel/CFRP double strap joints (with either CFRP sheets or CFRP laminates) were prepared using the enhanced epoxy and then tested in tension, however no obvious increase in joint stiffness or strength was observed. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Modified Johnston Failure Criterion from Rock Mechanics to Predict the Ultimate Strength of Fiber Reinforced Polymer (FRP) Confined Columns
Polymers 2014, 6(1), 59-75; doi:10.3390/polym6010059
Received: 31 October 2013 / Revised: 16 December 2013 / Accepted: 17 December 2013 / Published: 30 December 2013
Cited by 3 | PDF Full-text (876 KB) | HTML Full-text | XML Full-text
Abstract
The failure criteria from rock mechanics, Hoek-Brown and Johnston failure criteria, may be extended and modified to assess the ultimate compressive strength of axially loaded circular fiber reinforced polymer (FRP)-confined concrete columns. In addition to the previously modified Hoek-Brown criterion, in this [...] Read more.
The failure criteria from rock mechanics, Hoek-Brown and Johnston failure criteria, may be extended and modified to assess the ultimate compressive strength of axially loaded circular fiber reinforced polymer (FRP)-confined concrete columns. In addition to the previously modified Hoek-Brown criterion, in this study, the Johnston failure criterion is extended to scope of FRP-confined concrete, verified with the experimental data and compared with the significant relationships from the current literature. Wide-range compressive strengths from 7 to 108 MPa and high confinement ratios up to 2.0 are used to verify the ultimate strengths in short columns. The results are in good agreement with experimental data for all confinement levels and concrete strengths. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

Review

Jump to: Research

Open AccessReview FRP Composites Strengthening of Concrete Columns under Various Loading Conditions
Polymers 2014, 6(4), 1040-1056; doi:10.3390/polym6041040
Received: 12 December 2013 / Revised: 7 March 2014 / Accepted: 21 March 2014 / Published: 3 April 2014
Cited by 9 | PDF Full-text (440 KB) | HTML Full-text | XML Full-text
Abstract
This paper provides a review of some of the progress in the area of fiber reinforced polymers (FRP)-strengthening of columns for several loading scenarios including impact load. The addition of FRP materials to upgrade deficiencies or to strengthen structural components can save [...] Read more.
This paper provides a review of some of the progress in the area of fiber reinforced polymers (FRP)-strengthening of columns for several loading scenarios including impact load. The addition of FRP materials to upgrade deficiencies or to strengthen structural components can save lives by preventing collapse, reduce the damage to infrastructure, and the need for their costly replacement. The retrofit with FRP materials with desirable properties provides an excellent replacement for traditional materials, such as steel jacket, to strengthen the reinforced concrete structural members. Existing studies have shown that the use of FRP materials restore or improve the column original design strength for possible axial, shear, or flexure and in some cases allow the structure to carry more load than it was designed for. The paper further concludes that there is a need for additional research for the columns under impact loading senarios. The compiled information prepares the ground work for further evaluation of FRP-strengthening of columns that are deficient in design or are in serious need for repair due to additional load or deterioration. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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