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  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal

Showing 1-5 of 1234 Abstracts search results

Document: 

SP343

Date: 

November 3, 2020

Author(s):

fib and ACI

Publication:

Symposium Papers

Volume:

343

Abstract:

The first international FRC workshop supported by RILEM and ACI was held in Bergamo (Italy) in 2004. At that time, a lack of specific building codes and standards was identified as the main inhibitor to the application of this technology in engineering practice. The workshop aim was placed on the identification of applications, guidelines, and research needs in order for this advanced technology to be transferred to professional practice. The second international FRC workshop, held in Montreal (Canada) in 2014, was the first ACI-fib joint technical event. Many of the objectives identified in 2004 had been achieved by various groups of researchers who shared a common interest in extending the application of FRC materials into the realm of structural engineering and design. The aim of the workshop was to provide the State-of-the-Art on the recent progress that had been made in term of specifications and actual applications for buildings, underground structures, and bridge projects worldwide. The rapid development of codes, the introduction of new materials and the growing interest of the construction industry suggested presenting this forum at closer intervals. In this context, the third international FRC workshop was held in Desenzano (Italy), four years after Montreal. In this first ACI-fib-RILEM joint technical event, the maturity gained through the recent technological developments and large-scale applications were used to show the acceptability of the concrete design using various fibre compositions. The growing interests of civil infrastructure owners in ultra-high-performance fibre-reinforced concrete (UHPFRC) and synthetic fibres in structural applications bring new challenges in terms of concrete technology and design recommendations. In such a short period of time, we have witnessed the proliferation of the use of fibres as structural reinforcement in various applications such as industrial floors, elevated slabs, precast tunnel lining sections, foundations, as well as bridge decks. We are now moving towards addressing many durability-based design requirements by the use of fibres, as well as the general serviceability-based design. However, the possibility of having a residual tensile strength after cracking of the concrete matrix requires a new conceptual approach for a proper design of FRC structural elements. With such a perspective in mind, the aim of FRC2018 workshop was to provide the State-of-the-Art on the recent progress in terms of specifications development, actual applications, and to expose users and researchers to the challenges in the design and construction of a wide variety of structural applications. Considering that at the time of the first workshop, in 2004, no structural codes were available on FRC, we have to recognize the enormous work done by researchers all over the world, who have presented at many FRC events, and convinced code bodies to include FRC among the reliable alternatives for structural applications. This will allow engineers to increasingly utilize FRC with confidence for designing safe and durable structures. Many presentations also clearly showed that FRC is a promising material for efficient rehabilitation of existing infrastructure in a broad spectrum of repair applications. These cases range from sustained gravity loads to harsh environmental conditions and seismic applications, which are some of the broadest ranges of applications in Civil Engineering. The workshop was attended by researchers, designers, owner and government representatives as well as participants from the construction and fibre industries. The presence of people with different expertise provided a unique opportunity to share knowledge and promote collaborative efforts. These interactions are essential for the common goal of making better and sustainable constructions in the near future. The workshop was attended by about 150 participants coming from 30 countries. Researchers from all the continents participated in the workshop, including 24 Ph.D. students, who brought their enthusiasm in FRC structural applications. For this reason, the workshop Co-chairs sincerely thank all the enterprises that sponsored this event. They also extend their appreciation for the support provided by the industry over the last 30 years which allowed research centers to study FRC materials and their properties, and develop applications to making its use more routine and accepted throughout the world. Their important contribution has been essential for moving the knowledge base forward. Finally, we appreciate the enormous support received from all three sponsoring organizations of ACI, fib and Rilem and look forward to paving the path for future collaborations in various areas of common interest so that the developmental work and implementation of new specifications and design procedures can be expedited internationally. June 2018 Bruno Massicotte, Fausto Minelli, Barzin Mobasher, Giovanni Plizzari


Document: 

SP-343_37

Date: 

October 1, 2020

Author(s):

Berrocal, C.G.; Lundgren, K.; Löfgren, I.

Publication:

Symposium Papers

Volume:

343

Abstract:

In the present paper, long-term experiments involving natural corrosion of RC beams subjected to chloride solution cyclic exposure were carried out to investigate the effect of fibres on different aspects of the corrosion process as well as their contribution to the structural behaviour of RC elements damaged by corrosion. The long-term experiments were complemented with short-term accelerated corrosion experiments and mechanical tests to investigate the influence that low fibre contents may have on individual mechanisms that play an important role in the corrosion process of steel in concrete. These showed that fibres promote crack branching which results in a change of the internal crack pattern towards multiple thinner cracks, particularly near the reinforcement. This agrees with the long-term experiment results, which exhibited longer times to corrosion initiation for FRC beams with bending cracks and revealed a more distributed corrosion with more pits but less crosssectional loss compared to bars in plain concrete. Fibres also proved beneficial in delaying corrosion-induced cracks and preventing cover spalling, which greatly enhanced the bondbehaviour of corroded bars. Furthermore, a positive effect of the fibres was also observed on the residual flexural capacity of corroded beams, which generally increased the load-carrying capacity and rotation capacity.


Document: 

SP-343_11

Date: 

October 1, 2020

Author(s):

Ortiz-Navas, F.; Navarro-Gregori, J.; Serna Ros, P.; Leiva Herdocia, G.

Publication:

Symposium Papers

Volume:

343

Abstract:

In recent years, much research has shown improvements in shear behaviour and deformation capability when an adequate amount of macro fibres is provided in concrete. However, very few experiments have used macro synthetic fibres. In this paper, the shear capability of deformation in slender beams was studied by analysing the shear crack path, the crack openingslip relationship and shear deformation of polypropylene fibre-reinforced concrete (PFRC) beams. Shear cracks and deformations were measured by non-contact image measurement techniques. The results are compared with those of plain concrete (PC), steel fibre-reinforced concrete (SFRC) and reinforced concrete (RC) beams. Both types of fibres were dosed so that similar average residual tensile strengths would remain similar to one another. The crack path analysis results showed that synthetic fibres delayed the formation of shear cracks and their propagation into compression zone, and improved the behaviour of secondary cracks due to loss of bond with longitudinal reinforcement. Finally, the crack opening-slip relationship varied widely along the crack and location in beams.


Document: 

SP-343_45

Date: 

October 1, 2020

Author(s):

Look, K.; Mark, P.

Publication:

Symposium Papers

Volume:

343

Abstract:

An open design tool is developed that uses spreadsheet analyses, optimisation methods and iterative analytical routines. Its idea is to offer a universal, intuitive instrument to economically design and optimise steel fibre reinforced concrete members with or without rebar. The tool comprises non-linear evaluations of sectional forces with the yield line theory, a cross sectional design in ultimate and serviceability limit states as well as backward oriented optimisations of reinforcements, cross sectional properties or fibre classes. It should be free of specific code regulations and thus just basis on the assumption of plane strains, an ideal bond and requires the definitions of uniaxial stress-strain laws, strain boundaries and fundamental design formulas. Boundary conditions, material parameters and sectional properties as well as results like strain or stress distributions, performance ratios and potentials of improvements are given in visualisations and commented figures. The non-linear equations of equilibrium are iteratively solved with reduced gradient methods. Doing so, recursive initial parameter settings of the strain plane are – amongst other regularisations – incorporated to achieve robust solutions.


Document: 

SP-343_43

Date: 

October 1, 2020

Author(s):

Plückelmann, S.; Breitenbücher, R.

Publication:

Symposium Papers

Volume:

343

Abstract:

In special cases, concrete members are exposed to high locally concentrated loadings. Such concentrated loadings lead to a multi-dimensional stress state beneath the loaded area. Due to the load diffusion, large splitting tensile stresses are generated in the upper regions of the concrete member (i.e. St. Venant disturbance zone) and spread along directions perpendicular to the load. In order to resist these splitting tensile stresses, the state of the art is to reinforce concrete members with transverse steel reinforcement. An alternative approach is to add steel fibers to the concrete matrix. However, regarding economic concerns it may not appropriate to reinforce the entire concrete member with an adequate high amount of steel fibers, rather only those zones where high splitting stresses are expected. The main objective of the presented experimental study was to investigate the load-bearing and fracture behavior of hybrid concrete elements with splitting fiber reinforcement under concentrated load. For this purpose, in a first step, hybrid specimens were produced containing both plain and fiber concretes. The reference specimens consisted exclusively of plain concrete, while the hybrid specimens were partially strengthened with various types of steel fibers only in the St. Venant disturbance zone, instead of a full range fiber reinforcement. The thickness of the reinforcement layer was varied in order to determine the optimal configuration of fiber reinforcement. Taking into account the influence of the casting direction on the fiber orientation and consequently on the bearing and fracture behavior, the hybrid specimens were cast either in standing or in lying molds by means of a “wet-on-wet” casting technique. These hybrid elements were then tested under concentrated load. The test results showed that under concentric loads the maximum bearing capacity of the hybrid specimens increased progressively with growing thickness of the fiber reinforced concrete layer. In contrast to the plain concrete specimens, the fiber reinforcement led to a remarkable improvement in the post-cracking ductility. Compared to the fully reinforced specimens, the hybrid specimens that were only reinforced in the St. Venant disturbance zone exhibited - besides an almost identical bearing capacity - a similar local behavior in the postcracking zone. Furthermore, a significant impact of the casting direction on the bearing as well as fracture behavior could be proved.


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