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International Concrete Abstracts Portal

Showing 1-5 of 898 Abstracts search results

Document: 

SP-343_12

Date: 

October 1, 2020

Author(s):

Barros, J.A.O.; Foster, S.J.

Publication:

Symposium Papers

Volume:

343

Abstract:

For the development of reliable physical-mechanical models for predicting the behaviour of fibre reinforced concrete structures at service and strength limit conditions, constitutive models simulating comprehensibly the governing phenomena must be used. In this context, simulating the post-cracking mechanisms of the fibres, and their symbiotic relationship with the cementitious matrix that surrounds them, is required for the development of realistic modelling approaches that accurately represent empirical observations. Several experimental test setups and inverse analysis procedures have been proposed to derive the fundamental stress-crack width ( –w) law, but a consensus still does not exists on the best strategy for its determination. In structures governed by shear, fibre reinforcement increases the stiffness and shear stress transfer across a crack, but a methodology to capture the contribution of fibres in this regards is challenging. To overcome this, a clear strategy is needed in deriving relationships that simulate fibre reinforcement mechanisms in the mobilized fracture modes and, also, develop design approaches capable of capturing the relevant contributions of the fibres. This study firstly reviews current inverse analysis models used to describe the tensile (Model I fracture) relationship for FRC and, secondly, discusses a newly proposed model, referred to as the integrated shear model (ISM). The ISM is developed from mesoscale observations from gamma- and X-ray imaging on FRC elements under Modes I and II fracture conditions. The resulting model is compared to test data reported in the literature and a good correlation is observed.


Document: 

SP-343_03

Date: 

October 1, 2020

Author(s):

Vrijdaghs, R.; Di Prisco, M.; Vandewalle, L.

Publication:

Symposium Papers

Volume:

343

Abstract:

The creep behavior of FRC elements remains an important obstacle to use FRC in structural applications. Owing to the residual post-cracking strength properties of FRC, creep deformations play an important role in the cracked sections and influence durability and SLS requirements of structural elements. Therefore, it is of high importance to take creep deformations into account in the design phase. In this paper, the results of an experimental campaign involving both bending tests and uniaxial tensile creep tests on polymeric FRC are presented. In the bending tests, a notched FRC beam is subjected to loading-unloading cycles while the deformations over the cracked section were recorded. The uniaxial tensile creep tests were performed on precracked FRC samples to quantify time-dependent crack growth. The bending behavior of FRC can be accurately predicted by the uniaxial constitutive model of Model Code 2010 in the loading phase assuming a plane section approach. For the unloading phases, a bilinear deformation distribution is assumed and a scalar damage evolution function is fitted by an inverse analysis algorithm. The results of the sectional analysis compared favorably with the experimentally observed data. Finally, a sectional analysis approach is developed and presented in which bending creep deformations are calculated using the uniaxial creep compliances. The initial stress and deformation distribution in the cracked section is predicted by the inverse analysis. The results show that the bending creep deformations of FRC can be quite large, and creep coefficients as high at 7 are observed within 120 days. However, it should be noted that the creep algorithm does not (yet) take into account additional cracking in time, and as such, the predicted creep deformations are a lower limit of what can be expected in reality. More research is needed to upgrade the algorithm to allow predictions including the time-dependent cracking behavior.


Document: 

SP-343_47

Date: 

October 1, 2020

Author(s):

Lucchini, S.S.; Facconi, L.; Minelli, F.; Plizzari, G.A.

Publication:

Symposium Papers

Volume:

343

Abstract:

The use of mortar coating reinforced only with randomly diffused steel fibers represents an effective technique for seismic retrofitting of masonry buildings. The present work aims at proving the effectiveness of that technique by testing a full-scale two-story hollow clay block masonry building subjected to a quasi-static cyclic lateral loading. The experimental program includes two tests involving the same building. The first test performed on the building without coating is carried out to pre-damage masonry in order to simulate the effects of a seismic action significant for ultimate conditions. The second test is performed to assess the behavior of the pre-damaged building after retrofitting. The paper presents the main properties and details of both the test building and the proposed retrofitting technique. As the test on the retrofitted specimen is still ongoing, only the main results concerning the unstrengthened building are reported and discussed. To predict the response of the two experimental tests, 3D non-linear finite element simulations have been carried out and presented in the last section of the paper. The latter includes the comparison between the numerical prediction and the available experimental results.


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_39

Date: 

October 1, 2020

Author(s):

Zanotti, C.; Randl, N.; Gar, P.S.; Far, B.K.; Steiner, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

Fiber Reinforced Concrete (FRC) is being increasingly applied in structural repair and retrofit of reinforced concrete structures. Not only fiber reinforcement improves the durability of reinforced concrete structures, but it also enhances compatibility of the repair material to the existing structure, further enhancing structural effectiveness and service life of the intervention. Furthermore, studies have shown that fiber reinforcement can significantly improve substrate-repair bond in both tension and shear. However, this benefit is not fully utilized in repair/retrofit design due to test uncertainties and lack of comprehensive data on correlations with other fundamental factors. In this study, the question of the appropriateness, reliability and sensitivity of current bond tests in case of FRC repairs is addressed. Several tension and shear bond tests on plain and fiber reinforced cement-based repairs are performed in parallel by two research teams at UBC (Canada) and CUAS (Austria), following a rigorous testing procedure to allow consistency among results from the two laboratories. The influence of repair strength and casting direction is also investigated. The effect of fiber reinforcement on bond is assessed while correlation, comparability, and sensitivity of different test set-ups and stress conditions are discussed.


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