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International Concrete Abstracts Portal

Showing 1-5 of 84 Abstracts search results

Document: 

SP-343_16

Date: 

October 1, 2020

Author(s):

Meda, A.; Rinaldi, Z.; Spagnuolo, S.; De Rivaz, B.; Giamundo, N.

Publication:

Symposium Papers

Volume:

343

Abstract:

The interest in using fiber reinforced concrete (FRC) for the production of precast segments in tunnel lining, installed with Tunnel Boring Machines (TBMs), is continuously growing, as witnessed by the studies available in literature and by the actual applications. The possibility of adopting a hybrid solution of FRC tunnel segments with Glass Fiber Reinforced Polymer (GFRP) reinforcement is investigated herein. Full-scale tests were carried out on FRC segments with and without GFRP cage, with a typical geometry of metro tunnels. In particular, both flexural and point load full-scale tests were carried out, for the evaluation of the structural performances (both in terms of structural capacity and crack pattern evolution) under bending, and under the TBM thrust. Finally, the obtained results are compared, in order to judge the effectiveness of the proposed technical solution.


Document: 

SP-343_23

Date: 

October 1, 2020

Author(s):

Trabucchi, I.; Conforti, A.; Tiberti, G.; Plizzari, G.A.; Winterberg, R.

Publication:

Symposium Papers

Volume:

343

Abstract:

The use of fiber reinforced concrete in tunnel linings, with or without conventional rebars, has increased in the two last decades, especially in segmental linings. In the meanwhile, in the scientific community there was a growing interest on macro-synthetic fibers for use in underground structures. Within this framework, the present study investigates the possibility of using macro-synthetic fiber reinforcement in precast tunnel segments by means of a numerical study. Firstly, an experimental program based on three point bending tests was carried out on polypropylene fiber reinforced concretes (PFRCs) characterized by different fiber contents in order to assess their post-cracking residual strength. Secondly, the corresponding stress vs. crack opening laws, representative of the PFRCs investigated, were calculated through inverse analysis procedure. Then, a segment of a typical tunnel lining having small diameter was adopted as reference to optimize the reinforcement solution (macro-synthetic fibers and conventional rebars, i.e. hybrid solution) and to study its structural behavior by numerical analyses. Particular attention was devoted to the Tunnel Boring Machine (TBM) thrust jack phase, in which the TBM moves forward by pushing the thrust jacks on the bearing pads of the latest assembled ring, introducing high-concentrated forces in the lining.


Document: 

SP-343_21

Date: 

October 1, 2020

Author(s):

Pourzarabi, A.; Colombo, M.; Martinelli, P.; di Prisco, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

Fibre reinforced concrete (FRC) material is characterized by a high intrinsic scatter in the results when tested according to standard notched beams. However, it is observed that structures affected by a high stress redistribution show a significantly reduced scatter in their structural behaviour. Therefore, the use of the characteristic material constitutive parameters from a standard test leads to overly conservative design. The Model Code 2010 has introduced a coefficient, named structural redistribution factor, that is able to take into account a reduced variability of the structural response, when compared to that identified from a standard material test. The paper investigates the behaviour of FRC slabs to highlight the difference in structural response of FRC elements with respect to the expected response computed according to the standard specimens used for material characterization. To this aim, FRC slabs of 2×2 m, 15 cm thick, supported on four points at the mid-span of each side, are tested under a point load. Different slab solutions (R/C, FRC only and a Hybrid solution with FRC and steel rebars) are compared and discussed. The material considered can be classified as 5b according to Model Code 2010. A yield line approach is also adopted to validate the formulation proposed by Model Code 2010 for the structural redistribution factor in the cases investigated.


Document: 

SP-343_07

Date: 

October 1, 2020

Author(s):

Javadian, A.; Mahdavi, A.; Benamrane, O. ;Majeed, M.; Aoude, H.

Publication:

Symposium Papers

Volume:

343

Abstract:

This study examines the effect of fiber properties, single fiber type and hybrid fibers on the fresh-state and hardened-state properties of self-consolidating fiber-reinforced concrete (SCFRC). As part of the study, 16 mixtures are examined with variables including the effect of fiber type, length, aspect ratio, and hybrid use of fibers (short and long fibers). Properties in the fresh state are studied using standard SCC tests including: slump flow, V-funnel and visual stability index (VSI) tests. Mechanical properties are studied by testing prisms under four-point flexural loading in accordance with the ASTM C1609 standard. The results demonstrate that self-consolidating FRC mixtures are possible at moderate fiber contents, however, once the limiting fiber contents are exceeded workability and mix uniformity are lost. The results also show the effects of fiber content, fiber type, fiber properties and hybrid fibers on the flexural toughness of SCFRC.


Document: 

SP-343_19

Date: 

October 1, 2020

Author(s):

Conforti, A.; Trabucchi, I.; Tiberti, G.; Plizzari, G.A.; Caratelli, A; Meda, A.; Moro, S.; Hunger, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

There is a growing interest in the scientific community on the structural applicability of polypropylene macrofibers without or in combination with conventional reinforcement as spread reinforcement for precast tunnel segmental linings. Polypropylene macrofibers could be used in precast tunnel segments as shear reinforcement and for withstanding splitting and spalling tensile stresses which occur under and between Tunnel Boring Machine (TBM) rams, respectively. Fibers could also simplify and speed up the tunnel element production process. In this context, the present study investigates the possibility of using polypropylene macrofiber reinforcement in precast tunnel segments for both hydraulic and metro tunnel linings. Four full-scale segments (two counter-key segments of a hydraulic tunnel and two trapezoidal shaped segments of a metro tunnel) were experimentally evaluated under point load test. The latter simulate the TBM actions on segments during the excavation process (TBM thrust jack phase), which is generally the most critical temporary loading condition for segments. Two reinforcement solutions were studied: a typical conventional reinforcement (reference samples) and a combination of polypropylene macrofibers and conventional reinforcement (hybrid solution). Polypropylene macrofibers were observed to be very effective in combination with conventional reinforcement, underlining the fibers ability in controlling both splitting and spalling phenomena.


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