Browsing by Author "Araya Letelier, Gerardo Andres"

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    Adobe mixtures reinforced with fibrillated polypropylene fibers: Physical/mechanical/fracture/durability performance and its limits due to fiber clustering
    (2022) Burbano Garcia, Claudia Patricia; Silva Urrego, Yimmy Fernando; Araya Letelier, Gerardo Andres
    This study assesses the feasibility of the incorporation of fibrillated polypropylene fibers (FPFs), an engineere multidimensional and multifilament fiber mostly used to reinforce concrete mixtures, into adobe mixtures (AMs), a traditional and manually-made material used to produce adobe blocks. The incorporation of FPFs was assessed using increasing dosages (0%, 0.25%, 0.5%, and 1% in wt% of clay soil) of FPFs. These fibers were gradually added and mixed with the clayey soil prior to incorporation of water to promote uniform mixtures with adequate fiber distribution to reduce the formation of fiber clusters. The impact of FPFs was evaluated in terms of its effects on the bulk density (physical), compressive and flexural strength (mechanical), flexural toughness indices (fracture) and water erosion resistance (durability) of AMs. Results indicate that increasing dosages of FPFs monotonically reduce average values of bulk density, as well as compressive and flexural strength of AMs. On the other hand, these increasing dosages of FPFs monotonically increase average values of water erosion resistance as well as flexural toughness indices, varying the flexural failure mode from brittle (unreinforced AM) to ductile (reinforced AMs) because of the adequate bonding and FPF-bridging effect after the crack generation as confirmed by instrumentation as well as digital image correlation evaluations implemented in this study. The significant reductions of bulk densities and compressive and flexural strengths obtained for fiber-reinforced AMs were related to the increasing number of fiber clusters found for increasing dosages of FPFs within the fiberreinforced mixtures, which was evaluated using scanning electron microscopy analyses. For example, positively the AM incorporating 1% of FPFs increased, on average, the flexural toughness by 674% and reduced the bulk density and water erosion depth by, on average, 9% and 64%, respectively, when compared to the unreinforced AM. However, this large dosage of FPFs also generated a significant reduction of the compressive strength (60% on average) and the flexural strength (43% on average) when compared to the plain mixture. On the other hand, a small dosage of FPFs (0.25%) generated less significant improvements in terms of flexural toughness, bulk density, and water erosion (on average, increment of 58% and reductions of 2% and of 38%, respectively, when compared to the unreinforced AM). Yet, the latter mixture presented reductions, on average, of compressive and flexural strengths of 24% and 16%, respectively, when compared to the plain mixture, and these reductions were significantly smaller than the reductions obtained by the largest FPF dosage, due to the significantly smaller number of fiber clusters presented by the 0.25% dosage when compared to the 1% dosage. Finally, the mechanical performance limitations exhibited by the incorporation of FPFs, especially in large dosages, are related to generated fiber clusters due to the inherent morphology of these FPFs as well as the traditional manual confection process of AMs. Therefore, this study recommends the implementation of FPFs in AMs, but in small dosages and/or suggests the implementation of a mechanical mixing/compaction process that guarantee a more uniform fiber distribution that reduces the generation of fiber clusters.
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    Comparative seismic collapse assessment of Chilean code-conforming RC dual wall-frame buildings
    (Earthquake Engineering Research Institute, 2022) Gallegos, Marco; Araya Letelier, Gerardo Andres; López-García González, Diego; Parra Torres, Pablo Fernando
    Although the satisfactory performance of Chilean buildings in terms of collapse prevention is widely recognized, there is a need to quantify the actual collapse probability and level of protection provided by current seismic codes. In this study, the collapse potential of code-conforming reinforced concrete dual wall-frame buildings subjected to subduction earthquakes was assessed. A suite of four 16-story archetypes, located at two different seismic zones and on two different soil types, was evaluated considering the latest developments in performance-based earthquake engineering through incremental dynamic analyses of 3D nonlinear models. It was found that the probability of collapse in 50 years is in all cases less than the 1% ASCE 7 target probability, which is consistent with the adequate collapse performance of reinforced concrete buildings that has been observed in recent strong earthquakes (Mw ≥ 8.0) in Chile. It was also observed, however, that the collapse probability is not uniform but strongly influenced by the soil type. This observation suggests that the design response spectra indicated by the Chilean seismic design code for buildings might not correctly account for the influence of the soil type.