Browsing by Author "Guindos, Pablo"
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- ItemElectron tomography unravels new insights into fiber cell wall nanostructure; exploring 3D macromolecular biopolymeric nano-architecture of spruce fiber secondary walls(2023) Fernando, Dinesh; Kowalczyk, Michael; Guindos, Pablo; Auer, Manfred; Daniel, GeoffreyLignocellulose biomass has a tremendous potential as renewable biomaterials for fostering the "bio-based society" and circular bioeconomy paradigm. It requires efficient use and breakdown of fiber cell walls containing mainly cellulose, hemicellulose and lignin biopolymers. Despite their great importance, there is an extensive debate on the true structure of fiber walls and knowledge on the macromolecular nano-organization is limited and remains elusive in 3D. We employed dual-axis electron tomography that allows visualization of previously unseen 3D macromolecular organization/biopolymeric nano-architecture of the secondary S2 layer of Norway spruce fiber wall. Unprecedented 3D nano-structural details with novel insights into cellulose microfibrils (similar to 2 nm diameter), macrofibrils, nano-pore network and cell wall chemistry (volume %) across the S2 were explored and quantified including simulation of structure related permeability. Matrix polymer association with cellulose varied between microfibrils and macrofibrils with lignin directly associated with MFs. Simulated bio-nano-mechanical properties revealed stress distribution within the S2 and showed similar properties between the idealized 3D model and the native S2 (actual tomogram). Present work has great potential for significant advancements in lignocellulose research on nano-scale understanding of cell wall assembly/disassembly processes leading to more efficient industrial processes of functionalization, valorization and target modification technologies.
- ItemFlexural performance of full-scale two-span Nail-Laminated Timber Concrete composite slabs(2024) Adema, Andres; Chacon, Matias F.; Santa Maria, Hernan; Opazo-Vega, Alexander; Casanova, Euro; Guindos, PabloThis study examines the flexural performance of six 9-m full-scale two-span Nail-Laminated Timber Concrete (NLTC) composite slabs. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. The multi-span configuration of slabs reduces their deflections simply and effectively. Fivepoint monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pullout tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests of shear connections were also included to emulate the negative bending moments that occur in the middle of the slabs. Failure modes, load-mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab at the serviceability range. Moreover, an analytical elastic TCC beam with the Girhammar method was assessed and demonstrated as more precise than the traditional gamma-method. Finally, an accurate prediction of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity is observed, with errors in a range of 2-23% and 9-74%, respectively.
- ItemIn-plane testing and hysteretic modeling of steel-spline cross-laminated timber diaphragm connection with self-tapping screws(2024) Chacon, Matias F.; Jara-Cisterna, Alan; Benedetti, Franco; Veliz, Fernando; Guindos, PabloThis study examines experimentally and numerically the in-plane behavior of a steel-spline Cross-Laminated Timber (CLT) connection with self-tapping screws. Although this connection is a strong, rapid, and cost-effective alternative suitable for CLT diaphragms of tall timber-concrete buildings, no previous cyclic/monotonic testing has been documented. Two specimens were tested under axial and in-plane shear loads, where a ductile failure mode was observed due to bending and withdrawal of screws, and deformation and buckling of the strap. Mechanic properties, such as strength capacity, stiffness, ductility, energy dissipation, equivalent viscous damping, stiffness/strength degradation, and damage index characterize the joint. Furthermore, the yield point and ductility were calculated with the EEEP, CEN, and Yasumura-Kawai methods, the last approach most accurate, with a mean ductility of 7.25 and 5.50 for the axial and in-plane shear tests, respectively. Overstrength factors of about 2.6 and 1.9 were also estimated for respective tests by comparing analytical expressions from timber codes and literature. Finally, three numerical models (SAWS, DowelType, and ASPID) were assessed to measure their epistemic uncertainty, showing an adequate force and dissipated energy history simulation, with a normalized root mean square less than 8.8% and 4.5%, and R(2 )over 87% and 97%, respectively. {GRAPHICAL ABSTRACT}
- ItemSistema de muro de corte híbrido para construcción de edificaciones de madera de más de dos pisosGuindos, Pablo; Santa María Oyanedel, Hernan; Montaño, Jairo Alonso; Carrerro Roa, Tulio
- ItemStructural performance of strong timber diaphragms: High-capacity light-timber frames and cross-laminated timber(2024) Veliz, Fernando; Chacon, Matias F.; Lagos, Jorge; Berwart, Sebastian; Lopez, Nicol; Guindos, PabloThe construction of tall timber buildings is not only challenging because it requires stronger vertical lateral systems but also because it demands much Stronger Timber (ST) diaphragms in comparison to the ones required by low-rise timber construction. Two main ST alternatives exist: High -capacity Light -Timber Frame (HLTF) and Cross -Laminated Timber (CLT) diaphragms. Both approaches provide more strength, stiffness, and still have the potential to provide ductile failure than traditional timber diaphragms. However, it is unclear the structural performance differences between these two ST alternatives, which is the aim of this research. In this study, an experimental program comprising the monotonic and cyclic testing of several representative sheathing -toframing connections, plus the full-scale monotonic bending testing of six HLTF and CLT diaphragms was accomplished to characterize and compare the performance of both ST diaphragm configurations. Failure modes and mechanical properties such as stiffness, load -bearing capacity, and ductility were evaluated for all specimens. Results show that HLTF diaphragms have larger load -bearing capacity than CLT ones. Conversely, CLT diaphragms perform more ductile than HLTF ones, with a mean of /4 = 1.87 and /4 = 3.5, respectively, where the first was due mainly to high plastification of fasteners and the second to premature brittle failure of some components. Furthermore, the experimental findings were utilized to evaluate the precision of prevailing analytical and numerical models, thereby illustrating their capability to adequately represent the elastic and nonlinear responses of both ST alternatives. Finally, a sensitivity analysis of a two - story wall building with varying diaphragm (LTF, HLTF and CLT) and different light -frame shear walls (rigid and flexible) was studied. Both the diaphragms and shear walls were modeled under two different equivalent diagonal link models. The sensitivity analysis concluded that both flexible diaphragm assumption and envelope approach might not be an efficient solution, while semi -rigid approach with flexibility index eta ranging 0 - 0.5 may be expected when using ST with LTF shear walls. Finally, the diaphragm model employed enabled the validation of its elastic behavior under lateral loads, with use factors under 30% for typical setups.
- ItemSustainable Cement Paste Development Using Wheat Straw Ash and Silica Fume Replacement Model(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Bastías, Bryan; González, Marcelo; Rey-Rey, Juan; Valerio, Guillermo; Guindos, Pablo© 2024 by the authors.Conventional cement production is a major source of carbon dioxide emissions, which creates a significant environmental challenge. This research addresses the problem of how to reduce the carbon footprint of cement paste production using agricultural and industrial waste by-products, namely wheat straw ash (WSA) and silica fume (SF). Currently, accurate models that can predict the mechanical properties of cement pastes incorporating these waste materials are lacking. To fill this gap, our study proposes a model based on response surface methodology and Box-Behnken design, designed to predict the strength of cement pastes with partial substitutions of WSA and SF. Through mechanical and characterization tests, the model demonstrated high accuracy in predicting the strength of the pastes, validated with three mixes, which showed maximum errors of less than 6% at different ages (7, 28, and 56 days). Response surface analysis revealed that replacing cement with 0–20% WSA and more than 5% SF can effectively reduce the carbon footprint by maximizing waste incorporation. This model allows for the calculation of optimal cement substitution levels based on the required strength, thus promoting sustainability in the construction industry through the use of local waste/resources.
- ItemTesting and nonlinear modelling of industrialized light-frame wooden diaphragms including optimized nailing and nonstructural sheathing(2023) Veliz, Fernando; Estrella, Xavier; Lagos, Jorge; Guindos, PabloThis article presents the outcomes of a large project towards the investigation of the lateral performance of full-scale industrialized light-frame wooden diaphragms. 10 full-scale diaphragms of 3.6 m by 2.4 m were tested under in-plane lateral loading (monotonic and cyclic), considering different sheathing, nailing, and framing. Besides, the behavior of bare slabs (without any sheathing), gypsum finishes and the potential benefits of using optimized nailing patterns instead of regularly spaced nailing was also studied. Experimental tests were non-linearly modeled using the modified Steward hysteresis model (MSTEW) and MCASHEW software. Experimental strength and stiffness results proved to be consistent with those proposed by other international campaigns, and in particular, the design principles of SDPWS fitted well with the obtained results. However, chord tensions were 30 % greater than the ones obtained by principles of engineering mechanics, which might be explained by eccentric tensile load transfer. As expected, the behavior of both sawn lumber and I-joist framed diaphragms was mainly controlled by nailing. In fact, optimized nailing patterns allowed to equal the peak capacity, increase by 20 % stiffness and 75 % ductility with 8 % less nails. Screwed gypsum finishes increased the peak capacity and stiffness by 15 %, and 20 %, respectively. The modelling approach - mainly used only in shear walls in previous investigations - proved its capability of finely reproducing the behavior of all diaphragm configurations. The numerical results were also in good agreement with the prescriptions of the SDPWS standard.