Browsing by Author "Opazo-Vega, Alexander"

Now showing 1 - 8 of 8
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    A Study of the Properties of UV-Aged and Low Formaldehyde Emissions Particleboards Manufactured with Bio-Based Wood Protein Adhesives
    (2023) Nunez-Decap, Mario; Canales-Constanzo, Erickson; Opazo-Carlsson, Camila; Moya-Rojas, Boris; Vidal-Vega, Marcela; Opazo-Vega, Alexander
    The environmental crisis and the safeguarding of the population's health has led to research into different ways of mitigating harmful gases. Among the emissions that the wood industry has sought to reduce are those of formaldehyde, which is why new green adhesive methods for wood panels have been investigated in recent years. In this research, particleboard with two bio-based wood adhesive (PB-bbwa) formulations. The first PB-bbwa formulation, based on proteins obtained from compounds from the alcoholic beverage industry, and the second PB-bbwa formulation, based on proteins from a mixture of compounds from the alcoholic beverage and food industries, were manufactured and tested to evaluate the physical-mechanical, thermal and formaldehyde emission properties of untreated and UV-treated formulations at a laboratory scale. The results of the physical properties obtained in the PB-bbwa were similar or even better than those of the control PB. Additionally, PB-bbwas improve on the control PB sample's Janka hardness by least 28%, and a decrease in thermal conductivity in the edgewise position and formaldehyde emissions by 12% and 88%, respectively, in comparison to the control PB. The tests performed evidenced that PB-bbwas showed comparable performance against the control PB made with urea-formaldehyde and satisfied international standard requirements.
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    Flexural 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, Pablo
    This 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.
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    Non-Destructive Assessment of the Elastic Properties of Low-Grade CLT Panels
    (2021) Opazo-Vega, Alexander; Benedetti, Franco; Nunez-Decap, Mario; Maureira-Carsalade, Nelson; Oyarzo-Vera, Claudio
    The use of cross-laminated timber panels (CLT) made of low-grade structural timber has steadily increased in developing countries. These panels usually present several natural defects, which can cause a high local variation of their orthotropic elastic properties, generating future structural serviceability problems. Our work aims to estimate the local variability of the elastic properties in low-grade CLT panels by combining nondestructive transverse vibration testing, numerical simulations, and regional sensitivity analysis (RSA). Four three-layer Radiata pine CLT panels were subjected to transverse vibration tests with supports at four points. Besides, a series of numerical simulations of the panels, considering the local variability of the elastic properties of the panels in eight zones, were carried out using the finite element method. Then, RSA analysis was performed to study in which ranges of values the panels' elastic properties generated lower differences between the measured versus simulated dynamic properties. Finally, a structural quality control indicator was proposed for the CLT panels based on keeping low the probability that the elastic properties in the central zones do not exceed minimum acceptable values. The results obtained suggest that the proposed methodology is suitable for segregating CLT panels with high concentrations of defects such as pith presence.
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    Numerical Analysis of the Seismic Performance of Light-Frame Timber Buildings Using a Detailed Model
    (2022) Benedetti, Franco; Jara-Cisterna, Alan; Carlos Grandon, Juan; Astroza, Nicool; Opazo-Vega, Alexander
    Timber structures have gained interest for the construction of mid-rise buildings, but their seismic performance is still a matter under development. In this study, a numerical analysis of the seismic performance of light-frame timber buildings is developed through a highly detailed model using parallel computing tools. All of the lateral-load-resisting system components and connections are modeled. Combinations of lateral load capacity distributions in structures of one, three, and five stories are studied in order to assess the effects on the global performance of different triggered failure modes through nonlinear static and dynamic analyses. The results suggest that shear bracket connections and sheathing-to-framing connections control the buildings' responses, as well as the failure mode. For a ductile response, the lateral displacement must be dominated by the in-plane wall distortion (racking); therefore, the system must be provided with a story shear sliding stiffness and load capacity at least twice that of the walls. Furthermore, based on the pushover capacity curves, the performance limits are proposed by evaluating the stiffness degradation. Finally, the effect of the mobilized failure mode on the structural fragility is analyzed. Even though standard desktop PCs are used in this research, significant reductions in the computation effort are achieved.
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    STUDY OF WOOD ADHESIVES ON THE BONDING PROPERTIES IN SOLID AND HOLLOW GLULAM BEAMS OF PINUS RADIATA
    (2022) Nunez-Decap, Mario; Perez-Soto, Gustavo; Opazo-Vega, Alexander; Moya-Rojas, Boris; Vidal-Vega, Marcela
    The aim of this research was study of polyurethane (PUR), isocyanate polymer emulsions (EPI) and melamine-urea-formaldehyde (MUF) adhesives, on the bonding properties of solid and hollow glulam beams of Pinus radiata. The thermomechanical analysis (DMA) of the adhesives was carried out to evaluate their stiffness and reactivity. Glulam beams were evaluated by a bending test. The quality of the bonding was evaluated by resistance to shear and delamination. The morphology of the bonding was studied by microscopy. The DMA study showed that the MUF adhesive had the highest level of stiffness and reactivity. The results of the bending test showed that the highest modulus of rupture results were obtained in solid and hollow laminated beams with MUF adhesive, achieving increases of 30% over the PUR adhesive. The lowest delamination results were obtained in solid glulam beams with MUF and EPI adhesives, while the highest results were 32% and 47% for the PUR adhesive. Finally, glulam beams manufactured with MUF adhesive presented the best performance and results.
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    Use of Carbon and Basalt Fibers with Adhesives to Improve Physical and Mechanical Properties of Laminated Veneer Lumber
    (2023) Nunez-Decap, Mario; Sandoval-Valderrama, Barbara; Opazo-Carlsson, Camila; Moya-Rojas, Boris; Vidal-Vega, Marcela; Opazo-Vega, Alexander
    Climate change is one of the main factors influencing the research of environmentally friendly materials. This is why the use of engineering fibers as a reinforcement technique in wood, in order to increase its mechanical properties, has recently been investigated. This research presents the results obtained from the use of carbon and basalt fiber fabrics as a reinforcement for microlaminated Radiata Pine wood panels at a laboratory scale using the adhesives epoxy resin and polyvinyl acetate. Tests were carried out in comparison to the control boards, relating the physical properties obtained in terms of thickness swelling by 48 h-water immersion with a decrease of 19% for the polyvinyl acetate and carbon fiber matrix reinforcement, about the mechanical properties evaluated, a better performance was obtained for the epoxy resin and carbon fiber matrix reinforcement and in terms of flexural stiffness and strength (in flatwise), tensile strength and Janka hardness, with an increment of 31%, 38%, 56% and 41%, respectively.
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    Use of Carbon and Basalt Fibers with Adhesives to Improve Physical and Mechanical Properties of Plywood
    (2022) Nunez-Decap, Mario; Barra-Rodriguez, Yasna; Opazo-Carlsson, Camila; Moya-Rojas, Boris; Vidal-Vega, Marcela; Opazo-Vega, Alexander
    Currently, wood is presented as an alternative to traditional building materials and to mitigate climate change. Chile is one of the eight largest wood producers in the world; therefore, wood-based products are an easily accessible resource. The aim of this research is to reinforce at laboratory scale plywood panels with basalt and carbon engineer fibers using epoxy resin and polyvinyl acetate as an adhesive system to improve their physical and mechanical properties. Three-point static bending and Janka hardness tests were carried out. The results showed a better performance in the reinforced boards, which showed an increase in Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) properties in the parallel direction of about 48.2% and 52.8%, respectively. Additionally, for the perpendicular direction, there was an increase of 52.0% and 102.9%, respectively. On the other hand, the Fiber Reinforced Polymer (FRP) plywood panels showed an increase of at least 37% on the Janka hardness property, obtaining higher results with the polyvinyl acetate (PVA) adhesive. Finally, FRP-plywood, PVA-BF and PVA-CF may be a new option for composite wood materials, with their ductile behavior and superior mechanical properties, especially in the perpendicular direction, where the increases were greater than those shown in unreinforced plywood.
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    Vibration-based monitoring of a cross-laminated timber building in a high seismicity zone
    (2024) Jara-Cisterna, Alan; Benedetti, Franco; Rosales, Victor; Almazan, Jose Luis; Opazo-Vega, Alexander
    Cross-laminated timber (CLT) buildings have emerged as an alternative to make more sustainable and resilient cities. However, very few cases of vibration-based monitoring of these buildings have been reported. This paper discusses the variation of the dynamic properties of a 5-story cross-laminated timber (CLT) building through vibration-based monitoring over 23 months. The building combines different construction systems, is relatively slender for its type, and was built in a high seismicity zone. The monitoring strategy included periodic measurements of the dynamic properties during construction, reference measurements with high-sensitivity accelerometers, and 10 months of continuous measurements with low-cost equipment. In addition, continuous measurements allowed the analysis of the dynamic properties during special events associated with wind gusts and moderate-intensity earthquakes. During the construction stage monitoring and reference measurements, up to 5 modal shapes of the building with their respective vibration frequencies and damping ratios were detected. These dynamic properties allowed the calibration of a simplified numerical model of the building. Subsequently, during the continuous monitoring phase of the building, it was observed that the first two translation frequencies varied by up to 8% due to changes in climatic conditions and the moisture content of the timber. Finally, monitoring during a 5.4 Mw earthquake showed that vibration frequencies temporarily decreased by up to 15% and returned to their initial value after the seismic event had passed. The results of this research will contribute to the knowledge of the dynamic response of this type of building and the updating of their structural design codes.