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Alcaino, P., Santa-Maria, H., Magna-Verdugo, C., & Lopez, L. (2020). Experimental fast-assessment of post-fire residual strength of reinforced concrete frame buildings based on non-destructive tests. Constr. Build. Mater., 234, 10 pp.
Abstract: Assessment of the residual strength of reinforced concrete buildings subjected to fire is a problem that requires fast and sufficiently reliable resolution, necessary for the action of firefighters, forensic fire investigation, and structural assessment of post-fire condition of the building to take place. In all cases safety and integrity of firefighters and researchers can be at risk, and it is necessary to have rapidly and sufficiently reliable information in order to choose whether to enter freely, to enter with caution, or simply do not enter to the burned structure. This required prompt assessment gives no time or background to develop mathematical models of the structure and damage propagation. This work presents an experimental methodology for a fast assessment of post-fire residual strength of reinforced concrete frame buildings based on the high correlation between the loss of strength and non-destructive test results of frame concrete elements subjected to fire action. (C) 2019 Elsevier Ltd. All rights reserved.
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Avudaiappan, S., Moreno, P. I. C., Montoya, R. L. F., Chávez-Delgado, M., Arunachalam, K. P., Guindos, P., et al. (2023). Experimental investigation on the physical, microstructural, and mechanical properties of hemp limecrete. Sci. Rep., 13(1), 22650.
Abstract: This paper investigates the hemp limecrete mechanical and microstructural performance of a new sustainable and environmental friendly building material. Several studies have investigated the hemp limecrete focusing on the non-structural applications. The newly developed hemp limecrete consists of high mechanical and microstructural properties. The specimens were prepared with varying lengths and proportions of hemp fibers with lime and tested for compressive strength, flexural strength, thermal conductivity and microstructural analysis like SEM and EDS. The study found that the optimal fiber content for making mortars was between 2 and 4%. This conclusion was reached after analyzing the influence of fiber length and ratio on the properties of the mortars. The dry unit weight decreased when the fiber content was higher than 4%. In terms of strength, the study found that the flexural strength of the hemp limecrete improved with an increase in fiber ratio, but the compressive strength decreased. However, with 2% hemp fiber, compressive strengths of 3.48 MPa and above were obtained. The study also highlighted the good thermal insulation properties and dimensional stability of hemp limecrete. These findings have important implications for the use of hemp limecrete as a sustainable building material. The results suggest that hemp limecrete has the potential to be a viable alternative to conventional concrete in specific applications, particularly in areas where environmental sustainability is a priority.
Keywords: FIBER-REINFORCED CONCRETE; THERMAL-PROPERTIES; LIME; COMPOSITE
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Cando, M. A., Hube, M. A., Parra, P. F., & Arteta, C. A. (2020). Effect of stiffness on the seismic performance of code -conforming reinforced concrete shear wall buildings. Eng. Struct., 219, 14 pp.
Abstract: This study assesses the effect of the stiffness on the seismic performance of residential shear wall buildings designed according to current Chilean regulations, including DS60 and DS61. Specifically, the paper focuses on the effect of stiffness on the building overstrength, displacement ductility, fragility for Life Safety (LS) and collapse limit states, as well as the probability of achieving these two limits states in 50 years. The seismic performance is assessed for a group of four 20 -story residential shear wall buildings archetypes located in Santiago. Walls were modeled using the multiple vertical line element model (MVLEM) with inelastic hysteretic materials for the vertical elements, and a linear -elastic shear behavior. Pushover analyses were considered to estimate the buildings overstrength and displacement ductility, while incremental dynamic analyses were per- formed to estimate fragility curves. A probabilistic seismic hazard analysis, which considered the seismicity of Chile central zone, was performed to estimate the probability of achieving the two limits states in 50 years. The results show that an increase in the stiffness reduces the chance of exceeding the LS and collapse limit states for the same intensity level. Additionally, the probabilistic seismic hazard analysis shows that, when the stiffness increases, the probability of reaching the LS limit state in 50 years also decreases. Counterintuitively, the probability of collapse in 50 years increases as the stiffness increases, due to the considered seismic hazard and the design requirements. Since society is moving towards resilient structural designs that minimize damage, disruption and economic losses, it is concluded that the performance of reinforced concrete shear wall buildings is improved by increasing the stiffness.
Keywords: Reinforced concrete; Shear wall; Building; Collapse; Life safety; Stiffness; Fragility; Risk
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Cando, M. A., Hube, M. A., Parra, P. F., & Arteta, C. A. (2023). Effect of lateral stiffness on expected economic losses in reinforced concrete shear wall buildings. Eng. Struct., 297, 116894.
Abstract: This research paper evaluates the effect of lateral stiffness on expected economic losses in reinforced concrete shear wall buildings designed following current Chilean standards, including DS60 and DS61. Economic losses were evaluated for a group of four 20-story archetype buildings located in Santiago, Chile. The methodology developed by the Pacific Earthquake Engineering Research Center was considered to estimate economic losses. The expected annual loss (EAL) and the present value (PV) of the losses in 50 years were used as measures of economic loss. A probabilistic seismic hazard analysis, which considered the seismicity of central Chile, was performed to estimate both metrics. The results show that when the lateral stiffness of the building increases, the EAL also increases. This implies that stiffer buildings are more vulnerable from an economic point of view. This counter-intuitive finding results from the higher seismic hazard of stiffer buildings and the minimum design base shear required by DS61 that governed the design of the studied buildings. Additionally, it was found that the EAL and the PV of losses in 50 years for the four archetypes do not exceed 0.3% and 7.8% of the total construction cost of the buildings, respectively. These monetary losses are relatively low, which is consistent with the outstanding seismic performance of reinforced concrete shear wall buildings.
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Markou, G., & Genco, F. (2019). Seismic assessment of small modular reactors: NuScale case study for the 8.8 Mw earthquake in Chile. Nucl. Eng. Des., 342, 176–204.
Abstract: Reducing greenhouse gas emissions and improving energy production sustainability is a paramount of Chile's 2050 energy policy. This though, is difficult to achieve without some degree of nuclear power involvement, given that the geography of the country consists of many areas that are practically off-grid, whereas cannot be developed and financially exploited due to the lack of basic commodities such as water and electricity. Recently small modular reactors (SMRs) have gained lots of attention by both researchers and world policy makers for their promised capabilities of enhanced safety systems, affordable costs and competitive scalability. SMRs can be located in remote areas and at this time are being actively developed in Argentina, USA, Brazil, Russia, China, South Korea, Japan, India and South Africa. Chile's 2010 earthquake and Fukushima's 2011 nuclear disaster have increased significantly both the population's fear and opposition to Nuclear Power Energy for the possible consequences of radiation on the lives of people. This paper aims to study the seismic resistance of a typical nuclear structure, being at time proposed in Small Modular Reactors, by using earthquake conditions typically seen in Chile. Since many designs are under study, a NuScale reactor from USA is analyzed under these extreme loading conditions. The major advantages of the NuScale reactor are in the power scalability (it can go from 1 to 12 reactor cores producing from 60 to 720 MWe), limited nuclear fuel concentration, modules allocated below grade and high strength steel containments fully immersed in water. The cooling effect beyond Design Basis Accident is ensured indefinitely, which induces a significant safety factor in the case of an accident. For the purpose of this study a detailed 3D detailed structural model was developed, reproducing the NuScale reactor's reinforced concrete framing system, where nonlinear analyses was performed to assess the overall mechanical response of the structure. The framing system has been tested under high seismic excitations typically seen in Chile (Mw > 8.0), showing high resistance and capability to cope with the developed forces due to its design. Based on a Soil-Structure Interaction analysis, it was also found that the NuScale framing system manages to maintain a low-stress level at the interaction surface between the foundation and the soil, where the structural system was found to be able to withstand significant earthquake loads. Finally, further investigation is deemed necessary in order to study the potential damages of the structure in the case of other hazards such as tsunami events, blast loads, etc.
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Parra, P. F., & Moehle, J. P. (2017). Stability of Slender Wall Boundaries Subjected to Earthquake Loading. ACI Struct. J., 114(6), 1627–1636.
Abstract: Global instability of slender reinforced concrete walls occurs when the concrete section buckles out-of-plane over a portion of the wall length and height. Theoretical and numerical analyses were conducted on axially loaded prismatic members to evaluate the onset of global instability under tension/compression load cycles. A buckling theory suitable for hand calculations is introduced and evaluated using data available in the literature from tests conducted on columns. Computer simulations using force-based nonlinear elements with fibers are used to numerically simulate the tests and to study the influence of non-uniform strain profiles along the height of the member. The study shows that the onset of buckling can be identified using either the proposed buckling theory or finite element models. Furthermore, buckling is affected by gradients of axial load or strain along the length of the member. Design recommendations are made to inhibit global wall buckling during earthquakes.
Keywords: buckling; earthquake; reinforced concrete; slenderness; wall boundary element
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Parra, P. F., & Moehle, J. P. (2020). Effects of strain gradients in the onset of global buckling in slender walls due to earthquake loading. Bull. Earthq. Eng., 18(7), 3205–3221.
Abstract: Global buckling of slender walls, reported only in a few laboratory tests before 2010, became a critical issue in design of reinforced concrete buildings after it was observed following the 2010 Mw 8.8 Chile earthquake and the 2011 Mw 6.3 New Zealand earthquake. Researchers have proposed theoretical buckling models based on prismatic columns subjected to uniform tension/compression cycles, where the key parameters are slenderness ratio, number of curtains of reinforcement, and maximum tensile strain before buckling during load reversal. These models have shown sufficient accuracy in comparison with laboratory tests on columns under such loading conditions. However, buckling in walls is more complex because of variation of strains through the wall depth and variation of moment along the wall height. Nonlinear finite elements are used to evaluate the effects of these more complex loadings on buckling of wall boundary elements. Analyses showed that the maximum tensile strain (averaged over the wall out-of-plane unsupported height) required to buckle the wall during load reversal does not depend on the moment variation along the wall height. Moreover, for typical wall lengths, the wall boundary behaves like an isolated column subjected to axial force cycles, with minimal apparent bracing provided by the wall web. This allows to analyze a broad range of practical cases for buckling susceptibility using simplified approaches based on buckling models of axially loaded columns.
Keywords: Walls; Global buckling; Reinforced concrete; Earthquake
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