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Item type:Publication, Optimization of a reinforced geopolymer composite using natural fibers and construction wastes(Elsevier, 2020-10-20)Geopolymer technology has allowed the development of eco-friendly construction materials with high mechanical properties using industrial wastes and residues. However, geopolymers show fragility and low ductility behavior similar to Portland cement-based materials. This article focuses on the evaluation of jute and sisal fibers as reinforcement of a geopolymer matrix produced from residues of Fired Clay Brick Powder (FCBP). Control samples with no fibers and reinforced matrices with different contents of jute (ranging from 0.5 to 2.0 wt%) and sisal fibers (ranging from 0.5 to 3.0 wt%) were produced to study the effect of the fiber type and content on the mechanical properties of the resulting geopolymer composites. Mechanical characterization consisted of compression, splitting tensile, and three-point bending tests. The results of compression and splitting tensile tests showed the existence of an optimum fiber content that depends on the fiber type for reaching the maximum strength while the three-point bending test results indicated a linear relationship between the flexural strength and the fiber content. The addition of 2.5% (wt%) of sisal fibers increased the compressive, splitting tensile and flexural strengths up to 76%, 112%, and 270%, respectively, in comparison to the control samples. On the other hand, FCBP-based geopolymers with 1.5% (wt%) jute fiber reinforcement showed an increase up to 64%, 45%, and 222% of the compressive, splitting tensile and flexural strengths, respectively. Both, jute and sisal fiber addition at the optimum content, lead to a change in the failure mode of the samples from a brittle to a more ductile failure in all mechanical tests. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Production of a lightweight masonry block using alkaline activated natural pozzolana and natural fibers(Elsevier, 2020-08-30)Lightweight geopolymers are alternative low-carbon footprint building materials with high potential to produce value added products for the construction industry such as low-density masonry units. This work focuses on presenting the development of a new lightweight masonry block using natural pozzolana-based geopolymer mortar, hydrogen peroxide as a foaming agent and jute fibers as reinforcement additive. The experimental plan allowed the optimization of the production process and the definition of the optimum quantities of hydrogen peroxide content, pozzolana: fine aggregate ratios and the appropriate amount of fibers to be incorporated. The experimental results demonstrate the feasibility of the production of new masonry units, which can achieve up to 8.1 MPa of compressive strength after 28 days of fabrication with reduced bulk densities of 1269 kg/m3. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Mechanical characterization of a masonry system made of alkaline activated pozzolana blocks(Trans Tech Publications Ltdttp@transtec.ch, 2020-01-01)The development of alkaline activated materials has enabled the production of eco-friendly alternatives for the construction industry. In the present article, the mechanical characterization of a new structural masonry system composed of fiber-reinforced lightweight pozzolana-based blocks and cement-lime mortar was performed. The mechanical characterization involved uniaxial compression tests in prisms and diagonal compression in wallets. The results indicate that the compressive and shear strength of the masonry system is up to 3.24 MPa and 0.38, respectively. The results obtained indicate that the evaluated system is structurally efficient and that can be used as both non-load and load-bearing walls. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Non-destructive (NDT) and minor-destructive (MDT) testing tools to support the structural characterization of adobe constructions(Springer Nature, 2021-01-01)Adobe constructions are widely used worldwide as low-cost vernacular buildings and also as monuments and historical constructions. Beside low cost these materials have excellent thermal and acoustic properties. Some challenges of this material involves durability and high vulnerability to seismic motions due to its relatively high weight and brittleness. To improve safety levels of existing adobe structures it is often necessary to strengthen or retrofit them based on a structural characterization. The structural characterization requires assessment of the in situ condition, geometry, engineering properties of existing adobe construction and buildings using minimal to no intrusion. In this chapter we present a general overview of commonly used NDT and MDT methods for the assessment of existing adobe construction to obtain information such as: detailed geometry information, damage mapping, and multi-scale mechanical and physical characterization. Additional to literature review summarizing different applications of NDT and MDT, this chapter presents four case studies related to projects in Peru recently performed by the research group led by the first author. The descriptions and results of NDT and MDT tests carried out at these case studies highlight how the use of several NDT and MDT methodologies complement each other and allow a suitable multi-scale characterization of existing adobe structural systems, that can successfully be used for the diagnosis, and design of intervention and retrofit measures as needed. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Specific dissipated energy as a failure predictor for uniform sands under constant volume cyclic simple shear loading(Springer Science+Business Media, 2021-10-27)An experimental study was performed to investigate the dissipated energy to failure of sand samples subjected to uniform and non-uniform cyclic simple shear loading. The hypothesis evaluated was that for a given initial sample state the specific dissipated energy required to reach failure should be reasonably constant independent of the type of stress-time history used in the testing. Test samples consisted of dry Ottawa sand prepared at nine different initial states that were subjected to different stress controlled cyclic horizontal shear loading waveforms that included 15 uniform sinusoidal waves and up to 33 non-uniform loading wave forms. The experimental program presented showed that the measured cumulative dissipated specific energy to failure, defined when the double amplitude shear strain reaches 7.5%, for the different sample initial states was reasonably constant but with coefficients of variation ranging between 13 to 44%. As expected, the cumulative dissipated energy increased with increasing initial stress level and relative density. The findings support the notion that specific dissipated energy can be used as a reasonable failure predictor for uniform dry sands based on their initial state and are independent of the type of cyclic simple shear loading waveform using in the testing. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Safety issues in buckling of steel structures by improving accuracy of historical methods(MDPI, 2021-11-01)Buckling of structural elements is a phenomenon that has great consequences on the bearing capacity of structures. Historically, there have been serious buckling-related structural accidents that have resulted in loss of human lives and high material costs. In this article, an attempt is made to perform a historical analysis of the diverse models that experts have been using in designing and calculating compression buckling of simple metallic elements in the last 275 years. The analysis covers the lapse from the mid-18th century, in which the pioneers in this classic field of structural design are located, up to the present, highlighting the main standards that have been applied to steel structural analysis in the past and at present all over the world. What the study tries to provide is an overall view and a sense of continuity of the methods used for improving structural safety regarding buckling failures in the last three centuries. Each analyzed buckling model is compared with the results of a numerical finite element model of compressed steel columns. Finally, the conclusion reached is that in the last one hundred years, the convergence of solutions proposed in the field is gradually greater and more accurate. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Integration of non-destructive testing, numerical simulations, and simplified analytical tools for assessing the structural performance of historical adobe buildings(Elsevier, 2021-07-05)For existing structures, the development of seismic vulnerability studies requires the availability of information related to geometry, boundary conditions, material properties, and accumulated damage. In the case of historical constructions, modern conservation criteria recommend carrying out a comprehensive structural assessment that involves the use of concurrent experimental diagnosis complemented with numerical and analytical approaches for structural analysis. This paper presents a proposal for a comprehensive integration of these perspectives by the application of several tools for the seismic performance analysis of an iconic Andean historical adobe building: the 'San Pedro Apostol Church' located in Andahuaylillas, Southern Peru. In this church, several non-destructive techniques for geometrical and damage assessment were combined with structural exploration tools, nonlinear numerical modeling, and simplified analytical tools for performing predictive seismic analysis. The results indicate the feasibility of the integration of these techniques for studying existing earthen buildings and their capacity to properly predict observed damage in past earthquakes (i.e. failures of bell towers, façade walls, tympani, and triumphal arches). In particular, the analyses allowed the identification of high seismic vulnerability of the studied church in occasional earthquakes (earthquakes with a return period of 72 years) due to the activation of collapse mechanisms consisting of rocking of the façade walls and out-of-plane overturning of the lateral walls. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Experimental and numerical evaluation of a stackable compressed earth block masonry system: Characterization at cyclic shear loads(Elsevier Ltd, 2022-11-15)Soil is a traditional construction material that is currently experiencing a new boom as an eco-sustainable alternative for housing. In this article, a structural system made up of compressed earth blocks is analyzed as a construction alternative for seismic countries. This study evaluated the physical properties of base soil as well as an optimization process for the chemical stabilization of the mixture using cement and lime. The mechanical characterization of the blocks and of a masonry system designed to be stackable and dry joint was also performed, including the evaluation of its seismic response to cyclic shear wall tests. Results indicate that it is possible to improve the workability of the stabilized soil mixtures and the mechanical behavior of blocks in compression and tension, by using cement-lime additives in a ratio of 1:3 with respect to the dry weight of the materials. In addition, it was found that it is feasible to produce a stackable masonry system that has the capacity to dissipate energy due to friction between blocks. The parametric analysis and the calibration process of numerical models performed for the cyclic shear tests highlight the importance of using a micro-modeling approach to obtain representative models that correctly predict the experimental capacity curve in both maximum load and ductility. The use of those models in the present study allowed to adequately replicate the concentration of damage in the joints between blocks, corroborating what was observed through experimental testing. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, A simplified method to predict failure of sands under general cyclic simple shear loading(ICE Publishing, 2022-06-16)This paper describes a simplified approach based on constant-volume cyclic simple shear (CSS) tests with uniform sinusoidal loading that can predict failure of dry sands under general shear stress–time histories. The simplified method is based on the cumulative energy hypothesis that states that the dissipated energy required by a sand sample to reach failure depends only on its initial state (D r and [Formula: see text]) and is independent of the characteristics of the cyclic loading applied. The proposed method uses a sand-specific multivariable regression developed using a small number of CSS tests involving uniform sinusoidal loading without the need for advanced general cyclic loading tests. Furthermore, the regression requires only a small data set involving one uniform CSS test per sample initial state. The simplified method was evaluated using two comprehensive experimental studies involving two different test sands. The first data set is an experimental programme by the authors involving 20/30 Ottawa sand subjected to different cyclic loading types. The second data set is an independent experimental programme that used 0/30 Monterey sand. In both cases, the simplified approach was found to yield reasonable predictions of failure of the test sands when subjected to complex and irregular shear stress loading. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Daily and seasonal effects of environmental temperature and humidity on the modal properties of structures(Springer Science and Business Media B.V., 2022-07-01)In Structural Health Monitoring understanding the effect of the environment on the modal properties of structures is essential. In this study, we evaluate the influence of changes in ambient conditions on the natural frequencies of three real large-scale structures: A 9-story reinforced concrete (RC) building and two sixteenth century churches of adobe masonry. For these structures, both environmental parameters (ambient temperature and relative humidity) and modal parameters were continuously monitored for a combined period of 8-years (RC building) and 2-years (for each of the adobe churches) in order to assess the effect of daily and seasonal variations of environmental parameters on the modal response. The results of the seasonal comparison indicate a negative correlation between ambient temperature and natural frequencies for the concrete structure, while for adobe structures a positive correlation between humidity and natural frequencies was observed. For daily variations, an out-of-phase and lag response of natural frequencies to variations in the environment was observed. A change on the daily lag was observed depending on the time of the year. Both seasonal and daily comparisons show the existence of a strong seasonality in frequency variations, where the form of response of this to environmental effects is different depending on the season. The magnitude of the daily variability is smaller in comparison to the seasonal variations. Finally, it was determined that the variation in natural frequencies depends on several factors such as the predominant material of the structure (namely reinforced concrete and adobe), the type of environmental exposure (temperature or humidity), and the characteristics of the structure (dimension of main elements).
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