Browsing by Author "Santa María, H."

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    Analysis of instant and long-term performance of timber-concrete floors with boundary conditions other than simply supported
    (2022) Adema, A.; Santa María, H.; Guindos, P.
    This paper describes an analytical procedure for designing timber-concrete composites (TCC) subjected to boundary conditions other than simply supported. Currently available investigations of TCCs are mainly focused on simply supported slabs, as it is a typical configuration for timber buildings. However, in other structural applications, and remarkably for reinforced concrete buildings, the boundary conditions of the TCC slabs are not likely to be simply supported. Such distinct boundary conditions can significantly reduce the cross section height, mid-span deflection and self weight of the structure, the last one being crucial in seismic regions. The proposed procedure is derived from two simplified methods available in the literature, one general in its nature while the other being valid for simply supported beams. The short-term analytical model was compared against finite element models (FEM) and to the only experimental investigation on partially restrained TCCs available in the literature, while the long-term analytical model was compared only against FEM. At the end of the investigation, a full-scale continuous TCC beam was tested in the serviceability range, to compare with the prediction of the proposed analytical model. The model underestimated the mid-span deflection at 4.5 kN by 13%, concluding that the proposed simplified procedure is valid for boundary conditions other than simply supported. Further experimental campaigns are needed in the future to assess the versatility of the model in a wider range of boundary conditions, including short-term and long-term tests, which should enhance the applicability of TCC slabs in structures different from timber buildings and bridges.
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    Automated building characterization for seismic risk assessment using street-level imagery and deep learning
    (2021) Aravena Pelizari, P.; Geiß, C.; Aguirre, P.; Santa María, H.; Merino Peña, Y.; Taubenböck, H.
    Accurate seismic risk modeling requires knowledge of key structural characteristics of buildings. However, to date, the collection of such data is highly expensive in terms of labor, time and money and thus prohibitive for a spatially continuous large-area monitoring. This study quantitatively evaluates the potential of an automated and thus more efficient collection of vulnerability-related structural building characteristics based on Deep Convolutional Neural Networks (DCNNs) and street-level imagery such as provided by Google Street View. The proposed approach involves a tailored hierarchical categorization workflow to structure the highly heterogeneous street-level imagery in an application-oriented fashion. Thereupon, we use state-of-the-art DCNNs to explore the automated inference of Seismic Building Structural Types. These reflect the main-load bearing structure of a building, and thus its resistance to seismic forces. Additionally, we assess the independent retrieval of two key building structural parameters, i.e., the material of the lateral-load-resisting system and building height to investigate the applicability for a more generic structural characterization of buildings. Experimental results obtained for the earthquake-prone Chilean capital Santiago show accuracies beyond kappa = 0.81 for all addressed classification tasks. This underlines the potential of the proposed methodology for an efficient in-situ data collection on large spatial scales with the purpose of risk assessments related to earthquakes, but also other natural hazards (e.g., tsunamis, or floods).
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    Cyclic behavior of wood-frame shear walls with vertical load and bending moment for mid-rise timber buildings
    (2021) Orellana, P.; Santa María, H.; Almazán, J.L.; Estrella, X.
    In light wood-frame buildings, the gravitational and lateral force-resisting systems are composed of floor diaphragms and shear walls. During an earthquake, these walls are subjected to the simultaneous action of in-plane vertical force, shear force, and in-plane bending moment. In a mid-rise building, these internal forces can reach large magnitudes, especially on the lower stories, and could have an important influence on the lateral behavior of the walls. The historical use of light wood-frame construction has been in low-rise buildings. Consequently, few investigations have analyzed the effects of high gravitational forces or in-plane bending moment on the lateral behavior of wood shear walls designed for multi-story buildings. This paper presents an investigation of the cyclic lateral behavior of light wood-frame shear walls, designed for mid-rise buildings, subjected to large axial compressive load and in-plane bending moment. Eight wall specimens were experimentally tested with a cyclic lateral displacement protocol, a constant compressive load, and a cyclic in-plane bending moment. The effects of axial compressive load and in-plane bending moment were analyzed. Also, the wall length and the spacing of sheathing nails were varied to study the effects of these variables on the response. A numerical study was performed to show how these effects could influence the response of mid-rise timber buildings. An improvement in the lateral performance of the walls was observed compared to walls tested without compressive force nor bending moment, showing an increase in stiffness, load-carrying capacity, and dissipated energy.
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    Development and comparison of seismic fragility curves for bridges based on empirical and analytical approaches
    (2021) Allen, E.; Amaya, T.; Chamorro, A.; Santa María, H.; Baratta, F.; de Solminihac, H.; Echaveguren, T.
    The bridge network is an essential part of the transportation infrastructure for mobility. However, bridges are susceptible to seismic activity that produces damages and affects the entire transportation system. Their fragilities have been studied based mostly on analytical models but neglecting empirical data from reports. Few studies compared fragility curves from different development methods, analyzing their similarities, advantages, and limitations for a better risk assessment. This article aims to develop and compare fragility curves for bridges based on empirical and analytical methods. The empirical approach is based on damage reports from the 8.8Mw Maule earthquake, while the analytical approach is based on numerical simulations of the seismic response using ground motion components from stations that recorded the Maule earthquake. The curves are developed for bridges with steel and concrete beams, representative of 57% of Chilean bridges. The comparative Kolmogorov-Smirnov test revealed significant compatibility in moderate and severe damage curves when comparing these approaches, unlike the slight damage curves. The lognormal mean parameter varies between the methods by 36%, 1.5%, and 7.5% for the slight, moderate, and severe damage curves respectively for a particular bridge configuration, showing considerable differences in the slight damage curve between methods.
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    Experimental study of the effects of continuous rod hold-down anchorages on the cyclic response of wood frame shear walls
    (2021) Estrella, X.; Malek, S.; Almazán, J.L.; Guindos, P.; Santa María, H.
    When designing mid-rise wood frame buildings in high seismicity areas, overturning moments induce large tensile forces in the anchoring system that cannot be resisted by conventional discrete hold-downs. To address this issue, continuous rod hold-downs are used instead to transfer the generated tensile loads to the foundation. However, investigations on the lateral response of wood frame walls employing this anchorage system are quite limited. This paper presents an experimental-numerical study aimed at providing a better understanding of the response of such walls under lateral loads. Four specimens with different configurations were tested under lateral cyclic load, and their behavior was compared with that of walls with discrete hold-downs. Results showed that employing the continuous rod system increases the wall strength by 35.8%, with the specimens behaving elastically up to drifts of about 0.8%. The walls exhibited a marked stiffness degradation during the tests, keeping a residual value of about 15-20% of the initial stiffness. Further analyses showed that the Special Design Provisions for Wind and Seismic (SDPWS) guidelines underestimate the wall strengths by 39.9% and overestimate the stiffnesses by 37.5%, on average. Finally, a nonlinear model was developed to investigate the specimens of this research in depth, showing a special failure pattern that concentrates the damage in the nails located at the central studs of the wall.
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    New technique for self-centering shear keys in highway bridges
    (2022) Wilches, J.; Leon, R.; Santa María, H.; Fernández, C.; Restrepo, J.I.
    Shear keys are elements in bridges designed to prevent or limit transverse unseating, rotation, and/or collapse of the superstructure responding to strong-intensity earthquake input ground motion, as well as to absorb breaking and various self equilibrating forces. During the 2010 Maule earthquake, Chile's highway infrastructure was seriously impacted. Shear key failures were endemic and did not function as intended. As a result, some bridges experienced partial or complete collapse. Even when the shear keys appeared to have worked, the superstructure exhibited large offsets, which required expensive repairs. An expensive retrofit of undamaged bridges was also carried out as a result of the inadequate response of the bridge infrastructure. This paper addresses the behavioral issues of bridges designed incorporating conventional shear keys and proposes an innovative self-centering concept that eliminates residual displacements in the superstructure. The self-centering shear key concept, as it will be termed here, makes use of the bridge self-weight as a restoring force to ensure self-centering. This concept proposal takes advantage of the kinematics of the bridge. The self-centering shear key concept was validated for a typical Chilean bridge via an extensive study that made use of nonlinear time history analyses. The results indicate that the increase in seismic demand on the substructure is small enough to maintain the bridge base structure in the elastic range while eliminating any residual displacements in the superstructure.
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    Seismic behavior of innovative hybrid CLT-steel shear wall for mid-rise buildings
    (2021) Carrero, T.; Montaño, J.; Berwart, S.; Santa María, H.; Guindos, P.
    This paper examines the seismic behavior of CLT-steel hybrid walls at 6- and 10-story heights to increase seismic force resistance compared to conventional wooden walls. The ultra-strong shear walls proposed in this paper are called Framing Panel Shear Walls (FPSW), which are based on a robust articulated steel frame braced with CLT board panels and steel tendons. Timber structures are well-known for their ecological benefits, as well as their excellent seismic performance, mainly due to the high strength-to-weight ratio compared to steel and concrete ones, flexibility, and redundancy. However, in order to meet the requirements regarding the maximum inter-story drifts prescribed in seismic design codes, a challenging engineering problem emerges, because sufficiently resistant, rigid and ductile connections and lateral assemblies are not available for timber to meet both the technical and economical restrictions. Therefore, it is necessary to develop strong and cost-effective timber-based lateral systems, in order to become a real alternative to mid- and high-rises, especially in seismic countries. In this investigation, the dynamic response of cross-laminated timber (CLT) combined with hollow steel profiles has been investigated in shear wall configuration. After experimental work, research was also carried out into numerical modelling for simulating the cyclic behavior of a hybrid FPSW wall and the spectral modal analysis of buildings of 6- and a 10-stories with FPSW. A FPSW shear wall can double the capacity and stiffness.
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    Seismic performance factors for timber buildings with woodframe shear walls
    (2021) Estrella, X.; Guindos, P.; Almazán, J.L.; Malek, S.; Santa María, H.; Montaño, J.; Berwart, S.
    Seismic performance factors are an engineering tool to estimate force and displacement demands on structures designed through linear methods of analysis. In Chile, the NCh433 standard provides the regulations, requirements, and factors for seismic design of several structural typologies and systems. However, when it comes to wood frame structures, previous research has found that the NCh433 provisions are highly restrictive and result in over-conservative designs. Therefore, this paper presents an experimental and numerical investigation aimed at proposing new, less restrictive seismic performance factors for wood frame buildings. Following the FEMA P-695 guidelines and a novel ground motion set for subduction zones, this research embraced: (1) testing of several full-scale specimens, (2) developing of detailed and simplified numerical models, and (3) analyzing the seismic performance of a comprehensive set of structural archetypes. 201 buildings were analyzed and results showed that changing the current NCh433 performance factors from R = 5.5 & Delta(max) = 0.002 to R = 6.5 & Delta(max) = 0.004 decreases the average collapse ratio of wood frame structures by 13.3% but keeps the collapse probability below 20% for all the archetypes under study. Besides, it improves the cost-effectiveness of the buildings and enhances their competitiveness when compared to other materials, since savings of 40.4% in nailing, 15.9% in OSB panels, and 7.3% in timber studs were found for a 5-story building case study. Further analyses showed that the buildings designed with the new factors reached the "enhanced performance objective" as defined by the ASCE 41-17 standard, guaranteeing neglectable structural and non-structural damage under highly recurring seismic events. Finally, dynamic analyses revealed that the minimum base shear requirement Cmin of the NCh433 standard is somewhat restrictive for soil classes A, B, and C, leading to conservative results compared to archetypes where the Cmin requirement did not control the structural design.
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    Statistical analysis of pedestrian bridges damaged during 2010 Chile earthquake
    (2014) Toro, F.I.; Santa María, H.; Hube, M.; Cabrera, T.
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    Uncertainty in the inelastic behavior of reinforced concrete walls due to material properties
    (2020) Llera Martin, Juan Carlos de la; Gallardo, J. A.; Santa María, H.; Chacón, Matías F.
    Reinforced concrete (RC) walls are structural elements widely used to resist lateral forces in highly seismic countries. Design codes provide minimum requirements to ensure an adequate performance of shear walls during ground motions; however, during recent earthquakes such as the 2010 Maule earthquake in Chile, or the Canterbury, Christchurch 2010 and 2011 earthquakes in New Zealand, some shear walls underwent an unprecedented and somewhat unexpected brittle failure. This fact evidenced that current analysis and design procedures for shear wall buildings do not provide a close representation of the true seismic response of these walls under severe cyclic earthquake loading, which is an imperative in performance-based design. Keeping that in mind, the present research implemented a Nonlinear Finite Element Wall (NLFEW) model, which was validated using parametric analyses. A micro-model using layered-shell elements was selected that uses an effective material model for concrete based on theory of plasticity and continuum damage mechanics. The wall model was validated simulating the behavior of four experimental RC benchmark wall test specimens subjected to quasi-static cyclic loads. Five response parameters were considered to evaluate the accuracy of the model: the initial stiffness, peak base-shear force, peak displacement at the top, ultimate base-shear force, and energy dissipated throughout the cyclic loading. The same parameters were used to quantify the uncertainty generated by the material properties in the global response of each wall. Results show that the model fits very well the experimental tests, and localization of damage is correctly predicted. Moreover, results from sensitivity analyses suggest that the initial stiffness is mainly influenced by variables of concrete in tension; the maximum top displacement (ductility of the element) depends largely on the parameters of concrete in compression; and base-shear forces and dissipated energy are sensitive to the post-yield stiffness of steel reinforcement.