Browsing by Author "Brena, Sergio F."

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Analysis of the probability of failure for open-grown trees during wind storms
(ELSEVIER SCI LTD, 2014) Ciftci, Cihan; Arwade, Sanjay R.; Kane, Brian; Brena, Sergio F.; 0000-0001-9199-6437; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Ciftci, Cihan
Although trees convey important environmental, economic, and sociological benefits on humans and society, they can also cause significant economic and societal disruptions, especially when subjected to wind storms in urban environments. Tools for proper assessment of the risk of these disruptions can be of significant benefit to society. In this research an approach to quantifying the failure probability for trees subject to wind storms is presented and illustrated by application to two specific maple trees in Massachusetts, USA. The approach entails four specific steps: (1) Random wind time history samples were generated using a modified Ochi–Shin spectrum, (2) these wind time histories were used as loading time histories on finite element models of the example trees in both summer (in-leaf) and winter (leafless), (3) maximum bending moments generated by the random wind time histories were compared to the failure (yield) moment of the tree at 1.4 m above ground, (4) the failure/fragility curves of the trees were estimated by Monte Carlo simulation for a range of average wind speeds and for 1000 independent wind time histories at each wind speed.
Loss in moment capacity of tree stems induced by decay
(SPRINGER HEIDELBERG, 2014) Ciftci, Cihan; Kane, Brian; Brena, Sergio F.; Arwade, Sanjay R.; 0000-0001-9199-6437; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Ciftci, Cihan
Key message We model varying decay in tree crosssections by considering bending theory to estimate moment capacity loss (MCL) for the sections. We compare MCL with experiments on selected oak trees. Abstract Tree failures can damage property and injure people, sometimes with fatal consequences. Arborists assess the likelihood of failure by examining many factors, including strength loss in the stem or branch due to decay. Current methods for assessing strength loss due to decay are limited by not accounting for offset areas of decay and assuming that the neutral axis of the cross-section corresponds to the centroidal axis. This paper considers that strength loss of a tree can be related to moment capacity loss (MCL) of the decayed tree cross-section, because tree failures are assumed to occur when induced moments exceed the moment capacity of the tree cross-section. An estimation of MCL is theoretically derived to account for offset areas of decay and for differences in properties of wood under compressive and tensile stresses. Field measurements are used to validate the theoretical approach, and predictions of loss in moment capacity are plotted for a range of scenarios of decayed stems or branches. Results show that the location and size of decay in the cross-section and relative to the direction of sway are important to determine MCL. The effect of wood properties on MCL was most evident for concentric decay and decreased as the location of decay moved to the periphery of the stem. The effect of the ratio of tensile to compressive moduli of elasticity on calculations of MCL was negligible. Practitioners are cautioned against using certain existing methods because the degree to which they over- or underestimate the likelihood of failure depended on the amount and location of decay in the cross-section.