Treesearch

While wood has been used as a building material for millennia, "mass timber" buildings have only been realized within the past few years within North America. Mass timber refers to a class of wood composites that include glue-laminated timber (glulam), structural composite lumber, and cross laminated timber (CL T). These composites allow multi-story residential and non-residential buildings to be constructed more efficiently than traditional light-framed wood systems. While there are a host of environmental and other benefits to building with mass timber, these buildings are different from...

Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface-atmosphere coupling. However, methods to estimate ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum-flux data. At 69 forest sites, annual ha robustly predicted site-to-site and year-to-year differences in canopy heights (R2 = 0.88, 111 site-years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over...

The increasing use of cross laminated timber (CLT) panels in large multi-story buildings has highlighted the structural performance of CLT in fire as a critical issue concerning life safety and serviceability. It is well-known that wood material strength decreases when exposed to elevated temperature for an extended period of time. For CLT panels, another level of complexity lies in the mechanical properties of the glued interface under high temperature. In this study, the tensile strength of typical North American wood species and shear strength of the glued interface of commonly used...

A novel class of high performance polymer porous aerogel flm-based triboelectric nanogenerators (A-NGs) is demonstrated. The A-NGs, made of a pair of highly porous polymer flms, exhibit much higher triboelectric outputs than the corresponding dense polymer flm-based triboelectric nanogenerators (D-NGs) under the same mechanical stress. The triboelectric outputs of the A-NGs increase signifcantly with increasing porosity, which can be attributed to the increase in contact area and the electrostatic induction in the porous structure, thereby leading to additional charges on the porous...

Structural insulated panels (SIPs) were creep-tested to determine the magnitude of long-term deflection and recovery, as well as changes to strength and stiffness, compared with a control group. This report documents the second phase of a two-phase testing process. The first phase was reported in FPL–RN–0332. In this second phase, 56 SIP control specimens were tested in static bending to failure. Of these, 28 were 12 in. wide by 12.25 in. deep by 19 ft long and 28 were 12 in. wide by 6.5 in. deep by 10 ft long. A matching set of 56 specimens were instrumented for deflection and subjected...

Diapause and cold tolerance can profoundly affect the distribution and activity of temperate insects. Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), an alien invasive species from Asia, enters a winter dormancy in response to environmental cues. We investigated the nature of this dormancy and its effects on H. halys cold tolerance, as measured by supercooling points, lower lethal temperatures, and overwintering field mortality. Dormancy was induced by rearing individuals in the laboratory or under field conditions. We confirmed H. halys dormancy to be a state of diapause and not...

Shifting disturbance regimes can have cascading effects on many ecosystems processes. This is particularly true when the scale of the disturbance no longer matches the regeneration strategy of the dominant vegetation. In the yellow pine and mixed conifer forests of California, over a century of fire exclusion and the warming climate are increasing the incidence and extent of stand‐replacing wildfire; such changes in severity patterns are altering regeneration dynamics by dramatically increasing the distance from live tree seed sources. This has raised concerns about limitations to natural...

This paper focuses on the material study (radiocarbon dating, wood identification and strontium isotope analyses) of four large ‘India occidentali’ clubs, part of the founding collections of the Ashmolean Museum, in Oxford, and originally part of John Tradescant’s ‘Ark’,in Lambeth (1656). During the seventeenth century, the term ‘India occidentali/occidentales’ referred not only to the ‘West Indies’ (its literal translation), but to the Americas as a whole; hence, the Ashmolean clubs and, indeed, the c forty examples of similarly large, decorated clubs known in international museum...

Reliability calculations for lumber products ultimately depend on the statistical distributions that we use to model lumber stiffness and strength. Fits of statistical distributions to empirical data allow researchers to estimate the probability of failure in service. For these fits to be useful, the theoretical statistical distributions must be good matches for the empirical lumber property populations. It has been common practice to assume that the MOE of a grade of lumber is well-fit by a normal distribution, and the MOR of a grade of lumber is well-fit by a normal, lognormal, or...

This work reports a study on the effects of different types and aspect ratios of cellulose nanocrystals (CNCs) on properties of poly (vinyl alcohol) (PVA) composite fibers. CNCs were extracted from wood pulp and cotton and reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with the first stage drawing up to draw ratio 2. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5–15 wt. %) at the expense of their strain-to-failure. It was also observed that the mechanical properties of fibers reinforced...