Shear Moduli Determination Using Torsional Stiffness Measurements

The orthotropic shear moduli were determined for three different reconstituted wood materials. Shear moduli determination was accomplished using the respective formulae that define torsional stiffness for a linear elastic orthotropic rectangular parallelepiped. Applied test procedures required the experimental evaluation of torsional stiffness constants for rectangular specimens of decreasing width to thickness slenderness ratio. Anticlastic plate bending tests were also conducted to derive in-plane shear modulus values using standard ASTM D3044 procedures. In-plane shear modulus values derived from applied torsional theory were found to be in reasonable agreement with the standard ASTM test procedure

Iosipescu Shear Test Apparatus Applied to Wood Composites

In-plane and transverse (through-the-thickness) shear strength properties were evaluated for three wood composite materials. A modified Iosipescu test apparatus was used to determine shear strength relative to the six possible material orientations. In-plane shear was also characterized using ASTM D1037-87 test standards. The Iosipescu shear test method was developed originally for metals testing. However, different forms of the test device have evolved for purposes of shear evaluation with numerous nonisotropic materials being evaluated. Previous research for various materials has shown satisfactory results with repeatability and apparent shear failure. The current research specifically utilized the University of Wyoming version of the original shear test device. Iosipescu test results for in-plane shear strength were comparable to values derived from the ASTM test method. Transverse shear strength values were found to exceed the magnitude of previously published ASTM test results. Greater directional or material orientation differences were observed for transverse shear properties

Torsional Rigidity of Rectangular Wood Composite Materials

The torsional rigidity of wood members is necessary for predicting lateral torsional buckling of laterally unsupported beams, and is useful for estimating the stiffness of two-way floor systems and the natural frequency for wood floors. Current estimations of torsional rigidity of composite wood materials are based upon elastic constant ratios of solid wood. Recently published work has found differences in the elastic constant ratios of solid wood versus structural composite lumber (SCL) materials. These differences in elastic properties may indicate differences in torsional rigidity. Rectangular sections of solid-sawn lumber and various SCL materials were tested to determine values of torsional rigidity. Torsional rigidity of solid-sawn lumber was significantly different (

Laminating Creosote-Treated Hardwoods

A study was conducted to investigate the bondability of four selected hardwood species after being treated with creosote. A completely randomized block factorial design was employed. Experimental factors included five wood species (chestnut oak, red oak, red maple, yellow-poplar, and southern pine), five adhesive systems (elevated temperature cure phenol-resorcinol-formaldehyde, room temperature cure phenol-resorcinol-formaldehyde, resorcinol-formaldehyde, emulsion polymer isocyanate, and low-viscosity formulation emulsion polymer isocyanate) and two exposure levels (ambient room and vacuum/pressure/soak conditions). Exposure levels effects on the different wood species resulted in highly variable adhesive system performance. Exposure level effects were most evident for the higher density oaks. Shear strength and percent wood failure results for all wood species revealed a general trend towards a higher performance for the two phenol-resorcinol-formaldehyde systems. Res-orcinol-based adhesive systems had the highest shear strength values. Percent wood failure values were highest for the elevated temperature cure phenol-resorcinol-formaldehyde system for all species. Elevated temperature cure adhesive systems appeared to be required to successfully bond high-density creosote treated species. Successful bonding of medium-density species can be accomplished at room temperatures given proper adhesive system selection

Creosote Treatment Effect On Hardwood Glulam Beam Properties

Flexure tests were conducted to determine the effect of creosote treatment on the performance of Combination A northern red oak, yellow poplar, and red maple glued-laminated (glulam) beams. This testing was conducted in accordance with ASTM D198-84 (ASTM 1987a), and the beams were fabricated in accordance with AITC 119-85 (AITC 1986), ANSI/AITC 190.1-83(AITC 1983b), and AITC 200-83 (AITC 1983a). Shear tests were also conducted on samples taken from the beams to determine the glueline shear strength and percent wood failure (WF).There was no significant difference (P < 0.05) between the modulus of rupture (MOR) of creosote-treated and untreated northern red oak beams. However, the MORs of the creosote-treated red maple and yellow poplar beams were significantly (P < 0.05) higher than those for untreated beams. There was no significant difference (P < 0.05) between the treated and untreated apparent modulus of elasticity (MOE) of each species. Therefore, the post-fabrication creosote treatment process from 145.92 to 215.76 kg/m3 (9.11 to 13.47 pcf) average weight retention did not adversely affect the strength (MOR) or stiffness (MOE) of northern red oak, red maple, and yellow poplar Combination A glulam beams.Glueline shear strengths for treated and untreated specimens of each species met or exceeded minimum performance criteria in AITC 200-83. Creosote treatment significantly (P < 0.05) increased glueline shear strength of red maple, but had no effect on the shear strength of red oak and yellow poplar specimens. Mean percentage wood failure of treated shear specimens was significantly (P < 0.05) greater than of untreated specimens in each species. Mean percentage wood failures of red oak and yellow poplar gluelines exceeded AITC 200-83 performance criteria; percentage wood failure of untreated (48%) and treated (59%) red maple shear specimens did not meet AITC 200-83 performance criteria

The Version-2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979–Present)

The Global Precipitation Climatology Project (GPCP) Version-2 Monthly Precipitation Analysis is described. This globally complete, monthly analysis of surface precipitation at 2.58 latitude 3 2.58 longitude resolution is available from January 1979 to the present. It is a merged analysis that incorporates precipitation estimates from low-orbit satellite microwave data, geosynchronous-orbit satellite infrared data, and surface rain gauge obser-vations. The merging approach utilizes the higher accuracy of the low-orbit microwave observations to calibrate, or adjust, the more frequent geosynchronous infrared observations. The dataset is extended back into the prem-icrowave era (before mid-1987) by using infrared-only observations calibrated to the microwave-based analysis of the later years. The combined satellite-based product is adjusted by the rain gauge analysis. The dataset archive also contains the individual input fields, a combined satellite estimate, and error estimates for each field. This monthly analysis is the foundation for the GPCP suite of products, including those at finer temporal resolution. The 23-yr GPCP climatology is characterized, along with time and space variations of precipitation. 1

A dynamical framework for the origin of the diagonal South Pacific and South Atlantic convergence zones

The South Pacific Convergence Zone (SPCZ) and South Atlantic Convergence Zone (SACZ) are diagonal bands of precipitation that extend from the equator southeastward into the Southern Hemisphere over the western Pacific and Atlantic Oceans, respectively. With mean precipitation rates over 5 mm day−1, they are a major component of the tropical and global climate in austral summer. However, their basic formation mechanism is not fully understood. Here, a conceptual framework for the diagonal convergence zones is developed, based on calculations of the vorticity budget from reanalysis and Rossby wave theory. Wave trains propagate eastward along the Southern Hemisphere subtropical jet, with initially quasi-circular vorticity centres. In the zonally sheared environment on the equatorward flank of the jet, these vorticity centres become elongated and develop a northwest-southeast tilt. Ray tracing diagnostics in a non-divergent, barotropic Rossby wave framework then explain the observed equatorward propagation of these diagonal vorticity structures toward the westerly ducts over the equatorial Pacific and Atlantic. The baroclinic component of these circulations leads to destabilisation and ascent ahead of the cyclonic vorticity anomaly in the wave, triggering deep convection because of the high sea surface temperatures in this region. Latent heat release then forces additional ascent and strong upper-tropospheric divergence, with an associated anticyclonic vorticity tendency. A vorticity budget shows that this cancels out the advective cyclonic vorticity tendency in the wave train over the SPCZ, and dissipates the wave within a day. The mean SPCZ is consequently comprised of the sum of these pulses of diagonal bands of precipitation. Similar mechanisms also operate in the SACZ. However, the vorticity anomalies in the wave trains are stronger, and the precipitation and negative feedback from the divergence and anticyclonic vorticity tendency are weaker, resulting in continued propagation of the wave and a more diffuse diagonal convergence zone

Diurnal Characteristics of Rainfall over the Contiguous United States and Northern Mexico in the Dynamically Downscaled Reanalysis Dataset (US10)

The diurnal characteristics of summer rainfall in the contiguous United States and northern Mexico were examined with the United States reanalysis for 5 years in 10-km horizontal resolution (US10), which is dynamically downscaled from the National Centers for Environmental Prediction National Center for Atmospheric Research (NCEP-NCAR) Global Reanalysis 1 using the Regional Spectral Model (RSM). The hourly precipitation outputs demonstrate a realistic structure in the temporal evolution of the observed rainfall episodes and their magnitudes across the United States without any prescriptions of the observed rainfall to the global reanalysis and the downscaled regional reanalysis. Nighttime rainfall over the Great Plains associated with eastward-propagating, mesoscale convective systems originating from the Rocky Mountains is also represented realistically in US 10, while the original reanalysis and most general circulation models (GCMs) have difficulties in capturing the series of nocturnal precipitation events in summer over the Plains. The results suggest an important role of the horizontal resolution of the model in resolving small-scale, propagating convective systems to improve the diurnal cycle of summer rainfall.open3

A systems approach to risk and resilience analysis in the woody-biomass sector: A case study of the failure of the South African wood pellet industry

© 2017 Elsevier Ltd Currently more than 600 million of the 800 million people in SSA are without electricity, and it is estimated that an additional 2500 GW of power is required by 2030. Although the woody-biomass market in the developed world is relatively mature, only four woody-biomass plants in SSA have been established, all of which were closed by 2013. With its affordable labour, favourable climate and well-established forestry and agricultural sectors, South Africa appears to have the potential for a successful woody-biomass industry. This paper documents a first attempt at analysing why these plants failed. It aims to contextualise the potential role of a sustainable woody-biomass sector in South Africa, through firstly developing a SES-based analytical framework and secondly, using this to undertake a retrospective resilience-based risk assessment of the four former woody-biomass pellet plants in order to identify strategies for increasing the resilience of the industry. The SES-based framework advances previous theory, which usually focuses on natural resources and their supply, by introducing a production process (with inputs and outputs), internal business dynamics and ecological variable interactions. The risk assessment can be used at a broad level to highlight important aspects which should be considered during feasibility assessments for new plants. Further work is proposed to focus on splitting the social-ecological system at different scales for further analysis, and to investigate the long-term ecological impacts of woody-biomass utilisation