Creep Modeling of Wood Using Time-Temperature Superposition

The time-temperature superposition principle was used to develop long-term compression creep and recovery models for southern pine exposed to constant environmental conditions using shortterm data. Creep (17-hour) and recovery (40-hour) data were obtained at constant temperature levels ranging from 70 F to 150 F and constant equilibrium moisture content (EMC) of 9%. The data were plotted against log-time, and the resultant curve segments were shifted along the log-time axis with respect to the curve for ambient conditions to construct a master curve applicable to ambient conditions (70 F, 9% EMC) and a longer time period. The master curves were represented by power functions, and they predicted up to 6.4 years of creep and 5.8 years of recovery response. The validity of the master curves for predicting creep of wood exposed to the normal interior environment in buildings was tested by conducting ten-month creep tests in the laboratory. The fluctuating environment caused geometry changes in the surface of the specimens affecting the collected long-term data. Therefore, a good comparison between the master curves and the long-term data was not possible

Image Correlation Analysis of Multiple-Bolt Wood Connections

Displacement beneath the bolts in multiple-bolted wood connections was studied using digital image correlation. This method combines digital image analysis and image correlation to calculate surface displacements from a set of digitized video images of an object under an applied load. Double-shear connections constructed of clear, straight-grained yellow-popular were tested in compression parallel to grain. Five different bolt patterns were used to analyze the effect of number of bolts in a vertical row and number of bolts in a horizontal column on displacement distribution among bolts. It was discovered that for multi-bolt patterns in a vertical row, parallel to load displacements below the outer bolts, are higher than those below the center bolt(s) but not equal in magnitude as previously assumed and the surface displacements perpendicular to the load beneath the bolts split along the centerline of the bolts. Variation in material properties, rigid body motion, eccentric loading and/or wood failure beneath a bolt are detectable with digital image correlation and may influence the results if not carefully considered in experimental design

Analysis of Racked Wood Pallets

A rational analysis procedure for designing wood stringer pallets for use in warehouse storage racks was developed for manufacturers and pallet users and is part of a computerized automatic design and analysis program called the Pallet Design System (PDS). The procedure uses simplified analog models of pallets and matrix structural analysis methods to compute the stress and deflection of critical structural elements. Semi-rigid nail joints are modeled as spring elements. Pallets with 2, 3, 4, or 5 stringers and up to 15 deckboards can be analyzed with a variety of load types including distributed and concentrated loads. The strength and stiffness of experimental pallets were compared to predicted values and showed good agreement

A Review Of Creep In Wood: Concepts Relevant To Develop Long-Term Behavior Predictions For Wood Structures

A review is presented of the effects of constant and transient moisture and temperature conditions on the time-dependent behavior of wood as a material and as a structural element. A rational approach towards the identification of long-term behavior of wooden structures is proposed. Utilizing the fact that wood is a combination of several polymers, polymer viscoelasticity concepts are suggested to enhance the predictive capabilities. A finite element procedure is outlined to indicate how design predictions can be made. Some attention is given to structures such as domes where creep of the wood could lead to structural instabilities

Modeling The Nonlinear Moment-Rotation Relationship Of A Nail Plate Connector1

This paper presents a mechanics-based procedure for modeling the nonlinear moment resistance of multiple-dowel wood connections. The lack of a consistent methodology for predicting rotational resistance of multiple-dowel joints was identified as one of the barriers to adoption of a ready-to-assemble (RTA) wood framing system. Integral to the RTA system is a nail plate connector (NPC) that consists of a metal plate with multiple dowel and is used to assemble RTA framing members into complete structural systems. The principle of energy conservation is used to derive the model. The proposed procedure is formulated such that the nonlinear response of the nails and plate bearing are explicitly included in the model to accurately predict the moment-rotation relationship over a wide range of deformations. Therefore, the model provides the information on both the ultimate strength and deformation capacity needed to establish safety margins and to perform serviceability checks, respectively. The method requires input of the lateral load-displacement relationships for an individual nail and plate bearing on the end grain of wood framing member. These relationships can be readily measured using lateral test procedures or determined analytically. The formulation showed excellent correlation with test results (R2 = 0.98). The proposed model presents an engineering and research tool and has the potential to promote the use of timber frames assembled with multiple dowel joints

Addendum: Willard, D.T. and Loferski, J.R. Skateboards as a Sustainable Recyclable Material. <em>Recycling</em> 2018, <em>3</em>, 20

The authors would like to add the following statement to the published article [...

Skateboards as a Sustainable Recyclable Material

The exact number of skateboards manufactured every year is unknown, but it is estimated to be in the millions. Most skateboard decks are made from a high grade of maple (Acer spp.) veneer plywood and typically last only a few months before they break or deteriorate beyond use. Millions of used skateboard decks are discarded annually, ending up in landfills when, instead, they could be recycled into new products. But beyond artistic or aesthetic purposes, material properties of the used skateboard decks are unknown. The objective of this paper is to investigate the material properties of wooden composite panels created by reengineering the skateboard deck material. These aesthetically pleasing wooden panels may be a sustainable recycled product. This paper presents a method of analyzing material properties and structural aspects of used skateboard deck material. Tests were developed to measure the stiffness and strength in bending, moisture content, specific gravity, moisture durability, and species identification. The results show that this process of reengineering skateboard decks makes for a strong wood product and may be useful to those interested in developing new products from recycled materials