Browsing by Author "Loferski, Joseph R."

Now showing 1 - 20 of 81
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    Analysis and Testing of a Ready-to-Assemble Wood Framing System
    Kochkin, Vladimir G. (Virginia Tech, 2000-09-08)
    The concept of a ready-to-assemble kit fabricated in a factory and delivered to the customer is well known and commonly used by the furniture industry. In wood construction, the lack of a simple and reliable method of assembling the frame members creates a barrier to wide acceptance of prefabricated kit structures. This thesis focuses on a novel technology of assembling structural components of a wood frame using a metal nail plate connector (NPC). This technology was referred to as a ready-to-assemble (RTA) wood framing system. The RTA system simplifies the framing process and allows for rapid erection of a wood structural frame by a small nonprofessional crew. A 16 x 24 foot RTA building was constructed to demonstrate the feasibility of the RTA system concept. An effective assembly sequence was proposed and successfully implemented. The design procedure for the RTA buildings was presented. The lateral load path for the RTA building includes diaphragms and shear walls. The contribution of the RTA frame can be ignored from the lateral load analysis. This conclusion was validated for the diaphragms with aspect ratios up to 4:1. The finite element method was used to model the RTA structures. The models incorporated semi-rigid behavior of the NPC. An analytical model was developed to predict the nonlinear moment-rotation relationship of the NPC. The proposed model showed a good agreement (R2=0.98) with the experimental data. Tests were conducted to measure the load-drift response of the RTA shear walls.
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    Analysis of Anchors and Bracing Configurations for Personal Fall Arrest Systems in Residential Construction
    Morris, Justin Collins (Virginia Tech, 2013-06-20)
    Falls continue to be a major problem in the residential construction industry and account for a large number of injuries and fatalities each year (US Department of Labor, 2012).  The effects of a fall are catastrophic to the workers and their families as well as the construction company and surrounding community.  Prevention of these incidents has been the primary focus of organizations such as the Occupational Safety and Health Administration (OSHA).  To reduce the number of falls on residential construction sites, OSHA has put forth several standards that require the use of fall protection.  Although guidelines have been provided, there have been concerns and complaints regarding the standards as well as methods and materials that should be used. The goal of this research was to measure the behavior of a five truss roof system with various anchor points and bracing configurations loaded by a horizontal force.  A lab built roof system was used to test three different anchor types with three forms of temporary bracing.  The materials and methodology used in this testing were based on common materials and practices currently used in the residential construction industry. The results of this research show that anchors must engage multiple trusses to spread the applied load throughout the roof system.  Several forms of temporary bracing such as lateral, diagonal, and sway bracing, are also required to strengthen the roof system allowing it to withstand an applied load.  
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    Assessing the Cost and Operational Feasibility of "Green" Hardwood Winter Inventory for Southeastern Pulp Mills
    Gallagher, Thomas V. (Virginia Tech, 2003-05-23)
    Procuring hardwood pulpwood during the winter months for a pulp mill in the Southeast can be difficult. Saturated soils and low soil strength make logging difficult or impossible on many sites, forcing companies to store large volumes of hardwood pulpwood in woodyards for retrieval during wet weather. Hardwood fiber readily available in large volumes on ground that is operable during wet periods at a location near the pulp mill could provide a valuable alternative wood source. Thus, the objectives of this study are to 1) develop a decision model for a manager to use to determine the feasibility of strategically located, intensively-managed, short-rotation hardwood fiber farms as pulp mill furnish, 2) use the model to estimate wood costs for a hypothetical eastern cottonwood plantation, and 3) use the model to determine if a fiber farm grown on drier, upland sites ("green" inventory) could be used to reduce woodyard winter inventories and economically supply a nearby pulp mill during a wood shortage, thus reducing high cost, emergency "spot market" wood purchases. The decision model is incorporated in a spreadsheet and includes all the costs typical for a fiber farm. The model is tested using current establishment and management costs from the literature and yields from an experimental fiber farm in the southeast. Under current yields, delivered costs from the fiber farm averages $71/ton. With potential increased yields that could occur with genetic improvements and operational optimizations, delivered cost for fiber farm wood could be reduced to $56/ton. In comparison, the highest cost wood purchased by the three cooperating pulp mills during the study period was $50.23/ton. The net present values of a fiber farm as "green" inventory were determined using actual wood cost and inventory levels from three cooperating southeastern pulp mills. For the "green" inventory analysis, all three pulp mills would have lowered their overall wood cost using a fiber farm (with higher yield) as "green" inventory, primarily by reducing the amount of wood required as dry inventory on woodyards. Savings accrued during "dry" years offset the higher cost of hardwood plantation deliveries. A sensitivity analysis was performed to determine the optimal size fiber farm for one of the cooperating pulp mills and indicated that 800 acres would be the most beneficial.
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    Assessment of U.S. manufactured system built wooden homes as an affordable housing alternative for low income households in developing countries
    Kakkar, Gaurav (Virginia Tech, 2017-10-16)
    Millions of people around the developing world struggle to obtain safe, decent and affordable housing. The United States of America has substantially improved the residential construction sector by engineering new materials and developing efficient systems in wood construction. The goal of this research was to assess the potential of introducing system built wood construction system manufactured in the United States in urban social housing markets of developing countries. Peru, Ecuador and Colombia were three countries chosen for this study. Stakeholders in social housing in these three countries were interviewed to assess key aspects of traditional construction, current social housing deficits, perception of wood use in construction, and policies associated with social housing in selected markets. Findings indicate developing custom housing products for urban social housing programs can provide access to this untapped markets. Awareness about wood construction was very limited in the studied region. System built wood construction manufacturers in the U.S. were assessed to identify barriers and incentives for internationalization. Manufacturers in the U.S. also identify the need to expand their existing customer base. Findings of the survey conducted among the manufacturers identified various barriers to export. This research contributes to opening of new markets for exports of prefabricated wooden buildings in new geographical regions.
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    Behavior and modeling of partially restrained beam-girder connections
    Rex, Clinton O. (Virginia Tech, 1996)
    Beams in a typical steel framed floor design are assumed to have pinned supports for purposes of design. In reality, the connections between the beams and girders in a steel framed floor system are not pinned. The design bending moments and deflections of the attached beam could be reduced if the true rotational restraint provided by the beam-girder connections could be included in the design. The connection rotational restraint is characterized by the moment-rotation behavior. Consequently, a method for approximating the moment-rotation behavior of the beam-girder connection is required before the beneficial effects of the true connection rotational restraint can be considered in design. Experimental and analytical research on the moment-rotation behavior of a specific type of beam-girder connection is presented in this dissertation. The primary objective of this research is to develop a component model of the connection that can be used to approximate the moment-rotation behavior. The component model is based on the hypothesis that the connection behavior can be modeled as a combination of the connection component behaviors. The connection components are the fundamental pieces of the connection such as bolts, shear studs, and welds. In general, the component model can be very computationally intensive. Consequently, a secondary objective of this research is to develop a connection model that is simpler to use. Behavior models for each of the connection components are presented and/or developed. These models are derived from a combination of existing literature, experimental and analytical research, and basic mechanics. Next, a method of combining the component behaviors into a connection model that can be used to approximate the moment-rotation behavior is developed. Results from experimental research on the moment-rotation behavior of the beam-girder connection are then used to verify the model. Finally, a simplified model of the beam-girder connection is developed. This model is based on the same hypothesis as the component model; however, through a combination of assumptions, simplifications, and the results of parametric studies the simplified model becomes far less computationally intensive than the full component model.
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    Business-level competitive strategy in the United States hardwood lumber industry
    Bush, Robert (Virginia Polytechnic Institute and State University, 1989)
    Three related aspects of competition in the U.S. hardwood lumber industry were investigated. First, product and supplier attributes that are determinant in hardwood lumber purchase decisions were investigated within four segments of the market for hardwood lumber: Millwork producers, hardwood dimension and flooring producers, wood household furniture producers, and wood kitchen cabinet producers. Attributes with the highest determinant scores were: grading accuracy, supplier’s reputation, freedom from surface checks, competitive pricing, and within-load thickness consistency. The least determinant attribute was the presence of the suppliers logo or trademark. The importance of various attributes was generally consistent across the market segments and producers were relatively well attuned to the needs of lumber users. Lumber users were least satisfied with lumber quality. Lumber producers perceived users to be least satisfied with the availability of certain species. Business-level intended competitive strategy in the industry was investigated through quantitative identification of strategic groups in a sample consisting of the 100 largest U.S. hardwood lumber producers. Factor and cluster analyses were used to define strategic groups along the dimensions of cost leadership, focus, and differentiation. Five strategic groups were identified and examined as to strategic orientation and intra-group homogeneity. The differentiation dimension accounted for the greatest portion of strategic variation. Empirical evidence of the use of hybrid Overall Cost Leadership/Differentiation strategies was found—suggesting that strategic typologies that do not account for this strategy may not be applicable to a mature industry. Predicted strategic change in the industry concentrated on increasing differentiation orientation. Qualitative data concerning competition in the industry was obtained via in-person interviews with executives at twenty of the largest companies in the sample. ln general, the largest and smallest companies in the industry were found to be the most production oriented. Companies self-typed their competitive strategies using Porter‘s (1980) strategic typology. Overall Cost Leadership strategies were the most common followed by Differentiation and Focus strategies. The majority of companies interviewed competed for customers based on quality, customer service, and price—in that order of importance. Proprietary grading was an important competitive tool for larger companies.
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    Capacity Resistance and Performance of Single-Shear Bolted and Nailed Connections: An Experimental Investigation
    Smart, Jason Vincent (Virginia Tech, 2002-07-01)
    The experimental study reported upon in this thesis focused on the development of physical data characterizing the behavior of single-shear, laterally-loaded connections when loaded up to and beyond capacity (i.e., maximum resistance). Specimens included a wide array of connection configurations common in wood construction. All connections were tested monotonically in tension under displacement-controlled loading, parallel to the grain. Results of these tests are presented and discussed. Test variables of nailed connections included nail diameter, side member material type, and side member thickness. Test variables of bolted connections included bolt diameter, commercial species grouping of the main and side members, and main member thickness. Conclusions drawn from this research include mechanics-based explanations of numerous connection response trends observed with respect to test variables. Additionally, observed factors of safety and over-strengths of current design values are quantified on a capacity-basis.
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    Changes in Oriented Strandboard Permeability During Hot-Pressing
    Hood, Jonathan Patrick (Virginia Tech, 2004-06-04)
    Convective heat transfer during hot pressing in wood-based composite panel manufacturing is widely accepted as the most important means of heat transport for resin curing. The rate of convective heat transfer to the panel core is controlled by its permeability. Permeability in the plane of the panel also controls the flow of vapor to the panel edges, thereby influencing the potential for panel "blowing". This research considers how flake thickness, flake alignment and changing mat density during hot-pressing influences OSB mat permeability, through its thickness and in the plane of the panel. Some previous research exists but it fails to address the affects of horizontal and vertical density gradients as well as flake alignment. An apparatus was designed to allow cold pressing of aligned flakes to desired densities while enabling permeability measurements through the mat thickness. An additional apparatus was designed to allow the measuring of permeability in the plane of the mat. These designs permitted permeability measurements in mats that had no vertical density gradient, allowing for the direct study of permeability versus density (compaction ratio). Superficial permeability was determined using Darcy's law and for each sample, multiple readings were made at five different pressure differentials. Permeability through the mat thickness was highly dependent on compaction ratio and to a lesser extent flake thickness. As the compaction ratio is increased, the initial reduction in permeability is severe, once higher compaction ratios are achieved the reduction in permeability is less pronounced. Permeability decreased with decreasing flake thickness. Permeability in the plane of the mat decreases with increasing compaction ratio but in a less severe manner than through the mat thickness. In this case, the permeability-compaction ratio relationship appears linear in nature. Again, permeability decreases with decreasing flake thickness.
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    Characterizing the Durability of PF and pMDI Adhesive Wood Composites Through Fracture Testing
    Scoville, Christopher R. (Virginia Tech, 2001-06-13)
    The increased use of wood composites in building materials results in a need for a better understanding of wood adhesion. The effects of water and temperature exposure on the durability of wood products were assessed using the double-cantilever beam (DCB) method of fracture testing. The relative durability of phenol-formaldehyde (PF) and isocyanate (pMDI) adhesives was compared using a 2-hour boil test and an environmental test. The feasibility of using oriented strandboard (OSB), oriented strand lumber (OSL) and parallel strand lumber (PSL) for the DCB fracture method was assessed. The fracture resistance of PF was reduced significantly by the aging exposures. The fracture resistance of pMDI did not decrease after the 2-hour boil test. The DCB fracture method was shown to be useful with a square-grooved machined specimen using OSB and OSL.
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    Combined linear/nonlinear stability analysis of plane and space frames
    Zhou, Qing (Virginia Tech, 1993)
    The objective of this study is to apply the combined linear buckling and nonlinear analysis to the stability investigations of the plane and space frame structures. A comparative study of the combined analysis and the nonlinear analysis is conducted with ABAQUS to demonstrate the applicability and effectiveness of the combined analysis for the critical load predictions. Several test problems and a glulam dome cap are analyzed, and the critical load prediction curves and the nonlinear equilibrium paths are presented. It is verified that the B33 finite element in ABAQUS is capable of modeling the curved beam. The modeling procedure of the dome cap model is discussed. Finally, conclusions and recommendations are made for future studies.
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    Combined Tension and Bending Loading in Bottom Chord Splice Joints of Metal-Plate-Connected Wood Trusses
    O'Regan, Philip J. (Virginia Tech, 1997-05-01)
    Metal-plate-connected (MPC) splice joints were tested in combined tension and bending to generate data that were used in the development of a design procedure for determining the steel net-section strength of bottom chord splice joints of MPC wood trusses. Several common wood truss splice joint configurations were tested at varying levels of combined tension and bending loading. The joint configurations were 2x4 lumber with 20-gauge truss plates, 2x6 lumber with 20-gauge truss plates, and 2x6 lumber with 16-gauge truss plates. All the joints tested failed in the steel net-section of the truss plates. The combined loading was achieved by applying an eccentric axial tension load to the ends of each splice joint specimen. Three structural models were developed to predict the ultimate strength of the steel net-section of the splice joints tested under combined tension and bending loading. The test data were fitted to each model, and the most accurate model was selected. Data from other published tests of splice joints were used to validate the accuracy of the selected model. A design procedure for determining the allowable design strength of the steel net-section of a splice joint subjected to combined tension and bending was developed based on the selected model. The new design procedure was compared with two existing design methods. The proposed design procedure is recommended for checking the safe capacity of the steel net-section of bottom chord splice joints of MPC wood trusses subjected to combined tension and bending.
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    Comparison of Shear Modulus Test Methods
    Harrison, S. Kate (Virginia Tech, 2006-03-31)
    This research compared the results of three tests: ASTM D 198 torsion, ASTM D 198 three-point bending and the five-point bending test (FPBT) using machine-stress-rated (MSR) lumber and laminated veneer lumber (LVL) to determine if the shear properties evaluated by the different test methods were equivalent. Measured E:G ratios were also compared to the E:G ratio of 16:1 commonly assumed for structural wooden members. The average shear moduli results showed significant differences between the three test methods. For both material types, the shear moduli results determined from the two standard test methods (ASTM D 198 three-point bending and torsion), both of which are presently assumed to be equivalent, were significantly different. Most average E:G ratios from the two material types and three test methods showed differences from the E:G ratio of 16:1 commonly assumed for structural wooden members. The average moduli of elasticity results for both material types were not significantly different. Therefore, the lack of significant difference between moduli of elasticity terms indicates that differences between E:G ratios are due to the shear modulus terms. This research has shown differences in shear moduli results of the three test types (ASTM D 198 torsion, ASTM D 198 three-point bending, and the FPBT). Differences in the average E:G ratios per material and test type were also observed.
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    Developing an Evaluation Program for Lumber Drying Operations in Bolivia
    Espinoza, Omar A. (Virginia Tech, 2006-05-01)
    The Bolivian forest products industry has experienced substantial growth during the last ten years. Exports of value-added products have largely replaced logs and green lumber, and raw materials for wood products have shifted to lesser used species. Important investment has taken place in lumber drying capacity, which unfortunately was not always accompanied by sound drying practices. Several non-governmental organizations, with U.S. financial aid, are currently supporting the industry with technical assistance. This project assists these efforts by assembling much needed information regarding lumber drying, and providing tools for performance measurement of drying practices. A survey was conducted among Bolivian companies to determine lumber drying capacity, technology and practices. Results showed a total drying capacity of 6,104,250 board feet in 167 kilns. Technology and practices used are highly variable. Thirty six percent of kilns are home-made, and 59% are European commercial brands. Upon completion of the survey, a set of analytical tools was developed and tested in six Bolivian firms. These tools were designed to systematically evaluate lumber drying operations and formulate actions for improvement. Equilibrium moisture content (EMC) during storage, manufacturing and shipping was monitored in plants located in three Bolivian cities and inside containerized shipments of wood products. Findings showed differences between EMC and lumber moisture content from -1% to 7%. Differences between EMC inside dry-lumber storage and processing facilities varied between 0% and 3.6% and were greatly influenced by facility configuration. Climate during shipment of wood products largely depended on packaging materials and methods, which attenuate sharp changes in ambient conditions. Monthly values for outdoor EMC for the main cities of Bolivia were calculated based on historic weather data and are reported.
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    The development of a durability procedure for pallets with structural panel decking
    Cao, Jiqiang (Virginia Tech, 1993-05-07)
    The Pallet Design System (PDS) is a widely accepted engineering procedure for comparing the performance of competing pallet designs. As part of a new version of the PDS, the objective of this study was to develop a durability model for pallets with structural panel decking. An accelerated rough material handling test system, "the VPI unit-load material handling FasTrack" , was developed to simulate pallets used in the unit-load material handling environments. 100 pallets representing 14 different designs were tested in the "FasTrack." Damages to these pallets were recorded after each test cycle. A procedure relating damage to repair cost was developed. The effect of panel-deck pallet design on the resistance to damage was evaluated in terms of the total number of damaged parts and average damage cost or repair cost. Test results indicate that panel grade and type, species of related wood parts, size of stringer and deckboards, joints, and pallet configurations affect the resistance of panel deck pallet to damage. The plots of average total damage cost, Cu adjusted for repair as a function of test cycle, U, fit the equation: Ct = aU - 1. The equation provided good fits to all the pallet designs tested. Using the initial purchase prices, the average cost and the economic life were calculated for all the pallet designs. The VPI "FasTrack" was calibrated based on the number of physical handlings and the amortized life. Three typical in-field handling environments were compared with the VPI "FasTrack". It concluded that the 30-cycle test period in the VPI "FasTrack" simulates between 2 to 5 years of field uses depending on the field handling system being simulated. Thirty Canadian Pallet Council (CPC) pallets with known 7 years of amortized life in the field were tested in the VPI "FasTrack". The 30-cycle test in the VPI system simulated 6 years of use in the similar handling environment of the CPC pallet used by the grocery industry in Canada. The average total damage costs for different pallet designs were related to pallet structural characteristics using multivariate regression analysis. The shear resistance through the thickness of the top panel deck, bottom deck flexural strength, pallet flexural strength, fastener withdrawal resistance, and pallet configuration were used to predict the total damage cost. A multiple regression model was developed. The model was verified by comparing the predicted values with the tested values of 12 panel deck pallets representing 2 designs. The results indicated that the model is reliable for the future predictions.
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    Development of A Ready-To-Assemble Construction System
    Platt, Robert Terry (Virginia Tech, 1998-07-05)
    To accommodate an expanding global population, a renewable raw material resource base, in conjunction with new building technologies, must be applied to the residential housing sector. Desirable characteristics of housing systems are economy, safety, environmental sustainability, durability, design flexibility and a long service life. The system should be acceptable to the end-user, consist of renewable, indigenous resources, and require a minimum investment in labor and equipment for both production and erection. The objective of this research was to develop a ready-to-assemble (RTA) framing system. Integral to the framing system is a nail plate connector, developed in this project, that laminates wood or wood composite elements into larger building components. The laminated components can be bolted together to form various structural configurations. Decisions on the development of the RTA system were structured according to an Innovation Development Decision Model (IDDP) that was constructed from previous adoption and diffusion research. The IDDP model elucidates and illustrates the innovation process from conceptual idea to product adoption. The critical issues for product acceptance include system performance in terms of safety, cost, and building code approval. The objective of the experimental portion of the research was to test the performance of the RTA connection system in specific modes and to develop a theoretical method to predict the strength of the connection. A series of experiments to quantify the shear strength and stiffness of six joint configurations assembled with the RTA connector were designed and conducted. The joints were fabricated from solid sawn lumber and three different wood-base composites. The experimental results indicated that the strength of the RTA connector in perpendicular-to-grain and parallel-to-grain orientations can be predicted from a theoretical dowel yield model. The material properties used in the yield model were adjusted for duration of load and safety. Empirical test values were within ±6.3 % of the predicted values from the theoretical model. Joint stiffness was evaluated, modeled and quantified in the linear and non-linear ranges. A structural analysis program was used to design and model a simple RTA building for realistic gravity and wind loads. The structural model was used to predict joint forces that the RTA connector must resist in-service. The computer model predictions were compared to the empirical joint test data. The results indicate that the RTA system can be designed to meet safety and serviceability criteria. A comparison between the estimated costs of a RTA building and the costs of traditional on site construction of a building of equal dimensions indicated that the RTA system is economically competitive.
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    Development of tension and compression creep models for wood using the time-temperature superposition principle
    Bond, Brian H. (Virginia Tech, 1993-06-03)
    To date there are no long-term creep models or practical methods to investigate the effect of creep on the safety and serviceability of modem wood structures and structural wood composites. Long-term creep models were developed for wood in tension and compression using the Time-Temperature Superposition Principle (TTSP). The principle states that the long-term response of a polymer at lower temperature is equivalent to the short-term response at a higher temperature. Accelerated creep tests were conducted in tension and compression using small clear specimens of Douglas-fir, southern pine and yellow-poplar. The specimens were tested at moisture contents of 6 %, 9 %, and 12 %, and at temperatures between 20°C and 80°C. The strain was measured using bonded strain gages. The individual creep compliance for each temperature was shifted along the log-time axis to obtain a "master" curve that describes the creep response of the specimens. All compliance curves also required vertical shifting. The experimental horizontal shift factors followed the Arrhenius formulation that describes the shift factor relation for polymers in the glassy region.
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    Effect of Cracking on Lag Bolt Performance
    Ramskill, Thomas Edward (Virginia Tech, 2002-08-06)
    This dissertation presents the results of testing to determine the load-slip characteristics of single-shear single lag screw connections subjected to monotonic lateral loading parallel to grain. Of particular importance was the comparison of experimental capacity and 5% offset yield load resistances to load resistances as predicted by the American Forest & Paper Association's (AF&PA) publication General Dowel Equations for Calculating Lateral Connection Values, Technical Report 12 (TR-12). Additionally some other tests were conducted, including fracture, tension strength perpendicular-to-grain, lag screw connection inking, dowel embedment, specific gravity and moisture content. The results for the testing program are presented. Four hundred and forty eight lateral tests were conducted on lag screw connections. Each connection was comprised of a 2 x 6 x 14 in. long wood main member, 1/4 in. thick steel side plate, and a single lag screw. The parameters of interest were specific gravity, lag screw diameter, and pilot hole diameter. Two species of wood, Douglas-fir and spruce-pine-fir, three lag screws diameters, and three pilot hole diameters for each species of wood were implemented. Models were developed to predict lag screw connection capacity and 5% offset yield and are contained herein. Models were based on results from connection and inking tests and mechanical analysis. Recommendation for ASD and LRFD design values were derived from connection test results for connections that used AF&PA's National Design Specification for Wood Construction (NDSb) specified pilot holes. Using fracture mechanics results, work was performed to determine the effective load required to crack and separate fracture surfaces of wood main members due to the installation of lag screws with varying pilot hole diameters.
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    Effect of Minimum Suppression and Maximum Release Years on Compression Parallel to Grain Strength and Specific Gravity for Small-sized Yellow-poplar (Liriodendron tulipifera L.) Specimens
    Mettanurak, Thammarat (Virginia Tech, 2008-04-04)
    Several researchers have concluded that there is little or no relationship between specific gravity and ring width or growth rate in yellow-poplar (Liriodendron tulipifera L.). Because most mechanical properties of wood are also closely related to specific gravity, it would thus be of interest to learn how minimum suppression and maximum release years' evidence that can be extracted from radial growth patterns based on a modified radial growth averaging (RGA) technique's influence the compression parallel to grain strength and specific gravity of wood. This study is designed to evaluate the effects of growth suppression and release on ultimate crushing stress and specific gravity for small-sized yellow-poplar specimens. Additionally, the relationship between specific gravity and ultimate crushing stress is investigated. Twenty-three yellow-poplar cores were examined for their growth ring widths. Minimum suppression and maximum release years were identified based on the modified RGA criteria method. From each increment core, three 1 Ã 1 Ã 4 mm specimens from both minimum suppression and maximum release years were tested for their ultimate crushing stresses using a micro-mechanical test system. The specific gravity of each specimen was also recorded. These data were analyzed using a paired samples t test and a simple linear regression. The results indicate that the mean ultimate crushing stress and specific gravity of maximum release years were significantly higher than that of minimum suppression years. Furthermore, the ultimate crushing stress was linearly related to the specific gravity of the specimens.
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    Effect of Overturning Restraint on the Performance of Fully Sheathed and Perforated Timber Framed Shear Walls
    Heine, Christian Peter (Virginia Tech, 1997-12-05)
    This study investigates the monotonic and cyclic response of light-frame wood shear walls with and without openings. Effects of overturning restraint in the form of tie-down anchors and corner segments on light-frame shear walls with and without door and window openings were quantified. While the results are useful to refine a design methodology for shear walls containing openings, they also provide important knowledge that is needed to accurately quantify anchorage requirements for shear wall design, and assess remaining load and ductility capacity of wood frame buildings after earthquakes or hurricanes. Sixteen full-scale wall specimens were tested using monotonic and sequential phased displacement (SPD) patterns. A total of five different wall configurations, five anchorage, and two loading conditions were used. All walls were eight feet (2.4m) high. Straight wall specimens were forty feet (12.2m) long, whereas corner walls measured twelve feet (3.7m) in length. The analysis includes data from a previous investigation in order to further expand the scope of this study. Results reveal that ultimate capacity and stiffness increase with increasing overturning restraint. A shift in failure mode was observed when overturning restraints were omitted. Accumulated damage experienced by the wall specimens tested cyclically was fairly uniform, regardless of the amount of overturning restraint or size of openings present.
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    The Effectiveness of Splicing Notched Pallet Stringer Segments With Metal Connector Plates
    Tong, Chao (Virginia Tech, 1997-08-01)
    Notched stringer segments spliced with metal connector plates (MCPs) and pallets with spliced stringer(s) were tested in static bending in order to determine the relative effectiveness of different stringer splicing methods and under what conditions the process is or is not effective. The species tested were oak, southern yellow pine, yellow-poplar, and two combined species - oak and yellow-poplar, and oak and southern yellow pine. The metal connector plates used were 3 x 4-inch, 3 x 6-inch truss plates, and a 3 x 4-inch plug plate. The splice methods tested were a vertical splice (VS), a 45° angle splice (AS), and a vertical splice with -inch gap between segments (VSG). The results of bending tests of these specimens were compared to non-spliced whole stringers and pallets containing whole stringers. Multiple comparison, statistical methods were used to analyze all test data. An analysis of the failure locations and types of specimens was also used to analyze test results. Vertical spliced stringers with 3 x 4 and 3 x 6 inch truss plates were the best designs of those tested. Spliced stringers were an average of 112% and 74% bending strength and stiffness of new non-spliced stringer. These plates were an average of 26% stronger and 13% stiffer than the 3 x 4 inch plug plate splice stringer. There was no difference between the performance stringers spliced with 3 x 6 and 3 x 4 inch truss plate. An angle splice design and the addition of 1.25 x 6 inch truss plate on the tension side of spliced stringer did not appear to improve the strength and stiffness. A gap between segments significantly reduces splice strength and stiffness by an average of 35% and 16% respectively. When mixing stringer segment species, the performance is determined by the weaker segment. The average strength and stiffness of pallets containing spliced stringers were similar to that of pallets with whole stringers, however the variation in performance was greater when notched stringer pallets contain splices.