Many of the 1,400 timber bridges in Minnesota do not meet present day standards. Some of these bridges can be improved rather than replaced. When the desired service level can be attained by widening a bridge six feet or less, the bridge can be retrofitted by placing a second, wider, transverse deck onto the existing deck and substructure. Bridge components must be carefully inspected prior to a retrofit project. The retrofit of Bridge #6641 in Sibley County is a good example. First, the bituminous surface was removed. A longitudinal beam supported the extended deck. Grout was poured and leveled and then nail-laminated panels were laid transversely. A bituminous surface was laid over the full width of the new deck. The cost of the project was $51,632. (Replacing the bridge was estimated to take 2-3 years and cost $215,000.) The county quantified the strength change and load distribution characteristics by performing static and dynamic load tests before and after the retrofit. Adding a second deck effectively decreased the static deflections and improved the transverse load distribution. Nail-laminated timber bridge #2642, also in Sibley County, was retrofitted in 1992 and load-tested again in 1995. All dynamic deflections were lower than those of the post-retrofit tests in 1992. This improvement can be explained in part by the drying of the moisture that was introduced into the bridge deck during grouting. A retrofitted timber bridge is expected to last an additional 20-40 years.
The benefits of using shear connectors to join wood beams to a concrete slab in a composite floor or deck system are many. Studies throughout the world have demonstrated significantly improved strength, stiffness, and ductility properties from such connection systems as well as citing practical building advantages such as durability, sound insulation, and fire resistance. In this study, one relatively new shear connector system that originated in Germany has been experimentally investigated for use with U.S. manufactured products. The connector system consists of a continuous steel mesh of which one half is glued into a southern pine Parallam® Parallel Strand Lumber beam and the other half embedded into a concrete slab to provide minimal interlayer slip. A variety of commercial epoxies were tested for shear strength and stiffness in standard shear or “push out” tests. The various epoxies resulted in a variety of shear constitutive behaviors; however, for two glue types,shear failure occurred in the steel connector resulting in relatively high initial stiffness and ductility as well as good repeatability. Slip moduli and ultimate strength values are presented and discussed. Full-scale bending tests, using the best performing adhesive as determined from the shear tests, were also conducted. Results indicate consistent, near-full composite action system behavior.
Timber rivet connections, originally developed for use with glulam construction, may be a viable option for use with structural composite lumber (SCL) products. Tests were conducted on small samples to assess the performance and predictability of timber rivet connections in parallel strand lumber (PSL) and laminated strand lumber (LSL). The test joint configurations were designed to exhibit ìrivet failuresîósome combination of rivet yield and bearing deformation in the compositeóas opposed to wood failure modes, such as block-shear tear-out or splitting.
Results suggest that per-rivet design values should fall between 1 and 2 kN, depending on species and density of the composite and load direction with respect to grain of the composite strands. Timber rivets performed better in LSL than in PSL and better in yellow poplar PSL than in Douglas-fir or Southern Pine PSL; 40-mm rivets in yellow poplar LSL gave roughly equivalent performance to 65-mm rivets in yellow poplar PSL.
Solid-sawn lumber (Douglas-fir, southern pine, Spruce– Pine–Fir, and yellow-poplar), laminated veneer lumber (Douglas-fir, southern pine, and yellow-poplar), and laminated strand lumber (aspen and yellow-poplar) were heated continuously at 82°C (180°F) and 80% relative humidity (RH) for periods of up to 24 months. The lumber was then reconditioned to room temperature at 20% RH and tested in edgewise bending. Little reduction occurred in modulus of elasticity (MOE) of solid-sawn lumber, but MOE of composite lumber products was somewhat reduced. Modulus of rupture (MOR) of solid-sawn lumber was reduced by up to 50% after 24 months exposure. Reductions in MOR of up to 61% were found for laminated veneer lumber and laminated strand lumber after 12 months exposure. A limited scope study indicated that the results for laminated veneer lumber in edgewise bending are also applicable to flatwise bending. Comparison with previous results at 82°C (180°F)/25% RH and at 66°C (150°F)/20% RH indicate that differences in the permanent effect of temperature on MOR between species of solid-sawn lumber and between solid-sawn lumber and composite lumber products are greater at high humidity levels than at low humidity levels. This report also describes the experimental design of a program to evaluate the permanent effect of temperature on flexural properties of structural lumber, with reference to previous publications on the immediate effect of temperature and the effect of moisture content on lumber properties.
As part of the CORRIM Phase I research, this study completed a full gate-to-gate life-cycle inventory for the production of glued-laminated timbers (glulam) produced in two regions of the United States—the Pacific Northwest (PNW) and Southeast (SE). Data collected from surveys of manufacturers are presented for energy requirements, raw materials use, and emissions to land, water, and air allocated for one cubic meter and 1000 cubic feet of glulam. The glulam manufacturers surveyed represented 70 and 43% of the region's total glulam production for the PNW and SE, respectively. From both regions, 82% of the raw material and energy inputs and emission outputs were allocated to the glulam product, leaving the remaining 18% allocated to co-products. Contributions to the glulam process included impacts for the inputs of lumber and adhesives. Results show that wood drying and adhesive manufacturing make major environmental contributions to the glulam process. In addition, fuel sources, either biomass or fossilbased, have significantly different emission impacts to the environment. Wood fuel representing wood waste and hogged fuel accounted for nearly 50% of the cumulative energy consumed, while for wood fuel used for heat energy to dry lumber represented 65% and 100% for the PNW and SE glulam models. The cumulative energy from all fuel types including wood fuel allocated for one cubic meter of glulam was 6,748 MJ/m3 when manufactured in the PNW and 7,213 MJ/m3 when manufactured in the SE.
A life-cycle inventory (LCI) study is conducted of laminated veneer lumber (LVL) manufacturing. This gate-to-gate study includes all environmental impacts from the logs to produce either veneer or parallel laminated veneer (PLV) as input to the LVL process, through production of the LVL. The study includes all materials, fuels, and electricity inputs to produce LVL and related co-products and emissions. The input and site emissions data were collected through surveys of manufacturing facilities in the Pacific Northwest and the Southeast regions of the U.S. SimaPro software, a program to conduct life-cycle inventory studies, is used to process the data and measure environmental impacts in terms of material use and emissions. The data are allocated on a mass basis to LVL based on their contribution to the mass sum of all product and co-products produced in manufacturing. All data are provided on a production unit basis of 1000 m3 and 1000 ft3 (MCF). In addition to the LCI data, carbon flow data are also given. These data are publicly available through reports, this publication, and the U.S. LCI Database Project. The data are useful forgenerating cradle-to-gate product LCIs when combined with the LCIs to produce logs as input to the plants and the transportation impacts to deliver materials. The data are useful as a benchmark for assessing process performance, for conducting life-cycle assessments of structural assemblies and the shell of residential and light commercial buildings.
Use of structural composite lumber products is increasing. In applications requiring a fire resistance rating, calculation procedures are used to obtain the fire resistance rating of exposed structural wood products. A critical factor in the calculation procedures is char rate for ASTM E 119 fire exposure. In this study, we tested 14 structural composite lumber products to determine char rate when subjected to the fire exposure of the standard fire resistance test. Char rate tests on 10 of the composite lumber products were also conducted in an intermediate-scale horizontal furnace. The National Design Specification/Technical Report 10 design procedure for calculating fire resistance ratings of exposed wood members can be used to predict failure times for members loaded in tension. Thirteen tests were conducted in which composite lumber products were loaded in tension as they were subjected to the standard fire exposure of ASTM E 119. Charring rates, observed failure times in tension tests, and deviations from predicted failure times of the structural composite lumber products were within expected range of results for sawn lumber and glued laminated timbers.
Effects of Component Ratio of the Face and Core Laminae on Static Bending Strenght Performance of Three-Ply Cross-Laminated Wood Panels with Sugi (Cryptomeria Japonica)
In order to improve the bending strength performance of three-ply laminated wood panels and use them as construction-grade panel materials, twelve types of three-ply cross-laminated wood panels whose percentages of core lamina thickness versus total lamina thickness were 33%, 50%, and 80% were made with sugi (Japanese cedar), and the effect of component ratio of the face and core laminae on their static bending strength performance was investigated.
The moduli of elasticity (MOE), proportional limit stresses and moduli of rupture (MOR), perpendicular (C type) and parallel (C type) to the grain of face laminae markedly increased or decreased with increasing percentage of core lamina thickness. The percentages of core lamina thickness at which each strength property value of C type became equal to that of C type ranged from 65% to 80%. At each percentage of core lamina thickness, the MOE and proportional limit stress of C type were higher in C (45) specimens having perpendicular-direction lamina of 45° annual ring angle in the core than in C (90) specimens having perpendicular-direction lamina of 90° in the core, whereas there was little difference in MOR between C (45) specimens and C (90) specimens. For 45° specimens having the core lamina thickness from 60% to 70%, MOE as well as MOR parallel and perpendicular to the grain of face laminae exceeded the corresponding requirement values of structural plywood with 21.0-mm thickness specified in Japanese Agricultural Standards.
Timber construction has become completely modernized. It has gained considerably in market share with respect to competing building materials and is dominated by systems such as frame and solid timber construction.
Every timber construction is determined by its structure. Hence it is essential to know the connections and relationships from the design stage right through to the construction phase. Systems in Timber Engineering takes a whole new approach to this subject. It is a comprehensive, analytical, and visually organized treatment, from the simple single-family house to the large-scale multistore structure. It includes the building envelope, which is so important for saving energy, and systems for ceilings and interior dividing walls, which are so essential from the vantage point of construction.
This work uses plans, schematic drawings, and pictures to show the current and forward-looking state of the technology as applied in Switzerland, a leading country in the field of timber construction.
Cross-laminated timber (CLT) is a panel-shaped engineered wood product, assembled of layers of lamellas (mostly softwood) with perpendicular orientation of the grain direction. In contrast to other panel-shaped engineered wood products, CLT is not used as components of structural elements, but rather as load bearing plates and shear panels. The design of CLT used as load-bearing plates is often governed by serviceability criterions like maximal deflection and vibration susceptibility. Hence, predicting the respective behaviour of such panels requires accurate information about their elastic properties. With the aim of determining the global elastic properties of full-scale CLT panels directly in the production line, a fully automatic, non-destructive procedure based on experimental and theoretical modal analysis was developed: Resonance frequencies and mode-shapes of the plates are determined first by means of an experimental modal analysis. A simulation model based on Reddy's higher order plate theory is then used to analytically calculate natural frequencies and mode shapes as functions of the unknown elastic parameters. Finally, in an optimization process two in plane moduli of elasticity and three shear moduli can be identified by minimizing the differences between measured and analytically estimated resonance frequencies. First, the method was investigated in the laboratory. The applicability of the method was then proven on 42 CLT panels with different dimensions, layer sizes and from different producers, and validated by static bending experiments on full-scale panels and panel-bars. Finally the procedure was optimized for the application in the production line.
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