Poplar Laminated Veneer Lumber Research Articles

Mode I delamination R-curve in poplar laminated veneer lumber

Recent studies have shown that plywood, laminated veneer lumber are very efficient crashworthiness materials. Therefore, there is a need to determine the fracture toughness of these wood composite materials to be able to model their static, dynamic damage behavior. This study reports the results of the delamination propagation of plywood under mode I loading. Two different double cantilever beam specimens made of poplar were compared: one with an interfacial fiber orientation of 0°/0°, the second with 0°/90°. Failure scenarios, patterns are analyzed to establish a comparison between the two configurations, compute consistent R-curves.

Experimental Study of Mode-I and Mode-II Interlaminar Fracture Characteristics of Poplar LVL

Fracture is a common failure form of poplar laminated veneer lumber (LVL). In the present work, we performed an experimental study on the mode-I along-grain interlaminar fracture, mode-I cross-grain interlaminar fracture, and mode-II interlaminar fracture of poplar LVL. We investigated stress mechanisms, failure modes, and fracture toughness values of the different fracture types. The experimental results revealed that the crack in the mode-I along-grain interlaminar fracture specimen propagated along the prefabricated crack direction, and the crack tip broke. The mode-I cross-grain interlaminar fracture specimen had cracks in the vertical direction near the prefabricated crack. In the mode-II interlaminar fracture specimen, cracks appeared along the initial prefabricated crack direction. The load–displacement curves of these three specimens were linear in the early stage of loading. With the increase in the load, a nonlinear segment appeared before crack propagation and a descending segment appeared after crack propagation. The nonlinear segments of the mode-I along-grain interlaminar fracture and mode-II interlaminar fracture were very short, and cracks expanded quickly after their initiation, resulting in brittle fracture. The nonlinear segment of the mode-I cross-grain interlaminar fracture was long, resulting in plastic failure. The average toughness values of the mode-I along-grain interlaminar fracture, mode-I cross-grain interlaminar fracture, and mode-II interlaminar fracture were 15.43, 270.15, and 39.72 MPa·mm1/2, respectively.

Acrylic Resin Filling Cell Lumen Enabled Laminated Poplar Veneer Lumber as Structural Building Material

Wood is a viable alternative to traditional steel, cement, and concrete as a structural material for building applications, utilizing renewable resources and addressing the challenges of high energy consumption and environmental pollution in the construction industry. However, the vast supply of fast-growing poplar wood has bottlenecks in terms of low strength and dimensional stability, making it difficult to use as a structural material. An environmentally friendly acrylic resin system was designed and cured in this study to fill the poplar cell cavities, resulting in a new type of poplar laminated veneer lumber with improved mechanical strength and dimensional stability. The optimized acrylic resin system had a solid content of 25% and a curing agent content of 10% of the resin solid content. The cured filled poplar veneer gained 81.36% of its weight and had a density of 0.69 g/cm3. The static flexural strength and modulus of elasticity of the further prepared laminated veneer lumber were 123.12 MPa and 12,944.76 MPa, respectively, exceeding the highest flexural strength required for wood structural timber for construction (modulus of elasticity 12,500 MPa and static flexural strength 35 MPa). Its tensile strength, impact toughness, hardness, attrition value, water absorption, water absorption thickness expansion, and water absorption width expansion were 58.81%, 19.50%, 419.18%, 76.83%, 44.38%, 13.90%, and 37.60% higher than untreated laminated veneer lumber, demonstrating improved mechanical strength and dimensional stability, significantly. This method provides a novel approach to encouraging the use of low-value-added poplar wood in high-value-added structural building material applications.

Experimental study on the vibration of poplar LVL orthogonal ribbed box floor

In this paper, a new type of Popular Laminated Veneer Lumber (LVL) orthogonal ribbed box floor is proposed. Six full-scale specimens of box-shaped floors were tested using the natural excitation method and the human induced excitation method in order to examine the dynamic characteristics and vibration response. The results indicate that the box-type floor specimens with the thickness of the cladding plate, the height of the rib beam, and the distance between the short rib beams of 18.3, 285, and 600 mm exhibit the largest fundamental natural vibration frequency and damping ratio, as well as the best dynamic characteristics. With increasing cladding panels and higher rib beams, peak acceleration decreases, whereas it increases with increasing thickness and shorter rib spacing. The peak acceleration of the floor gradually increases as stride frequency and walking number increase. With the same stride frequency, the peak acceleration of the floor when a single person jumps is greater than when stepping or walking continuously. Combined with related specifications, the root mean square acceleration, peak acceleration, and acceleration vibration level were used to evaluate the vibration comfort of the floors. The methods are presented to predict the fundamental natural frequency and the peak acceleration of the Popular LVL orthogonal ribbed box floor under single walking or jumping conditions, and the predicted results agree well with the experimental results. The research results provide designers with theoretical support for solving the vibration comfort problem on wooden floors.

Mechanical performance of poplar laminated veneer lumber truss joints

ABSTRACT Poplar laminated veneer lumber (LVL) offers many advantages such as high strength and small variability. This study explored the application of poplar LVL for making light timber trusses in China. A total of 12 poplar LVL truss joint specimens were designed and constructed, including truss support joints and ridge joints connected by bolts and tooth plates. The mechanical properties of the poplar LVL truss joints were experimentally tested and theoretically calculated. It was found that (1) the average bearing capacity of 10-mm bolted joints was 12.98%–22.62% higher than that of 8- or 12-mm bolted ones; (2) the average bearing capacity of ridge joints with 133 mm × 75 mm tooth plates was 23.03% and 28.22% higher than those with 152 mm × 75 mm and 152 mm × 50 mm tooth-plate connected ones; (3) the average bearing capacity of the bolted joints was higher than that of the tooth-plate connected ones when the shape of both joints were the same; (4) The damage of LVL dowel grooves and pull-out of tooth-plates from LVL were observed in the bolted and tooth-plate connected joints, respectively; and (5) The calculated values were, in comparation with the experimental results, were conservative for bolted joints and were in good agreement with the tooth-plate connected ones.

Experimental study of the behavior of box floor with orthogonal ribbed beams by poplar LVL

Considering the unidirectional layout of ribbed beams and simple structure in traditional wooden floors, it is not suitable for large-span wooden buildings. Six groups of floor ribbed beams with plane size of 4.8 m×3.6 m were designed and manufactured by using poplar laminated veneer lumber (LVL), among which five floor specimens were orthogonal ribbed beams and the other one was traditional. A bending performance test was carried out to analyze the influence of different ribbed beam spacing and high span ratio on the mechanical performance of poplar LVL orthogonal ribbed beams, and its results were compared with that of the traditional floor with ribbed beams. The results showed that the box floors with orthogonal ribbed beams had good integrity during the bending process. Moreover, the change of the high span ratio had an important influence on the bending performance of the box floors with orthogonal ribbed beams, and the change of the spacing of the ribbed beams had a relatively small influence on the flexural performance of the box floors with orthogonal ribbed beams. Under the same conditions, the bending performance of the box floors with orthogonal ribbed beams was better than that of traditional floor.

Creep behavior of orthogonal rib box floor of poplar laminated veneer lumber

Poplar laminated veneer lumber (LVL) orthogonal rib box floor is a new type of floor composed of orthogonal LVL rib beams and oriented strand board (OSB). To study the creep performance of the box floor, four 3600 mm × 4800 mm floor specimens were designed and manufactured. The creep tests of the box floor with local damage, repeated load, and different stress ratio loads were conducted. The creep of the floor increased with ambient temperature and humidity. Because of the local damage of the box floor, the creep increased. Repeated loading increased the creep deformation of the floor, and increasing the load accelerated the creep of the floor. Combined with the creep mechanism of wood materials, a creep theoretical calculation formula of the box floor with LVL orthogonal ribs was established. Comparing the creep model analysis with the test data, it was found that the modified Burger mode can well simulate the creep performance of LVL box floor. Therefore, the modified Burger model can be used to calculate the creep deformation of the box floor.

Experimental study on flexural behavior of box floors with orthogonal rib beams made of poplar laminated veneer lumber

This study examined the flexural behavior of the poplar laminated veneer lumber (LVL) box floor with orthogonal rib beams. Four 3.6 m × 4.8 m box floor samples made of poplar LVL orthogonal rib beams and oriented strand board (OSB) plates were tested under vertical uniform loading, from which the bearing capacity, stiffness, and failure characteristics were analyzed. There was no damage in all box floor samples at the normal service load of 2.5 kN/m2, and the maximum deflection was far less than the allowable value. When the maximum load was applied, the load-displacement curve of each floor sample exhibited a linear relationship without obvious failure. However, localized failure was manifested as the dislocation slip of the rib beams relative to the upper and lower floor slabs at the corner nodes and the joint expansion and staggered floors at the bottom plate, with obvious failure signs. The rib beam height had the most significant impact on the floor stiffness, followed by the spacing of short-side rib beams, whereas the OSB plate thickness had lest impact. The mid-span deflections of poplar LVL orthogonal ribbed box floor samples, which were calculated using the analog slab method, were in good agreement with the experimental results with an error being less than 10%.

Experimental Investigation on Bending Behavior of Innovative Poplar LVL Floor Diaphragms

Poplar laminated veneer lumber (poplar LVL) is made of fast-growing poplar veneer and structural adhesive, which owns the advantages of sustainability and stable quality. Here an innovative poplar LVL floor diaphragm is presented, mainly made up of orthogonal rib beams fitted together using L-shape steel connectors. The paper mainly deals with an experimental study on the bending behavior of the floor under transverse uniform load. Full-scale testing on eight 3.6 m × 4.8 m specimens shows that the damage phenomena of the floor mainly exhibited as the separation between the rib beams and pulling out from the rib beam for the tapping screw. Though some local damage phenomena appeared before the preset maximum loading level, the load-deflection curves basically kept linear for most of the specimens. Under the service load level of 2.5 kN/m2, the distribution of deflection and strain for the full-length rib beam substantially exhibited the characteristic of a two-way slab. In contrast, for the segmented rib beam, the situation was much more complex. Due to the parametric design of the specimens, testing results illustrated that the rib beam height played the most important role in floor stiffness. Next was the sheathing panel, while the role of segmented rib beam spacing was relatively unremarkable. At last, a revised pseudo-plate method was proposed to evaluate the maximum deflection of the novel floor, which considered the composite action by rigidity factors.

Mechanical performance of three types of connections used in orthogonal ribbed beams made of poplar laminated veneer lumber

This study elucidated the mechanical performance of different connections used in orthogonal ribbed beams made of poplar laminated veneer lumber (LVL). Three types of connections (namely, U-, T-, and L-shape) were fabricated and used to connect the second beam and the middle part of a main beam to form an orthogonal rib beam. A concentrated load was applied to the intersection between the main beam and the second beam. The results showed: (1) all three types of ribbed beam connection specimens showed good connecting performance and the ductile failure, including the pull-out of partial self-tapping screws, crushing of LVL at the end of the ribbed beam, and connection failure; (2) the variation of load capacity of JD2-type specimens was approximately 3.2%, which was smaller than that of the JD1- and JD3-type specimens, slightly less than 10%; (3) the ultimate bearing capacity of a connection specimen was proportional to the number of self-tapping screws; and (4) the mechanical performance of the U-shaped connection specimens was worse than that of the L-and T-shaped connection specimens. The L-shaped connection was recommended due to its better mechanical performance, simpler configuration, and more convenient fabrication.

Mechanical behaviour of poplar laminated veneer lumber with fiber reinforced polymer under shear and compression stresses

ABSTRACT This paper presents experimental results of the mechanical behaviour of LVL (Laminated Veneer Lumber) made of poplar reinforced with fiber reinforced polymer (FRP) subjected to shear and compressive stresses. Through mechanical properties such as strength, stiffness, maximum displacement and non-destructive measurements of elastic moduli in compression and shear, the influence of different variables was analysed: 1) Type of FRP (carbon or basalt); 2) Fiber direction; 3) Quality of veneer. The influence of veneer quality under compressive stresses and the difference between carbon and basalt under shear stresses have been verified. In addition, for the unidirectional carbon reinforcement, improvements up to 21% in compressive and shear stiffness and elastic modulus was achieved, respectively.

Lateral loading behavior of the poplar LVL light wood shear wall

Poplar laminated veneer lumber (poplar LVL) is made of fast-growing poplar veneer and structural adhesive, which can well meet the developing requirement of the modern wood structures. This paper mainly focuses on the lateral loading behavior of the poplar LVL shear wall. For this purpose, six shear wall specimens with different opening types were fabricated and tested under the action of monotonic and cyclic loading. Performances were analyzed on the failure pattern, the load-displacement curve, the shear strength, the ultimate displacement, the elastic lateral stiffness, and the energy dissipation. To strengthen the corner joint, an innovative custom-designed hold-down was adopted, and the mechanical performance was also considered. The results showed that the failure of the specimen was mainly due to the yield of the nails and the separation between the stud and the base plate, while the hold-down can greatly improve the shear strength, the ultimate displacement, and the energy dissipation performance of the poplar LVL shear wall without openings. At last, the evaluation formula of the bearing capacity for the light wood shear wall is proposed so as to promote the theoretical basis for the application of poplar LVL in the light wood frame construction.

Microwave-assisted laminated veneer lumber (LVL): Investigation on the effect of preheating time and moisture content on resin penetration and bonding quality

This research presents the effect of microwave preheating and moisture content on phenol-formaldehyde resin penetration and bonding quality of poplar laminated veneer lumber (LVL). Effective penetration and maximum penetration factors were measured individually in the surface and core layer to investigate the bonding characteristics. The bonding quality of the LVL is also measured through shear strength (parallel to grain direction) and the ratio of delamination. The results showed that by increasing moisture content, from 3 to 8%, the shear strength of the LVLs decreased while the ratio of delamination was raised. On the other hand, microwave preheating improved the bonding properties and the core temperature of the preheated LVL reached 100 °C in a shorter time. Results revealed the correlation of penetration parameters on the LVLs shear strength and the ratio of delamination. LVL made from layers with 3% moisture content and 180 s preheating had minimum resin penetration. The highest effective and maximum penetration were observed in samples made with 8% moisture and without preheating which then indicated the weakest shear strength and the highest ratio of delamination. The positive effect of microwave preheating on bonding quality was much more tangible for the billet with higher moisture content.

The Effect of Press Temperature and Duration on the Bonding Strength of American Poplar Laminated Veneer Lumber

In this study, the effect of press temperature and duration on bonding strength of laminated veneer lumber (LVL) was investigated. For this purpose, LVLs were produced from I 77/51 American poplar clone (Populus deltoides) by using 2 different press temperatures (140 and 170⁰C) and 3 press duration (10, 15 and 20 minutes). Phenol formaldehyde (PF) adhesive was used for bonding of poplar veneers. The bonding strength and wood failure rate of produced LVLs were determined according to TS EN 314-1 standard. According to experimental results, the LVLs pressed at 170⁰C showed better bonding strength compared to LVLs pressed at 140⁰C. On the other hand, a decrease was observed in the wood failure rate due to the increase in temperature. The highest bonding strength was obtained by press duration of 10 minutes at press temperature of 170⁰C and a significant decrease in bonding strength was observed when press duration was extended.

Racking performance of poplar laminated veneer lumber frames and frame-shear hybrid walls

This study examined the racking performance of poplar laminated veneer lumber (LVL) frames using bolted steel filling plates to connect beam-column joints, poplar LVL frames using the embedment bars to connect beam-column joints, and frame-shear hybrid walls made of poplar LVL studs and oriented strand board (OSB) sheathing panels. A new design load spreader beam was used on the side of the top of a specimen to apply monotonic and cyclic loadings. It was found that the lateral force resistance, stiffness, and ultimate loads of poplar LVL pure frames with bolted steel filling plate connections and closed rod connections were much lower than those of the poplar LVL frame-shear wall hybrid structure. The highest initial stiffness of the poplar LVL hybrid frame-shear wall was 1.77 kN/mm, which was 24% and 22% lower than that of the conventional shear wall made with spruce-pine-fir studs and OSB or plywood sheathing panels, respectively. The poplar LVL frame-shear wall hybrid structure showed lower degradation in stiffness than the conventional shear wall. The hybrid frame-shear wall structures made of poplar LVL could meet the requirements of Chinese standard; however, diagonal braces were required in use of poplar LVL pure frames.

The effect of structural changes on the compressive strength of LVL

Laminated veneer lumber (LVL) is an important engineered wood product. Internal structural changes have a substantial influence on the mechanical performance of LVL. To investigate the relationship between the internal structural changes and the compressive strength, poplar LVL layering is manufactured by taking into account the veneer lathe checks, namely lathe checks both facing inwards (TLLT), lathe checks both oriented outwards (LTTL) and lathe checks in one layer facing outwards (LTLT). Macroscopic compressive strength of the samples is measured using a universal testing machine. Microscopic internal structural changes are periodically recorded with X-ray CT when the samples are compressed using a load cell. The results show that the compressive strength of LTLT is significantly higher than that of LTTL and TLLT types of LVL. During the compression test, density increase in the samples is non-homogenous. There is a minor increase in density of the glue line, while this is larger in regions with a low density. Density increase is mainly induced by collapse of large vessels. However, the presence of phenol formaldehyde resin can enhance the resistance of vessels against collapse. Structural changes, i.e., vessels collapse and collapse propagation, are likely to occur in locally heterogeneous regions. Propagation of collapsed vessels is more frequently observed in regions where large vessels are contiguous.

Mechanical Behavior of Light Trusses Made of Poplar Laminated Veneer Lumber and Connected with Bolts and Tooth Plates

Mechanical Behavior of Light Trusses Made of Poplar Laminated Veneer Lumber and Connected with Bolts and Tooth Plates

意杨旋切板胶合木中式木框架抗侧性能研究

意杨旋切板胶合木中式木框架抗侧性能研究

意杨旋切板胶合木箱型梁受弯性能试验研究

意杨旋切板胶合木箱型梁受弯性能试验研究

Highly Mechanical Performance of Laminated Veneer Lumber Induced by High Voltage Electrostatic Field

The high voltage electrostatic field (HVEF), as a novel technology, was applied in the study to obtain a highly mechanical performance of LVL (laminated veneer lumber) by increasing limiting value of shear failure strength directly affected by bonding strength. The surface property of wood, polymerization extent of PF, bonding interface of wood-to-PF and mechanical properties of LVL were investigated under the HVEF treatment. The results showed that increased free radicals and total surface energy were acquired under the HVEF treatment resulting from more polar groups (?OH, ?CHO) and ions were triggered leading to decreased contact angles identified both for Poplar and Masson specimens. The HVEF provided more reactions among wood-to-UF and more cross linking reaction of PF occurred in the treating step. The tendency of vertical density profile was more extremely steep than the control with max density increased by 24.93% and 30.24% for Poplar and Masson LVL respectively since adhesive aggregated continuously and orderly along bonding interface and permeation depth reduced to around 200 ?m, accounting for improved bonding shear strength, which eventually brought an enhancement on mechanical properties of LVL with horizon shear strength (?and?), modulus of elasticity and static bending strength significantly enhanced by 14.65%, 10.68%, 20.67% and 12.34% for Poplar LVL and that of Masson LVL enhanced by 17.30%, 13.93%, 18.55% and 12.72%. Besides, the delamination ratio was decreased by 49.57% and 58.32% respectively both for Poplar and Masson specimens.