Rolling Shear Strength Research Articles

Optimizing Lumber Densification for Mitigating Rolling Shear Failure in Cross-Laminated Timber (CLT)

Rolling shear in cross-laminated timber (CLT) has been identified as the governing factor influencing design value. Likewise, densification has been found to be an effective method of enhancing the rolling shear strength of lumber and in turn, CLT. In this study, utilizing knowledge of material properties, optimization of the compression ratio for densification has been presented. Three-layered CLT beams made from non-densified lumber, grade #1 loblolly pine (Pinus taeda L.), were subjected to a bending load at a span-to-depth ratio of eight and had a rolling shear failure at the mid-layer with a shear strength of 3 MPa. Assuming the same modulus of rupture (MOR) for both lumber and CLT made from the same species and grade, the MOR of lumber was used to calculate the minimum required shear strength (MRSS) of the transverse mid-layer to change the failure mode of the CLT beam from rolling shear to tensile failure. Using the relationship between the compression ratio and the increase in rolling shear strength, the optimized compression ratio for densification was calculated. This procedure resulted in a compression ratio of 16.67% for densification of the mid-layer to avoid rolling shear in the case of CLT beams with a span-to-depth ratio of eight. To verify this process, CLT beams with mid-layers densified at 16.67% were fabricated and submitted to a bending test. Rolling shear failure was mitigated and densified CLT beams failed in tension with a MOR similar to that of lumber, 47.45 MPa. Likewise, rolling shear strength was observed to increase by 48% for CLT that had a densified mid-layer at 16.67%.

Influence of densification on structural performance and failure mode of cross-laminated timber under bending load

The effect of densification of the laminas was studied relative to the shear performance of cross-laminated timber (CLT) specimens submitted to the bending test. The three-layered CLT panels were fabricated using loblolly pine (Pinus taeda L.). A compression ratio (CR) of 50% was used to densify the lumber using the thermomechanical densification technique. The process included plasticizing the lumbers by soaking them in boiling water for 10 minutes and then hot-pressing to the target thickness at 140 °C. Four groups were made, i.e., a control sample with all three layers non-densified, only mid-layer densified, all layers densified, and all layers planed to the same thickness of densified layers. Specimens were tested in short-span bending with a span-to-depth ratio of eight. For specimens having densified mid-layer, the failure mode changed from rolling shear to tensile failure of the outer layer, and the maximum shear stress was increased by 34%. Densification of the mid-layer at CR of 16% was sufficient to change the failure mode from rolling shear in mid-layer to tensile in outer layer. In the case of all-layer-densified specimens, the maximum rolling shear strength was increased by 129% compared to the control.

Rolling shear properties of cross-laminated bamboo (CLB) specimens: A comprehensive study

This study explores the rolling shear properties of cross-laminated bamboo (CLB), an innovative engineering bamboo material. Two typical test methods are used for the experimental work: the modified planar shear tests (MPS) and the three-point short beam bending tests (SBB). The rolling shear strength and modulus are measured in MPS. The shear analogy method is used to calculate the rolling shear strength in SBB. Subsequently, comprehensive numerical models of MPS and SBB are developed, taking into account the material properties of bamboo and adhesives through user material and cohesive zone model. The stress-strain curves and failure propagations of the models align very well with the experimental results. Rolling shear failure was initiated at the interface between the middle layer and outside layer and extended diagonally. Parametric analysis on the cohesive strength of the MPS model shows the variation of loading curves and failure modes. The failure modes of SBB under different span-to-depth ratios are investigated by integrating the shear analogy method and numerical model.

Rolling Shear Strength of Cross Laminated Timber (CLT)—Testing, Evaluation, and Design

Cross laminated timber (CLT), with its typical orthogonal layering and exposure to out-of-plane bending, develops inherent rolling shear stresses. These stresses need to be checked during the ultimate limit state design process. With the ongoing revision of Eurocode 5, a discussion regarding the characteristic value of the rolling shear strength of CLT has arisen. One obstacle in the discussion is seen in the lack of harmonized regulations concerning how to determine rolling shear properties. This circumstance manifests in the greatly diverging test results of different institutions testing the rolling shear strength. The paper at hand aims to propose a candidate for such harmonized regulations. To achieve this, the most common test setups, such as the inclined shear test, three- and four-point bending tests, etc., were numerically and experimentally investigated. Within the numerical investigations, a comparison of the most common calculation methods (Timoshenko beam theory, modified γ-method, Shear Analogy Method, and Finite Element Analysis) for evaluating rolling shear stresses was included. In the experimental program, parameters such as the specimen width, number, and thickness of the cross layer(s), shear length, optional reinforcement against the stresses perpendicular to the grain, and the overall test setup were varied. It was found that the used test setups themselves and the area of the cross layer(s) (shear length, number, and thickness of the cross layer(s)) have a major impact on the rolling shear strength. In contrast, no effect was found from the calculation methods. Based on these findings and on a database of approx. 300 four-point bending rolling shear tests on CLT specimens from five well-established CLT manufacturers, a model for the regulation of the rolling shear strength of CLT is proposed, in combination with a corresponding four-point bending test setup. Afterwards, with two additionally conducted four-point bending test series, the proposed model is successfully validated. The conclusions and recommendations in respect to the test setup (four-point bending), evaluation procedure (Timoshenko beam theory), reference characteristic rolling shear strength, and the model, which allows adapting the reference rolling shear strength to individual conditions, are seen as a worthy basis for a more objective discussion on this topic.

DEVELOPMENT AND CHARACTERIZATION OF SELF-HEALING TRANSDERMAL PATCH OF LIDOCAINE FOR THE MANAGEMENT OF PAIN

Pain management is a significant challenge due to the side effects associated with commonly prescribed medications like NSAIDs and opioids. Local anesthetics, such as lidocaine, offer an alternative with fewer side effects when formulated in topical patches. Transdermal delivery systems, including heated patches, enhance drug absorption and provide targeted pain relief. This research paper aims to develop and characterize a self-heating transdermal patch of lidocaine for pain management. The drug sample of lidocaine was characterized using UV-visible spectrophotometric analysis, melting point determination, and differential scanning calorimetry. The results confirmed the purity of the drug sample. Pre-formulation studies were conducted to determine the solubility and partition coefficient of lidocaine, as well as drug-excipient interaction studies. The formulation of the lidocaine transdermal patch included the selection of excipients such as solvents, adhesives, solubilizers, and permeation enhancers. The patch was developed in three trial batches, with the final batch prepared using a drug-in-adhesive type approach. The developed patch was evaluated for physical characteristics, solvent residual content, rolling ball test, shear strength, drug crystallization, drug content, and in-vitro permeation. The results of the evaluation showed that the developed lidocaine transdermal patch had the desired physical characteristics, uniform thickness, good folding endurance, and appropriate solvent residual content. It exhibited satisfactory rolling ball test and shear strength. Microscopic examination confirmed the absence of drug crystallization. The drug content of the patch was determined to be within the desired range, and the in-vitro permeation study demonstrated successful drug release through the dialysis membrane. In conclusion, the development and characterization of a self-heating transdermal patch of lidocaine for pain management provide a promising approach for effective and targeted pain relief. The patch formulation demonstrated suitable physical properties, drug content, and permeation characteristics, suggesting its potential as an alternative pain management solution. KEYWORDS: Lidocaine, transdermal patch, pain management, self-heating, drug delivery

SUITABILITY OF ASPEN (POPULUS TREMULA L.) FOR CROSS-LAMINATED TIMBER (CLT)

Cross-laminated timber (CLT) CLT is an excellent material for building and high load-bearing structural applications, but its fabrication and use are limited to softwood only. The suitability of aspen (Populus tremula L) wood for manufacturing CLT was assessed by using two adhesives, one-component polyurethane (1C-PUR) and melamine adhesive (ME). Physical properties like water absorption (WA), thickness swelling (TS), delamination, and mechanical properties like bond shear strength, bending modulus of elasticity, bending strength, and rolling shear strength were evaluated to examine its suitability. Compared to ME-bonded CLT, 1C-PUR bonded CLT panels displayed superior physical characteristics, with 70% passing the delamination test. CLT panels bonded with 1C-PUR adhesive also have better mechanical properties than ME-bonded CLT. CLT panels experienced three types of bending failure: rolling shear, delamination, and tension. Aspen CLT has similar or higher mechanical properties than traditional softwoods, making it suitable for CLT manufacturing.

The effects of densification on rolling shear performance of southern yellow pine cross-laminated timber

This study evaluated the improvement in the shear performance of cross-laminated timber (CLT) through the densification of the transverse layers. Loblolly pine (Pinus taeda L., one of ten species known as Southern Yellow Pine (SYP)) lumber was used to fabricate CLT rolling shear specimens. Considering the compression ratio, thickness reduction to the initial thickness, lumber with an average density of 641.23 kg/m3 was compressed to three different levels: 16.67%, 33.33%, and 50.00%. For this compression, a thermomechanical densification technique was employed, in which lumber was softened by soaking in boiling water for 10 min and then hot-pressed at 140 °C to the target thicknesses. To differentiate the improvement in the shear performance due to the increased density from that of the aspect ratio, non-densified lumbers with the same aspect ratio as densified specimens were also used to fabricate CLT rolling shear specimens. The rolling shear performance of CLT specimens was evaluated using modified planar shear testing. The rolling shear strength increased by about 108% when the transverse layer was compressed for 50%. Likewise, it was found that there is a linear relationship between the percentage of increase in rolling shear strength and the compression ratio. Although the increased aspect ratio improves the rolling shear strength, results revealed that specimens with densified transverse layers outperformed those with non-densified specimens at the same aspect ratio.

Experimental and numerical analysis of specimen configurations for Cross Laminated timber on rolling shear stiffness and strength response

This work aimed to perform the numerical and experimental analysis of three test setups (bending, vertical shear, and inclined shear) of CLT used to determine the rolling shear stiffness and strength. CLT specimens were manufactured with four different Brazilian wood species and two-component polyurethane adhesive. The stress distributions in the CLT test setups were simulated by Finite Element Method using ANSYS software. Rolling shear stiffness and strength was directly proportional to wood density. The CLT stiffness differed for each test setup. CLT strength was independent of the applied test setup. The numerical models provided the stress distribution in the areas of most interest of the specimen models which justified the failure modes obtained in the experimental tests. The inclined shear specimen was the one that best represented failure by rolling shear.

Structural Properties of Commercial Australian Plantation Hardwood CLT

Significant volumes of plantation hardwood are available in Australia to produce value-added engineered wood products such as cross-laminated timber (CLT). To validate the possibility of utilising this available resource, the bending structural properties of plantation Eucalyptus nitens solid board and finger-jointed feedstock were measured. The studied CLT panels produced from finger-jointed lamellas were subjected to bending strength, bending stiffness, rolling shear strength in bending, and pure rolling shear tests to obtain characteristic design values. Solid and finger-jointed timber test results suggested that boards used in longitudinal lamellas have a bending strength of 36.0 MPa and a modulus of elasticity (MOE) of 13,000 MPa. Finger-jointed timber in crossed lamellas presented a declared bending strength of 25.0 MPa. CLT panels showed a bending strength of 24.0 MPa and a rolling shear strength of 2.0 MPa. The experimental results for the CLT panels evidenced that the CLT bending stiffness matches up very well with the modelled results when an MOE of 13,000 MPa is used to describe the stiffness of longitudinal boards. The results presented in this study establish a basis for the commercial use of Australian plantation hardwood CLT in structural applications such as floors and roofs in commercial and residential buildings.

Properties of mixed species/density cross laminated timber made of rubberwood and coconut wood

The utilization of rubberwood (Hevea brasiliensis) and coconut wood (Cocos nucifera L.), the essential economic crops in Thailand and tropical countries, was proposed for manufacturing mixed species/density cross-laminated timber (CLT) for building construction. Six 3-layer CLT configurations, which are composed of either medium-density (600 – 799 kg/m3) rubberwood (MRB) or coconut wood (MCC) or high-density (800 – 999 kg/m3) coconut wood (HCC) laminations, were determined considering the mechanical properties and material costs. The outer layers of the control MCC CLT were replaced with either MRB or HCC to improve its mechanical properties, while either outer or core layers of the control MRB CLT were replaced with HCC to reduce its material cost. The material properties of the three wood types and the six CLT configurations were examined. The densities of the produced CLTs were not affected by the chosen manufacturing parameters showing a strong correlation to the lamination's density. From the bonding performance perspective, the mixed-species approach significantly increased the average wood failure percentage of the control MRB CLT. However, only the control MCC CLT achieved the average wood failure percentage greater than 80%, as required in North America's CLT standard. The compressive strength properties of the CLTs in their major strength directions, σclt, were governed by the outer laminations' parallel-to-grain compressive strength. Unlike softwood CLTs, neglecting the load sharing contribution of the core layer in the σclt estimation resulted in 15% underestimation. Rolling shear strength, τrs, was determined by the core laminations regardless of the CLT layups. MRB achieved the highest τrs followed by HCC and MCC, and all values were significantly larger than the common softwood used in CLT production. The results imply that the mixed species/density approaches can effectively improve the mechanical properties of the coconut wood CLT and reduce the material cost of rubberwood CLT without compromising structural performance.

Moisture and short-term time-dependent behavior of Norway spruce clear wood under compression perpendicular to the grain and rolling shear

ABSTRACT Material properties of wood under compression perpendicular to the grain and rolling shear are important for the engineering design of timber structures. This regards the short-term stiffness and strength, their dependence on the moisture content of wood, as well as the time-dependent behavior. Norway spruce clear wood properties in the transverse plane of wood were studied in an experimental campaign exploiting an earlier developed biaxial test setup. The moisture dependence of the stiffness and strength and the short-term time-dependent creep deformations under compression in the radial direction and under rolling shear were characterized. Loading and unloading stiffness, as well as the strength, were determined in quasi-static tests at five different moisture contents from 4% to 29%. The elastic and viscous stiffnesses were identified in creep tests at three compressive stress levels of 0.50, 0.75, and 1.00 N/mm 2 , and at two rolling shear stress levels of 0.33 and 0.50 N/mm 2 . The test data complements the existing experimental database, especially with novel data regarding the moisture dependence of the rolling shear strength, which showed less moisture dependence than the compressive strength perpendicular to the grain. The results of the creep tests revealed different material properties for the different loading and material directions of wood.

Rolling Shear Strength of Laminae for CLT with Four Japanese Softwood Species Obtained by the Compression Method.

Rolling Shear Strength of Laminae for CLT with Four Japanese Softwood Species Obtained by the Compression Method.

Comparative Study on Various Strength Parameters of Structural Elements Made from Cross-Laminated Timber

Cross laminated timber (CLT) is an innovative and environment friendly engineered timber product with superior structural performance. CLT offers strong resistance against both in-plane and out-of-plane loading. Hence, it is widely used as floors, roofs or wall elements. Considerable experimental research on CLT under various loading conditions has been done in the recent past. This article presents a comprehensive review of various design methods to determine basic mechanical properties such as tension, compression and rolling shear strength of CLT with primary focus on Norway spruce. All relevant experimental data available from existing literature were collated and consequently been used to evaluate the performance of various methods to design CLT structures. The comparison revealed that different methods show considerable variance in predicting the capacity of CLT panels due to the variation in timber species, which affects the corresponding mechanical properties of the lamella. In addition to species, rolling shear properties can also vary considerably depending on the type of experimental technique used for testing. A predictive model has also been proposed to correlate rolling shear strength obtained from shear analogy method to that obtained using planar shear.

Influence of the connector shape parameters in the structural behaviour of the adhesive- free timber floor panels

Timber-to-timber panels (TTPs) are adhesive- and steel-free structural components formed by carpentry joints of Scots pine to be used as floors. Figure 1 shows a schematic on the TTPs and a detail on the connectors. A numerical model simulating bending tests on TTPs and considering timber as an orthotropic and bi-modulus material was validated from experimental results of deflection, and rolling shear strength. Since the serviceability and ultimate limit states of the TTPs was mainly defined by the rolling shear properties of the connectors, this paper aims to study the influence of different connector shape parameters in the structural behavior of the panels. For that, values of the connector height (hc varying between 40 and 100 mm), width (b1 varying between 40 and 100 mm) and the dove-tail angle (α varying between 45º and 75º) were introduced in the numerical models to obtain both failure load and stiffness for different span TTPs. Results showed that TTP deflection and shear stresses on the connectors decreases with the increase of the height and the width of the connectors. As the width of the connector (b1) increases, the maximum shear stress decreases up to 42%. For a same connector height, the angle of the dove-tail shows low influence in the maximum shear stress; however, it plays a greater role in the deflection of the panels. For the connectors of 40 mm of height TTP deflection was barely influenced by connector width; however, for higher connectors (hc ≥ 60 mm), TTP deflection decreased up to 41% as width increases. So, new TTPs configurations varying the connector parameters showed an improvement on the deflection and on the shear stresses of the connectors.

Investigation of rolling shear properties of cross-laminated timber (CLT) and comparison of experimental approaches

The structural behaviour of a cross laminated timber (CLT) system is dictated in-part by the rolling shear properties (both strength fr and modulus Gr) of its laminates. To investigate the rolling shear properties of CLT, short-span four-point bending tests, modified planar shear (MPS) tests with timber sandwich plates, and MPS tests with steel sandwich plates were conducted on Australian grown Eucalyptus nitens and radiata pine, as well as European grown Norway spruce. A strong positive relationship between aspect ratio and strength was found, which agrees with previous research. However, the annual ring orientation distribution rather than the aspect ratio was shown to have the most pronounced effect on the shear modulus. The load direction, which has not been accounted for by researchers, was shown to have a substantial effect on the measured rolling shear strength. When the applied load direction was parallel to the annual rings, the Eucalyptus nitens, radiata pine and Norway spruce specimens exhibited rolling shear strengths of 4.1, 2.7 and 1.7 MPa respectively. These average recorded strengths were found to decrease by 16%, 40% and 52% respectively when the load direction was changed to run perpendicular to the rings instead. By directly measuring the shear deformations of two specimens tested under different MPS approaches using Digital Image Correlation (DIC), the impact of the plate material on the recorded shear modulus was isolated. This revealed that the MPS tests with steel plates recorded average rolling shear modulus values which were as much as 42% higher than their counterparts with timber plates, as well as identifying substantial errors in laser and LVDT-like measurement tools. It is recommended that a DIC approach is employed to complement or replace a UTM or laser sensor deformation measurement approach to mitigate these potential errors.

Experimental investigation on the influence of lamination aspect ratios on rolling shear strength of cross-laminated timber

Experimental investigation on the influence of lamination aspect ratios on rolling shear strength of cross-laminated timber

Experimental study on bending properties of cross-laminated timber-bamboo composites

Using bamboo and timber to manufacture cross-laminated timber-bamboo (CLTB) composites could utilize the advantages of two material to improve the mechanical properties and expand the raw material source of cross-laminated timber (CLT). To explore the feasibility of using engineered bamboo as CLT lamination, the rolling shear properties of two bamboo scrimbers and one bamboo plywood were evaluated. Two types of CLTB specimens, using bamboo scrimber as transverse layer or as both transverse layer and the outermost longitudinal layer, were developed in this study. The bending properties of CLTB and generic Spruce-pine-fir (SPF) CLT specimens were evaluated by dynamic tests and third-point bending tests, respectively. The shear analogy method was employed to calculate the apparent bending stiffness of CLT/CLTB specimen. The results indicated that the rolling shear modulus and strength of bamboo scrimber (group RB(F)-4.5) were 92.81% and 98.64% higher than those of bamboo plywood, respectively, and were 330.19% and 121.13% higher than those of SPF dimension lumber, respectively. The CLTB specimens, group BWBWB, had 23.69% and 60.50% higher apparent bending modulus and peak load than those of generic SPF CLT specimens. Most of the CLTB bending specimens had main failure mode of tensile failure in the bottom layer which replaced rolling shear failure in transverse bamboo scrimber layer. The apparent bending stiffness values of CLT/CLTB specimens obtained from dynamic test and shear analogy method were in good agreement with the static experimental values. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panel products fabricated with bamboo scrimber.

Research Trends in Hybrid Cross-Laminated Timber (CLT) to Enhance the Rolling Shear Strength of CLT

In this study, hybrid CLT research and development trends were analyzed to improve the low rolling shear strength of CLT, a large wooden panel used in high-rise wooden buildings. Through this, basic data that can be used in research and development directions for localization of CLT were prepared. As a way to improve the low rolling shear strength, the use of hardwood lamina, the change of the lamina arrangement angle, and the use of structural composite materials are mainly used. Rolling shear strength and shear modulus of hardwood lamina are more than twice as high as softwood lamina. It confirmed that hardwoods can be used and unused species can be used. Rolling shear strength 1.5 times, shear modulus 8.3 times, bending stiffness 4.1 times improved according to the change of the layer arrangement angle, and the CLT strength was confirmed by reducing the layer arrangement angle. Structural wood-based materials have been improved by up to 1.35 times MOR, 1.5 times MOE, and 1.59 times rolling shear strength when used as laminas. Block shear strength between the layer materials was also secured by 7.0 N/mm2,which is the standard for block shear strength. Through the results of previous studies, it was confirmed that the strength performance was improved when a structural wood based materials having a flexural performance of MOE 7.0 GPa and MOR 40.0 MPa or more was used. This was determined based on the strength of layered materials in structural wood-based materials. The optimal method for improving rolling shear strength is judged to be the most advantageous application of structural wood based materials with strength values according to existing specifications. However, additional research is needed on the orientation of CLT lamina arrangement according to the fiber arrangement of structural wood-based materials, and the block shear strength between lamina materials.

Effects of Grain Pattern on the Rolling Shear Properties of Wood in Cross-Laminated Timber

Rolling shear modulus and strength are the key factors affecting the mechanical performance of some wood products such as cross-laminated timber (CLT). As reported, rolling shear property strongly depends on the sawing pattern such as the aspect ratio and grain direction (grain mode). However, the mechanism behind this phenomenon has not yet been clarified. In this work, the rolling shear modulus and strength of spruce-pine-fir (SPF) with different grain modes and aspect ratios were experimentally investigated. In addition, a theoretical investigation was carried out to reveal the mechanism behind this phenomenon. The results exhibited that the rolling shear moduli of 0° and 90° grain-mode wood were the same. This value can be called the pure rolling shear modulus. Rolling shear modulus of wood with angles other than 0° and 90° can be calculated from the pure rolling shear modulus and grain angle. Therefore, this modulus can be called the apparent rolling shear modulus. Thus, using 0° and 90° grain-mode specimens to determine the pure rolling shear modulus and strength of wood is recommended.

Effects of manufacturing parameters on properties of rubberwood-cross laminated timber manufactured via hot pressing

In this study, cross-laminated timber (CLT) was manufactured from rubberwood via hot pressing. The effects of manufacturing parameters, such as resin content and clamping pressure, on the following properties of CLT panels were investigated: density (ρ), water absorption (WA), thickness swelling (TS), bonding strength (BS), compressive strength in the major strength direction of CLT (σmajor), compressive strength in the direction perpendicular to the flat plane of CLT (σFlat)), and rolling shear strength (RS). The relationships among the properties of the CLT panel, those the original rubberwood material, and the manufacturing parameters was also explored. The results showed that the resin content and clamping pressure did not significantly affect most of the examined properties of the CLT panels. The ρ, WA, σmajor, σFlat, and RS of the panels could be estimated directly from the properties of the original rubberwood, while the TS could be estimated directly from the clamping pressure applied on the panel. However, no such relationship was found for the BS value. Compared with typical softwood-CLT, the rubberwood-CLT exhibited superior mechanical properties. This implies that CLT made of rubberwood can achieve better structural performance than standard CLT can.