Rolling Shear Failure Research Articles

Shear strength of cross laminated timber based on larch lamina combination

Cross-laminated timber (CLT) fails in the outermost tensile lamina under bending loads, or rolling shear failure occurs in the Minoir direction lamina. This study investigated the effect of lamina width (90 mm, 120 mm), modulus of elasticity (MOE), and placement of major direction lamina on the shear strength of Larix kaempferi Carr CLT. The shear test was conducted using the short span bending test. Results showed that the specimen with 90 mm width of lamina underwent rolling shear failure at the minor direction lamina. The specimen with 120 mm width of lamina had suppressed rolling shear failure and failed at the outermost tensile lamina, which resulted in 52% higher shear strength compared to the 90 mm width specimen. CLT with high MOE placed in the outermost tensile lamina had increased shear strength. The specimen with four laminas in the major direction had both the highest strength and the lowest reliability due to the high standard deviation. This suggested that the width of the larch lamina and the MOE affect the strength of CLT. The CLT strength obtained using the FEA and the theoretical analysis were compared with the measured strength values.

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%.

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.

Mechanical properties of hybrid cross-laminated timber with wood-based materials

In this study, four wood-based materials (plywood, laminated veneer board (LVB), oriented strand board (OSB), and particle board (PB)) were proposed as layered materials for CLT to improve its shear performance. The fabricated hybrid CLT exhibited better bending, shear performance, and compressive strength than that of traditional CLT. The out-of-plane bending performance, in terms of modulus of elasticity and modulus of rupture, improved by 2912–5836 MPa and 1.89–18.54 MPa compared with that of traditional CLT. The out-of-plane shear modulus and strength of the LVB CLT and PLY CLT improved by 31.19–76.15 MPa and 0.5 MPa, respectively, compared with that of traditional CLT. The compressive strength of the hybrid CLT improved by 6.86–24.6 MPa. The cross-arranged veneer with the LVB and plywood exhibited rolling shear failure. The ratio of tensile and shear failure of LVB CLT and PLY CLT increased compared to traditional CLT. The failure mode of the hybrid CLT with OSB and PB exhibited shear failure in the middle of the panel thickness of the OSB and PB. This study confirmed an improvement in the mechanical properties of hybrid CLTs with wood-based materials. LVB and plywood hybrid CLTs exhibited the best results. Additional studies are required on the mechanical properties of hybrid CLTs in the arrangement direction of wood-based materials and in the minor direction of the hybrid CLT.

Influences of lamination grade and loading waveform on fatigue performance and DOL effect of CLT fabricated from fast-growing Chinese fir

As load-bearing members, the mechanical properties of cross-laminated timber (CLT) under long-term and fatigue loads play a crucial role. To broaden the application of fast-growing Chinese fir in CLT, the effects of lamination grade and loading waveform on low-cycle fatigue (LCF) performance and duration-of-load (DOL) effect of CLT were evaluated. In this paper, fast-growing Chinese fir was used as laminations to manufacture 3-layer CLT specimens with different lamination grades. The LCF performance was also investigated under triangular and trapezoidal loading waveforms by bending and shear tests. Furthermore, the LCF performance and DOL factors were predicted and calculated through damage accumulation model. The results showed that rolling shear failure and tension failure were presented in fatigue specimens, accompanied by failures in bonding lines and longitudinal layers. A good fit was observed between the adopted model and experimental results. Compared to low-grade laminations and trapezoidal wave loading, using high-grade laminations and triangular wave loading in CLT could get better LCF performance, respectively. For the DOL factors of bending and shear specimens under standard-term and long-term load, an improvement was obtained in specimens with high-grade laminations. Similarly, triangular wave loading specimens exhibited higher DOL factors than trapezoidal wave loading specimens. We also found that the DOL factors of bending specimens were generally greater than those of shear specimens. Moreover, the long-term DOL factors of most specimens made from fast-growing Chinese fir were close to or higher than those recommended in CLT Handbook.

Experimental Behavior of L-Shaped and T-Shaped Cross-Laminated Timber to Evaluate Shear Walls with Openings

There is increasing interest in using cross-laminated timber (CLT) in buildings because of its high strength and stiffness. In Japan, structural design guidelines for CLT buildings were established in 2016 and construction of mid-rise buildings is increasing. Wide-panel walls can exceed widths of 10 m and integrate cut-outs for window and door openings. However, under lateral loads, corner cracks at the openings have been the most prevalent failure mechanism. To investigate the initiation and propagation of corner cracks, a series of bendings are undertaken on L- and T-shape specimens extracted from the CLT panels. In addition, three-point bending and shear tests are also carried out on beam sections extracted from the CLT panels. Three types of brittle failure were observed: bending failure of the beam or column, and rolling shear failure.

Study on the interlaminar shear properties of hybrid cross-laminated timber (HCLT) prepared with larch, poplar and OSB

In order to better understand, and ultimately improve, the interlaminar shear performance of CLT, this paper explores the influence of three different laminates—larch, poplar and OSB—as transverse layers on the interlaminar shear performance of CLT. The results showed that, although larch, poplar and OSB have little difference in overall density, the interlaminar shear strength of CLT was significantly affected with the use of each as the transverse layer. The interlaminar shear strength in the major direction of CLT prepared with three different materials as transverse layers is: 4.18 MPa (Larch - Poplar - Larch), 3.52 MPa (Larch - Larch - Larch) and 2.71 MPa (Larch - OSB - Larch). The interlaminar shear strength in the minor direction of CLT prepared with three different transverse layers is: 0.91 MPa (Larch - Poplar - Larch), 1.11 MPa (Larch - Larch - Larch) and 0.22 MPa (Larch - OSB - Larch). The interlaminar shear failure modes of the three CLT specimens are different: in the major strength direction, when larch was used as the transverse layer, the interlaminar shear failure mode was rolling shear failure of the transverse layer. When poplar was used as the transverse layer, the interlaminar shear failure modes of CLT were transverse layer shear failure and surface layer shear failure. When OSB was used as a transverse layer, the interlaminar shear failure mode of CLT was the internal shear failure of OSB. In the minor strength direction, the interlaminar shear failure mode of each of the three CLT specimens starts from the unsized gap on the side of the bottom laminate element, and the typical bending failure mode occurs in the transverse layer. CLT prepared with poplar as the transverse layer has lower density, but better interlaminar shear performance in the major strength direction. The interlaminar shear strength in the strong axial direction is affected by the structure of the transverse laminates, and as such homogeneous laminates are more suitable for use as transverse laminates.

Behavior and Damage Characterization of Impulsively Loaded Cross-Laminated Timber Panels

This research bridges the gap between the quasi-static and high-strain-rate loading regimes in cross-laminated timber (CLT) by investigating two areas that have remained unstudied or elusive, i.e., rolling shear failure of CLT under impulsive, blast-like loading and intermediate strain rates in CLT. To study the conditions that would promote shear modes of failure, a novel, highly adaptable center-point testing system and methodology were developed that permitted the application of impulsive loading to undamaged CLT panels in a highly controlled and repeatable manner. The loading condition and low span-to-depth ratio (6.40 ≤ L:h ≤ 6.55) CLT were selected to encourage the development of shear modes of failure. Changes to the rotational rigidity at the boundary conditions allowed for the empirical simulation of realistic boundary conditions. Digital Image Correlation (DIC) and load cell data were used to identify failure modes following loss in resistance in the specimens. Overall, the experiment was successful in consistently eliciting shear modes of failure and providing damage characterization in impulsively loaded CLT. Shear modes of failure resulted in the dramatic loss of resistance in all specimens tested. Strain-rate enhancement in the dynamic apparent flexural stiffness of CLT of 1.3 to 7.2 times was observed. Lower levels of damage were observed in specimens with higher levels of boundary-condition rotational rigidity.

Mechanical performance and failure characteristics of cross laminated timber (CLT) manufactured from tropical hardwoods species

Abstract The study on the mechanical properties of cross laminated timber (CLT) panels made from tropical hardwood species is essential in order to promote the use of CLT as buildings material in Malaysia. The objective of this study were to evaluate the mechanical performance and failure characteristics of CLT fabricated from tropical timbers species, namely, batai (Paraserianthes falcataria), sesendok (Endospermum malacensis), rubberwood (Hevea brasiliensis) and kedondong (family Burceraceae). The modulus of rupture (MOR), modulus of elasticity (MOE), and compressive strength were determined. The failure characteristics of each samples were visually examined and recorded. The results indicated that CLT made from kedondong (KKK) had the highest value of MOR (82.63 N/mm2) and MOE (11,371.33 N/mm2) compared to other species. For compressive strength, CLT made from kedondong (KKK) and rubberwood (RRR) were not significantly different. The failure characteristics observed from bending test were tension, rolling shear and glue line failure while the crushing, shearing and splitting failure were found during compression test. Based on the results obtained, it showed that, the tropical hardwood is suitable to be used as raw material to produce CLT. However, more study should be conducted to observe the performance of CLT on durability and outdoor weathering.

Rolling shear failure damage evolution process of CLT based on AE technology and DIC method

Rolling shear failure damage evolution process of CLT based on AE technology and DIC method

CLT concrete composite floors with steel kerf plate connectors

This paper presents experimental investigations on timber-concrete-composite (TCC) floors with transversely installed steel kerf plates as shear connectors. The TCC system was comprised of 245 mm thick, 7-ply cross-laminated timber (CLT) panels with 150 mm concrete topping. Three embedment depths of the steel kerf plates in CLT (35 mm, 70 mm, and 90 mm) were evaluated at hand of 18 small-scale shear tests. It was shown to be beneficial to only engage the top layer of the CLT panel in order to avoid rolling shear failure. Subsequently, two full-scale TCC floor segments were tested under symmetric four-point bending. The tests confirmed that the TCC floors with steel kerf plates can be designed using the established gamma procedure, and that they exhibited adequate capacity and stiffness to provide an economical solution. The results from this research were utilized to make project-specific design decisions for “The Arbour”, a 10-storey mass timber building for George Brown College, located in Toronto, Canada.

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.

Experimental study on the system effect of bending cross-laminated timber fabricated with Karamatsu larch

Cross-laminated timber (CLT) is recognized as acode-compliant construction material, which is commonly used as bending members (e.g., floor diaphragm and roofs) of mid- and high-rise timber structures. For one CLT bending panel that performs as an orthotropic plate, its transverse laminas can be regarded as a continuous load-distribution system, which connects the equally spaced longitudinal laminas. Therefore, for one CLT panel with more longitudinal laminas in its outermost layers, a higher bending strength might be resulted in due to the system effect, which is denoted by the system strength factor. In this study, for investigating the system effect of CLT panels, bending tests were conducted on 3-layer non-edge-glued CLT panels, which consisted of 3 longitudinal laminas, 5 longitudinal laminas, and 7 longitudinal laminas in their outermost layers, respectively. All the CLT were fabricated with the Karamatsu larch grown in China, which can be served as a potential wood species for CLT manufacturing. Then, their bending resisting properties and failure modes were analyzed. The bending strength or the flexural modulus of the Karamatsu larch CLT was evaluated. Finally, the system effect of the CLT bending strength was analyzed; the system strength factor for the CLT with 3 laminas, 5 laminas, and 7 laminas in its outermost layers was calculated, respectively. Results show that the CLT will provide more stable bending properties, whilst be more prone to the rolling shear failure in its transverse laminas, when the number of the outermost longitudinal laminas enhances. The system effect exists for the CLT bending strength; for the Karamatsu larch CLT consisting of 3 longitudinal laminas, 5 longitudinal laminas, and 7 longitudinal laminas in its bottom layer, the corresponding system strength factor can be approximated as 0.570, 0.720, and 0.920, respectively.

Performance evaluation of a novel cross-laminated timber made from flattened bamboo and wood lumber

A novel flattened bamboo-wood composite cross-laminated timber (CCLT) made from flattened bamboo and hemlock lumber was developed, and its mechanical performance was investigated and quantified in this work. The results demonstrated that the CCLT columns and control hemlock CLT counterparts had nearly equal axial compression strength, but the CCLT yielded a higher compression modulus of elasticity (MOE). Additionally, the CCLT compression behaviors were not significantly affected by the height. Compared with hemlock CLT, the CCLT exhibited a slightly higher flatwise bending MOE and strength in the major strength direction. Furthermore, the MOE and strength of the CCLT under edgewise bending were 17.3% less and 16.2% greater than those under flatwise bending, respectively. The load-carrying capacity of the CCLT was mainly governed by the interfacial failure between the bamboo and wood, in which no rolling shear failure was observed. Those features are unique for the new CCLT for engineered applications.

Rolling Shear Properties of Hybrid Cross-Laminated Timber

Cross-laminated timber (CLT) is an innovative wood product that can be used to build midrise and tall wood construction as an alternative to concrete, masonry, and steel. As floor, roof, and wall made of CLT is subjected to out-of-plane bending, rolling shear (RS) failure of cross-layers can arise prior to bending failure of the outermost layers, which governs the load-carrying capacity of CLT. In fact, the global deflections of CLT depend on the rolling shear modulus of cross-layers, which is much lower than shear modulus parallel to grain. Therefore, it is necessary to determine and improve the rolling shear strength and modulus of cross-layers. In this paper, several test methods were firstly summarized, after which the main influence factors on rolling shear properties were reviewed. Finally, seven configurations of hybrid CLT with three layers were tested to assess the rolling shear properties of hybrid CLT, in which the outer layers are made of Spruce-Pine-Fir (SPF) and the cross-layer is made of different materials such as birch, compressed wood (CW), laminated veneer lumber (LVL), Parallel strand lumber (PSL), plywood, oriented strand board (OSB), and glued laminated bamboo (GLB). The CLT made of SPF was also tested, whose rolling shear properties were regarded as reference. The rolling shear properties of GLB are about twice as high as those of SPF. Other materials do not exhibit superior rolling shear properties to SPF. The compressed wood shows a significant ductility in rolling shear failure.

Shear properties of hybrid CLT fabricated with lumber and OSB

Recently, to enlarge the source of raw materials and improve the mechanical properties of cross-laminated timber (CLT), some local wood species, hardwood and Engineering wood products were used to fabricate CLT. This project studied mainly the feasibility of using construction oriented strand board (COSB) to fabricate hybrid CLT (HCLT). The shear properties of the HCLT were reported in this paper. The mechanical properties of COSB in major and minor strength directions were firstly obtained by various span bending tests and compression tests. The shear resistance and stress in major and minor strength direction of five groups of 3- and 5-layer HCLT, having different lay-up arrangements, were evaluated by experiments, shear analogy theory as well as FE methods. Results showed COSB had higher mechanical properties in minor strength direction compared with SPF dimension lumber. Different HCLT groups had different failure modes observed for major and minor direction. Except to the rolling shear failure of SPF transverse layer and tension failure of gaps between the lumber of the bottom layer, the longitudinal and transverse shear delamination failures and tension failure of COSB were observed during four-point short-span bending tests of HCLT. All the HCLT specimens had higher shear resistance than that of regular CLT with the same number of layer. The difference of the shear resistance between the two strength directions of HCLT decreased as the number of COSB layer increased. In addition, the shear resistance and stress of HCLT can be predicted according the shear analogy theory, and the developed FE models can predict the shear stress of HCLT well. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panel products fabricated with COSB.

Bending performances and rolling shear strength of nail-cross-laminated timber

ABSTRACT This current research work was aimed to develop an innovative panel by combining the nail-laminated timber (NLT) and cross-laminated timber (CLT) into a single product named nail-cross-laminated timber (NCLT) to take advantage of both structural panel products in a single product as a structural member. To investigate the mechanical properties of the NCLT, its bending performance and rolling shear were examined and compared to those of conventional CLT and NLT floor panels. The NCLT and the CLT panels were fabricated in 3 layers such as the CLT. Polyurethane adhesive was used on the laminations. The cross layers of the NCLT were made of a 30-mm-thick vertically laminated NLT. The NLT floor panels were fabricated by vertically nailing the laminations using a zigzag nailing pattern. Results showed no significant differences in the bending strength properties of the three panel types. Both CLT and NCLT showed a comparable rolling shear strength, however, the rolling shear failure in the NCLT was much more ductile than that of the CLT. Overall, the NCLT panels indicated an appropriate short-term bending and rolling shear performances.

Experimental analysis and structural modelling of the punching behaviour of continuous two-way CLT flat slabs

A newly developed bonding technology makes it possible to rigidly connect timber elements parallel to the grain. This technology allows to build two-way and point-supported flat slabs in cross-laminated timber (CLT). In such a structure high loads have to be transferred from the slab into the columns. This paper presents punching tests on different CLT plates. The results of these tests allow for a better understanding of the important parameters of a point-supported CLT slab and should help create the basic design criteria for these connections. To transfer vertical forces from higher storeys through the CLT slab without subjecting it to stresses perpendicular to the grain, the columns are directly connected to each other through an opening in the slab. Even though the opening leads to a stress concentration in the CLT plate, the rolling shear failure was the governing failure mode during the tests. With numerical models the behaviour of the tested plates was simulated and the strains around the opening were calculated. The results show good correlation with the measured strains. After the punching tests, every plate was cut in cubes and the visible failures were recorded. In addition, material samples were cut out of the plates and tested to determine the rolling shear strength of single boards. The achieved shear resistance in the punching tests was 1.4 times higher, than the rolling shear strength determined in shear tests on single boards would allow. An additional rolling shear test series showed that an anchoring effect contributes to the increased rolling shear resistance in punching tests. The results of the punching tests confirm the potential of CLT slabs to be used as biaxial, continuous, point-supported floor slabs.

Retrofit techniques for Cross-Laminated Timber (CLT) elements subjected to blast loads

This paper presents an experimental program that examined the behaviour of seventeen full-scale reinforced cross-laminated timber (CLT) slabs subjected to simulated blast loading using a shock tube. The CLT slabs were retrofitted with steel straps and glass fibre-reinforced polymers (GFRP).The results from the experimental program show that reinforcing the panels with steel straps had minimal effect on the ultimate strength, but significantly affected the post-peak resistance and ductility. The horizontal straps were able to restrict the failure to small regions and promote flexural failure by preventing rolling shear failure. Applying GFRP enhanced the overall behaviour of the slabs, resulting in a significant increase in peak resistance, ductility, stiffness as well as the post-peak resistance.

Evaluation of the Out-of-Plane Shear Properties of Cross-Laminated Timber

The out-of-plane shear properties of cross-laminated timber (CLT) substantially influence the overall mechanical properties of CLT. Various testing methods and theories related to these properties have recently been developed. The effects of the number of layers (three and five layers) and testing method (short-span three- and four-point bending tests) on the out-of-plane shear properties of CLT were evaluated. The out-of-plane shear strength values were calculated based on different theories for comparison. The failure mode in the short-span four-point bending (FPB) method was mainly the rolling shear (RS) failure in the cross layers, indicating that the FPB method was appropriate to evaluate the RS strength of CLT. The out-of-plane shear capacity obtained using the three-point bending (TPB) method was higher than that tested by the FPB method. The testing methods significantly influenced the out-of-plane shear capacity of the three-layer specimens but not that of the five-layer specimens. With an increase in the number of layers, the out-of-plane shear strength of the specimens decreased by 24%. A linear correlation was found among the shear strength values obtained from different theories.