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Modelling of Laminated Veneer Lumber (LVL) beams with holes using cohesive elements
No full textOpenings are usually required in timber beams to allow services like plumbing, sewage pipes, and electrical wiring to run through. These openings can cause significant stresses perpendicular to the grain direction, which may create cracks in the timber due to the low tensile strength perpendicular to grain. Initiation and propagation of cracks markedly decrease the load-carrying capacity of a beam with a hole with respect to a beam without a hole. The use of plywood or screw reinforcement can recover the full capacity of the beam. Crack initiation and propagation in timber is a challenging issue that requires a good numerical model for an accurate prediction. Analysis methods such as linear elastic fracture mechanics (LEFM) have previously been used to predict the failure load of beams with holes with initial and iteratively extended crack length. In this paper, cohesive elements with traction-separation behavior are used for the modeling of the fracture layer in laminated veneer lumber (LVL) beams with holes. In this case, the crack can propagate in the timber as the applied load increases. The model was calibrated on experimental tests carried out at the University of Canterbury, New Zealand, on LVL beams with holes, with and without plywood and screw reinforcement. The model shows great potential for predicting the load-carrying capacity of the timber beams with holes. Cohesive elements can be effectively used to investigate timber members with notches where crack propagation can govern the failure of the member
Modelling of Laminated Veneer Lumber (LVL) beams with holes using cohesive elements
No full textOpenings are usually required in timber beams to allow services like plumbing, sewage pipes, and electrical wiring to run through. These openings can cause significant stresses perpendicular to the grain direction, which may create cracks in the timber due to the low tensile strength perpendicular to grain. Initiation and propagation of cracks markedly decrease the load-carrying capacity of a beam with a hole with respect to a beam without a hole. The use of plywood or screw reinforcement can recover the full capacity of the beam. Crack initiation and
propagation in timber is a challenging issue that requires a good numerical model for an accurate prediction. Analysis methods such as linear elastic fracture mechanics (LEFM) have previously been used to predict the failure load of beams with holes with initial and iteratively extended crack length. In this paper, cohesive elements with traction-separation behavior are used for the modeling of the fracture layer in laminated veneer lumber (LVL) beams with holes. In this case, the crack can propagate in the timber as the applied load increases. The model was calibrated on experimental tests carried out at the University of Canterbury, New Zealand, on LVL beams with holes, with and without plywood and screw reinforcement. The model shows great potential for predicting the load-carrying capacity of the timber beams
with holes. Cohesive elements can be effectively used to investigate timber members with notches where crack propagation can govern the
failure of the member
"Experimental results of fracture energy and fracture toughness of radiata pine laminated veneer lumber (LVL) in mode I (opening)"
No full textPrediction of load-carrying capacity of notched timber beams can be performed using Linear Elastic Fracture Mechanics (LEFM). However, some material properties such as fracture toughness and energy are needed for the analysis. Unfortunately, due to the complexity of the wood at the micro and macroscopic level, little and sometimes unreliable data are available.
Due to the highly anisotropic nature, wood has different fracture properties in three directions. Fortunately, not all of these values are usually required in fracture analysis because the wood tends to crack mainly in grain directions due to the low tensile strength perpendicular to grain. This consideration allows a significant reduction in the number of experiments required for the fracture properties, with considerable saving of resources.
The paper presents the results of an experimental study aimed to investigate the fracture toughness of Radiata Pine Laminated Veneer Lumber (LVL) in mode I (opening). Results are presented for the fracture toughness properties in the grain direction, and include five percentile values and Coefficient of Variation (COV). The influence of the specimen size and moisture content on the fracture toughness is also presented. Numerical analyses by use of ABAQUS software were also carried out and compared with the experimental tests showing good agreement. Obtained experimental results are in the range of experimental values found in literature for wood
Effect of hole location on the load-carrying capacity of laminated veneer lumber (LVL) beams
No full textPredicting load-carrying capacity of timber beams with holes requires a model capable of accounting for the microscopic material behaviour that influences crack initiation and propagation. The complex stress distribution around the periphery of a hole causes additional tension perpendicular to grain stresses which can change the failure mode of the beam. This situation can also be affected with a change of hole location within the beam depth because stress intensity factor will be increased by tensile stresses and decreased by compressive stresses. This is not an unlikely situation as services often have to pass through beams at different depths. This paper investigates the effect of changing the hole location through the depth of Laminated Veneer Lumbers (LVL) beams utilising an experimental and numerical investigation. Experimental tests to failure of LVL beams and numerical simulations using finite element methods have shown that for a hole eccentricity of less than 20% of the beam depth, the load-carrying capacity of the beam did not change significantly. The numerical method showed that for the three-point loading condition the hole location along the beam length did not affect the failure load of beam as long as the hole was located at a distance of at least the beam depth from the supports and from the concentrated load. For uniformly distributed loading, a linearly decreasing stress intensity factor from the support to mid-span was exhibited, showing an increase in load-carrying capacity as the opening approached mid-span
"Design of reinforcement around holes in laminated veneer lumber (LVL) beams"
No full textMany practical situations require holes in timber beams. When the hole is large
relative to the depth, the failure of the beam is governed by crack initiation and propagation around the hole. Cracking of a timber beam decreases the capacity of the beam considerably. This paper presents a method for designing the reinforcement around holes in Laminate Veneer Lumber (LVL)
beams so as to recover their full flexural capacity. The design procedure is complemented by a worked example where all verifications are discussed with great detail
Analytical cracking load estimation of Laminated Veneer Lumber (LVL) beams with holes
No full textPredicting the load-carrying capacity of timber beams with holes cannot be performed by usual analysis methods if the failure of the beam is governed by the crack
initiation and propagation around the hole at low load
levels. Predicting the cracking load is an important design issue because it corresponds to the load-carrying capacity of the timber beam before the crack propagation. One of the models that can be used for the fracture formulation is
that of a beam on elastic foundation. In this model a part of the beam is assumed to follow the conditions of beam with elastic foundation which has spring stiffness equal to the fracture properties of the material in the crack surface. Based on beam on elastic foundation model, the cracking load prediction is the target of the paper. Some closed form
solutions for the beam with hole are presented. The formulation has been derived for two cases of pure shear and pure bending moment. Finally a semi-empirical formulation for combination of shear and bending moment in the section is presented. The model predictions are compared with the results of an experimental program showing good correlation. The analytical model can therefore be proposed for future revisions of codes of practice such as the Eurocode 5
"Design of reinforcement around holes in laminated veneer lumber (LVL) beams"
No full textMany practical situations require holes in timber beams. When the hole is large relative to the depth, the failure of the beam is governed by crack initiation and propagation around the hole. Cracking of a timber beam decreases the capacity
of the beam considerably. This paper presents a method for designing the reinforcement around holes in Laminated Veneer Lumber (LVL) beams so as to recover their full flexural capacity. The design procedure is complemented by two worked examples where all verifications are discussed in detail
"Numerical investigation of the load carrying capacity of laminated veneer lumber (LVL) joists with holes"
No full text"Design of reinforcement around holes in laminated veneer lumber (LVL) beams"
No full textMany practical situations require holes in timber beams. When the hole is large relative to the depth, the failure of the beam is governed by crack initiation and propagation around the hole. Cracking of a timber beam decreases the capacity
of the beam considerably. This paper presents a method for designing the reinforcement around holes in Laminated Veneer Lumber (LVL) beams so as to recover their full flexural capacity. The design procedure is complemented by two worked examples where all verifications are discussed in detail
“Tension perpendicular to grain strength of wood, laminated veneer lumber (LVL), and cross-banded LVL (CBLVL).”
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