An Experimental and Analytical Study on the Bending Performance of CFRP-Reinforced Glulam Beams

The fiber-reinforced polymer is one kind of composite material made of synthetic fiber and resin, which has attracted research interests for the reinforcement of timber elements. In this study, 18 glued-laminated (glulam) beams, unreinforced or reinforced with internally embedded carbon fiber–reinforced polymer (CFRP) sheets, were tested under four-point bending loads. For the reinforced glulam beams, the influences of the strengthening ratio, the modulus of elasticity of the CFRP, and the CFRP arrangement on their bending performance were experimentally investigated. Subsequently, a finite element model developed was verified with the experimental results; furthermore, a general theoretical model considering the typical tensile failure mode was employed to predict the bending–resisting capacities of the reinforced glulam beams. It is found that the reinforced glulam beams are featured with relatively ductile bending failure, compared to the brittle tensile failure of the unreinforced ones. Besides, the compressive properties of the uppermost grain of the glulam can be fully utilized in the CFRP-reinforced beams. For the beams with a 0.040% strengthening ratio, the bending–resisting capacity and the maximum deflection can be enhanced approximately by 6.51 and 12.02%, respectively. The difference between the experimental results and the numerical results and that between the experimental results and analytical results are within 20 and 10%, respectively.

Distribution of load effects and reliability of reinforced concrete frames: intact and with columns removed

abstract: The design of reinforced concrete (RC) frames is made on a member-by-member basis. Similarly, in the literature, the reliability of RC beams and columns is often studied in isolation from the rest of the structure. Yet, in the construction of regular frames, symmetry and regularity are often exploited, resulting in the same design for each element type. This is despite of different load effects on different parts of the structure, which leads to significant variations in the failure probability of the elements. Hence, in this paper, we investigate the reliability of members and the distribution of load effects in regular RC frame buildings, considering intact and column loss cases, where symmetry is lost. Results show that the ratios of normal-to-bending loads change significantly along building height, and this has a significant impact on reliability of individual columns.

SHAFT LOADS ON AZIMUTH PROPULSORS IN OBLIQUE FLOW AND WAVES

A range of model experiments have been carried out in calm water and waves for an oil spill vessel model with twin tractor azimuth thrusters at different heading angles and advance coefficients in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Propeller shaft bending loads have been measured using a shaft dynamometer capable of measuring all shaft side force and bending moment components as well as propeller torque and thrust. The results include the loads on the propeller shaft with and without the presence of a ship hull model at the same heading angles and advance velocities in order to study the wake influence from the ship hull on the hydrodynamic loads. Results show that the ship hull wake has a much stronger effect on the propeller loads when the propeller is azimuthed outward from the ship hull centreline than inward. Measurements from the experiments in waves are also presented for the same thruster model in a straight-line course for both the head and following sea states under different wave conditions. Larger bending loads are found in head sea conditions compared with the following sea conditions. Generally it is found that the shaft bending loads and lateral forces are quite large, which is important to consider in the mechanical design layout and for dimensioning of components.

Ex vivo study of the intradiskal pressure in the C6-7 intervertebral disk after experimental destabilization and distraction-fusion of the C5-C6 vertebrae in canine cadaveric specimens

OBJECTIVE To evaluate intradiskal pressure (IDP) in the C6-7 intervertebral disk (IVD) after destabilization and distraction-fusion of the C5-C6 vertebrae. SAMPLE 7 cadaveric C4-T1 vertebral specimens with no evidence of IVD disease from large-breed dogs. PROCEDURES Specimens were mounted in a custom-made 6 degrees of freedom spinal loading simulator so the C5-C6 and C6-C7 segments remained mobile. One specimen remained untreated and was used to assess the repeatability of the IDP measurement protocol. Six specimens underwent 3 sequential configurations (untreated, partial diskectomy of the C5-6 IVD, and distraction-fusion of the C5-C6 vertebrae). Each construct was biomechanically tested under neutral, flexion, extension, and right-lateral bending loads. The IDP was measured with a pressure transducer inserted into the C6-7 IVD and compared between the nucleus pulposus and annulus fibrosus and across all 3 constructs and 4 loads. RESULTS Compared with untreated constructs, partial diskectomy and distraction-fusion of C5-C6 decreased the mean ± SD IDP in the C6-7 IVD by 1.3 ± 1.3% and 0.8 ± 1.3%, respectively. During motion, the IDP remained fairly constant in the annulus fibrosus and increased by 3.8 ± 3.0% in the nucleus pulposus. The increase in IDP within the nucleus pulposus was numerically greatest during flexion but did not differ significantly among loading conditions. CONCLUSIONS AND CLINICAL RELEVANCE Distraction-fusion of C5-C6 did not significantly alter the IDP of healthy C6-7 IVDs. Effects of vertebral distraction-fusion on the IDP of adjacent IVDs with degenerative changes, such as those in dogs with caudal cervical spondylomyelopathy, warrant investigation.

Predicting interlaminar damage behaviour of fibre-metal laminates containing adhesive joints under bending loads

This study includes experimental and numerical investigations on fibre-metal laminate structures containing adhesive joints under static bending loads. Experimental tests were carried out on Glare® 4B specimens manufactured in-house and containing doubler joint features. Numerical analyses were performed using Abaqus software including damage in the glass fibre reinforced polymer layers, ductile damage in the resin pockets (FM94 epoxy) and plasticity in the metal layers. A new cohesive zone model coupling friction and interfacial shear under through-thickness compressive stress has been developed to simulate delamination initiation and growth at the metal/fibre interfaces with the adhesive joint under flexural loading. This model is implemented through a user-defined VUMAT subroutine in the Abaqus/Explicit software and includes two main approaches, firstly, combining friction and interfacial shear stresses created in the interlaminar layers of the fibre-metal laminate as a result of through-thickness stresses and secondly, considering elastic-plastic damage behaviour using a new cohesive zone model based on the trapezoidal law (which provides more accurate results for the simulation of toughened epoxy matrices than the commonly used bilinear cohesive zone model). Numerical results have been validated against experimental data from 4-point bending tests and a good correlation observed with respect to both crack initiation and evolution. Delamination and shear failure were noted to be the predominant failure modes under bending stresses as expected. This is due to the higher mode-II stresses introduced during bending which cause different damage evolution behaviour to that seen for axial stresses. Finite element results revealed that both friction and shear strength parameters generated from through-thickness compression stresses have a significant effect in predicting damage in fibre-metal laminate structures under this type of loading.

The Effect of Boundary Conditions and Stacking Sequence on the Nonlinear Behavior of Laminated Composite Plates in Bending

This paper presents an effectively numerical approach based on quadrilateral isoperimetric element. Indeed, the Von-Karman’s large deflection theory and the first-order shear deformation theory (FSDT) are also used in the formulation of the element to formulate the geometrically nonlinearity analysis. The nonlinear finite element code has been developed by using Matlab. Therefore, the governing nonlinear equations obtained are solved using Newton–Raphson iterative technique. Finally, the results obtained are compared with those available in the literature and with those obtained by ABAQUS. It has been found that the present approach is accurate and efficient to predict the nonlinear behavior of laminated composite plates under bending loads. Moreover, the effects of the boundary conditions and the stacking sequence on the nonlinear deflection of the plate are treated.

Glulam beams: Performance of PVA and PUR adhesives on bending strengths of locally selected Nigerian timber species

The applicability of structural timber to construction is due to its desirable qualities such as lightweight, aesthetics and eco-friendliness. However, continuous use of timber for structural purposes comes with the challenge posed by the anisotropic nature of various timber species. Advanced societies have developed and modified their sawn timber species in form of glue-laminated structural members such as beams, columns, joist etc. Nigeria timber species are yet to be fully explored along glued-laminated beams production. This paper assesses the suitability of three selected Nigerian timber species namely; Gmelina Arborea (ML), Terminalia superba (AF) and Pycnanthus angolensis (AK) for production of glued-laminated (glulam) beams. They are locally known respectively as Melina (ML), Afara (AF) and Akomu (AK). The applicability and glue-ability of the glues and their ultimate effect on the flexural strength were investigated through the use of two different types of glue components namely; polyvinyl acetate (PVA) and polyurethane (PUR) glue. The physical properties of the timber species such as moisture content (MC) and densities were determined using BS EN 408. The beams produced which are 1680mm by 150mm by 120mm in dimension were subjected to two points loading system to determine their flexural strengths and failure loads in accordance with ASTM D-198. The flexural strengths results indicated that Pycnanthus angolensis offered most resistance to bending loads with an average flexural strength value of 16.04N/mm2 when PUR glue was used and 13.04N/mm2 when PVA glue was used. The ANOVA result showed that glue types have significant effect on the flexural strength at confidence level of 95%. It was concluded that Pycnanthus angolensis is most suitable for structural applications. PUR is considered the better glue in terms of strength and glue-ability while PVA glue is considered better in terms of workability and applicability based on almost perfect glue line integrity achieved.