AVALIAÇÃO DA INTEGRIDADE DE ESTRUTURAS DE MADEIRA LAMELADA-COLADA EM SERVIÇO

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Evaluation of glue line shear strength of laminated timber structures using block and core type specimens

Publication . Gaspar, Florindo; Cruz, Helena; Gomes, Augusto

Monitoring and evaluation of glued laminated timber structures in service is essential to warrant its integ rity, where non-destructive techniques play an important role. This paper describes the results obtained on glued laminated timber beams of maritime pine, with and without preservative treatment, and of spruce, exposed to natural outdoor environment as well as to artificial weathering. The assessment of glue lines’ shear strength was investigated through the extraction and testing of cores parallel and per pendicular to the glued lines and block shear specimens with 50 mm×50 mm and 20 mm×20 mm shear area. The results highlight the different performances of the various types of specimens tested, showing that the measured shear strength depends on the specimen size and that the size effect depends on the material strength giving a decreasing modification factor with the increase of strength in opposi tion to the constant factor suggested by standard EN 14080. They also show that shear testing of cores drilled perpen dicular to the glued joints may be a promising tool in the assessment of glulam structures on site.

2018Journal article

Open access

Modeling the influence of delamination on the mechanical performance of straight glued laminated timber beams

Publication . Gaspar, Florindo; Cruz, Helena; Gomes, Augusto

Delamination at the glue lines is a key factor to take into account when assessing glued laminated timber members in service. In order to gain a more objective and wide knowledge about the importance of delamination in relation to its type and extension, a numerical study was developed. Finite element modeling (FEM) was used to evaluate the influence of delamination – near the surface, on the vertical faces and ends – on the mechanic performance of straight glued laminated timber beams. The FEM was validated by comparing stresses and deformations obtained with the model and with the application of the beam theory, showing satisfactory results. Results show that when delamination is non-symmetric regarding the member’s cross section, it can cause the member’s lateral instability, thus increasing its stresses and deformations. Delamination is not a problem when it occurs in members or member areas with low shear stresses, particularly when it is symmetric and does not reach the whole width of the beam. The stresses corresponding to the bending or deformation limit-states get near the elastic limit only for very important delamination. Moreover, delamination depth higher than 60% of the cross section width may be regarded as a turn point beyond which the structural integrity may be at risk.

2015-11Journal article

Open access

Fatigue Crack Growth in Maraging Steel Obtained by Selective Laser Melting

Publication . Capela, Carlos; Lima Santos, Luís; Antunes, Fernando; Ferreira, José; Costa, José; Jesus, Joel; Prates, Pedro

The fatigue crack growth properties of G20Mn5QT cast steel and corresponding butt welds, using compact tension specimens, were monitored and investigated via acoustic emission (AE) techniques. Fatigue crack growth is a combination of cyclic plastic deformations before the crack tip, tensile crack fractures, and shear crack fractures. The cyclic plastic deformations release the maximum amount of energy, which accounts for half of the total energy, and the second-largest number of AE signals, which are of the continuous-wave type. The tensile crack fractures release the second-largest amount of energy and the largest number of AE signals, which are of the burst-wave type. The shear crack fractures release the least amount of energy and the lowest number of AE signals, which are similar to the burst type, albeit with a relatively longer rise time and duration. Crack tip advancement can be regarded as a discontinuous process. The critical area before the crack tip brittlely ruptures when the fatigue damage caused by cyclic plastic deformations reaches critical status. The ruptures produce a large number of tensile crack fractures and rare shear crack fractures. Through fractography observation, the shear crack fractures occur probabilistically around defects caused by casting or welding, which lead to stress and strain in the local complex.

2019-10-18Journal article

Open access