Modelling of Glulam beams pre-stressed by compressed wood

Finite element models were, in the first time, developed to simulate the pre-stressing behaviour of Glulam beams with insertion of compressed wood blocks, which were further used to simulate the structural behaviour of the pre-stressed beams subjected to subsequent destructive bending. Here, both the Glulam and compressed wood were modelled as orthotropic elasto-viscoplastic materials. The moisture-dependent, including spring back, swelling of the compressed wood block and the creep of the Glulam were considered in the modelling. The models developed were validated against the corresponding experimental results, with reasonably good correlation in terms of the free swelling, the precamber, initial stress state of the Glulam beams reinforced and load-deflection relationships. With validated models, further studies were then undertaken to investigate effects of the thickness, depth and spacing of compressed wood blocks on the precamber, initial bending stiffness and ultimate load carrying capacity of the beams pre-stressed. The results indicate that there are significant enhancements on the precamber (up to 1/288 of the deflection/span ratio), the initial bending stiffness (up to 23.8%) and the ultimate load carrying capacity (up to 10.4%

Lateral impact response of end-plate beam-column connections

The behaviour of different steel beam to column connections has been studied intensively against static and seismic loading regimes. However, there is a lack of knowledge on the response of such connections against impact and blast. In order to close this gap, the most common connections with partially depth end plate (PDEPCs), as a simple connection, and flush plate (FPCs), as a moment resisting connection, were investigated under both quasi-static and impact loads. Here, eight specimens were tested under those loading conditions with different locations. 3 D finite element models were then developed and validated against the corresponding experimental results. Full range analyses of the connection responses under both loading regimes are then carried out using the validated FE models to examine the internal forces of the connections. Finally, the results of full analyses under both loading regimes were compared and dynamic increase factors (DIF) were proposed to assist predicting the impact response of these types of connections using the static analysis. The results showed that failure modes under both loading regimes were similar, but with the larger fracture on the PDEPC under quasi-static load than that under lateral impact. The DIFs were found to be between 1.02 and 1.21, 1.03 and 1.36 and 1.22 and 1.45 based on the bolt tensile strength, axial resistance and bending resistance of the connections, respectively. However, if based on the energy approach, the range of DIFs was recorded between 1.25 and 1.38 using the experimental results and between 1.19 and 1.34 using the finite element analysis results

The impact behavior of composites and sandwich structures

For many years there has been considerable concern regarding the response of composite materials and lightweight sandwich structures to localized impact loading. Extensive testing has shown that very low impact energies are capable of generating significant damage over a large region. The first part of this paper reviews some of the key studies in this area, focusing primarily on experimental attempts to characterize damage initiation and propagation in these structures. The second section of this paper reviews the attempts to use numerical techniques to model the impact response of composites and sandwich structures

The analysis of the ultimate blast failure modes in fibre metal laminates

Finite element modelling has been applied to simulate various failure modes in fibre metal laminate (FML) panels under localized high intensity blast loading. A relatively simple material model, based on continuum damage mechanics, has been proposed to describe the constitutive response of the composite material in the FMLs. Simulations of the blast response of FMLs with various stacking configurations has been carried out, capturing both perforation and non-perforation failure modes. Blast loading was modelled by a pressure function applied on the front face of the FML panel. The definition of the pressure function accounts for both the temporal as well as the spatial distribution of the blast. The capability of the models has been assessed by comparing the predictions associated with both low and high intensity blast cases with published experimental data. Good qualitative and quantitative agreement has been observed for lay-ups with similar proportions of aluminium and composite. It is believed that the models can be employed for use in parametric studies that would facilitate the adoption of FMLs in wider engineering design

Damage initiation in composite materials under off-centre impact loading

© 2018 Elsevier Ltd The effect of off-centre impact loading on damage initiation in a woven glass fibre reinforced epoxy resin was studied experimentally. Low velocity impact tests were conducted, in which the incident impact energy was increased until damage was observed in the laminates. It was shown that multiple impacts, with increasing incident energy at the same location, did not greatly influence the critical force for damage initiation, Pcrit. Subsequent testing on a range of panel sizes showed that the critical force is highest for central impacts, decreasing slowly as the impact location moves towards the boundary. It was also shown that, for off-centre impact loading, Pcrit, follows a t3/2(t = laminate thickness) relationship that has previously been established for central impact. The slope of the plot of Pcritversus t3/2decreases as the impact location moves away from a central location, suggesting that the effective interlaminar shear stress also decreases with increasing offset. Tests at energies well above the damage threshold confirmed that off-centre impact is more serious than central impact loading. An energy-balance model was used to predict the off-centre impact response of the panels. Agreement between the energy-balance model and the measured impact response was good at energies that did not generate significant damage. Finally, it is suggested that the energy-balance model can also be used to predict a lower bound on the damage threshold energy in composite plates