Basalt FRP Spike Repairing of Wood Beams
This article describes aspects within an experimental program aimed at improving the structural performance of cracked solid fir-wood beams repaired with Basalt Fiber Reinforced Polymer (BFRP) spikes. Fir wood is characterized by its low density, low compression strength, and high level of defects, and it is likely to distort when dried and tends to fail under tension due to the presence of cracks, knots, or grain deviation. The proposed repair technique consists of the insertion of BFRP spikes into timber beams to restore the continuity of cracked sections. The experimental efforts deal with the evaluation of the bending strength and deformation properties of 24 timber beams. An artificially simulated cracking was produced by cutting the wood beams in half or notching. The obtained results for the repaired beams were compared with those of solid undamaged and damaged beams, and increases of beam capacity, bending strength and of modulus of elasticity, and analysis of failure modes was discussed. For notched beams, the application of the BFRP spikes was able to restore the original bending capacity of undamaged beams, while only a small part of the original capacity was recovered for beams that were cut in half.
Locally reinforced timber joints with expanded tube fasteners
The study presented focuses on the development of a novel timber joint. Traditional timber joints with mechanical fasteners, particular dowel type fasteners, such as bolts exhibit a low strength and an unreliable stiffness and ductility caused by the presence of hole clearance and the unpredictable splitting of timber. The novel joint tackles all of these shortcomings. Local reinforcement glued to the timber members in the jointed area prevents unexpected splitting and results in the enhancement of the strength. By choosing a steel (gas) tube instead of a solid fastener, that fit in an over-sized hole, and by expanding the diameter after assembly of the joint, easy assembly and no hole clearance is insured. Due to the ductile behaviour of the reinforcement and the plastic deformation capacity of the tube the ductility of the joint is guaranteed. To assess the performance of this joints a comprehensive study was performed and reported in this article. Summarising the experimental results, it can be stated that densified veneer (ply)wood is an excellent mate.rial to reinforce the timber joint. It possesses a high embedding strength and stiffness compared to softwood and is able to sustain the high concentrated loads imposed by the tubes. It is demonstrated that the new joint possess a reliable and high strength and stiffness capacity in monotonic loading. When certain requirements are fulfilled the joint shows a superior behaviour in cyclic loading. Design examples show that when used in portal frames a considerable amount of timber can be saved, up to about 40%, compared to joints with traditional dowel type fasteners, without a loss of safety.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.