This paper offers a detailed, quantitative and exhaustive experimental comparison in terms of mechanical properties of three different layouts of carbon composite materials (CFRP) used to strengthen existing old timber beams highly affected by diverse natural defects and biological attacks, testing the use of pultruded laminate attached on the tension side of the element (LR), CFRP fabrics totally U-shape wrapping the timber element (UR), and the combined use of both reinforcement solutions (UR-P). Moreover, unidirectional and bidirectional fabrics were considered and compared. Timber elements used for the experimental program were extracted from a recent rehabilitation of the roof of the current Faculty of Law building, University of Granada (Spain), catalogued as a historical edifice. Experimental results from bending tests show that in all cases reinforcement provides a clear improvement in terms of bending capacity and stiffness as compared with the control specimens (without reinforcement). However, improvements in terms of ductility differ considerably depending on the kind of layout.

This paper proposes the monitoring of old timber beams with natural defects (knots, grain deviations, fissures and wanes), reinforced using carbon composite materials (CFRP). Reinforcement consisted of the combination of a CFRP laminate strip and a carbon fabric discontinuously wrapping the timber element. Monitoring considered the use and comparison of two types of sensors: strain gauges and multi-resonant acoustic emission (AE) sensors. Results demonstrate that: (1) the mechanical behavior of the beams can be considerably improved by means of the use of CFRP (160% in bending load capacity and 90% in stiffness); (2) Acoustic emission sensors provide comparable information to strain gauges. This fact points to the great potential of AE techniques for in-service damage assessment in real wood structures.

Due to the strong demand for wood, and the need to reduce the carbon footprint in construction, fast-growing low-graded planted species like poplar are promising wood for the supply chain in the context of engineered wood products, EWPs. Finger joints constitute a key technology for the manufacture of long structural elements of EWPs. Thus, evaluation of the mechanical properties of finger joints is important when designing these structural members. This paper shows the results of mechanical behaviour in tension of poplar timber of the I-214 cultivar, for specimens with and without finger joints, using experiments monitored by DIC (Digital Image Correlation) and simulated by the Finite Element Method. For moderate and intermediate loads, the samples with finger joints showed behaviour similar to those without joints. However, the presence of the fingers decreased the mechanical properties of the modulus of elasticity in the longitudinal direction anywhere from 7.7 to 23.7%; and there was a decrease of around 27.5% in tensile strength. An agreeable correlation between the DIC results and FEM simulations is obtained for the longitudinal, transversal, and shear strain fields, thus demonstrating the high potential of both methodologies.

Acoustic emission (AE) released by pine beams retrofitted with fiber reinforced plastic (FRP) and poplar planks in bending is analyzed. Basalt fabric (FB), carbon fabric (FC), and carbon pultruded laminate (LC) have been used as FRP. Experimental results and AE behavior are discussed based on an elastoplastic finite-element numerical model. The model demonstrates a strong strain concentration at the end of poplar planks, which causes high AE activity in these areas and acts as a precursor of the delamination of the poplar plank. Based on the experimental results, some AE criteria for predicting the onset of the delamination are tentatively proposed.