Summary of Webinar 15: Scott Smith, Southern Cross University, Australia

00:00:00 - 00:50:00

Scott Smith from Southern Cross University in Australia discusses the potential of using FRP (Fiber Reinforced Polymer) to enhance the capacity of timber structures, particularly with regard to historical timber structures that require rehabilitation. The suitability of different types of timber and factors such as moisture content, direction of grain, density, and natural growth characteristics are important considerations when selecting a species of timber. Smith presented various testing procedures for FRP reinforcement methods, such as externally bonded and near-surface mounted reinforcement, and the importance of measuring strain and slip between the FRP and the substrate. Finally, he discusses the need for further research and testing to develop reliable models for FRP-to-timber interfaces.

• 00:00:00 In this section, Scott Smith, a professor in Southern Cross University in Australia, discusses his experiences and research projects involving the application of FRP composites with timber, particularly the use of Anchorage devices to enhance the capacity of the bonded interface between the FRP and the concrete to increase strength and deformability. He also talks about his interest in timber engineering and historical timber structures, which led him to explore the possibility of using FRP to retrofit and repair timber structures. He concludes by proposing a bond strength model that can be used to design beams or beam-to-event connections for timber structures and discussing the motivation behind his project on strengthening timber frames to prepare for seismic attacks.
• 00:05:00 In this section, Scott Smith from Southern Cross University discusses the historical dominance of timber as a construction material in Australia and the application of FRP (fiber-reinforced polymer) to rehabilitate historical structures like bridges. Smith highlights an Italian design guideline from 2007 which provides techniques for applying FRP to timber, including externally bonded plates and near-surface mounted FRP. Smith also notes that the application of FRP to timber has received limited research attention compared to its use in concrete and metal, making it a promising area for fundamental research.
• 00:10:00 In this section, the speaker discusses the suitability of timber as a construction material and the factors that are most important when working with it. He explains that timber is a widely used construction material, and has been used much longer than concrete. The speaker outlines the different types of timber and discusses the importance of factors such as moisture content, direction of the grain, density, and natural growth characteristics when selecting a species of timber. He also presents a table for the design of timber based on its grade and highlights the differences in strength and elastic modulus between timber, concrete and steel. Finally, the speaker briefly touches on FRP as a brittle material.
• 00:15:00 In this section, the speaker discusses the various parameters that affect the behavior and strength of FRP (Fiber Reinforced Polymer) when applied to timber. The research questions that should be asked while applying FRP to timber include the type of timber, its properties like species, density, and moisture content, the shape and type of FRP and resin used, elastic modulus, and interior geometry, among others. The durability and changing moisture conditions of timber should also be considered as it can lead to dimensional changes and stresses. To answer these questions, a series of tests on joints is necessary, and the speaker presents the findings of their tests, isolating variables such as the type of FRP, bond length, and species.
• 00:20:00 In this section, Scott Smith of Southern Cross University in Australia discusses the properties and testing procedures for externally bonded and NSM (near-surface mounted) FRP (fiber reinforced polymer) reinforcement methods. He presents the typical test setups, including a single-lap shear test on a timber block for external bonding and a saw cut with an embedded DF map be played for NSM reinforcement. Smith explains the importance of measuring strain and slip between the FRP and the substrate, as well as the elastic modulus and compressive strength of the substrate material, which are necessary for determining the effectiveness of the FRP reinforcement.
• 00:25:00 In this section, Scott Smith of Southern Cross University in Australia discusses the testing of epoxies for FRP systems strengthening concrete and masonry. The study involved six types of epoxies, three orphan types of seeker, and one type of Erudite. The tests showed that the epoxies that were commonly used in FRP systems were the most effective, and the elongation of the epoxies increased as the product became more ductile. The preferred failure mode is timber to adhesive, as it allows for the strength of the bond at the interface to be related to the strength of the timber. The study also observed adhesive rupture in the EB, which was caused by the epoxy not being fully impregnated into the fibers, so the viscosity of the epoxy used is important.
• 00:30:00 In this section, Scott Smith discusses the difference between side A and side B of timber sections and the bond lengths required for effective joint strength. He notes that the dominant failure mode is typically between the growth rings of side A, while failures are more predictable and consistent for side B. He also presents six different types of adhesive and their efficiency for bonding to both hardwood and softwood. Overall, Smith's research suggests that the 420 epoxy is the most effective adhesive for hardwood, while the failure mode for softwood is predominantly an attempt between the growth rings.
• 00:35:00 In this section, Scott Smith of Southern Cross University in Australia discusses the behavior of concrete, timber, and FRP in joint applications. He notes that, as bond length shortens, the behavior of the materials changes and must be accounted for in constitutive laws used for numerical modeling. Smith also presents experimental data showing the efficiency of NSM and EB joints, as well as a model for predicting the strength of these joints based on plate thickness, elastic modulus, and bond type. Finally, he explains how these models were calibrated using test results.
• 00:40:00 In this section, Dr. Scott Smith of Southern Cross University in Australia discusses the development of frameworks for researchers to build their databases and pattern models for materials like concrete, steel, and masonry. Plus, we can already design a timber beam using a standard sectional analysis using a linear elastic and yielded models. Additionally, FRP application to frames, specifically moment resisting frames, are explored in this research project, aiming to develop strengthening and repair techniques for timber joints with steel downs for seismic attack resistance. After conducting various FRP configurations around single bolt test of moment resisting timber joints, they calibrated hysteresis modeling by nonlinear static analysis and nonlinear time history analysis. They then tested different techniques like injecting locally crushed bolt holes with epoxy repair, externally bonded FRPs, or near-certain and McAfee assemblies, looking at how the FRP is arranged in horizontal or longitudinal direction to fully support the bolt.
• 00:45:00 In this section of the webinar, Scott Smith from Southern Cross University presented on their research on the behavior of fiber-reinforced polymers (FRP) for timber structures. The research team tested displacement controlled moving beams retrofitted with externally bonded or near surface mounted FRP and repaired damaged joints with epoxy. The failure modes showed local yielding and crushing of the timber and the team reinstated damaged joints by gluing in epoxy wedges. The team found the most effective seismic retrofitting application to be where the FRP is perpendicular to the road direction. The presentation concluded by highlighting the opportunity for further research in this underdeveloped field.
• 00:50:00 In this section, the speaker discusses the challenges of using FRP materials in timber structures and the need for further research and testing to develop reliable models. He explains that timber is a variable material, making it difficult to work with, and that researchers need to compile a database of test data to develop and calibrate models for FRP-to-timber interfaces. While there are similarities in techniques used for FRP-concrete and FRP-timber, the behaviors of these two materials are different, requiring further research. The speaker references his and others' ongoing long-term research on this topic and encourages anyone with questions or information to contact him.