This study aims to develop an improved understanding of the interfacial bond behavior of softwood glulam joints with bonded-in threaded steel rod. A total of 39 glulam joints with bonded-in single-threaded steel rods were tested to failure in the pull-pull configuration. The test results were presented in term of failure modes, load-relative movement response, pullout strength, and the corresponding slip. The distributions of bonded-in rod axial strain, interfacial bond stress, and relative movement were also analyzed to evaluate the local bond stress– relative movement response in the bond line. The results confirmed that the bond-relative movement response is dependent on the locations along the anchorage length, and the bond-relative movement responses located near both the loaded end and the anchorage end were observed to be stiffer than those at other locations. Finally, the predictions for the load capacity of the glulam joints with bonded-in threaded steel rod were carried out based on several existing empirical formulas.
This paper describes the test program of glued-in deformed bar timber joint conducted in pull-pull configuration, which aims to investigate the bond behavior of glued-in deformed bar systems in glulam. The varying parameter are bar slenderness ratio and glue-line thickness. In order to obtain the bond stress distribution along the anchorage length, special deformed bar with strain gauges attached internally were designed. Test results show that both the bar slenderness ratio and glue-line thickness have obvious influence on withdrawal strength and bond behavior of glued-in deformed bar joint. Failure modes of specimens are also analyzed in this paper. Ductile failure modes of glued-in rod timber joint could be realized with reasonable design.
This paper presents an experimental evaluation of the fire resistance of glued-in rod timber joints using epoxy resin, with and without modification. A heat-resistant modified resin was designed by adding inorganic additives into the epoxy resin, aiming to improve the heat resistance. Joints that were made using the modified epoxy resin at room temperature showed a bearing capacity comparable to those with commercial epoxy resin. Twenty-one joint specimens with the modified epoxy resin and six with a commercial epoxy resin were tested in a fire furnace to evaluate the fire resistance. The main failure mode was the pull-out of the rod, which is typical in fire tests of this type of joints. As to the effects of the test parameters, this study considered the effects of adhesive types, sectional sizes, stress levels, and fireproof coatings. The test results showed that the fire resistance period of a joint can be evidently improved by modifying the resin and using the fireproof coating, as the improvements reached 73% and 35%, respectively, compared with the joint specimens with commercial epoxy resin. It was also found that, for all specimens, the fire resistance period decreased with an increase in the stress level and increased with an increase in the sectional sizes.
This paper presents the results of long-term experiments performed on three timber-concrete composite (TCC) beams. An innovative fabricated steel plate connection system, which consists of screws and steel plates embedded in concrete slabs, was adopted in the TCC beam specimens. The adopted shear connection can provide dry-type connection for TCC beams. Steel plates were embedded in concrete slabs while the concrete slab was constructed in factories. The timber beam and concrete slab can be assembled together using screws at the construction site. In this experimental programme, the beam specimens were subjected to constant loading for 613 days in indoor uncontrolled environments. The influence of long-term loading levels and the number of shear connections on the long-term performance of TCC beams was investigated and discussed. The mid-span deflection, timber strain, and interface relative slip at the positions of both connections and beam-ends were recorded throughout the long-term tests. It was found the long-term deflection of the TCC beam increased by approximately 60% while the long-term loads were doubled. Under the influence of the variable temperature and humidity, the TCC specimens with 8 shear connections showed slighter fluctuations compared with the TCC beam with 6 shear connections. In the 613-day observation period, the maximum deflection increment recorded was 6.56 mm for the specimen with eight shear connections and 20% loading level. A rheological model consisting of two Kelvin bodies was employed to fit the curves of creep coefficients. The final deflections predicted of all specimens at the end of 50-year service life were 2.1~2.7 times the initial deflections caused by the applied loads. All beam specimens showed relative small increments in mid-span deflection, strain and relative slip over time without any degradations, demonstrating the excellent long-term performance of TCC beams using the innovative steel plate connection system, which is also easily fabricated.
IASS WORKING GROUPS 12 + 18 International Colloquium 2015
April 10-13, 2015, Tokyo, Japan
This paper summarizes an experimental investigation on several innovative reinforcing techniques for the “Single Large Diameter Dowel Connection”, SLDDC in timber truss structures. Besides lateral reinforcing or prestressing, also steel plates glued on two sides of the glulam specimens were used as reinforcing measure. To study the efficiency of these techniques, 15 full-scale quasi-static tensile tests on glulam members with a SLDDC on either ends of each member were performed. It was found that the reinforcement significantly enhanced the bearing capacity of the SLDDCs. All of the reinforcing techniques showed a satisfactory efficiency, preventing splitting of wood. Moreover, most of the specimens remains showed a remarkable post failure strength.
This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure of glued laminated timber (glulam) beams using fiber reinforced polymer (FRP) and steel materials. A series of four-point bending tests were conducted till failure on both unreinforced and reinforced Douglas fir glulam beams in a simply-supported scheme. The focus of this research was to evaluate the effects of reinforcing materials, reinforcement ratio and arrangement on the flexural behavior. Test results showed that the flexural capacity, flexural global stiffness and timber tensile strain at failure were all improved considerably for reinforced timber beams when compared to the unreinforced control beams, in which the average improvement reached 56.3%, 27.5% and 49.4%, respectively. On the bases of the experimental results, a theoretical model was proposed to predict the flexural capacity and flexural stiffness of the reinforced timber beams. Most of the differences between theoretical and experimental results for both flexural capacity and flexural stiffness were within 10.0%, which showed a high accuracy of the proposed model. Subsequently a parametric analysis, which includes the axial stiffness ratio of reinforcement to timber, the relative location of tensile reinforcement, and the strength ratio of reinforced timber between flexural tension and compression, was undertaken to investigate the effects of the influential factors for both flexural capacity and flexural stiffness.
Glued-in rod is a type of effective connector for timber structures. In the last decades, considerable researches have been conducted on the bond behavior between timber and glued-in rod experimentally and theoretically. This paper presents the numerical simulation on the bond behavior of glulam joints with glued-in steel rod. Glulam is modelled as the orthotropic elasto-plastic material. Adhesive and steel rods are modelled as isotropic materials. Non-linear spring element was employed to simulate the local bond stress-slip relations at different locations along the bonded length. The numerical results indicate that non-linear spring element can be used to simulate the bond behavior of the glued-in steel rod glulam joints effectively. Moreover, The numerical results obtained by considering the local bond relations at different locations is in a better agreement with the experimental results than that obtained based on the bond stress-slip relation at loaded end.
This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure of glued laminated timber (glulam) beams using bonded-in carbon fiber reinforced polymer (CFRP) bars. A series of four-point bending tests were conducted till failure on unreinforced, passively reinforced and prestressed Douglas fir glulam beams in a simply-supported scheme. The focus of this research was to evaluate the reinforcing efficiency of both passively reinforced and prestressed beams. Test results showed that the flexural capacity of the reinforced, prestressed, prestressed & reinforced (bottom prestressed and top reinforced) beams greatly increased by 64.8%, 93.3% and 131%, respectively. While the maximum improvement of the bending stiffness reached 42.0%. Another important finding was that the extreme fiber tensile strain of timber beams at failure could be remarkably increased due to the presence of the tension reinforcement, which indicated it overcomes the effects of local defects and therefore the failure mode was changed from brittle tension failure to ductile compression failure. Based on the experimental results, a theoretical model was proposed to predict the flexural capacity of unreinforced, reinforced and prestressed timber beams, which was validated by the test data.