Glued-laminated timber arches are widely used in gymnasiums, bridges, and roof trusses. However, studies on their mechanical behaviours and design methods are still insufficient. This paper investigates the in-plane loading capacity of circular glued-laminated timber arches made of Douglas fir. Experiments were conducted on four timber-arch models with different rise-to-span ratios under concentrated loads at mid-span and quarter-point locations. The structural responses, failure modes, and loading capacity of the timber arch specimens were obtained. The results show that the timber arches presented symmetric and antisymmetric deformation under mid-point and quarter-point loading conditions, respectively. The downward shifting of the neutral axis of the cross section was observed under mid-point loading condition, which contributes to higher loading capacity compared to that under quarter-point loading condition. The loading condition significantly affects the ultimate loads and the strain distribution in the cross section. Based on the design formula in current standards for timber structures, an equivalent beam-column method was introduced to estimate the loading capacity of the laminated timber arches under vertical concentrated loads. The moment amplification factor in the formula was compared and discussed, and the value provided in the National Design Specification for Wood Construction was recommended with acceptable accuracy.
An innovative multi-layer (3 and 5) composite laminated panel (CLP) with various layups were developed using sawn lumber and structural composite lumber (SCL) to address the rolling shear and gap issues of cross laminated timber (CLT). The bending properties including apparent and effective bending stiffness, shear stiffness, moment capacities and failure modes of CLPs were evaluated by a combination of modal tests and third-point bending tests of beam specimens cut from the panels. The static bending test results showed that the apparent bending stiffness values of 3-layer and 5-layer CLPs were up to 20% and 43% higher than the corresponding values of 3-layer and 5-layer generic CLT, respectively. The bending moment capacity values of 3-layer and 5-layer CLPs were up to 37% and 87% higher than the corresponding values of 3-layer and 5-layer generic CLT, respectively. The use of SCL in transverse layers eliminated the potential rolling shear failure in CLT and increased the stiffness properties. The apparent and effective bending stiffness predicted by shear analogy method had a good agreement with corresponding values measured by bending tests and/or modal tests. The prediction of bending moment capacity using shear analogy method cannot be validated due to the rolling shear failure and tension failure modes observed in certain groups.
International Journal of Advanced Structural Engineering
Summary
This paper investigates the mechanical performance of longitudinally cracked glulam columns under eccentric compression loads. Experimental investigation was conducted to explore the influence of initial cracks on the failure modes and load bearing capacity of glulam columns. Two different crack patterns named DC and IC, and two column lengths (i.e. 600 and 1100 mm) were considered in the experiments. It was indicated that these two crack patterns reduced the capacity of slender glulam columns and the difference of failure modes was observed between glulam columns with and without initial cracks. Further, a numerical model was developed and validated by the test results. With the application of cohesive zone material model, the propagation of initial cracks could be considered in the numerical modeling. A parametric study was carried out by the verified model and the influence of crack lengths and crack locations was further investigated. From the numerical analysis, it was found that through cracks reduced the capacity of glulam columns significantly. Also, crack location impacts the capacity of glulam columns and the extent of impact relates to the slenderness ratio of the columns, while cracks with different lengths have similar influence on the capacity of columns.
This paper presents an experimental campaign conducted on the beam-to-column glulam joints combing glued-in rods and steel brackets (BCGS glulam joints) aiming to investigate the mechanical behaviour of these glulam joints under low cyclic loading. Three types of steel brackets were designed for connecting the beam and column combing with glued-in rods and to work as energy dissipaters. In each group of specimens (except for group MJ4), two specimens were tested under monotonic loading and the others were subjected to low cyclic loading. The test results were summarized comprehensively in terms of failure modes, joint stiffness, hysteresis loops, ductility and energy dissipation ability. Generally, the difference of load capacity between BCGS glulam joints and the beam-to-column glulam joints only with glued-in rods (BCG glulam joints) was not significant. The joint stiffness of BCG glulam joints was higher than that of the BCGS glulam joints, while the stiffness degradation of the later is slower than the former. The hysteresis loops of the BCGS glulam joints exhibited less pinching effect obviously compared with the BCG glulam joints, which indicated that the energy dissipation ability of the glulam joints with glued-in rods could be improved significantly by using the steel brackets as energy dissipaters. Moreover, it should be noted that the hysteresis loops of groups CJ1 showed slipping effect obviously during testing. This might due to the insufficient shear resistance of these two groups, so that further investigations on BCG glulam joints with shear-resisting components are urgently needed.
To support the transition to a bio-based society, it is preferable to substitute metallic fasteners and adhesives in timber construction with an eco-friendly alternative. Recent studies have identified compressed wood dowels and plates as a possible substitute for metallic fasteners in contemporary and mainstream applications. In this study, a spliced beam-beam connection system using compressed wood dowels and slotted-in compressed wood plates was examined under four-point bending. The study has considered specimens with compressed wood dowels of 10 mm diameter and compressed wood plates of 10 mm thickness. The load carrying capacity of connections using compressed wood dowels and plates were compared to connections utilising steel dowels and plates of equivalent capacity. Typical failure modes, moment resistance and rotational stiffness of both connection systems are evaluated on the basis of the experimental results. Tests have demonstrated similar failure modes when comparing steel-timber and compressed wood-timber connection systems. The mean failure load for the compressed wood-timber connection system is only 20.3% less than that achieved for the steel-timber connection system. The mean rotational stiffness of the compressed wood-timber connection system is 18.55% less than that achieved for the steel-timber connection system. These preliminary results demonstrate the potential for the use of compressed wood elements in the manufacture of timber connections.
