This study evaluated the effects of subfreezing temperatures and moisture content on the shear behavior of glulam beams. Full-scale glulam beams (79 mm by 229 mm deep) at two moisture contents (12 and 28%) and three temperatures (20 °C, 0 °C, and - 40 °C) were tested in four-point bending until failure. Temperature was observed to affect the failure mechanism of the beams, with the beams tested at 0 °C and 20 °C failing in shear and the beams tested at - 40 °C failing in tension. Further, the strengths of the beams and their stiffnesses were observed to increase with decreasing temperature, with these effects being more pronounced in the higher moisture content beams. Over the temperature range of 20 °C to - 40 °C, the 12 percent moisture content beams observed strength and stiffness gains of 17 and 22%, while the 28 percent moisture content beams observed respective gains of 37% and 66%.
In this study, flexuralbehaviors of glue laminated timber beams manufactured from Pinussylvestristree were investigated by comparing the results with those of massive timber beams. The main variables considered in the study were number of laminations, types of adhesive materials and reinforcement nets used in the lamination surfaces. In scope of the experimental study, glue laminated beams with 5 and 3 lamination layers were manufactured with 90 x 90 mm beam sections. In the lamination process epoxy and polyurethane glue were used. Morever, in order to improve the bond strength at the lamination surface, aluminium, fiberglass and steel wire nets were used at the lamination surfaces. Load–displacement responses, ultimate capacities, ductility ratios, initial stiffness, energy dissipation capacities and failure mechanisms of glue laminated beams were compared with those of massive beams. It was observed that the general bending responses of glue laminated beams were better than those of massive beams. In addition to that the use of reinforcement nets at the lamination surfaces increased the ultimate load capacities of the tested beams. The highest ultimate load capacities were oberved from the tests of glue laminated beams manufactured using five laminated layers and retrofitted with polyurethane glue using steel wire reinforcement nets, in the direction normal to the lamination surface. Finally, the finite element simulations of some test specimens were performed to observe the accuracy of finite element technology in the estimation of ultimate capacities of glue laminated timber beams.
Wood as building material is gaining more and more attention in the 21st century due to its positive attributes such as light weight, renewability, low carbon footprint and fast construction period. Cross-laminated timber (CLT), as one of the new engineered wood products, requires more research emphasis since its mechanical performance can allow CLT to be utilized in massive timber structures. This thesis focuses on revealing one of the key failure mechanisms of CLT, which is usually referred to as the rolling shear failure. The scientific research conducted in this thesis combined both analytical modelling and experimental material testing. The stresses in CLT cross-layers obtained from a finite-element model were analyzed to differentiate various failure modes possible. Tension perpendicular to grain stress was found to cause cross-layer failure in combined with the rolling shear stress. Experimentally, specimens prepared from 5-layer CLT panels were tested under center-point bending condition. Detailed failure mechanism of CLT cross-layers were recorded with high speed camera to capture the instant when initial failure happened. It is evident that some of the specimens failed in tension perpendicular to grain which verified the modelling results. Variables such as the rate of loading and the manufacturing clamping pressure were designed in experiments to compare their influence to the failure of CLT specimens. In this research, the failure of CLT cross-layer was updated to a combined consequence of both rolling shear stress and tension perpendicular to grain stress. Future research topics and product improvement potentials were given by the end of this thesis.
Notched connections are extensively used in timber-concrete (TC) composite beams and floors. Their main advantage is a significantly higher shear strength and stiffness compared to mechanical fasteners. Several mechanical and geometrical aspects, however, should be properly taken into account for design optimization of notched connections, as they strongly affect their structural performance and the corresponding failure mechanisms. In this paper, a preliminary Finite-Element (FE) numerical investigation is carried out by means of full 3D numerical models. The mechanical behaviour of each connection component (e.g. the reinforced concrete topping, the steel coach screw, the timber beam) is properly implemented. Shear or crushing failure mechanisms in the concrete, possible plasticization of the coach screw, as well as longitudinal shear or tension perpendicular to the grain failure mechanisms in the timber beam are taken into account using cohesive elements, damage material constitutive laws and appropriate surface-tosurface interactions. The results of parametric FE studies are compared to experimental data derived from literature, as well as to the results of simplified analytical models, demonstrating that the FE model is capable to capture the experimental behaviour of the connection including the failure mechanisms.
The focus of this research was to investigate the fire performance of post-tensioned timber beams. This was completed through a series of full-scale furnace tests, and the development of a fire resistance design method. Previous research has focused on the seismic performance and gravity frame performance of post-tensioned timber, both of which yielded promising results. There is however a commonly perceived increase in fire risk with timber building, particularly multi-storey timber buildings, and the fire performance of post-tensioned timber had not previously been investigated.
: This paper describes a series of full-scale furnace tests on loaded post tensioned LVL beams. Each beam was designed to exhibit a specific failure mechanism when exposed to the standard ISO834 fire. In addition to the beams a number of steel anchorage protection schemes were also investigated. These included wrapping the ends in kaowool, using intumescent paint, covering the anchorage with fire rated plasterboard and covering the anchorage with timber (LVL). The results of the full-scale tests cover temperature distributions through the timber members during the tests, the temperatures reached within the cavity and those of the tendons suspended within the cavity, the relaxation of the tendons during the test, the failure mechanisms experienced, and a summary of the anchorage protection details and
their effectiveness. Recommendations for the design of both post-tensioned timber beams and associated anchorages are also provided.
The structural use of wood in North America is dominated by light wood-frame construction used in low-rise and – more recently – mid-rise residential buildings. Mass timber engineered wood products such as laminatedveneer-lumber and cross-laminated timber (CLT) panels enable to use the material in tall and large wood and woodbased hybrid buildings. The prospect of constructing taller buildings creates challenges, one of them being the increasein lateral forces created by winds and earthquakes, thus requiring stronger hold-down devices. This paper summarises the experimental investigation on the performance a high-capacity hold-down for resisting seismic loads in tall timberbased structural systems. The connection consists of the Holz-Stahl-Komposit-System (HSK)™ glued into CLT with the modification that ductile steel yielding was allowed to occur inside the CLT panel. The strength, stiffness, ductility and failure mechanisms of this connection were evaluated under quasi-static monotonic and reversed cyclic loading. The results demonstrate that the modified hold-down-assembly provides a possible solution for use in tall timber-based structures in high seismic zones
Cross-laminated timber (CLT) wall systems are composed of massive timber panels that are fastened together and to the horizontal elements (foundations or intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the shear response of such systems depends strongly on the connections used. This paper proposes a numerical model capable of predicting the mechanical behavior and failure mechanisms of CLT wall systems. The wall and the element to which it is anchored are simulated using three-dimensional (3D) solid bodies, while the connections are modeled as nonlinear hysteretic springs. Typical racking tests of wall systems are reproduced by varying the assumptions used to schematize the behavior of the connections. Results are compared with test data published in the literature, and the differences are discussed. The influence of the boundary conditions (vertical load applied on top of the wall and friction at its base) and aspect ratio of the panel are investigated via a parametric numerical study. Finally, the performance of a wall system assembled with two CLT panels is analyzed, highlighting how the properties of the anchoring connections and vertical step joints affect the load-displacement response and energy dissipation.
This paper describes numerical modelling to predict the fire resistance of engineered timber floor systems. The floor systems under investigation are timber composite floors (various timber joist and box floor cross sections), and timber-concrete composite floors. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies is also being undertaken to calibrate and validate the models, with a number of full scale tests to determine the failure mechanisms for each floor type and assess fire damage to the respective system components. The final outcome of this research will be simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems.