The fracture characteristics and deformation ability in timber engineering is very important criteria for structural design. However those fracture patterns are complex and confusing, so the quantitative evaluation is very difficult. In our past study, we could see the three fracture types and defined them the brittle, ductile and inter-mediate type with bolted connections loaded perpendicular to the grain. This definition isn’t enough because it’s not clear definition and we couldn’t study the deformation ability or ductility factor.In this study, for those connections, we would apply the evaluation method proposed by Ian et al. In this evaluation method, fracture pattern would have relevance to ductility factor. And the evaluation methods proposed by us, AIJ code and Ian et al would be compared. As a result, it is confirmed that fracture pattern based on mechanical calculation proposed by Ian could be agree with the pattern based on our video observation. Then proposed method would be useful for structural design.
This paper deals with assessment of glulam twinned columns to beam circular bolted connection. This kind of connection is used for embedded assembly. Because of the moisture content variations, cracks often occur in the direction parallel to the grain. The aim of the study is to understand the mechanism responsible of the cracks happening. In the same time, another aim of this study is to evaluate the residual resistance of a damaged assembly. The assembly has been designed according to Eurocode 5. Two different initial conditions have been tested. For the first assembly, the columns and the beam have been dried before machining and tested dry. For the second assembly, the beam was wet and the columns were dry before machining, then the assembly was tested dry. The difference of moisture content implies a huge tensile strain in the direction perpendicular to the grain of the columns before loading. In order to qualify the assembly behavior, strain gauges techniques have been used. This analysis allows a better understanding of the phenomenon of cracks initiation and propagation due to the coupled effect of shrinkage/swelling and loading.
Journal of Structural and Construction Engineering: Transactions of AIJ
Cross Laminated Timber (CLT) panel is consisted of several layers of lumber stacked crosswise and glued together on their surfaces. In Europe, mid-to-high-rise building using CLT has been already built. Recently, CLT structure attracts attention in Japan as one of the means to promote Wooden Public Buildings. Since the lamina can utilize small or middle diameter wood as the raw materials, expansion of CLT demand would promote local forestry and wood industry. There are various joint methods of CLT such as LSB joints, screw joints with steel side-plates, and so on. In this study, we examined tensile bolt joint which is one of the effective joint methods of the end of panel when the wall panel showed rocking behavior, assuming architectural structure using the panels of around 1-2m in width.
The outcomes of an experimental study aimed to investigate the structural behaviour of wood-steel-wood glulam frame moment-resisting connections that were subjected to static bending are presented in this paper. Each frame test assembly was consisted of two glulam beams simply supported at their far ends and were connected to an inverselyloaded glulam column in the centre using two steel T-stub connectors. Two test variables including bolt’s end distance and number of bolt rows were investigated in eight full-size glulam beam-column assemblies. Test results revealed that increasing the number of bolt rows from two to three, with each row included two bolts, significantly increased the connection moment capacity with much greater increments compared to those added by increasing the bolt’s end distance from four- to five-times bolt diameter. However, brittle failure modes were found to be more pronounced in the connections with three rows compared to the connections with two rows of bolts.
Information on ductile and brittle failure modes is critical for proper design of timber connections in Crosslaminated Timber (CLT). While considerable research has been conducted in Europe and Canada on the ductile performance of connections in CLT, little is known about the brittle behaviour. This paper presents new information from testing programs and analysis performed in Canada and in New Zealand on the brittle performance of dowel-type fasteners in CLT. The testing programs have been designed to trigger brittle failure modes based on minimum end distances and fasteners spacings specified in the Canadian timber design standard. Timber rivets and bolts/dowels are covered under this study. At the time of writing of this abstract, the testing program is advancing and results will be available at the time of paper submission.
Fire-testing data, such as charring rates and failure modes of structural elements exposed to ISO-standard fires, for unprotected cross-laminated timber (CLT) panels made of domestic timber were investigated to apply the reduced-cross-section method to CLT panels. For the charring rates, a series of fire tests without loading was conducted...
This paper presents a research study about timber connections in moment resisting frames, with materials commercially available in Costa Rica. With new developments in engineered timber, the Costa Rican Seismic Code included a chapter on timber structures, defining moment resisting timber frames with several values of structural global ductility, depending on the local ductility of the connections. A research study was then carried out, with the objective of determining the structural behaviour and static ductility factor of a beam to column connection. Twelve specimens were constructed and tested, varying the geometric characteristics, wood species and type of bolts. The specimens consisted of a glulam beam and column segment connected with a different bolt pattern. The beam segment was loaded at its free end to induce a moment in the connection, and the ends of the column segment were simply supported. The rotation of the connection was measured by placing two LVDTs in the beam and two LVDTs in the column. It was found that the ductility factors achieved by the test specimens ranged from 2.0 to 2.7 in average. The moment capacity of the connections can be safely estimated using the nominal values of bending yield strength of the bolts and the dowel bearing stresses. These results are an important input for the Costa Rican Seismic Code and for the development of engineered timber in Costa Rica.
Innovative steel - Cross Laminated Timber (CLT) connections are key elements in developing hybrid steel-timber composite floors with desirable strength and serviceability performance. The performance of floors mainly relies on the load-slip behavior of connections for composite action. The long-term behavior of timber is mainly affected by elastic and mechano-sorptive creep, resulting in a different total slip than the initially observed one. In this study, the long-term load-slip behavior of two different types of connections with pre-tensioned high-strength bolts and dog screws are experimentally assessed at two different stress levels. Furthermore, the effect of grain orientation on the results is studied by considering specimens with parallel and perpendicular grain orientations under sustained loads. Load-slip curves show a stable performance of a composite action over time. Furthermore, an analytical model is fitted to the load-slip vs time data which can be used to predict long-term behavior of floors in future.
The paper deals with the analysis of the load-carrying capacity of a timber semi-rigid connection created from a system of two stands and a rung. The connection was made from glued laminated timber with metal mechanical dowel-type fasteners. Not only a common combination of bolts and dowels, but also fully threaded screws were used for the connection. The aim of the research and its motivation was to replace these commonly used fasteners with more modern ones, to shorten and simplify the assembly time, and to improve the load-carrying capacity of this type of connection. Each of these two types of connections was loaded statically, with a slow increase in force until failure. The paper presents results of the experimental testing. Three specimens were made and tested for each type of the connection. Experimental results were subsequently compared with numerical models. The achieved results were also compared with the assumption according to the currently valid standard. The results indicate that a connection using fully threaded screws provides a better load-carrying capacity.