For demanding applications with increased requirements in terms of load-carrying capacity and long spans, the HighTech Timber Beam® (HTB) – a hybrid composite beam made of glulam and high-performance materials – was developed at the Bauhaus University in cooperation with a local SME . The applicability of the High-Tech Timber Beam® for TCC constructions (Timber-ConcreteComposite) is examined in ongoing research. In former investigations several studies with new technologies and materials for rehabilitation and strengthening of historic timber structures were carried out at the Bauhaus University . Within those studies, several formulations of glue-mortar based on epoxy resin and mineral fillings (hereinafter also referred to as PC – polymer concrete) were developed to implement a direct and continuous bond between timber and reinforcing materials or elements (for instance LVL, CFRP lamellas, bars made of GFRP or steel). The different mixtures of PC were adjusted to their application purposes through a range of modifications to the composition and detailed material analysis.
The performance of timber-concrete composite bridge constructions crucially depends on the design of the joint between concrete deck and timber main girders. In research studies at the Bauhaus-University Weimar, innovative joining techniques based on grouting with highly-filled, tolerance-compensating polymer glue mortars have been developed to improve the shear capacity of this joint significantly. By applying a thin layer of polymer mortar on the top of the wooden main girder a continuous, slip-free connection to the timber can be realized. This layer can be utilized for the embedding of steel plates with welded-on shear studs (stud connectors), so that the joint to the concrete side is ensured by a standardised connection. The steel plates are rigidly anchored in the polymer mortar by adhesive bond and form closure. As an alternative, a slip-free grout-glued connection between concrete and timber can be realized by the glue mortar itself, so that also a continuous connection to the concrete is accessible, whereby manufacturing tolerances can easily be compensated due to the high degree of mineral filling of the polymer mortar. The paper focuses on experimental results of shear and bending tests for the new composite joint configurations.
The development of wide-span structures occurs high reaction forces at the bearings. The load-bearing capacity is strongly limited, because of the low compression strength and stiffness of wood perpendicular to the grain. One common possibility of strengthening the support is the application of self-tapping screws ,. Subject of the presented research project is the study of a new, practicable and quite easy to manage type of reinforcement for load transfer areas. To increase the load carrying capacity drill holes and block shaped areas filled with polymer concrete are inserted into the timber. Due to the rigid bond between wood and polymer concrete as well as a geometrical adaption to the stress distribution, it is possible to increase the load carrying capacity and the compressive stiffness significantly compared to conventional reinforcement by self-tapping screws.
First inchoate versions of bearing reinforcement have been designed and used very successfully as part of another research project to increase the bending capacity of glulam beams by hybrid material composites ,. Figure 1 shows one example of the tested designs. The diagram in Figure 2 illustrates the increase of the transversal load bearing capacity compared to FE-simulation of the same member without reinforcement.
Wood in Europe, especially in Germany, is a good available row material. It has a high load capacity and stiffness in comparison to the low death weight. Timber is traditionally used for bending beams and columns with low processing. Since it is a natural material, there are variations in properties and quality. There is a demand for homogenisation for using in modern engineering and for the exploitation of the good properties of timber. Therefore, the timber is sliced, sorted and remounted as glued laminated timber or even as veneer lumber, to eliminate defects, knots or cracks. For increased requirements in terms of load-carrying capacity and long spans, a hybrid composite beam made of glulam and highperformance materials was developed at the Bauhaus University Weimar in cooperation with a local SME.
The main material of the developed High-Tech Timber Beam is still glulam with more than 90 % of the girders volume. Replacing one or two lamellas at the bottom side of the glulam by laminated veneer lumber (LVL) allows a significant homogenization of the timber beams properties.
For upgrading the compression zone of the bending beam, the upper lamella of the glulam is replaced by a decking of polymer concrete (PC). This is made of a mineral mixture with a special grain-size distribution and a binder on base a of 2-component epoxy resin. The PC has a high compression strength and also a high stiffness because of its high rate of filling with mineral grits.