Glued laminated timber constructions enable high spans. If these are necessary in outdoor areas, larch is often used. Larch heartwood can be used there according to DIN 68800-1/-3 without preventive chemical wood protection. The approval for gluing in steel bars offers new variations to the planner. Joints with glued-in steel rods can now also be used in larch glulam for bridges or other load-bearing structural elements in outdoor applications.

Cross laminated timber offers a varied basis for complex constructions such as e.g. extensions, multi-storey timber construction and prefabricated building elements. Large-area components for walls, ceiling and roof elements as well as stiffening panes can now be reliably connected with glued-in steel rods in conformity with the standard thanks to the extended approval. Combining these construction methods with connections made of glued steel bars opens up new possibilities for planners and architects in the design of timber construction objects.

BAUBUCHE is “the new wood” under construction. Now that beech has been recognised as construction timber, the discussion about possible glued joints has been positively decided. The gluing of steel rods into laminated veneer wood made of beech is now permitted due to the extension of the approval. The enthusiasm of architects and planners is great, because now more filigree constructions can be realized by connections with glued-in steel rods. Due to the higher strength values of beech compared to other types of construction timber, constructions can be made slimmer overall. With the connections described, junctions also convey a much more elegant appearance.

If structures made of glued laminated timber with glued-in ribbed concrete reinforcements are subjected to fatigue loading by dynamic loads, a specific fatigue check can be carried out depending on the number of load cycles and consideration of the service class. Up to now, this type of design was only permitted for structures with predominantly static loads.

Fa. Züblin (vormals Fa. Finnforest Merk)

(Fa. Rubner Holzbau, Brixen)

(Fa. Grossmann, Rosenheim)

(Mayr-Melnhof Holz Reuthe GmbH)

The bonding process was successfully used for the first time as early as 2016 within the framework of an approval in individual cases for the renovation of a two-storey sports hall in Berlin (BAUEN MIT HOLZ 3.2017, S. 22 ff). The wooden girder grid of the roof had been strongly deformed. In the course of the refurbishment, the entire roof structure was lifted and the previously open spaces between the crossed glulam beams were closed with fillers, which were glued into the structure with the WEVO special resin (in this case still the refurbishment resin EP 20 VP 1) and non-positively connected without the use of pressure. In this way, the overall stiffness of the support grating was significantly increased.

• Surface bonding of wood-based panels for glulam renovations
• Special renovations (see report from “Bauen mit Holz” 3.2017, p.22ff.)
• Production of composite beams from the same or different glulam cross-sections, if the necessary pressing pressure cannot be generated for conventional adhesives.
• Large-area bonding
• Aesthetically sophisticated bonding (without screws)
• Special formats

As a rule, the thickness of the repaired cracks must not exceed 4 mm. Increased joint thicknesses of up to a maximum of 8 mm may occur in certain areas over a length of a maximum of 0.5 m and an area of a maximum of 0.10 m², if such joint sections in the longitudinal direction of the support are adjoined in both directions by areas with at least 5 times the length of this joint area, in which the crack thickness is a maximum of 4 mm. Exceptions to this are cracks in the area of supports, connections, etc., which have a crack extension in only one direction. In these cases the mentioned condition is only to be guaranteed for one direction.

In the area of the joints to be renovated, the wood moisture content must not exceed 17% (EP 20 VP 1) or 18% (EP32S).

During renovation, the temperature in the joint area must be between 17°C and 35°C.

In general, the cracks to be repaired must not show any detached or loose old adhesive residues or layers or detached wood splinters or fibre layers. In case of doubt, the cracks must be cut open over depths of approx. 4 cm to 10 cm at least on the side surfaces of the component. Before filling, the cracks/joints to be repaired must be freed from dust by blowing out with oil-free compressed air (pressure approx. 10 bar). The surface preparation may be done at the earliest 3 days before filling the crack.

Before filling, the cracks to be repaired must either be covered with a transparent adhesive tape (adhesive method) or filled with a suitable material, e.g. thickened repair adhesive (filling method).

The injection/filling method used must be proven to ensure that the cracks are completely filled with adhesive and that no adhesive can flow away during the curing process. Care must be taken to ensure a sufficient number of injection openings, venting openings must be arranged as required. When pressing with a hand lever press, a distance between the injection openings of between approx. 100 mm and 250 mm, depending on the thickness of the crack, and up to 300 mm in the case of cut cracks, has proved to be a good solution. With other pressing devices, larger distances can be selected if necessary, if it is ensured that a reliable distribution of the adhesive is achieved. If no filling nipples with non-return valve are used for pressing in the adhesive, suitable dowels must be kept available to close the drill holes. It is essential to ensure that both the filling nipples and the dowels seal the drill holes as tightly as possible so that the filled adhesive cannot flow out.