P_1.2.4 reinforce_connection

Connection Techniques under Extraction Stress and their Application as Reinforcements and High-performance Knot Solution in Timber Engineering Carried out by Engineers

In supporting constructions of wide spans, today mainly even or spatial pin-pointed bar structures and solid-walled glulam support elements with the strain on bending are used. With loose structures we mainly find low cross dimensions with the construction challenge resting with the connection technique of the knot solution. With solid-walled glulam support elements, cross-section heights of up to 3.0 m together with transport lengths of up to 40 to 50 m are no rarity. As far as solid-wall supports of this dimension are concerned, it is a known fact that the probability of weak spots increases the larger the volume. This goes hand in hand with a volume-conditioned dependence of the characteristic specific parameters relevant for dimensioning. Additionally to bending, tension and pressure in the grain direction, the characteristics of shearing and cross tension as well as the usually given interactions are of importance. For the process of dimensioning this can mean that these values that have so far been considered “minor specific parameters“ (or derived specific parameters) gain a certain significance and determine the cross section. Similar to building in concrete, also in timber engineering, and particularly with solid walls, the question of reinforcement will gain in importance.

The transverse tension reinforcements known today in the form of screws or glued-in rods will in the future be more and more used as reinforcement measures in shear-strained cross section zones. First studies in this field were carried out by A. Bernasconi and E. Gehri, among others. What is still missing, however, is a systematic representation and procedure accompanied by a model formation in order to have a better understanding in the future as to where and how these reinforcement measures shall be applied. While in building in concrete, reinforced steel is used, in timber constructions carried out by engineers self-drilling woodscrews and glued-in steel anchors are used and are usually applied at angles of 45° to 90° to the rod axes (here, too, and analogy to building in concrete can be seen).

Contrary to solid-wall supports, glued-in steel anchors are also inserted parallel to the grain direction. Here, they primarily serve as high-performance connection techniques for introducing high loads into the wood parallel to the axes. As an example, the design of a bending resistant joint can be mentioned. Also, this may serve the design of high-performance knot solutions in trelliswork. As has already been pointed out, the screws or glued-in steel anchors are inserted at 0° to the rod axes and are stressed mainly concerning extraction.

At the beginning of the work, the main focus shall be on the state of the art of these connection systems, and in particular on the glued-in steel rods so that the missing aspects can be demonstrated. In the form of a so-called ‚morphological methods’ the relevant research directions shall be shown and tackled. It has already been revealed that what is required are well-founded statements concerning the bearing behaviour of the individual connection techniques. Predominantly what is meant here are axially strained connection techniques that are arranged at angles ranging from 0° to 90°in the grain direction. With glued-in steel rods, the special characteristics and used glue shall be explored. Based on these findings, optimised connection system for highly strained joints shall be developed.

Especially in this context, groups of connection techniques ranging from 2 to 6 individual connection tools are explored. Another thing that shall be examined are the different reinforcement measures, and especially the cross-inserted glued-in rods, and those arranged at an angle of 45°. In the future, these shall be increasingly used as an element of construction in timber engineering carried out by engineers when it comes to the absorption of tensile tension and/or (excess) shear strains.