Project Field C: Bond Old-New
The strengthening with textile fabrics can be done both two- and three-dimensional. The bond between the new and the old is thereby generated by means of applying a slack textile using mineral or polymer matrices (Subproject C1 and Subproject C3). A sufficient bond strength between the structural member and the strengthening is necessary to guarantee the load carrying properties.
In concrete construction, textile fabrics are applied to structural members using a matrix of fine grained concrete, which is laminated or sprayed on. In timber construction, two- or three-dimensional textiles act as a strengthening for old and new constructions, which are applied using synthetic resin - and it offers various possibilities for practice and application. There, the strengthening compensated the significant differences of strength and stiffness along and across the wooden fibres. The behaviour during the break is very ductile in combination for both composite materials - textile reinforced concrete and wood - in spite of brittle source materials.
The knowledge about mechanisms of the bond (Subproject C1, Subproject C3) and its durability (Subproject C5) during the utilization time is an important prerequisite to handle the textile strengthening technology. The therefore planned investigations give also information about the bond-slip-relationship of the joint as well as its damage mechanisms like cracking, delamination and aging.
Different technological application methods are considered for investigating the mechanic behaviour of the bond - spraying on the fine grained concrete in horizontal and vertical direction (Subproject C1) and laminating by hand in timber and concrete construction (Subproject C1, Subproject C3). In addition, larger timber members are laminated in using an autoclave.
New manufacturing methods for textile fabrics offer interesting strengthening possibilities in timber construction. Connections of technical wooden profiles with circular cross section and crotch-shaped core pieces (Subproject C3) are of special interest. The strengthening using three-dimensional knitted fabrics makes an essential contribution to recuce the anisotropy of the connection range. It affects a significant increase of the limit load and a significant increase of the ductility at the same time. The universality of the textile strengthening will be used over the additional course of the CRC by investigating the efficiency for a structural wood preservation regarding humidity, pests and fire (Subproject C5). First information concerning structural wood preservation are available from the first project stage.
A surface-related shell theory is developed for finite element methods to solve plane and curved problems as well as complex geometries and load conditions (Subproject C2). The theoretical method of resolution includes physical and geometric non-linearities and allows the determination of the state of shear and contact stress, which is an essential prerequisite for the structural design and optimization of textile strengthening in concrete and timber construction. Thus, an universal tool for simulation (Subproject C2) of the load carrying behaviour of the bond is available, which provides a useful service for substantial, textile and structural problems over the additional course of the CRC.