Tuesday, October 23, 2012

Wood-Concrete-Composite Slab

A wood-concrete-composite is a connection between supporting timber beams and a concrete slab mounted on them. A rigid connection is achieved with shear connectors or screws which transfer shear forces between beams and slab. Wood-concrete-composite floors are utilized when large beam spacing’s or spans must be bridged and high pay loads must be carried after retrofitting the ceiling. This bonding is deemed to be the ideal solution for increasing the load-carrying capacity and stiffness of ceiling systems.

The SWG solution

The SWG solution includes a combination of wood and concrete construction. The essence is a system solution that is build around the ASSY Plus full thread screw, composed of the ASSY Plus VG and precast connectors (FT-Connectors). The ASSY Plus VG is inserted into the FT Connector whereby a fast and comfortable screwing of concrete slabs is possible. It is also possible to pre-install the precast connectors to the beam and pour the concrete on site. But in general it is easier to work with custom made concrete slabs in which the FT-Connectors are already embedded.

Commercial Benefits of Our Solution

  • Higher added value for wood construction businesses
  • The valuable soffits are preserved
  • No separating layer necessary to protect the wood from entry of moisture and contamination
  • No idle time on site caused by setting concrete
  • Less money and time required for assembly
Dreidimensionale Darstellung des Fertigteil-Verbinders (FT-Verbinder) in der Betondecke

Technical Benefits of Our Solution

  • The combination of wood/concrete construction
  • The high prefabrication degree
  • The short assembly time on site → placing and screwing together of precast concrete parts with ASSY Plus VG.
When precast concrete parts are used: no entry of moisture into the wood construction; full load bearing capacity of composite slab right after screw application; no formwork necessary; no support structure required, no assembling of further components on concrete; useable for large beam spans and large beam spacing.
The uniqueness lies in the fact that only a comparably small number of screws are needed when using the FT-connectors, which minimizes the amount of work and effort.

Examples of Applications

Wood-concrete-composite floors of all kind, e.g.:
  • Floor ceilings and basement ceilings in old and new buildings
  • Combination of FT-connectors and shotcrete ceilings when reconstructing old buildings
  • Wall and ceiling components in prefabricated houses
  • Bridge building

FT-Connector allows for easy cooperation between the concrete and wood industry. Pre-manufactured concrete elements can now be offered and installed to and from wood working companies.


Monday, October 15, 2012

Self-tapping screws as reinforcement for timber structures


Modern self-tapping and continuously-threaded woodscrews enable new methods for
strengthening and joining timber and glulam construction elements. As these screws have a
high axial strength and an excellent continuous bond to the wood they can be used similar
to steel reinforcement in concrete construction.

Different from concrete the natural construction material timber shows a high grade of
anisotropy, resulting in low values of strength and stiffness for tension and compression
perpendicular to the woodfibre and for shear forces parallel to the woodfibre. Self-tapping
screws can be systematically used to reinforce these ‘weak’ directions either in sections of
load concentration, e.g. bearing areas, or to increase strength and stiffness of whole
structural elements.

In several series of tests conducted by the Chair of Structures and Structural Design at the
RWTH Aachen University, screws forming an internal truss system improved the shear
stiffness of glue-laminated timber beams. Similarly the reinforcement of the flexural
tension zone by steel plates attached with screws in a truss arrangement significantly
increased the bending stiffness and ultimate load of the beams.

A second field of the application of reinforcing screws are high-performance joints. Tests
on rigid frame corners connected with self-tapping screws proved a significant higher load
bearing capacity compared to conventional joints with dowels or glued finger-joints. The
layout for the configuration of the screws was done by modelling the internal flow of forces
with strut-and-tie-models in a related way to reinforced concrete design.

The presented reinforcing method with self-tapping screws opens new perspectives for
joining and upgrading all kinds of timber elements creating innovative engineering
solutions for challenging high-performance timber structures.