Determination of the Capacities of a new Composite Timber-Steel Connection System, the TiSCo (Technical Report)

by Alexander C. Schreyer

This is a research report about structural tests of the TiSCo-Connector (Timber-Steel-Connector), a glued end-grain wood-to-steel connection for heavy timber structures. This connector is inserted into a tubular hole at the end of a wood beam and connects to steel fittings using threaded rod.

Abstract: The TiSCo-Connector (Timber-Steel-Connector) is a reliable new end grain connection that fulfills a multi-purpose use in heavy timber construction. It combines ease of fabrication with a high load-carrying capacity. Whereas other connectors cause problems being inserted into end grain (which often results in a reduction of the transferable load), this one takes advantage of the direct load transmission longitudinal to the fibers. The principle of being a tube resolves in a maximization of load transmitting surface. This connection system can provide a degree of efficiency of nearly 100%.

The test program focused on the properties of one type of the TiSCo-connector. As this system is still in the development stage, some modifications will take place before the connector will reach its final product level. The version which was provided for this research had a sandblasted surface. Attempts to improve the reliability of the surface fabrication have lead to a version with grooves or threads on it. Both are or have been manufactured on behalf of the German anchoring-systems company Upat GmbH & Co. in Emmendingen.

The properties and behavior of the connection in a tension and a compression situation had to be examined. Also the required edge distance and the relating strength capacities in a laterally loaded single or double connector joint were to be found. An additional test should examine the behavior of the entire connection under climatic influences. This ended in a pull- out test where the remaining maximum load carrying capacity was determined.

In order to understand how all components behave, a focus had been laid upon the strength capacities of the adhesive. It is very important to know how the adhesive reacts as this connection strongly depends on the properties of it. Results from these tests lead to a determination of characteristic values for the maximum load as well as the slip modulus. Both have been found for tension and compression. Also, characteristic shear load values were discovered and related to minimum edge distances.

Two methods for their determination have been presented. An applicability of this connection system in Parallel Strand Lumber has been proved and an improvement attempt to straighten out the connection in the mortar bed using spacers has been conducted. This also resulted in reliable values. An additional test showed that the cleaning of the drilled hole is not improving the carrying capacity substantially. The cyclic climatic influence that was induced on a few specimen lead to a reduction of the maximum load of about 15%.

A mortar test was performed as a double-lap shear test and values for the maximum shear capacity and the modulus have been determined. All tension and compression testing was done in a test setup that allows a broad range of specimens. Also, a data sheet that encompasses a fully standardized test evaluation was developed. Concluding from these tests it was found that the TiSCo-connection system is generally applicable with the presented values and the shown manufacturing method.

These values can only be related to the TiSCo-version that was used for these tests. A projection on different versions can not easily be done as failure modes might differ. Only the shear tests allow a certain reproducibility for different versions as these tests mostly rely on the wood properties.

Published: 2006

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