Beam-column connections in glulam structures, with gusset plates of birch plywood and self-tapping screws
Master thesis
Submitted version
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https://hdl.handle.net/11250/2683270Utgivelsesdato
2020Metadata
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- Master's theses (RealTek) [1826]
Sammendrag
Multi-storey timber buildings are often built around a post and beam system made of glulam. Typically adopted connections for such structures are those which make use of slotted-in steel plates and dowels. Even though such connections are able to transfer large loads, they have a number of deficiencies. Besides being relatively costly in terms of both materials and manufacturing, connections with slotted-in steel plates and dowels require a very high level of accuracy both in manufacture and assembly. By replacing steel plates and dowels with plates of birch plywood and self-tapping screws, there are possible benefits; The connection would be lighter, cheaper, and easier on the environment by avoiding the great carbon dioxide emissions from steel production. One could also benefit from the superior fire properties of wood compared to steel, as well as the possibility of adding external plywood plates to the outside of the connection. This thesis presents an experimental investigation of the mechanical characteristics of such plywood connections, ended with an assessment of its use in real design.
The experimental work of this research was introduced with preliminary tests to identify weaknesses in the test setup. Changes were made and main tests with eight different test groups were conducted. Six of these portrayed a situation where continuous plates of birch plywood connect a column to a beam on both sides. Two configurations represented connections between lateral columns with beams attached on one side. The effects of using both one and two slotted-in plates were investigated, along with the effect of variation of grain angle in the plywood. Configurations were also made to represent the case where a glulam column is prefabricated, with glued continuous plywood plates throughout the column.
Test results and hand calculations have confirmed that beam-column connections with gusset plates of birch plywood, may reach sufficient capacities for realistic design in the Ultimate Limit State (ULS). By utilizing both external and slotted-in gusset plates of plywood, one could reach the same capacity and stiffness as a slotted-in steel plate connection. To further reduce the amount of steel in the connections, results showed that prefabricated glued columns with plywood can be an opportunity. Trekonstruksjoner som strekker seg over flere etasjer er ofte bygd rundt et bjelke-søylesystem bestående av limtre. Typiske forbindelser i slike systemer, benytter seg av innslissede stålplater og ståldybler. Selv om forbindelser som disse er i stand til å overføre store laster, har de en rekke svakheter. I tillegg til at de er relativt kostbare både når det gjelder innkjøp og produksjon, krever stålplateforbindelser med dybler en veldig høy grad av nøyaktighet, både ved fabrikasjon og montering. Ved å erstatte stålplater og dybler med kryssfinér av bjørk og selvborende treskruer, er det flere mulige fordeler; Forbindelsen vil være lettere, billigere, og mindre belastende på miljøet ved å unngå de store CO2-utslippene fra stålproduksjon. Man kan også dra nytte av de utmerkede brannegenskapene til tre sammenlignet med stål, i tillegg til muligheten til å feste eksterne kryssfinérplater til utsiden av forbindelsen. Denne oppgaven presenterer en eksperimentell undersøkelse av de mekaniske egenskapene til slike kryssfinérforbindelser. Avslutningsvis legges det frem en vurdering av mulighetene for bruk av slike forbindelser i reelle konstruksjoner.