Dowel type connections in laminated bamboo with multiple slotted-in steel plates

Abstract

The main focus of this research was testing of dowel-type connections using slotted-in steel plates in laminated bamboo loaded parallel-to-grain. Since laminated bamboo is a relatively new material, a proper design standard and design formulas have not yet been established. Strength testing of this material is currently being done by a number of research institutes. Those researches have already resulted in a range of properties and strength parameters. To analyse the possibility of calculating laminated bamboo connections with these already obtained strength parameters using timber design principles, this research focussed on strength testing of a variety of connections and comparing the obtained test results to expected capacities calculated from such timber design formulas. To calculate the expected capacity, design formulas from EC5 were used. From EC5 also the spacing requirements (end, edge and dowel spacing distances) were adopted into the test piece design. Several connection variants were designed and tested. These variants all made use of one dowel of a constant steel grade and dowel diameter. The connection variants were designed such that results were obtained in every failure mode. This thus included testing of three variants of one slotted-in plate (modes 1, 2 and 3) and six variants with two slotted-in steel plates. Of these six variants three displayed failure mode 1 in the middle member and three displayed mode 3 in the middle member (and 1, 2, and 3 in the outer members). This variety in test specimens made it possible to not only compare the measured capacities to design codes but also to compare the capacity and behaviour of connections with multiple slotted-in plates to that of connections with only one slotted-in plate. To make the best use of the available material and have as little wasted bamboo as possible, the test specimens were equipped with equal connections at both ends. So that when loaded, actually two results could be obtained. One of these results was the capacity of the connection that failed. The other result was the knowledge that the other connection was, at least, stronger than the measured capacity. The use of such symmetrically loaded specimens however also causes the average of all measured capacities to be somewhat lower than normal, since half of the fabricated connections were stronger and are still intact. To overcome this, a method was devised which was adopted into the result analysis and by which the measured capacities were adjusted so that a representative value for all connections was obtained. From the comparison of the adjusted test results and design codes then was concluded that all of the tested variants had a capacity that was well above the EC5 value. This confirmed that the design of connections in laminated bamboo can safely be done using the design principles of EC5 for timber. Although further research is necessary to determine the necessary minimum end and edge distances for laminated bamboo. The benefits of using multiple slotted-in plates were investigated in three ways. Final recommendations are to investigate a possible effective number of slotted-in steel plates by also testing connection variants using three slotted-in plates. Of course in this further research extensions can be made by testing multiple dowels or dowel diameters, different materials or even more specimens to reduce the natural variation in test results to get a more accurate number of effective slotted-in plates.