Dr Dilum Fernando, Moin Rahman, Pranav Rawal, Maddy Courtney, Emma Parisi,

Yiwen Zhu, Chuang Miao, Matt Piesker , Li MinSchool of Civil Engineering, The University of Queensland,

Australia

For more information:www.civil.uq.edu.au/icarus

HFT Thin-Walled MembersINTRODUCTIONThe increasing interest in timber as a sustainable constructionmaterial has led to the development of a new type ofstructures called “hybrid FRP-timber thin-walled” structures. Inthese structures FRP is combined with timber veneers thatmakes it light weight, high performing and easy-to-construct. Itharnesses orthotropic properties of both by orienting materialfiber directions for optimal composite properties and efficientthin-walled cross sectional geometry.

The goal behind this project was to study and develop anunderstanding of the behaviour of HFT thin-walled sections thatare ‘rectangular’ and ‘square’ from existing studies donepreliminary on HFT ‘Cee’ sections.

STEEL PLATE & DOVETAIL JOINTThe Steel Plate design consisted of 2mm thick steel plate(140X300mm) that was attached to the center of the outer webof the two members via six M8 bolts. Two additional plateswere attached on the inner flanges with 4 M8 bolts Dovetailswere cut into the web of each member using a water jet with0.4mm diameter. Member 1 had three pins and two tails whileMember 2 had three tails to fit the pins of Member 1 and twopins to fit the tails of Member 1. The dovetails were reinforcedwith a coat of polyurethane and an extra coat of FRP.

BACKGROUNDThe project was done in 3 stages – dimensioning & designing,manufacturing and testing. Firstly, portal frame was selectedas the structure and several design ideas for itsconnections/joints were discussed aiming at the centralmembers of the frame to address only flexural/bending forceson the members. From multiple designs three joints werechosen, ‘steel plate’, ‘timber/screw joint’ and ‘dovetail joint’.Each of these were then fabricated on separate HFT squareor rectangular timber hollow sections. Once that wascompleted, the fabricated samples were tested via “4-pointBending Test” in the UQ Structures Lab.

FINDINGSPreliminary calculations for each joint hypothesized failure at aload of less than 1 kN. Each testing was undertaken in a 4-Point Bending Test on a Tecnotest Testing Machine in theUQ Structures Labs. Upon testing, Joint 1 withstood a load of4 kN before failure, Joint 2 withstood 9.6 kN and Joint 3withstood 7 kN.Future work with the HFT-Timber composite members includesthe design of joints at perpendicular or otherwise angledmembers, and modelling of stress distribution to furtherenhance the understanding of HFT Thin-Walled CompositeMembers.

TIMBER/SCEW REINFORCED JOINTThe Screw Reinforced Joint design allowed web and flangesto be reinforced with timber as well as get attached by coatsof polyurethane and FRP. Timber supporting the web wasapproximately 10mm thick while the flanges were supportedby 35mm. Initial designs used four 100mm long M12 screwsand bolts supporting the two flanges. However, for testingpurposes, only the outer two screws remained.

Figure 2: Other Steel Plate Joint

Figure 1: Dovetail Joint (Left), Timber/Screw Joint (top-right) , Steel Plate Joint (bottom-right)

Figure 3: 4-point bending test on Joints