PSI - Issue 11

Roberto Scotta et al. / Procedia Structural Integrity 11 (2018) 282–289 R. Scotta et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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3. Description of an innovative aluminium bottom rail

An innovative foundation system has been recently developed to solve the aforementioned issues. The system consists of a bottom-rail beam, realized by extrusion of an aluminium billet of grade AW 6060-T5 according to EN 755-2 (2016), and conceived to avoid the rising dampness from foundation to timber elements. The cross-section was designed to withstand vertical loads typical of a two- to three-storey timber building. Three different versions of the aluminium profile have been proposed by varying the cross-section shape and dimensions to fit CLT, platform-frame or Blockhaus systems as well as different wall thickness, Fig. 4.

(a)

(b)

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Fig. 4. Geometry and dimensions (in mm) of the three versions: (a) ALUBEAM 120; (b) ALUBEAM 100; (c) ALUBEAM 100L

ALUBEAM 120 (Fig. 4a) has a rectangular cross-section with dimensions of 120x150mm. Specific grooves in the upper and bottom faces allow to install the necessary fasteners to fix the beam to the concrete slab underneath, by means of mechanical or chemical anchors. The two lateral faces are realized with channels, in which aluminium linear joints can slide and behave as fixing points for the brackets, needed to fasten the timber panel to the aluminium beam. The brackets are then rigidly fixed to the beam by self-drilling bolts that block both the bracket and the linear joint to the vertical web of the channel. A symmetric disposition of the brackets with the wall centred with respect to the beam axis represents the most efficient usage of this system. ALUBEAM 100 (Fig. 4b) represents a narrower shape than the previous one (dimensions of 100x150mm) with only one axis of symmetry. Aim of this version is to fit thinner CLT panels, typically designed for one- or two storey residential buildings. The upper grove has been removed to distribute better vertical loads on the four webs. The extruded beam is pre-drilled with a constant spacing to let the head of concrete anchors being tightened without interference with the timber panel. ALUBEAM 100L (Fig. 4c) is a lighter version than the previous two, in which the vertical distance of the panel base to the concrete foundation is reduced to 60mm. This version actually substitutes the traditional larch base beam, while maintaining the levelling properties of the innovative system. Therefore, it requires the realization of a concrete curb as discussed in the previous section. The beam has one vertical upper flange, in which a screwed or nailed connection transmits the horizontal shear actions from the panel to the beam. Traditional hold-downs can be used to withstand tensile forces due to panel rocking. Fig. 5 and 6 show the installation phases of the aluminium foundation system in case of a newly-realized timber building. First, the aluminium profiles are laid all along the RC foundation. Then, the beam is horizontally aligned by means of adjustable screws attached to special provisional inserts, fastened to the lateral grooves (elements a,b in Fig. 5 in case of ALUBEAM 120/100) or by means of vertical self-tapping screws inserted throughout the beam (Fig. 6a for ALUBEAM 100L). The remaining gap between beam and concrete is infilled by self-levelling mortar. Subsequently, pass-through concrete anchors are used to secure the beam into position by tightening rectangular washers designed to fit the upper groove (elements c and d in Fig. 5). In order to provide the required airtightness a rubber strip is laid on top of the beam before setting the timber panel into position (Fig. 6c). The panel is then fastened to the beam with specifically-designed aluminium brackets that exploit the aforementioned linear joints (elements e and f in Fig. 5) or with traditional connections to the concrete foundation, Fig. 6d. These operations allow an accurate and rapid positioning, so greatly reducing costs and time for installation. Corrosion issues due to galvanic effects between steel and aluminium are avoided by using aluminium alloys for both the main beam and the connecting plates and interposing plastic elements between possible contact zones with steel parts.