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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2. Traditional techniques

Fig. 2 shows details of typical techniques to prevent damage due to rising dampness in timber walls, ensuring a sufficient distance of the wall base to the Reinforced Concrete (RC) foundation level, as opposed to a direct contact, which likely would lead to durability problems. The first strategy is the realization of a RC curb between the wall and the foundation slab, Fig. 2a. The second strategy is the use of a larch base beam, having better durability properties than other typical species for structures, as spruce. It is worth noting that, even if made with more durable species and arranged with the direction of the grain parallel to foundation, resulting in limited rising dampness, also the base timber beam should not be in direct contact with the slab. Therefore, when the second strategy is chosen, the RC curb should be anyway realized, Fig. 2b. These techniques are not sufficient to prevent durability problems, whether suitable waterproofing is not realized. Fig. 2 shows also examples of correct waterproofing (Fig. 2a,b) and another of wrong waterproofing (Fig. 2c). It should be noted that waterproofing must be applied so as to permit a correct drying of timber, when a moisture source is present. These traditional techniques may be a good strategy to prevent timber decay. However, they are affected by the quality of works built on-site. It is worth noting that the RC slab is normally realized with excessive geometric inaccuracies respect to timber assembly tolerances and consequent discrepancies between the concrete surfaces and the timber panels occur. This leads to incorrect alignment of walls (Fig. 3) and must be arranged through edge planning works or filling the gaps. The base larch beam could be a strategy to overcome this problem, but the compression perpendicular to grain limits its load-bearing capacity for mid- and high-rise buildings.

(a) ✓ (c) ✗ Fig. 2. (a,b) Optimal waterproofing according to ÖNORM 2320 (2017); (c) example of wrong waterproofing (b) ✓

(a) (c) Fig. 3. (a) Example of vertical misalignments between CLT wall and RC curb and consequent gap (see also Scotta et al., 2017); (b)(c) Examples of horizontal misalignments between CLT wall and RC foundation and of wrong waterproofing (b)