EWPAA Structural Plywood and LVL Design Manual - Engineered ...

Serviceability Requirements for Type 1 Screwed JointsAS 1720.1-1997 does not differentiate between nails and screws regarding joint deformations even thoughintuitively one may feel a screwed and nailed joint of identical construction would result in the screwed jointbeing stiffer.13.12 Design of Bolted ConnectionsAlthough the basic philosophy for the design of nailed and bolted joints is similar, there are somedifferences that need to be recognised, particularly with regard to the modification factors.In FIGURE 13.4 the importance of direction of load application relative to nominal grain direction hasalready been highlighted. In a nailed (or screwed) connection timber thickness is aligned with the depth ofnail penetration required to develop the full strength of the connector.In a bolted connection the bolt capacity is presented as a function of timber thickness, which in thetabulated data of AS 1720.1-1997, is referred to as the effective thickness (b eff ).FIGURE 13.8 defines (b eff ) for loads parallel and perpendicular to the grain in seasoned and unseasonedtimber.For Type 1 bolted connections the contents of FIGURE 13.8 can be summarized thus:• for loads parallel to grain (b eff ) is the smallest aggregate cross-section of members loaded parallelto grain:• for loads perpendicular to grain (b eff ) is the aggregate cross-section of the elements in themember with loads perpendicular to grain.The characteristic strength of a single bolt in a Type 1 timber connection is a function of a number ofvariables:• bolt diameter – M6 to M36.In seasoned timber the bolt hole is the nominal diameter of the bolt.In unseasoned timber the bolt hole is 10 to 15% oversize.• timber joint strength group – J1 to J6 and JD1 to JD6;• timber effective thickness – in AS 1720.1-1997 – 25 to 200mm unseasoned and 25 to 120mmseasoned;• moisture content;• angle between force application and the grain direction;• bolt spacings – edge, end, along and across grain to prevent splitting and allow development of thefull bolt capacity.Type 2 bolted connections do not depend on timber embedment of the bolt for load transfer and aretherefore largely independent of timber thickness. Type 2 joints depend upon:• bolt tensile strength;• crushing strength of the timber under the washers at each end of the bolt.13.13 Modification Factors – Bolted JointsModification factors applied to bolted connection design perform a similar function, and take the sameform, as those used in nailed connection design. However, a number of the factors relevant to nailedconnections are not relevant to bolted connection design, e.g. the factors k 13 and k 14 .202