Info

Particleboard or OSB (EC5, equation (8.22))

fh,k

= 65 d-0Jt0A

(10.32)

d is the diameter of the nail (in mm). pk is the characteristic density of the timber, LVL or panel material (in kg/m3). t is the panel thickness (in mm).

d is the diameter of the nail (in mm). pk is the characteristic density of the timber, LVL or panel material (in kg/m3). t is the panel thickness (in mm).

10.3.3.3 Characteristic embedment strength when using bolts, nails (diameter > 8 mm) and dowels

When using timber to timber or LVL, the embedment strength of bolts, nails (with a diameter greater than 8 mm) and dowels is dependent on the direction of the applied load relative to the grain and for such fasteners the embedment strength is determined by using Hankinson's equation [7], referred to in 5.3.2.

Applying the Hankinson equation to determine the characteristic embedment strength, fh,a,k, when the fastener is loaded at an angle a to the grain, as shown in Figure 10.8, the equation can be written as:

/h,0,k ' fh,9°,k /moos /h,a,k = --—-—-^ (1°.33)

/h,0,k sin a + fh,9°,k cos2 a where fh,a,k is the characteristic embedment strength at an angle a to the grain, /h ° k is the characteristic embedment strength parallel to the grain, and fh,9°,k is the characteristic embedment strength perpendicular to the grain.

Failure load on fastener, Fk

Failure load on fastener, Fk

Fig. 10.8. Embedment strength of a bolt, dowel or nail (d > 8 mm) fastener loaded at an angle a to the grain.

Fig. 10.8. Embedment strength of a bolt, dowel or nail (d > 8 mm) fastener loaded at an angle a to the grain.

Table 10.7 Characteristic embedment strength using bolts, nails (greater than 8 mm in diameter) or dowels

Condition

For timber and LVL Loaded parallel to grain (EC5, equation (8.32))

Loaded at an angle a to grain (EC5, equation (8.31))

For panel to timber loaded at any angle to the face grain where the panel material is plywood, the characteristic embedment strength in the panel material will be: (EC5, equation (8.36))

For panel to timber loaded at any angle to the face grain where the panel material is either particleboard or OSB, the characteristic embedment strength in the panel material will be: (EC5, equation (8.37))

d is the diameter of the fastener. pk is the characteristic density of the material being considered. t is the thickness of the panel material. a is the angle of the load in the fastener relative to the grain. kga = (1.35 + 0.015d) for softwoods; (1.3 + 0.015d) for LVL; (0.9 + 0.015d) for hardwoods.

In EC5, the above equation is reduced to:

k90 sin2 a + cos2 a where k90 = fh, 0, k/fh, 90,k and values for softwood, LVL and hardwoods are given in Table 10.7.

For bolted panel-to-timber connections, the embedment strength in the panel material is the same for all angles of load resulting in factor k90 equalling unity and equation (10.34) simplifying to the embedment strength of the panel material.

The characteristic embedment strength for bolts up to 30 mm diameter, nails greater than 8 mm diameter and dowels greater than 6 mm and up to 30 mm diameter, in timber, LVL and panel product connections, is given in Table 10.7.

10.3.3.4 Characteristic embedment strength when using screws

The characteristic embedment strength when using screws is:

• as that for nails, when using smooth shank screws with a diameter <6 mm, and

• as that for bolts, when using smooth shank screws with a diameter >6 mm.

10.3.4 Member thickness, t1 and t2

In a connection the members are classified as member 1 and member 2 as shown in Tables 10.2 and 10.3 and defined in the following sub-sections.

Fig. 10.9. Staple dimension.

10.3.4.1 ti and t2 for a nail connection ti is:

• the nail headside material thickness where the connection is in single shear;

• the minimum of the nail headside material thickness and the nail pointside penetration in a double shear connection.

• the nail pointside penetration where the connection is in single shear;

• the central member thickness for a connection in double shear.

'Nail headside material thickness' is the thickness of the member containing the nail head and 'nail pointside thickness' is the distance the pointed end of the nail penetrates into a member.

10.3.4.2 ti and t2 for a staple connection ti and t2 are as shown in Figure 10.9.

10.3.4.3 t1 and t2 for a bolt connection t1 is the bolt headside member thickness where the connection is in single shear or double shear (assuming the connection is symmetrical).

t2 is the bolt threaded end member thickness when the connection is in single shear and the central member thickness when in double shear.

10.3.4.4 t1 and t2 for a dowel connection t1 is:

• the dowel length in member 1 when the connection is in single shear;

• the minimum dowel length in the outer members when the connection is in double shear.

• the dowel length in member 2 when the connection is in single shear;

• the central member thickness for a connection in double shear.

10.3.4.5 t1 and t2 for a screw connection

The definitions given for nails will apply.

10.3.5 Friction effects and axial withdrawal of the fastener

The basic Johansen yield equation for each failure mode for connections in single or double shear can be derived by the use of a static analysis (as shown in STEP 1 [8]) or by the virtual work approach commonly used in the plastic analysis of steel structures. To simplify the equations, the ratio of the characteristic embedment strength of member 2 in the connection, (/h,2,k), to the characteristic embedment strength of member 1, (/h,1,k), is used and written as:

0 0

Post a comment