movements. All purlin connections for the various frames are bolted using 4, M12, Grade 8.8 bolts. The same type of bolts as for the eaves and apex joints of a particular span are used for any connection in the web of the cold formed channels of the frames. The cleat angles form the interface between these two sizes of bolts.

Tests carried out by Dundu and Kemp (2006b) proved that simpler connections, one with two vertical bolts and the other with two diagonal bolts could be used in place

of this connection (Figs. 5(b) and 5(c)). These are cheaper connections than the continuous connection in Fig. 4, in terms of number of bolts and length of the connection. Zpurlins and rails are connected to the main frame through the same angle cleat, but with a slightly different bolt arrangement. In all the two arrangements the angle cleat is connected on one side of the section whilst the splicing flat bar is on the other side of the section. An arrangement with the rafter facing the opposite direction would represent the rail-column connection. The cleat angle is

able to resist a horizontal load PL of (1) where, P=concentrated load transferred at the purlin-rafter connection;

m=distance between the shear centre and mid-plane of web of the rafter;

h=depth between bolts in the web of a rafter.

The corresponding splicing bars for the purlins in Fig. 5 are shown in Fig. 6. These flat bars are now 340 mm shorter than the flat bars in Fig. 4.

5. Loading of Portal Frames

The frames were designed to carry

(a) Dead load (weight of purlin and roof cladding or weight of rail and side cladding and its self-weight)

(b) Uniformly distributed imposed load acting vertically downwards on the roof. Nominal imposed roof loading is given in SANS 10160 (1989), and ranges from 0.5 kN/m2 for tributary roof areas up to 3 m2 to 0.3 kN/m2 for areas from 15 m2 upwards, with a straight-line variation between these limits.

(c) Wind loading normal to the inner or outer surface of the roof or sides of the building, acting either as a positive or a negative pressure. The dead and imposed loads applied to the frame are as follows:

Cladding=0.08 kN/m2

Weight of purlin=0.06 kN/m

Weight of frame=0.12 kN/mImposed load=0.3 kN/m2

The wind loads are estimated from SANS 10160 (1989) and depend on the building dimensions, location of the building and speed of the wind. The characteristic

wind pressure (pz), acting on the faces of the building is calculated from a free stream velocity pressure (qz) and a pressure coefficient (Cp) as shown in the following

equations:

pz=qzCp (2)

qz=0.60 Vz

2 (3)

Vz=krkzV (4)

where V is the basic wind speed, Vz is the characteristic wind speed, kr is the mean return period factor and kz is the terrain category, class and height factor. The

coefficient of pressure acting on each face is determined from a combination of an external pressure coefficient (Cpe) and an internal pressure coefficient (Cpi). External pressure coefficients are obtained from Table 6 and 7 of SANS 10160 (1989), whilst internal pressure coefficients are taken from Table 10 of the same code. Cpi has a value of +0.2 for pressure and a value of −0.3 for suction for a building where there is only a negligible probability of a dominant opening occurring during a severe storm. The wind load is calculated using a basic wind speed of 40 m/

s. Three pressure cases are considered for design, that is, internal pressure case (wind angle α=0ο), internal suction case (wind angle α=0ο) and internal pressure case (wind angle α=90ο). The internal pressure case is found to be the most critical of all the three cases. The wind pressure factors, (kr and kz), characteristic speed (Vz), free stream velocity pressure (qz), external pressure coefficients (Cpe),

and the characteristic pressure (pz) for the critical case of the three portal frames are shown in Table 1.