NOTES:

$1$ Structural elements supporting more than $200m^2$ of roof area shall be designed to support $0\mathrm{.}25$kPa on

the $200m^2$ of the supported area that gives the worst effect.

$2A=$ the plan projection of the surface area of roof supported by the member under analysis, in square

metres.

$3$ For structural elements in roofs of houses, the uniform distributed actions shall be $0\mathrm{.}25$kPa and the

concentrated actions shall be $1\mathrm{.}1kN.$ The Figure shows the plan view of a steel portal frame building. Roof layers $($roof sheeting, insulation, and roof bracing$)$ are supported by purlins which are in turn supported by $5$ roof beams $(2\backslash$times exterior beam RB$1$ and $3\backslash$times interior beam RB$2).$ In contrast to the $2\mathrm{.}4$ m cantilever roof on the other side, the $3\mathrm{.}2$ m cantilever roof extends to cover all the roof beams, whereas the $2\mathrm{.}4$ m cantilever roof on the other side only covers some of the middle section.

Roof beam spacing Z $=5040$ mm$.$ Roof sheeting self$-$weight g$1=55$ Pa or $0\mathrm{.}055$ kPa; self$-$weight of insulation and roof bracing g$2=6\mathrm{.}6$ kg$/$m$^2.$ For self$-$weights of beams $(360$UB$56\mathrm{.}7)=56\mathrm{.}7$ kg$/$m and purlins $($Z$15015)=3\mathrm{.}59$ kg$/$m$,$ see OneSteel and Lysaght catalogs. Use Table $3\mathrm{.}2$ of AS$/$NZS $1170\mathrm{.}1$ to determine imposed action on roof which is $0\mathrm{.}25$ KPa $($using only distributed load is sufficient$).$

$($a$)$ Develop the line load diagrams using a basic design loading combination of $1\mathrm{.}2$G $+1\mathrm{.}5$Q for development following members:

$($i$)$ A typical purlin

$($ii$)$ One of the RB$1$ beams

$($iii$)$ The critical RB$2$ beam