Question $4$

A novel simply supported composite beam with a span of $15$ m is to be designed. This composite beam is composed of a partially concrete$-$filled steel box section and a concrete slab. Geometry and dimensions of the cross$-$section of the composite beam are given in Figure Q$4.$ The beam spacing is $2\mathrm{.}1$ m centre to centre. The composite beam is fully restrained against lateral torsional buckling.

The grade of steel is S $460($design yield strength $f_{yd}=460\frac{N}{m}{m}^2).$ The grade of concrete is C$30/37($with a characteristic compressive cylinder strength of $30\frac{N}{m}{m}^2)$ for the top concrete slab, and C$50/60($with a characteristic compressive cylinder strength of $50\frac{N}{m}{m}^2)$ for the infilled concrete.

Note: please distinguish the different conditions for the concrete slab and infilled concrete, unconfined or confined.

$($i$)$ Assume full shear connection in the composite section, evaluate the moment resistance $($Unit: kNm $)$ of the beam at mid$-$span from first principles.

$($ii$)$ Explain the shear force transfer mechanism between concrete slab and steel section for this novel composite beam.

$($iii$)$ State features and advantages of this novel composite beam.

$($iv$)$ If the lower part of the steel section is also infilled with concrete, will it contribute to the moment resistance of the composite beam?

$($v$)$ State some possible approaches to optimise the design of this novel composite beam.

$[30$ marks$]$