Please select a suitable channel section for the following beam. Assuming the allowable tensile stress is $320$MPa, allowable compressive stress is $280$MPa and allowable shear stress is $180$MPa after considering buckling effect and factor of safety. $($Hint$,$ you can select an DURAGAL ${?}^{}$ CHANNEL section from one$-$steel product table based on maximum bending stress and then check the maximum shear stress. When check shear stress, you can consider the section as a combination of $3$ rectangles and ignore the influence of radius on channel corners $)$H