What tomleslie said is that your expression "eq" contains a variable named "MI" which doen't appear in the screen capture you give.
The fact alpha=sqrt((G*A)/(E*MI)) doesn't change anything to tomleslie's remark. Worse than that it introduces a new cariable "G" whish is not in the screen capture.
I suspect you have written "MI" but the source this screen capture comes from uses "I" instead?
In this case, the first thing to do is to tell Maple that "I" is not the imaginary unit (a protected name in Maple).
You can do this either by declating I as local (local I;) or by redefining the imaginary unit (interface(imaginaryunit=J)).
Once done type eval(eq, MI=I).
The expression in the screen capture is obviously an ad hoc arrangement done by someone who thought the expression was prettier written this way (the numerator is H^4*something and the denominator is H^4*something else).
Nut Maple is not an IA system who could know what "beauty" means for an equation. It uses algorithms through procedures like (look to these names in the help pages) simplify, collect, normal, expand, subs, algsubs, eval, freeze, thaw, ... and the result suits you or not. If not you will have to write the equation in the form whivh suits you the best and, as Carl Love said, verify that your expression is identical to "eq".
To give you an hint how complicated it would be to transform "eq" into the pretty form you want, jist look to this very simple exemple which concern the last [...] term in this latter form: