set width of a rich column on the fly?

I'm trying to开发者_C百科 set the width of a rich column on the fly like:

<rich:column width="#{extraColumnWidth}">

where:

<c:set var="extraColumnWidth" value="#{document.instanceList.size() * 20}px"/>

But it does not work..i mean the width is not taken as it should but it remains the same no matter how much size of the list is..

Do you know why?

Solved: my other columns already had width attributes and there was not enough space for my last column to be expanded:)