Let $F \hookrightarrow X \to B$ be a fibre bundle with structure group $G$, where $B$ is $(d{ -}1)$-connected and of finite dimension, $d \geq 1$. We prove that the strong L-S category of $X$ is less than or equal to $m + \frac{ \dim B}{ d}$, if $F$ has a cone decomposition of length $m$ under a compatibility condition with the action of $G$ on $F$. This gives a consistent prospect to determine the L-S category of non-simply connected Lie groups. For example, we obtain $\cat{ PU(n)} \leq 3(n{ -}1)$ for all $n \geq 1$, which might be best possible, since we have $\cat{ \mathrm{ PU}(p^r)}=3(p^r{ -}1)$ for any prime $p$ and $r \geq 1$. Similarly, we obtain the L-S category of $\mathrm{ SO}(n)$ for $n \leq 9$ and $\mathrm{ PO}(8)$. We remark that all the above Lie groups satisfy the Ganea conjecture on L-S category.
Categories: math.AT