Uppercase, bold and underlined chapter title

You need to have a handle on the chapter title, and the only way to do this is to use the explicit option with titlesec:

\documentclass{report}

\usepackage[explicit]{titlesec}
\usepackage{lipsum}

\titleformat{\chapter}
  {\normalfont\Large\bfseries}{\thechapter \quad \MakeUppercase{#1}}{.5em}{\vspace{.5ex}}[\titlerule]
\titlespacing*{\chapter}
  {0pt}{0pt}{15pt}

\begin{document}

\chapter{Introduction}

\lipsum

\end{document}

This option allows you to explicitly state the sectional title as #1, where you can now wrap it within \MakeUppercase.

Use the correct places for the various parts: the spacing before the rule should go in the last argument (the optional one), so you can finish the title argument with a one parameter macro such as \MakeUppercase.

\documentclass{report}

\usepackage{titlesec}
\usepackage{lipsum}

\titleformat{\chapter}
  {\normalfont\Large\bfseries}
  {\thechapter}
  {.5em}
  {\MakeUppercase}
  [\vspace{.5ex}\titlerule]

\titlespacing*{\chapter}
  {0pt}
  {0pt}
  {15pt}

\begin{document}

\chapter{Introduction}

\lipsum

\end{document}