\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfgantt}

\begin{document}
\begin{ganttchart}{1}{12}
    \gantttitlelist{1,...,12}{1} \\
    \ganttbar{Core 1}{1}{2} 
    \ganttbar[bar/.append style={dashed}]{}{3}{5}
    \\
    \ganttbar{Core 2}{1}{2} 
    \ganttbar[bar/.append style={dashed}]{}{3}{5}
    \\
    \ganttbar{Core 3}{1}{2} 
    \ganttbar[bar/.append style={dashed}]{}{3}{5}
    \\
    \ganttbar{Core 4}{1}{1} 
    \end{ganttchart}
\end{document}

