Display year value before a set of posts

You need to compare the year value between the current post and the previous post and based on that display your h3 tag with your year-based content

I’m not going to reproduce your code, only the important parts. Note that I may need to strip some tags in order to add my section of code

if ( $query_case_studies->have_posts() ) {
    // Define the variable to hold the year value from the post date
    $date_variable="";

    while ( $query_case_studies->have_posts() ) {
    $query_case_studies->the_post(); 

        // Get the post date, but only the year part
        $year = get_the_date( 'Y' );

        // Now lets compare $year with $date_variable and display the year accordingly
        if ( $date_variable != $year ) // Year values are not the same
            echo '<div class="heading"><h3 class="normalh3">' . $year . '@apos; Case Studies</h3></div>';

        // Set $date_variable to $year
        $date_variable = $year;

        // Rest of what you need to do