$(function(){
    $('.blokmetrondehoeken')
        .addClass('row')
        .wrap('<div class="content-row"></div>')
        .before('<div class="rc-t"><div class="rc-t-l"></div><div class="rc-t-r"></div></div>')
        .after('<div class="rc-b"><div class="rc-b-l"></div><div class="rc-b-r"></div></div>');    
})