Bootstrap Responsive column resets. Clear columns without rows. For use within looped content where you can't inject more markup. http://getbootstrap.com/css/#grid

col-reset.php

<!--Example #1-->
<?php //Your Loop Start?>
<div class="row your-wrapper">
    <div class="col-md-6">
        <!--Your stuff with 50% columns-->
    </div>
    <div class="duel-clear clearfix"></div>
</div>
<?php //Your Loop END?>      

<!--Example #2-->
<?php //Your Loop Start?>
<div class="row your-wrapper">
    <div class="col-md-3">
        <!--Your stuff with 25% columns-->
    </div>
    <div class="quad-clear clearfix"></div>
</div>
<?php
//Your Loop END?>

the-style.css

/*Hide clear by default*/
.duel-clear,.quad-clear { display:none;} 
/*Only show clear when needed. This is on a per column or layout basis */
.your-wrapper div + div.duel-clear:nth-of-type(4n), .your-wrapper div + div.quad-clear:nth-of-type(8n)  {display:block;}