Brick bbq grill problems with heat?

I'm a little discouraged. I just made a large bbq grill outside for charcoal. It has cinder block lining with red brick along the outside. I left an open area for storage underneath and bridged it with a 3/16 piece of metal (3' x 2'). I raised the bottom holder for the charcoal about 2" above the metal and just tried using it today. To my dismay the heat from the charcoal made the whole piece of metal warp and caused several cracks through some of my bricks. Is there something I can do to make the metal plate not warp or some sort of fix?