With this project, the homeowner wanted to build an addition to the deck behind the house. However, we found a serious problem here – the rim beams that were supporting the decks on the rear of the house were grossly undersized. This not only presented a serious deflection problem, but a life safety issue also. To solve this problem, we engaged a structural engineer (Runkle Consulting, Inc.) to examine the situation. The repair was to turn the rim beams into “flitch beams”, which are steel plates sandwiched inside timber 2x’s.
There is a steel plate sandwiched in the 2x's.
Here is a video that gives much more information: