I seen someone make a bench with (1) 2x4x8 & (1) 2x8x8 and 2.5” screw nails. It’s a short, small bench. I want to use that same concept to make a larger, taller bench. I want a counter height bench 69x15x27 (or similar dimensions to it). Given how the previous bench was made (dimensions ≈ 48x16x21.5) with no middle beam support, I figured with my dimensions I would need a middle beam. But the biggest thing is that I want my bench to be able to support 850Lbs at least. How can I go about doing this?

Side note: I’m not an expert on wood working. I don’t have any knowledge on what kind of wood I need. I’m more so concerned on the support of the bench and if (2) 2x8x5.5 beams can support Minimum 850Lbs horizontal.