chksix has given the reference. Rule of thumb is typically 95% of the weight on the main gear, and this is equally spread amongst the wheels on the main gear (4 wheels for the -500).
If you are building a floor, design it for the heaviest 737-900 since no-one will remember you've used the -500 in design. Or use a wild rule of thumb and add 2 inches to the designed concrete depth.