Calculation for large tank on engineered joists

[ribletman]

I have a modern house, built using Weyerhaeuser TJI 230 engineered floor joists. Mine are 2 5/16th inch x 11 7/8th inch joists. These have a maximum vertical shear of 1,655 pounds. With a 40 PSF live load and 20 PSF dead load, they are specified for a 19’ 10” span with 16” o.c. spacing. The joist ends are supported by a 2x6 wall 9’6” tall over a concrete basement floor. The joist span in the room where I wish to put my tank is 18’ with the joists perpendicular to the length of the tank.

Separated into 16” wide chunks (purely for mathematical purposes), each should hold 900+ pounds of live load (40x18x1.25), and 1205+ pounds of live shear force (1655-(20x18x1.25)) with a safety factor greater than 1.5x. In reality, the tank would span 4’/6’/8’/10’ of joists, sharing across 4-8 joists. On an 18’ span (instead of 19’ 10”), 16” o.c., live load is 43.5 PSF instead of 40 PSF used for the calculations for even greater safety factor.

I am planning on a tank 30” front-to-back and 24” deep. This yields 49.87 gallons per 16” width of tank. At 8.33 pounds per gallon, this is 415 pounds of water. Add 75 pounds of rock, coral, and random stuff; 90 pounds of glass tank (long tank, ¾” thick-glass); 50 pounds of tank stand for 630 pounds per 16" width.

The floor joists underneath where I want to put the tank are also overlapped, giving two joists for each 16” spacing. The overlap is 18” from the wall. This provides greater shear strength at the wall edge of the tank, but I am not sure if this provides much deflection resistance though deflection so close to the wall would be very minor.

Based on these calculations and even with a sump and other equipment there is still plenty available load and shear for furniture and people moving around the room, greater than 2,500 pounds over ten foot for example.

Are my calculations and assumptions reasonable, or did I miss something important? I would very much prefer not to have to build additional support beneath the tank in the basement, but I could if I really need to.