A concrete wall form tie with an ultimate strength capacity of 2,400-lbs is designed for use in a concrete wall form with an 18-in center to center spacing. During formwork inspection it was discovered that the actual spacing is 24-in center to center. Using the actual spacing, the percent change in load on the wall form tie is most nearly: 

Solution:

Determine design tributary area: 1.5-ft x 1.5-ft = 2.25-ft²

Determine actual tributary area: 2-ft x 2-ft = 4-ft²

Determine design ft² load:    2400-lbs / 2.25-ft² = 1066.67-lbs/ft²

Determine actual load on 4-ft²:  1066.67- lbs/ft² x 4-ft² = 4266.68-lbs

Increase in load is:  4266.68-lbs - 2400-lbs = 1866.68-lbs

Calculate % change = 1 - (4266.68-lbs / 2400-lbs) = 78%

The load increase is 78% on the wall form tie.