STATNAMIC METHOD DESCRIPTION
The Statnamic load test is based on Newton’s second and third laws which state that force is equal to mass times acceleration (F=MA) and that for every action there is an equal and opposite reaction. Loads ranging from 5 tons up to 5,000 tons are generated (axially or laterally) by propelling a reaction mass upward off the foundation. Since the mass is in contact with the foundation prior to the test, the force associated with propelling of this mass acts equally and oppositely onto the foundation. Statnamic load testing requires no reaction piles, no reaction beam, no hydraulic jack, and is set up in a fraction of the cost and time.
A speciel fuel is burned to generate gas pressure inside a cylinder and ram (analogous to a gas actuated jack). As the pressure builds, it reacts against a heavy mass above the pile (typically 5 to 7 percent of the desired test load). The pressure builds rapidly which propels the reaction mass upward, in turn a downward load is simultaneously applied to the pile top which is many times greater than the weight of the reaction mass. The fuel type produces a smooth increasing force and controlled venting of the pressure produces a soft unloading. The load produced is not an impact but rather an impulse load typically with a duration on the order of 1/2 second or less. Load is measured with a calibrated load cell and displacement is measured with a photo-voltaic sensor triggered by a stationary laser reference. Three motion sensors (accelerometers) provide redundant measurement of displacement at the pile top. The fuel weight to load relationship provides redundancy in load measurement. Gas pressure can be measured providing additional redundancy of load measurement. Note that the upward acceleration of the reaction mass is not significant in the analysis of the foundation, only a by-product of the load produced.
Stages of a Statnamic Load Test
Before the test - reaction mass is in contact with pile.
A - Foundation Member B - Calibrated Load Cell C - Laser Displacement System D - Piston & Cylinder E - Silencer F - Reaction Mass G - Catch Mechanism
Burning fuel creates high pressures simultaneously propelling the reaction mass up and loading the pile in downward compression. The applied load and pile displacement are measured using high precision instrumentation and a data acquisition system.
After the load test, the reaction mass is safely caught using hydraulic systems or by mechanical means. It is easily lowered for cyclic loading on the same pile.