33_HWKTTE 4004c

# 33_HWKTTE 4004c - accelerometers The velocity is then...

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23 t L c 2 = (3-10) where L Length of the Pile t Time Required for the Pulse to Travel Twice the Pile Length The dynamic modulus of the pile material, E, is presented in Equation 3-11. The mass density of the pile material is represented by ρ and the wave speed c. 2 c E ρ = (3-11) Equation 3-12 presents the impedance, Z, of a pile as a function of the dynamic modulus, E, the wave speed, c, and the pile cross-sectional area, A. c EA Z = (3-12) The force within the pile can be obtained from the strain transducers and knowing the elastic modulus of the pile material and cross-sectional area, according to Equation 3- 13. EA P ε = (3-13)

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24 The velocity is obtained from the integration of the acceleration signal acquired by the accelerometers. It should be noted that the force and velocity used in the PDA calculation is the result from the average of the two strain transducers and the two
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Unformatted text preview: accelerometers. The velocity is then converted to force units by multiplying by the pile’s impedance (Z). The result of the force and velocity are then plotted in a graph versus time for a given blow. Figure 3-2 shows an example of the force and velocity traces for a given hammer blow.-1000-500 500 1000 1500 2000 2500 0.01 0.02 0.03 0.04 0.05 0.06 Time (s) Force Velocity Figure 3-2. Typical Force and Velocity Traces from PDA The main equation used by PDA to determine the static capacity of piles was derived assuming that the pile is linearly elastic and has constant cross section properties along the length. This equation is based on the force and velocity records at a time T 1 and at a time T 2 equal to T 1 plus 2L/c, and the Case damping constant. Equation 3-14...
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33_HWKTTE 4004c - accelerometers The velocity is then...

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