In a series of tests, the effect of the hammer orientation on the 

 force input to the timber pile was assessed. The PCB hammer held at 

 three different orientations was used to strike a solid pile: handle of 

 the hammer parallel to the axis of the pile when vertical; handle of the 

 hammer perpendicular to the axis of the pile when vertical; and handle 

 of the hammer perpendicular to the axis of the pile when horizontal. 



The hammer orientation affected the amplitude and frequency band of 

 the input force and output signal received (Figure 25) . A standard method 

 of hitting with the handle of the hammer perpendicular to the axis of 

 the laboratory test pile laying horizontally in the water was established. 



The hydrophone and accelerometer impact tests were repeated on the 

 standard pile and conducted on the same test timber piles used previously. 

 The data collected during the impact laboratory tests are shown in Fig- 

 ures 26 and 27. These curves generally exhibit a decrease in frequency 

 of the highest amplitude peak with an increase in percent cross-sectional 

 wood loss. 



Figure 26 shows the regression analysis of the hydrophone data col- 

 lected for all of the laboratory test piles. In addition, the R-value 

 for the curve, the standard deviation, and the standard error of estimate 

 are shown. The standard deviation is very high, resulting in a high 

 standard of error. Figure 27 shows the regression analysis of the accel- 

 erometer data collected for the standard, 5x, and 4x1 test piles; again, 

 the standard error is very high. 



The other variations expected between solid and damaged wood, which 

 included changes in bandwidth and number of discrete frequency bands, 

 were evaluated. However, no correlation to the percent of cross-sectional 

 wood loss could be found. 



As expected, the solid areas of the test piles generally had a higher 

 frequency response than the damaged regions, but this was not true for 

 every test. Variations were observed between repeated tests, and several 

 contradictions between damaged and solid regions were found. 



Impact Field Testing 



Field impact tests were conducted at the corrosion test pier on the 

 piles inspected with the ultrasonic test equipment. Preparations made 

 before impact testing were the same as those outlined in the NCEL Ultra- 

 sonic Field Testing section. The only difference was that the hydrophone 

 or the accelerometer rather than the transducers (receiver and trans- 

 mitter) was employed. 



The general procedure followed for the impact field tests closely 

 resembled the procedure followed for the laboratory impact tests described 

 in the preceding section. However, the high electrical noise level in 

 the cable lines and ambient noise level in the harbor severely distorted 

 the impact signal of the PCB hammer. Consequently, a 3-pound sledge 

 hammer was utilized during the field impact tests, and the impact imparted 

 to the timber pile was not recorded. 



43 



