Dear all, Why we place two strain transducers and two piezoelectric accelerometers at diametrically opposite locations in the dynamic pile load test? It seems to me that 4 strain transducers and 4 piezoelectric accelerometers at 90 degrees OR 2 strain transducers and 2 piezoelectric accelerometers at perpendicular positions would cancel the bending and the temperature effects. I appreciate your answers. Thanks.
You are right. For redundancy, you should install two "sets" of transducers diametrically opposed, i.e. four locations. If one transducer fails, then you can rely on the other "set". Your second option of installing transducers at 90 degrees will not acheive a redundant system for you!
Temperature effects are meaningless for dynamic testing since the data is zeroed for every impact. 2 strains are the recommended MINIMUM and are sufficient for most computations (capacity, energy average stresses, tension, integrity). The transducers are quite reliable so the redundancy issue is rarely a problem. If you want to know the absolute maximum bending in the pile, then 4 strains at 90 degrees is an improvement. All accelerometers will give about the same result so contributes practically no extra information even on bending (except for redundancy, there is no real benefit for more than one or at most two accelerometers in general) Garland Likins, Pile Dynamics