Failure Detection of High-Strength Tendons in Prestressed Concrete Bridges by AE

Three types of beams post-tensioned by steel bar, strand, and parallel wire cable with three different grout conditions (unbonded, partially grouted and fully grouted) were tested in a laboratory.  Failure was introduced by artificial corrosion, charging anodic current to tendons.  It is found that acoustic emission (AE) signals with extremely high amplitudes are generated by ruptures of high-strength tendons.  Detectability of failure is demonstrated to be 82-86%.  Then, continuous AE monitoring was carried out in two highway bridges in service.  The analysis of detected AE signals proves that meaningful AE events due to tendon failure are clearly discriminated from other signalsof traffic noises and hammering

Theoretical evidence for the superluminality of evanescent modes

Though both theoretical and experimental investigations have revealed the superluminal behavior of evanescent electromagnetic waves, there are many disputes about the physical meaning and validity of such superluminal phenomenon, which is due to the fact that the traditional investigations are based on the theory of tunneling time, and concerned with the problem of what the group velocity of evanescent waves means. In this paper, by studying the quantum probability amplitude for photons to propagate over a spacelike interval along an undersized waveguide, we present theoretical evidence for such superluminality