A non-destructive evaluation method is proposed to identify the sectional loss of the external tendon of prestressed concrete structures by detecting the change of the magnetic flux in the external tendon exposed to a magnetic field. The method uses a solenoid-shaped device with two coils: a primary coil for producing magnetic field and secondary coil for damage detection, wrapping the external tendon. A current applied to the primary coil in the device causes the magnetic field. Then, the change in the magnetic flux by the damage in the external tendon is detected by the variation of the voltage in the secondary coil in the device as the device moves along the tendon. An alternating current is applied to the primary coil to minimize the effect of the moving speed of the device. As a result, the damaged area can be detected with a low-level energy current. In addition, a wrapping solenoid-shaped device that is easy to disassemble and assemble was developed for in situ inspection. The measured signal from the secondary coil has a sinusoidal form with the same frequency as the applied current to the primary coil, and the peak curve of the measured signal provides enough information to detect the damage. It is shown that the proposed method can quantitatively identify one or multiple damaged-tendon locations as well as damages of at least 2 cm.

As part of the efforts to improve the performances and reliability of the elastomeric bearings produced in Korea, this paper evaluates experimentally the validity of the ultimate loads of the design allowable values of KS F 4420 purposed for the design of elastomeric bearings in Korea. To that goal, a series of tests including ultimate compression test, ultimate shear test and shear fatigue test were conducted on elastomeric bearings designed in compliance with KS F 4420. The results showed that failure occurred at loads 16 to 26 times larger than the allowable compressive stress and made it possible to conclude that the so-designed elastomeric bearings secured sufficient reliability regard to the vertical performance. In the case of the shear performance, the elastomeric bearings failed in a load range larger than the allowable design values but the performances were also seen to fluctuate sensitively according to the fabrication conditions of the bearings. Especially, the tests revealed that the shear performance degraded significantly or that early failure occurred when the internal rubber layer of the bearings were not fabricated using a single rubber layer. Since the elastomeric bearing can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, the bearing should secure high shear performance. The routine by which some companies are fabricating the internal rubber layer by stacking several rubber pads to form one layer is not only degrading the performance of the elastomeric bearing but may also provoke unexpected failure. This stresses the need for the establishment of specifications forbidding such customary practice.

A survey of previous studies for the seismic performance investigation of existing non-seismic bridges in Korea revealed that numerous studies have been made on piers failing in bending, but studies on piers failing in shear were rather neglected despite their large presence. Accordingly, full scale specimens with aspect ratios of 2.67 and 2.25, being prone to behave respectively in flexure-shear and shear modes, and reduced scale specimens with an aspect ratio of 2.67 were fabricated and subjected to a seismic performance test. The failure behaviour of the specimens was then examined with respect to the amount of lap-spliced longitudinal steels in the plastic hinge region, the aspect ratio, and the scale factor. Test results verified that piers with an aspect ratio expecting flexure-shear behaviour showed flexure failure mode due to the reduced scale factor, and also showed the flexural failure or bond failure of the longitudinal steels according to the lap-spliced details. Based on the experimental results, formulas for the yield and ultimate displacements of circular reinforced concrete bridge piers without seismic details are proposed to evaluate the seismic performance of existing non-seismic bridge piers. These formulas will be useful for the repair and strengthening of non-seismic bridge piers by rationally evaluating their seismic performance.