Kozo Nakada

Quality Control Acceptance Criteria Improvements for Pre-Stressed High Strength Concrete Pile Driving Operations in Japanese Building Construction

The current practice in Japan for most driven pre-stressed high strength concrete (PHC) piling sites utilizes an ″energy formula″ approach involving the ″set-penetration test.″ In its current state, driven PHC piles in the Japanese construction industry are at increased risk of being damaged due to inferior driveability evaluation procedures leading to an increased probability of damaged piles remaining undetected after installation. This study presents two case studies in Okinawa, Japan which utilized dynamic analysis as the primary piling quality acceptance criteria and compares results to the energy formula approach which is more common to Japanese construction sites. Based on the observations of these two case studies, the applicability of dynamic testing, particularly the high-strain dynamic test, the low-strain integrity test, and wave equation analyses is analyzed. In conclusion, a case is presented that Japan′s over reliance on an energy formula approach should be augmented by additional QC procedures. A combination of wave equation analysis, dynamic testing and simple visual inspection of post-driven PHC pile conditions is recommended to better protect the integrity of driven PHC piles throughout Japan.

Axial Compression Capacity of Shear-Damaged Reinforced Concrete Columns and Lashing Belt Prestressing

The compressive strength and ductility of concrete can be considerably improved by lateral confinement. In this study, an emergency seismic retrofit technique using lashing belt prestressing is used as to manually retrofit damaged reinforced concrete (RC) columns. The initial prestressing is an important aspect of this technique and is introduced by the ratchet buckle. Thus, this technique offers active and passive confinement as well as shear strengthening. Furthermore, diagonal cracks in the damaged RC columns can be closed by using the active confinement of lashing belts, and the lateral and vertical load-carrying capacity and ductility of the damaged RC columns are recovered. In this study, the recovered axial compression capacity of the retrofitted RC columns and repaired RC columns using epoxy resin was investigated. Finally, the hysteretic behavior of the shear-damaged RC columns after the proposed emergency retrofit was investigated.