Development and Testing of Hollow-Core Retrofits

Abstract

Precast concrete floors are the predominant flooring system in New Zealand. Cost efficiency, low self-weight and the ability to span long distances are some reasons for their popularity. The 2016 Kaikoura Earthquake, however, exposed significant vulnerabilities of precast flooring systems in Wellington’s multi-storey buildings. In particular, precast, prestressed hollow-core floors performed unsatisfactorily even at low drift levels and raised concerns about the ability to withstand moderate to severe future seismic events. While previous research on hollow-core floors has mainly focused on improving the seating details, little attention was devoted to the retrofitting of earthquake-prone hollow-core floors in existing structures. This emphasises the importance and urgent need of the development and the experimental validation of retrofit solutions, particularly for areas with high seismicity such as Wellington.

Therefore, an experimental test programme has been initiated to provide engineers with appropriate assessment methods and retrofit techniques. The first part of the test series consists of sub-assembly tests, representing the connection of the support beam to a single unit with topping concrete. These tests will be used to trial various retrofit solutions. Following, the suitable retrofit solutions will be tested in two three-dimensional full-scale super-assembly tests.

Various retrofit designs addressing the detrimental effect of steel sections placed flush against the soffit as seating extension has been successfully tested in the simple sub-assembly tests. Further investigations looking at over-reinforced support details as well as the negative effect of poor bond conditions of prestressing strands on seismic performance are underway.