Influence of high temperature heating on pull-out properties of mechanical anchor embedded in concrete

Surface layer of concrete becomes the most heavily damaged part affected by high temperature heating when concrete structure is subjected to fire accident. In the surface layer of concrete structures, the anchor bolts are used for fixing the equipment or the seismic strengthening elements. There are large variety of concrete anchors and construction methods in anchorage. And many design recommendations are published. About the anchors used for many situations, there are some investigations on pull-out behavior of chemical anchors subjected to high temperature heating. However, the properties on metal-based mechanical anchors affected by high temperature heating have not been cleared. In this research, the influence of high temperature heating up to 1000°C on pull-out properties of two types of mechanical anchors, which were a hammer drive anchor and an undercut anchor, embedded in concrete was investigated. Relationship between the pull-out strength of anchors and the fracture energy was also investigated. Follow conclusions were found within the range of this study (1) Failure mode of both the hammer drive anchor and the undercut anchor, loaded in tension was almost the cone type failure. However, the splitting type failure was observed when specimens were heated over 200°C. (2) Relationships between the heating temperature and the surface failure area or the anchorage depth were not clarified. The failure depth of hammer drive anchor tended to become deeper with the increase of heating temperature, but the failure depth of undercut anchor extensively changed with the increase of heating temperature. (3) The deformation of anchor by heating was not confirmed, but the color of gilding was changed with a temperature rising and expanded over 800°C. (4) Regard to load-displacement curves, the load reduction after the maximum load became gradual by the increase of heating temperature. (5) The pull-out strength of hammer drive anchor a little changed up to a heating temperature of 300°C, but decreased as the heating temperature beyond 300°C. (6) The pull-out strength of undercut anchor was changed by accordance of an anchorage depth up to a heating temperature of 300°C. (7) There is an association between the pull-out strength of anchor bolt subjected to high temperature heating and compressive strength of concrete. (8) Good correspondence was obtained between an actual value observed by the experiment and the theoretical value calculated by the homer evaluation formula substituting the pull-out strength and fracture energy. In addition, it was suggested that the formula could predicting the pull-out strength of anchor bolts under the condition of high temperature heating.