Experimental Research on the Pull-Out Performance of FRP Bar Connectors Considering Concrete Age

To investigate the pull-out performance of FRP bar connectors during the construction stage， this study designed and conducted pull-out tests on four groups with a total of twelve FRP bar connectors， with concrete strength （C25， C15） and insulation layer thickness （50 mm， 70 mm） as the research parameters. The failure modes， pull-out bearing capacity， load-slip curves， and load-connector strain curves were systematically analyzed. The experimental results indicated that all specimens failed due to concrete anchorage failure at the connector end. Concrete strength grade had a significant influence on the pull-out bearing capacity of the connectors. When the concrete strength increased from C15 to C25， the pull-out bearing capacity of specimens with insulation layer thicknesses of 50 mm and 70 mm improved by 18.1% and 21.0%， respectively. In contrast， insulation layer thickness had a relatively minor effect on the pull-out bearing capacity. When the insulation layer thickness increased from 50 mm to 70 mm， the pull-out bearing capacity of specimens with concrete strength grades of C15 and C25 increased by 3.3% and 7.4%， respectively. At failure， the strain of the connectors along the pull-out direction remained well below the ultimate tensile strain of the FRP material， and no damage was observed in any of the connectors.