Pull out testing of self-screwing retrofit wall to diaphragm anchorage system

An overview of the observations from building performance inspections undertaken after few recent damaging earthquakes was presented, with an emphasis on the performance of wall to diaphragm anchors in unreinforced masonry (URM) buildings. Based on these observations, key variables affecting the pull out capacity (POC) of typical tension anchors were identified. The identified variables included type of anchor, embedment length, installation quality, anchor location, and condition of the substrate material. Seismic performance of a newly developed self-screwing retrofit wall to diaphragm anchorage system was then investigated through two series of pull out tests. Of these, the first series involved the testing of 30 anchors installed into salvaged timber diaphragm sections and reconstructed heritage URM wallettes whilst in the second series 10 anchors installed in a historic masonry building were tested in-situ. The experimental results were used to infer dependable tension capacities using statistical analysis and were compared to values recommended in literature for typical adhesive anchors. The POC of the anchorage system ranged from 13.01 kN to 23.12 kN when installed into typical heritage URM walls and between 9.54 kN to 12.16 kN when driven from side into two consecutive floor joists of a heritage timber diaphragm. The POC for anchors installed with excellent installation quality was observed to be 16% higher than that with average installation quality, whereas the installation in mortar joint and damp masonry resulted in a reduction of POC by 24% and 13% respectively.