Retrofitting techniques in masonry multi skin wall construction

Abstract

The main focus of this study was to investigate different proprietary ties used in the masonry construction industry. This dissertation focused on analysing the bond behaviour of DryFix and GeoSteel Grid ties when inserted in different materials. A number of variables were studied and compared with results obtained from other researchers. Globigerina limestone blocks, mortar and concrete were used as a parent material. A total of 48 specimens were prepared, 30 isolated specimens, 15 of which prepared with DryFix ties in the middle of the globigerina limestone block and the other 15 with the GeoSteel grid ties, 6 specimens having DryFix ties inserted in the rnortar joint and 12 cylinders with DryFix ties, 6 of which were cast with an M2 mortar mix and the others with a C20 concrete mix. Three variables were studied being (i) Lile change In diameter of DryFlx ties, (II) the change in grade of GeoSteel grid ties, and (iii) three different anchorage lengths. Pull out testing was the main test conducted for this study. Results of mechanical pinned ties, being the DryFix ties, showed two types of failures referred to as bond failure and bond failure with local cone damage. Results tor DryFix ties also showed that with an increase in diameter, the pull-out force is decreased. Compressive strength might also influence the maximum pull-out force resisted by mechanically pinned ties. GeoSteel Grid ties showed three main types of failures referred to as, bond failure with local cone damage, yielding of steel and grout failure. Results also showed that when a higher grade steel grid was used, the force withstood was lower than those with a lower steel grade. DryFix and GeoSteel grid ties gave different results for the same variables. DryFix ties experienced higher rates of displacements for similar pull-out forces. With an increase in anchorage length, bond strength for DryFix ties increased while with GeoSteel grid ties bond strength decreased with the increase in anchorage length. GeoSteel grid ties might not be utilizing the full length available because failure of the grout might be occurring before the whole length is utilised. Bond strength might be influenced by the preparation process as well since after failure, stone dust was noticed around some of the GeoSteel grid ties. Observations also showed that some ties, both DryFix and GeoSteel grid ties experienced slip from the very beginning. This meant that the bond between the substrate and the tie was ineffective and were considered to be defective.