CONSTRUCTION FIXINGS The results of testing for pull-out
from cellular concrete blocks of the aforementioned three groups of anchors, when analysed enable us to note the following.
Figure 3 Results of testing of anchors from 3 groups
Trademark Manufacturer SXS 10X100
SXR 10X100 KAT N
FTP K10 KBT 10
FIS V 360 S ITH 380 MIT-P
Results of testing*, kN NRu,m 1.5
1.75 1.5 3.8 4.2 7
0.35 0.35 0.4
0.35 0.35 1.5 1.9 3.1 0.5 0.5
* Load values are taken as an average value for testing 5 samples
1. Pull-out resistance (bearing capacity) of anchors belonging to the first group, using a polyamide plug, depends (for majority of them) mainly on the contact area between the cylindrical plug surface and an anchor bore in a block, and also on the strength and density of the cellular concrete block. The bearing capacity of anchors with polyamide sleeve differs slightly according to different manufacturers. It should be noted that the pull-out behavior of all anchors is related to a sliding of the polyamide plug along a zone of contact with the base material.
2. Pull-out resistance (bearing capacity) of polyamide anchors with threaded design of polyamide sleeve were 4 - 5 times higher than the bearing capacity of the first group’s samples. This was due to the increased contact area with cellular concrete and formation of a pull-out cone in case of fracture (Fig. 4). One should note that, as the tests demonstrated, anchors of this type require that the installation technique should be properly followed in accordance with producers’ recommendations. Even slight additional screwing in of the anchor during installation can cause a fracture of the cellular concrete structure in the threaded zone of the anchor, which results in a sharp decrease of the anchor bearing capacity.
Figure 6 In anchoring the new
design, pull-out resistance of the anchor unit is provided not only by adhesion between the block material and injection resin, but also by the additional volume of the cellular concrete block that is involved into the work. This can be seen in Figure 7, when a conical anchor under the trademark FIS V 360 S (fischer) is pulled out from a cellular concrete block, pull-out resistance is provided by a considerable mass of the block located around the cone. At the same time the bearing capacity of the conical anchor under the trade mark FIS V 360 S (fischer) is 5 - 6 times higher than that of all other trademarks of anchors and, taking into account an anchor unit fraction behavior, the safety factor for anchor pull-out resistance calculations can be taken as the same as for evaluation of cellular concrete blocks strength according to the construction norms and regulations SNiP11-22-81 “Stone and reinforced stone structures”, i.e. k= 2.25.
Conclusion Analysis of experimental results obtained in the course
of determining the pull-out resistance of anchors in cellular concrete blocks enables us to note: For fastening elements of façade systems to the walls made
3. Bearing capacity of chemical anchors being installed into a drilled hole in a cellular concrete block depends mainly on the quality of adhesion between injection resin and cellular concrete. As the density and strength of cellular concrete is low, breakout of the anchor when it is pulled out takes place along the resin – concrete contact zone (Fig. 5). Provided that
of cellular concrete blocks it is recommended to use anchors of the second group, with a thread design. In especially critical structures, such as high-rise or unique
buildings, consideration should be given to the fischer FIS V 360 S utilising the special conical drill.
Note: The results and recommendations of this report are
published as submitted by the authors and have not been verified independently.
82 Fastener + Fixing Magazine • Issue 68 March 2011
the seating depth of chemical anchors is the same as that of anchors belonging to the first group, bearing capacity of chemical anchors appear to be higher by 30% - 40%. However, it is hardly possible to forecast increase of the anchor bearing capacity, because of the difficulty to control the quality of filling a drilled hole in cellular concrete with injection resin.
Figure 5 With the objective of increasing the bearing capacity of anchor
installed in a cellular concrete block, experts from the company fischer proposed a new design of chemical anchor. The new design envisages a change of the drilled hole shape, thanks to the use of a new drill (Fig. 6).