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CONSTRUCTION FIXINGS

Anchoring in cellular concrete blocks

Doctors A.V. Granovsky PhD and D. A. Kiselev, from the TSNIISK Central Research Institute for Building Structures submitted this report on “Experimental investigation on bearing capacity of anchor fasteners installed into walls made from cellular concrete blocks”. It presents an interesting insight to some of the issues in the Russian Federation construction fixings market.

A

s of today, there is a heavy deficit of cellular concrete of good quality in the Russian Federation. Because of a shortage of quality products, consumers have to purchase concrete manufactured by makeshift working

methods, namely non-autoclave cellular concrete and aerated concrete. Considering the application of cellular concrete variants in the form of small-sized blocks in self-supporting walls, with separations by floors, for residential and public building, the absence of proper control of their strength and density leads to wide-scale usage of aerated concrete block - for example: with strength between 0.8MPa and 2.5MPa and density below 500kg/m3

. The aforementioned problem has

become the most challenging one in relation to the attachment of bearing substructures of façade systems to walls made of such materials, and with installation of metal reinforcing bonds in two- or three-layer walls. We would like to note that in 1982 experts from several

research institutes issued the State Standard GOST 25485-82 that clearly divides cellular concretes, depending on class of concrete and its density, into the following types: structural, structural and heat-insulating, and heat-insulating concrete. “Recommendations for application of small-sized wall blocks from cellular concretes”, issued in 1992 by experts from TSNIISK, NIIZhB (Research Institute of Reinforced Concrete) and LenZXIIEP (Leningrad Zonal Research Institute c Experimental Design), prohibited the use of cellular concrete blocks of the grade below 2.5MPa and with density lower than 500kg/m3

for

self-supporting walls. Unfortunately, these requirements are nearly forgotten today. At the same time, wide-scale usage of cellular concrete blocks, classified as belonging to structural and heat-insulating types, leads to a sharp reduction of service reliability of both walls and façade structures (including hinged ventilated façades) that are attached to the walls. Because of immensely increased volume of works for building hinged ventilated façades, the question of the reliability of fastening façade structures to the walls made of cellular concrete blocks becomes especially vital.

Selection of the most efficient types of anchorage used for fastening facade structures to walls made of cellular concrete blocks.

Experimental investigations for determining pull-out strength

of various types of anchors installed into walls made of cellular concrete blocks have been carried out at the TSNIISK. The objective of these investigations was to select the most effective types of anchors used for fastening façade structures to the walls made from cellular concrete blocks. Anchors from the companies fischer, Sormat, Mungo and Hilti, which are available in the Russian Federation market,

were chosen for testing. Tests of anchors with the objective of determining their pull-out strength were carried out in accordance with a technique developed by the TSNIISK. The compression strength class of concrete was B 1.2. Depending on their design the anchors were divided

into 3 sub-groups.

1) Anchors consisting of a working body in the form of screw (7mm diameter, length 105mm) and an insert – a polyamide plug (10mm diameter, length 100mm). Examples of this group of anchors include fischer SXR, Mungo MB-S, Sormat KAT N, Hilti HRD-UGS. Generally speaking these anchors differ one from another only by the profile of the polyamide plug and are recommended by their producers for installation into cellular concrete blocks. An example is shown in Figure 1.

Figure 1

2) Thread design anchors. These anchors have a polyamide spiral external thread that, using a setting tool, is designed to cut another thread into the base material. Examples of these anchors were only found from the companies fischer (FTP K10) and Sormat (KBT 10). An example is shown in Figure 2.

Figure 2

3) Chemical anchors consisting of the following elements: • Working body - thread stud 10mm diameter. • Injection resin. • Polyamide or metallic net-shaped sleeve.

This group includes anchors from fischer, (FIS V360 S),

Sormat (ITH 380) and Mungo (MIT-P). Example of a typical system shown in Figure 3.

80 Fastener + Fixing Magazine • Issue 68 March 2011

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