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Anchors for fastening to floors and walls

Introduction

Most fixed mechanical systems have to be fastened to a floor or wall.   The notes below relate to the general design principles involved in designing and specifying these fasteners.  These notes are rule of thumb notes for initial guidance-- It is important that final design details should only be fixed using suppliers literature and following consultation with the suppliers and the relevant structural /civil engineers.

An important factor when fastening to floors and walls is the material and condition of the surface.  These notes relate generally to masonry walls and concrete floors.   It is important to know the grade of the concrete prior to selecting the anchors.   The civil engineer should be advised of the expected static and dynamic forces being transferred into the structure.  The civil engineer needs the forces in the local x,y,z directions and the associated moments about the local x, y and z axes

Concrete Floors

Ideally mechanical equipment is fastened to cast-in blocks, brackets etc which are cast in the walls and floor during building construction.    Large machines are often positioned on raised plinths for floor mounted machines these should be at least 100mm above the normal floor level.   These plinths can include pockets into which special bolts are cast.

It is modern practice to drill holes and fasten equipment using special proprietary anchors.   The links below identify many suitable anchor designs.    The strength of these fittings are generally based on a concrete strength typically (30N/mm2 (C20/25)).   When fastening to lightweight concrete and concrete with different grades to that identified in the brochure the strength values must be adjusted..

The support strength of proprietary anchors is normally not affected if the concrete is reinforced.   It is however important not to drill into the reinforcement.  It is therefore prudent to consult the structural drawings to confirm the minimum depth of unreinforced concrete prior to selecting the anchors.

The centre distance between the anchors and the distances from the anchor to the edge of a concrete surface is an important factor in the strength ratings of the anchors as provided in the literature.  If the distances are reduced then the rated strength needs to be reduced according to the suppliers recommendations.

Masonry Walls

Structures, made of cut stone and cast concrete, made into shapes and fitted up tightly together, or laid up with mortar or similar material, are considered masonry structures.  This type of structure is generally strong enough to support engineering components using proprietory achors.  These should be drilled into the solid bricks or concrete blocks and not into the mortared joints.

Again the preferred option is consult the architect /civil engineer an request cast in plates, or studs or female sockets..

Care must be taken in the choice of anchor to ensure the base material is not cracked or split due to expansion forces. It should not be positioned in the mortar joints and must be located away from the edges. Site tests may be required to determine the suitability of the anchor for the base material.

The fixing holes should be restricted to 30mm from the remote face and 300mm from vertical and horizontal edges of the brickwork where possible.

Blockwork Masonry Walls

These are the lowest strength wall constructions and one should avoid mounting mechanical equipment off masonry walls..Bonded anchors are preferred and torque controlled anchors should not be used..

Wooden Walls

Note: More detailed information on this topic is found at Timber connections

There are a wide range of wooden wall options starting at thin lathes of wood to walls made up of thick timber logs.    Generally solid wood has significant strength and mechanical components can be fastened to wooden wall to provide horizontal support and some vertical support.  However it is always recommended that mechanical equipment is primarily supported off solid floors.

It is important when fastening to wood using wood screws or bolts that suitable pilot holes are provided.   This is very important when using larger screws. (Lag-screws.   If pilot holes are not drilled then there is a significant risk when tightening the wood screw that the wood will split.

It is generally accepted that through bolts with nuts e.g coach bolts are preferred to screws which directly screw into the wood.  For wood joint subject to high shear loads it is advisable tobolt the wood through shear plates.  These are discs with sharp edged collars which dig into the wood and provide a large dia shear area for the wood as opposed to the small dia of the bolt.

Partition Walls

These are internal walls made from hardwood or plasterboard fastened to wooden structures.   It is not advisable to mount any engineering component of any significant mass to a partition wall.   The preferred option if wall mounting is required is to provide a seperate support structure which is fastened to the wall and supported primarily off the load bearing floor.


..to be continued



Sites Providing Information On Anchors
  1. Strongtie-Liebig..Information on Anchor Bolts
  2. Hilti..Information on Anchor Bolts
  3. Canadian Wood Council ..Connections very very informative site on Fastenings for Wood

This Page is being developed



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Last Updated 24/01/2013