Friday, 10 Aug 2012 06:37 GMT

Fixing 2

The consequences of signs secured to solid structures failing cannot be understated. Simon Havard asses the risks of getting it wrong and details how to get it right, first time

Getting the right fix to avoid failure

In all probability, the majority of signs are attached to some sort of existing structure. This may be a simple flat panel screwed or taped to an internal wall, or it may be a large projecting sign attached to the external wall of a panel-clad building. In either instance the correct fixings for the wall type are required. However, the comparative risks and potential danger as a result of either failing are huge. In other words, if the small panel falls off it will be embarrassing, but little real danger will ensue. But if the large projecting sign fails, someone could be killed.

This month I want to discuss the potential risks involved in attaching signs to existing structures. This could range from additional panels on existing signs or lamp posts, through to attaching large panels to lightweight panel clad buildings.

Signs, lamp posts and fences

To create well designed, durable and securely fixed
signage—such as the projects created by Ashby Sign
Supplies pictured (Above and Below)—attention to detail and
a consideration of all the structural elements and most
extreme external forces is needed

Most lightweight structures are sensitive to added ‘load’, whether this is wind or weight. By adding
a sign panel to a lamp post or open style fencing you may be increasing the windload on that structure to a point where it may fail in high winds.

The same may be true for an existing sign—just because there is space between the posts of an existing sign does not necessarily mean it can be filled with extra panels or that the sign can cope with the added windload.  For safety’s sake it is at least worth asking the question.

Panel clad buildings

These often prove the most of difficult structures to attach to. These can vary from a corrugated sheet clad steel frame, as commonly found in warehouse style units where the structure is visible from the inside, to a more sophisticated composite style facing panel—with hidden structure and decorated interior, such as those increasingly found in modern office buildings.

When attaching flat panels to these buildings, the temptation is to fixing directly to the cladding. Self-drilling screws will allow even the largest panel to be fixed easily and quickly. But beware, as these lightweight panels are not designed to take significant weight or wind pressure from point loads—wind on the sides of building will rush across the face of a sign panel and try to
literally ‘suck’ it off the wall.

Cladding panels tend to be continuously fixed around all edges and are designed to resist evenly distributed windloads. They are not designed to withstand the same sort of windload exerted through a few screws in the middle of the panel. Even when attaching internally consider the sort of point load you may exert on the panel.

So, if your sign needs to be attached to a panel clad building you may need to fix it to the main building structure. This is easier with the warehouse style building as usually the structure is visible and can be easily surveyed. With hidden structures, ‘as built drawings’ backed up by a physical survey may be required. But always ensure you secure the sign to an element of the main building structure and request that the client has your proposals checked by an appropriate engineer.

Brick, block and concrete

Attaching to these structures is generally more straightforward, but a degree of consideration is still worthwhile, as each has its pitfalls.

When securing to brick walls care should be taken in checking whether the wall is double thickness, if there is a cavity and what condition the wall is in. Preferably secure into the bricks not the mortar as the performance of fixings specifically for brick will only apply if you fix into the brick itself. It is also important to remember the strength of a fixing will depend upon how well the brick is bonded into the wall—so do not try to hang a large sign from one or two bricks only as I have witnessed several instances of individual brick failure.

Block work requires a similar treatment to brick. Consider the cavity and softness of blocks, they are designed to resist compression not significant lateral load. So care should be taken when securing into the sides. If the risk involves significant weight or windloads ensure the correct fixing for the correct block type is used.
The final usual suspect is concrete, this will generally provide a continuous, consistent fixing base, but beware that some concrete floor or wall slabs will be stressed with considerable steel reinforcement. Again do not assume that just because it is concrete that it will automatically strong enough—I would always advise that a proposed fixing is checked first.

A ‘whistle stop’ tour of likely existing structures, but keeping in mind only the main points detailed above will help improve sign safety and may even save a lot of wasted time and money.