“History may not repeat itself – but it does rhyme.” – Joseph Anthony Wittreich
What is sign engineering and does it concern you? In almost any sign fabrication setting, engineering of a kind does concern you, because, whether you’re welding girders or hot-gluing foamboard displays, the way any type of sign structure goes – and stays – together involves several critical factors: an intelligent analysis of all mechanical and stress aspects, proper materials and intelligent completion actions. Therefore, you become a type of mechanical engineer the moment you decide how to join two parts.
• Is the joint or structure load (weight) bearing?
• How are the pieces to fit together?
• How will you join them?
• Are your chosen materials and joining process tested, and will it endure the various stresses the junction or supporting scheme may encounter?
• Does your joining modus align with the job cost projections?
• Can the joining be done in-house or do you need to outsource the process?
• And, because the signmakers’ task is to make attractive signs, is your joining method undetectable and pleasant to view?
Hopefully, this will remind of the need for engineering-type thinking, even in everyday fabrication and installation operations, especially when you’re in the field and dealing with existing conditions you may not have created or contemplated.
EXISTING SIGN STRUCTURES
Lately, because I enjoy photographing old structures, I’ve seen and studied some what I’ll call archaic sign installations and couldn’t help but wonder if they have remained safe. With this in mind, I telephoned Sean McFarland of McFarland Engineering (Advance, NC) because his firm handles big-time sign engineering jobs, but he also offers practicality when it comes to everyday sign engineering and installation. McFarland has one of those minds I enjoy being around. Ask him a question and you can almost hear him mentally ticking through complex details before he decides which concept is most relevant for him to present. For example, I asked about old pole signs, because I had recently studied one that appeared more like a salvage-yard find than an able structure. It was dented by car bumpers and speckled with rust, looking more like the surface of an overbaked pizza than a sign pole. Still, it supported three cabinet signs.
I didn’t park my car underneath it.
I asked McFarland, “What should a signshop know before mounting a new sign on an old pole structure?”Advertisement
I swear I heard his mind clicking. He said to look for an access – inspection– hole in the pipe, and, if you can see inside, try to determine if the pole has ever held standing water that could cause excessive interior rust. There are sensor devices that measure rust damage, but visual indications of pitted steel or flaking could be serious warnings that, say, the original pipe wall thickness is now considerably lessened.
McFarland explained that pole-sign framework modifications are also indicators of a weakened structure. We’ve all seen such late-in-life modifications – angle-iron tangles – to sign structures. I don’t park underneath these, either.
Pole-sign, match-plate modifications are of special concern to McFarland, because modifications here – new plates with unmatched bolt holes, say – can cause the plate to stand offside the original plan and change the torsion factors, which cause new stress dynamics, especially in windy conditions.
Be cautious also of wall-sign replacements, e.g., replacing same-size wall signs that were installed years ago when zoning codes and weather patterns may have been different, and thinking you can reuse a similar mounting system. Not so. He also cautioned regarding wall-sign installation on brick façades, noting that brick is a veneer and each brick wall has a limited-load capacity, which can be influenced by how often one makes attachments to it. A classic example, he said, is when using a steel plate to mount a blade sign, one with bolt holes that are closely spaced and therefore weaken the brick veneer’s capacity to handle the load.
Benjamin Jones, PE, in his book, Engineering Sign Structures, writes of the many common sign phenomena. Regarding wind, he writes, “Vortex shedding is one example of phenomena loosely called ‘aerodynamics effects.’ Some others are galloping, flutter and aeroelastic effects – the interaction of wind with a moving structure.”Advertisement
Sign flutter? You bet. And, like the constant bending of a wire coat hanger to break it, flutter can break a sign-support bolt or bracket. Jones’ book includes a series of sketches that exhibits the action of wind on sign surfaces. They look like untethered ships being tossed about by a Caribbean hurricane.
You should have a copy of Jones’ book (available from Amazon.com) on your desk, one that’s heavily highlighted and flagged with 3M sticky notes.
Your sign isn’t going outside? It’s a digitally-printed, hot-glued cutout for a retail store? No wind, no worries, right? What about the prosecutions of a bored, six-year-old schoolboy?
MONEY AND SIGN ENGINEERING
In his book Sign Structures and Foundations: A Guide for Designers and Estimators, Peter B. Horsley, a founder of modern sign engineering, writes of the economic realities of running a business. In that passage, his primary focus relates to material costs and taxes.
You should have a copy of Horsley’s book (available from Amazon.com) on your desk, too, one that’s also heavily marked.
Horsley’s business was in Canada, a more socialistic economy than the US, and thus one with higher taxes. However, an exploration of Horsley’s tax and expense list reveals shop expenses similar to those faced by US signshops – although the percentages might vary. He lists excise tax on imported parts or components, income tax, sales tax, property tax, gasoline tax, business tax, business permits, vehicle license plates, medical tax, worker’s compensation, unemployment insurance, pension plans, corporate tax, auditing expenses, wages for holidays and vacations, and regular operations expenses, e.g., telephone, power, maintenance and more.Advertisement
Horsley introduces cost reminders because he recognizes that any aspect of contracted engineering must fall within the arena of affordable shop expenses, i.e., operating costs, as well as adding to the business profit picture. Thorough engineering can cut costs and lower future risks. Flawed engineering eventually adds to shop costs, especially if a structure failure occurs that causes re-engineering and outlays in fixing, redesigning or reworking the failure. Or, worse, damage and litigation costs.
THE TEN-CENT BOLT
H.W. Morrow says, in his book, Statics and Strengths of Materials, a “structure” comprises a series of connected structural members or rigid bodies that are designed to support loads or forces, and notes that all acting forces (on structures) are applied to the joints, as well as that members, joints and loads lie in a plane. Therefore, stress at one point will, in some way, affect the other structure components. He notes that one must determine the external forces acting on a structure – wind is the big concern with signage – but also the forces that hold the parts together. Bolted material (plates, for example) becomes compressed and correspondingly, the composite material being compressed presses back against the bolt head and nut, which adds tension to both bolt and plates. Thus, sometimes tightening is best measured by a torque device rather than strong-arm actions. Also, tension failures of connecting plates can be caused by holes, fractures or a general yielding of the plates. Shear failure usually befalls bolts or similar fasteners first.
In his columns for Road & Track magazine, my friend Allan Girdler once wrote of his brother losing a sports car race due to a ten-cent bolt that broke on the last lap. It’s not an uncommon story, so don’t buy cheap bolts. Girdler, in summation, advised expensive fasteners and close visual inspection of all joined components.
In The Design of Design, Frederick P. Brooks, Jr. says amateurs make a lot of mistakes that a professional would not, but when they do goof, professionals do it in a big way – making bridges that collapse, houses without stairs between floors, and my favorite, computers that radically waste memory bandwidth, as does my new Lenovo laptop. What the hell is a Mixed Reality Viewer, anyway?
You can search Google for a recent history of sign failures: Sign falls on car; Potomac Mills sign falls; downtown Atlanta sign [mural] falls off building; Taco Bell sign falls; sign falls on family; and the erstwhile but always notorious Las Vegas Hilton sign collapse.
The worst recent engineering failure relates to the Florida Intl. Univ. and City of Sweetwater’s 174-ft.-wide, 950-ton pedestrian bridge installed across eight lanes of Tamiami Trail. You saw it on the news. Due to engineering wants, it fell onto the roadway and crushed eight cars, killing six people. This happened March 15, only a few days after the pre-fabricated bridge section had been installed.
Outside expert reports say that a particular truss member was “underdesigned” and not strong enough to withstand the pressure from the weight of the bridge. True? I have no idea, but you can be sure the cause will be contested for years.
Frankly, I’d rather design and build signs than sit in court. You?
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