Key Elements of Safe Structures
By Jeff M. Reder, P.E and Dan Peak
Almost every successful live event shares the same key elements: affordable, profitable, accessible, enjoyable, and safe. The last of these elements, safety, has become increasingly important in an era of bigger stages, bigger crowds, bigger displays, and bigger stakes. What makes an event safe can take many forms, ranging from more security to food inspections to a well-developed emergency plan. No matter what position you have in the entertainment industry, safety is a priority.
As a structural engineer working in the entertainment industry, my contribution to event safety is to ensure that all stage, tower, deck, and framing components have been properly designed. Time-tested methods of constructing safe event structures still hold true, such as adequate ballast, sufficient member strength, and properly executed emergency plans. However, as events become bigger, faster, and more intricate, our experience points to one element playing a more important role in safe structures than any other: COMMUNICATION.
You may be thinking to yourself: “a structural engineer is telling us that communication is more important than math?” Yes. Without proper conveyance of information, the math does not matter. For example, let’s review a four post-concert roof of a non-descript nature. The lighting designer develops a plan which includes numerous moving lights and a suspended high definition video wall. In addition, sound cabinets are to be hung from the downstage cantilever and the band wants to place a large banner at the rear of the stage. Sounds like a pretty standard set up for the average show.
As the engineer, I am going to ask important questions such as:
How much does each lighting truss weigh?
How large are the video walls?
What type of ballast is available?
What are the ground surface conditions?
Do you have other wind walls or sidewall scrim?
By now, these questions should be standard for an event or a temporary structure build. However, it can be surprisingly difficult to obtain these answers, and they are often provided at the last minute.
Engineers are often expected to be capable of instantly analyzing a complex structure and providing their client with an immediate response regarding the acceptability of what has been proposed or constructed. This is especially prevalent in the entertainment industry where time tables are tight, problems appear suddenly, and answers are needed immediately. This is an extremely dangerous situation. Providing information early and completely can help keep an event on schedule and everyone on site safe.
When determining the safety and stability of any structure, entertainment or otherwise, every engineer will conduct the same process:
Calculate the anticipated loads on each element, such as the self-weight of each element, movable loads such as lights and speakers, or wind loads based on expected wind area and wind speed.
Determine how those calculated loads will travel through elements to the ground (or surrounding structure).
Prove that each structural element is strong enough to resist the calculated loads.
Each of those steps takes time. Depending on the complexity of the system, the process can involve a quick mental calculation or days of analysis. Every stage, truss, deck, and tower used in any event should have undergone this process, either years before in a testing facility or moments before on a calculation pad. Regardless of which extreme of that timeframe is followed, it always starts with clear communication between the event management team, stagehands, and the engineer.
In addition to communication prior to an event, communication during an event is of equal importance. The operation management plan for an event often includes special instructions which should be followed religiously to prevent dangerous situations from evolving. From a structural perspective, such actions can include checking rigging elements for damage and tightness, ensuring ballast is on firm ground, or monitoring the weather for excessive wind speeds. These actions are very dependent on well planned communication between the field team and the design team.
Everyone can do their part to keep both attendees and staff safe at every event. When it comes to event structures, make sure your design and site team is aware of every new load, every changed layout, and any component that could catch some wind. It’s through intentional communication that we, as design professionals, can do our job right to keep everyone safe.