Knowing The ABC's Of Structural Engineering Will Help You Communicate With Your Engineer
The structural engineer is a key member of any renovation or new construction of a theatre or performing arts facility. In a project of any scope, it is important to know where and how the main support of the building exists — whether it is steel, wood, or reinforced concrete columns — or where the weight-bearing walls are and how much they will bear. This also includes any ceiling where anything will be hung, from scenery to rigging systems. This is why the structural engineer is there. Some structural engineers understand entertainment needs, and others are not familiar with them at all. But most entertainment professionals don't know how to talk to the structural engineer.
What I have found is that there are two kinds of structural engineers: ones that specialize in working on their own, directly with the owner of a project, and ones that work through an architect, where the owner has very little contact with the structural engineer. Of course, there are firms that do both. By understanding what the engineers need to do their work, owners and project managers can shortcut extra expenses in having things redone (change orders) that can be caught early on in the project. In any major renovation or new building, a structural engineer will be a necessary part of the team.
“On larger projects, the architect is usually the lead design professional, retained by the owner, and the engineers become part of a coordinated design team,” explains Richard J. Nix, project coordinator for Entertainment Structures Group, a division of Steven Schafer Associates Inc., a Cincinnati-based company that specializes in structural engineering for the entertainment industry. “In this case, the architect serves as a coordinator, as a buffer for information, as a team leader, and also as the design professional of record to coordinate the overall building design. The engineers are subordinate to the architect in the overall construction project.”
This brings up a level of hierarchy depending on how large the project is. If you hire a structural engineer to do one specific task, for instance, then you need to know how much weight a specific ceiling or stage can take, so you can be very specific with your questions. A structural engineer might give you one specific point and then put a disclaimer on the rest of the ceiling you didn't ask him to review. Be cautious. It may mean the work the engineer did needs to be expanded and will cost more money.
On a larger project, you'll probably have an architect, a structural engineer, a theatre consultant, a mechanical engineer, and an acoustician, just to name a few of the people needed to build a modern entertainment space. If you're going to hire the structural engineer alone, at the first meeting you need to have drawings of what you want, where it's going to be, which codes may be needed to be followed; if you're asking for a permanent structure, a temporary structure, or something else; whether it's indoor or outdoor, etc.
For productions, you'll probably need someone like an architect to check egress (how many stairs or doors and how wide they need to be to evacuate the building in an emergency) and any other kind of certificate of occupancy use changes. If you're planning to raise the ceiling, bring in any kind of heavy equipment, or hang any heavy equipment, whether a temporary or a permanent installation, you need a structural engineer. If you're building a stage and you're going to have any heavy equipment or scenery on it, you should have a structural engineer look at the drawings and stamp them with his or her rating, which should cover any local laws or accepted practice (to keep the fire department and your insurance agency satisfied).
Daniel Clark, PE of Entertainment Structures Group, notes, “We generally work with architects on the full-scale projects, and rarely do we work with architects on the entertainment side, where we are hired by the owner directly, or work with subcontractors to review their drawings for code compliance and verify for new code requirements,” he says. “Some of our regular clients experience new codes or code revisions to which they must update their equipment. So they hire an engineer to make recommendations for the systems and help get them up to code. The client drawings are usually where an engineer's seal applies, so they should accurately reflect the systems and equipment being installed. Architects do not do a structural analysis, and so our company works with them more on building-related issues rather than on equipment-specific issues.”
To best deal with these issues, Chris Buckley, a theatre consultant and president of Production & Performance Facility Consulting LLC in New York City, has established a worksheet with a list of initial items to be addressed. “These are big issues that I bring up with the architect and structural engineer at the start of any project,” he says. His list includes the issue of floor loads (live and dead) for the stage, seating, and support areas, considering such elements as stage floor capacity, basket-weave floors, forklifts, and portable seating systems. “This includes a discussion with the architect to confirm minimum capacities required by code,” Buckley adds.
His list also includes rigging loads, — the basic capacities of grids, loading bridges, and line sets — with an explanation of how loads can be dynamic and will change constantly, about vertical and lateral loads imposed by the various rigging systems, and motor and tie-off points that impose varying and eccentric loads. “Obviously,” he points out, “all these items have a direct effect on roof steel, footings, and the entire structural system.”
For acoustics, Buckley notes acoustic isolation will have an effect on how structural systems and details (i.e., floating slabs, isolated connections, etc.) are designed. “All of these issues should be taken into consideration from the beginning of the design,” he says. “If it is a renovation, determining the existing capacities and conditions is critical.”
There are also issues from the engineer's point of view, as Kyle Kusmer, PE at Entertainment Structures Group, points out. “Sometimes we hire a local engineering firm to deal with the local construction and installation,” he says. “There are projects in Canada where we need to hire another firm to verify our engineering analysis. A lot of our regular clients are used to dealing with us and know the terms. They understand the time factor. We have a difficult task using the right kind of term to help educate our clients with the fact that we may be dealing with unusual truss systems. You ask a lot of people about their lateral stability, and they don't know what you're talking about.”
The engineers also have some pointers on floor loads, live loads and dead loads, and acoustics. “For outdoor structures, we have to deal with the snow load and the rain, and for floor loads, we usually use 150 pounds per square foot,” Kusmer says. “For a pit lift and a dancefloor, it helps to know if forklifts will be used up on the pit filler. We would ask, ‘Is this going to be only a dancefloor, or will it get more use than that?’ That certainly would affect the construction technique. Pit lifts are often used for storage in the space below the stage. If this is the case and you need to put heavy equipment like a forklift on a pit lift, the engineer needs to check the footings underneath the screw jacks or hydraulics that create the structure holding up the pit lift.”
Clark adds: “Motor and tie-off points need to be specified so the engineer can make sure the point will take the load that you need to accomplish what you're planning on doing in the structure.” He also weighs in on the subject of acoustics. “Acoustics are a very important part of most entertainment construction, whether temporary or permanent. The structural engineer's work needs to work closely with the acoustician's in most cases,” Clark notes. “You have to be careful, especially on an indoor project. I am not an acoustician, but I've worked in theatres where either a subway goes by and there's noise from next door, or the steel is connected to some other mechanical thing that vibrates noise into the theatre. You need to be careful and isolate as much as you can.”
This is only scratching the surface of things related to structural engineering for a theatrical facility. “In the past, we've experienced difficulty using the right kind of terminology to help educate our clients,” says Clark. “If we can educate them, then they know that the next time they call what questions we'll ask, and they'll have the answer.”
As production director and director of capital projects for Manhattan Theatre Club, Michael Moody supervised the company's renovation of the Biltmore Theatre, completed in 2003.