13
LIGHTING TRUSSES

The use of found space for a theatrical production is not new. Barns, grassy fields, arenas, convention centers, and all manner of multipurpose rooms have been used for performances. The elaborately equipped buildings designed for large symphonies and opera, as well as those built specifically for drama in the early 20th century, are in the minority when it comes to what is being used for concert entertainment venues today. Because nearly all of the large theatres were built with stage houses of a similar size and design (except for thrusts), it used to be relatively easy to mount a touring opera or theatrical production. Most of the buildings had permanent lighting pipes in neat rows to provide lighting luminaire support. But what about buildings that do not have accommodating theatrical lighting as their primary mission?

TRUSS DESIGN

There are as many variations on the theme of truss design as there are companies designing and building them. Each company feels that its design offers the best solution to a particular problem, such as simplicity and speed of setup, strength, luminaire capacity, or method in which the sections are interconnected. For flexibility in design applications, remember that, whether you mount luminaires internally or not, the four sides of the box and even the ends are available for mounting, so bottom corners can be used as well as top corners. A major advantage of truss use is the flexibility afforded by corner blocks and angle blocks to connect truss sections into shapes. The many possibilities for truss layouts are discussed toward the end of this chapter.

THE FIRST TRUSSES

The early rock & roll concerts were considered not artistic enough for many city and college theatres, and they were generally relegated to school gymnasiums. Where do you hang luminaires in a gym? The answer was to bring along your own structures to mount them, to create a performance area in a found space. Finding or constructing portable units that could be trucked easily from show to show became the Holy Grail for early designers.

Portable units also had to have time-saving features. It is not unusual for recording artists to travel and perform in a different city almost every night, whereas plays usually have a run of a week or longer with possibly a day or two of rehearsal and time to make adjustments to the new space. For concerts, speed of setup is extremely important. At first, solutions to this problem were hit and miss, but eventually new design ideas emerged. Creative people took on the challenge, and a whole new concept was born: a structure, somewhat like a bridge, that allows designers to place luminaires overhead instead of on standing poles or trees.

The structures themselves have no historical precedent in theatrical design. The first touring truss was designed by Chip Monck and Peter Feller, with Bernie Wise, for the 1972 Rolling Stones tour. During a recent conversation with Chip from his home in Australia, we reminisced about that truss. It might have been 37 years ago, but Chip had his facts down.

It was built of 6061T aluminum alloy built into a 4 × 4 box square of 5- to 10-foot sections. In the photograph shown in Figure 13.1, the truss shows sections stacked for loading with short-nose PAR-64s that fit in the truss. After the bars holding them were lowered below the truss, the snoots were added to each luminaire to extend color life. These bars were staggered in height so the front row did not interfere with the backlight beams (Figure 13.2). There were five sections to complete a 50-foot span. The truss was supported by a single hydrologic ram on each end. These were made by Gallaway Company (Azusa, CA) and could go much higher than Chip needed, but they were raised to 32 feet for optimal light angles. I asked him how they stopped the ram from fully extending. The answer was that they attached a string and weight, and when the string was fully extended they stopped the ram manually! Each truss section could hold up to 9 PARs in each of two rows; however, the final 5 feet were needed for the lifting ram, so a total of 72 PARs could be mounted. After that tour, the system went out with Rod Stewart and Faces. I became involved when I left my first tour and joined Bob See in Los Angeles for the rest of that tour. Seeing that structure over our heads each night was quite a sight, and the audience loved it.

In 1973, a box truss with luminaires mounted inside during travel was introduced by Bill McManus, with the assistance of Peter Feller and Bernie Wise. It was the first truss grid and measured 50 × 28 feet.

It was flown, not ground supported, using Columbus McKinnon (CM) LodeStar hoists. It was designed for the Jethro Tull tour of that year, known as “The Passion Play.” Other young rock & roll companies such as Showco, Tom Fields Associates (TFA), Sundance Lighting, and See-Factor were not far behind in developing individualistic designs that with ach tour brought new ideas to the road. It was also a time of sharing; Tom would try a new idea and, if it worked, would call Bob or me and let us in on the idea, and we would reciprocate. Maybe this sounds Utopian, but the fact was we were not getting clients willing to take us clear across the country, so we often all participated in the same tour regionally, and the goal was for the client to have the same system when he crossed over into another company territory.

TRIANGLE TRUSS

Triangle trusses fall into two groups: commercial towers and specialty trusses. Trusses built commercially as antenna towers are available in several widths and tubing sizes. Do not use them. They are not designed

to be placed in the horizontal position. Yes, they were used in the very early days of touring, but there are many commercially built units that are specifically engineered for horizontal use now. I only mention antenna towers here for historical reasons.

If you want the look of a triangle, several commercially make versions available in different sizes that offer special features and are engineered to withstand the horizontal stress and loads placed on them by concert lighting (Figure 13.3). Initially, some were constructed of a heavy chromium molybdenum (chrome-moly) material, but most today are made of a lightweight aluminum. Again, be warned to use only commercially made products that are specifically designed for horizontal stress.

Two types of design are used in triangle trusses. The first is a solid triangle with each side ranging from 12 to 30 inches. The second design is constructed with a hinged joint at the top and a removable or hinged spreader bar attached on the horizontal side (Figure 13.4). Removing the spreader bar allows the sides to close for compact storage. In both cases, luminaires must be attached once the truss is supported in position. For a one-time production, this may not be a problem, but the following disadvantages should be considered before using these trusses:

1. The luminaires should only be focused safely from the ground using a ladder.
2. The luminaires must be attached and plugged into power each time the truss is set up, a time and labor disadvantage.
3. Because luminaires must be attached to the triangle, the usual method is individually via

C-clamps or hanger straps on either end of a 6-lamp bar. Adding 60 to 200 C-clamps, at about 2 pounds each, is considerable additional weight. Also, the C-clamp is very prone to denting the aluminum structure and making it unsafe. Specialty clamps are available to solve this problem.

SQUARE OR BOX TRUSS

Square or box trusses come in many configurations. Some, even though constructed as rigid units, still use hanger straps to mount the luminaires to the structures onsite. An example of a box truss is shown in Figure 13.5. They can be used not only to mount lighting luminaires but also to rig drapery, follow spot chairs, and sound systems. The sections are easily connected, but if a corner or an angle must connect sections, something like the 6-way corner block shown in Figure 13.6 can be used to join trusses in several configurations.

Other box trusses are large enough to semipermanently mount the luminaires internally to T-connectors that slide on a 1/2-inch solid pipe mounted in the truss. Some have a system that allows the bar to raise and lower to expose the luminaires below the truss for a better focus angle. The prerigged truss sections shown in Figure 13.7 demonstrate both single- and double-lamp bar designs in the transport

position; the lamp bars drop down to place luminaires below the truss, and the units have wheels. Taking a cue from the folding triangle truss, folding box trusses (Figure 13.8) have been designed for easy shipping. A rather new design includes a catwalk (Figure 13.9) that can work as a mother grid to which other trusses are connected or for follow spots and other flown effects. These units can have lift-up floor sections so workers can more easily access luminaires, as well as standard-height hand rails.

MODERN TRUSS DESIGN

The very basic design of a triangle truss does not leave much room for creativity. The box truss, however, has spawned some highly creative modifications of its basic form. One design created by Bill

McManus Enterprises years ago for a Kiss tour (Figure 13.10) had a unique stacking feature that nested the trusses together, with only the bottom truss section on casters; a cable tray held the long runs of multicable already attached to a raceway, thus eliminating cable boxes in

the truck load and saving room. Figure 13.11 shows moving luminaires packaged in a truss for travel storage of approximately four moving luminaires on casters, but the unit flips open to allow total clear beam rotation. By flipping up the sides, the truss becomes a safety rail for technicians walking the truss (but this does not replace the need for fall protection gear).

For location television lighting, an issue may be the size of the luminaires. More and more we see such situations, especially award shows, music specials, and other event programming that use a combination of PAR-64, moving luminaires, ellipsoidal reflector spotlights (ERSs), and cyc lights, all of which would fit comfortably within these trusses. However, if a 5-kW Fresnel is desired, then perhaps a very small box truss or triangle truss would be better so the luminaires can be underhung. These are generally one-time events and are not toured, so storage does not enter into the picture.

Speaking of moving luminaires, yes, they are often bigger than the PAR-64, so more room is needed in the truss, and a size different than the standard 18 inches may be required and must be factored into the design. Truss manufacturers have come up with a number of designs that deal specifically with this problem. Some are designed to hold only a specific number of moving luminaires. Others are flexible and can accommodate both conventional luminaires as well as moving luminaires. Some are specifically designed for a moving light manufacturer and can accommodate only their products. It should be noted, however, that because of their delicate electronics many moving luminaires are boxed separately and attached to the truss onsite. Before designing a truss structure, the designer should be aware of the recommendations of specific moving light manufacturers with regard to transportation, which can affect the load-in scheduling time. For example, removing 100 moving luminaires from boxes and attaching them to a truss is a two-person job, and it is easy to see how the load-in time could be extended.

ENGINEERING AND CONSTRUCTION

Most trusses are built of 6063-T5 aluminum tube with a 1- or 2-inch outer diameter (OD) or HE30 aluminum alloy with a fairly heavy inside wall thickness. Chrome-moly can be used because it is less expensive and easier to weld; however, the added weight (about twice that of aluminum) makes the use of chrome-moly undesirable for touring purposes. If the trusses are for semipermanent installations, chrome-moly could be considered for its cost savings, but the additional weight must be factored in. Its other advantage is that it can be arc welded, whereas aluminum requires the use of the more difficult heliarc method. The welder does not have to be as highly skilled to arc weld as he does to use the heliarc method.

Although steel welding is less expensive with regard to materials and equipment and labor is more readily available, steel is seldom used in the United States, largely due to its weight and to the controversy surrounding the employment of amateur or semiqualified welders, which can create a tremendous liability problem and should be avoided. The potential for a wrongful death or injury suit is substantial.

Touring trusses should be built by companies that specialize in entertainment structure design. A list of some of these companies is provided in Figure 13.12. Unless your design requires custom fabrication, most rental lighting companies will have a complete collection of different style and size trusses in stock. Make sure you are provided with certified mechanical stress test information (Figure 13.13) or x-ray records if you are simply renting gear yourself and are going to assemble the lighting. Because the rental house is not the person attaching luminaires or other things on the trusses, they cannot be held responsible if you misuse the truss. Many manufacturers now provide stress data information in their brochures (Figure 13.14).

The engineering of trusses is critical and is probably the biggest reason why one-off shows should not try to contract for special built trusses. Figure 13.15 shows the basic procedure used to test the trusses for load. Most rental companies I have surveyed say they do this procedure about once a year, although if the trusses come back from a long tour they will sometimes test them before sending them back out. The trusses can be sent to a lab that does stress analysis, but some rental houses keep the equipment in-house to check for the manufacturer's recommended deflection. A few admit to only doing a close physical inspection, looking for stress lines in the welds. Even fewer actually have the trusses x-rayed for very fine cracks. There is no industry standard here. Maybe the Entertainment Services and Technology Association (ESTA) will get involved and set American National Standards Institute (ANSI) standards.

Prolyte Products Group, a Netherlands-based company, has published a good booklet called Prolyte Black Book, which discusses rigging methods, safe spans, stress, and types and use of hardware. Remember, though, that this is only a guide, and an experienced rigger should always be in charge of any rigging.

It is best to lease trusses from an established concert rental company. If you are considering constructing your own, I recommend you use only certified welders. Actual construction time could be as much as 5 days for a 40-foot truss, but it is essential to take the time to have a certified structural engineer design or check your plans. The added cost and time are other reasons to lease if your project is short term. Be sure to ask the company for certification of the structural stress and load capacity. This can be done by specialized engineering firms and should cost less than $1000, depending on what procedures they use and how far you carry the tests.

SPANS

As there is a large difference between the strongest and weakest truss, a certificate of load capacity is very important. Moreover, the clear spanning capability of the truss must be determined. Some trusses can only be supported up to a clear span of 40 feet. Not only length but also the size of the tubing and design of the truss are important considerations. You must also add in the weight of the luminaires, cable, someone focusing the luminaires, and maybe truss-mounted follow spots and operators. Generally, truss sections come

in 8- and 10-foot lengths. The rental companies will help you fit your design into the lengths they have in their inventory. Even better, contact the company for a breakdown of what is available before you begin a design, then have an Entertainment Technician Certification Program (ETCP) Certified Arena Rigger create a rigging plot.

Now that most trusses are flown, the full 40 feet of a standard portable stage are usable (ground support lifts reduced the usable width to 32 feet). That is why 40 feet is considered the average truss length. Larger productions, however, are now calling for 50- and 60-foot lengths.

It is rare to see lengths over 40 feet being floor supported. If your design requires a truss over 40 feet wide, it is time to consider a flown system. Why can a longer truss be flown when it cannot be ground supported? The solution is found in placement of the rigging pickup points. Bridles are assemblies that enable the suspension of an object at a particular location; they are composed of two overhead load points of lesser load-bearing capacity that are joined to lift a heavier load. They help to distribute the weight evenly. It is common for a 40-foot truss to have two motor or winch pickup points. These, in turn, will usually be bridled about 4 to 6 feet apart. The proper bridle configurations for a given load must be determined by a qualified rigger. Figure 13.16 shows some of the calculations needed to determine the stresses; however, the method for making these calculations is much more complicated and should only be done by an experienced rigger.

Ground-supported trusses are generally not considered as safe as flown because they are subject to ground movement. No, I am not talking about a California earthquake. Out of necessity, the ground-supported trusses are at the mercy of many factors, such as portable stages with uncertified construction that could collapse under the weight. In several reported cases, lighting companies have refused to set up a ground-supported truss because they felt the stage was unsafe. If the towers supporting the truss are on the cement off the portable stage, there is a better chance that the system will be safe, but do not let down your guard; make sure the structure is level and securely attached to the truss. If the event is outdoors and the support tower is on grass, use extra caution; for example, thick plywood squares to spread the load could be placed under the tower (see Chapter 14 on lifts and towers).

INTEGRATION OF ELECTRICAL CONNECTIONS

The electrical raceways and cables attached to the truss affect the structures. There are several ways to get power to the luminaires; the simplest method is for luminaires to be wired onsite. Another method is to use a six-circuit Socapex multicable assembly. Some lamp bars are designed with internal wiring to a male Socapex connector so the technicians only have to make the one connection to energize six luminaires at a time. This speeds up the load-in.

The standard electrical raceway takes this method a step further. It is either placed on the truss onsite or attached semipermanently to the truss. The connection of the luminaires can then be easily accomplished if the luminaires are to be mounted each time or patched and left for the run of the production if the raceway is an integrated part of the truss. The luminaires can be permanently wired to a raceway, as well. This last method, however, inhibits design changes and luminaire replacement and is generally considered inefficient for any use other than a straight all-PAR-64 production design. DMX-512 low-voltage control cables and AC power for moving luminaires can also be integrated into trusses to speed assembly.

LIGHTING GRIDS

A total lighting grid can be formed with one type of truss or with a combination of sizes and designs. It is not uncommon to see a single square truss in the front and on the sides and a double-row truss in the back for the more important backlight. These trusses are joined together in several ways. End blocks with bolts, aircraft fasteners with a ball-lock capture pin, cheese-boros such as are used on scaffolding, and other highly specialized connectors have been designed especially for this use. Some trusses have been designed in such a way that a single-row truss will attach to another to create three or four rows of luminaires.

The way in which designers lay out the configuration of trusses to accomplish their lighting needs is limited only by the load limitations of the truss, lifts, winches, and motors used to place these structures in the air. A current trend that many sports arenas have adopted is to lower a master or semipermanent grid for entertainment events. One advantage is the time savings for the tour rigger in establishing high steel attachment points. Also, riggers are given a plan with the grid size and weight-bearing points to make the installation quicker. The tour may still use their motors to keep their trusses well below this grid when raised into the air. A big advantage is that facility managers can be assured of the structural loads on their motors and lift points. They also don't have to worry about riggers falling from the high steel. But, caution: the added weight of the truss, luminaires, etc., that will be suspended from the structure must be calculated.

The simple tour truss design in Figure 13.17 consists of two 32-foot trusses supported by Genie Superlifts (see Chapter 14). Note that the backdrop is also hung from the truss; this should only be done when wind conditions are not a factor. Better yet, don't do it at all. Grids can also be dressed up such as in Figure 13.18, which is a photograph of the 2008 papal visit. Figure 13.19 is a photograph of the 2008 Def Leppard tour that shows the grid and luminaire before being flown.

A designer, with the guidance of a qualified rigger, should also consider the capability of the roof structures of the halls before using a flown truss layout. While designers are not expected to be qualified riggers, they should have some understanding of types

of venues and what shows have played in them previously. Consulting a tour rigger before you are committed could save you a lot of problems.

ADVANTAGES OF PORTABLE TRUSSES

A truss that has been loaded with luminaires and cables and has been checked in the shop prior to

going to the location will offer savings in onsite setup time. The efficiency of the structure means that less labor is used in the field. This does not mean that the main reason to use a truss is to put people out of work. Trusses still require labor to prepare them in the shop and touring crew to guide the local stagehands in their assembly. Use of prerigged trussng can even mean savings of a day or more of site setup time, which translates into possible rental savings. More important, it may be the only way to get the production to fit into the very tight schedule of the venue.

Trusses provide a very convenient, adaptable lighting system, but the safety element must be stressed again. Getting luminaires up to a fixed pipe 20 feet in the air creates a very real hazard. I have ducked out of the way of many falling items during many a theatre load-ins. The problem of working at this height rather than at ground level should be obvious. Trusses have been in use since the 1970s and have proven a reliable and efficient method of supporting luminaires of all types as well as drapery, projection screens, and scenery. Their adaptability for use in films, television, and theatre rigging has been a great boon to flexible and safe mounting of luminaires under a wide variety of conditions.

One other thing is attached to trusses—people. A very popular design element is to place the follow spot on the flown truss to give an angle not possible from the house positions. These chairs can be placed either on top of the truss or below. The follow spot has a post already attached, so the follow spot and person need only be added (Figure 13.20). Two notes of caution: First, never place someone on a ground-supported truss until you can be assured that any movement has been secured via a safety system appropriate for the task. Second, place stagehands on a flown truss only after the supplier and rigger have approved the trussing and its rigging for such use. Anyone who climbs the truss to focus luminaires, to man follow spots, or for any other reason must wear appropriate fall protection gear.

BUILDING A GRID

A major advantage of truss use is the flexibility afforded by corner blocks and angle blocks to connect truss sections into shapes.

The basic structure of a triangle does not allow much room for creativity in internal design. The box truss, however, has spawned some highly creative modifications to its basic form. With all the moving luminaires now available, special trusses had to be constructed to hold these larger units and protect their more delicate mechanisms. Some units are purpose built to hold only moving luminaires, while others can be adapted to support both conventional and moving luminaires.