0428

Another type of girder used for girder bridges is a plate girder. Plate girders are I-beams made of individual structural steel plates welded (or bolted or riveted) together to form the vertical web and horizontal flanges of the beam. A plate girder bridge (Figure 14.14) is suitable for short to medium spans and is used in instances where railroads, highways, or other traffic need to be supported. Deck-type bridges are also girder bridges. These bridges involve supporting a steel or reinforced concrete bridge deck on top of two or more plate girders. Ladder-deck bridging includes the use of additional beams that may span across the main gird- ers. Further elements may be attached to provide cross-bracing and prevent the girders from buckling. Truss Bridges A truss bridge (Figure 14.15) is one of the oldest types of modern bridges. It consists of a truss-like assembly of triangles and is commonly made from a series of straight structural shapes. This type of bridge has a fairly simple design and is particularly inexpensive to construct owing to its effi- cient use of materials. Figure 14.14 Plate Girder Bridge The roadbed of a truss bridge may be situated on top, in the middle, or at the bot- tom of the truss. The most common type of truss bridge carries the roadbed either on top or on the bottom as this allows both the top and the bottom to be stiffened, which in turn forms a box truss. When the roadbed is on top of the truss it is called a deck truss (Figure 14.16), when it is on the bottom, it is called a through truss (Figure 14.17), and when the sides are extended above the roadbed but are not connected, it is called a pony truss or half-through truss. Figure 14.16 Deck Truss Figure 14.17 Through Truss Unit 14 — Erecting Bridges 14.9 Figure 14.15 Truss Bridge UNIT 14

Sometimes both the upper and lower chords support roadbeds, forming a double-decked truss (Figure 14.18). This type of truss bridge can be used to separate rail from road traffic or to separate two directions of automobile traffic, thereby reducing the likelihood of head-on collisions. Another type of truss bridge is a can- tilever bridge (Figure 14.19). When used for small footbridges, canti- lever bridges may consist of simple beams; however, because of the road or rail traffic larger cantilever bridges are expected to handle, they are built from structural steel and/or box gird- ers made of pre-stressed concrete. Because it can span distances of more than 1,500 feet, the steel truss can- tilever bridge is considered a major engineering feat. Figure 14.18 Double-Decker Truss Bridges 14.10 Structural Steel Erection A simple cantilever span is formed by two cantilever arms extending from opposite sides of the obstacle to be crossed, meeting at the center. A sus- Figure 14.19 Cantilever Bridge pended span is a common variant in which the cantilever arms do not meet in the center; instead, they support a central truss bridge which rests on the ends of the cantilever arms. The suspended span may be built off-site and lifted into place, or it may be constructed in place using special traveling supports. One way of constructing steel truss and pre-stressed concrete cantilever spans is to counterbalance each cantilever arm with another cantilever arm projecting in the opposite direction, forming a balanced cantilever. When they attach to a solid foundation, the counterbalancing arms are called anchor arms. In other words, for a bridge built on two foundation piers, there are four cantilever arms: two arms which span the obstacle, and two anchor arms which extend away from the obsta- cle. Because of the need for more strength at the balanced cantilever’s supports, the bridge superstructure often takes the form of towers above the foundation piers. UNIT 14

Arch Bridges An arch bridge (Figure 14.20) is one of the oldest bridge types and has great natural strength. Unlike girder bridges, arches are well suited to the use of stone, so much so that stone arch bridges built by Romans and others centuries ago still stand to this day. Most arch bridges today are made of steel or concrete, and are often very beautiful (see, for example, Figures 14.21–14.23). They tend to be good choices for crossing valleys and rivers since the arch does not require piers in the center. Modern arch bridges have spans of over 800 feet. One of the longest arch bridge spans today belongs to the New River Gorge Bridge (Figure 14.24), which spans over 3,000 feet. Figure 14.21 Lake Powell Bridge Figure 14.20 Old Arch Bridge ’ Figure 14.23 Close-Up of an Figure 14.22 Hell s Gate Bridge Arch Bridge Figure 14.24 New River Gorge Bridge Unit 14 — Erecting Bridges 14.11 UNIT 14

Because of its design, the arch in an arch bridge literally squeezes together (see Figure 14.25). This squeezing force is carried outward along the curve to the abutments at each end. The abutments push back on the arch and prevent the ends of the arch from spreading apart. Figure 14.25 Forces on the Arch The curved structure of arch bridges also provides a high resistance to bending forces. Unlike girder and truss bridges, both ends of an arch are fixed in the horizontal direction (i.e., no horizontal move- ment is allowed in the bearing). Thus, when a load is placed on the bridge (e.g., a car passes over it) the horizontal forces occur in the bearings of the arch, where they are then dissipated. As a result, arches can only be used where the ground or foundation is solid and stable. The tension in an arch is negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch. The greater the degree of curvature (the larger the semicircle) of the arch, however, the greater the effects of tension on the underside of the arch are. As with a beam bridge, the limits of size will eventually overtake the natural strength of the arch as stress increases exponentially with size. The roadway of an arch bridge may pass over the arch (Figure 14.26), through the arch (Figure 14.27), or in some cases both over and through the arch (Figure 14.28). Figure 14.26 Roadway Over the Arch Figure 14.27 Roadway Through the Arch Figure 14.28 Roadway Passing Over and Through the Arch 14.12 Structural Steel Erection UNIT 14

Suspension Bridges Of all the bridge types in use today, the sus- pension bridge allows for the longest spans. Modern suspension bridges can span over 3,000 feet. The world’s longest suspension bridge, the Akashi Kaikyo Bridge (Figure 14.29), spans close to 13,000 feet. A suspension bridge does just what its name implies: it suspends its deck by means of large cables secured at each end and passed over the tops of high towers. Two modern suspension bridges can be seen through Figures 14.30 and 14.31. Though suspension bridges are leading long span technology today, they are in fact a very old form of bridge. Some primitive examples of sus- pension bridges used vines and ropes for cables. A typical suspension bridge is a continuous girder with one or more towers erected above piers in the middle of the span. The girder itself is usually a truss or box girder, although plate girders are not uncommon in shorter spans. Large anchors or counterweights are placed at both ends of the bridge to hold the ends of the cables. Figure 14.32 shows several of the major parts of a suspension bridge. Figure 14.32 Parts of a Suspension Bridge Unit 14 — Erecting Bridges Figure 14.29 Akashi Kaikyo Bridge Figure 14.30 Verrazano Bridge, NYC Figure 14.31 Golden Gate Bridge, San Francisco 14.13 UNIT 14

The basic parts of a typical suspension bridge fall into two categories: superstruc- ture and substructure. The superstructure is composed of a deck (or roadway or girder), two towers, and the main suspension cables. The substructure is composed of the piers (caissons or tower foundations) in the middle of the span that support the towers and the anchorages (anchors) for the cables at each end of the bridge. The main cables are stretched from one anchor over the tops of the tower(s) and attached to the oppo- site anchor. The cables pass over a special structure known as a saddle (see Figure 14.33). The saddle allows the cables to slide as loads pull from one side or the other; it also permits the smooth transfer of the load from the cables to the tower. From the main cables, smaller cables known as hanger cables or hanger ropes are hung down and attached to the girder. Note: Some suspension bridges do not use anchors, but instead attach the main cables to the ends of the girder. These self-anchoring suspension bridges rely on the weight of the end spans to balance the center span and anchor the cable. Unlike other bridges, which rest on piers and abutments, the girder or roadway of a suspension bridge is literally hanging suspended from the main cables. The majority of the weight of the bridge and any vehicles on it are suspended from the cables. Since the cables are held up only by the towers, these towers must be able to support an incredible amount of weight. Figure 14.34 shows the towers of the San Francisco Bay Bridge. Figure 14.33 Suspension Bridge Tower Figure 14.34 San Francisco Bay Bridge 14.14 Structural Steel Erection Long span suspension bridges, though strong under normal traffic loads, are vul- nerable to the force of wind. Special measures are taken to ensure that these bridges do not vibrate or sway excessively under heavy winds. UNIT 14

This wind danger was famously dem- onstrated by the Tacoma Narrows Bridge in Washington. Today, the Tacoma Narrows Bridge is a mile-long (1600 meter) suspension bridge with a main span of 2800 feet that carries traf- fic across the Tacoma Narrows of Puget Sound between Tacoma and Gig Harbor. When it was first built, it was the third-largest suspension bridge in the world. However, the first version of the bridge collapsed dramatically in 1940 due to wind, an event that was caught on motion picture film. Figure 14.35 Original Tacoma Narrows Bridge Figure 14.35 shows the bridge before the col- lapse, Figure 14.36 shows the bridge oscillating just before the collapse, and Figure 14.37 shows the beginnings of the collapse. The replacement bridge opened in 1950. Cable-Stayed Bridges Suspension and cable-stayed bridges may look similar at first glance but they are quite different. Both have roadways that hang from cables and both have towers, but the two bridges support the load of the roadway in very different ways. The difference lies in how the cables are connected to the towers. In suspension bridges, the cables ride freely across the towers, transmitting the load to the anchorages at either end. In cable-stayed bridges (see, for example, Figure 14.38), the cables are attached to the towers and, as a result, the tow- ers bear the load. Figure 14.36 Tacoma Narrows Bridge Just Prior to Collapse Figure 14.37 Tacoma Narrows Bridge Beginning to Collapse 14.15 Figure 14.38 Leonard P. Zakim Bunker Hill Bridge Unit 14 — Erecting Bridges UNIT 14

The cables in cable-stayed bridges can be attached to the roadway in two primary patterns: radial and parallel. When a radial pattern is used, the cables extend from several points on the road to a single point at the top of the tower. When a parallel pattern is used, the cables are attached at different heights along the tower, and run parallel to one other. 14.16 Structural Steel Erection UNIT 14

▶▶OBJECTIVE 4: STEPS IN ERECTING A BRIDGE There are hundreds (thousands for larger bridges) of steps involved in building a bridge. The major steps, however, include the following: 1. Once a bridge is determined to be needed and the site is selected, a survey of the construction site is performed. The purpose of this survey is to collect information to aid the designers in the development of the design. Typical information collected includes soil type, drainage, current structures, existing vegetation, etc. 2. Before anything is moved into the area, the construction site is cleared of all trees and vegetation. Note: Environmental protection of the construction site as well as of the surrounding area must be taken into consideration at all times. This is especially critical when the land includes wetlands or other areas that require special protection. Environmental protection includes measures and controls instrumental in preventing and/or minimizing damage and degradation of the environment as well as ensuring the sustainability of the area’s living resources. 3. Excavation for, and placement of, piers, abutments, and bents is then undertaken. 4. Piles are driven to prevent settlement of the pier, abutment, or bent (see Figure 14.39). 5. Rebar and post-tensioning cables are unloaded and placed for footings. Figure 14.39 Bridge Site Excavation and Piles 7. The structural steel for the bridge is unloaded, shaken out, and stored. 6. The footings are poured. Unit 14 — Erecting Bridges 14.17 UNIT 14

Note: Unloading, shaking out, and storing materials for bridges is done in much the same manner as for any other structure, except the following factors must be taken into account: • Proximity to water means more dangers. • The steel pieces used in bridges are usually longer and weigh more than the pieces used for buildings; larger dunnage must therefore be used. • The pieces to be erected may be transported to the job site by barge. • The job site tends to be crowded, so shaking out space must be well-utilized. 8. Cages for columns are fabricated to build the piers (see Figure 14.40). 9. Forms for the piers, abutments, and bents are constructed. See Figures 14.41, 14.42 and 14.43. Figure 14.40 Column Cage Constructed on Site Figure 14.41 Forms for a Pier Figure 14.43 Dirt Being Placed Against an Figure 14.42 Bridge Abutment and Bent Abutment and Bent 14.18 Structural Steel Erection UNIT 14

10. Rebar is placed in the forms (rebar beams, cages, and/or columns are typically fabricated on site). Note the cage rebar extending out of the top of the forms in Figure 14.41. Figure 14.44 shows a complex fabrication of reinforcing bars being placed in a large form for the Woodrow Wilson Bridge in Washington, DC. 11. Cranes are assembled for the hoisting/erection of the girders. Figure 14.44 Reinforcing for the Woodrow Wilson Bridge 12. Falsework is erected and the location and elevations of the girders are checked. Figures 14.45, 14.46, and 14.47 show examples of bridge falsework. 13. Girders (including fabricated plate girders) arrive at the construction site, and are dressed and rigged for hoisting (Figure 14.48). Figure 14.46 Close-Up of Bridge Falsework Figure 14.48 Girder Arrives Unit 14 — Erecting Bridges Figure 14.45 Bridge Falsework Figure 14.47 Falsework on the Blennerhassett Bridge 14.19 Girder arriving at job site UNIT 14

14. Connectors set the girder (pier to pier, pier to falsework, girder splice to pier or falsework, etc.). See Figures 14.49 and 14.50 for examples of girders being set. Note the diaphragms (or cross braces or cross bucks) in the right side of Figure 14.50. 15. Ironworkers hoist, connect and, as seen in Figure 14.51, bolt the diaphragms. Figure 14.49 Crane Setting the Girder 16. Ironworkers bolt up the girder/splice connection (see Figure 14.52). 17. Decking is set and welded in place (Figure 14.53 shows a deck in place). 18. Expansion dams are set and welded. 19. Ironworker rodmen place rebar on the bridge deck. Figure 14.50 Ironworkers Setting the Girder Figure 14.52 Ironworkers Bolting Up a Girder Figure 14.51 Ironworker Bolting a Diaphragm Figure 14.53 Bridge Decking in Place (Shown From the Underside of the Bridge) 14.20 Structural Steel Erection UNIT 14

▶ ERECTING TOWERS UNIT 15 ▶ OBJECTIVES After completion of this unit, you should be able to describe the general process of erecting towers. This knowledge will be evidenced by correctly completing the assignment sheet and by scoring a minimum of 70% on the unit test. Specifically, you should be able to: 1. Identify the three types of towers generally erected by Ironworkers 2. Describe various uses of towers 3. Explain the procedures for erecting towers 4. Describe the procedures for tensioning tower guy wires and cables 5. Describe the procedures for erecting communications towers 6. Identify safety concerns, standards, and regulations applicable to the erection of towers Each of these objectives is covered in the pages that follow. Unit 15 — Erecting Towers 15.1 UNIT 15

▶▶OBJECTIVE 1: TYPES OF TOWERS The word tower brings to mind different images for different people. One person may think of the Leaning Tower of Pisa (Figure 15.1), while someone else imagines a water tower (Figure 15.2), and yet another person thinks of a multistoried office building (Figure 15.3). Figure 15.1 Figure 15.2 Figure 15.3 Leaning Tower of Pisa Water Tower Multistoried Office Building While these are all technically towers, and some are even the type typically con- structed by Ironworkers, these are not the types discussed in this Unit. The three types of towers erected by Ironworkers and discussed here are: guyed towers, self-supported towers, and monopoles. 15.2 Structural Steel Erection Guyed Towers Guyed towers (Figure 15.4) are generally the tallest of the three tower types. They are three-sided structures of lattice framework design, and have at least one set of three guy wires supporting them. Figure 15.4 Guyed Tower and Guyed Tower Marked by Contrasting Paint for Aircraft UNIT 15

An area of land is needed to support each set of guy anchors, so guyed towers require more land space than the other two types of towers. The base of a guyed tower is usually the same size as the top of the tower. These towers are erected with extreme speed in a competitive market. However, it takes experience and training to safely and efficiently erect them. This is true of any tower, but it is especially true of guyed towers, as they will only stand securely under very specific conditions. These conditions are outlined in each guyed tower’s drawings. Self-Supporter Towers A self-supporter (Figure 15.5) is a tower built with a lat- tice framework design similar to guyed towers, but unlike guyed towers, it requires no other type of support to keep it from falling over once erected (whereas guyed towers need the support of the guyed wires). These towers are typically four-sided structures with the base of the tower larger than the top. As a rule, self-supporters are not as tall as most guyed towers. The amount of land area needed for a 1400' self- supporter to have a base large enough to support it would be enormous. The cost to purchase or lease the land, fabricate the steel, and erect such a large tower would be much more than the cost of building an equivalent guyed tower. Self-supporting towers take more time to erect and can therefore be more costly to erect than guyed towers. Monopoles A monopole (Figure 15.6) is a tower in its most simplified form. Usually smaller in height than the average self-supporter or guyed tower, a monopole looks similar to a steel telephone pole or a flag- pole, except that it is larger in diameter. The base of a monopole is larger in diameter than its top. While monopoles appear at a distance to be round, they are actu- ally polygons, and come in 12-, 14-, 18-, 24-, and 32-sided poles. These towers are erected (generally with a crane) most often where great height is not a necessity and where available ground space is extremely limited. They can be erected on piers and attached by means of anchor bolts, or placed in a hole drilled in the ground a predetermined depth. Figure 15.6 Monopole Figure 15.5 Self-Supporter Unit 15 — Erecting Towers 15.3 UNIT 15

▶▶OBJECTIVE 2: USES OF TOWERS While towers can take different forms, their uses vary even more. Some towers are erected to support electric transmission lines as they travel from an energy producing power plant to homes and businesses. Other towers support signs, scoreboards, lights, ski lifts, flare stacks, and communications equipment. Still oth- ers (called falsework towers) are used as temporary supports for other structures under construction. Electric Transmission Line Towers After electricity is produced at power plants, it has to be delivered to the customers who use it. To accomplish this, it is sent to a transformer at the plant and then pushed into transmission lines (also called power lines). Transmission lines and their towers can be seen in Figures 15.7–15.8. Figure 15.7 Power Plant Transmission lines go into substations (Figure 15.9) near towns, cit- ies, businesses, factories, neighborhoods, and homes. At the substa- tions, other transform- ers change the very high-voltage electricity Figure 15.8 Power Lines Supported by Towers initially sent (electric- ity travels long distances better at higher voltages, and is therefore sent in voltages up to 400,000 volts) into useable lower-voltage electricity. The construction of towers to hold trans- mission lines sometimes falls into the work jurisdiction of Ironworkers. Figure 15.9 Substation Structural Steel Erection 15.4 UNIT 15

Note: This jurisdiction is debated and disputed heavily. Sometimes linemen or electricians install these towers. The collective bargain- ing agreement, or other work agreement covering the geographical area, will determine whether or not these types of towers are within Ironworkers’ jurisdiction. Signs, Scoreboards, and Lights Towers are also used to support signs, scoreboards (see Figure 15.10), and lights (see Figure 15.11). A tower can hold a scoreboard, sign, or lighting individually, or in combination. Figure 15.10 Tower Supporting a Figure 15.11 Tower Used to Support a Scoreboard Lighting Array Towers are used to support signs in stadiums, as well as to support and elevate signs beside and over roads and high- ways, as in Figure 15.12. Towers supporting scoreboards, signs, and lights are usually either self-supporters or monopole towers. Signs and scoreboards present a unique problem to the tow- ers on which they are mounted. These towers must not only support the weight of a sign itself (and any ice load in the winter months), they must also be able to withstand addi- tional forces caused by having a large solid surface exposed directly to the wind (referred to as the “sail effect”). Figure 15.12 A Tower Used to Support and Elevate a Sign Over or Beside a Highway Note: Regardless of whether a tower is constructed for a sign, score- board, light, or combination thereof, there will likely be some spe- cific mounting hardware supplied by both the tower and the sign, scoreboard, and/or light manufacturer. All of this hardware should be installed following manufacturer recommendations. Unit 15 — Erecting Towers 15.5 UNIT 15

Ski Lift Towers A ski lift consists of a continuously circulating wire rope loop strung between two end terminals. The rope is usu- ally supported by intermediate towers – ski lift towers (see Figure 15.13) – and has chairs or gondolas attached to it on which skiers ride. The number of ski lift towers used is based on the length of the lift and the type of terrain it covers. A bullwheel in each terminal redirects the rope, while sheaves on the towers support the rope well above the ground. The rope stretches and contracts as the tension exerted upon it increases and decreases, and it bends and flexes as it passes over the sheaves and around the bull- wheels. It must be regularly lubricated to ensure safe opera- tion and long life, and it must be tensioned to compensate Figure 15.13 for sag caused by wind load and passenger weight, to account Ski Lift Tower for variations in rope length due to temperature, and to maintain friction between the rope and the drive bullwheel. Tension is maintained by a counterweight system or by hydraulic rams, both of which adjust the position of the bullwheel carriage to maintain design tension. Ski lift towers are typically monopoles. Like other monopoles, they are either buried in the ground to a predetermined depth or attached to anchor bolts on a pier or footing. Depending on the manufacturer and the design of the individual lift system and the terrain, they are either placed plumb or (unlike any other monopoles) perpendicular to the ground, as is illustrated in Figure 15.14. Ski lifts are the primary means of transpor- tation at most ski areas, but they are also found at amusement parks and at various tourist attractions, and they are sometimes even used in urban transportation. They are a safe and efficient mode of transport: depending on its size and loading effi- ciency, a lift can move up 4,000 people per Figure 15.14 Monopole Towers for a Ski Lift System: 15.6 Structural Steel Erection hour. One Placed Plumb and One Placed Perpendicular UNIT 15

Flare Stack Towers A flare stack tower (Figure 15.15) is most commonly found in refineries or other industrial plants that produce by-products that are not useful for other processes. These towers raise the flame or flare which burns these by-products to a safe eleva- tion above ground level. Most flare stack towers are less than 300 feet in height and are almost always either a self-supporting or a guyed tower. These towers must support their own weight as well as the weight of piping, instrumentation, igniter(s), flare head/tip/arrestor(s), and working/maintenance platform(s), ladder(s), and any ice or snow that may form on these. Communications Towers Figure 15.15 Flare Stack Tower Once cellular technology was licensed in the U.S. by the Federal Communications Commission (FCC) and in Canada by the Canadian Radio and Telecommunications Commission (CRTC) and approved for commercial and public use, transmission and receiver towers (Figure 15.16) came into high demand. Continued advances in technology have kept this demand high; communications towers now dot the landscape in both urban and rural areas. Some of these towers approach 2,000 feet in height. Because of the heights involved, and unlike for most structural steel erection projects, the Ironworkers who erect a communications tower typically install all of the wiring, lights, beacons, transmission lines, and antennas as well. They usually also paint the tower when painting is required. Communications towers come in all three types: guyed, self-supporting, and monopoles. Figure 15.16 Guyed, Self-Supporter, and Monopole Communications Towers Unit 15 — Erecting Towers 15.7 UNIT 15

Specialty Communications Towers One type of specialty communications tower is a Loran tower. These guyed towers transmit and receive naval or marine signals. The entire tower, much like an AM tower, is hot, and the tower base rests on an insulator. Note: Before doing any maintenance work on a Loran tower, ensure that the tower is turned down (i.e., that all signals have been reduced) and that a qualified person has installed a ground lead to ground the tower. All maintenance work should be performed from the inside of the tower instead of from the tower face. Another type of specialty self-supporting communications tower is a river-crossing tower. These towers are constructed to carry high-voltage power lines from one side of a river to the other. They are built tall enough that the electric lines they carry across the river will not sag below applicable elevation specifications. Note: Because of their intended purpose, these towers are extremely hazardous: all maintenance work should be performed from inside of the tower when possible. Comply with all safe working distances for the high-voltage lines. Falsework Towers Some structures, or parts of some structures, are not capable of supporting their own weight during construction. When this problem presents itself, engineers or steel erection contractors will sometimes choose to solve it by using falsework tow- ers (also called shoring). Falsework towers are different from almost any other tower: they are temporary structural towers not erected with a gin pole. Falsework towers typically take one of two forms: specifically-engineered and pre-engineered. Specifically-engineered falsework towers (Figure 15.17) are constructed of structural steel pieces that are Figure 15.17 Specifically-Engineered Falsework Towers 15.8 Structural Steel Erection UNIT 15

designed, detailed, and fabricated for the sole purpose of being erected to tempo- rarily support part of a larger structure until the construction advances enough that it is able to support itself. This type of falsework is primarily used on a project because the intended load on the shoring is larger than what can be reasonably sup- ported by using pre-engineered falsework. This type of shoring should be erected using the same rules, guidelines, practices, and procedures that apply to any other structural steel members. Pre-engineered falsework towers (Figure 15.18) are most easily described as scaffolding. Most scaffold manufac- turers and distributors have engineer- ing departments that provide shoring plans for almost any load. Scaffold erection rules and regulations (federal, state, provincial, and local, as well as manufacturer guidelines) should be followed when erecting this particular type of falsework. Figure 15.18 Pre-Engineered Falsework Towers Here are some tips for erecting/dismantling pre-engineered falsework: • Follow all applicable federal, state, provincial, and local laws and codes. • Follow all manufacturer specifications and guidelines. • Ensure that the falsework has been designed by a qualified person. • Follow the shoring design and never omit parts or sections or make any unapproved changes. • Post all falsework safety rules as supplied by the manufacturer so that they can be seen by all workers. • Provide a firm, solid, and compacted base for the falsework. • Inspect all components before erecting the tower and never use damaged, rusty, or incomplete parts. • Never mix shoring parts from more than one manufacturer. • Ensure that the shoring load is carried on all of the intended legs. • Use screw jacks and only the proper extensions. • Plumb and level all frames as the construction progresses. • Make certain that all components are in firm, secure contact with each other. • Never climb the braces on a falsework tower. Unit 15 — Erecting Towers 15.9 UNIT 15

• • • • • • • Make sure that a qualified person inspects the falsework before its intended load is applied and at regular intervals until it is dismantled. Avoid shock-loading the falsework. Make certain that the falsework is free of debris before beginning the dismantling process. Clear the area of any unnecessary personnel (when dismantling or erecting the falsework). Always dismantle shoring from the top down. Never remove braces, ties, or pins on any level until that level is being dismantled. Lower all components safely to the ground; never throw them down. Note: It is imperative that all drawings and/or manufacturer specifica- tions are followed. This is always the case, but it can not be stressed enough when dealing with falsework as falsework is used to support heavy members or entire buildings until they can support themselves. No falsework should be removed until all of the required work has been performed to specification and a qualified individual has inspected the structure and deemed it safe to dismantle the shoring. 15.10 Structural Steel Erection UNIT 15

▶▶OBJECTIVE 3: PROCEDURES FOR ERECTING TOWERS No matter the type of tower, or its intended use, there are three critical aspects to tower erection: 1. Planning the site layout of the steel 2. Coordination and communication • with the manufacturer of the tower • with the engineer • with the company doing the civil work at the tower site • with the crane rental company, if one is to be used to erect the lower section(s) 3. Ensuring that the base section of the tower is perfect In general, erecting towers calls for much preliminary work, the use of gin poles and other rigging devices, and then the actual erecting (called stacking) of the tower. Note: Most first-responder EMS crews are not qualified to conduct high-altitude rescue operations. Every tower crew should have at least one tower-rescue certified individual, especially if the tower is to be in excess of 300 feet tall. Preliminary Work There is an enormous amount of preliminary work that can be done before any tower is erected. Every tower is distinct, but the following can often be done before actual erection begins: • Inventory all hardware to find any shortages. (Most tower manufacturers or fabricators send a kit with all of the necessary materials, pieces, and fasteners that are needed to erect the structure.) • Shake out materials as close to the erection site as possible. • Assemble sections on dunnage or cribbing. • Install temporary or permanent lighting. Unit 15 — Erecting Towers 15.11 UNIT 15

• Install any needed handrail or work platforms (Figure 15.19). • When applicable, cut guy cables to length. • When applicable, attach guys. • When applicable, affix torque stabilizers or torque arms. • When applicable, put line ladders on individual sections. Rigging Figure 15.19 Sign Tower with Handrail, Lights, and Miscellaneous Parts Assembled Before Sign Section is Placed on the Monopole All of the rigging rules and regulations outlined in other courses should be followed when erecting towers. There is no instance where an Ironworker would be allowed to use a piece of defective rigging hardware just because he or she is involved in erecting a tower as opposed to erecting a structural building. Ropes and Cranes Ironworkers who are involved in erecting towers use ropes and blocks more often than probably any other area of the trade. They need to be very well-versed in their knot and block skills. Soft ropes can be used with blocks to achieve a very large mechanical advantage without the need for re-rigging the heavy wire rope from the winch constantly. A soft line and blocks can be used in the top of a tower with minimal concern for overloading the tower, which is a major concern when rigging on any tower. When erecting any type of tower that is under the 300-foot range in height, a mobile crane can be used economically with few problems provided that there is sufficient access for heavy equipment to the site. Gin Poles Because mobile cranes have a very limited working height, once the 200 to 300 feet threshold is crossed, it becomes impractical, if not impossible, for most mobile cranes to do a tower erector any good at all – not withstanding the fact that many tower construction sites are not accessible to pieces of very large equipment. Since any other type of crane is impractical or impossible to use for tower erection because of towers’ great heights, there are different rigging practices and equipment – some of them particular to the tower industry – used to erect towers that reach heights greater than 300 feet. 15.12 Structural Steel Erection UNIT 15

The most complex and unique rigging practice in tower construction involves the use of a piece of rigging equipment called a gin pole or simply “the pole.” The pole is best described as a “dead” boom. It is a basic support that can be fastened to the tower being erected (see Figures 15.20 and 15.21) and extended far enough above the top to facilitate the installation of the next section. When erecting a self-sup- porting tower, the pole is usually rigged inside of the tower and the tower is then built around the pole. Figure 15.20 Gin Pole Being Erected and Fastened to the Tower A gin pole must be strong enough to withstand the load forces applied, but light enough so as not to over- load the tower during construction. It may be acceptable to use a gin pole that is not commercially manufac- tured, but all gin poles used must be load rated and regularly inspected. An example of a gin pole identifica- tion, rating, and inspection tag can be found in Figure 15.22. Figure 15.21 Gin Pole Head Being Erected and Fastened to the Tower Figure 15.22 Sample Gin Pole Tag Warning! Do not use a gin pole that is not load rated. Unit 15 — Erecting Towers 15.13 UNIT 15

Unlike the boom on a crane, the hoist is a completely separate piece of equipment for a gin pole, and is located on the ground. These hoists (Figure 15.23) are usu- ally double drum winches: one line is for hoisting the load while the other line is dedicated solely to jumping the pole. As with gin poles, hoists should not be used unless they have been load rated and inspected. This rating and inspection should be displayed by a tag permanently attached to the hoist (see Figure 15.24). The hoisting line is run through blocks up to the pole and back down to the ground where it is attached to a headache ball (Figures 15.25 and 15.26). These hoists and the way in which they are used are very similar to a derrick and its hoist system. The hoist and the pole must be compatible, and both must meet the specific tasks of each individual project. In other words, the pole and the hoist must both be suitable for the job, and the weight of the pole must be correctly calculated for tower loading. Both pole and hoist must also be capable of lifting the maximum intended lift, the hoist must have enough line on the drum, and they must both be Figure 15.23 Hoist Figure 15.24 Hoist Tag Lines for hoisting and jumping the pole Next section staged close to the tower for erection. Figure 15.25 Lines Running from the Winch through a Snatch Block and up to the Gin Pole Figure 15.26 Headache Ball Tied to the Tower at the End of the Work Day 15.14 Structural Steel Erection UNIT 15

compatible with the strength of the line rigged on the hoist. Some gin poles will use a series of more than two hoists so that they can perform more than one function at a time, reducing rigging time for repetitive operations. Note: At the end of the work day, if the gin pole extends above the height of the tower more than 20 feet, the pole will likely need to be illuminated to be in compliance with most regulations. Some tower crews will install a light on the top of the pole before hoisting the pole into the tower and will run a jumper line or extension cord down the center of the pole to plug in at the end of the day. Jumping the Pole Ironworkers who are erecting towers need to know not only how to rig a gin pole to a tower to install the next section – what height and angle, and which face of the tower on which to place the pole – but also how to jump the pole (move it vertically up the tower). Jumping the pole is a special skill performed in different ways on dif- ferent projects. Some of the factors that determine how to jump the pole include the pole, winches, towers, individual personal preferences, and previous experiences. Jumping the pole is one of the most critical steps in tower construction as it dictates the speed at which the tower can be stacked. Tagging a Load Tagging a load out and away from the tower is a very critical job; it prevents the load from hitting and damaging the tower during erection. If a load isn’t tagged out, or isn’t tagged out properly, very expensive antenna can be damaged during the rig- ging and hoisting, or the tower could be struck and damaged, causing an expensive and time-consuming delay in the completion of the job. Worse yet, careless tagging could cause a fatal fall. Warning! Tagging a load out puts stress forces on the tag point and on the rigging involved in the hoisting of the load. Make certain that these forces have been considered and that the line used for tagging is of sufficient size and strength. Ironworkers have been killed while erecting towers because a tag line failed. The act of tagging a load alone can put enough stress on a pole to buckle it. In Figure 15.26, the tag line is visible. It is tied above the ball and extends back to the winch. Unit 15 — Erecting Towers 15.15 UNIT 15

Communication Communication with the winch operator is a main point to consider when working on a tower project. Advances in two-way radios have helped to fill communication gaps in most areas of the ironworking trade, including tower erec- tion (Figure 15.27). However, when erecting towers, on occasions when pushing a button to talk is impossible for an Ironworker who has both hands occupied, and when let- ting go to flag or talk to the operator on a radio could cause injury or death, the age-old whooping method is still employed. Whooping involves using a series of shrill/loud high-pitched yells or “whoops” to indicate to the operator what action is needed at the top of the tower. This practice should never be used by an inexperienced Ironworker, nor should it be used without prior discussion with the operator as to exactly what action each whoop or set of whoops means. Erecting There are two crews that make up a tower crew: the top crew and the ground crew. The top crew consists of three or four Ironworkers who jump the pole and assemble the pieces sent to them by the ground crew. The ground crew, meanwhile, has responsibilities very similar to those of a hooker-on in a typical steel erection project. The ground crew must understand what is going on at the top of the tower at any given time and plan the next moves accordingly. Ironworkers working in the ground crew must know if the top crew is preparing to jump the pole, if the top crew is ready (or almost ready) for the next section or piece, and what tools may be needed next. The ground crew must also know how to properly rig the next section, antenna, antenna mount, dish, deck, or other load so that the top crew can easily maneuver the load into position and easily unhook it when ready. The ground crew should also rig the load so that it will be turned properly when it reaches the top, and tag out loads to prevent them from hitting the structure on the way up. Figure 15.27 Hoist Operator Using Ear Muff Style Headset for Two-Way Radio Communications 15.16 Structural Steel Erection UNIT 15

One of the most important parts of erecting a tower is installing the base section (called the stub on a guyed tower. See Figure 15.28). It must be placed precisely at the proper height above ground level, it must be level and plumb with no twist, it must be ori- ented in the correct direction, and it must be attached to the foundation properly. A crane or construction forklift can usually be used to set the base section. Figure 15.28 Stub Section for a Guyed Tower For a guyed tower, once the limits of the machinery used to set the stub are met, the remaining sections of the tower – usually 20 to 25 feet high per section – must be stacked using a gin pole. After each section of tower is erected and secured, the pole must be jumped. Using this process, an experienced tower crew can stack an average of six to eight sections each work day, or the equivalent of 120 to 200 feet. A last feature of the erection process is the installation of lighting. Because of the heights involved with towers, Ironworkers usually install the lighting on a commu- nications tower. Some of the lighting systems – and especially strobe lighting – have very complex controls and electrical circuits. It is also necessary to incorporate temporary lighting when erecting a tower: an incomplete tower is just as dangerous as a fully erected one. A pilot or skydiver would not notice or care that a tower was incomplete if she or he happened to come into contact with one! Caution! Tower erection companies have received very hefty fines for failing to install temporary lighting on a tower under construc- tion (and for thus posing a hazard to possibly hundreds of people in one day). For these safety reasons, the installation of the lighting on a tower should not begin only after the erection of the structure is finished. The lighting system must also be maintained at all times, just as the paint schemes for daytime markings must be. Unit 15 — Erecting Towers 15.17 UNIT 15

▶▶OBJECTIVE 4: TENSIONING GUY WIRES AND CABLES To plumb an erected tower and maintain structural stability, guy wires and cables are attached to the tower or torque stabilizers and to the guy anchors on the ground (Figure 15.29 and 15.30). Figure 15.29 Guy Cable Attached to a Figure 15.30 Guy Anchor(s) Torque Stabilizer Note: If the tower being constructed is a guyed tower, the manu- facturer will make the determination as to how much tower can be stacked above each guy point before the next set of guys must be installed. Because guy wires do more than just give a method of plumbing the tower (they prevent twist and add structural stability), this is not an arbitrary number determined by guesswork in the field. These calculations are engineered into the design of the tower and should not be deviated from without the approval of the EOR. It should be very easy for an Ironworker to understand how improper tension on any guy wire in a set of three will cause a tower to be out of plumb. To correct this problem, all that has to be done is to tighten or loosen one or more of the guys to bring the tower back to plumb. The plumbness of a tower can be checked by the use of a transit or theodolite (or by two set up at a 90° angle from each other). It is also possible that a tower can be perfectly plumb and still have improper ten- sion in the guys. Too little tension could allow the tower to move laterally and fail. Too much tension could also cause the tower to fail, even if not immediately. Such a failure could occur, for example, during a snow or ice storm (which may add stress to the structural members in the tower). 15.18 Structural Steel Erection UNIT 15

Tension can be checked by using the pulse method, the sag method, a shunt meter, or a dynamometer: • The pulse method involves striking the guy wire and recording the amount of time it takes for the vibration to return to the ground. Refer to the manufacturer’s charts for time vs. tension calculations. • The sag method involves sighting through a tube attached to a guy wire to locate the line of sight intersection on the tower, and then determining the vertical measurement on the tower where this intersection occurs and referring to manufacturer supplied charts to determine the tension. • A shunt meter is a device that can be attached to the guy wires. It measures the amount of force needed to deflect the wire; this is the amount of tension in the wire. • A dynamometer (Figure 15.31) is a device placed in a parallel line with the guy wire. A chain hoist (come-a-long) is used to transfer the tension from the guy to the device, giving an accurate tension reading. Figure 15.31 Dynamometer Note: The pulse and sag method are less accurate than using a shunt meter or a dynamometer. Unit 15 — Erecting Towers 15.19 UNIT 15

▶▶OBJECTIVE 5: ERECTING COMMUNICATIONS TOWERS Communications towers differ from many other towers in that they have antennas and transmission lines that must be erected. Note: Because of the extreme heights involved, in addition to erect- ing communications towers, Ironworkers typically perform any needed maintenance work on them. This includes repainting as needed and required, and periodically inspecting and replacing bulbs, beacons, lenses, wires, circuit boards, etc. Antennas also need periodic realignment. All of this maintenance translates into work for Ironworkers on an almost never-ending basis. Antennas There are several different types of antennas mounted on towers. These include, but are not limited to, the following: • Corner reflector antenna • Dipole antenna • Omni-directional antenna • Panel antenna • Parabolic antenna • Yagi antenna These antennas vary in appearance and size, as do their mounting brackets. Some standoff brackets can place an antenna several feet (horizontally) from the face of a tower. Both mounting brackets and antennas also vary in their required placement on a tower itself. It is the responsibility of the engineer to determine the type of antenna required, and its placement tolerances, but it is the responsibility of the Ironworkers to meet the placement and path alignment specifications. 15.20 Structural Steel Erection UNIT 15

Note: There is more than one method of aligning antennas with their transmission path. These methods vary widely depending on the type and location of the tower and the antenna itself, and must therefore be learned at the job site. Take extra care when hoisting and installing anten- nas and mounting brackets on a tower: antennas must be aligned properly or the antenna may be damaged and the entire purpose of the tower (to form a communication path for signals) will be destroyed. A monopole, when used as a communications tower, will generally have its antenna array (referred to in this case as a top hat) on or towards the top of the tower. The top hat usually has a deck and railings for antenna maintenance and adjust- ment. Some monopoles have more than one level of antenna decks, as is shown in Figure 15.32. Transmission Lines Even if antennas are perfectly installed and aligned to the path of the signal, they will serve no purpose if the signal is lost in poorly installed transmission lines. All communications towers include communications transmission lines. The type of transmission line used is determined by the type of signal it will carry and will be indicated in the project’s drawings or specifications. Transmission line installation involves the erection of an ice bridge, the installation of the lines, weatherproofing, and grounding. Ice Bridges Installation of transmission lines begins by erecting an ice bridge at the base of the tower. This bridge extends from the tower to a nearby building, is elevated, and must be strong enough not only to support the transmission lines and any snow or ice that may form on it in the winter months, but also to withstand the impact of ice that may melt and fall off of the tower. Ice bridges are generally constructed of grip strut or expanded metal for the deck and pipe posts concreted into the ground for support legs. The lines are fastened to the bottom side of the deck so that the deck will protect them from falling ice and maintenance/construction debris. The ice bridge should never, unless specified in the plans, be supported solely by the communications building and the tower. Unit 15 — Erecting Towers 15.21 Figure 15.32 Communications Tower Monopole with More than One Level of Antenna Decks UNIT 15

Ice bridge Figure 15.33 Ice Bridge Before Transmission Figure 15.34 Ice Bridge with Transmission Lines Are Installed Lines Installed Figures 15.33 and 15.34 show an ice bridge before and after transmission line installation. Installation After the ice bridge is installed, the transmission lines themselves should be installed. Take extreme care when handling these lines. If kinked (there are charts to refer to for maximum bending radius of different diameter and types of lines), not weatherproofed properly, or in any other way damaged (even if not visible to the casual eye), the signal(s) the tower was erected to receive, transmit, or retrans- mit will be weakened or completely lost. This could be a very expensive problem not only to find but to correct. The reel of line should be placed on a sec- tion of pipe and set on stands to spool off of the reel (Figure 15.35). Once the line is at the proper height, it should be attached to the line ladder, fol- lowing all manufac- turer specifications regarding quantity, spacing, and bolt ten- sion (Figure 15.36). Figure 15.35 Transmission Line on a Reel that is Placed on a Stand to Be Spooled Off Figure 15.36 Transmission Lines Run up a Tower and Attached to a Line Ladder 15.22 Structural Steel Erection UNIT 15

Some line ladders are part of a tower’s structural design while others are attached to the backside of the climbing ladder. Some line ladders allow for vertical and horizontal attachment. All line ladders are bolted to one or more faces of the tower. In any case, unless the line ladder is part of the tower’s structural design, transmis- sion lines should never be directly attached to the tower in a vertical run; instead, they should climb and be fastened to the line ladder, which is fastened to the tower. This makes for a uniform method and point of fastening for each level of the tower for the transmission lines, and for a professional-looking job. The lines in Figure 15.36, for example, appear straight and look professionally installed. Note: Monopoles typically have transmission lines run through the hollow center of the tower (Figure 15.37). On the rare occasion that transmission lines are on the exterior of a monopole, it is usually because so many antennas have been added that there is not enough room in the core of the tower to place any more lines. Figure 15.37 Transmission Lines Running into the Center of a Monopole Weatherproofing Proper attachment of transmission lines involves using the appropriate connector for the type and size of line and good effective weatherproofing. The proper instal- lation of connectors takes skill, care, and experience. Before the connections are weatherproofed, they should be clean and dry. The two most common methods of weatherproofing are taping and heat shrink. Note: Cold shrink is not weatherproof! Unit 15 — Erecting Towers 15.23 UNIT 15

Grounding Globally, there are approximately 100 intense recordable lightning strikes per sec- ond. Grounding a tower means installing a method to allow an electrical surge (generally from lightning) to pass to the ground without damaging equipment on the tower. This usually involves installing some or all of the following: • A lightning rod • Ground lead • Bus bars • A ground halo Follow all grounding guidelines – from the manufacturer’s specifications regarding the antenna and transmission lines to the owner’s requirements – when installing these and any other grounding elements. 15.24 Structural Steel Erection UNIT 15

▶▶OBJECTIVE 6: SAFETY CONCERNS, STANDARDS, AND REGULATIONS Any live or operating tower possesses specific hazards. One of these hazards is radio frequency (RF). RF is emitted from antennas and will burn a human being from the inside out. Ironworkers working with towers must have specific training in this and other safety hazards associated with towers. Another danger of towers is their extreme height. To make towers more worker- friendly, most of them are equipped with either a ladder (see Figure 15.38) or “step bolts” (shown in Figure 15.39). Either of these two climbing systems may also use a safety cable with an ascender for fall arrest (see Figure 15.40). If an ascender is not present, however, Ironworkers are not freed from having to be tied off at the required federal, state, provincial, local, contractor- or owner-regulated height. An Ironworker properly tied off while climbing a tower can be seen in Figure 15.41. Figure 15.38 Ladders in a Tower for Climbing Figure 15.39 Close-Up of Step Bolts Figure 15.40 Step Bolts with Ascender Figure 15.41 Ironworker Properly Tied Off While Climbing a Tower Unit 15 — Erecting Towers 15.25 UNIT 15

Tip: When conducting maintenance work, wear a saddle belt and have a harness that has a D-ring in the chest for fall arrest. This D-ring works very well when tying off to a ladder ascender. Figure 15.42 demonstrates a D-ring in use. Figure 15.42 D-Ring Attached to a Cable Ascender Because of their great height, towers can also pose a very dangerous threat to sky- divers, hot air balloons, blimps, helicopters, and airplanes. Because the greatest threat is to aircraft, the U.S. Federal Aviation Administration (FAA) and Navigation Canada (NAVCAN) regulate tower markings to ensure that they are visible and stand out from their surroundings to warn pilots and others of possible danger. These regulations can be obtained from the FAA or NAVCAN, and are standards like “Obstruction Marking and Lighting.” Generally, these standards state that any temporary or permanent object that exceeds an overall height of 200 feet above ground level should be marked and/or lighted. At the discretion of the FAA or NAVCAN, these guidelines can be changed to be more lenient or strict on a case-by-case basis, but even then these marking and/or lighting combinations must be maintained at all times. Companies have been fined greatly for failing to maintain marking and lighting of towers. The Electronics Industry Association/Telecommunication Industry Affiliation (EIA/TIA) also has standards for towers that must be followed. These standards regulate a number of areas, including the following: • • • • Fabrication (including tolerances and coatings not only for tower sections, but for tower anchors) Load (including wind- and ice-loading, not only for the tower itself, but also for any antennas, dishes, or guy wires) Foundations (piers and footings) Plans and markings (blueprints and piece numbers) 15.26 Structural Steel Erection UNIT 15

• Guy wires and connectors (including cables extending from the anchor point on the ground to the attachment point on the tower, and thimbles, shackles, clevises, turnbuckles, and cable clamps). Figure 15.43 shows guy wires and connectors. • Climbing devices (ascenders, step bolts, and ladders) • Grounding • Plumbness. Figure 15.44 illustrates a tower that is Figure 15.43 Guy Wires and Connectors plumb. • Twist (i.e., horizontal linearity from tower base to top). Figure 15.45 illustrates a tower in twist. When working with towers, make sure you know and fol- low all applicable federal, state, provincial, and local regulations, as well as any owner, general contractor, or construction man- ager rules or regulations. Make certain, too, that you keep your knowledge current: these regu- lations are constantly evolving, changing, and being updated. Figure 15.44 Plumb Figure 15.45 Twist Caution! Tower erection is a very specific part of the Ironworking trade and has its own specific standards and regulations. There are, for example, regulations that dictate when it is permissible to ride the load line in the tower industry. These are very different from regulations governing the same act in other parts of the trade. When working on a tower, make sure you know which standards and regu- lations are specifically applicable to that tower. Unit 15 — Erecting Towers 15.27 UNIT 15

15.28 Structural Steel Erection UNIT 15

▶ ERECTING WIND TURBINES UNIT 16 ▶ OBJECTIVES After completion of this unit, you should be able to identify the basic parts of, and describe the general process for erecting and maintaining, wind turbines. This knowledge will be evidenced by correctly completing the assignment sheet and by scoring a minimum of 70% on the unit test. Specifically, you should be able to: 1. Describe the history of wind turbines 2. Identify the basic types and parts of wind turbines 3. Describe a wind turbine’s blade considerations and rotation control measures 4. Explain the procedures for erecting wind turbines 5. Describe typical wind turbine maintenance Each of these objectives is covered in the pages that follow. Note: This unit will present information on erecting wind turbines in general. For details regarding erecting a wind turbine produced by a specific manufacturer, refer to the installation manual for that wind turbine. Unit 16 — Erecting Wind Turbines 16.1 UNIT 16

▶▶OBJECTIVE 1: HISTORY OF WIND TURBINES Around the world, the majority of electrical power is generated from fossil fuels, hydropower, nuclear power, biomass, and to a smaller extent, wind and solar sources. The burning of fossil fuels, primarily coal and natural gas, has severe envi- ronmental consequences. Because of this, sustainable energy sources such as wind power, which is a zero-emission technology, are increasingly being used. Indeed, according to the Global Wind Energy Council (GWEC), there is now over 59,000 MW (megawatts or millions of watts) of installed wind capacity in the world. Increases in the use of energy sources such as wind power have also followed advances in technology that have increased their economic feasibility. In 1981, wind energy cost approximately $0.35/kWh (kilowatt hour) to generate. Due to improved technology and federal incentives, large wind systems are now in the competitive range at $0.03–$0.07/kWh. These increases have also followed from heightened demand for electricity through- out the world: from year-end 2000 to 2005, the U.S. wind industry has grown at an annual rate of 29%, while worldwide growth increased an average of 30% per year over the last ten years. Generation from coal and nuclear power, meanwhile, has grown only about 1 to 1.5%. In North America, most wind power development is onshore, which is about half as expensive as building offshore. In the United States, the Midwestern states, along with California and Texas, have been particularly aggressive in building wind farms (see Figure 16.1), places where a number of wind turbines are located together. Ironworkers are erecting more and more wind turbines and helping to create more and more wind farms. Figure 16.1 Wind Farm 16.2 Structural Steel Erection UNIT 16

▶▶OBJECTIVE 2: TYPES AND BASIC PARTS OF WIND TURBINES A wind turbine (Figure 16.2) is a machine that converts wind’s kinetic energy into mechanical energy. If the mechanical energy is used directly by the machinery, such as with a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is instead converted to electricity for other purposes, the machine is called a wind turbine. Electrical generators inherently produce alternating cur- rent (AC) power. Older style wind generators rotated at a constant speed to match power line frequency; however, newer wind turbines often turn at whatever speed gener- ates electricity most efficiently. This variable frequency current is then converted to direct current (DC) and then back to AC, matching the line frequency and volt- age. In some cases, especially when turbines are sited offshore, the DC energy is transmitted from the turbine to a central (onshore) inverter for connection to the grid. Figure 16.2 Wind Turbine Typical wind turbines are rated between 500 kW and 2 MW [670 to 2,700 hp]. Currently, the most powerful turbines are rated at or higher than 6 MW [8,000 hp]. There are two main types of wind turbines: horizontal-axis wind turbines (HAWTS) and vertical-axis wind turbines (VAWTS). The axis refers to the shaft that turns or powers the generators, not the blades. Turbines that rotate around a horizontal axis are more common than those that rotate around a vertical axis. Both HAWTS and VAWTS are more frequently oper- ated onshore, but offshore operations are also possible. Horizontal-Axis Wind Turbines (HAWTS) A HAWT, as shown in Figure 16.3, has its main rotor shaft and generator at the top of a tower, and must be pointed into the wind. Small HAWT turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servomo- Figure 16.3 Horizontal Axis Wind Turbine (HAWT) Unit 16 — Erecting Wind Turbines 16.3 UNIT 16

tor. Most have a gearbox, too, which turns the slow rotation of the blades into a quicker rotation more suitable for generating electricity. Because a HAWT tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. The turbine’s blades are made stiff and placed a con- siderable distance in front of the tower (and sometimes tilted up four degrees) to prevent high winds from pushing them into the tower. For large, commercial-size HAWTS, the generator is mounted in a nacelle at the top of a tower, behind the hub of the turbine rotor. A speed-increasing gearbox may be inserted between the rotor hub and the generator so that the generator cost and weight can be reduced. Vertical-Axis Wind Turbines (VAWTS) A VAWT (see Figure 16.4) has its main rotor shaft running vertically. The advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom near the ground so the tower does not need to support it, and that the turbine does not need to be pointed into the wind. The drawbacks, however, include pul- sating torque produced during each revolution and the difficulty of mount- ing VAWTs on towers. This means that VAWTs must operate in the slower, more turbulent air flow near the ground with lower energy extraction efficiency. Offshore Wind Turbines Offshore wind turbines (Figure 16.5) are considered to be less obtrusive than onshore turbines, as their appar- ent size and noise can be diminished with distance. Since water has less sur- face roughness than land, the average wind speed is usually higher over open water, so offshore wind turbines can also generate more electricity. Figure 16.4 Vertical-Axis Wind Turbine (VAWT) 16.4 Structural Steel Erection Figure 16.5 Offshore Wind Turbines UNIT 16

In stormy areas with extended shallow continental shelves, wind turbines give espe- cially good service and are therefore practical to install. The offshore environment is, however, more expensive in general. With their submerged height, offshore towers are generally taller than onshore towers, and offshore environments tend to be corrosive and abrasive, requiring offshore wind turbines to be outfitted with extensive corrosion protection measures. Offshore foundations are also generally more difficult to build, while repairs and mainte- nance on offshore wind turbines are much more difficult and costly than repairs and maintenance on onshore wind turbines. Power transmission from offshore turbines is generally undertaken through under- sea cables, which are more expensive to install than cables on land. The expense involved in erecting and operating offshore turbines means that, while there is a significant market for small land-based windmills, offshore wind turbines have recently been, and will probably continue to be, the largest wind turbines in operation. This is because the larger these wind turbines are, the more electricity they produce and the more cost-effective they are. For similar reasons, offshore wind farms tend to be quite large – often involving over 100 turbines – in compari- son to onshore wind farms, which can operate competitively even with fewer wind turbines. Basic Parts of a Wind Turbine There are six basic parts of a wind turbine: 1. The foundation (sometimes called base) is the rebar, concrete, and anchor bolts that support the fully assembled wind turbine. It must be able to support the tower, blades, generator, and other components while the turbine is in operation and during high winds. 2. The tower sections comprise the bulk of the tower and consist of three or four sections depending on the turbine manufacturer. 3. The nacelle houses the generator that produces the electricity as the blades turn. 4. The turbine rotor (often called the hub) attaches to the nacelle and holds the blades. 5. The blades catch the wind to turn the turbine rotor. 6. The down tower assembly (DTA) or control console is the control unit. It is placed onto the foundation. Unit 16 — Erecting Wind Turbines 16.5 UNIT 16

These components (except for the foundation and DTA) are illustrated in Figure 16.6 and can be seen laid out prior to erection in Figure 16.7. Figure 16.6 Wind Turbine Components Figure 16.7 Wind Turbine Parts Ready For Erection 16.6 Structural Steel Erection UNIT 16

▶▶OBJECTIVE 3: BLADES AND ROTATION CONTROL Typical wind turbines have diameters of 130 to 300 feet, with a mass approximately propor- tional to the cube of the turbine’s blade length. The wind power captured by the blades is proportional to the square of the blades, while blade length itself is limited by the strength and stiffness of the blades’ material. The number of blades used on a turbine is determined through considerations of aerody- namic efficiency, component costs, system reli- ability, and aesthetics. Over the last fifty years, however, wind turbines have almost universally used either two blades (see Figure 16.8) or three blades (see Figure 16.9). This is because increas- ing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, while increasing the blade count from two to three yields an additional three percent in aerodynamic efficiency. Increasing the number of blades beyond this point, however, requires that the blades be made thinner (so as not to contribute too much additional weight to the nacelle), resulting in decreased blade stiffness and minimal improvement in aerodynamic efficiency. Having fewer blades also tends to mean lower material and manufacturing costs. Rotation Control Modern wind turbines are designed to spin at varying speeds. The use of aluminum and composites in their blades contributes to their low rotational inertia, which means that newer wind turbines can accelerate quickly if the winds pick up, keep- ing the tip speed ratio – the ratio between the speed of the wind and the speed of the tips of the blades – more nearly constant. High efficiency three-blade turbines have tip speed to wind speed ratios of 6 to 7 (6:7). Operating close to optimal tip speed ratio during energetic gusts of wind allows wind turbines to improve energy capture from sudden gusts. Figure 16.8 Two-Blade Design Figure 16.9 Three-Blade Design Unit 16 — Erecting Wind Turbines 16.7 UNIT 16

However, the speed and torque at which a wind turbine rotates must be controlled for a variety of reasons: • To optimize the aerodynamic efficiency of the rotor in light winds • To keep the generator within its speed and torque limits • To keep the rotor hub within its centripetal force limits (centripetal force from spinning rotors increases as the square of the rotation speed, which makes wind turbines vulnerable to problems of overspeeding) • To keep the rotor and tower within their strength limits. Because the power of the wind increases as the cube of the wind speed, turbines must be built to survive much higher wind loads (such as gusts of wind) than those from which they can practically generate power. Since the blades generate more downwind force (and thus put far greater stress on the tower) when they are producing torque, most wind turbines have ways of reducing torque in high winds. • To enable maintenance (because it is dangerous to have people working on a wind turbine while it is active, it is sometimes necessary to bring a turbine to a full stop) • To reduce noise (as the turbine rotates faster it is louder) Wind turbine rotation is gener- ally controlled through the DTA, which can change the angle of the blades relative to the wind to reduce the speed of rotation. Rotation speed can also be reduced through electrical braking and mechanical braking (Figure 16.10 shows a mechanical brake). Figure 16.10 Mechanical Brake 16.8 Structural Steel Erection UNIT 16

▶▶OBJECTIVE 4: ERECTING WIND TURBINES From a construction perspective, the erection of a wind turbine is relatively straightforward. Workers are divided into different crews (the unloading crew, the base setting crew, the erection crew, the rote assembly crew, the mechanical completion crew, the punch list crew, etc.) and once materials are unloaded from the trucks, work rarely stops until the project is finished. These materials, and other parts and tools required to install a wind turbine, will be listed in the manufacturer’s installation manual, which should be reviewed to ensure that all of the required materials, parts, and tools are available and in proper condition. Note: The installation contractor is typically required to design and procure all lifting devices and provide a lift plan. The wind turbine manufacturer will provide typical weight dimensions and center of gravity information for lifting manufacturer-provided components. Tower Foundation There are two basic types of foundations used to support wind turbines: spread footing and casing. Spread footing begins with the excavation of a large hole (e.g., 40' × 40' × 6' deep), which is then filled with reinforcing bars. Once the rebar is in place, concrete is poured to create the foundation. The casing method begins by excavating large holes (e.g., 60' × 60') to accommodate the foundation casings required by each wind turbine. Each foundation must sup- port a wind turbine structure weighing approximately 40 to 50 tons with a height of 300 feet or more. Typically, when casings are used, two casings are lowered into the hole, with the larger of the two casings lowered into the ground first and the smaller casing then placed inside the larger casing. Unit 16 — Erecting Wind Turbines 16.9 UNIT 16

When either type of foundation is completed, anchor bolts are attached to the foun- dation to erect the base section of the tower. These anchor bolts (see Figures 16.11 and 16.12) need a plastic sleeve installed on site to protect the metal. The next step is to prepare the foundation for the tower base section (Figure 16.13) by verifying that the foundation is level. To do this, follow these procedures: 1. Tap each bolt lightly to break it free of any cement seepage. 2. Clean the foundation. 3. Depending on the foundation configuration, install either the leveling nuts or shim plates to ensure that the tower level can be adjusted properly. If using shims, grind the foundation to ensure that the shims have a hundred percent contact with the foundation. 4. Remove the nuts and washers from the anchor bolts. 5. Using an instrument, determine the proper elevation of the leveling nuts or shims at four location points per quarter section of the foundation, and mark the results at each location. 6. Return to the highest point recorded within the circumference and use it as a reference point to adjust the leveling nuts or shims to ensure that the grout thickness required on the drawings or specifications can be achieved. Grout will be applied after the base section is installed (and likely before the nacelle is set), following manufacturer instructions. Figure 16.11 Anchor Bolts Figure 16.13 Preparing the Foundation Figure 16.12 Foundation Reinforcing and Anchor Bolts 16.10 Structural Steel Erection UNIT 16