Chapter 5 Construction Methods and Materials: Heavy Construction

Heavy construction refers to construction in which builders use large bulks of materials and extra-heavy structural members such as steel, timber, concrete, or a combination of these materials. Projects most often deal with sewer treatment plants, water treatment plants, freeway overpasses and interchanges, high-rise buildings, rapid transit, and many other elements that comprise the infrastructure of the nation.

 In the Naval Construction Force, heavy construction also includes the construction of bridges, waterfront structures, and steel frame structures. In civilian construction, it also includes The design and construction of various new heavy structures, or their rehabilitation, may be included in the Seabees’ current tasking as they support the Navy’s and the Marine Corps’ operating forces. As an EA, you need to understand the terminology, basic principles, and methods used to construct heavy facilities. That knowledge of heavy construction will help you prepare engineering drawings (original, modified, or as-built), provide a foundation for a successful assignment in quality control, and broaden your perspective for civilian construction.

When you have completed this lesson, you will be able to:

1. Describe the different types of bridge construction.
2. Describe the purpose and types of foundations and piles.
3. Describe the different types of waterfront structures.
 4. Identify the different types of timber fasteners and connectors.
5. Identify the different types of structural steel.

Contents

1.0.0 Bridge Construction

2.0.0 Foundations and Piles

3.0.0 Waterfront Structures

4.0.0 Timber Fasteners and Connectors

5.0.0 Structural Steel

Summary

Review Quiz


1.0.0 BRIDGE CONSTRUCTION

A bridge spans and carries traffic over a depression or an obstacle, and consists of two principal parts: the lower part, or substructure, and the upper part, or superstructure. All bridges have two abutments, or supports; a bridge supported only at its two end abutments is a single-span bridge. A bridge with one or more intermediate supports is a multi-span bridge (Figure 5-1). Bridges may be fixed or floating, but this course address only fixed bridges.

 

Figure 5-1 — Multi-span bridge.

1.1.0 Abutments

There are different types of fixed bridge abutments to support the ends of a bridge. Figure 5-2, Views A and C show two footing-type abutments. View A is a timber-sill abutment, and View C is a timber-bent abutment. Three elements are common to any footing-type abutment; each has a footing, a sill, and an end dam. Figure 5-2, View A is a timber-sill abutment, the same footing-type abutment shown for the bridge in Figure 5-1. In this type of abutment, loads are transmitted from the bridge deck, to the stringers, to the sill, and finally to the footing. The footing then distributes the combined load over a sufficient area to keep the entire bridge and load from sinking into the ground.  5-4 The end dam is a wall of planks that keeps the approach-road backfill from caving in between the stringers. A timber-sill abutment should be a maximum of 3 feet high for spans of 25 feet or less. Figure 5-2 — Types of fixed-bridge abutments. Figure 5-2, View C is a timber-bent abutment. With timber or steel stringers, it is practical for bridges with spans up to 30 feet. A deadman is used to provide horizontal stability. These abutments do not exceed 6 feet in height. Figure 5-3 — Typical concrete abutments.  5-5 There are other types of fixed-bridge abutments, including pile abutments and concrete abutments. Pile abutments (either timber or steel) can be used with steel or timber stringers, support spans of any length, and reach a maximum height of 10 feet. Figure 5-2, View B is a timber-pile abutment. Concrete abutments (Figure 5-3) are the most permanent. They may be mass or reinforced concrete, be used with either steel or timber stringers, span any length, and reach as high as 20 feet.

1.2.0 Intermediate Supports

Bents and piers provide support for the bridge superstructure at points other than the bank or abutment ends. A bent is a single row of posts or piles, while a pier consists of two or more rows of posts or piles. The pile bent shown in Figure 5-4 consists of the bent cap, which provides a bearing surface for the bridge stringers, and the piles, which transmit the load to the soil. The support for the loads may be derived either from column action when the tip of the pile bears on firm stratum, such as rock or hard clay, or from friction between the pile and the soil into which it is driven. In either case, earth pressure must provide some lateral support but traverse bracing is often used to brace the bent laterally. The timber pile bent shown in Figure 5-4 consists of a single row of piles with a pile cap. In addition to the shown transverse bracing, to provide any additional necessary longitudinal stability, it should be braced to the next bent or to an abutment. This bent will support a combined span length of 50 feet. Figure 5-4 — Typical pile bent.  5-6 Figure 5-5 — Typical timber trestle bent. Figure 5-5 is a trestle bent. It is similar to a pile bent except that posts (instead of piles) transmit the load from the cap to a sill. The sill transmits the load to the footings, and the footings transmit the load to the soil. Normally constructed in dry, shallow gaps where the soil is firm, they are not suitable for use in soft soil or in swift or deep streams. The bent can support a combined span length of up to 30 feet and can be 12 feet high.  5-7 Figure 5-6 — Typical pile pier. Figure 5-6 is a pile pier. It is composed of two or more pile bents. In this figure, notice the common cap. The cap transmits the load to the corbels, which transmits the combined load to the bent caps. Piers are usually braced longitudinally as well as transversely.

1.3.0 Superstructure

A bridge’s superstructure consists of stringers, flooring (decking and treads), curbing, walks, handrails, and other items forming the bridge above the substructure (the combined elements below the stringers.) Stringers, the main load-carrying members of the superstructure, rest on the substructure caps and span the distance between the intermediate supports or abutments. They receive the load from the flooring and transmit it to the substructure. The flooring system includes the deck, the wearing surface (or tread) that protects the deck, and the curb and handrail or barrier system. A plank deck is the simplest to design and construct, providing considerable timesaving compared to other types of decks. Plank decking is normally placed perpendicular to the bridge centerline (direction of traffic) for ease and speed of construction, but decking placed at about a 30- to 60- degree skew is a better arrangement. In either arrangement, builders should allow approximately ¼-inch space between planks to allow for swelling, water drainage, and air circulation. Three inches is the  5-8 minimum thickness allowed for decking. If the required thickness exceeds 6 inches, builders should use a laminated type of decking. Figure 5-7 — Nomenclature of a fixed highway bridge superstructure. Figure 5-7 is a bridge superstructure. The figure shows both steel and timber stringers, and both standard and laminated decking for demonstration purposes only. In practice, only one type would normally be used.

 

Test Your Knowledge

1. A bridge consists of two principle parts, the _____ and the _____.

A. superstructure, abutments
B. substructure, abutments
C. substructure, superstructure
D. footings, superstructure

2.0.0 FOUNDATIONS and PILES

A foundation is a building or structure’s element that is located below the surface of the ground. A foundation distributes the dead load and live load of a building or structure over an area of subgrade large enough to prevent settlement and collapse. Also transferring load to the natural earth, a pile is a slender structural unit driven into the ground to transmit loads to the underground strata. It does so by friction along its surface or by direct bearing on compressed soil at some distance below ground. A  5-9 bearing pile drives vertically and sustains a downward load. When a bearing pile is driven other than vertically, it is termed a batter pile. Another type of pile is the sheet pile, used to resist lateral soil pressure. You may need to include foundations and piles in your drawings.

2.1.0 Foundations

In general, all foundations consist of three essential parts:

• Foundation bed — the soil or rock upon which the building or structure rests

• Footing — widened foundation that rests on the foundation bed

• Foundation wall — rises from the footing to a location above the ground Contrary to its name, a foundation wall may be a column or a pedestal instead of a wall. However, when it is a wall, it forms what is known as a continuous foundation (or continuous footing). A continuous footing is most commonly used for small buildings. The size of the footing and the thickness of the foundation wall are specified based on the type of soil at the site. Most building codes require the bottom of a footing be horizontal and any slopes be compensated for by stepping the bottom of the footing. Figure 5-8 shows common types of foundations. Figure 5-8 — Typical wall, column, and step footings. A grade-beam is another type of foundation. A grade beam (Figure 5-9) is a reinforced concrete beam located at grade level around the perimeter of a building. It may be supported by a series of concrete piles. The building loads are supported by the grade beam, which distributes the load to the piles, which distribute the load to the foundation bed. Figure 5-9 — Typical grade beam.  5-10 A spread foundation (spread footing) (Figure 5-10) is often required for heavy concentrated loads from columns, girders, or roof trusses. Figure 5-10 — Typical spread footing. Spread footings, flat, stepped, or sloped, and generally reinforced with steel, are located under isolated columns or at intervals along a wall where concentrated loads occur. Figure 5-11 shows a typical mat foundation. Figure 5-11 — Typical mat foundation. A mat foundation is a heavily reinforced concrete slab extending under the entire building to distribute the total building load over the entire site. This minimizes problems created by unequal settlement when subsoil conditions are uneven. A mat foundation may also be referred to as a floating foundation.  5-11

2.2.0 Pile Construction

While all foundation piles serve the same function, to distribute a structure’s load to the foundation bed, there are many different types and materials.

2.2.1 Bearing Piles

The small end of a pile is called the tip; the larger end is called the butt. Timber bearing piles are usually straight tree trunks with the limbs and bark removed. They are used for low design loads because of their vulnerability to damage while being driven, but will last for centuries if kept continuously wet. Timber piles range from 16 to 90 feet in length with a tip diameter of at least 6 inches and a butt diameter seldom less than 12 inches. A steel bearing pile might be an H-pile (H-shaped cross section), usually used for driving to bedrock. A steel pile can also be a pipe pile (circular cross section) and be either open-ended or closed-ended, depending on the tip end. Figure 5-12 — Types of concrete piles. Concrete piles (Figure 5-12) may be precast or cast in place. Most precast piles today are pretensioned and manufactured in established plants. They may be square, cylindrical, or octagonal; if driven into soft or mucky soil, they are usually tapered. Cast-in-place piles are cast on the jobsite and classified as shell or shell-less type. The shell type is formed by driving a closed-end, hollow steel tube (shell) into the ground and filling it with concrete. The shell-less type is formed by driving a casing and core to  5-12 the required depth. The core is removed, the casing is filled with concrete, and then the casing is removed, leaving the concrete in contact with the foundation bed.

2.2.2 Sheet Piles

Sheet piles, made of wood, steel, or concrete, are designed and intended for joining along the entire length of their edges and driven to form a continuous wall or bulkhead. The following are a few common uses for sheet piles:

• Resist lateral soil pressure as part of a temporary or permanent structure, such as a retaining wall

• Construct cofferdams or structures built to exclude water from a construction area

• Prevent slides and cave-ins in trenches or other excavations

Figure 5-13 — Typical steel sheet piles. The edges of steel sheet piles are shaped for locking the piles together edge-to-edge and are called interlocks; the section between the interlocks is called the web (Figure 5- 13).  5-13 Wood sheet piles may be a single, double, or triple layer of planks (Figure 5-14). Figure 5-14 — Typical wood sheet piles. Concrete sheet piles are cast with tongue-and-groove edges for joining (Figure 5-15). Figure 5-15 — Typical concrete sheet piles.

 

Test Your Knowledge

2. When a bearing pile is driven other than vertically, it is termed a _____ pile.

A. bent
B. batter
C. sheet
D. deadman

3.0.0 WATERFRONT STRUCTURES

Waterfront structures may be broadly divided into three types:

• Harbor-shelter structures

• Stable-shoreline structures

• Wharfage structures

3.1.0 Harbor-Shelter Structures

Harbor-shelter structures (as the term implies) are offshore structures designed to create a sheltered harbor. A breakwater is an offshore barrier erected to break the action of the waves and thereby maintain an area of calm water inside the breakwater (Figure 5- 16). Figure 5-16 — Typical breakwater.  5-15 A jetty is a similar structure, except its main purpose is to direct the current or tidal flow along the line of a selected channel (Figure 5-17). Figure 5-17 — Typical jetty. A rubble-mound (rock-mound) is the simplest type of breakwater or jetty (Figure 5-18). The width of its cap may vary from 15 to 70 feet. The width of its base depends on the width of the cap, height of the structure, and the slopes of the inner and outer faces. Figure 5-18 — Typical rubble-mound breakwater or jetty. For a deepwater site, or one with an extra-high tide range, a rubble-mound breakwater may be topped with a concrete cap structure, thus becoming a composite breakwater or jetty.  5-16 Figure 5-19 — Typical composite breakwater or jetty. In Figure 5-19, the cap structure is made of a series of precast concrete boxes called caissons, which are floated into position and sunk with a monolithic (single-piece) concrete cap cast along the top. Sometimes, breakwaters and jetties are built entirely of caissons (Figure 5-20). Figure 5-20 — Typical caisson breakwater or jetty.  5-17 A groin is similar to a breakwater or jetty, but it has a third purpose. A groin is used where a shoreline is subject to alongshore erosion caused by wave or current action parallel or oblique to the shoreline. The groin is run out from the shoreline (usually a succession of groins at intervals) to check the alongshore wave action or deflect it away from the shore. Figure 5-21 — Typical series of groins. A mole is a breakwater paved on the top for use as a wharfage structure. To serve this purpose, it must have a vertical face on the inner side, or harborside. A jetty may be similarly constructed and used, but it is still called a jetty. Figure 5-22 — Typical breakwater mole.  5-18

3.2.0 Stable-Shoreline Structures

These structures are constructed parallel to the shoreline to protect it from erosion or other wave damage. Figure 5-23 — Types of seawalls. A seawall is a vertical, battered, or sloping wall that offers protection against erosion and slippage caused by tide and wave action. It is usually a self-sufficient structure, such as a gravity-type retaining wall, which depends on the weight of its mass (stone, concrete, or other heavy material) to resist pressure from fill. Seawalls are classified according to the types of construction. A seawall may be made of riprap or solid concrete. Figure 5-23 shows several types of seawalls. A bulkhead has the same general purpose as a seawall, to establish and maintain a stable shoreline. However, while a seawall is self-contained, relatively thick, and supported by its own weight, the bulkhead is a relatively thin wall. Bulkheads are classified according to types of construction (Figure 5-24):

5-19 Figure 5-24 — Types of bulkheads. Most bulkheads are made of steel sheet piles supported by a series of tie wires or tie rods that are run back to a buried anchorage (or deadman). The outer ends of the tie rods are anchored to a steel wale that runs horizontally along the outer or inner face of the bulkhead. The wale is usually made up of pairs of structural steel channels that are bolted together back to back. In stable soil above the groundwater level, the anchorage for a bulkhead may consist simply of a buried timber, a concrete deadman, or a row of driven and buried sheet piles. A more substantial anchorage for each tie rod is used below the groundwater level. Figure 5-25 shows two common types. Figure 5-25 — Tie-rod anchorage types.

• Figure 5-25, View A shows the anchorage for each tie rod is a timber cap supported by a batter pile and bolted to a bearing pile.  5-20

• Figure 5-25, View B shows the anchorage is a reinforced concrete cap supported by a pair of batter piles. In both views, the tie rods are supported by piles located between the anchorage and the bulkhead. Bulkheads are constructed from working drawings (Figure 5-26). Figure 5-26 — Typical bulkhead working drawing. The detail plan for this bulkhead reveals the following sequential information:

• Anchorage is a row of sheet piles with tie rod inner ends anchored to a channel wale.

• Anchorage will lie 58 feet behind the bulkhead with 2 equally spaced support piles for each tie rod. The detail plan also reveals the following sequential construction:

• Excavate the shore and bottom to the level of the long, sloping dotted line.

• Drive the sheet piles for the bulkhead and anchorage.

• Drive the tie rod support piles.

• Set the tie rods.

• Bolt on the wales and attach the tie rods.

• Moderately tighten the tie rods with turnbuckles.  5-21

• Backfill over the anchorage, out to the sloping dotted line.

• Tighten the turnbuckles on the tie rods to set bulkhead plumb.

• Backfill the remaining out to the bulkhead.

• Outside the bulkhead, dredge the bottom to a depth of 30 feet. To enable ships to come alongside, the bulkhead is fitted with a timber cap and batter fender piles (Figure 5-27). Figure 5-27 — Cap and fender pile for bulkhead. Installed at intervals, the piles will provide bulkhead protection from the impact of ships and protect the ships’ hulls from undue abrasion. 3.3.0 Wharfage Structures Wharfage structures are designed to allow ships to lie alongside for loading and discharge. Figure 5-28 shows various plan views of wharfage structures. Any of these may be constructed of fill material supported by bulkheads. However, a pier or marginal wharf is usually a substructure of timber-, steel-, or concrete-pile bents, with a timber, steel, or concrete superstructure.  5-22 Figure 5-28 — Types of wharfage structures. NAVFAC P-437 Volume 1, Facilities Planning Guide contains working drawings for advanced-base piers. Figure 5-29 and Figure 5-30 are portions of the advanced-base drawing for a 40-foot (wide) timber pier. Figure 5-29 — General plan of ABFC 40-foot timber pier (partial). A bay is that part of a pier lying between pile bents, and the length is equal to the oncenter spacing of the bents. This ABFC 40-foot wide pier has one 13-foot inboard bay, one 13-foot outboard bay, and as many 12-foot interior bays as needed to meet the length requirements for the pier.  5-23 The cross section in Figure 5-30 reveals the following about the substructure:

• Each bent consists of six bearing piles.

• Bearing piles are braced transversely by diagonal braces partially above the median high water line (M.H.W).

• Longitudinal bracing between bents consists of 14-foot lengths of 3 by 10 planks bolted to the bearing piles below M.H.W.

• Each bent also has transverse bracing by a pair of batter piles driven in a 5 in 12 angle on either side of the bent (shown in the general plan).

• Butts of the batter piles have longitudinal batter-pile caps bolted to the undersides of two adjacent bearing-pile caps.

• Batter-pile caps are placed 3 feet inboard of the centerlines of the outside bearing piles in the bent.

• Blocks bolted to the bearing-pile caps act as a kicker for the batter-pile caps. Figure 5-30 — Cross section of ABFC 40-foot timber pier (partial). The superstructure consists of 19 inside stringers fastened to the pile caps with driftbolts, 2 outside stringers fastened to the pile caps with bolts, and a single layer of deck planks. The deck planks are fastened to the stringers with spikes. After the deck is laid, lengths of curbing are laid over and bolted to the outside stringers between planned bitts and cleats.  5-24 The pier has a fender system for protection against shock from contact with vessels coming (lying) alongside. Fender piles are driven along both sides of the pier and bolted to the outside stringers with countersunk heads; a wale is bolted to the back of the fender piles. Fender-pile chocks are cut to fit between the piles and bolted to the outside stringers. The general plan also includes two 14-pile dolphins located 15 feet beyond the end of the pier to protect the unfendered end of the pier. A dolphin is an isolated cluster of piles; a similar cluster attached to a pier is called a pile cluster. Figure 5-31 shows three typical dolphin configurations. Figure 5-31 — Typical dolphin configurations.

 

Test Your Knowledge

3. Waterfront structures may be broadly divided into _____ types.

A. two
B. three
C. four
D. five

4.0.0 TIMBER FASTENERS and CONNECTORS

Usually it is unnecessary on working drawings to call out the types of fasteners used for light frame construction, but that is not the case for heavy timber construction. For heavy timber construction, you need to identify the fasteners. An EA preparing timber structure drawings needs a working knowledge of how builders will use timber fasteners and connectors.

4.1.0 Timber Fasteners

Bolts used to fasten heavy timbers usually come in 1/2-, 3/4-, and 1-inch diameters with square heads and nuts. They are installed with round steel washers under both the head and the nut, and then tightened until the washers bite well into the wood to compensate for future shrinkage. Spacing should be a minimum of 9 inches on center and no closer than 2 1/2 inches to the edge or 7 inches to the end of the timber. Driftbolts (driftpins) are used primarily to prevent timbers from moving laterally in relation to each other rather than to resist separation. They are used more in dock and trestle work than in trusses and building frames. A driftbolt is a long threadless rod driven through a hole bored through a member and into the abutting member. The hole is bored slightly smaller than the bolt’s diameter and about 3 inches shorter than its length. Driftbolts are from 1/2 to 1 inch in diameter and 18 to 26 inches long (Figure 5-32). Figure 5-32 — Typical driftbolt (driftpin).  5-26 Customarily, butt joints are connected using driftbolts. However, another butt-joint connection is a scab, a short length of timber spiked or bolted to the adjoining members (Figure 5-33). Figure 5-33 — Typical scab connection.

4.2.0 Timber Connectors

A timber connector is any device used to increase the strength and rigidity of bolted lap joints between heavy timbers. For example, the split ring (Figure 5-34) embeds in a circular groove cut into the faces of the joining timbers with a special bit. Split rings come in diameters of 2 1/2 and 4 inches; the 2 1/2-inch ring requires a 1/2- inch bolt, and the 4-inch ring uses a 3/4- inch bolt. Figure 5-34 — Typical split ring and split ring joints. Shear plates (Figure 5-35) are intended for wood-to-steel connections (View B), but used in pairs they can also be used for wood-to-wood connections (View C).  5-27 Figure 5-35 — Typical shear plate and shear plate joints. When making a wood-to-wood connection, the fabricator cuts a depression into the face of the wood members to the same depth as a shear plate. Then a shear plate is set into each of the depressions with the back faces of the plates flush with the outside face of the wood members. The wood members are then slid into place and bolted. Because the faces are metal and flush with each other, the timber members should slide into position easily, reducing the labor necessary to make the connection. Shear plates are available in 2 5/8- and 4-inch diameters. Toothed rings are sometimes used for special applications (Figure 5-36). Toothed ring connectors function much the same as the split ring connectors, but can be embedded without cutting grooves in the members. Figure 5-36 — Toothed ring, joints, and embedment. The toothed ring is embedded by the pressure provided from tightening a high-tensile strength bolt. Unlike the hole for driftbolts, the hole for this bolt is drilled slightly larger than the bolt diameter so the bolt may be extracted after embedding the toothed ring.  5-28 The spike grid also has a special application, as shown in Figure 5-37. A spike grid may be flat (for joining flat surfaces), single-curved (for joining a flat and a curved surface), or double-curved (for joining two curved surfaces). A spike grid is embedded in the same manner as a toothed ring, by pressure from tightening a high-strength bolt. Figure 5-37 — Spike grid and spike grid joints.

 

Test Your Knowledge

4.  It is unnecessary on working drawings to call out the types of fasteners used for heavy timber construction.

A. True
B. False

5.0.0 STRUCTURAL STEEL

Structural steel is one of the basic materials commonly used in many types of structures, such as industrial and commercial buildings, bridges, and piers. Produced in a wide range of shapes and grades, it permits great flexibility in design and use while being relatively inexpensive to manufacture and the strongest and most versatile material available to the construction industry. This segment will describe shapes, terminology, usage, and methods of connection as applicable to structural steel members.

5.1.0 Structural Steel Shapes

Structural steel is manufactured in a wide variety of cross-sectional shapes and sizes. Figure 5-38 shows several of these various shapes.  5-29 Figure 5-38 — Structural steel shapes and designations. Figure 5-39 shows cross-sectional views of the W-shape (wide flange), S-shape (American Standard I-beam), and C-shape (American Standard channel). The W-shape is the most widely used structural member for beams, columns, and other load-bearing applications. It has parallel inner and outer flange surfaces with constant thickness. This flange design provides greater cross-sectional area in the flanges, resulting in greater strength than the S-shape, which has inner flange surfaces sloping approximately 17 degrees. The C-shape is similar to the S-shape with a sloping inner flange surface of the same degrees. It is especially useful where a single flat surface on one side is required. The C-shape is not very efficient when used alone as a beam or column. However, channels assembled together with other structural shapes and connected by rivets or welds can provide an efficient built-up member.  5-30 The W-, S-, and C-shape structural members are designated by their nominal depth( in inches) along the web and the weight (in pounds) per foot of length. A W14 x 30, for example, indicates a Wshape that is 14 inches deep along its web and weighs 30 pounds per linear foot. Hence, a 20-foot length of this size Wshape would weigh a total of 600 pounds. Figure 5-39 — Structural steel shapes. The bearing pile, HP-shape, is almost identical to the W-shape. The difference is in the thickness of the web and flange; the thicknesses of the bearing pile’s web and flange are equal, while the thicknesses of the W-shape’s web and flange are not equal. Figure 5-40 shows the cross section of an angle, the structural shape resembling the letter L. Angles are available with equal or unequal legs. The legs’ dimensions and thickness are used to identify an angle, measured along the outside of the angle, for example, L6 x 4 x 1/2. The dimension of the wider leg is always given first and the third dimension is the thickness of the legs, which are always equal in thickness. Angles are used primarily to support, brace, or connect other structural members, but they may also be used as single members, or in combinations of two or four to form main members. Figure 5-40 — Structural steel angle shapes. Steel plate is a structural member with a width greater than 8 inches and a thickness of 1/4 inch or more, used primarily as connections between other structural members. However, they may also be used as component parts of built-up structural members, such as the column in Figure 5-41.  5-31 Plates cut to specific sizes may be obtained in widths ranging from 8 inches to 120 inches or more and in various thicknesses. Plates are often used as covers during excavation operations when the site must be temporary bridged for traffic, or secured. Plates are identified by thickness, width, and length, all measured in inches, for example, PL 1/2 x 18 x 30. Figure 5-41 — Flat plate used in a builtup column. Plate may also be referred to by its approximate weight per square foot for a specified thickness. In Figure 5-42, 1 cubic foot of steel weighs 490 pounds. This cubic foot weight divided by 12 (inches) gives you 40.8 pounds, the square foot weight of a steel plate measuring 1 inch thick. By dropping the fractional portion, a 1-inch plate is called a 40-pound plate; with similar reasoning, a 1/2-inch plate is called a 20-pound plate. Figure 5-42 — Steel plate weight and thickness. The structural shape referred to as “bar” has a width of 8 inches or less and a thickness greater than 3/16 inch. The edges of bars usually are rolled square, like universal mill plates. The dimensions are expressed in a similar manner as that for plates, for example Bar Flat 3/16 x 6 x length.  5-32 Bars are available in a variety of crosssectional shapes: round, hexagonal, octagonal, square, and flat (Figure 5-43). Both squares and rounds are commonly used as bracing members of light structures. Their dimensions, in inches, apply to the side of the square or the diameter of the round. Figure 5-43 — Structural steel bar shapes.

5.2.0 Steel Frame Structures

 Building a framework of structural steel involves two principal operations: fabrication and erection.

• Fabrication involves the processing of raw materials or stock dimensional materials to form the members of the structure.

• Erection includes all rigging, hoisting, lifting, squaring, and vertical plumbing of members into their proper places and making the finished connections between members. Wide varieties of structures are erected using structural steel, but they can be listed as buildings, bridges, and towers; most other structures are modifications of these three.

5.2.1 Buildings There are three basic types of steel frame building construction:

• Wall-bearing construction

• Skeleton construction

• Long-span construction

NOTE Wall-bearing construction is applicable to non-steel structures as well; it is one of the oldest and most common methods in use. Although modern developments in reinforced concrete masonry make this method feasible for high-rise structures, wall-bearing construction is normally restricted to relatively low structures, such as residences and light industrial buildings.  5-33 In wall-bearing construction, exterior and interior masonry walls support structural members such as steel beams and joists, which carry the floors and roof (Figure 5- 44). Figure 5-44 — Example of steel frame building wall-bearing construction. A tall building with a steel frame is an example of skeleton construction (Figure 5-45). Figure 5-45 — Example of steel frame building skeleton construction. In steel frame skeleton construction, the structural frame carries all the loads, live and dead; the exterior walls are nonbearing curtain walls. Roof and floor loading transmits to  5-34 the beams and girders that are supported by columns. The horizontal members (beams) connecting the exterior columns are spandrel beams. With additional rows of columns and beams, skeleton construction can support almost unlimited floor and roof area. Skeleton construction’s limitation, however, is the distance between columns. Large structures such as aircraft hangars or large maintenance facilities require greater distances between supports than standard structural steel shapes can safely span. For long-span steel construction, several methods can be used. One method uses built-up girders to span the distances between supports. Figure 5-46 shows two types of built-up girders. In a built-up girder or box girder, steel plates of various shapes are riveted or welded (the more common method) together to meet the necessary design strength. Figure 5-46 — Typical built-up girders. Another method of long-span construction, which is usually more economical, is to use a truss to span large distances (Figure 5-47). Figure 5-47 — Examples of long-span truss application.  5-35 A truss can be designed and fabricated in many configurations with its framework of structural members: top chord, bottom chord, and diagonal web members usually placed in a triangular arrangement. A third long-span construction method is to use bar joists (Figure 5-48). Although not as versatile as trusses, bar joists are much lighter and are fabricated in several different types. Prefabricated bar joists designed to conform to specific load requirements are obtainable from commercial companies. Figure 5-48 — Example of long-span bar joist application. There are other long-span construction methods involving several different types of framing systems, steel arches, cable-hung frames, and other types of systems, but they will not be covered in this course.

5.2.2 Bridges

Figure 5-49 shows the structural framework of a single-span truss bridge. Figure 5-49 — Typical truss bridge and nomenclature.  5-36 As with all bridges, the stringers carry the floor and traffic loads of a truss bridge. In the truss bridge, however, the stringers are supported by transverse beams rather than by bridge abutments (and intermediate supports when needed). The structural framework of the trusses provides support for these transverse beams. The entire bridge structure plus any traffic load is transmitted through the end pedestals and bearing plates (below the diagonal end members called end posts) to the supporting abutments. A truss’s framework and its use may differ depending upon the design of the bridge. Figure 5-50 shows three examples of bridge trusses. View A shows an underslung (or deck) truss span with transverse beams carried by the top chord and a lateral bracing system between the trusses. View B shows a semi-through (or pony) truss span; top lateral bracing is not used due to the small depth of the trusses. View C shows a through truss span; the transverse beams are carried by the bottom chords, and the top chords are braced by a lateral bracing system. Figure 5-50 — Types of bridge spans.

5.2.3 Towers

Towers are framework structures designed to provide vertical support. Figure 5-51 shows a typical trestle tower used in bridge construction. Towers may be used to support another structure, such as a bridge, or used to support a piece of equipment, such as a communication antenna.  5-37 Since the prime purpose of a tower is to provide vertical support for a load applied at the top, the compression members providing this support are the only ones that require highstructural strength. The rest of the tower structure is designed to stiffen the vertical members under compression and prevent bending. To accomplish this, the bracing members are designed to provide the tension support in a series of diagonals. Figure 5-51 — Example of a trestle tower.

5.2.4 Pre-engineered Metal Structures

Military construction commonly uses pre-engineered metal structures. The structures are typically designed and fabricated by civilian industry to conform to specifications set by the military. Some of the more commonly used structures, particularly at overseas advanced bases, are rigid frame buildings, steel towers, communications antennas, and steel tanks. Figure 5-52 — Typical preengineered building and nomenclature.  5-38 The primary advantage of a factory built, preengineered structure is that each structure is shipped as a complete kit, including all materials and instructions needed to erect it, and designed to be erected in the shortest possible time. Probably the preengineered metal structure most familiar to Seabees is the preengineered metal building (PEB). Figure 5-52 shows the nomenclature of the various parts of the PEB; for further information refer to the current Steelworker NRTC.

5.3.0 Structural Steel Connectors

Bolts, welds, pins, and rivets are the four basic methods used to make structural steel connections. Bolts and welds are the most common for military construction, but pins are also used for connections at the ends of bracing rods and various support members that require freedom of rotation. In addition, some prefabricated steel assemblies may be received in the field with riveted connections.

5.3.1 Bolts

Bolts are the most common type of connectors and relative to the other types, the easiest to use with the least equipment. High-strength steels and improved manufacturing processes have produced bolts capable of strong structural steel connections. In steel frame buildings, especially skeleton construction, specifications for bolted structural joints call for high-strength steel bolts in holes, slightly larger than nominal bolt size, torqued to a designated high tension. Joints required to resist shear between connected parts are designated as either friction-type or bearing-type connectors. Parts should fit solidly together WITHOUT gaskets or any other type of compressible material, and bolt holes should be nominal in diameter, not more that 1/16 inch larger than nominal bolt diameter. When bolted parts are assembled, all joint surfaces should be free of scale, burrs, dirt, and other foreign material. Contact surfaces with friction-type joints must also be free of oil, paint, or other coatings.

5.3.2 Welds

Welding is a highly specialized skill, and welding load-bearing parts of a structure should be performed by properly qualified and certified personnel only. Welding inspection and QC is also a specialized skill. As an EA, you will not be expected to perform welding operations or inspections. However, you should have a general knowledge of the basic welding processes, be familiar with different types of welds and their applications, and recognize how welding symbols are used to identify the different welded connections shown in working drawings. The two principal welding processes used in structural work are electric arc welding and oxy-MAPP gas welding (Figure 5-53).

• In the electric arc welding process, welding heat, sufficient to fuse the metal together, is developed by an electric arc formed between a suitable electrode (welding rod) and the base metal (the metal of the parts being welded).  5-39 Figure 5-53 — Examples of electrode welding and oxy-MAPP welding.

• In the oxy-MAPP gas welding process, heat is obtained by burning a mixture of MAPP gas and oxygen as it is discharged from a torch designed for this purpose. Electric arc welding is normally used for metals 1/8 inch or larger in thickness; oxyMAPP gas welding is usually restricted to thinner metals. Figure 5-54 shows the principal types of welds suitable for structural steel work. Figure 5-54 — Types of welds.  5-40 Figure 5-55 shows the types of weld joints suitable for structural steel connections. Figure 5-55 — Types of weld joints. Special symbols are used on drawings to show the kinds of welds to be used. The American Welding Society (AWS) has standardized them, and you should become familiar with basic welding symbols and the standard location of all elements of a welding symbol. Note: There is a distinction between a weld symbol and a welding symbol.

• A weld symbol is the basic symbol used to indicate the type of weld to be made. Basic weld symbols are shown at the top of Figure 5-56. The supplementary symbols are only used in connection with the basic weld symbols when necessary.

• A welding symbol consists of the following eight elements, or as many of these elements as are required: 1. Reference line 2. Arrow 3. Basic weld symbol 4. Dimensions and other data 5. Supplementary symbols 6. Finish symbols 7. Tail 8. Specification, process, or other reference These elements of the welding symbol have specific standard locations with respect to each other, also shown in Figure 5-56. When a finish symbol is used in a welding symbol, it indicates the method of finish, not the degree of finish. For example, a C indicates finish by chipping, an M indicates machining, and a G indicates grinding.  5-41 Figure 5-56 — Standard symbols for welded joints. Figure 5-57 shows the use of a welding symbol. This figure shows a steel-pipe column that is to be welded to a base plate. The welder will interpret the welding symbol as the following:

• The weld is a fillet weld.

• It will extend completely around the pipe-to-column joint.

• It is to be made in-place in the field rather than in a fabrication shop.

Figure 5-57 — Example of a welding symbol’s information. Symbols for Welding and Nondestructive Testing, ANSI/AWS A2.4-86 contains a detailed explanation of welding symbols and their use.  5-42 You can find welding terms and definitions in Standard Welding Terms and Definitions, ANSI/AWS A3.0-89.

5.3.3 Pins

Pins for very large structures are manufactured especially for the type of job. They could have diameters of 24 inches or more and be several feet in length, but for most jobs, pins between 1 1/4 inches and 10 inches in diameter are more common. The most commonly used types are threaded-bridge pins and cotter pins (Figure 5-58). Figure 5-58 — Example of pins for structural steel connections. Threaded recessed nuts hold threaded pins in place after insertion, while cotter pins are held in place by small cotters that pass through holes drilled in the pins. If necessary, washers and separators, made from lengths of steel pipe, can also be added to the pins to space members longitudinally on the pins.

5.3.4 Rivets

Rivets are manufactured of soft steel in various nominal sizes and lengths (Figure 5-59). Figure 5-59 — Examples of structural rivets.  5-43 Since the development of high-strength bolts, rivets are rarely used as connectors in the field, but some members could be fabricated in the shop with rivet connectors and then brought to the field for bolt or weld connecting. All holes for rivets, whether driven in the shop or in the field, are punched or drilled in the fabricating shop. The sizes most often used in structural steel work are 3/4 inch and 7/8 inch in diameter; lengths differ according to the thickness of materials to be connected. Rivets are inserted into the rivet holes while they are red hot; consequently, the holes are drilled or punched 1/16 inch larger than the nominal diameter of the cold rivet. Rivets are manufactured with one head already fixed. The rivet shank is cylindrical and the second head is formed by driving it with a pneumatic hammer. The rivet set, inserted in the end of the hammer, has a cavity of the proper shape to form the second head of the rivet. Most rivets used for structural steel building are complete when the hammer has formed a second full head. However, manufactured rivets may also be obtained in a countersunk shape to fit into holes countersunk in the material. In those instances, the rivet is driven with a flat-ended rivet set to fill the countersunk cavity in the material.

Summary

Heavy construction is a part of Seabee capability and history, from the massive rebuilding operation in Japan following WWII to constructing the Diego Garcia naval complex in the Indian Ocean during the 1970s and 1980s. Engineering Aids were part of all those large efforts to provide lasting infrastructure. Heavy construction is also a large segment of civilian construction industry. Your knowledge and understanding of the basic terms and the purpose of heavy construction elements will serve you well both in your Naval career and your chosen follow-on career.

Review Questions 

1. What does the term “heavy construction” refer to in the Naval Construction Force (NCF)? A. Project in which extra-heavy structural members are used B. Project in which large bulks of materials are used C. Bridge or waterfront construction D. All of the above 2. What term is used to describe a bridge having only one intermediate support? A. Single-span B. Intermediate-span C. Multi-span D. Double-span For questions 3 through 7, select the term being defined from the table below. 1. Substructure 2. Abutment 3. Sill 4. Foundation 5. Corbel 6. Pier 3. That part of an overall bridge structure that transmits the combined live and dead loads over an area of subgrade large enough to prevent settlement and collapse. A. 1 B. 2 C. 3 D. 4 4. The aggregate total of all bridge components located below the stringers. A. 1 B. 2 C. 5 D. 6  5-45 5. A type of structural framework that includes two or more rows of posts or piles. A. 2 B. 3 C. 5 D. 6 6. One of two supports located at the ends of a bridge superstructure. A. 2 B. 3 C. 4 D. 5 7. The part of a timber-sill abutment that carries the loads imposed by the stringers. A. 1 B. 3 C. 4 D. 5 8. Which of the following components is NOT a part of the flooring system of a bridge? A. Curb B. Deck C. Stringers D. Handrails 9. What structural member of a bridge receives the load from the flooring and transmits it to the substructure? A. Abutment sill B. Pile or post cap C. Stringer D. Corbel 10. Which, if any, of the following characteristics is common to both foundations and piles? A. Both are always constructed of reinforced concrete. B. Both distribute the total weight of a building or structure to the natural earth. C. Both are used to resist only a vertically applied load. D. None of the above  5-46 11. What element of a foundation ultimately carries the total dead and live loads imposed by a building or structure? A. Foundation bed B. Foundation wall C. Footing 12. What type of foundation can a structural engineer design to minimize the effects of uneven subsoil conditions? A. Continuous B. Spread C. Grade beam D. Mat 13. What term refers to the larger end of a tapered precast concrete pile? A. Butt B. Tip C. Shank D. Closed end 14. What type of piles should you specify for use in preventing the walls of a trench from caving in? A. Bearing B. Sheet C. Batter D. H 15. To join the edges of concrete sheet piles, in what form or shape are the edges cast? A. Deep B. Arch C. Interlock D. Tongue and groove 16. In which of the following ways are a breakwater and a jetty both (a) similar and (b) different? A. (a) Both are used to direct the current flow in a channel; (b) whereas a breakwater is an alongshore structure. B. (a) Both are alongshore structures used to break the action of waves; (b) whereas a jetty has a paved top for vehicular traffic. C. (a) Both are offshore structures used to break the action of waves; (b) whereas a jetty directs the current flow along the line of a channel. D. (a) Both are harbor-shelter structures; (b) whereas a breakwater extends out from the shoreline.  5-47 17. In which of the following conditions can a concrete cap structure be used on a breakwater or jetty? A. Deep-water site only B. Extra-high tide range only C. Deep-water site or extra-high tide range D. Shallow-water site 18. How are the individual units of a precast cap structure for a breakwater (a) taken to and (b) placed in their proper location? A. (a) Floated; (b) sunk B. (a) Carried; (b) driven C. (a) Craned; (b) dropped D. (a) Barged; (b) unloaded 19. What type of structure should the engineer design to establish a definite shoreline and maintain it against wave erosion? A. Seawall B. Breakwater C. Jetty D. Groin 20. In which of the following ways are a seawall and a bulkhead both (a) similar and (b) different? A. (a) Both protect a shoreline against erosion; (b) a seawall is thin whereas a bulkhead is supported by its own weight. B. (a) Both protect a shoreline against erosion; (b) a seawall is supported by its own weight whereas a bulkhead is relatively thin. C. (a) Both are relatively thin and self-contained; (b) bulkheads are normally cast-in-place concrete structures. D. (a) Both are relatively thick and self-contained; (b) a bulkhead can be constructed using wooden sheet piles. 21. What type of structure should be used to allow ships to lie alongside for loading and unloading? A. Wharfage B. Offshore C. Stable shoreline D. Mole 22. To allow ships to come alongside, bulkheads are fitted with _______. A. wales and anchors B. piles and quays C. timber caps and batter fenders D. mooring cleats and dolphins  5-48 23. In what way does a dolphin differ from a pile cluster? A. Dolphins are used to protect a pier, while pile clusters protect offshore structures. B. Dolphins are used to protect moles, while pile clusters protect groins. C. Dolphins are used to protect ships only, while pile clusters protect piers only. D. Both provide protection for piers and ships; however, a dolphin is an isolated cluster of piles, and a pile cluster is attached to a pier. 24. What type of heavy-timber fastener has square heads and nuts? A. Pin B. Bolt C. Spike D. Rail 25. In timber construction, what is the minimum spacing, in inches, between bolts? A. 1 1/2 B. 3 1/2 C. 7 D. 9 26. A timber fastener that is used primarily to prevent one member from moving laterally in relationship to another is called a _____. A. lag bolt B. driftbolt C. cleat D. dowel 27. A short length of timber that is spiked or bolted to the adjoining members of a joint is a _____. A. cleat B. block C. scab D. connector 28. What is the general term applied to the variety of devices used in bolted-lap joints between heavy timbers? A. Driftpins B. Spike grids C. Expansion bolts D. Timber connectors  5-49 29. What type of connector is embedded in circular grooves in the faces of the timbers being jointed? A. Spike grid B. Toothed ring C. Split ring D. Shear plate 30. Which, if any, of the following is/are embedded by pressure? A. Toothed ring only B. Spike grid only C. Toothed ring and spike grid D. None of the above 31. What standard structural shape is most commonly used for columns? A. C B. HP C. S D. W 32. For what reason does the W-shape provide greater strength than the S-shape? A. Its flanges have a greater cross-sectional area. B. Its web has a greater cross-sectional area. C. The inner faces of its flanges are tapered towards the web. D. The width of the flanges is always much greater than those of the Sshape. 33. What does the structural-steel designation “W14 x 74” signify? A. A W-shape member that is 74 inches long with 14-inch-wide flanges B. A W-shape member that is 74 feet long with a 14-inch-deep web C. A W-shape member with a 14-inch-deep web and a weight of 74 pounds per linear foot D. A W-shape member that weighs 14 pounds per linear foot and is 74 feet long 34. In what way does an HP-shape member differ from a correspondingly sized Wshape structural steel member? A. The width of its flanges is slightly larger. B. It has a greater cross-sectional area overall. C. Its flanges have a greater cross-sectional area only. D. Its web and flanges are always of equal thickness.  5-50 35. What letter of the alphabet does the cross section of S-shape structural steel resemble? A. C B. I C. S D. W 36. How are the American Standard S-shape and C-shape similar? A. Both have sloping inner flange surfaces of the same degree. B. Both have non-tapering flange surfaces. C. Both have flanges of equal width. D. Both have a sloping web. 37. A structural steel shape whose cross section resembles the letter L is a/an _____. A. bar B. angle C. tee D. plate 38. What dimension should you list first when designating a structural steel angle having unequal legs? A. Wider leg B. Narrow leg C. Thickness D. Length 39. What structural shape is typically specified for bracing and connecting other structural members? A. S-shape B. C-shape C. Angle D. Flat or round bar 40. A flat structural steel shape having a cross section that measures 16 inches by 3/4 inches is called _____. A. steel plate B. sheet metal C. bar D. slab plate  5-51 41. A 40-pound steel plate is the same as a _____ plate. A. 1-inch B. 1 ½-inch C. 2-inch D. 2 ½-inch 42. The processing of raw materials to form finished members of steel structures is called _____. A. erection B. manufacturing C. prefabrication D. fabrication 43. What process involves the rigging and hoisting of steel members to their proper places in a steel structure? A. Fabrication B. Erection C. Construction D. Prefabrication 44. What method of steel construction uses masonry walls to support structural floorand roof-framing members? A. Skeleton B. Long span C. Wall bearing D. Tilt-up 45. Horizontal structural members connecting the exterior columns of a skeleton structure are called _____. A. lintels B. girders C. floor beams D. spandrel beams 46. In skeleton construction, by what means can the size of a structure be enlarged to provide additional floor space? A. Add additional columns only B. Add additional beams only C. Add additional columns and beams D. None; you cannot enlarge a structure of skeleton construction.  5-52 47. What methods of steel construction all commonly use built-up girders, trusses, and/or bar joists? A. Skeleton B. Long span C. Wall bearing D. Tilt-up 48. When a vehicle passes over a steel-truss bridge, in what order is the imposed loading from the vehicle transmitted through the bridge members to the supporting abutments? A. Decking, stringers, transverse beams, trusses, end pedestals, bearing plates B. Decking, trusses, stringers, transverse beams, bearing plates, end pedestals C. Trusses, decking, transverse beams, stringers, end pedestals, bearing plates D. Trusses, transverse beams, decking, stringers, end pedestals, bearing plates 49. Which of the following reasons is an advantage of preengineered metal structures? A. They can be quickly erected. B. The individual members or components are factory-built. C. They are chipped as complete kits. D. All of the above 50. In the military, what connectors are most commonly used for steel construction? A. Pins and welds B. Pins and rivets C. Bolts and welds D. Rivets and bolts 51. What type of connector is used at the ends of bracing rods or where freedom of rotation is required? A. Bolt B. Pin C. Weld D. Rivet 52. In steel building construction, what type of connector is used more that any other type? A. Rivet B. Weld C. Pin D. Bolt  5-53 53. When bolts are used, how does the hole size compare to the nominal bolt size? A. Half-size larger B. Same size C. Slightly smaller D. Slightly larger For answering questions 54 through 56, refer to figure below. 54. What type and size of weld is to be made on the “other side”? A. 1/4-inch bevel weld B. 1/4-inch vee weld C. 1/2-inch fillet weld D. 1/2-inch bevel weld 55. What does the numeral 4 mean? A. Length of the weld in inches B. Length of the weld in millimeters C. Center-to-center spacing of the weld in inches D. Center-to-center spacing of the weld in millimeters 56. What does the small flag shown in the symbol indicate? A. The “other side” weld only is to be made in the shop. B. The “arrow side” weld only is to be made in the field. C. Both the “other side” and “arrow side” welds are to be made in the shop. D. Both the “other side” and “arrow side” welds are to be made in the field. 57. What part of a welding symbol can be omitted when a reference is not required? A. Arrow B. Reference line C. Tail D. Detail reference symbol  5-54 58. For structural work, the diameters of rivets most often used are _____. A. 1 and 1 1/4 inches B. 3/4 and 7/8 inch C. 1/2 and 5/8 inch D. 1/4 and 3/8 inch 59. What size hole should be drilled for a 1-inch-diameter rivet? A. 1 inch B. 1 1/16 inches C. 1 3/16 inches D. 1 1/4 inches 60. From what type of material are rivets manufactured for structural steelwork? A. Iron B. Hard steel C. Soft steel D. Aluminum