Chapter Eighteen. Structural Drawing

Structural drawings include foundation plans, wall section and framing details, structural steel framing and details, beam and column drawings and details, and others.

Structural drawings are created using either 2D or 3D CAD software. 3D CAD offers better visualization, as well as analytical and simulation capabilities, but owing to the complexity of large structures, 3D CAD requires a considerable modeling effort. Wireframe 3D models can sometimes reduce the amount of modeling effort and still provide sufficient information. Structural analysis of piping is an example where 3D wireframe models are used. 2D CAD provides the ability to make accurate orthographic drawings and easily reuse standard details.

The materials most commonly used in construction are wood, glass, structural steel, aluminum, concrete (plain, reinforced, and prestressed), structural clay products, and stone masonry (plain and reinforced). Each of these materials presents its own benefits and challenges as a construction material. Each material also has standard members that are manufactured in stock sizes and shapes. CAD software often provides libraries for these stock parts and features.

S2S: Surface two sides.

S2E: Surface two edges.

S4S: All four faces are to have finished surfaces.

The working drawings must show whether standard dressed, standard rough, or special sizes are to be used.

Wood is commonly used for sills, columns, studs, joists, rafters, purlins, trusses, and sheathing in homes and other buildings. Methods of fastening timber members include nails, screws, lag screws, drift bolts, bolts, steel plates, and various special timber connectors.

Ordinarily, a structural timber is cut so that the wood fibers, or grain, runs parallel to the length. The strength resistance of wood is not the same in a direction perpendicular to the grain as it is parallel to the grain. Therefore, in designing connections, the direction of the force to be transmitted must be taken into account. Also, proper spacing, edge distance, and end distance must be maintained for screws, bolts, and other connectors.

The open joint of the ring should be in a direction at right angles to that of the stress, so that as the stress is applied the ring is deformed slightly and transmits the pressure to the wood within the ring as well as to that outside the ring. With this connection, the tensile and shearing strengths of wood are developed to a higher degree than by other methods of connection, and it is possible to use timber in tension much more economically.

It is standard practice to show ring connectors by solid lines, as shown in Figure 18.7.

Another resource you can find on the Web is the Truss Plate Institute, which provides design and verification services as well as a variety of publications for connecting wood structural members. You can find their resources at www.tpinst.org.

Design drawings show the overall dimensions of the structure, such as the location of columns, beams, angles, and other structural shapes, and list the sizes of these members. Detail in the form of typical cross sections, special connections required, and various notes are also included.

For example, a building floor plan shows the steel columns in cross section and the beam or girder framing using single heavy lines, as shown in Figure 18.10. Members framing from column to column, providing end support for other beams, are called girders; smaller beams framing between girders are called filler beams. The designer’s plans are sent to the steel fabricator who will furnish the steel for the job. From these plans the fabricator makes the necessary detailed shop drawings and erection plans. Before shop work begins, the fabricator’s drawings are sent to the design engineer for final checking and approval. The design engineer is the authority who makes any changes necessary to ensure the required strength and safety of connections. Once the fabricator receives shop drawings approved by the engineer, the shop work can begin.

Shop drawings consist of detail drawings of all parts of the entire structure, showing exactly how the parts are to be made. These drawings show all dimensions necessary for fabrication, usually calculated to the nearest 1/16″. They also show the location of all holes needed for connections, the details of connection parts, and the required sizes of all material. Notes specify fabrication or construction methods on the detail drawings whenever such items are not covered by separate written specifications. Fabrication, shop methods, and field construction methods must be fully understood by the detailer.

The design of details and connections is an important part of the engineering of the structure. The connections of the various members must be sufficient to transmit the forces in these members. Connection details should be drawn to a scale large enough to show them without crowding. Overall lengths of members are not always drawn to scale in order to show connections clearly. Break lines can be very useful. Show all necessary dimensions. Measurements should never be made from detail drawings by the shop or in the field by the workers making the piece.

An erection plan for the roof steel framing on a building addition is shown in Figure 18.12. This structure is for a paper roofing products pulp mill. New steel is shown by full lines. Existing roof members are shown by dashed lines. Connections to existing steel members are shown in sectional views. The timber framing for the support of large roof ventilators is also shown.

Most CAD programs have structural shape symbol libraries available. Templates are also available to save time in drawing structural symbols by hand.

Fifteen types or grades of structural steel are available. These differ in chemical composition and physical properties. An ASTM (American Society for Testing Materials) specification defines each type. There are considerable variations in the strengths and costs of the various grades. Economical selection of steel grade depends on physical properties of steels, such as strength, ductility, corrosion resistance, and cost. Specify the type by giving the ASTM designation on the drawing. The most commonly used grade is ASTM A36; the number 36 specifies that the guaranteed minimum yield strength is 36 ksi (36,000 lb/in.²). Many lightweight cold-formed C and Z section shapes are also available.

Field rivets are heated in a forge at the construction site. The heated rivet is held firmly in the hole with a dolly bar while the pneumatic hammer or rivet gun forms a round, smooth head.

A shop drawing for a riveted roof truss is shown in Figure 18.14. Only the left half is drawn, because the truss is symmetrical about the centerline. Note the use of the gage lines (lines passing through rivets or holes like centerlines) of the members. Locate gage lines close to the centroid of the axes of the members, and at the joints where members intersect. These gage lines should intersect at a single point to avoid unnecessary moment stresses due to off-center locations (eccentricities). The open holes indicate where the field splices are to be—usually at the centerline of the truss () for the top chord and at from the centerline for the bottom chord.

Figure 18.15 shows standard two-angle framed beam connections in a typical detail drawing of a floor beam. This drawing illustrates several important features. Shop rivets are shown as open circles on shop drawings. Holes for field rivets or bolts are blacked in solid. Gage lines are always shown. Line up holes or rivets on these lines when possible rather than “breaking the gage.”

It is necessary to locate the gage line of an angle for each leg, unless it has already been shown for the identical angle elsewhere on the drawing. The edge distance, from end rivet or hole to the end of the angle, must be given at one end; the billed length of the piece is worked out to provide the necessary edge distance at the other end. It is not necessary that the beam extend the full length of the back-to-back distance of end angles. It is shown “set back” at both ends; the length of beam called for is 1″ less than the distance.

Below the drawing, the mark B25 is the piece or shipping mark that appears on the erection plan and is to be painted on the member in the shop for identification. The end connection angles are fully detailed at the left end of the beam and are given the assembly mark aa. At the right end where these same angles are again used, only the assembly mark 2–aa, to indicate two angles, is needed. The value is called an extension figure. This is the distance from the back of the left-end angles to the center of the group of four holes. Note that this dimension is on the same horizontal line as the figure just to the left. It is customary, in giving feet and inches, to give the foot mark (′) after dimensions in feet, but not to give the (″) inch mark, designating inches.

A beam with end connection angles shop welded to the beam web is shown in Figure 18.16. The remaining legs of the angles are to be welded to the connecting columns in the field, as shown in the end view. This view pertains only to field erection. Open holes in the far legs facilitate positioning for the bolts.

A shop drawing of a diagonal bracing between two columns is shown in Figure 18.17. Here the diagonal members are shop welded to gusset plates that are to be bolted to the column flanges as a permanent installation in the field.

Figure 18.18 is the complete shop drawing for a symmetrical welded roof truss. Because it is symmetrical, only the left half of the structure needs to be shown. Symmetry is shown on the drawing by the note Sym. abt. . In this drawing,

• The clip angles marked aa are to be used for the attachment of roof purlins to the truss.

• The only plate material is the small gusset plate marked pb.

• Most of the connections of web members to chords are made by fillet welding the angles to the webs of the chords.

• The chords are of structural tee (WT) type.

• The top chords are joined at the ridge by butt welding, which is also used at the end of the truss where the chords join.

• Weld symbols and member marks are used.

• Sizes and quantities are listed in the bill of material (BOM).

• The drawing is uncluttered and clear, with lots of important information conveyed under the heading “General Notes.”

Figure 18.19 shows a high strength steel bolt used to transmit a force from the center plate into the two outside plates. When the bolt is fully tightened, the connecting parts are held together by friction, preventing joint slip. This minimizes fatigue failures due to impact or stress reversals. The slip resistance depends not only on the amount of clamping force but also on the nature of the contact surfaces.

Figure 18.19 shows hardened washers under both head and nut. Whether one or two washers are needed, or none, depends on the method of tightening, the yield stress of the material being joined, and whether the joint is to be the “slip-critical” or “bearing” type.

A bearing-type connection relies on the strength of the bolt shank bearing against the material, and no allowance is made for friction due to clamping action. Specifications for accepted practice, along with installation and inspection procedures, design examples, and reference tables, are covered in High Strength Bolting for Structural Joints (published by Bethlehem Steel Corporation, Bethlehem, PA).

Figure 18.20 shows the complete shop drawing of a steel column of two-floor height. The floors are indicated by reference lines B, 1, and 2 of the drawing. High-strength bolts are used to attach connection material to the W12 × 96 column shaft. The top views at levels 1 and 2 show the outstanding legs of the angles in section plan views. Open holes are shown by the round dots located by dimensions taken from the column centerlines. The open holes are for the insertion of field bolts in beam connections when the entire assembly is erected.

Faces A, B, C, and D are designated. Viewing a column from above, designate the faces in counterclockwise order, with faces A and C designating the flanges. For web faces B and D, usually only face B needs to be drawn. However, when the connections on face D are exceptionally complicated, it should be drawn as an additional elevation view.

Note how the drawing shows shop bolts and their designation “HSB” (high-strength bolts).

At the top of this column, splice connection material is provided by Bars (b), for attachment of the shaft above. All material for this column is listed in the bill of material on the drawing.

Consider the effect of tolerance stacking on the fit of steel members. Review the dimensioning and tolerancing practices in Chapters 11 and 12. Using baseline dimensioning can aid in defining the shape so that tolerances don’t accumulate.

Using CAD, you can accurately list dimensions for the lengths of angled members that would have required trigonometric calculation prior to the advent of CAD.

Do not let the ability of CAD to list accurate dimensions cause you to overlook the fact that real-world fabrication will necessarily have some variation from the exact dimension value.

The compressive strength of concrete depends on the mix design, but concrete has been manufactured to develop an ultimate strength at 28 days as high as 7,000 psi. The material’s tensile strength is limited to about one tenth its compressive strength. High-strength concrete, used in high-rise construction, has a compressive strength up to 17,000 psi.

Portland cement is a controlled, manufactured product, in contrast to natural cements. Its name is derived from its color, which resembles the color of a famous stone found on the island of Portland in southern England.

Because the tensile strength of plain concrete is very limited, its use as a building material can be improved by embedding steel reinforcing bars so that the steel resists the tension, and the concrete mainly resists the compression. The two materials act together in resisting forces and flexure. Concrete combined with steel in this way is called reinforced concrete.

When the steel is pretensioned before the superimposed load is applied, producing an interior force within the member, the material is called prestressed concrete. The type of steel used in prestressed concrete is flexible but very strong.

The manual recommends the preparation of two sets of drawings: an engineering drawing and a placing drawing. The engineering drawing is prepared by the manufacturer that fabricates the reinforcing steel. It shows the general arrangement of the structure, the sizes and reinforcements of the several members, and such other information as may be necessary for the correct interpretation of the designer’s ideas. The drawing is also used for making forms with precise dimensions before placing the reinforcing bars and casting concrete.

The placing drawing shows the sizes and shapes of the several rods, stirrups, hoops, ties, and so on, and arranges them in tabular forms for reference by the building contractor.

An engineering drawing for a two-way slab and beam floor of a multistory building is shown in Figure 18.21. For examples of placing drawings, consult the American Concrete Institute manual referred to earlier.

Figure 18.22 shows detail views for the reinforced concrete intake for a hydroelectric site. Note that the steel bars, even though embedded in the concrete, are shown by solid lines and that the concrete is stippled in cross section. Unlike shop drawings for structural steel, concrete drawings are ordinarily made to the same scale in both directions. Often a scale of 1/4″ to the foot is adequate, although when the structure is complicated, scales of 3/8″ or 1/2″ to the foot or larger may be used. Note the scale clearly below each detail view. Avoid a cluttered appearance (usually the result of crowding the drawing with notes) by using tables and schedules for listing bar sizes and other necessary data. Cover important points in a single detail drawing or a set of notes.

As with concrete, it is possible to reinforce brick and tile masonry by embedding steel rods, thus adding greatly to tension resistance and strength. This material is called reinforced brick (or tile) masonry (RBM).

Information on the manufacture, weight and strength properties, and various uses and applications of structural clay products can be found in the Brick Institute of America handbooks Principles of Brick Engineering and Principles of Tile Engineering.

Bricks are made in various sizes, with the ″ building brick being most common. Thickness of mortar joints usually varies from 1/4″ to 3/4″, with 3/8″ and 1/2″ most common. Of the several methods of bonding brick (Figure 18.23), the following are the most common:

In running bond, all face brick are stretchers and are generally bonded to the backing by metal ties.

In American bond, the face brick are laid alternately, five courses of stretchers and one course of headers.

In Flemish bond, the face brick are laid with alternating stretchers and headers in every course.

In English bond, the face brick are laid alternately, one course of stretchers and one course of headers.

These standard methods of bonding are frequently modified to produce various artistic effects. Typical brick lintel arches are shown in Figure 18.24.

In addition to its use as a basic building material, tile is used in fireproofing structural steel members. Most building codes require that the steel members be enclosed in concrete or masonry so that fire will not cause collapse of the structure. Hollow tile units, which are light and relatively inexpensive, are well adapted to this use.

Ashlar masonry (also spelled ashler) is formed of stones cut accurately to rectangular faces and laid in regular courses or at random with thin mortar joints.

Rubble masonry is formed of stones of irregular shapes laid in courses or at random with mortar joints of varying thickness.

Manufactured stone is concrete made of fine aggregate for the facing and coarse aggregate for the backing. The fine aggregate consists of screenings of limestone, marble, sandstone, or granite, to present an appearance similar to natural stone. Manufactured stone is made of any desired shape, with or without architectural ornament.

Architectural terra cotta is a hard-burned clay product and is used primarily for architectural decoration and for wall facing and wall coping.

Brick, stone, tile, and terra cotta are combined in many different ways in masonry construction. A few examples are shown in Figure 18.25.

Architectural Terra Cotta

Ashlar Masonry

Beam Web

Bill of Material

Chords

Clip Angles

Design Drawings

Elevation

English Bond

Erection Plans

Extension Figure

Filler Beams

Fillet Weld

Flange

Flemish Bond

Gage Line

Girders

Green Lumber

High-Strength Concrete

High-Strength Steel Bolts

Joints

Manufactured Stone

Member Marks

Members

Piece Mark

Plate Material

Prestressed Concrete

Purlins

RBM

Reinforced Concrete

Rubble Masonry

Running Bond

Shop Drawings

Structural Drawings

Structural Steel

Trusses

Weld Symbols

• Cost and safety are important considerations when designing a structure that people will use, such as a building or bridge.

• Structural drawings are precise, detailed instructions for general contractors, who must create the structure according to the information in the drawings.

• Steel is commonly used in commercial construction because of its strength and durability. Steel shape and size designations are different from those for other materials, such as wood.

• Structural drawings show both plan and elevation views.

• Details about how structural members are connected and fastened to each other are critical parts of a structural drawing.

• Structural drawings use more notes about size, shape, location, and fastening details than other types of drawings.

• Safety is dependent on correctly following the engineer’s design. Careful proofing and checking of every note and detail is an essential part of the engineering process.

• The list of materials, including their size, shape, and detail information, is often included in a material schedule that appears in table form in a corner of the drawing.

• When components are welded together, standard welding symbols and notes must be used.

2. Draw four different structural steel shapes and label each shape.

3. How is reinforced concrete different from regular concrete?

4. What is shown in the plan view of a structural drawing?

5. What is shown in the elevation view of a structural drawing?

6. Would the spacing for steel roof trusses be shown in a plan view or an elevation view?

7. Would the individual members of a roof truss be shown in a plan view or an elevation view?

8. What are the most common fastening techniques for joining structural steel?

Exercise 18.1 Calculate point-to-point lengths (the distances between centers of joints) of the web members of the roof truss based on a design by Timber Engineering Company. Make a detailed drawing of web member piece No. 4.

Exercise 18.2 Make a complete detail of the top chord member of the truss shown for a 30° angle of inclination.

Exercise 18.3 Assuming riveted construction, with rivets of 3/4″ or 20 mm diameter, make a complete shop drawing for a typical filler beam of the steel floor design plan shown. Detail the same beam for welded construction. Consult the AISC Manual of Steel Construction.

Exercise 18.4 Assuming the column size to be W8 × 31, detail the W16 × 36 girder at the center of the drawing.

Exercise 18.5 Make a complete detail for a truss of the same length, but change the height from 10′-0 to 6′-8. Use angle members of the same cross section sizes as those shown, but of different lengths, as needed.

Exercise 18.6 Make a similar bracing detail as for the detail drawing of the column bracing shown, also changing the distance between column centers from 20′-0 to 18′-6.

Exercise 18.7 Draw cross sections through panel D in both directions for the engineering drawing for a two-way slab and beam floor shown. Include the supporting beams in each cross section, and show all dimensions, size and spacing of reinforcing steel, and dimensions to locate the ends of bars and the points of bend for the bent bars. Also show and locate the stirrups in these views.

Exercise 18.8 Detail the brickwork surrounding a window frame for an opening 4′-7/8″ wide by 6′-9″ high. Use the type of curved arch lintel as shown. Assume standard-size building brick with mortar joints.

Exercise 18.9 Consult Principles of Tile Engineering and draw a cross-sectional view through a 12″ wall of composite brick and tile construction.

Exercise 18.10 Referring to the figure, redraw a complete detail of this proposed deck, changing the total width of the deck from 12′ to 14′ and the length from 52′ to 54′.

Exercise 18.11 Referring to part b of the figure, adjust the dimensions on the posts from 4″ × 4″ to 6″ × 6″. Redraw a complete detail of the railing view and Section A–A.

Exercise 18.12 Referring to part a of the figure, adjust the post dimensions from 4″ × 4″ to 6″ × 6″. Redraw a complete detail of part a.

Exercise 18.13 Referring to part c of the figure, insert the adjustments made to the post detail in Exercise 18.12 and redraw the complete foundation plan.