Presentation on theme: "Structural Steel Construction"— Presentation transcript:
1Structural Steel Construction Chapter 4Structural Steel ConstructionStructural Steel Construction • Structural Steel Construction Methods • Structural Steel Members • Fastening Systems • Panel Members
2Structural steel members are erected, braced, and secured together to create a structural framework. Structural steel members are lifted into place with various lifting equipment. See Figure 4-1. Structural steel members are erected, braced, and secured together to create the structural framework. This framework is covered with the materials for floors, walls, and roofing.
3In beam and column construction, beams and girders support floor and roof loads and distribute the loads to the vertical columns.The most common structural steel construction method is beam and column construction. Beam and column construction is a structural steel construction method consisting of bays of framed structural steel that are repeated to create large structures. See Figure 4-2. A bay is the space between the centers of adjacent columns along exterior walls. Steel columns are erected over foundation members consisting of a series of footings, foundations, piers, or pilings. The columns are set onto the foundation members and secured with anchor bolts and plates.
4In long span construction, long distances are spanned with built-up structural steel girders and trusses.Long span construction is a structural steel construction method in which large girders and trusses constructed of large horizontal steel members are fastened together (built up) to span large areas. In long span construction, a series of built-up girders and trusses is used for spanning large areas without the need for excessive intermediate columns or other supports. See Figure 4-3. Long span construction is commonly used for structures such as bridges and large arenas. In bridge construction, large girders and beams span between bridge abutments, piers, and other supports. Concrete or steel decking is supported by large structural steel members. Details and shop drawings indicate the arrangement of the various angles, channels, and other members used to construct girders and trusses.
5In wall bearing construction, horizontal steel beams and joists are supported by other construction materials such as masonry.Wall bearing construction is a structural steel construction method in which horizontal steel beams and joists are supported by other construction materials such as masonry and reinforced concrete. Structural steel members span floors and roofs between masonry or reinforced concrete walls. The masonry or concrete walls support the vertical loads and the structural steel beams and joists support the horizontal loads. See Figure 4-4. Bearing base plates installed on the masonry or reinforced concrete walls provide proper load distribution where the steel members rest on the walls.
6Pre-engineered metal buildings consist of prefabricated structural steel members including beams, columns, girts, and trusses.Pre-engineered metal building construction is a structural steel construction method consisting of prefabricated structural steel members including beams, columns, girts, and trusses. The width of pre-engineered metal buildings ranges from 10¢ to 360¢. Basic types of pre-engineered metal buildings include rigid frame, beam and column, and truss frame. See Figure 4-5. Interior columns are erected as indicated on the erection plans. Lengths of pre-engineered metal buildings are based on the number of bays. Bays vary in length from 18¢ to 30¢. Pre-engineered building manufacturers use specialized systems of fasteners, braces, and rafters based on their particular product design.
7Erection plans provide information regarding structural steel construction. Erection plans include working drawings that provide information about anchor bolt layout, plan views of the structural steel members at each floor level, sections, elevations, and details that include steel member and component information and connections. See Figure 4-6. The number of drawings required and their complexity depend on the size of the structure and the amount of steel to be placed.
8A dimensioned grid of letters and numbers provides reference points on erection plans. Erection plans include the location of each structural steel member, assembly information, dimensions, the number of steel components comprising a member, and any additional information needed for steel erection. Steel members are placed and oriented based on a letter and number grid shown on plan views. See Figure 4-7. The distances between grid lines are shown around the building perimeter on the erection plans. Columns, beams, girders, joists, and braces are identified according to the letter and number grid on the plan views. The letter and number grid system on the plan views is related to all other drawings, including elevations, details, and fabrication drawings. Uppercase letters denote the main structural members, such as “B” for beam or “C” for column. Lowercase letters denote components, such as “b” for bracket.
9Various types and grades of steel are used in structural steel construction. Various types and grades of steel are used in structural steel construction including carbon steel, high-strength steel, high-strength low-alloy steel, corrosion-resistant high-strength low-alloy steel, and quenched and tempered alloy steel. See Figure 4-8. The most common type of steel used for structural steel construction is classified by ASTM International as A36 and has minimum yield stress strength of 36,000 psi (pounds per square inch). The uses and applications of the various types of steel depend on the engineering requirements for a particular structure.
10A variety of steel shapes are commonly used in structural steel construction. Standard abbreviations and designations are included on erection plans to indicate structural steel members.Many steel shapes are required for the construction of a steel structure including wide-flange, S-shape, and HP-shape beams as well as C and Z channels, angles, tees, bearing piles, plates, flat bars, tie rods, and pipe columns. See Figure 4-9. A variety of symbols, letters, and numbers are used to indicate structural steel shapes on prints.
11Shop drawings provide detailed information required for the fabrication of structural steel members. A column is the principle vertical load-bearing member in a steel structure. Columns are supported by and secured to foundations or footings. Columns are typically the first members erected for beam and column construction. Shop drawings indicate the overall column height, spacing of holes for attaching beams and braces, column locations, steel angles to support beams, shear tabs for connections to beams and girders, and base plate information such as plate thickness and size. See Figure 4-10.
12Columns are commonly constructed using M-, S-, or wide-flange shapes. Architects and engineers use standard tables to determine sizes of structural steel members to be used for columns. M-, S-, or wide-flange shapes are commonly used for steel columns. See Figure Structural steel columns may also be round steel pipe or square steel tubing where relatively light loads will be imposed. The size and design of the columns may be provided on a schedule and related details. The load requirements for the column determine column size and design.
13Column locations are shown on erection plans with letter and number designations. Specific information about web depth and weight (in lb/ft) is provided for each column.The design, size, and weight of each column may also be noted at the intersection of the grid lines. For example, a notation of W12 × 53 indicates a column made of a wide-flange beam measuring 12″ outside the flanges and weighing 53 lb/ft. See Figure A column schedule may also be provided with design, web, and weight information about each column.
14Wide-flange beams are identified on erection plans with the letters “W” or “WF”. A “WF” or “W” is used to indicate wide-flange beams on prints along with the nominal depth and weight per linear foot. See Figure The actual depth of a wide-flange beam is greater than the nominal depth. The actual size depends on the flange and web thicknesses as well as the beam manufacturer specifications. American Standard beams, commonly referred to as I beams, are designated on prints with the letters “S” or “I”. The nominal and actual sizes of American Standard beams are equal. Various lightweight beams are shown on erection plans with the letter “B” or “JB” for junior beams.
15Structural steel beams are fabricated based on shop drawings. A shop drawing for beam fabrication shows the beam type, weight, length, cutouts to allow for intersection with other structural steel members, dimensions for all beam holes, and any required connecting angles. See Figure 4-14.
16Open web steel joists span between beams and girders Open web steel joists span between beams and girders. The standard designation for open web steel joists includes the nominal depth (in inches), span classification (K, LH, or DLH), and chord diameter.Structural steel joists may be formed of a single structural member or built up from smaller steel members. An open web steel joist is a structural steel member constructed with steel angles and bars that are used as chords with steel angles or bars extending between the chords at an angle. See Figure The standard designation for open web steel joists includes the nominal depth (in in.), span classification (K, LH, or DLH), and chord diameter. For example, an open web steel joist with a designation of 26K7 has a nominal depth of 26², is a standard K-series joist, and has a chord of #7 steel bar (7/8² diameter).
17Erection plans indicate structural steel joist spacing and installation information. Open web steel joists are secured to beams or other supporting members using bolts or by welding.The spacing of structural steel joists and their placement direction is noted on erection plans. See Figure The type of joist to be installed may also be noted by a manufacturer identification code, standard classification format, or fabrication shop code number. An elevation to the top of the joists may be indicated on the plan views or elevations. Openings for stairwells or other access between levels of a structure are shown on a plan view using dashed lines in an “X” pattern. Solid lines in an “X” pattern between joists indicate cross braces.
18A wide variety of structural steel shapes are joined together to form a truss. Common steel truss designs include the bowstring, flat, Howe, Pratt, scissors, and Warren.Steel trusses may be used to span long distances while providing maximum strength with minimal weight. Engineers determine all loads and stresses that the truss must be able to withstand. Various sizes and shapes of steel members, including tees, angles, plates, and bars, are fastened together to provide structural, compressive, and tensile support. Each size and shape is indicated on the truss fabrication drawings. See Figure 4-17.
19Bridging and braces maintain alignment between structural steel columns, beams, and joists and increase resistance to loads.A variety of structural steel shapes may be used for final bracing of a steel structure. Steel angles are commonly used for bracing. Angles, indicated by the Ð symbol, are specified by the width of the longer leg, width of the shorter leg, steel thickness, and length of the steel angle. For example, a notation of Ð5 × 4 × 1/2 × 6¢-5² denotes an angle that has one leg that is 5² wide, one leg that is 4² wide, and is 1/2² thick and 6¢-5² long. Steel angles are commonly used as bridging between open web steel joists and between beams and purlins. See Figure 4-18.
20Tie rods are used to brace across long distances. Tie rods are used to brace structural steel structures. A tie rod is a cylindrical steel member with threads on each end. The ends of tie rods are inserted through holes in opposing members. A beveled washer and nut are attached to each end of the tie rod to secure the structural steel members in position. See Figure Tie rods are indicated on erection plans with the letters “TR”. The rod diameter is specified in inches and fractions of an inch.
21Proper bolt and nut installation is essential for proper structural fastener performance. Erection plan details are the primary reference for bolted connections.Structural steel drawings may contain tables concerning the amount of torque to be applied to bolts and the nut rotation for connections. Variable-torque impact wrenches are used to ensure all connections meet torque specifications. Details for bolted connections are a source of information on bolts, washers, and nuts. See Figure 4-20.
22Ribbed bolts may be used where steel members are drawn tightly together before fastening. High-strength hex head bolts are identified with markings on the bolt head.Structural ribbed bolts are used to make high-strength steel connections. See Figure Ribbed bolts are driven into holes in adjoining members and tightened to the proper amount of torque. Low-carbon steel bolts, designated as A307, can be used for light framework and low-stress applications for column splices and beam and girder connections. High-strength hex head bolts are divided into two basic categories—A325 and A490—by ASTM International. A325 bolts are made by heat-treating medium-carbon steel bolts. A490 bolts are made from alloy steel. A325 bolts have a lower shear capacity than A490 bolts. High-strength hex head bolts contain an A325 or A490 marking on their heads. Additional markings include a manufacturer identification symbol.
23Details provide information regarding welded connections. Many structural steel construction operations, including the installation of braces, decking, and final connection of structural members, require the use of welding and cutting equipment. Many connections between steel members are permanently joined using shielded metal arc welding (SMAW). Erection plans provide information concerning the type of weld joint, location of weld, welding process, size of weld bead, and surface finish of the weld. See Figure 4-22.
24The standard format used for weld symbols provides information regarding location, length, and type of welded joint.Erection plans include standard weld symbols specifying the required welds. See Figure The basic components of a weld symbol include the reference line, the arrow indicating the location of the weld, dimensions for the length of the weld and the depth of penetration, and symbols that describe the type of weld joint. Details included on the erection plans contain weld symbols for each weld joint.
25Steel members may be cut to length using an oxyacetylene cutting torch. While not specified on erection plans, cutting operations may be required to fabricate steel members on the job site. Structural steel members are cut at the job site using oxyacetylene or plasma arc cutting equipment. Oxyacetylene cutting is an oxygen cutting process in which heat is generated by an oxygen and acetylene flame to sever and remove the metal. See Figure Plasma arc cutting is an arc cutting process that uses a constricted arc to heat the metal and removes the molten metal with a high-velocity jet of ionized gas. Plasma arc cutting produces a cleanly cut edge on many types of metals.
26Metal floor decking, manufactured in a variety of designs and dimensions, is attached to the top of open web steel joists to create a floor platform.Metal floor decking provides a work platform during construction and a base for finish flooring materials. Metal floor decking is commonly covered with concrete to form a floor slab but may also be covered with noncementitious material. Corrugated metal decking is secured to the tops of the joists using self-tapping screws or by welding. Various types of metal floor decking are available. See Figure 4-25.
27Erection plans provide information regarding metal decking installation. A plan view on the erection plans indicates the decking panel layout and opening locations. See Figure Details indicate methods for framing openings, bracing around columns, and edge treatments of the decking.
28Metal decking may be used as bridge deck forms Metal decking may be used as bridge deck forms. The decking remains in place after the shores and falsework are removed.The most common bridge decking material is reinforced cast-in-place concrete. Formwork is suspended from the girders and beams and may be supported from below by shoring or falsework. Concrete is placed on top of the formwork. When the concrete has reached a specified strength, the shores and formwork are removed and structural steel or concrete structural members support the completed deck. For some applications, metal decking may be used as bridge deck forms. See Figure The metal decking remains in place after the shores and falsework are removed.
29The exteriors of many light-gauge metal buildings are covered with prefinished metal panels. Erection plans and elevations provide information about fastening metal panels to the steel framework. Information may include the type of panel, direction of application, finish trim members at corners and other intersections, and manufacturer name, product numbers, and panel color. Letters representing the panel types are shown on the elevations and keyed to a schedule. See Figure Wall panels are attached to purlins or girts with self-tapping and self-sealing screws. Metal panels may also be used for soffit and canopy coverings.
30Metal roof decking is available in a variety of designs and dimensions. Metal roof decking panels provide a high strength-to-weight ratio that reduces the amount of dead load on a structure. Roof decking panels vary in the width and height of the corrugated ribs and the metal finish. See Figure Some types of metal roof decking are designed to create a finished surface with watertight joints between decking panels. Other types of metal roof decking are designed to be covered with additional insulation and roofing materials such as elastomeric or green roofing systems.
31Roof decks may be formed of metal decking only or covered with waterproofing materials and insulation.A plan view of a steel roof panel layout is included in the erection plans. See Figure Letters representing the panel types are shown on the elevations and keyed to a schedule. The schedule includes information about the types and sizes of the panels so that the panels can be placed properly and efficiently. Roof panels are attached to purlins or ceiling joists with self-sealing screws or weld clips. Elevations and details provide additional information about insulation or roofing materials for waterproofing.