Mississippi Structural Steel

Key Concepts

Prestressing principles (Ch. 2) - Seven-wire strand conforming to ASTM A-416 is almost exclusively used for unbonded tendons (Ch. 1 Definitions – Strand); its breaking stress is 270,000 psi (1860 MPa). - Stress progression for a 1/2 in. Ø strand: stressed to 216,000 psi (= 33 kips) → after wedge seating-loss, elastic shortening and tendon friction, about 189,000 psi (= 28.9 kips) → after long-term volume changes and steel relaxation occurring from one to five years, about 173,000 psi (= 26.5 kips). - Partially prestressed = tensile stresses are allowed under working load; additional mild steel rebar may be required to control cracking. Sufficient prestressing steel offsets most member self-weight and other sustained dead loads, occasionally a small portion of live load (Ch. 2, §2.4). - Load balancing: tendons placed in a parabolic curve and stretched exert an upward uniform load (w_bal) on the member (Ch. 2, §2.3). - Post-tensioning advantages over pre-tensioning: structural continuity of members, stage prestressing, field prestressing, reduced prestress losses, field connections for precast elements, construction in limited or restricted access areas (Ch. 2, §2.2).

Fabrication (Ch. 3) — Extrusion begins with bare strand run through a P/T coating applicator; the extruder cross head then applies the melted plastic sheathing. Bundles are identified with job name, floor, pour, etc., plus a PTI tag with information on loading, handling and other special care instructions.

Key Concepts

Concrete basics (Chapter 3 — Concrete and Reinforced Concrete, Definitions) - Concrete is one part cement, about 1½ to 2½ parts fine aggregate (usually sand), about 3 to 5 parts coarse aggregate (gravel, crushed stone, or blast-furnace slag), and clean water. - Concrete attains its full rated strength in a specified length of time, usually 28 days. - High-early-strength cement produces about the same strength in about one-half or one-third of the time required with ordinary cement. - Standard test cylinders are 6 inches in diameter and 12 inches high (Chapter 6).

Bond (Chapter 6 — Reinforcing Steel: Purpose and Location in Concrete) - Adhesion of concrete to the bar surface plus resistance from the deformations/ribs keeps bars from slipping. This gripping of the bars by concrete is bond.

Bar sizes, grades, identification (Chapter 7) - Deformed bars are designated by a number denoting the approximate diameter in eighths of an inch — a #8 bar is 8/8 in. = 1 inch; a #5 bar is 5/8 inch. - Plain bars (smooth, no deformations) are used for dowels at expansion joints (sliding in a sleeve), expansion/contraction joints in highway pavements, and column or pier spirals. - The grade designation equals the minimum yield strength in ksi — Grade 60 = 60 ksi (Table 7-2). - Grade lines (Fig. 7-2): Grade 60 = one line, Grade 75 = two lines, Grade…

Key Concepts

Scope of Subpart R. §1926.750(a): the subpart "sets forth requirements to protect employees from the hazards associated with steel erection activities involved in the construction, alteration, and/or repair of single and multi-story buildings, bridges, and other structures where steel erection occurs." It does not cover electrical transmission towers, communication and broadcast towers, or tanks.

Covered activities. §1926.750(b)(1): hoisting, laying out, placing, connecting, welding, burning, guying, bracing, bolting, plumbing and rigging structural steel, steel joists and metal buildings; installing metal decking, curtain walls, window walls, siding systems, miscellaneous metals, ornamental iron and similar materials; and moving point-to-point while performing these activities. §1926.750(b)(2) adds rigging, dismantling, grinding, sealing, caulking and related work when they occur during and as part of steel erection.

Controlling contractor duties. §1926.750(c): duties "include, but are not limited to," those specified in §§1926.752(a) and (c), 1926.755(b)(2), 1926.759(b), and 1926.760(e).

Key definitions (§1926.751). - Anchored bridging — steel joist bridging connected to a bridging terminus point. - Bridging terminus point — a wall, a beam, tandem joists (with all bridging installed and a horizontal truss in the plane of the top chord), or other element at an end or intermediate point of a line of bridging that provides an anchor point. - Bridging clip — a device attached to the steel joist to allow bolting of the bridging to the joist. - Construction load (for joist erection) — **any…

Key Concepts

Signs, tags and barricades (Subpart G). Danger signs are used only where an immediate hazard exists (§1926.200(b)(1), Page 201); red upper panel, black border, white lower panel (§1926.200(b)(2)). Caution signs are used only to warn against potential hazards or to caution against unsafe practices (§1926.200(c)(1)), yellow predominating with black upper panel. Exit signs: legible red letters not less than 6 inches high on a white field, principal stroke at least three-fourths inch wide (§1926.200(d)). Safety instruction signs: white with green upper panel (§1926.200(e)). Accident prevention tags are a temporary warning of an existing hazard and shall not be used in place of, or as a substitute for, accident prevention signs (§1926.200(h)(1)).

Medical services and first aid (§1926.50, Page 33). Employer insures availability of medical personnel; provisions for prompt medical attention must be made prior to commencement of the project. Where no infirmary, clinic, hospital or physician is reasonably accessible, a person with valid first-aid training must be available at the worksite. First aid supplies shall be easily accessible; kit contents go in a weatherproof container with individually sealed packages and shall be checked by the employer before being sent out on each job and at least weekly on each job (§1926.50(d)(2)). Where 911 is not available, telephone numbers of physicians, hospitals or ambulances shall be conspicuously posted (§1926.50(f)(1)).

Key Concepts

Product descriptions (SDI Manual, Section 1 — General, All Deck Products) - Steel deck is made by cold forming structural grade sheet steel into a repeating pattern of parallel ribs. Standard deck width varies with the product, but full sheets are usually 12", 18", 24", 30" or 36". - Deck is attached to the building frame with arc spot ("puddle") welds, self-drilling screws, or powder/pneumatically driven pins. Sheet-to-sheet fastening uses screws, button punching (crimping), clinching, or welds.

Roof deck (Product Descriptions — Roof Deck section) - Roof deck rib openings are usually narrower than floor deck rib openings — this provides adequate support of rigid thermal insulation board. - Roof deck is typically installed to end lap approximately 2" over supports; it can be butted or lapped more than 2" to solve field fit problems.

Cellular and acoustic deck (Product Descriptions) - Cellular deck is made by attaching a bottom steel sheet (or another deck section) to a roof deck or composite floor deck panel; it creates a chase for electrical, telephone, and computer wires. - In open rib acoustic decks, sound absorbing elements are normally field installed by the roofing contractor, shortly before installation of the exposed roof.

Key Concepts

Products and designations (Chapter 1 – Products) - Standard SJI products: K-Series (incl. KCS and joist substitutes), LH-Series, DLH-Series, Joist Girders, and CJ-Series composite joists. Barrel, bowstring, gable, and scissor joists are non-standard and are erected per the AISC Code of Standard Practice Section 7 and OSHA 1926.756. - 18K7: "18" = nominal depth in inches, "K" = series, "7" = chord number designation. 36G9N6K: 36-in depth, "G" = joist girder, "9N" = 9 joist spacings, "6K" = 6 kips unfactored concentrated load per panel point (ASD). 30CJ2188/1168/420: 2188 = total factored composite design load (plf), 1168 = factored composite live load (plf), 420 = factored composite dead load (plf). - Chords and webs of K-, LH-, DLH-Series and joist girders are normally hot-rolled angles or cold-formed sections. CJ-Series shear connection is made by welding studs 3/8 in to 3/4 in diameter through the steel deck.

Erection bridging (Chapter 5; Chapter 8) - Load table shading: RED = a single row nearest mid-span; BLUE = two rows nearest the third points, spans over 60 ft but less than and including 100 ft; GRAY = all rows, spans over 100 ft. - Spans over 60 ft through 100 ft: all rows must be bolted diagonal bridging; at least two rows nearest the third points installed and anchored before releasing hoisting lines; no more than two employees until all other bridging is…