where R
required strength Rn
nominal strength specified in the AISI Specification 
safety factor specified in the AISI Specification Rn /
allowable design strength Unlike the allowable stress design method, the LRFD method uses multiple load factors and resistance factors to provide a refinement in the design that can account for different degrees of the uncertainties and variabilities of analysis, design, loading, material properties, and fabrication. In this method, the required strengths are not to exceed the design strengths as follows: R  R u n where Ru

iQi
requires strength Rn
nominal strength specified in the AISI Specification 
resistance factor specified in the AISI Specification i
load factors Qi
load effects Rn
design strength The load factors and load combinations are also provided in Chapter A of the AISI Specification for the design of different types of cold-formed steel structural members and connections. For design examples, see AISI Cold-Formed Steel Design Manual, 1996 edition. The Committee on Specifications of the American Iron and Steel Institute has strived to put all formulas in the Specification for the Design of Cold-Formed Steel Structural Members on nondimensional bases so that their use with English or SI units is rigorous and convertible. (AISI Cold-Formed Steel Design Manual, American Iron and Steel Institute, 1101 17th St., NW, Washington, DC 20036.) In buckling of flat, thin compression elements in beams and columns, the flat-width ratio w/ t is an important factor. It is the ratio of width w of a single flat element, exclusive of any edge fillets, to the thickness t of the element (Fig. 8.4). Local buckling of elements with large w/ t may be resisted with stiffeners or bracing. FIGURE 8.4 Compression elements. Flat compression elements of coldformed structural members are accordingly classified as stiffened or unstiffened. Stiffened compression elements have both edges of the element parallel to the direction of stress stiffened by a web, flange, or stiffening lip. If the sections in Fig. 8.1a to n are used as compression members, the webs are considered as stiffened compression elements. The wide, lipless flange elements and the lips that stiffen the outer edges, however, are unstiffened elements. Any section can be broken down into a combination of stiffened and unstiffened elements. Only part of an element may be considered effective under compression in computation of net section properties. The portion that may be treated as effective depends on w/ t for the element. The cold-formed structural cross sections shown in Fig. 8.5 indicate that the effective portions b of the width of a stiffened compression element are considered to be divided into two parts, located next to the two edge stiffeners of that element. (A stiffener may be a web, another stiffened element, or a lip in beams. Lips in these examples are presumed to be fully effective.) In computation of net section properties, only the effective portions of stiffened compression elements are used and the ineffective portions are disregarded. For beams, because flange elements subjected to uniform compression may not be fully effective, reduced section properties, such as moments of inertia and section moduli, must be used. For computation of the effective widths of webs, see Art. 8.7. Effective areas of column cross sections are based on full cross-sectional areas less all ineffective portions for use in the formula for axially loaded columns, Eq. (8.22), in Art. 8.13. The critical load, Pcr , kips, for elastic flexural buckling of a bar of uniform cross section, concentrically end loaded as a column, is given by the Euler formula: P
2EI /L2 (8.1) cr FIGURE 8.5 Effective width of stiffened compression elements with stiffening lips assumed to be fully effective. where E
modulus of elasticity, 29,500 ksi for steel I
moment of inertia of bar cross section, in4 L
column length of bar, in Bryan, in 1891, determined the critical buckling stress, cr , ksi, for a thin rectangular plate compressed between two opposite edges with the other two edges supported, to be given by
k2E(t /w)2 /12(1   2) (8.2) cr where k
a coefficient depending on edge-support restraint w
width of late, in t
thickness of plate, in

Fire Resistance and Sound Rating Brick Technical Manual 54 110mm - Dry Press Single skin bricks. 12mm cement render both sides. Wall thickness: 134mm. 110mm - Dry Press Single skin bricks. 13mm plasterboard direct fixed one side. 13mm plasterboard screw fixed to resilient mounted furring channels with 9kg/m3 polyester insulation on other side. Wall thickness: 177mm. Rw 52 (-1;-5) ATF Report 1125 Rw 56 (-3;-9) ATF Report 1391 150mm - TW Single skin bricks. Wall thickness: 150mm. 150mm - TW Single skin bricks. 13mm plasterboard direct fixed one side. 13mm plasterboard screw fixed to resilient mounted furring channels with 9kg/m3 polyester insulation on other side. Wall thickness: 217mm. Rw 56 (-2;-9) ATF Report 1117 Rw 50 (-1;-5) ATF Report 1594 110mm - Boxer LW Single skin bricks. 10mm plasterboard direct fixed one side. 10mm plasterboard screw fixed to 64mm steel stud built 20mm from wall with 64mm track top and bottom with 9kg/m3 polyester insulation other side Discontinuous construction. Wall thickness: 214mm. Rw 56 (-2;-8) ATF Report 1899

Erectors receive the material and the position and connect the steel into its final location at the project site. Erectors may have specific equipment on unique projects with which they are able to perform cost-effective operations. Such equipment may require attachment points or stiffening of the frame elements, in which case approval of the designer is requested. Structural steel consists of hot-rolled steel shapes, steel plates of thickness of 1/8 in or greater, and such fittings as bolts, welds, bracing rods, and turnbuckles. The owner and the engineer should understand fully what will be furnished by the fabricator under a contract to furnish structural steel. To promote uniformity in bidding practices, the American Institute of Steel Construction (AISC) has adopted a Code of Standard Practice for Buildings and Bridges (American Institute of Steel Construction, One East Wacker Drive, Suite 3100, Chicago, IL 60601-2001). Additional design guides are shown in Table 7.1. Codes, specifications, and standards provide steel designers with sound design procedures and guidelines. These documents cover selection of service and design loads, criteria for proportioning members and their connections, procedures for fabrication and erection, requirements for inspections, and standards for protection against corrosion and fire. Use of these documents generally ensures safety, economical designs, and sound operational techniques. The applicable building code defines the minimum legal requirements for a design. Most building authorities incorporate in their building code one of the model building codes (Art. 1.10), but some write their code requirements. Usually, the basis for the requirements for steel design and construction in building codes are the American Institute of Steel Construction specifications for structural steel buildings (Table 7.1). Note that two AISC specifications are available, one applicable to allowable stress design and plastic design (ASD) and the second to load and resistance factor design (LRFD). Table 7.1 also lists other codes and specifications most frequently used by steel designers. Requirements for special-function buildings, needs of governmental agencies, and other unique requirements has led to promulgation of many other codes and specifications. Some of the organizations that publish these standards are the General Services Administration, U.S. Department of Commerce, Corps of Engineers, and U.S. Navy Bureau of Yards and Docks. The steel shapes, plates, and bars that make up most of the materials used for structural steel are produced by mills as hot-rolled products. These products are made in a batch process; each production run of steel comes from a heat. The TABLE 7.1 Basic Steel Construction Codes and Specifications Organization Document Scope American Institute of Steel Construction (AISC) One East Wacker Drive Chicago, IL 60601-2001 Code of Standard Practice for Steel Buildings and