Load

The live loading for which roofs are designed is either totally or primarily a snow load. Since snow has a variable specific gravity, even if one knows the depth of snow for which design is to be made, the load per unit area of roof is at best only a guess. The best procedure for establishing snow load for design is to follow the ASCE 7 Standard 1.2 . This standard uses a map of the United States giving isolines of ground snow corresponding to a 50-year mean recurrence interval for use in...

Earthquake Load

Recommended Lateral Force Requirements and Commentary. San Francisco, CA Seismology Committee, Structural Engineers Association of California, Los Angeles, CA, 1990. 1.48. Anil K. Chopra and Ernesto F. Cruz. Evaluation of Building Code Formulas for Earthquake Forces, Journal of Structural Engineering, ASCE, 112, 8 (August 1986), 1881-1899. 1.49. Anil K. Chopra. Dynamics of Structures, Theory and Applications to Earthquake Engineering. Englewood Cliffs, NJ Prentice-Hall, Inc., 1995....

Wind Load

In SI units. q 0.63 ' for < in MPa and V in m sec. where Ct. is an exposure factor that varies from 1.0 (for 0-40-ft height) to 2.0 (for 740-1200-ft height) Ct, is a gust factor, such as 2.0 for structural members and 2.5 for small elements including cladding and Cr is a shape factor for the building as a whole. Excellent details of application of wind loading to structures are available in the ASCE 7 Standard 1.2 and in the National Building Code of Canada 1.9 . The commonly used static wind...

Snow Loads

O'Rourke and Ulrich Stiefel. Roof Snow Loads for Structural Design, Journal of Structural Engineering, ASCE, 109, 7 (July 1983), 1527-1537. 1.40. J. T. Templin and W. R. Schriever. Loads due to Drifted Snow, Journal of the Structural Division, ASCE, 108, ST8 (August 1982), 1916-1925. 1.41. Michael O'Rourke, Wayne Tobiasson, and Evelyn Wood. Proposed Code Provisions for Drifted Snow Loads, Journal of Structural Engineering, 112, 9 (September 1986), 2080-2092. 1.42. Michael J....

Allowable Stress Design ASD

The safety factor'1 FS used in Eqs. 1.8.9 through 1.8.12 was not determined consciously by using probabilistic methods. The values used in the AISC ASD Specification have been in use for many years and are the result of experience and judgment. It is clear that the safety required must be a combination of economics and statistics. Obviously, it is not economically feasible to design a structure so that the probability of failure is zero. Prior to the development of the AISC LRFD Specification...

Design Formula for Moment on Single Line of Fasteners

M T np) Substitution of Eq. 4.12.25 into Eq. 4.12.26 gives Solving Eq. 4.12.27 for n2, one obtains * Thomas C. Shedd, Structural Design in Sreel (John Wiley & Sons, New York 1934). p. 287. Resisting section consisting of connector resistance uniformly distributed Figure 4.12.9 Moment on a single line of fasteners, which as a first approximation becomes Resisting section consisting of connector resistance uniformly distributed Figure 4.12.9 Moment on a single line of fasteners, which as a...

Selected References

History of Steel Beam Design, Engineering Journal, AISC, 14, 4 (Fourth Quarter 1977), 141-147. 7.2. Joint Committee of Welding Research Council and the American Society of Civil Engineers. Commentary on Plastic Design in Steel, 2nd ed., ASCE Manual and Reports on Practice No. 41, New york. 1971. 7.3. Joseph A. Yura, Theodore V. Galambos, and Mayasandra K. Ravindra. The Bending Resistance of Steel Beams, Journal of the Structured Division, ASCE, 104, ST9 (September 1978),...

Shear And Tension From Eccentric Loading

In a bracket connection such as in Fig. 4.14.1 a and d, the eccentric load produces both shear and tension in the upper fasteners. As in most other connections, the manner in which the pieces behave is complex. However, nominal forces carried by the fasteners are usually determined by using one of two approaches (1) that of neglecting any initial tension in the fasteners or (2) that of considering the initial pretension forces in the fasteners. When fasteners such as A307 bolts are used, the...

Biaxial Bending

The nominal strength of members under axial compression and biaxial bending has been studied by Birnstiel and Michalos 12.34 , Culver 12.35, 12.36 , Harstead, Birnstiel, and Leu 12.37 , Syal and Sharma 12.38 , Santathadaporn and Chen 12.39 , and Chen and Atsuta 12.38 , Even with a number of simplifying assumptions, the analysis is complex. Some tests have been performed 12.41 which, though limited, have shown agreement with computer studies. Tebedge and Chen 12.43 have given interaction...

L

(f) Pipe (g) Structural (h) Bars (i) Plates Figure 1.5.1 Standard rolled shapes. flange shape (Fig. 1.5.1a) which is formed by hot rolling in the steel mill. The wide-flange shape is designated by the nominal depth and the weight per foot, such as a W18X97 which is nominally 18 in. deep (actual depth 18.59 in. according to AISCManned) and weighs 97 pounds per foot. (In SI units the W18X97 section could be designated W460X144, meaning nominally 460 mm deep and having a mass of 144 kg m.) Two...

Example 393

Select a tension diagonal member for a roof truss of A572 Grade 50 steel using AISC Load and Resistance Factor Design. The axial tension is 60 kips dead load and 6 kips live load and the member is 12 ft long. Assume -in.-diam bolts are located on a single gage line in standard holes. Assume the preferable limit on slenderness ratio L r is 240 (not an LRFD limit). a. Select the lightest single angle member. b. Select the lightest double angle member having legs separated by in. back-to-back....

Combined Bending And Axial Load Example 12141

Investigate the acceptability of a W16X67 used as a beam-column under the loading shown in Fig. 12.10.1. The total service loads are P 350 kips and M 60 ft-kips, and Fv 60 ksi. Use Allowable Stress Design. (a) Column effect. Check local buckling slenderness ratio limits for axial compression.

Concentrated Loads Applied To Rolled Beams

When concentrated loads are applied to beams, beam bearing at supports, and reactions of beam flanges at connections to columns, a localized yielding from high compressive stress followed by inelastic buckling in the web region adjacent to the toe of a fillet occurs in the vicinity of concentrated loads. This entire behavior was formerly combined under the category web crippling. Typical of compression-related situations, there are two possible behaviors yielding and instability. The recent...

Continuous Beams

(c) Check segment A (Fig. 10.5.1) with W24X76. - 15 ft) > (Lu 11.8 ft) Fb < 0.60Fy 12.000Cb 12.000(1.0) , , N F(F1-8) T f TsoW 171 ksi > (f 13'5 ks,)< OK which indicates segment A is OK and no need to check ASD Formula (Fl-6). Q, TT5 nA)< (L 1L8ft) OK Fb 0.60Fy 22 ksi 242(12) fb i . 16.5 ksi < 22 ksi OK 176 (e) Show final check for segments B and C W24X76 Fh - 0.60FV 22 ksi f,, - 21-5 ksi < 22 ksi 0K Use W24X76, Fy - 36 ksi. A comparison with Example 10.3.1 where LRFD using...

P M

+ n 1.0 12.8.1 Pv I ASM,, l where PH and M are the axial force and primary bending moment, respectively, that occur when maximum strength is achieved. When the numerator and denominator are divided by a factor (FS) to bring all terms into the service load range, PJ(AS FS) 1.18M 5(FS) 'U UZ.i4.iz, hoi SI which gives as a design requirement. The ASD Specification has used an expression more conservative than Eq. 12.14.14 by using 1.0 instead of 1.18, and instead of M9 5(FS) , which for I-shaped...

Fxampff 1421

Pctcimme the buckling loud f , and effeeOve length A'I, for a braced rigid frame, as in Fig. 14.2.4, sUnch has I 21O0 mC i.W24X7CO - 706 mO i VI4a 4i bWacou The stubihiy equation to be satisfied is Fq . 14.2.18. which inverted is sin d* d> cos d> I 70fx36i ' - - -0.4H7 bile snub lest value of satisfying the buck iing equation is tlie critical value i.e the one thai governs, As . approaches zero, an isolated pinned column is indicated, with (h1 rr7 As girder stiffness increases. A should...

Cm Cm

Where M,rx, Muy factored moments about the x- and y-axes, respectively Mpx, Mpy plastic moment strength about the x- and y-axes, respectively Mnx, Mnx nominal moment strength about the x- and y-axes, respectively (may be equal to or less than plastic moment strength) C IX, Cmy moment gradient terms whose meaning is treated in Chapter 12 on beam-columns. It is always conservative to take these equal to 1.0 meaning constant bending moment between lateral supports. < f> h 0.90 for flexure For...

Basic Column Strength

To determine a basic column strength, certain conditions may be assumed for the ideal column 6.7 . With regard to material, it may be assumed (1) there are the same compressive stress-strain properties throughout the section (2) no initial internal stresses exist such as those due to cooling after rolling and those due to welding. Regarding shape and end conditions, it may be assumed (3) the column is perfectly straight and prismatic (4) the load resultant acts through the centroidal axis of...

Nominal Moment Strength Of Fully Composite Sections

The nominal strength M of a composite section having its slab in compression (positive moment) depends on the yield stress and section properties (including sleuderness A - ., for the web) for the steel beam, the concrete slab strength and the strength of shear connectors providing the interface shear transfer between slab and beam. The nominal strength (commonly called ultimate strength) concepts were first applied to design practice as recommended by the ASCF-ACI Joint Committee on Composite...

Load and Resistance Factor Design Maximum

Equation 11.3.9 when rounded becomes h- 'FV (F 16.5) which is the LRFD-Appendix Gl general limitation (Fv in ksi). In the presence of transverse softeners, higher ratios are permitted. Based on the recommendations of the ASCE-AASHO Joint Committee, Subcommittee 1 on Hv-brid Girder Design 11.10 . LRFD-Appendix G1 gives the maximum hft,x. as when stiffener spacing a to web depth h does not exceed 1.5. Values for Eqs. 11.3.10 and 11.3.11 are given in Table 11.3.1.

Framed Structures

Most typical building construction is in this category. The multistory building usually consists of beams and columns, either rigidly connected or having simple end connec- tions along with diagonal bracing to provide stability. Even though a multistory building is three-dimensional, it usually is designed to be much stiffer in one direction than the other thus it may reasonably be treated as a series of plane frames. However, if the framing is such that the behavior of the members in one plane...

Size And Length Limitations For Fillet Welds 21

Figure 5.11.1 Effect of thickness on cooling rate. whereas the thinner plate is essentially limited to a horizontal dissipation. In other words, the thicker the plate, the faster heat is removed from the welding area, thereby lowering the temperature in the region of the weld. Since a minimum temperature is required to cause the base metal to become molten, it is therefore necessary to provide as a minimum, a weld of sufficient size (and heat content) to prevent the plate from removing the heat...

W18 X

Repeat Prob. 8.10, considering the ends torsionally fixed. 8.12. Repeat Prob. 8.8, with the load applied in the plane of the y-axis of a channel, C15X50. 8.13. For the case (or cases) assigned by the instructor, select the lightest W14 section, using the (3 modified flexure analogy approach, to carry a concentrated load W at midspan, in addition to the weight of the beam. The ends of the simply supported span are assumed to have torsional simple support. Check the stresses in the section...

Triangular Bracket Plates

When the Miflener ten- a bracket is cut into a triangular shape, as in Fig. 13.4.3b. the plate behaves in a different manner than when the free edge is parallel to the direction of applied load in the region where the greatest stress occurs, as in Fig. 13.4,5,. The triangular bracket plate arrangement and notation are shown in Fig. 13.5,1. The behavior of triangular bracket plates has been studied analytically by Salmon .13.45 and experimentally by Salmon, Buettncr. and 0'.Sheridan 13,46) and...

Composite Flexural Members Containing Formed Steel Deck

Composite llexural members may be made using formed steel deck, as shown in Fig. 16.E2. The formed metal deck may be placed perpendicular to or parallel with the supporting beam. Furthermore, the beam may actually be an open web joist. Typically, the deck plate varies in thickness from 22 ga. (0.0336 in., 0.853 mm) to 12 ga, (0.1084 in 2.75 mm). The deck rib height typically is . 2. and 3 in. for spans oE say. 8. 10, and 15 ft. As shown in Fig, 16,1.2, the thickness of the concrete slab above...

Bearing Criterion

In order to bring bearing stiffener plates tight against the flanges, one corner of each stiffener plate must be cut off so as to clear the flange-to-web fillet weld. The remaining area of direct bearing is less than the gross area of the stiffener plates. The strength in bearing under LRFD-J8.1 or the service load stress in bearing under ASD-J8.1 must be satisfactory. Load and Resistance Factor Design. The bearing requirement of LRFD-J8 is Rn nominal bearing strength 1.8FyAph (11.12.8) Apb...

Load And Resistance Factor Design

The concepts relating to the nominal moment strength M* have been presented in Chapters 7 and 9, and reviewed in Sec. I l .2. Complexity in design arises using M, and L, expressed by Eqs. 9.6.5 and 9.6.6. respectively, for plate girders. For rolled beams, not only are the values of M, and L, available in the LRFD Manual but also all of the properties, including the torsion properties, are readily available. For plate girders all of the properties must be computed for each girder. Thus, while...

Combined Bending And Axial Load

12.15 DESIGN PROCEDURES ALLOWABLE STRESS DESIGN To aid in selection of a beam-column section, it is usually advantageous to convert, in an approximate way, the resulting bending moment into an equivalent axial compression load and then to make use of column tables, as was done in Sec. 12.12 for LRFD. Occasionally, conversion of the axial load into equivalent moment will be helpful. The stability interaction equation, Eq. 12.14.3, may be written P M ( C l AgFa FhS - fjfj Multiplying by Ag Fa...

Effective Laterally Unbraced Length

Design equations, such as those of LRFD and ASD-F1, are based on the assumption of torsional simple support (see Figs. 8.5.4 and 8.7.2) at the ends of the unbraced segment. This means that for torsional behavior only the effective laterally unbraced length KLh equals the actual laterally unbraced length Lh that is. the effective length factor K - 1.0. Nearly any type of lateral brace or end connection will prevent rotation (that is. keep the angle of twist equal to zero see Fig. 9.4.1c) about...

Biaxial Bending Of Symmetric Sections

Flexural stresses on sections with at least one axis of symmetry and loaded through the centroid may be computed using Eq. 7.10.19, which when modified to give where Sx IJ(d 2) and Sv I, b 2) are the section modulus values. The nominal strength of a section subject to biaxial bending is not readily determined. Such strength will certainly depend on the proportions of the section and the relative magnitudes of the applied moments Mx and My. The use of an interaction equation such as used for...

Holes In Beams

For tension members the effect of fastener holes has been discussed in Chapter 3, where holes are deducted and net section is used. For compression members, since the fasteners occupy most of the space in the hole, the fasteners are assumed in design to completely fill the holes and a deduction for holes is not made. When the nominal strength Mn reaches the plastic moment Mp, certainly tension flange holes reduce that strength however, there will be a shift in neutral axis associated with a...

Hybrid Composite Girders

The general discussion of the hybrid plate girder appears in Sec. 11.7. The hybrid girder is one that has either the tension flange or both flanges of the steel section made with a higher strength grade of steel than used for the web. There are, particular economic advantages to the hybrid girder in composite construction where the concrete slab, provides a large compression capacity, The neutral axis will lie near the compression face of the composite section, causing the higher stressed...

Allowable Stress Design

The safety requirement for axially loaded columns in Allowable Stress Design (ASD) according to ASD-E2 may be stated where fa service load compression stress P Ag P service load axial compression force Ag gross cross-sectional area of column Fa allowable stress at service load Eqs. 6.7.9 or 6.7.10 Equations 6.7.9 and 6.7.10 are used for typical rolled W sections satisfying the local buckling limitations on width thickness ratios for plate compression elements given in ASD-B5.1. Table 6.8.1...

Types Of Joints

The type of joint depends on factors such as the size and shape of the members coming into the joint, the type of loading, the amount of joint area available for welding, and the relative costs for various types of welds. There are five basic types of welded joints, although many variations and combinations are found in practice. The five basic types are the butt, lap, tee, corner, and edge joints, as shown in Fig. 5.4.1. The butt joint is used mainly to join the ends of flat plates of the same...

Compression Members 276 Parti Columns 276

6.2 Euler Elastic Buckling and Historical Background 276 6.6 Development of Column Strength Curves Including Residual Stress 287 6.7 Structural Stability Research Council (SSRC) Strength Curves 295 6.8 Load and Resistance Factor Design 300 6.10 Load and Resistance Factor Design of Rolled Shapes (W, S, and M) Subject to Axial Compression 311 6.1 1 Allowable Stress Design 317 6.13 Design of Latticed Members 321 6.14 Introduction to Stability of Plates 327 6.15 Strength of Plates under Uniform...

Loads Applied Eccentric To The Plane Of Welds

When an applied load is eccentric to the plane of the weld configuration, as in Fig. 5.19.1, the strength method of analysis may still be used as long as the plane of the welds is rigid. The weld plane is rigid in Fig. 5.19.1 because the welds are on each Figure 5.19.1 Welds in shear and bending. Figure 5.19.1 Welds in shear and bending. side of a plate i.e there is sufficient rigidity between the two lines of wreld such that there will be no bending of the material being welded in the plane of...

Basic Processes

Welding is the process of joining materials (usually metals) by heating them to suitable temperatures such that the materials coalesce into one material. There may or may not be pressure, and there may or may not be filler material applied. Arc welding is the general term for the many processes that use electrical energy in the form of an electric arc to generate the heat necessary for welding. This section treats those processes used in arc welding carbon and low-alloy steel for buildings and...

Muitiaxial Stress Induced by Welding

In general, welding creates a built-in restraint that gives rise to biaxial and triaxial stress and strain conditions, which result in brittle behavior. To illustrate, consider the loaded simply supported beam of Fig. 2.9.3, which in turn supports a plate in tension. Due to flexure, the bottom flange of the beam is in tension therefore, the stress at point A is uniaxial tension (neglecting the small effects of beam width and attachment of flange to web). Connecting the tension plate with angles...

Factors Affecting The Quality Of Welded Connections

Obtaining a satisfactory welded connection requires the combination of many individual skills, beginning with the actual design of the weld and ending with the welding operation. The structural engineer needs to be aware of the factors that affect the quality of a weld and design the connections accordingly. Proper Electrodes, Welding Apparatus, and Procedures After the proper electrode material is specified to match the strength of the steel in the pieces being joined (see Sec. 5.13), the...

Vertical Flange Buckling Limit State

The maximum limit on the web slenderness h tu. is based on the stiffness needed in the plane of the web to prevent the compression flange from buckling vertically (Fig. 11,3. lc). Note that h, the clear unsupported height of the web in a rolled section, is the depth h of the web plate in a welded I-shaped section. Furthermore, some flexural stiffness is needed from the web along the flange-to-web connection to preclude torsional buckling of the flange (Fig. 11.3.1b). Fiange aas KUkp ndeMh when...

Comparison of LRFD with ASD for Tension Members

The comparison of safety obtained for tension members designed by the two AISC methods is indicative of the general result expected. Direct comparisons are more difficult in design of other types of members because the nominal strengths R are not necessarily the same in the two methods. For tension members acted upon by gravity dead and live loads, the resistance factor < j> 0.90, and using Eq. 1.8.3 gives for LRFD 1.2 D + 1.61 0.90 R 1.8.3 In ASD the factor of safety FS 1.67 for axial...

Jjl

(a) Cross-section (b ) Elevation at end of span Figure 11.1.2 Typical components of a welded plate girder. Where practically all riveted girders were composed of plate and angle components having the same material yield strength, the tendency now with welded girders is to combine materials of different strength. By changing materials at various locations along the span so that higher strength materials are available at locations of high moment and or shear, or by using different strength...

Types Of Connections

Steel construction is categorized by LRFD-A2.2 and ASD-A2.2 into various 'Types depending on the amount of restraint developed by the connections. Three types are identified Fully Restrained (also called Rigid Frame, or Continuous Frame). This situation occurs when full continuity is provided at the connection so that original angles between intersecting members are maintained essentially constant during loading of the structure i.e., with rotational restraint on the order of 90 or more of that...

Compression Members Example 6104

Design column A of the unbraced frame of Fig. 6.10.4 as an axially loaded compression member carrying a dead load of 55 kips and a live load of 220 kips using A36 steel. In the plane perpendicular to the frame the system is braced, with supports at top and bottom of a 21-ft height. PH 1.2D + 1.6L 1.2(55) + 1.6(220) 418 kips (b) Select a preliminary size as a basis for evaluating the effective length factors K. While it is rare that a frame member would be designed as axially loaded, it may...

Introduction And Historical Development

Plate girders, showing welded stiffeners in place, rocker bearings for vertical supports at the pier, transverse cross bracing between girders, and hinges to provide a simple support for the spans to the right of the hinges. (Photo by C. G. Salmon) Plate girders, showing welded stiffeners in place, rocker bearings for vertical supports at the pier, transverse cross bracing between girders, and hinges to provide a simple support for the spans to the right of the hinges. (Photo by C. G. Salmon)...

Introduction And Historical Development 189

Thomas Fletcher 5.1 in 1887 used a blowpipe, burning hydrogen and oxygen and showed that he could successfully cut or melt metal. In 1901 -1903 Fouche and Picard developed torches that could be used with acetylene and, thus, the era of oxyacetylene welding and cutting began. The period between 1903 and 1918 saw the use of welding primarily as a method of repair, the greatest impetus occurring during World War I (1914-1918). Welding techniques proved to be especially adapted to repairing ships...

Problems

All problems are to be done according to the ALSC Load and Resistance Factor Design or Allowable Stress Design, as indicated by the instructor. The requirement of W section is intended to include W. S, and M sections, All given loads are service loads unless otherwise indicated. If needed, assume service loads are 2 3 I factored loads unless otherwise indicated. Assume lateral support consists of transnational restraint but not moment i rotational) restraint, unless otherwise indicated. Assume...

Analogy Between Torsion And Plane Bending

Because the differential equation solution is time consuming, and really suited only for analysis, design of a beam to include torsion is most conveniently done by making the analogy between torsion and ordinary bending. Consider that the applied torsional moment T of Fig. 8.6.1 can be converted into a couple PH times h. The force PH can then be treated as a lateral load acting on the flange of a beam. The substitute system will have constant shear over one-half the span, a diagram as given in...

Torsion In Sections With Open And Closed Parts

Generally this problem is treated by combining the principles discussed separately for open and closed parts. The procedure to be used for determining resisting moment, stiffness, and shear center location for such sections is presented with examples by Chu and Longinow 8.33 , The following is a summary of pertinent equations Total resisting moment is where J X bt3 for open parts only. In addition, each of the closed cells must satisfy Eq. 8.10.14

Example 3102

Design sag rods to support the purlins of the industrial building roof of Fig. 3.10.2. Sag rods are spaced at the third points between roof trusses, which are spaced 24 ft apart. Use 20 psf snow load, A36 steel, and AISC LRFD Specification. Solution, a Loads. Assume cold-formed steel roofing is used, weighing 3 psf, and that the purlins have already been designed. Their weight may be approximated as a 3.5 psf roof load. Snow load customarily is prescribed as having an intensity given in pounds...

Historical Background Of Highstrength Bolts

The first experiments indicating the possibility of using high-strength bolts in steel-framed construction were reported by Batho and Bateman 4.1 in 1934. They concluded that bolts with a minimum yield strength of 54 ksi 370 MPa could be relied on to prevent slip between the connected parts. Follow-up tests by Wilson and Thomas 4.2 substantiated the earlier work by reporting that high-strength bolts smaller in diameter than the holes in which they were inserted had fatigue strengths equal to...

Semi Rigid Connections

Wind Stresses in Semi-Rigid Connections of Steel Framework Transactions. ASCL. 115 i 10 gt 0 u 3S2 402. 13.6, Robert A. lieehtman and Bruce G, Johnston. Riveted Sard Rigid Beam-m- Cohami Building Connections, Progress Report Number F Chicago. IF American Institute of Steel Construction. November 047 pp.h 13.7. I,eo Schenker, Charles G. Salmon, and Bruce G. Johnston. Structural Steel Concatunx, Armed Forces Special Weapons Project. Report No, 752. Engineering Research...

Practical Situations Of Torsional Loading

There are relatively few occasions in actual practice where the torsional load can cause significant twisting, and frequently these situations arise during construction. In most building construction the members are laterally restrained by attachments along the length of the member and therefore they are not free to twist. Even though torsional loading exists, it may be self-limiting because the rotation cannot exceed the end slope of the transverse attached members. Torsion exists on spandrel...

Bearing Stiffener Design

Concentrated loads, such as at unframed end reactions, must be earned by stiffeners placed in pairs. Whenever concentrated loads, such as end reactions or columns supported by plate girders, exceed the local web yielding, web crippling, or side sway web buckling strengths, bearing stiffeners must be provided. Local web yielding and web crippling were discussed in Sec. 7.8 since they are also of concern on rolled beams. Local web yielding formerly called web crippling is provided for in LRFD and...

Example 1061

Examine the effect of a shear splice at the point of contraflexure in the 40-ft span of the two-span continuous beam of Example 10.3.1. A36 steel. a Full dead load plus live load. If full continuity is maintained, partial loading in some spans to account for live load in various locations is unnecessary. Note that the moment Mp 445 ft-kips see Fig. 10.6.la can develop even when the adjacent span has a reduced load. In other words, each span may be treated separately, as long as continuity...

W12x96 A36

P - 40 kips dead load 60 kips live load 12.6. Determine the service axial load P which the W12X45 may be permitted to carry. Lateral support is provided at ends and at midspan. Compare for A36 and A572 Grade 50 steels. 14 0.2 kips ft dead load 0.5 kips ft live load 12.7. Select the lightest W14 section to carry a service load P as shown in the accompanying figure, with an eccentricity e 12 in. with respect to the strong axis. Assume the member is part of a braced system, and conservatively...

Info

The new value of lt j gt cFcr for Q 0sQo 0.926 0.950 0.880 is KVQ 0.70lV0.880 0.658 lt pcFcr 0J09QF, 0.709 0.880 100 62.4 ksi Another iteration could be made since 62.4 is not identical to 65.0 upon which the effective width bE was based. The true answer will be slightly above 62.4 and Q will be slightly higher than 0.880. For practical purposes, use 62.4 ksi. Thus, lt f gt cPn lt f gt t.FcrAg 62.4 12.75 796 kips Pn 796 4 796 0.85 - 936 kips

Traditional Elastic Vector Analysis

For many years eccentrically loaded fastener groups have been analyzed by considering the fastener group areas as an elastic cross-section subjected to direct shear and torsion. The stresses resulting are nominal in the sense that they have stress units say, psi and provide a guide to safety but are not real stresses because the service loads are actually carried by friction. This elastic analysis method has been used because it makes use of simple mechanics of materials concepts and has been...

Longitudinal Web Stiffeners

Longitudinal stiffeners, as shown in Fig. 11.13.1, can increase the bending and shear strengths of a plate girder. In general, they are not as effective as transverse stiffeners however, they are frequently desired on highway bridge girders for esthetic reasons. Studies of longitudinal stiffener effectiveness, as related to stiffener size and location, have been made by Cooper 11.18, 11.19 and others at Lehigh University. These studies and others are summarized in the SSRC Guide 6.8, pp....

Example 7111

Select the lightest W or M section to carry service dead load moments Mx 15 ft-kips and My 5 ft-kips, and live load moments Mx 45 ft-kips and My 20 ft-kips. Consider that adequate lateral bracing is provided to preclude instability. Use steel having Fy 50 ksi. Use Load and Resistance Factor Design. a Compute factored loads Mux and Mur. Mux 1.2 15 1.6 45 - 90 ft-kips Muy 1.2 5 1.6 20 38 ft-kips b Using Method 2. determine required section modulus Sx and select section. Equation 7.11.4 gives From...

Breitie Gilbert

For concrete-encased structural steel F K 29,000 J- 0.2 j rm r, gt 0.34,, , 16.2. Gottfried Brendel. Strength of the Compression Slab of T-Beams Subject to Simple Bending ' .4 7 Journai Proceedings, 6.1, January 1964. 57-76. 16.3. Conrad R Heins and Horn Ming Fan. Effective Composite Beam Width at Ultimate Load, Journai of the Structural Division, ASCE. .102, ST1 1 November 1978o 2163-2179. 16.4. Cesar R Vallenilla and Reidar Bjorhovde. Elective Width Criteria for Composite Beams Engineering...

Shear Stresses Due To Bending Of Thinwall Open Crosssections

Before treating the computation of stresses due to torsion of thin-wall open sections restrained from warping, a review of shear stress resulting from general flexure will be developed. Recognition of a torsion situation precedes concern about calculation of resulting stresses. Extensive treatment of thin-wall members of open cross-section is given by Timoshenko 8.11 . Referring to the general thin-wall section of Fig. 8.3.1, where x and y are centroidal axes, consider equilibrium of the...

Nominal Strength Of Welds

Since welds must transmit the entire load from one member to another, welds must be sized accordingly and be formed from the correct electrode material. For design purposes fillet welds are assumed to transmit loads through shear stress on the effective area no matter how the fillets are oriented on the structural connection. Groove welds transmit loads exactly as in the pieces they join. The electrode material used in welds should have properties of the base material. When properties are...

Highway Live Loads

Highway vehicle loading in the United States has been standardized by the American Association of State Highway and Transportation Officials AASHTO 1.3 into standard truck loads and lane loads that approximate a series of trucks. There are two systems, designated H and HS. that are identified by the number of axles per truck. The H system has two axles, whereas the HS system has three axles per truck. There are several classes of loading however, the usual ones are known as H20 and HS20, shown...

Fatigue Strength

Repeated loading and unloading, primarily in tension, may eventually result in failure even if the yield stress is never exceeded. The term fatigue means failure under cyclic loading. It is a progressive failure, the final stage of which is unstable crack propagation. The fatigue strength is governed by three variables 1 the number of cycles of loading, 2 the range of service load stress the difference between the maximum and minimum stress , and 3 the initial size of a flaw. A flaw is a...

Causes Of Rivet Obsolescence

Riveting is a method of connecting members at a joint by inserting ductile metal pins into holes in the pieces being joined and forming a head at each end to prevent the joint from coming apart. Typical types of rivets are shown in Fig. 4.3.1 see also Fig. 4.1.1a . Riveting required a crew of four or five experienced persons. On the other hand, the crews required for high-strength bolt installation do not need to be highly skilled. Inspection was difficult, and cutting out and replacing bad...

A618

Hot-formed welded and seamless square, rectangular, round, or special shape structural tubing for bolted and welded general structural purposes Grade II has corrosion resistance about twice that of carbon steel Grade I has corrosion resistance about four times that of carbon steel Grade III for enhanced corrosion resistance may have copper specified A709 Carbon high-strength low-alloy and quenched and tempered alloy Structural shapes, plates, and bars in Grades 36, 50, and 50W for use in...

Allowable Stress Design Point Bracing

For ASD a factor of safety FS must be applied so that the service load P may be used instead of Pcr. If FS 2. the strength requirement may be expressed in term of service load P however, the stiffness required will be the same in ASD as in LRFD. Where the strength of the compression member being braced is controlled by an elastic limit state Fcr Fy, as would be the case for columns, the foregoing is applicable. When large plastic strain must be accommodated at bracing points, the design...