151
In 1607, a Venetian engineer named Faustus Verantius published a description of a suspended bridge partly supported with several diagonal chain stays Fig. 15.1a . The stays in that case were used in combination with a main supporting suspension catenary cable. The first use of a pure stayed bridge is credited to Loscher, who built a timber-stayed bridge in 1784 with a span of 105 ft Fig. 15.2a . The pure-stayed-bridge concept was apparently not used again until 1817 when two British engineers,...
533 Moment Connections
The most commonly used moment connection is the field welded connection shown in Fig. 5.56. This connection has been in common use throughout the U.S. for many years. In current seismic design covered by the AISC ''Seismic Provisions for Structural Steel Buildings,'' it is permitted for use in ordinary moment-resisting frames Art. 9.7 without requirements for physical testing. It is also permitted for use in special moment-resisting frames, when the member sizes used for the specific project...
15
See AASHTO Specifications for full requirements that apply. See AASHTO Specifications for full requirements that apply. range for Case II, with ADTT lt 2,500, the AASHTO standard specifications specify 500,000 loading cycles for truck loading and 100,000 for lane loading. Table 12.20 also lists for the four types of connections the allowable stress ranges Fsr for the redundant-load-path structure based on the connection stress category and the number of stress cycles. The fatigue stress in the...
6262 Shear Connectors
The purpose of shear connectors is to ensure composite action between a concrete slab and a steel beam by preventing the slab from slipping relative to or lifting off the flange to which the connectors are welded. Headed-stud or channel shear connectors are generally used. The studs should extend at least four stud diameters above the flange. The welds between the connectors and the steel flange should be designed to resist the shear carried by the connectors. When the welds are not directly...
Stiffeners
FIGURE 5.61 Bracing for girders. a Stiffeners brace a girder that is continuous over the top of a column. b Knee brace restrains a girder seated atop a column. c Open-web joist provides lateral support for a girder atop a column. eccentricity of welds and fasteners may be neglected at the ends of single-angle, doubleangle, and similar members. At panel points, several types of connections may be used. Members may be pin-connected to each other Art. 5.6 , or they may be connected through gusset...
818 Vibrations
Although a floor system may be adequately designed from a strength standpoint, a serviceability problem will result if unacceptable vibrations occur during normal usage of the floor. The anticipated performance of the floor can be analyzed by computing the first natural frequency and the amplitude, that is, deflection when subjected to a heel-drop impact, of the floor framing member and plotting the result on a modified Reiher-Meister scale Fig. 8.28 to determine the degree of perceptibility to...
536 Connections For Bracing
The lateral force-resisting system of large buildings is sometimes provided by a vertical truss with connections such as that in Fig. 5.63. The design of this connection is demonstrated in the following example by a method adopted by the AISC, the uniform-force method, the force distributions of which are indicated in Fig. 5.64. The method requires that only uniform forces, no moments, exist along the edges of the gusset plate used for the connection. Example AISC LRFD. Design the bracing...
Section Aa Vhy
FIGURE 15.37 Anchorage for Verrazano Narrows Bridge. suspender is attached to the cable band by standard zinc-poured sockets. Since bending of the suspender is not required, the suspender generally is a structural strand. Properly attached, zinc-poured sockets can develop 100 of the strength of strands and wire rope. The end fittings or sockets of structural strand or rope are standardized by manufacturers and may be swaged or zinc-poured. These fittings include open or closed sockets of...
1214
Hence, the radius of gyration should be at least r 22.7 X 12 140 1.95 in. Similarly, for interior panels, minimum r 23.6 X 12 140 2.02 in. Assume for the diagonals a WT6 X 26.5 Fig. 12.42 . It has the following properties Sx 3.54 in3 rx 1.51 in ry 2.48 in A 7.80 in2 y 1.02 in To permit the slenderness ratio about the vertical axis to govern the design, provide a vertical brace at midlength of each diagonal. The minimum slenderness ratio then is Horizontal Buckling. For a column of Grade 36...
628 Builtup Compression Members
Design of built-up compression members should comply with the basic requirement for prevention of local and overall buckling of compression members as summarized in Arts. 6.16 and 6.23. To ensure, however, that individual components, such as plates and shapes, of a built-up member act together, the AISC ASD and LRFD specifications for structural steel buildings emphasize proper interconnection of the components. Many of the AISC requirements are the same for ASD and LRFD. The ASD specification,...
204
under this loading as a continuous beam spanning between diaphragms. The maximum negative moment for design purposes may be taken as The stress due to lateral bending should be added to that due to Mn to obtain the maximum stress in each flange. Where provision is made for composite action, however, the lateral bending stress in that flange may be neglected. For preliminary design purposes, a rough approximation of the effects of curvature may be obtained by use of where p percent increase in...
513 Fillers
A filler is a plate inserted in a splice between a gusset or splice plate and stress-carrying members to fill a gap between them. Requirements for fillers included in the AISC specifications for structural steel for buildings are as follows. In welded construction, a filler V4 in or more thick should extend beyond the edge of the splice plate and be welded to the part on which it is fitted Fig. 5.10 . The welds should be FIGURE 5.10 Typical welded splice of columns when depth Du of the upper...
1122 Bearings
Bridges should be designed so that a total movement due to temperature change of 1V4 in per 100 ft can take place. Also, provisions should be made for changes in length of span resulting from live-load stresses. In spans over 300 ft long, allowance should be made for expansion and contraction in the floor system. Expansion bearings may be needed to permit such movements. See also Art. 11.26. In addition, to control of the movements, at least one fixed bearing is required in each simple or...
972 Limitations on Concentric Braced Frames
Concentric braced steel frames are much stiffer and stronger than moment-resisting frames, and they frequently lead to economical structures. However, their inelastic behavior is usually inferior to that of special moment-resisting steel frames Art. 9.6 . One reason is that the behavior of concentric braced frames under large seismic forces is dominated by buckling. Furthermore, the columns must be designed for tensile loads and foundation uplift as well as for compression. Figure 9.12 shows...
28 Shop Preassembly
When the principal operations on a main member, such as punching, drilling, and cutting, are completed, and when the detail pieces connecting to it are fabricated, all the components are brought together to be fitted up, i.e.,temporarily assembled with fit-up bolts, clamps, or tack welds. At this time, the member is inspected for dimensional accuracy, squareness, and, in general, conformance with shop detail drawings. Misalignment in holes in mating parts should be detected then and holes...
110 Effect Of Cold Work On Tensile Properties
In the fabrication of structures, steel plates and shapes are often formed at room temperatures into desired shapes. These cold-forming operations cause inelastic deformation, since the steel retains its formed shape. To illustrate the general effects of such deformation on strength and ductility, the elemental behavior of a carbon-steel tension specimen subjected to plastic deformation and subsequent tensile reloadings will be discussed. However, the behavior of actual cold-formed structural...
311 Principal Stresses And Maximum Shear Stress
When stress components relative to a defined set of axes are given at any point in a condition of plane stress or plane strain see Art. 3.10 , this state of stress may be expressed with respect to a different set of axes that lie in the same plane. For example, the state of stress at point O in Fig. 3.15a may be expressed in terms of either the x and y axes with stress components, fx, fy, and v or the x' and y' axes with stress components fx,, fy,, and vxy Fig. 3.15b . If stress components fx,...
125
12.3. Characteristics of Plate-Girder Stringer Bridges 12.20 Design of Composite, Plate-Girder Bridge 12.23 12.5. Example Load-Factor Design of Composite Plate-Girder Bridge 12.34 12.6. Characteristics of Curved Girder Bridges 12.48 Design of Curved Stringer Bridge 12.56 12.8. Deck Plate-Girder Bridges with Floorbeams 12.69 Design of Deck Plate-Girder Bridge with 12.10. Through Plate-Girder Bridges with Floorbeams 12.104 Design of a Through Plate-Girder Bridge 12.105 12.12. Composite Box-Girder...
210 Builtup Sections
These are members made up by a fabricator from two or more standard sections. Examples of common built-up sections are shown in Fig. 2.2. Built-up members are specified by the designer when the desired properties or configuration cannot be obtained in a single hot-rolled section. Built-up sections can be bolted or welded. Welded members, in general, are less expensive because much less handling is required in the shop and because of more efficient utilization of material. The clean lines of...
Info Egv
The following are approximate values for all the steels Modulus of elasticity 29 X 103 ksi. Shear modulus 11 X 103 ksi. Poisson's ratio 0.30. Yield stress in shear 0.57 times yield stress in tension. Ultimate strength in shear to 3 4 times tensile strength. Coefficient of thermal expansion 6.5 X 10 6 in per in per deg F for temperature range 50 to 150 F. Density 490 lb ft3. f See ASTM A6 for structural shape group classification. Where two values are shown for yield stress or tensile strength,...