7.35.5 End-Plate Connections The art of welding makes feasible connections that were not possible with oldertype fasteners, e.g., end-plate connections (Fig. 7.50). FIGURE 7.50 End-plate connection between beam and column flange. Of the several variations, only the flexible type (Fig. 7.50c) has been standardized with tabulated data in the AISC Manual. Flexibility is assured by making the end plate 1/4 in thick wherever possible (never more than 3/8 in). Such connections in tests exhibit rotations similar to those for framed connections. The weld connecting the end plate to the beam web is designed for shear. There is no eccentricity. Weld size and capacity are limited by the shear strength of the beam web adjoining the weld. Effective length of weld is reduced by twice the weld size to allow for possible deficiencies at the ends. As can be observed, this type of connection requires accurate cutting of the beam to length. Also the end plates must be squarely positioned so as to compensate for mill and shop tolerances. The end plate connection is easily adapted for resisting beam moments (Fig. 7.50b, c and d). One deterrent, however, to its use for tall buildings where column flanges are massive and end plates thick is that the rigidity of the parts may prevent drawing the surfaces into tight contact. Consequently, it may not be easy to make such connections accommodate normal mill and shop tolerances. 7.35.6 Special Connections In some structural frameworks, there may be connections in which a standard type (Arts. 7.35.1 to 7.35.5) cannot be used. Beam centers may be offset from column centers, or intersection angles may differ from 90, for example. For some skewed connections the departure from the perpendicular may be taken care of by slightly bending the framing angles. When the practical limit for bent angles is exceeded, bent plates may be used (Fig. 7.51a). Special one-sided angle connections, as shown in Fig. 7.51b, are generally acceptable for light beams. When such connections are used, the eccentricity of the fastener group in the outstanding leg should be taken into account. Length l may be reduced to the effective eccentricity (Art. 7.32). Spandrel and similar beams lined up with a column flange may be conveniently connected to it with a plate (Fig. 7.51c and d). The fasteners joining the plate to the beam web should be capable of resisting the moment for the full lever arm l for the connection in Fig. 7.51c. For beams on both sides of the column with equal FIGURE 7.51 Examples of special connections. reactions, the moments balance out. But the case of live load on one beam only must be considered. And bear in mind the necessity of supporting the beam reaction as near as possible to the column center to relieve the column of bending stresses. When spandrels and girts are offset from the column, a Z-type connection (Fig. 7.51e) may be used. The eccentricity for beam-web fasteners should be taken as l1, for column-flange fasteners as l2, and for fasteners joining the two connection angles as l3 when l3 exceeds 21/2 in; smaller values of l3 may be considered negligible. 7.35.7 Simple, Rigid, and Semirigid Connections Moment connections are capable of transferring the forces in beam flanges to the column. This moment transfer, when specified, must be provided for in addition to FIGURE 7.52 Methods of constructing flexible welded connections. and usually independent of the shear connection needed to support the beam reaction. Framed, seated, and end-plate connections (Arts. 7.35.1 to 7.35.5) are examples of shear connections. Those in Fig. 7.17 (p. 7.32), are moment connections. In Fig. 7.17a to g, flange stresses are developed independently of the shear connections, whereas in h and i, the forces are combined and the entire connection resolved as a unit. Moment connections may be classified according to their design function: those resisting moment due to lateral forces on the structure, and those needed to develop continuity, with or without resistance to lateral forces. The connections generally are designed for the computed bending moment, which often is less than the beams capacity to resist moment. A maximum connection is obtained, however, when the beam flange is developed for its maximum

The characteristics of a luminous environment that determine quality are contrast, diffusion, and color rendering. Contrast, created by shadows or by relatively bright areas in a field of vision, affects visibility, mood, comfort, and eyestrain (Art. 15.10). Diffusion, the dispersion of light in all directions, may be produced by transmission or reflection. Diffuse transmission occurs when light from a bright source passes through a material that disperses the incident light, with consequent reduction in brightness. Translucent materials or specially constructed lenses are often employed for this purpose in lighting fixtures. Diffuse reflection occurs when incident light on a surface is reflected almost uniformly in all directions by tiny projections or hollows. Such surfaces appear nearly equally bright from all viewing angles. Diffusion tends to reduce contrast and promote uniformity of lighting. Brightness Ratios. For good quality of lighting, the degree of contrast of light and dark areas in the field of vision should be limited to provide for viewing angle changes. The reason for this is that the eye adapts to the luminance of a task after a period of time. When the eye leaves the task and encounters a field of different brightness, the eye requires an appreciable time to adapt to the new condition, during which eyestrain or visual discomfort may be experienced. To promote quick, comfortable adaptation, brightness ratios in the visual environment should be kept

A range of stress may be resolved into two componentsa steady, or mean, stress and an alternating stress. The endurance limit sometimes is defined as the maximum value of the alternating stress that can be superimposed on the steady stress an indefinitely large number of times without causing fracture. Design of members to resist repeated loading cannot be executed with the certainty with which members can be designed to resist static loading. Stress concentrations may be present for a wide variety of reasons, and it is not practicable to calculate their intensities. But sometimes it is possible to improve the fatigue strength of a material or to reduce the magnitude of a stress concentration below the minimum value that will cause fatigue failure. In general, avoid design details that cause severe stress concentrations or poor stress distribution. Provide gradual changes in section. Eliminate sharp corners and notches. Do not use details that create high localized constraint. Locate unavoidable stress raisers at points where fatigue conditions are the least severe. Place connections at points where stress is low and fatigue conditions are not severe. Provide structures with multiple load paths or redundant members, so that a fatigue crack in any one of the several primary members is not likely to cause collapse of the