Seismic Use Group SDI  0.067g 0.067g  SDI  0.133g 0.133g  SDI  0.20g 0.20g  SDI A B C D A B C D A C D D Where Em equals the earthquake force where seismic forces and dead loads counteract. All parts of the structure between separation joints shall be interconnected, and the connections shall be capable of transmitting the seismic force induced in the connection by the parts being connected. Any smaller portion of the structure shall be tied to the remainder of the structure with 5% the weight of the smaller portion. A positive connection for resisting horizontal forces acting on the member shall be provided for each beam, girder, or truss to its support. The connection shall have strength sufficient to resist 5% of the dead and live load vertical reaction applied horizontally. Analysis Procedures for Seismic Design Categories B, C, D, E, and F. For Seismic Design Categories B and C, IBC 2000 proposed equivalent lateral-load force procedure shall be used. A more rigorous analysis is permitted, too. However, for Seismic Design Categories D, E, and F, the analysis procedures are identified in

To compute the natural period, the actual structure may be conveniently represented by a system of masses and massless springs, with additional resistances provided to account for energy losses due to friction, hysteresis, and other forms of damping. In simple cases, the masses may be set equal to the actual masses; otherwise, equivalent masses may have to be computed (Art. 5.18.6). The spring constants are the ratios of forces to deflections. For example, a single mass on a spring (Fig. 5.108b) may represent a simply supported beam with mass that may be considered negligible compared with the load W at midspan (Fig. 5.108a). The spring constant k should be set equal to the load that produces a unit deflection at midspan; thus, k  48EI/L3, where E is the modulus of elasticity, psi; I the moment of inertia, in4; and L the span, in, of the beam. The idealized mass equals W/g, where W is the weight of the load, lb, and g is the acceleration due to gravity, 386 in / s2. Also, a single mass on a spring (Fig. 5.108d) may represent the rigid frame in Fig. 5.108c. In that case, k  2
12EI/h3, where I is the moment of inertia, in4, of each column and h the column height, in. The idealized mass equals the sum of the masses on the girder and the girder mass. (Weight of columns and walls is assumed negligible.) The spring and mass in Fig. 5.108b and d form a one-degree system. The degree of a system is determined by the least number of coordinates needed to define the positions of its components. In Fig. 5.108, only the coordinate y is needed to locate the mass and determine the state of the spring. In a two-degree system, such as one comprising two masses connected to each other and to the ground by springs and capable of movement in only one direction, two coordinates are required to

1.397E/F , u P
1.40td F (8.28) n au where da
average diameter, in, of the arc spot weld at midthickness of sheet
d  t for a single sheet
d  2t for multiple sheets (not more than four lapped sheets over a supporting member) d
visible diameter of outer surface of arc spot weld, in de
effective diameter of fused area, in
0.7d  1.5t  0.55d t
total combined base steel thickness, in (exclusive of coatings) of sheets involved in shear transfer Fxx
stress-level designation in AWS electrode classification, ksi Fu
tensile strength of the base steel as specified, ksi The distance measured in the line of force from the centerline of a weld to the nearest edge of an adjacent weld or to the end of the connected part toward which the force is directed should be at least e , in, as given by min e
e (8.29) min e where e
P/ (Fu t) e
factor of safety for sheet tearing
2.0 when Fu /F 1.08 sy
2.22 when Fu /Fsy  1.08 P
force transmitted by weld, kips Fsy
yield strength of sheet steel, ksi, as specified t
thickness of thinnest connected sheet, in In addition, the distance from the centerline of any weld to the end or boundary of the connected member should be at least 1.5d. In no case should the clear distance between welds and the end of the member be less than d. The nominal tension load Pn, kips, on an arc spot weld between a sheet and a supporting member should be computed as the smaller of either: P
0.785d2F (8.30a) n exx