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CITY OF SANTA ANA Planning and Building Agency Seismic uirements for Bulldina S FOR PERMITROMMNCE The simplified design procedure of the 1997 UBC, the 2000 IBC and the 2003 IBC is iot found in the 2006 IBC, the 2009 IBC or ASCE 7-05. Instead, a new complete set of simplified seismic design requirements is placed in the stand-alone Section 12.14 of AS aster ID: 7-05. The applicability of the simplified procedure is clearlydefined through a list (6ate: limitations. The simplified procedure is limited in its applicability to simple and redund int structures falling under Occupancy Categories I and H, not exceeding three stories in hei where the seismic force -resisting elements are arranged in a torsion -resistant, regular layout. Furthermore, only bearing wall and building frame systems are allowed to be designed by this procedure. Moment frames are excluded from the simplified procedure because the simplified procedure does not require a drift check as part of the design and drift is a major concern for moment frames. The simplified design procedure allows interstory drift to be taken as 1.0 percent of story height when an estimation of drift is required for determining structural separations or to meet specific design requirements. For easier and faster navigation, parts of ASCE 7-05 Table 12.2-1 are reproduced as Table 12.14-1, to provide the R-values for only the structural systems that are permitted to be designed by the simplified method. However, Table 12.14-1 does not include values for the System Overstrength Factor, 920, and the Deflection Amplification Factor, Ca, because the simplified analysis procedure uses a blanket 2.5 value for 920 or all permitted structures, while not requiring any drift calculation using Cd. Furthermore, equations are reproduced in thin ' 0 icati a Overstrength Factor, 00, in the a uation ' _ .5, while g is taken I.Q. Also because only sim le for ' s t structures are oermitte . seismic inn --- shear of simplified analysis varies (ASCE 7-05 Equation 12.14-11) with the building height and is 20 percent higher than the upper -bound design base shear of the equivalent lateral force procedure for a three-story building. The importance factor, I, is equal to 1.0, since only Occupancy I and II structures may be designed by this procedure. Also, because only short -period structures may be designed by this procedure, the upper -bound design base shear governs. As noted previously, the response modification factor, R, to be used when utilizing this method is given in Table 12.14-1. The vertical distribution of the design base shear is simpler than that given by ASCE 7-05 Section 12.8. The lateral force at a floor level is proportional to the weight at that floor level. When all the floors in a building support equal weight, the distribution of V along the height of the building is uniform. For horizontal distribution of the lateral loads, the simplified analysis permits diaphragms constructed of untopped steel decking, wood structural panels, or similar light -framed construction to be considered flexible. This essentially eliminates the need to calculate diaphragm deflections for these types of systems. As mentioned before, no drift limitation is imposed and no drift calculation is necessary, because only short and stiff structures are permitted to be designed by the simplified procedure. However, a design drift, where needed to estimate the necessary building separation, etc., is allowed to be taken as 1 percent of the building height. Application of the simplified design procedure is illustrated in Example 16-9, Part 2 of this chapter. It may be instructive to compare the simplified seismic design procedures of the 1997 UBC, particularly since the 1997 UBC procedure, with not very substantive modifications, was retained through the 2003 IBC. The slight differences between the 1997 UBC procedure and the 2000 and 2003 IBC procedure are pointed out at the end of the comparison. Limitations on the use of the respective procedures are and were given in ASCE Section 12.14.1.1 and UBC Section 1629.8.2. The limitations were fewer and less stringent in the UBC. The simplified design base shear Equation 12.14-1 1 of ASCE 7-05 and Formula (30-1 1) of the 1997 UBC are the same, if one uses the conversion: SD.S = 2.5C„ except that the constant 1.2 of the UBC is replaced by the variable F in ASCE 7-05, which is 1.2 for three-story buildings, but lesser for shorter buildings. ASCE 7 allows the Structural Provisions 149