1. Characterization of Irregularities in Existing Tall Buildings in San Francisco using GIS Department of Civil, Environmental and Geomatic Engineering MSc Civil Engineering Cagatay Demirci Supervisor: Carlos Molina Hutt Abstract Since the city of San Francisco has a large number of older structures and because of its proximity to major active faults, it may be considered one of the most seismically cities in the globe. A database of existing tall buildings in downtown San Francisco was developed in previous studies in order to select a representative archetypal tall building that could be used to assess the likely seismic performance of these structures. The database tabulates building characteristics by location, height, number of storeys, year built and lateral system type. This study aims to refine the existing building database and characterize irregularities using GIS technology and determine the effect of irregularities using a computer software GSA. The focus is to characterize irregularities in building shape and height (stiffness irregularity, vertical geometric irregularity, re-entrant corners, torsional irregularities, etc.) and to assess the impact of those irregularities on the performance of existing tall buildings in downtown San Francisco. Structural Models A prototype building was produced in research by Molina Hutt et al. (2012). In this research the prototype building was used in order to compare the strength and deflection parameters between regular and irregular buildings in this research. Based on the irregularities of the tall buildings in San Francisco, 4 irregular buildings were modified. Figure 1. The location of steel moment frame buildings Prototype BuildingModified Building 1 (H1)Modified Building 2 (H2)Modified Building 3 (V1)Modified Building 4 (V2) Design Considerations Stress Check Allowable element stress limits per UBC 73 is 0.6*Fy, therefore the maximum strenghts should be within the parameter as below; Ft = 0.6*248.1 = 148.93 N/mm 2 for beams Ft = 0.6*289.58 = 173.75 N/mm 2 for columns. Deflection Check Since UBC 73 does not include interstory drift limits for the evaluation, the drift limit recommendations from Appendix D of the SEAOC Blue Book are considered, which are 0.0025 for wind loading and 0.005 for seismic loading for seismic for buildings taller than 13 stories. Database In our database, there are more than 200 buildings which are considered as tall and have diverse irregularities in two directions; horizontal (plan) and vertical (stiffness, strength and mass). The Emporis database (www.emporis.com) was used in order to define which buildings in California fall into the category of tall steel moment- frame buildings. As listed in the Table 1 below, since most of the buildings are steel moment frame in our database, the chosen building class is tall steel moment-frame (SMF) buildings in downtown San Francisco. Structural TypeNumber RC Core Walls with Outrigger1 RC Core Walls Steel Gravity2 Dual System RC Wall Steel MF2 RC Moment Frame3 Dual System RC Wall RC MF7 RC Core Walls RC Gravity7 Dual System Steel CBF/EBF Steel MF9 Steel Moment Frame49 Table 1. Classification of structural types in the database Design Verifications of Alternate Buildings The two table below show the first section sizes and the increased section sizes of prototype building in order to meet the strength and IDR limits. Level Range Wide Flange BeamsBuilt-up Box Columns Ext. L=20'Int. L=20'Int. L=40'InteriorExt. Short (x)Ext. Long (y) Base to 10W36x256W36x282W30x12422x22x3.0x3.026x26x3.0x3.020x20x2.5x2.5 11 to 20W33x169W36x194W27x8420x20x2.0x2.026x26x2.5x2.520x20x2.0x2.0 21 to 30W33x118W33x169W27x8418x18x1.0x1.024x24x1.5x1.518x18x1.0x1.0 30 to RoofW24x62W27x84W24x7618x18x0.75x0.7524x24x1.0x1.018x18x0.75x0.75 Table 2. Beam and Column section sizes per UBC 73 Design (Source. Molina Hutt et al., 2012) Level Range Wide Flange BeamsBuilt-up Box Columns Ext. L=20'Int. L=20'Int. L=40'InteriorExt. Short (x)Ext. Long (y) Base to 10W36x247W36x232W36x25626x26x3.0x3.026x26x2.75x2.75 11 to 20W33x291 W33x31824x24x2.0x2.024x24x1.75x1.75 21 to 30W33x241 W33x26324x24x1.5x1.5 30 to RoofW30x132 W30x14824x24x1.0x1.0 Table 3. Increased Beam and Column section sizes per UBC 73 Design Results Stress and Deflection Checks 1. Prototype Building 2. Modified Building 1 (Horizontal 1) 3. Modified Building 3 (Vertical 1) Conclusion and Future Work As a result of this research study, first and foremost the present study strengthened the idea that conventional building codes were not suitable in order to design tall buildings. Secondly horizontally irregular buildings were found more susceptible among others in terms of strength and deflection demands. Therefore, more studies should be conducted for building codes in designing tall buildings and the buildings possessing horizontal (plan) irregularities.