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Home My WebLink AboutAdministrative Permit APX2009015 - Supporting Documentsree-standing walls, typically of concrete or masonry construction, have numerous functions such as separating adjoining properties, screening service areas, and protecting pools. N_o permit or inspection is required for such walls 6 feet or less in height per the 2006 International Building Code (IBC) Section 105.2. However, how is a free-standing wall greater than 6 feet in height designed for seismic forces? Should the wall be considered a nonstructural component and designed in accordance with 2005 American Society of Civil Engineers/ Structural Engineering Institute's Minimum Design Loads for Buildings and Other Structures (AS CE 7-05) Chapter 13, or should it be considered a nonbuilding structure and designed in accordance with ASCE 7-05 Chapter 15? Answers to FA(ls It is surprising the code doesn't directly address some- thing as common as a free-standing wall, yet there is no clear answer to the question of how to design these elements for seismic forces. -Now is a free-standing wall greater than.6 feet in height designed for seismic forces? Should the .wall be considered a nonstructural component, or should it be considered a nonbuilding structure? In the 1997 Uniform Building Code (UBC), there is a -verydear-cut entry for "masonry or concrete fences over 6 fee_ t high" in Table 16-0, Item 2.H, where an ap = 1.0 and an = 3.0 are specified. Unfortunately, such a clear-cut entry is_ not in ASCE 7-05 Table 13.5-1. F : ;However, the entry "Wall Element" under "Exterior Jon-structural Wall Elements and Connections " in ASCE :-05.Table 13.5-2 may be interpreted as an applicable entry for_"masonry or concrete fences over 6 feet high." And the corresponding ap = 1.0 and Rp = 2.5 are in line with values specified in the 1997 UBC. In this case, the seismic load '%st- .,applieduniformly along the height of the wall with the Y=_ _resultant load applied at mid-height. 7thers may interpret Table 15.4-2 as being applicable in 's situation. The entry, which reads, "All other steel and orced concret d mass cantileverditibt t turesesruesrucnot "covered herein including stacks, chimneys, silos, and :supported vertical vessels that are not similar to build- Structural Engineer APRIL 2009 ings," most closely matches a free-standing wall, and an R = 3.0 is assigned. In this case, Chapter 15 dictates a triangular vertical distribution of the seismic load with the resultant load at a height of 2/3 the wall height above grade. When compared with the Chapter 13 design, Chapter 15 results in a slightly higher moment at the wall base, which would govern the design of the footing and the wall rein- forcing near the base of the wall. This matter has been brought to the attention of those involved in making revisions to ASCE 7-05 seismic provi- sions, and hbgefully iin the next edition, there will be an entry in Table 15.4-2 for free-standing walls with an R = 3.0. The issue of whether an item should be treated as a non- structuralcomponent or a nonbuilding structure for purposes of seismic design comes up not only for free-standing walls, but for a host of other items. The following list of additional items can be considered either nonstructural components or nonbuilding structures: billboards and signs, bins, chim- neys, conveyors, cooling towers, stacks, tanks, towers, and vessels. When in doubt, the designer always has the option of calculating the force demand in accordance with the nonstructural component equation in ASCE 7-05 Chapter 13 and the nonbuilding structure equation in ASCE7-05 Chapter 15 and using the more conservative design. The design force equation for nonstructural compo- nents is indirectly dependent on the period of the item (is it-flexible or rigid?), whereas the design force equation of nonbuilding structures is directly dependent on the period of the structure. For nonstructural components, the period of the item affects the determination of the amplification factor, ap. Because of differences in the form of the two sets of equations and the defined parameters, they can yield quite different results. A comprehensive article by Robert Bachman and Susan Dowty discussing ways to differenti- ate between the nonstructural components and nonbuild- ing structures is available at www.skghoshassociates.com/- sk-publication/ Bachman,Dowty_reprint.pdf. v S.K. Ghosh Associates Inc., is a structural seismic, and code con- sulting firm located in Palatine, Ill., and Also Viejo, Calif. President S.K. Ghosh, Ph.D., and Susan Dowty, S.E., are active in the development and interpretation of national structural code provi- sions. They can be contacted at skghosh@aol.com and susandowty@ gmail.com, respectively, or at www.skghoshassociates.com. www,gostructu ral.com ik Engineering Alignment Systems, Inc. 1913 East 17th Street, Suite 203 Santa Ana, CA 92705 Tel: 714-664-8991 Fax: 714-664-8913 August 18, 2009 Department of Building and Safety 2000 Main Street Huntington Beach, CA. 92648 Re: Permit #82009-001134 & 1135 Residence at 8341 Elmcrest Lane Waiver of CMU Fence Height To Whom It May Concern: A forty foot section of the CMU wall exceeds 6'-0" in height and rests at approximately 6'-6". The additional wall height is a decorative cap block that occurs at the wall's step down. Upon review, the additional six inches in height does not affect the walls structural integrity. If you have any questions please do not hesitate to contact our office. Very truly yours, Engineering Alignment Systems, Inc. Martin A. Muska, SE, SECB Principal Attachment: 1. Wall Photograph 2. Foundation Plan 3. Calculation File: Copy f! S' ;.9 HuntingtonpE, PLp,NrdING Elmcrest Lane 8341 Elmcrest Lane Map produced by information contained in the City of Huntington Beach Information Services Department Geographic Information System. Information warranted for City use only. Huntington Beach does not guarantee its completeness or accuracy. Map Produced on 9/22/2009 N 0 29 One inch equals 29 feet 58 ADDRESSES A STREET NAMES CITY BOUNDARY At STREET CENTERLINES (OCTACIass) Smartstreet rJ Major Collector Primary Secondary Residential Travelway Alley ISOBATHS CM-rajP- MAO 0 CODE S`1' PLE By S. K. Ghosh, Ph.D., and Susan Dowty, S.E. ree-standing walls, typically of concrete or masonry construction, have numerous functions such as separating adjoining properties, screening service U areas, and protecting pools. No permit or inspection is required for such walls 6 feet or less in height per the 2006 International Building Code (IBC) Section 105.2. However, how is a free-standing wall greater than 6 feet in height designed for seismic forces? Should the wall be considered a nonstructural component and designed in accordance with 2005 American Society of Civil Engineers! Structural Engineering Institute 's Minimum Design Loads for Buildings and Other Structures (ASCE 7-05) Chapter 13, or should it be considered a nonbuilding structure and ', designed in accordance with ASCE 7-05 Chapter 15? Answers to FAQs It is surprising the code doesn't directly address some- thing as common as a free-standing wall, yet there is no clear answer to the question of how to design these elements for seismic forces. ow is a free-standing wall greater than.6 feet n height designed for seismic forces? Should the ;wall be considered a nonstructural component, or ould it be considered a nonbuilding structure? -In the 1997 Uniform Building Code (UBC), there is a }veryclear-cut entry for "masonry or concrete fences over 6 eet high" in Table 16-0, Item 2.H, where an as =1.0 and an " `30ifid Uflhl. are spece.nortunatey, suc a cear-cut entry is`not in AS CE 7-05 Table 13.5-1. 9wever, the entry "Wall Element" under "Exterior onsfructural Wall Elements and Connections " in ASCE 053able 13.5-2 may be interpreted as an applicable entry masonry or concrete fences over 6 feet high." And the cotresponding ap = 1.0 and Rp = 2.5 are in line with values cifid i h97 UBC Ihihii lden te 19.n ts case, te sesmcoa _1 applied uniformly along the height of the wall with the 1 y resultant load applied at mid-height. hers may interpret Table 15.4-2 as being applicable in s situation. The entry, which reads, "All other steel and forced concrete distributed mass cantilever structures covered herein including stacks, chimneys, silos, and supported vertical vessels that are not similar to build- tructuralEngineer APRIL 2009 ings," most closely matches a free-standing wall, and an R = 3.0 is assigned. In this case, Chapter 15 dictates a triangular vertical distribution of the seismic load with the resultant load at a height of 2/3 the wall height above grade. When compared with the Chapter 13 design, Chapter 15 results in a slightly higher moment at the wall base, which would govern the design of the footing and the wall rein- forcing near the base of the wall. This matter has been brought to the attention of those involved in making revisions to ASCE 7-05 seismic, provi- sions, and hQgefully n the next edition, there will be an entry in Table 15.4-2 for free-standing walls with an R = 3.0. The issue of whether an item should be treated as a non- structural component or a nonbuilding structure forpurposes of seismic design comes up not only for free-standing walls, but for a host of other items. The following list of additional items can be considered either nonstructural components or nonbuilding structures: billboards and signs, bins, chim- neys, conveyors, cooling towers, stacks, tanks, towers, and vessels. When in doubt, the designer always has the option of calculating the force demand in accordance with the nonstructural component equation in ASCE 7-05 Chapter 13 and the nonbuilding structure equation in ASCE7-05 Chapter 15 and using the more conservative design. The design force equation for nonstructural compo- nents is indirectly dependent on the period of the item (is inflexible or rigid?), whereas the design force equation of nonbuilding structures is directly dependent on the period of the structure. For nonstructural components, the period of the item affects the determination of the amplification factor, ap. Because of differences in the form of the two sets of equations and the defined parameters, they can yield quite different results. A comprehensive article by Robert Bachman and Susan Dowty discussing ways to differenti- ate between the nonstructural components and nonbuild- ing structures is available at wwwskghoshassociates.com/- sk_publication/ Bachman,Dowty _reprint.pdf. v S.K. Ghosh Associates Inc., is a structural seismic, and code con- sulting firm located in Palatine, Ill., and Also Viejo, Calif. President S.K. Ghosh, Ph.D., and Susan Dowty, S.E., are active in the development and interpretation of national structural code provi- sions. They can be contacted at skghosh@aol.com and susandowry@ gmail.com, respectively, or at www.skghoshassociates.com. www.gostructural.com f. k 4l Engineering Alignment Systems, Inc. 1913 East 17th Street, Suite 203 Santa Ana, CA 92705 Tel: 714-664-8991 Fax: 714-664-8913 August 18, 2009 Department of Building and Safety 2000 Main Street Huntington Beach, CA. 92648 Re: Permit #82009-001134 & 1135 Residence at 8341 Elmcrest Lane Waiver of CMU Fence Height To Whom It May Concern: 0 A forty foot section of the CMU wall exceeds 6'-0" in height and rests at approximately 6'-6". The additional wall height is a decorative cap block that occurs at the wall's step down. Upon review, the additional six inches in height does not affect the walls structural integrity. If you have any questions please do not hesitate to contact our office. Very truly yours, Engineering Alignment Systems, Inc. Martin A. Muska, SE, SECB Principal Attachment: 1. Wall Photograph 2. Foundation Plan 3. Calculation File: Copy V16 SL gee NuctiNNNGDEPT