Read Voters Comments text version

American Society of Civil Engineers

ASCE/SEI 7-10 Minimum Design Loads for Buildings and Other Structures - Public Comment

Public Voter Comments Ballot Closing: November 30, 2009

Ballot Item 23 Approve Revisions to Chapter 26, Wind Loads - General Requirements

Affirm With Comment

Staff Note: In accordance with the ASCE Rules for Standards Committees a ballot need not be conducted to formally resolve comments submitted as "Affirm with Comment" unless the comments result in substantial changes to the provisions of the standard. Hence no further action is required by the standards committee for comments below whose resolution has been determined to be "nonpersuasive."

Coulbourne, William Section 26.5.1 and Figures 26.5.1a, b, c Change the word Occupancy on the maps to Risk Category Either add sub-maps for each risk category map with details for the various parts of the Atlantic and Gulf Coasts as currently exist in ASCE7-05 or add a link to a web site where wind speeds can be obtained by zip code or some other easy way for practitioners to obtain the design wind speed. The current maps shown as Figures 26.5.1a, b, c are unreadable for design purposes and pdfs of these files will be no better. Resolution: Persuasive Editorial the change suggested regarding "occupancy" will be made for consistency with Chapter 1 of ASCE 710. Please see the responses above regarding the readability of the maps. No further action is required during this revision cycle. Keyes, Conrad The following sections need more than just common units: 26.2 Hurricane Prone Regions 26.7.3 Exposure B for 30ft 26.9.1.1 for 300 ft Eq. 26.9-5 and 26.9-11 and 26.11-1 26.10.3 Chapter 26 figures mostly only have common units; therefore it seems that they need to have a source unless the conversion for velocity is also placed on the figures somewhere. Resolution: Persuasive Editorial during the overall editing of the standard in preparation for printing all of the figures, tables, equations and text will be reviewed for the possible edition of SI

Page 1 of 14

units where feasible. Shackelford, Randall HURRICANE PRONE REGION: The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed per Figure 26.5.1a is greater than 115 mi/h, and... Change "for Risk Category II buildings" to "per Figure 26.5.1a". To me that is clearer, the existing wording may leave the user to wonder what to do if their building is not Risk Category II. Resolution: Persuasive Editorial The wording will be revised as follows: The U.S. Atlantic Ocean and Gulf od Mexico coasts where the basic wind speed from Figure 26.5.1a for Risk Category II buildings is greater ... 26.5.3, second paragraph, second line, delete "(1)". Needs to be deleted since (2) has been deleted entirely. Resolution: Persuasive Editorial revise as follows: In hurricaneprone regions, wind speeds derived from simulation techniques shall only be used in lieu of the basic wind speeds given in Figure 26.5.1 when (1) approved simulation... Table 26.1-1 In title, change "ASCE 7-05" to "ASCE 7-10" Resolution: Persuasive Editorial revise as suggested. 26.7.2. I know you are not balloting the Commentary, but be sure to revise the caption on the picture of the power plant on the shoreline to match the new Exposure D definition. Resolution: Persuasive Editorial revise as suggested. Tezak, E Scott The wind maps presented in Figure 26.5.1a, b, and c should be presented as the large US map, and with regional maps as currently presented in ASCE 7-05 (Chapter 6). Currently, only 3 large maps are provided. Providing 3 regional maps for each larger map would greatly improve the ability of the design professionals to use the maps. Resolution: Editorial please see the responses above. No further action is required during this revision

cycle to resolve this comment.

The tornado wind speed map in presented in Figure 26.5.4 used to be (and currently still is) presented in the Commentary for this Chapter for informational purposes only. It is not introduced in Chapter 26, Section 5, nor is it used for design purposes therefore it should be removed from the standard and remain in the commentary. Resolution: Persuasive, Editorial this figure on "tornadic gust wind speeds" should remain in the

Page 2 of 14

commentary. In Section 26.4.4, the minimum wind pressures for roofs and walls can be calculated per this chapter and are presented in Chapter 26 Commentary Figure C26.4.7. For concurrence with the standard, the 10 psf values for minimum pressures in the commentary figure remain from the ASCE 7-05 values; these values should be updated to reflect the minimum pressures set forth in Chapter 26. Resolution: Persuasive, Editorial revise as suggested. Also, several figures and tables are still numbered for Chapter 6 (of ASCE 7-05). Please revise the figure and table numbers to correspond with the new chapter numbering scheme. Resolution: Persuasive Editorial. This change will be made. Negative Guirguis, Magdy Figure 6-4 is indicated to be applicable to Method 2 only, whereas it also applies to Method 1, since the definition of the symbol Kzt under equation 6-1 refers to section of 6.5.7 in method 2. Resolution: Persuasive, Editorial Delete "Method 2" from the heading on both pages of Fig. 26.8.2 for Kzt. Harris, Benchmark I can understand the motivation for the changes to the wind speed maps. However, I believe the changes to Chapters 2 and 26 regarding the wind loads and load combinations will most definitely create life safety issues. I realize the new speeds are higher. And, I realize that the fine print within ASCE 7-10 will appear to be "self-contained". However, it is highly likely in reality that many unsuspecting designers will inadvertently use the lower load factors from ASCE 7-10 Chapter 2 in concert with the older maps which have the lower loads...creating life safety issues. This could happen by a number of mechanisms that I do not believe ASCE 7 has soberly considered. For example, there are many reference standards, guides, textbooks, and software that are based on "Basic Wind Speeds" defined by ASCE 7-05. I, for one, do not want my children walking in and around buildings that may be underdesigned by as much as 33%! I have personal knowledge, as do many others accross the country, of the extreme confusion and inappropriately underdesigned structures which resulted when these very same wind speed maps changed from fastest mile to 3 second gust. In other words, I can guarantee this life safety concern is legitimate. I have many "mental scars" from that period of time dealing with engineers, architects, building officials, contractors and owners who for many years after the change eventually caught a clue as to what happened, realizing their errors too late. I do not even see anything on the maps that is convenenient nomenclature such as we had in changing from "fastest mile" versus "3 second gust" to help in educating the public. In addition, I believe it will be even more difficult to educate the public this time because if you ask them if they know about the change in wind speed, they will say "yes"

Page 3 of 14

because they learned only several years ago about the change to 3 second gust speeds. This will retard the education process associated with this "new" change. The timing of these changes to wind speeds is completely inappropriate because of the recent changes in the IBC reference standard adoption process. If ASCE 7 wanted to truly act in the best interest of the public, ASCE 7 would notify all material standards of the intent to change these wind speeds at least one code cycle before implementing them so that all of these committees may be prepared to update their referenced standards accordingly. ASCE 7 did not do this until the changes were balloted with too little time for all these other standards to react because the IBC standard adoption schedule has significantly decreased the time allowed for the 2012 IBC. If ASCE waited until next cycle, all these other standards could not only react...but also react in time for adoption by the IBC. The risk of these life safety concerns far outweighs the technical reasons that ASCE 7 may wish to implement the changes. For example, the rational from ASCE 7 regarding these changes does not improve life safety at all. Furthermore, the change of the importance factor is not consistent with those for other loads...undermining the whole principle driving the changes in the first place. In addition, the use of several different maps rather than a factor is unnecessarily onerous for the designer, who now must reference a different map for each structure based on occupancy, each of which must be verified by local building officials...rather than simply multiplying a known importance factor by a benchmark value on a single figure. I believe ASCE 7 could have easily increased the wind speeds without creating this burden. And finally, I don't believe ASCE 7 has considered the effect of these changes with regard to the meteorological reporting methods used today. The public and everyone in the construction industry have "calibrated" their experience with measurements from past events. This change will disrupt the continuity of that experience, potentially leading designers and researchers into errors. To address my negative comment, I suggest ASCE 7 not implement these changes at all. If that is unacceptable, I suggest ASCE 7 not implement these changes until the next cycle and notify all material standards used by the IBC of this intent. If ASCE 7 cannot deign to have any pity on us poor commoners who have to actually use this code, I at least suggest that ASCE 7 have the wherewithal to throw us a bone and editorially give us some kind of nomenclature on the figures to clearly designate the difference between the new speeds and the previous speeds...such as "Strength Design" wind speeds or "Factored" or at least a notation about the history of the changes from fastest mile to 3 second gust and now this change. As a side note, I think I'm going to buy stock in wind speeds! Resolution: Previously considered ­ nonpersuasive, editorial clarifications as noted. Several issues raised in the comment may be able to be addressed editorially. Specifically, the addition of a "user note" in Chapter 2 alerting users to use the combinations only with the loads determined in accordance with this standard may be of assistance in preventing the "mixing and matching" of loads and load combinations described in the comment. Likewise, an editorial change in the nomenclature from "V" to "Vult" will be considered.

Page 4 of 14

As to the timing of the changes and coordination with the material standards, it should be noted that all of the major material standards (steel, concrete, masonry and wood) are involved with both the ASCE 7 Main Committee and the ASCE 7 Wind Load Subcommittee in different ways in accordance with their own preference. The specific change to an ultimate event wind speed has been discussed within the ASCE 7 committee for approximately the past 10 years and that the actual change within ASCE 7 was introduced in the committee over 2 years ago. Unfortunately though one certainly would hope otherwise, the coordination among standards and documents referencing or utilizing the standards is less robust than desired. The suggestion to use a single factor to adjust the wind speeds simply isn't technically correct and if implemented would unfairly penalize areas whose wind speeds are currently significantly above the perceived 50year MRI of the current map. The membership of ASCE 7, the Wind Load Subcommittee and the ASCE/SEI leadership in general are aware of and try diligently to be attuned to the problems encountered by the profession in the adoption and use of the new wind speed maps and all of the provisions of ASCE 7. In addition to the variety of guides and continuing education courses that are available, SEI is pursuing the posting of wind load design examples for free on their website as well a series of new webinars and local presentations regarding the changes to ASCE 7. As these concerns have been discussed, balloted upon and previously found to be nonpersuasive, no further action in required in this revision cycle to resolve this comment. Lai, James 1 26.5 Wind hazard map - Revise to read: "The basic wind speed, V, used in the determination of design wind loads on buildings and other structures shall be as given in Figure 26.5.1a, except as provided in Section 26.5.2 and 26.5.3. [delete the balance of this paragraph." Reason: This provision provides three wind speed maps fig. 26.5.1 a, b and c. Proposed deletion of the I-factor and replacement of it with three "Risk Category/ Occupancy Category" wind speed maps is an unneeded increase in complication of the provisions that will create even more confusion for designers. It also creates complication for determining the wind speeds to use for the different "Risk/Occupancy" categories in special wind-speed zones. Resolution: Previously considered: The apparent desire by the commenter to base the determination of wind loads upon a single map has been discussed extensively within both the WLSC and the ASCE 7 MC with the view expressed by the commenter found to be nonpersuasive. Discussed in detail in the commentary of ASCE 710, the change to ultimate event maps rather than MRI maps was driven primarily by the desire to provide an approximately uniform level of safety to the public. By utilizing a single MRImap along with a single value of the load factor associated with the wind load, a situation was created whereby the true design return period and hence safety, varied greatly because the slope of the hazard curves varied greatly. The commentator is referred to the commentary of Chapter 26. No further action is required to resolve this comment during this revision cycle.

Page 5 of 14

2. 26.5.1 Basic wind speed - The contours maps are too small a scale to be of practical use. Restore the I factor and use only wind speed map based on risk category 2 occupancy. Reason: Basis of development of the hazard map has not been justified. The proposed maps would give 115 mph wind speed in Risk Category III and IV and 110 mph in Risk category II in most of the west coast. The relative ratio of force level is 1.09 or a direct reduction of the importance factor from 1.15 to 1.09. This may be unintended reduction, but the risk of damage has not been established for various risk categories, and the reduction of risk for risk category III and IV buildings. Resolution: Previously considered and Editorial. Regarding the desire to return to a single wind speed map, please see the response to the response to the previous comment by Lai. The issue of the maps being too small is editorial in nature and is being addressed in three different ways. First, the maps in ASCE 710 will be printed across two separate pages thereby increasing their size. Secondly, it is intended that PDF versions of the maps will be posted on the SEI website thereby permitting users to "zoom" in on their area of interest a note of the available will be added editorially. And finally, efforts are underway to develop online versions of the maps to permit a user to input a longitude and latitude and receive back a table of wind speeds for their consideration. This third option is heavily dependent upon the availability of sufficient funding but is none the less being pursued. 3. 26.9.2 Approximate natural frequency - Delete this section in its entirety. Reason: Proposed equations 26.9-2 through 26.9-5 do not correspond to period equation in chapter 12 of this Provision, and do not represent variations in building stiffness and actual building behavior in the West coast. The equations belong in commentary to this section as viable means to determine approximate natural frequency in seismic SDC A or B only. Resolution: Nonpersuasive ­ previously considered These approximate frequencies are intentionally different than those in the seismic provisions. In wind, it is necessary to underestimate a natural frequency (i.e. overestimate the period) in order to conservatively determine the response from wind. In, seismic the opposite is true. The reliance upon the method for determining period within Chapter 12 was raised and found nonpersuasive during the committee deliberations so no further action is required for the resolution of this comment during this revision cycle. Midlam, Lewis The definitions of "open", "partially enclosed" and "enclosed" are logically flawed. Consider a simple building with four walls and a roof. Each wall has openings totaling 70% of that wall's surface area. Since the total of the openings in each wall does not exceed 80%, this building does not meet the definition of an "open" building. And, since the openings in any wall does not exceed 110% of the gross openings in the other walls, this building does not meet the definition of a "partially enclosed" building. Therefor, this building would have to be designed and constructed as an "enclosed" building. This flies in the face of logic to define such as building as "Enclosed". Resolution: New business This problem has existed for several cycles, it is not associated with ASCE710 changes. It has been considered in past committee discussions but not resolved.

Page 6 of 14

Suggested language and definition changes would be welcome. This comment addresses a portion of the standard that was not modified during the revision cycle and hence essentially constitutes a new proposal. The Wind Load Subcommittee will place this issue on its agenda for consideration during the next revision cycle of the standard. Scott, Paul I am voting negative on the wind changes because the entire wind code provisions have evolved into a monster of a code!! I will be sending Lew a proposed wind code for buildings 60 feet or less in height ( it's the old Phoenix code provisions from the mid 1980's). As a compromise position I am OK using the very very complicated wind analysis as in the proposed draft for buildings over 60 feet tall. The amount of time that has been spent by engineers and plans examiners desperately trying to understand the wind is both ridiculous and sad. Our time should be spent designing and detailing the buildings...not on determining if the wind is 14.1 psf or 14.5 psf! THE CODE SHOULD BE LIKE A BOY SCOUT KNOT...EASY TO TIE AND EASY TO UNTIE. The wind provisions of the code have lost any sense of "easy to tie and easy to untie" and measures should be taken to change this now. My negative can be resolved by adopting , as an option to the code , the mid 1980's Phoenix code provisions for buildings 60 feet or less in height. I think if design engineers and plans examiners were polled , the response would at least 90% for my proposal. The "optional" code is about a page and a half long and it was easy to use and check...just like a Boy Scout knot! Thank You Paul Scott S.E.

STAFF NOTE: This copyrighted material is available upon request. If you wish to review this material, please send an email request to Lee Kusek, Codes and Standards Administrator, at [email protected]

Resolution: Previously considered. The desire expressed by this comment for greater clarity of the wind load provisions is shared by many members of ASCE 7. A substantial portion of the effort of the Wind Load Subcommittee and the ASCE 7 Main Committee during this revision cycle has been spent on attempting to reformat and present the wind load provisions in such a manner as to be clearer and easier to use with the result being the introduction of an entirely new "simplified" method that is applicable for buildings up to 160 feet in height. In approving the reformatted wind provisions comments calling for a single value or a return to decades old approaches as expressed by this comment were voted upon and found to be nonpersuasive in support of the various forms of "simplified" methods now embodied in the standard. As the issues presented in the comment have been extensively discussed by both the WLSC and the ASCE 7 MC no further action is required during this revision cycle. Valancius, Joseph As a member of the Structural Engineers Association of Southern California (SEAOSC) ad-hoc wind committee, I have been asked to submit this public comment regarding Figures 26.5.1 a through c (Ultimate Design Basic Wind Speed Maps). SEAOSC is concerned about the special wind regions in the ASCE 7-10 ultimate design wind speed maps. Based on the information we have gathered, it

Page 7 of 14

appears that the special wind regions originated in the 1982 ANSI A58.1 standard and may have been placed on the map by a single meteorologist. Further, we have been informed that with the exception of the deletion of the special wind regions around the shores of the Great Lakes and in the Seattle/Tacoma area, there has been no further evaluation of these wind regions since their development 27 years ago. Despite the fact that no data has been developed that would have affected the location of the regions, the shapes, sizes, and locations of the regions have been morphing over time, presumably due to data loss as the regions are copied from map to subsequent map. I am providing scans of the various maps in chronologic order so that you can see the progression of the regions over time. No such changes to the special wind regions occurred in the Uniform Building Code, which governed wind design in California for decades. Obviously, significant changes in the special wind regions have occurred over the last 27 years. While a complete overhaul of these regions is probably in order for ASCE 7-15 (including a more detailed look at whether some of these areas have now been accounted for by the topographic factor (Kzt) since the development of the regions in 1982), we would like to get the maps corrected as much as possible for incorporation into ASCE 7-10 and the 2012 IBC, particularly in the western states, more particularly in California, (and most particularly in Los Angeles County). In our review of the maps, it appears that Los Angeles appears to have been inadvertently added to the special wind regions between the 1993 and 1995 editions of ASCE 7. Until the adoption of the IBC in California, practicing engineers do not appear to have had any reason to check the ASCE maps in the area of Los Angeles until now, since the governing code was the UBC, which very closely matches the 1982 ANSI wind regions and never incorporated the graphical error that now appears to be in ASCE 7. The SEAOSC ad-hoc wind committee hasn't uncovered any evidence that a special wind region is required for this large area of Los Angeles County and we haven't found any evidence that the special wind region was added intentionally... We've been in contact with Peter Vickery, Don Scott, and Jon Peterka as well as other highly knowledgeable wind experts and no one has any evidence that the inclusion of LA County was deliberate or deliberated. Right now, we have building officials who are mandating what appears to be an unjustified 40% increase in design forces (from 85 mph to 100 mph in terms of the 3-second ASD basic wind speed) simply because they see the special wind region over all of southern LA County. This all seems to be stemming from a simple graphical error 12 years ago. Please note that we will also be submitting a request for interpretation that will ask specifically what data (if any) was used to justify dramatically expanding the special wind regions in California from the 1993 to the 1995 editions of ASCE 7; we will ask whether any reputable data exists that would justify increased design wind speeds in Los Angeles County (and in particular in the Los Angeles Basin). The SEAOSC ad-hoc wind committee has amassed a significant amount of meteorological data, none of which appears to support the need for a special wind region over the greater Los Angeles area; we would be happy to share that data with the ASCE 7 Committee. Please do not hesitate to contact either me or Gary Searer, the ad-hoc committee chair, at (818) 303-1300. We look forward to working with you regarding this issue. Sincerely, Joseph Valancius, S.E. Resolution: New business. The issues raised in this comment pertain to a portion of the basic wind

Page 8 of 14

speed maps that is unchanged from previous editions and hence essentially constitutes a new proposal for revising the standard. This item will be placed on the agenda of the Wind Load Subcommittee for the next revision cycle. No further action is required to resolve this comment during the current revision of ASCE 7. Wilson, Garland Exposure Categories require ground and topographical informatin that is not readily available to a design office. Additionally, this factor has now become too complicated. For example, if a structure is on the ocean shore, is it surface roughness C or D? The Risk Categories are too vague and leave too much room for individual interpretation. Resolution: Nonresponsive, previously considered 26.10 deals with Enclosure Classification not Exposure Category or Risk Category. For info on Exposure Category, the only change has been the need to consider water surfaces in hurricane zones for Exposure D. The design professional needs to be aware of the surroundings for the structure being designed or if in doubt use the most conservative condition. As to the vagueness of the Risk Categories, this comment has been previously considered by the committee during deliberations on the revisions by the General Provisions Subcommittee (expressed as the desire to retain the bulleted list) and been found non persuasive.

Additional Comments Received Unassociated with a Specific Ballot

Staff Note: As these comments were not associated with a specific ballot they fall outside of the regular process for resolution. However, all of the comments have been reviewed with a resolution as noted however no further action is required unless noted. Scott, Donald NCSEA Wind Committee ASCE 7 2010 Public Review Comments:

Section # Comment Editorial Technical Proponent

26.1

Need clearer description of when Chapter 27 should be used for calculating wind loads and when Chapter 28 should be used for calculating wind load. There will be significant initial confusion.

X

JS

NonPersuasive No alternate language submitted.

26.2 Definitions for variables required to determine enclosure are included in Building, Open and Building, Partially Enclosed and in Section 26.3. No need to repeat. Other similar conditions exist. X JS

NonPersuasive There is no change from what was ASCE 705. For clarity some notation is provided in

Page 9 of 14

the 26.2 definitions and then listed specifically in 26.3 symbols and notation. Could be considered as newbusiness.

26.2 Definition of Building, Torsionally Regular Under Wind Load needs to be clarified. Is displacement assessed in X Y directions or SRSS? X JS & DP

NonPersuasive XY direction loads are covered in Fig 27.4.6 Case 1 for comparison to Case 3 displacements in the same direction.

26.2 Definitions Building, Simple Diaphragm. Definition does not make sense and should be reworded. X JO

NonPersuasive No alternate language submitted.

26.2 Definitions Building, Simple Diaphragm. Definition does not match wording used in various other sections. (i.e., 27.5.1) X DS & JO

Persuasive, Editorial The wording in 27.5.1 will be revised to refer to the definition in 26.2 as is now done in 28.6.2 as follows: 27.5.1 Design Procedure. The design procedure specified herein applies to the MWFRS of enclosed simple diaphragm buildings as defined in Section 26.2 with a mean roof height h 160 ft where both windward and leeward wind loads are transmitted only by roof elements and vertically spanning wall elements through continuous floor and roof diaphragms to the MWFRS.

26.5.2 & 26.5.3 With the transition to the new three map system the required recurrence interval for the different risk categories is not clearly indicated. Thus the building official is not given clear direction on what recurrence interval to use. X JO

Persuasive Editorial, The titles of all the maps, including those in the serviceability appendix, will be revised to reflect both the MRI and probability of exceedance.

26.5.3 With the elimination of Note 2 in the second paragraph the indication of Note 1 can be eliminated. X DS

Persuasive, Editorial revise as follows: In hurricane prone regions, wind speeds derived from simulation techniques shall only be used in lieu of the basic wind speeds given in Figure 26.5.1 when (1) approved

Page 10 of 14

simulation...

26.5.3 The reference to a minimum recurrence interval needs to be included in this section. X JO

NonPersuasive No alternate language submitted.

26.7 The word "facilities" at the end of the sentence yields the impression that this needs to be a building or similar structure for human occupancy. Propose using the word "object" instead to account for signs, walls and similar structures. X DS

Persuasive, Editorial revise as suggested.

26.7.2 For Surface Roughness C all reference to "water surfaces" has been removed. Depending on the fetch of the "water surface" it still can be classified as Surface Roughness C. X DS

This item is taken care of as noted below.

26.7.2 The reference to water surfaces in Category C have been removed. The commentary describes the reasoning for removing this statement; however it is felt that the statement should be moved from category C to category D in the body of the code to alert the user to the change. X JO

This item is taken care of as noted below.

26.7.2 Surface Roughness D. This section has been reworded, and it appears that the intent is the same. However, it is still difficult to interpret the requirements. X JO

This item is taken care of as noted below.

26.9.1 Natural frequency is to be determined in each direction, which implies the structure can be classified as flexible in one direction and rigid in another. Different wind load provisions could then be used for each direction, or should flexible provisions be used for both? The scoping statements for each of the various procedures, i.e. flexible vs. rigid, should be modified to limit the use of the procedures to the most restrictive. X JS

Persuasive Editorial It was determined that the most consistent wording to accomplish what the proponent is suggesting is to modify the text as follows. "26.9.1 Frequency Determination. To determine whether a building or structure is rigid or flexible as defined in Section 26.2, the fundamental natural frequency, n1, in the direction under

Page 11 of 14

consideration shall be established using the structural properties and deformational characteristics of the resisting elements in a properly substantiated analysis. Low Rise Buildings, as defined in Section 26.2, less than or equal to 60 feet in height are permitted to be considered rigid."

26.9.1 The last sentence in this section indicates that "all" building less than or equal to 60' in height are permitted to be considered rigid. For certain situations this can be a nonconservative assumption. It is proposed that this statement be removed or qualified. X DS

Persuasive, Editorial The words "lowrise" will be used instead of "regular". See item above.

26.10.3.1 In the last paragraph of this section the use of "occupancy" category should be revised to "risk" category. This mix of terms occurs throughout the wind chapters. X JS

Persuasive, Editorial a search and replace will be performed to delete "occupancy" and substitute "risk".

26.10.3.2 In the last paragraph of this section the use of "occupancy" category should be revised to "risk" category. This mix of terms occurs throughout the wind chapters. X JS

Persuasive, Editorial a search and replace will be performed to delete "occupancy" and substitute "risk".

26.11.1 "...Table 26.11.1..." is noted in the code for selection of GCpi, however this should be "Figure 26.11.1." X JO

Persuasive, Editorial revise as suggested however the content of Fig. 26.11.1 is in actuality the "table" of internal pressure coefficients hence Fig. 26.11.1 will be retitled as Table 26.11.1 with corresponding changes in the text.

Figures 26.5.1a, b & c Basic Wind Speed Maps: The larger scaled maps for the hurricane coastlines have not been included. We would request that the larger maps be included in ASCE 710 due to the close spacing of the wind speed contours along the hurricane coastlines. This will require the inclusion of (9) additional maps total. X JO

Page 12 of 14

Nonpersuasive, Editorial see previous responses.

Figures 26.5.1a, b & c

The term "Occupancy Category" in the titles should be revised to "Risk Category."

X

JS

Persuasive, Editorial revise as suggested.

Figure 26.5.4 This figure is not referenced in the body of the chapter and appears to have been moved from the commentary. Should this figure remain in the commentary? X JO

Persuasive, Editorial this figure on "tornadic gust wind speeds" should remain in the commentary and will be renumbered and cited accordingly.

Figure 26.8.2 The figure number on the 2nd page of this figure should be revised from "Figure 64 (cont'd)" to "Figure 26.8.2 (cont'd)". X DS

Persuasive, Editorial revise as suggested.

Figure 26.11.1 The figure number should be revised from "Figure 65" to "Figure 26.11.1." X DS

Persuasive, Editorial revise as suggested.

Figure 26.11.1 Note 2 The reference to Section 6.5.12 is incorrect. It should be revised to Sections 27.4 and 28.4. X DS

Persuasive, Editorial revise as suggested. Scott, Donald (Representing the NCSEA Wind Comm.) 26.5.3 ESTIMATION OF BASIC WIND SPEEDS FROM REGIONAL CLIMATIC DATA. In areas outside hurricane prone regions, regional climatic data shall only be used in lieu of the basic wind speeds given in Figure 26.5.1 when (1) approved extreme value statistical analysis procedures have been employed in reducing the data; and (2) the length of record, sampling error, averaging time, anemometer height, data quality, and terrain exposure of the anemometer have been taken into account. Reduction in basic wind speed below that of Figures 26.5.1 shall be permitted. In hurricane prone regions, wind speeds derived from simulation techniques shall only be used in lieu of the basic wind speeds given in Figure 26.5.1 when (1) approved simulation and extreme value statistical analysis procedures are used (the use of regional wind speed data obtained from anemometers is not permitted to define the hurricane wind speed risk along the Gulf and Atlantic coasts, the Caribbean, or Hawaii). In areas outside hurricane prone regions, when the basic wind speed is estimated from regional

Page 13 of 14

climatic data, the basic wind speed shall be not less than the wind speed associated with the specified mean recurrence interval defined in Figure 26.5.1 for each Risk Category building and structure, and the estimate shall be adjusted for equivalence to a 3s gust wind speed at 33 ft (10 m) above ground in exposure Category C. The data analysis shall be performed in accordance with this chapter." REASON FOR PROPOSAL: In the previous edition, the required recurrence interval for determining the wind speed was defined in this section. With the change to the three map system, a specific location would now have three different recurrence intervals based on the building or structure risk category. Reference should be made to the recurrence intervals required in determining the wind speed for each risk category, which are defined in the notes for figures 26.5.1a-c. Persuasive, Editorial revise as suggested. 26.7 EXPOSURE For each wind direction considered, the upwind exposure category shall be based on ground surface roughness that is determined from natural topography, vegetation, and constructed facilities objects. REASON FOR PROPOSAL: The term facility tends to indicate a building or structure constructed for human occupancy or a large complex of buildings or structures. Objects is a more generic term that encompasses such structures as signs, towers, fences, or other non-occupied structures that should be considered in the determination of the exposure category. Persuasive, Editorial revise as suggested. 26.9.1 FREQUENCY DETERMINATION. To determine whether a building or structure is rigid or flexible as defined in Section 26.2, the natural frequency, n1, in the direction under consideration shall be established using the structural properties and deformational characteristics of the resisting elements in a properly substantiated analysis. Regular-shaped Bbuildings less than or equal to 60 feet in height are permitted to be considered rigid. REASON FOR PROPOSAL: The inclusion of the term "regular-shaped" (which is defined in Section 26.2) removes the possibility of an unusually shaped building being defined as rigid when it should be considered flexible. Persuasive, Editorial The words "lowrise" will be used instead of "regular". See item above. Additional Material Valancius, Joseph See Maps of Special Wind Regions (.pdf)

Page 14 of 14

Information

Voters Comments

14 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

32316


You might also be interested in

BETA
Voters Comments