| GENERAL (Section 1) |
Last Update: 2/17/12
Question: Does the Standard apply to the design of antennas? |
Response: The TIA-222-G Standard applies to the design and manufacturing of both structures and antennas.
(1.1) February 17, 2012 |
Last Update: 1/5/12
Question: Do we have to do a structural analysis on wooden poles? |
Response: TIA-222-G addresses all communication structures regardless of the material used.
(1.2) January 5, 2012 |
| LOADS (Section 2) |
Last Update: 7/30/12
Question: As everyone is aware, many jurisdictions are now adopting the IBC 2012, which has updated wind speed maps. Regarding TIA-222-G, can the converted (Vasd) wind speeds from the IBC 2012 be used instead of the wind speeds listed in TIA-222-G, or do we need to take the more stringent of the two? I know this gets a little tricky when the risk category/structure class is something other than II, since the importance factors in TIA are more elaborate (wind speed with no ice, with ice, ice weight) than those in the IBC (who simply provide a number for the wind speed with no ice). We do a lot of work on the Atlantic coastline, and these changes would be most beneficial to our clients. Any interpretation of this would be greatly appreciated. |
Response: Per TIA-222-G Section 2.6.4.1 the wind maps per ASCE 7-10 may be used to determine the basic wind speeds. The ASCE 7-10 wind maps for Category I, II and III structures include the appropriate load and importance factors based upon the structure classification; therefore, the load factor and importance factor for use with TIA-222-G must be equal to 1.0.
In addition, when ASCE 7-10 basic wind speeds are used, hurricane coastal areas must be considered as Exposure D as an exception to TIA-222-G Section 2.6.9.1 which allows the use of exposure C for hurricane coastal areas. ASCE 7-10 wind speeds have been reduced in the hurricane coastal areas based on new research. In addition, hurricane coastal areas are now considered as exposure D based on research which has indicated that the roughness of the ocean is more representative of exposure D conditions.
In the current version of revision G and previous versions of ASCE 7 the roughness of the ocean was believed to be more representative of exposure C conditions.
(1.0) July 30, 2012 |
Last Update: 6/8/12
Question: Section 2.6.6 (2.6.6.1 and 2.6.6.2) My colleagues and I have been discussing the proper method of determining which topographic category to apply to a given site. Sections 2.6.6.1 and 2.6.6.2 are somewhat vague as to the correct method of approach. For example, section 2.6.6.2 subsection 2 reads, "The hill, ridge or escarpment protrudes by a factor of two or more above the average height of the surrounding terrain features within a 2 mile radius." The word "surrounding" seems to suggest that only features around the central feature and not the central feature itself are included in "the average height." Is this correct?
Also, in determining this average height, are all surrounding peaks in a two mile radius included, or only those along the lines of multiple wind directions? For example, we have encountered locations in which using the average height of surrounding peaks to determine the topographic category yields a category 1. However, along a particular 2 mile upwind path the topography clearly suggests a category 3 or 4. Should the topographic category be determined based on a single wind direction, i.e. that of the worst case scenario?
In the case that one considers only a particular wind direction, should the topographic features be considered only in the 2 mile upwind segment, or should the entire 4 miles (2 miles upwind + 2 miles downwind) be used?
Are the peak heights of the surrounding terrain features measured from the lowest point within the two mile radius? I restated and numbered each of my questions below to make them easier to reference in your response.
1.) In section 2.6.6.2 subsection 2, the word "surrounding" Seems to suggest that only features around the central feature and not the central feature itself are included in "the average height." Is this correct?
2.) In determining this average height, are all surrounding peaks in a two mile radius included, or only those along the path of a particular wind direction?
3.) Should the topographic category be determined based on a single wind direction, i.e., that of the worst case scenario?
4.) In the case that one considers only a particular wind direction should the topographic features be considered only in the 2 mile upwind segment, or should the entire 4 miles (2 miles upwind + 2 miles downwind) be used?
5.) Are the peak heights of the surrounding terrain features measured from the lowest point within the two mile radius?
6.) Should the base of a crest height measurement be taken from that point where the slope exceeds 0.10 or from the base of the feature itself?
7.) Finally, Section 2.6.6.1 seems to indicate that wind speed-up effects need only be taken into account if all four conditions are met. Is this correct? |
Response:
1. Yes
2. The surrounding peaks along the path of each wind direction considered shall be used. ASCE 7 may be used as a guide for a specific site.
3. Each wind direction must be considered to determine the direction that results in the maximum response per Section 2.6.9.
4. The topographic features in the two mile upwind direction shall be considered.
5. The peak heights of the surrounding terrain and the central feature shall be determined from the lowest point within the surrounding terrain.
6. The base of a crest height measurement shall be taken from the base of the feature.
7. Yes
(1.7) June 8, 2012 |
Last Update: 6/7/12
Question: I would like an interpretation as to what Gh should be used for attaching antenna mounts to existing building walls and for figuring ballast for roof top antenna mounts. I've been using 1.35 and then paying the price when evaluating the ballast impact on the roof structure. The first paragraph talks about mounting to flexible structures. The second paragraph talks about using the Gh for the parent structure. Most buildings we encounter have height width rations of much less than 5. |
Response: In accordance with TIA-222-G Section 2.6.9 a gust factor of 1.0 and a directionality factor per Table 2-2 shall be used for roof mounted appurtenances. The TIA standard does not specifically address wind speed up for appurtenances mounted on roof top structures; however, ASCE 7 provides guidance to address this issue. Section 2.6.7.4 was not intended for antenna mounts on roof tops.
(1.0) June 7, 2012 |
Last Update: 6/7/12
Question: Is there reciprocity between ANSI/TIA-222-G and CSA S37-01? In other words, if a tower is designed to CSA S37-01, does it also meet ANSI/TIA-222-G Standard? And vice versa? |
Response: There is not reciprocity between the two Standards.
(1.0) June 7, 2012 |
Last Update: 5/1/12
Question: While considering the appurtenance load including ice in Rev G, should we consider the default ice thickness or the escalated design ice thickness calculated per Section 2.6.8 of TIA-222-G? |
Response: Section 2.6.8 and Figure 2-1 require the use of the escalated ice thickness when computing the effective projected area of an appurtenance.
(1.1) May 1, 2012 |
Last Update 5/1/12
Question: For square towers: How can we calculate the DF and DR factors for other wind directions? |
Response: The intent of the Standard is to investigate wind loading at 30 degree increments for triangular cross sections and 45 degree increments for square cross sections. The Df and Dr values for these directions are provided in the Standard. The intent of the Standard when other increments are desired to be investigated is that engineering judgment will be required to determine appropriate Df and Dr values.
(1.1) May 1, 2012 |
Last Update: 3/27/12
Question: Can I use loading that is less than the values prescribed by the written TIA-222-G and claim compliance with the standard? If so, under what conditions? |
Response: The standard provides force coefficients for basic appurtenance shapes as provided in Table 2-8 and for generic microwave antennas as provided in Annex C. Antennas and other discrete appurtenances with complex shapes may be idealized by the simple shapes provided in the standard or may be determined using Wind Tunnel testing, CFD computations or other rational methods that may result in lower force coefficients.
TIA-222-G specifically provides standard prescribed methods to calculate the Effective Projected Area of combinations of appurtenances commonly used for antennas supporting structures. These methods include the many factors not easily taken into consideration in design such as shielding, dynamic loads, etc. The intent of the Standard is not to allow the use of other methods that result in less loading than these prescribed methods.
(1.0) March 27, 2012 |
Last Update: 3/27/12
Question: Is it acceptable to use the results of Computational Fluid Dynamics (CFD) testing as a substitute to the requirements outlined in section 2.6.9.2? If so, what conditions must be meet? If so, can we claim the tower is compliant with TIA-222-G if the wind tunnel data is used? |
Response: Many variables affect the outcome of CFD computations. CFD computations are theoretical models that do not include all of the complex interdependent issues and variables that exist with actual installations. TIA-222-G specifically provides standard prescribed methods to calculate the Effective Projected Area of combinations of appurtenances commonly used for antennas supporting structures.
These methods include the many factors not easily taken into consideration in design such as shielding, dynamic loads, etc. The standard methods listed represent the minimum acceptable values. Other methods shall not be used to justify lower EPA values. If there are data that indicate the methods outlined in the Standard can be improved, these data should be submitted and approved by the committee and revisions to the Standard will be considered.
The above is in regard to calculating wind loads from groups of appurtenances such as mounting frames, ring mounts, panel antennas, etc. and their interaction with the supporting structure, transmission lines, etc. CFD computations may be performed for antennas and other discrete appurtenances with complex shapes as indicated in Section 2.6.9.2 for microwave antennas and other discrete appurtenances.
(1.0) March 27,2012 |
Last Update: 3/27/12
Question: Is it acceptable to use the results of wind tunnel testing as an acceptable substitute to the requirements outlined in section 2.6.9.2? If so, what conditions must be meet? If so, can we claim the tower is compliant with TIA-222-G if the wind tunnel data is used? |
Response: Many variables affect the outcome of wind tunnel testing. Wind tunnel tests do not include all of the complex interdependent issues and variables that exist with actual installations. TIA-222-G specifically provides standard prescribed methods to calculate the Effective Projected Area of combinations of appurtenances commonly used for antennas supporting structures. These methods include the many factors not easily taken into consideration in design such as shielding, dynamic loads, etc. The standard methods listed represent the minimum acceptable values. Other methods shall not be used to justify lower EPA values.
If there are data that indicate the methods outlined in the Standard can be improved, these data should be submitted and approved by the committee and revisions to the Standard will be considered. The above is in regard to calculating wind loads from groups of appurtenances such as mounting frames, ring mounts, panel antennas, etc. and their interaction with the supporting structure, transmission lines, etc. Wind tunnel testing may be performed for antennas and other discrete appurtenances with complex shapes as indicated in Section 2.6.9.2 for microwave antennas and other discrete appurtenances.
(1.0) March 27, 2012 |
Last Update: 3/27/12
Question: What does the term “In the absence of more accurate data” mean? |
Response: The standard provides force coefficients for basic appurtenance shapes as provided in Table 2-8 and for generic microwave antennas as provided in Annex C. For other shapes Wind Tunnel testing, CFD computations or other rational methods may be performed for antennas and other discrete appurtenances with complex shapes.
The intent of the wording in the Standard "In the absence of more accurate data" is to allow determination of force coefficients for individual discrete appurtenances using other rational methods.
(1.1) March 27, 2012 |
| DESIGN STRENGTH OF STRUCTURAL STEEL (Section 4) |
Last Update: 3/27/12
Question: I knew this table 4-8 is used to calculate the polygonal tubular member yield stresses. Note 1. indicated "For polygonal members, w/t shall not exceed 2.14(E/Fy)^(1/2)". I saw other engineers still using the table to calculate the pole yield stress even the w/t ratio exceeds 2.14(E/Fy)^(1/2) limit. My understanding is once the w/t limit exceed, the pole will have local buckling issues and the pole will be failing. I just want to make sure there is not any addendum to the standard so the local bucking can be ignored. |
Response: There is no other addendum. The yield strength required for nominal strength may be substituted for the minimum yield strength of the material in the maximum w/t expression.
(1.1) March 27, 2012 |
Last Update: 2/17/12
Question: Is it acceptable to ignore the 0.9 upper limit on the shear lag factor specified in TIA-222-G Section 4.6.3.2 in order to get the full benefit allowed by AISC Steel Construction Manual, 13th Edition, Section D3.3 for shapes that meet the criteria of Table D3.1, Case 2?
The 0.9 upper limit is conservative compared to AISC and is unnecessary. My particular concern is with channel shapes, but this applies to other shapes as well. For channels where only the web is connected by fasteners, Case 2 in Table D3.1 is appropriate for calculating the shear lag factor as it is for bolted connections and excludes only plates and HSS. Case 7, which does provide for an upper limit, may be used as an ALTERNATIVE for W, M, S, and HP members and their T-shapes. However, the table does not require Case 7 to be used.
In fact, Case 7 specifies that “the larger value (of Case 2 and Case 7) is permitted to be used.” This is reiterated in the commentary (AISC-13 p.16.1-253), which states that Cases 7 and 8 “are now given as alternate U values to the value determined from 1-x/l given for Case 2 in Table D3.1.
It is permissible to use the larger of the two values.” Therefore, TIA-222 should not set an upper limit on the shear lag factor since it is not limited in AISC. An example is attached that shows a channel bolted to a pole with a long connection. Because the connection is very long in order to develop the full capacity of the member, the calculated shear lag factor is 0.971.
TIA-222-G currently penalizes the strength of this member by imposing a maximum shear lag factor of 0.9. |
Response: TIA-222-G Section 4.6.3.2 was not intended to apply to unique connections such as the submitted channel connection with an extended connection length. Per Section 4.1 Scope, the intent of the Standard is to apply the provisions of AISC for unique connections that are not within the scope of the Standard.
(1.3) February 17, 2012 |
| INSULATORS (Section 8) |
Last Update: 1/5/12
Question: What is the technical basis of the resistance factors in section 8.2? |
Response: The values were established based on consensus taking into account the load factors of the standard compared to the safety factors used for ASD designs, comparisons to the strength reduction factors for guys (section7.6.20) and comparisons to other Limit States Design (LRFD) Standards such as CSA S37-01 and consultation with insulator manufacturers.
(1.1) January 5, 2012 |
| EXISTING STRUCTURES (Section 15) |
Last Update: 6/7/12
Question: Section 15.5 indicated "A feasibility report shall state that final acceptance of changed conditions shall be based upon a rigorous structural analysis". I would like to confirm my interpretation regards this section. Does it mean for any equipment upgrade on the tower, a rigorous analysis is required? If the rigorous analysis is required, then the reactions comparison for foundation capacity is not enough? A site-specific geotechnical and foundation data are required? A lot of the clients are questioning why a rigorous analysis is needed for anybody to go on the tower. Why the reactions comparison is not adequate? |
| Response: A rigorous structural analysis is only required for significant changes as defined in Section 15.4. When foundation details are missing, associated assumptions must be documented along with the results of a rigorous structural analysis in accordance with Section 15.5.2. It is not within the scope of the Standard to determine the significance of the assumptions made for a rigorous analysis for a specific structure. (1.0) June 7, 2012 |
| DESIGN CRITERIA MAPS (Appendix 1) |
Last Update: 3/26/12
Question: Why were the tables and Note 3 removed from the figures? |
Response: The table was a unit conversion table. This lead to confusion. Some interpreted the table to represent load combinations. The table listed conversion from Imperial to Metric units. Since conversions were provided in Annex M the tables were removed to avoid confusion.
Removal of the tables had no impact on the design ice thickness and basic wind speed to use for a given location. The ice thickness zones are indicated by solid lines and wind speed zones are indicated by dotted lines. The tables cannot be used as a substitute for the values indicated on the maps. The wind speeds adjacent to ice thicknesses in the conversion tables are irrelevant.
The data is simply presented from lowest to highest value and does not specify the wind speed appropriate to consider with a given design ice thickness. Again, it is important to note that the table is literally a conversion of values, i.e. 1.25 in. is 31.8 mm and separately 70 mph converts to 31 m/s. It was never intended to be a “load.”
For example, it should not be considered a load combination that requires the user to select a 70 mph wind when considering an ice load of 1.25 inches. Each column is a separate conversion list, not a load combination.
(1.0) March 26, 2012
|
| QUESTIONS IN TIA 222-F |
Last Update: 3/28/11
Question: For triangular towers: How can we calculate the Df for other wind directions such as 30 and 45 degrees? |
Response: The intent of the Standard is to investigate wind loading at 30 degree increments for triangular cross sections and 45 degree increments for square cross sections. The Df and Dr values for these directions are provided in the Standard. The intent of the Standard when other increments are desired to be investigated is that engineering judgment will be required to determine appropriate Df and Dr values.
(1.0) March 28, 2011 |
Last Update: 3/28/11
Question: How can we include the CaAa with ½” ice for dipoles and yagi’s? |
Response: Section 2.3.10 of Revision F provides a defined method for computing the effective projected area of appurtenances including antennas. In addition, Section 2.6.9.2 of Revision G provides a comprehensive approach for determining the effective projected area of appurtenances. The intent of the Standard is to allow the use of the Revision G provisions for determining effective projected areas for a Revision F analysis.
(1.0) March 28, 2011 |
Last Update 3/28/11
Question: Some antenna manufacturers provide flat equivalent area and few of them just provide the dimensions. How can we address the CaAa without ice and with ½” ice for discrete appurtenance without flat equivalent area known? |
Response: Section 2.3.10 of Revision F provides a defined method for computing the effective projected area of appurtenances including antennas. In addition, Section 2.6.9.2 of Revision G provides a comprehensive approach for determining the effective projected area of appurtenances. The intent of the Standard is to allow the use of the Revision G provisions for determining effective projected areas for a Revision F analysis.
(1.0) March 28, 2011 |
