ESICS: Bracket Checker
This article is an overall overview of the ESICS Bracket checker. It will thoroughly explain every input and input variation also the system and MAFI components chosen by the user. The purpose of the ESCIS Bracket checker calculator is to help the user design/check the MAFI brackets used in a system. Currently, the calculator supports all the locations in Europe and all calculations are in accordance with the Eurocode and the appropriate national annex. This report is in conjunction with the ESICS Wind Calculations report which thoroughly explains the wind calculations in the ESICS calculators. The Bracket Checker calculator is designed to perform calculations for the most common bracket systems and it may not adhere to every possible bracketry system available. For this purpose, proper warning messages prompt the user and notify them of the program's limitations as they input their data. More information on the calculator's limitations and capabilities will be explained in Section 1.
1.0 Calculator Capabilities and Limitations
The ESICS Bracket Checker can perform calculations for 3 different categories of brackets, an offset bracket that can hold one offset pole, a symmetrical bracket that can hold two offset poles and an antenna offset that does not support any offset poles and only supports one antenna. Figure 1 demonstrates the maximum equipment (antennas, RRUs and dishes) that can be supported by each bracket category.
Figure 1. Maximum Equipment Supported based on Bracket Category.
The number of brackets can vary from two to six. However, for some bracket types, this number can be limited. For example, for antenna brackets, the number of brackets allowed is two since there are only two slots available on the antenna to hook the antenna to the brackets. The type of main parent pole structure can be pole, square and angle. This input is also dependent on the bracket type. Keep in mind that all of the limitations above are warned to the users in the Bracket Checker. Figure 2 demonstrates an error message prompt to the user for a wrong number of brackets input.
Figure 2. Error Message Prompt to the User.
Note that currently the calculator does not support two antennas on one pole and equipment on the parent pole for antenna offset and symmetrical brackets.
All the inputs in the Bracket Checker are pre-determined with default values. Default values demonstrate the most common and simplest case for a bracket system. The user can change these values based on their project specifications. Here is a list of the four important input sections. All of these input sections are explained thoroughly in the following sections
- Antenna Properties
- Equipment Properties
- Bracket Properties
- Pole properties
2.1 Antenna Properties
In this section, the user can define the type and the number of antennas for their design. The antenna selector lets the user choose between more than 180 antenna types. Figure 2, demonstrates the Antenna selector of the Bracket Checker Calculator. For choosing 2 antennas the user has to select a symmetrical bracket in the bracket properties section. After choosing the right symmetrical bracket, the user is then prompted to another antenna type selector for the second antenna (antenna 2) located on the second pole.
** Figure 2. Antenna Selector of the Bracket Checker Calculator**
Note that if the user cannot find their antenna in the antenna selector they can choose "custom" at the bottom of the list as shown in Figure 3. Once the user selects custom as their antenna type, a table is prompted to the user that allows the user to define the geometric properties of the custom antenna.
Figure 3. Custom Antenna Selection Process
In the Antenna Properties section, the user also has to define an antenna orientation. This is a very important feature since it is later used for calculating the coordinates and the forces on the antenna. Figure 4 is an image that demonstrates an example of the orientation of the antenna. As seen in Figure 4 antenna orientation is the orientation of the front of the antenna in the clockwise direction where 0 degrees is the true North.
**Figure 4. Orientation of Antenna **
2.2 Equipment Properties
In the Equipment Properties section, the user defines the number of dishes and RRUs and which pole they will be supported by. Also, the user can define the geometric properties of the dishes and RRUS using the RRU and dish properties tables. Figure 5 demonstrates the Equipment on Offset Poles table with one RRU and one dish supported by offset pole 1. Note that the user can’t mount RRUs or dishes on a poleless mount, so for brackets like the 3115 (antenna offsets) the number of equipment is zero
The calculator assumes that the RRUs will be supported on one of the MAFI RRU-mount families of kits. The offsets used in the calculation are worked out from the dimensions of the various kits and the dimensions entered for the RRUs themselves.
Figure 5. Equipment on Offset Poles Table
2.3 Bracket Properties
Helping the user select the best MAFI Bracket is the ultimate goal of this calculator therefore the bracket properties section is a very important input section of the Bracket Checker calculator. This section starts by asking the user the type of bracket they would like to choose by prompting them to a selector as shown in Figure 6. At the right side of the selector, the utilization checks help the user decide which bracket best suits their system. Once the user is happy with their selection they can preview the bracket image and also its properties in the bracket properties table. The default value of the number of brackets selected for the bracket checker is two brackets however if the design is failing for the bracket of choice the user can add more brackets by changing the number of brackets. It is not recommended to select higher than 6 brackets and it is not possible to select more than this number. With the exception of the 311X series, each additional bracket arm will add a weight capacity equal to the bracket arm capacity + 80kg. A pair of bracket arms has a built-in capacity for a 160kg rigger, but more than one rigger is not expected to be present, so the spare capacity is used for increasing the permitted equipment load.
Figure 6. Bracket Type Selector
The orientation and the direction of the bracket are two other important inputs that help with the calculation of the forces on the brackets, Therefore careful consideration shall be given to these values. Figure 7 demonstrates the orientation of an offset bracket when the bracket is located 100 degrees clockwise from True North. Note If using a symmetric bracket, consider the Antenna 1 arm as the bracket orientation vector.
Figure 7. Orientation of Bracket
The direction of the brackets could be a tricky concept to comprehend. The user has to imagine the direction of the offset pole as it is rotating anticlockwise (A) or clockwise (B) around the parent pole. Figure 8 demonstrates an example of the direction of the bracket. Note that this input plays a very critical role in determining the coordinates of the antennas and equipment.
Figure. 8. Example Direction of Bracekt
The Offset distance of poles is also important information that should be carefully selected. As seen in Figure 9 the offset distance is the horizontal distance between the parent pole and the offset pole and it could vary depending on the location of the hook which is holding the offset pole.
Figure 9. Offset Distance of Offset Bracket
2.4 Pole Properties
In this section, the user can assign properties such as type, and diameter to the parent pole and offset poles. the length of the offset pole is also prompted to the user solely to calculate the weight of the offset pole supported by the bracket and parent pole. The default value of the length of the offset pole is set to 2500 mm but the user can change this value in 500 mm increments. keep in mind that once a symmetrical bracket is selected the same properties are assigned to both offset pole one and offset pole two. The user also can choose the type of the main parent structure between, pole, angle and square. This selection is dependent on the type of bracket. You can check this information in the "Bracket Type" debug mode (Figure 10) where all the properties of the bracket are explained.
Figure 10. Bracket Type Debug Mode
2.5 Bracket on a Bracket
The bracket-on-a-bracket feature of the bracket checker allows the user to design an arrangement with a symmetric bracket being held by an inner bracket as seen in Figure 11.
Figure 11. Example Bracket-on-a-Bracket System
To activate this feature the user has to select a symmetrical bracket in the bracket selector. Once a symmetrical bracket is selected this toggle shown in Figure 12 is prompted to the user asking them whether they would like to design a bracket-on-a-bracket system. As the bracket-on-a-bracket arrangement is selected, another set of bracket properties inputs is visible to the user that will define the properties of the inner bracket.
**Figure 12. Bracket-on-a-Bracket Toggle **
3.0 Calculation of forces
Considerable effort has been put into the curation of the ESICS wind force calculations. ESICS Deliberately calculates the wind forces on the entire bracket system using the maximum peak velocity pressure qp(z) calculated in accordance with EN-1991-1-4 2005. Please take a look at the ESICS Wind Calculations article for more information on how the maximum peak velocity pressure qp(z) is calculated.
3.1 Methodology for Calculating the Forces and Torques
As mentioned in the ESICS Wind calculation article, the peak velocity pressure is calculated in all twelve directions. ESICS uses these values to calculate the forces and torques in all twelve directions and then selects the maximum for the result summary. This method is complex and an immense amount of analysis has been performed by the engineers at ClearCalcs to identify the different force situations and geometries that every bracket system may have. Therefore the detailed methodology of the calculation of forces and torques is out of the scope of this report. However, a simple calculation of the forces on an antenna is provided for any user that is interested to understand the analysis procedure at the end of this report.
4.0 Summary of Results
the summary section on the left-hand side of the calculator demonstrates all the capacity utilization and structural checks that the Bracket Checker performs for the user. The summary starts with a simple weight utilization check which is mainly used to identify whether the number of brackets used is enough for the proposed design. Then the user can check the torque and horizontal bending capacity of the offset and main parent poles. Note that if the utilization checks are not to the user's satisfaction or are higher than expected, they can reduce the loading (equipment) on the system or choose a stiffer pole. Utilization above 100% means failing.
5.0 Example Force Calculation on an Antenna