Part 1, this was too long for one post!
I did the best I could and I am open for comment. IF you have input, I would love to hear it. I did most of this from memory, I haven’t done any structurals my self in over 8 years. So if I missed something let me know. Remember that I wanted to do a high level view.
So you have been assigned to beef up a tower? Do you know what the job requires? Do you know what steps you need to take? Do you know what the end plan is? What is going on the tower? So let’s look over the high level view of what is involved in the structural analysis of a tower and other structures that antennas hang on.
First, let me start with a story. I did work for some governments to install wireless data. We were installing hi speed data point to point microwave, full IP radios as well as some DS3 radios. They also wanted some point to multipoint access systems connected to add data to all of their buildings. We thought they would have had the original structural analysis for all of their towers. You know what, for half of them all they had were the original drawings from when the towers were built. You know what was on these towers, mostly dishes and public safety systems. They asked us to run the first structurals on them. It was not easy task, it wasn’t cheap either because all of the towers had to be mapped.
Let me tell you, with the growth of LTE, specifically with the addition of all of the RRHs on the tower, there is a new end to end plan. The structural analysis for the tower is not longer going to wonder if that new platform with the antennas will hold the ice and survive the wind. Now, the RRH is up on the tower. Everyone is adding weight to the tower. At least all the carriers, AT&T Wireless, Verizon Wireless, Sprint, and T-Mobile. Do you remember hearing from Verizon Wireless, (not so long ago) that they would never put the RRH on the tower along with some of the large OEMs like Alcatel Lucent and Ericsson. Well guess what, the game has changed. Now they are all doing it. They are all adding not 1,2, or even 3 to a tower. It will start at 3 but could go up to 9 or even 12. Now, these are 12 outdoor radios that weigh anywhere from 40lbs to 80lbs each. Get ready climbers, they will want you to hang this per the specifications. You may even have to use a crane, but that is another post. This fact has the climbing businesses nervous, and I will tell you why. The towers are already loaded. Carriers need to remove the 2G and 3G equipment and install the LTE equipment just to help the situation, but they can’t wait the old systems down before they install the new systems. So they are going to pile on the weight.
To start, this will add incredible loading to the tower, so let’s begin with the structural analysis. Each tower will need a structural run. Then they will try to see how to lighten the load on the tower. With the growth of fiber, the dishes may be removed if the carriers decide not to use them as a backup. So this will help. Then they need to look at what 2G and 3G equipment that they can remove. This may help. Then they need to look at what they will be adding, and if you are adding 6 RRHs at 50lbs each, 300lbs just for the RRH weight on all sides of the tower. Don’t forget the platform, if they are adding a new platform then add another 300 to 500 lbs. Then the antennas, grounding, jumpers, fiber splice boxes, cables down the tower, and any addition crap you may need. Then you have to account for icing and wind. WOW! That’s going to be a tremendous load! What can you do? You hope the structural analysis tells you what to do and how to beef up the tower.
What is a structural analysis on a tower? I call it a structural and here is a high level of what is done. It begins with research of the tower, the installation, brand name, make, and how it should have been installed. They should have the structural information of when it was installed or if it was done since. Research is a big part of the plan.
Then the team of climbers and maybe a structural engineer will be on site. The structural engineer does not have to be there because they rely on the data. When you build a tower they ask what you plan to add to the tower and the exact location, so you build it to those specifications. So a structural analysis is done at the time it is built. They will take into consideration the loading, the wind in that region, and the weather such as icing, hurricanes, and the soil. It all plays into what is needed to build a tower. This should be left to the experts since they will be held responsible. Trust me, you can’t build a tower anywhere. The soil matters as much as the wind. There is a complete plan here. So the foundation will be so critical to keep the tower upright. Then the tower will be expected to hold all the steel that’s on it in rain, wind, ice, and hurricanes.
However, over time things are added to the tower that cause extra loading. Also, there could be changes in requirements by the FCC that would require an update. Also, let’s not forget that you need to add equipment to the tower. Look at how much things have changed. I will address that later. For now let’s look at a structural analysis. Go to http://web.mscsoftware.com/support/library/conf/wuc93/p03393.pdf and http://www.armortower.com/services/engineering/structural-analysis/1066-ft-guyed-tower-analysis.pdf and look over what one looks like. If it is done properly the structural engineer will have all the details on the steel, the foundation, and everything on the tower. Then they will need to know what the requirements are for that are. Requirements? They would be the wind, ice, loading, and tower details. Also, they do them for smoke stacks, http://www.armortower.com/services/engineering/structural-analysis/smokestack-analysis.pdf and for rooftops, http://www.armortower.com/services/engineering/structural-analysis/rooftop-analysis.pdf. So don’t think it is only towers that get studies done. However the structural engineer should know what he/she is doing for a tower.
Let’s look at wind, it sounds simple, right? Well it’s not. Wind needs to be looked at from several angles. What direction will the force of the wind come from? That makes a huge difference, although they will look at it from all directions. How strong do they expect wind to be in that location? Hurricanes and tornadoes may affect the results. Are they common for that region? Everything you put on the tower increases wind drag! If wind is hitting a flat surface then it puts force on the tower, force that the tower will have to withstand, force that may push the tower over. One piece of steel could really add wind loading to the tower. By the way, most of you have probably climbed in wind or felt the force. I know one guy that got blown off the tower. He was wearing his safety climb and guess what!?! He is alive to talk about how his safety climb saved him! He often talks of that day and how it felt like God pulled him off the tower, he was stunned and had to come down, he could not work the rest of the night. He was doing a change out in a night climb. You must respect the wind because it can kill you! So make sure to be tied off 100% all the time in the air.
What about ice, yes ice, it builds up on a tower. I once had my truck get $5K damage because the ice came pummeling off the tower, and I thought I was far enough away to avoid the ice! Ice builds up on a tower and it can blow around. I have seen it take towers down. Ice is heavy. Ice can build and build on a tower adding so much weight to it. I have had to break ice off of antennas and tower legs. I have seen towers freeze up and then a freak burst of warm air blows through and melts the ice so quickly it starts breaking off, unbelievable to see it but pretty neat all at the same time. I often think that when carriers started putting out the small cabinets they were asking for trouble. That is why there are ice shields to protect small cabinets, cables, dishes, antennas, and anything else near the tower. Ice is heavy and the structural engineer needs to be aware of the loading.
End of part 1, I will send out part 2 next week.
A few notes from Wade4wireless. I am coming out with a wireless field aid book that I think will be helpful. It should be out soon. I also plan to improve this website but I just need the time to do it. I plan to make it look a little better. Remember to like me on Facebook and feel free to post your pictures on my page. I like the tower pictures and the more I have the better. If you are looking to buy something on Amazon take a look at my affiliate link. I am still looking for more information about tower climbing regulation in other countries. I got some great feedback from Australia, thank you Dennis Lundin at http://dennislundin.com/!
Alright everyone, be smart and be safe. Come up with a plan to do both! Then follow the plan. Good action gives good results!