Monthly Archives: February 2013

Tower Install – Day 5 “Concrete Pour”

Today was the day of the big pour. The weather was bright and sunny as it’s been for this entire project. This is somewhat unusual for Northern California in winter, as the weather is usually rainy or overcast.

The concrete was scheduled to arrive at noon, so the first order of business was to build the temporary wooden forms around the excavation. The only purpose of these forms is to make the above ground concrete pad look pretty. None of the form extends underground — the concrete is poured against undisturbed soil. Since the forms are temporary and will be removed when the concrete cures, they went together quickly and everything was ready for the arrival of the concrete crew and pumper crew.

Form Form Completed and Ready for Concrete

The tower foundation is quite large and measurements revealed that it would require around 25 cubic yards of concrete to fill. This is three full truck loads plus another partial load to top it off. That’s a lot of concrete — it weighs around 100,000 pounds. Our house is at the top of a steep, narrow private road with no room to turn around at the top, so the trucks had to back up the hill.

mixer First Cement Truck Arrives

The tower site has restricted access, so it wasn’t possible to back the trucks up to the hole for a straight pour so we had to hire a concrete pump to get the concrete to where it needed to be. The cement truck and pumper stayed out on the road and pumped the concrete through a 4″ rubber pipe that snaked through the fence and around the house to the tower.

pumper Cement Truck and Pumper

Once the concrete started flowing, one of the crew directed the flow to the bottom of the hole, while the others moved the concrete around with shovels and another used a “stinger” to vibrate the concrete to ensure it was free of voids. The whole process went quickly.

pouring Starting to Pour

pouring2 Halfway Done

Once the hole was filled, the crew used 2x4s to level the surface and floats to smooth it. This took some time as the crew had to wait until the concrete set enough so it would hold its shape. The nearly final result looks like this:

done Smoothing the Surface

Now comes the wait until the concrete cures enough to erect the tower. Then the real fun begins, but that’s a topic for another blog entry.

I wonder if my current antenna, a vertical dipole, knows its days are numbered? It’s served me well on 20M for the past several years but will soon be relegated to a back up 40M antenna.

dipole N6BT Vertical Dipole

Tower Install – Day 4 “Final Assembly and Inspection”

We finished up the last remaining tasks on the tower assembly today, including drilling the rotator plate and top plate and mounting the rotator adapter and Rohn thrust bearing. We also installed the climbing bolts, which are used to climb the tower. Climbing without them would be difficult due to the layout of the diagonal braces.

After that, we tightened all of the tower bolts while pulling the tower sections together with a come-along to ensure everything was straight and true.

The County inspector arrived in the afternoon to inspect the foundation excavation and rebar work. He consulted the plans and measured the hole to verify compliance with the design and then signed off.

The next step is pouring the concrete, which should happen next week, followed by waiting for it to cure.

No pictures today.

Tower Install – Day 3 “Rebar and Tower Assembly”

The tower installation continued today after a three week hiatus. We made up for it, however, getting the rebar work completed and about 95% of the tower assembled.

The large size of the foundation (11′ x 11′ x 5′) necessitated quite a large rebar cage be built and installed in the excavation. This in turn required rebar of several different sizes.

Rebar Rebar Awaiting Installation

The three man rebar crew cut, bent, and wired the cage together in record time and by the end of the day everything was finished.

FirstLayer First Layer of Rebar in Place

RebarComplete Rebar Work Completed

While the rebar work was underway at the site of the tower foundation, Steve, his two helpers, and I assembled the tower itself. The tower consists of six separate 10′ sections that bolt together to form the 60′ height. Each section consists of three vertical members along with cross bracing. Both the vertical members and cross bracing are formed from sheet steel, so assembling the sections is perfectly analogous to the erector sets we had as kids. The pieces bolt together in a horizontal position and we did the work in the driveway in front of the garages.

Section1 First Tower Section Assembled

The first section took almost 1-1/2 hours to assemble, and much of that was reading the instructions and interpreting some of the more subtle aspects of the process. Once we completed the first section, we progressed much faster. The last two sections were assembled in just an hour. Steve and I marked and drilled the rotator plate and top plate while the last section was being assembled. These nestle inside the last section and are secured by beefy bolts. These plates are 1/4″ steel and massive overkill for their intended function.

TowerComplete Tower Assembly Nearly Complete

We didn’t complete the top plate drilling as our cordless drill batteries gave out. We’ll finish up assembly tomorrow, when we complete the installation of the drilled top plate and then tighten up all of the fasteners (all of the tower bolts are just finger tight at this point) while making sure everything is nice and straight.

Another big milestone happening tomorrow is the first inspection. The County inspector will inspect the rebar work and sign off, giving us the go-ahead for the next step, which is pouring the concrete. This will probably happen sometime next week — stay tuned. Then comes the really exciting part: grabbing the tower with a crane, lifting it over the garages, and bolting it to the base embedded in concrete.