Loading...
HomeMy Public PortalAboutMinutes_City Council Special Meeting_03122019CITY COUNCIL SPECIAL MEETING MARCH 20, 2019— 6:00 P.M. IONA COMMUNITY CENTER PRESENT: Mayor Dan Gubler, Council President Rob Geray, Council Member Peter Wadsworth, Council Member Michael Thompson, Public Works Director Zech Prouse, Officer Chris Hinton, and Treasurer Amy Sullivan. ABSENT: Council Member Kathy McNamara and City Clerk Keri West. VISITORS: Nick Belmont and Kevin Peacock representing DN Tank, Jason South representing Dome Technology, and Forsgren Associates Engineer, David Noel. Mayor Gubler welcomed everyone and Council President Rob Geray led with the Pledge of Allegiance. A roll call was taken to open the meeting. DN Tanks: Kevin Peacock requested to allow some Type III standards to be added to the specs. Mr. Peacock stated that the D 110 and D 115 type tanks that our City Council is currently evaluating have set minimum requirements and these minimum requirements are not because of design loads. The standards say depending on how you pour your concrete that you have to meet certain minimums if you have a pre -cast structure or a cast in place structure. For example, a D115 tank, because of internal wall tube tensioning, requires a 9 inch minimum wall thickness. Post tension wall ducts are embedded in the walls and these need to be well covered. (Kevin Peacock presented a D110 type III tank wall model.) The Type III wall has external pre -stressing instead of having internal ducts. The D 110 type III standard is for a 4 inch minimum wall thickness. Mr. Peacock stated that when looking at preliminary design for our project that a minimum of 5 inch wall thickness would be required. This would be well above what is required by design. What you are going to get is what is appropriate by design for longevity of the tank. Some of the design enhancements of the type III tank are the embedded steel diaphragm (liner) within the concrete structure. Another key element is the anchored flexible base. Walls are able to flex and bend and contract with the daily demand of filling and draining a tank. Over the life time of a tank, fixed solid concrete structures have the potential for micro cracking. We have had great success over decades with the anchored flexible base. Mayor Gubler stated, but the wall is still flexing because it has a base that allows it to move? So regardless of what type of tank it is over time the movement could cause micro fracturing? Mr. Peacock stated that it's how the forces are transferred because when you have a fixed connection there is more stress on the wall. Council Member Wadsworth asked what is the bearing pad product and what do you use to water proof it? 1 Mr. Peacock explained that it's a pad so that you don't have concrete on concrete. It's a PVC water stop material. A couple other benefits of the type III tank is a pre -cast dome (pre -cast roof panels) that are set in place filled with concrete completing it with a waterproof membrane over the top. Public Works Director Prouse asked what type of method DN Tanks uses to compress the dome. Mr. Peacock stated that there is a dome ring that will have additional pre -stressing at the base of the tank where it connects to the wall. Floor thickness: The 4 inch thinner floor slab allows for differential settlement while the thicker floor is more rigid. Idaho Code requires that all structures that are in contact with potable water be compliant with the NSF standards. If you have a concrete structure that is above 350 gallons and the concrete uses certified aggregate measures, no additional testing is required. If this is the case the tank would not have to be lined at an additional cost to the city. Mayor Gubler: Can anyone answer why capacity would have anything to do with that? Mr. Noel: A lower capacity is going to have less dilution of the water so there can be nothing in those ad mixtures that may leach out into the water. So a small tank with a little bit of leaching can be worse than a larger tank. We have some challenges in this area because of the aggregates that are prevalent to this area and having to deal with ASR abatement. There are two ways we can deal with ASR abatement and the best way is with a Type F fly ash. However, fly ash is a by-product and there are no two fly ashes that are chemically absolutely the same. NSF recognizes fly ash as an ad mixture but there are zero fly ash mixtures that are currently NSF certified or that have any history of NSF certification. The benefits of an inside liner is that we can definitely be NSF certified and getting a concrete mix that is NSF certified is going to cost. To get an ASR certified concrete mix the cost would be $10,000. An inside liner is a benefit in keeping a barrier between the concrete and water. In our specs we do not allow for fly ash as a cement substitute. However, we do allow fly ash for ASR abatement as long as it doesn't reduce the cement numbers. Council Member Wadsworth: Question on wall thickness -in concluding with your statements I understand that the suggested 5" wall thickness is because of the backfill and slope. And in the chance of a seismic event and the wall starts to slip 9 inches is thicker than 5 inches. Mr. Peacock stated that they have to evaluate the grade with the slope with the tank empty and with the geotechnical report they will get specific with the design. Council Member Wadsworth stated that our engineering firm that we have hired has suggested that this is what we have so that we have enough reinforcement that if our tank is empty we are still safe. Mr. Belmont stated that whoever the tank manufacturer is would be responsible for the structural design of the tank. Council President Geray: When you ended up with the 5" wall thickness that you mentioned earlier that was your rough estimate, that you needed at least 5" was already dictated by the 2 standard, that you evaluate for the back fill and everything else to make sure that you have the required thickness to be a satisfactory safe tank. Mr. Peacock stated that the standard says a 4" minimum, and based on what we knew at the time, a 5" wall thickness would be the estimated minimum. Council Member Thompson: How do you handle the seams between the pre -cast wall panel cold joints? Mr. Peacock: When you stand up the wall of the pre -cast wall panel, on the outside of the wall panel there's a steel liner (diaphragm) and the slot is 12 inches with a key way to have a good mechanical connection between pre -cast panel and the closure strip. There will also be a steel plate that goes up the entire slot and this is filled with grout. The tank will then also be wrapped to seal up the joints. Council Member Thompson: Does the sealant go bad over time? Mr. Peacock: It's embedded in the concrete and will last for the life of the tank. Dome Technology: Jason South stated that Rexburg chose to build a D110 Tank, a type I tank for a specific reason stating that it was a better quality tank, more durable and more of a life span. There's no question a Type III tank will work but they are not going to perform the same as a solid monolithic reinforced concrete structure. Mr. South suggested going and taking a look at the tanks being built in Rexburg and Sugar City. The Type I tank and the D115 are much closer in design than the Type III tank. The difference in the D115 tank is a cast in place wall, with monolithic reinforced concrete all the way around, and it has continuous reinforcing with that. The main difference between the Type I tank and the D115 tank is the tendons are on the inside of the wall and the Type I, D110 tank has a wire wrap on the outside of the tank. But both have a solid core with solid reinforcing all the way through. Both of them also have a roof that is monolithic with continuous reinforcing through them. On our tanks the exterior coating that we use is a membrane of the highest quality. If you are looking at longevity of a structure you are looking at protecting the concrete. If you protect it from wetting and drying cycles it will last a lifetime. The liner that we put on the interior of the tank is of the highest quality you can buy. Mayor Gubler: How long has Dome Technology been building this type of structure? Jason South stated that they have been building this kind of tank since 1976. We have altered the compression ring, adding the compression ring to the wall element. Everything is monolithic with continuous reinforcing through the entire structure. The D110 or the D115 with a cast in place dome roof or a shot-crete roof structure is more robust than a Type III tank. Council President Geray: Would you contest anything that Mr. Peacock stated about the D115 tanks or object to anything he mentioned about DN Tanks? Mr. South stated that if the Type III tank is a cheaper alternative, why is it cheaper and would like to make a point about the ASR. If you put a liner on the inside you aren't going to have the water exposure. 3 Council President Geray would like to give the time to DN Tanks for a rebuttal. Mr. Peacock stated that some of their Type III tanks that were built back in the 80's have seen seismic activity and have performed well. Also, concrete tanks are doing well with all the ASR in the area. Mayor Gubler: Let's talk about the history of our project and what our requirements were before we have Forsgren's Engineer Mr. Noel present the specs and plans that have been designed. We started this project two years ago. We had our city engineer do an evaluation of the system. We also discussed what type of tank we wanted. The consensus was at the time that we wanted a cast in place tank like the tank we have right now because of the performance of that tank. The tank is going to be 60 years old next year. We decided on this type of tank. We settled on D110 type I because it mimics the tank we have right now. Then we asked if there was another form of construction that could compete with it and as we looked through the specs we came up with the D115 tank because of the similar thicknesses of the finished product. So the specs were drawn up with these two types of tanks. DN Tanks came to us because they wanted to be part of the bidding process. We didn't want a type III tank and at a previous meeting DN Tanks even stated that a Type I tank was more robust. We haven't wanted a pre -cast tank. But at DN Tanks request, we went back and looked at a Type III but we want the tilt up to be the dimensions like the Type I tank would be. So to accommodate DN Tanks we have had the specs today built to include the tilt up style of construction but with the specs we dictate. We got a bond to build the product we want, a Type I tank. He also mentioned that Structural Technologies was also invited to this meeting. Council President Geray stated that two of the current council members were not involved with the original discussion. He also stated that he didn't at the time have all the back ground etc. on all the different styles and types of tanks. So recently he went and visited with a concrete company and with all the ad mixtures, all the codes, and all the specs we have to meet 4 inches of concrete if designed right could be just as strong and have the same break strength as 8, 9, 10 inches of concrete depending on what you do with it. The American Water Works Association founded in 1881, consists of the largest group of water professionals in the world. They have put a lot of thought into what these specs should be. If we trust the AWWA to define the D115 specs, why don't we trust what the AWWA specs say for the Type III tank. Let the standard do the job for us. Let the Type III in and push the competition. Mayor Gubler stated that we didn't want a bolted steel tank. The D 110 and the D115 were more apples to apples than anything else in the equation. We didn't look at a Type III tank because we didn't want a Type III tank. This is what we designed to, based on our input to the engineer. We allowed the Type III tank to be added in to our specs and plans when last week we had the specs and plans ready for us to vote on to move forward on what we had all agreed upon previously. Council Member Thompson stated that he was in agreement with Council President Geray. He also stated that he feels bad for DN Tanks for wanting to build a Type III tank that we are asking to build to our specs. The AWWA has a standard to make sure this pre -cast lasts for so many years but we can't dictate how many years these are going to last. 4 Public Works Director Prouse stated that we should not be relying on how many years these should last, we should be comparing finished product performance specs. Mr. Noel reviewed the hand out for the specs and plans for final approval to go out to bid. Mayor Gubler stated that the specs and plans have been prepared to allow a different style of construction which allows three styles of tanks to be bid against each other. Any questions or concerns? Entertained a motion to either approve or deny the plans and specs that have been prepared for us by our engineer to go out for bid. Council Member Wadsworth moved that we approve the specs and plans to go to bid that have been prepared by Forsgren Engineering placed before us that we will take all bids put before us into consideration. Council Member Thompson seconded the motion. Council Members Wadsworth and Thompson in favor. Council President Geray opposed. Forsgren Associates Iona North Tank Specs and Plans Public Comments attached Meeting adjourned 8:12 p.m. COUNCIL APPROVED: April 16, 2019 ATTEST: 5