ContractorQuestions.pdf

· The solicitation specifies three (3) strain gages per diagonal, 12 diagonals per leaf. To be clear, the total number of strain gages required per leaf is 36?

(plus 12 spare total)?

Corps’ Response: Correct, each diagonal should have 3 strain gages x 12 diagonals = 36 gages total per gate leaf. The redundancy is required in case we lose a gage during the prestressing procedure. Then we ensure we can maintain readings from at least two gages. 12 spare gages is acceptable.

· The strain gage bridge configuration is not specified. Do you require a single gage (1/4 bridge) arrangement?

Corps’ Response: Yes. Although less common, we have used single gage ¼ bridges on the last few contracts.

· How many trips to the site should we plan on making? We interpret the requirements as:

o Trip 1- Install strain gages on the 1st leaf o Trip 2- Measure stresses in 1st leaf, then install the gages on the second leaf and measure.

Is this correct?

Corps’ Response: Not entirely correct. The contractor should anticipate being on site a minimum of seven days, although not concurrently.

1 Day: In the past we have had a one-day site visit prior to the dewatering/prestressing activities to review site logistics, power requirements, and safety protocol.

6 Days: We generally prep the upstream or downstream gate leaf one day prior to prestress (place the gages/wiring), prestress the following day as well as moving the wiring to the next leaf, and finish the second leaf on the third day.

Depending on our crews ability to prepare the second set of leafs, there is usually a one-month layover before the second prestress occurs.

In the event we encounter problems with a particular gate leaf, it is possible that we would be required to spend more than one day on a gate leaf, however in the past four years we have never needed more than one day to prestress one leaf.

o What is the anticipated duration of the stressing for each leaf?

Corps’ Response: The past few years, we have been able to stress each leaf in one day (There are 4 leafs total, so anticipate 4 days of prestressing activities). Since we generally prestress the upstream or downstream leafs on back-to-back days, the first day (Day 1) is spent placing the gages/wiring on one leaf, prestressing it the following day (Day 2)[as well as moving the instrumentation to the next leaf], and then prestressing the next leaf the following day (Day 3). Depending whether we begin on the upstream or downstream leafs, we generally have a month before the next set of leafs are ready.

Contractor should anticipate being on site on 2 different occasions for approximately three days duration.

o Where would the data collection station be in reference to the leaf to be measured? This is would determine cable lengths for the strain gages.

Corps’ Response: Generally, we have placed the data collection station on the top of the lockwall adjacent to the gate leaf being prestressed. The bottom of the lock chamber can still be wet/icy even after it is dewatered.

o Is there a complete drawing of the leafs, showing strain gage locations and dimensions that we can refer to?

Corps’ Response: Please refer to attached drawings. Note that dimensions for the upstream and downstream gates differ. The 23’ Gate represents the upstream miter gates and the 25’ Gate represents the downstream miter gates. Strains gages have typically been placed near the intersection of the diagonals.