Instrumentation for Prestressing Diagonals for LD 7

 

 

SCOPE

 

This section covers the delivery, installation of instrumentation, real-time data reporting and final report for the prestressing the diagonals for the miter gates during the dewatering at Lock 7 (La Crescent, Minnesota). This scope includes instrumentation services that will be required to prestress the upstream and downstream gates (48 diagonals total). The Contractor will be required to provide a technician and equipment that will be available up to seven consecutive days for a minimum of eight hours a day, with notice five days prior to the commencement of work. Contractor must be available 01 January 2012 through 15 March 2012, including weekends.

 

The general procedure for prestressing the gates is as follows. The respective diagonals are installed slack. The Corps will ensure that the quoin end of the gate is plumb and that the bottom girder will be horizontal. At this point the diagonals will be clamped.  The Contractor shall install the strain gages. The Corps will stress the diagonals to their intended load and measure the deflection. The Contractor will report the average strain in the diagonals. In an iterative process, the Corps will then adjust the stress in the diagonals as needed. The Corps will measure the out of plumb deflection and then the Corps will make any final adjustments to the diagonals based on gate deflections and strain readings.

 

INSTRUMENTATION - WELDABLE STRAIN GAGE REQUIREMENTS

 

1. 
   
2. A triple set of electrical resistance strain gages shall be installed on each diagonal, (there are twelve diagonals per leaf), so that simultaneous readings for each diagonal may be taken during the prestressing operation. Enough strain gages shall be on hand to ensure that both leafs (24 diagonals) of the upper gate or lower gate can be prestressed simultaneously. A spare strain gage shall be available for each strain gage mounted on any diagonal of any leaf which is undergoing the prestressing operation. Upon completion of prestressing the upper or lower leafs, the Contractor has a maximum of two days to install and wire strain gages and prepare the other set of leafs for prestressing. The technician is responsible for reporting to the Prestressing Chief (Eric Wittine).
   

 

Prestressing of the gates will occur during winter rain and/or snow conditions on the miter gates of Lock 7. High winds and low temperatures should be anticipated. The Contractor must ensure that gages are adequately protected during this phase of work. Contractor will be provided with a radio to stay in communication with the Corps' staff.

 

 

 

 

1. 
   
2. It is required that a technician proficient in operating the strain gages and software output shall be present for the entire prestressing operation. The technician shall be able to provide "real-time" results to the work crew prestressing the gates. Power will be available on-site for all pertinent equipment. A snorkel lift and operator will be provided as Government furnished equipment for strain gage installation.
   

 

The software technician for the strain gages shall expect to work hours in excess of eight hours a day and shall be available for weekend work as well. The technician shall be on-site within five days notice prior to the start of the work.

 

1. 
   
2. Strain gage readings shall be recorded in the following tables and submitted to the Corps' at the conclusion of prestressing the gates. Final output is due to the USACE within five days of work completion.
   

 

SUBMITTALS

 

The following shall be submitted before performing the work:

 

1. 
   
2. Catalog cuts for all instrumentation to be used to record the strain readings during the prestressing operation shall be submitted for approval by Engineering Division. A description, with an example of the output, of the software is also required for approval.
   

 

 

 

 

 

 

 

DIAGONAL PRESTRESSING VALUES - UPPER GATE, LANDWALL

Final

Stress After Tool Removed

Avg. Strain

Pass 2

Stress (psi)

Avg. Strain

Gage Pressure (psig)

Pass 1

Stress (psi)

Avg. Strain

Gage Pressure (psig)

Diagonal

U0-L1 (-)

U1-L2 (-)

U2-L3 (-)

L0-U1 (+)

L1-U2 (+)

L2-U3 (+)

U0-L1 (+)

U1-L2 (+)

U2-L3 (+)

L0-U1 (-)

L0-U1 (-)

L0-U1 (-)

Sequence*

1

2

3

4

5

6

1

2

3

4

5

6

Upstream Diagonals

Downstream Diagonals

 

* - Stress matching numbers (in sequence column) simultaneously during the prestress process.

 

 

BID SCHEDULE

 

Strain Gage Installation                            _____ hrs

Strain Gage Reading/Reporting                _____ hrs