New Jersey

Department of Transportation

Standard Specifications

for Road and Bridge Construction


NJDOT S-3 Verifying Direct Tension Indicators (DTI)

  1. Scope. Use this test method to verify and install high-strength steel bolts using direct tension indicators (DTIs).

  2. Apparatus. Use the following apparatus:

    1. Calibrated bolt tension measuring device, such as a Skidmore-Wilhelm Calibrator, with a special flat insert in place of normal bolt head holding insert. The special insert is required to allow access to measure the DTI gaps.
    2. Tapered leaf thickness (feeler) gauge 0.005 inch. Use the same gauge as to be used to inspect the bolts after installation.
    3. Steel section to mount bolt calibrator, such as a flange of girder or cross frame that is accessible from the ground.
    4. Impact and manual wrenches to tighten bolts. Equipment should be the same as to be used in the work.

  3. Procedure. Perform the following steps:

    1. Install bolt, nut, DTI, and standard washer into bolt tension measuring device. Ensure that the assembly matches that to be used in the work unless bolts are too short to fit in the device. If the bolts are too short, use longer bolts of the same diameter and from the same manufacturer to perform the DTI verification. Test 3 assemblies for each rotational-capacity lot.
    2. Tighten the nut to the tension listed in Table S-3-1. Use another wrench on the bolt head to prevent rotation of the head against the DTI if the DTI is under the bolt head. If an impact wrench is used, tighten to a load slightly below the required load and use a manual wrench to attain the required tension.

    3. Table S-3-1 Bolt Tension for A 325 Bolts
      Bolt Size 1/2 5/8 3/4 7/8 1 1-1/8 1-1/4
      Bolt Tension, kips1 13 20 29 41 54 59 75
      1 Bolt Tension equals 1.05 (Minimum Installation Tension)

    4. Determine and record the number of spaces between the protrusions on the DTI that the 0.005 inch thickness gauge is refused. The total number of spaces and the maximum verification refusals are listed in Table S-3-2. If the number of spaces that the gauge is refused exceeds the maximum verification refusals listed in Table S-3-2, the DTI fails the verification test.

    5. Table S-3-2 DTI Maximum Verification Refusals
      Bolt Size 1/2 5/8 3/4 7/8 1 1-1/8 1-1/4
      Number of Spaces on DTIs 4 4 5 5 6 6 7
      Maximum Verification Refusals1 1 1 2 2 2 2 3
      1 If the DTI is coated and under the nut, the maximum verification refusals is the number of spaces on the washer minus 1.

    6. Further tighten the bolt until the 0.005-inch thickness gage is refused at all spaces but a visible gap exists in at least one space. Record the load as read on the tension measuring device.
    7. Remove the bolt from the calibrator and turn the nut on the threads of the bolt by hand. If the nut is able to be turned on the complete length of the threads, the DTI is acceptable. If the nut is unable to go the full length, but the load at the minimum DTI gap measured in Step 4 is less than 95 percent of the average tension recorded during the rotational-capacity test, the DTI is acceptable. If the nut cannot be run the full thread length and the tension at the smallest gap condition is greater than 95 percent of the average tension recorded during the rotational-capacity test, the DTI is not acceptable.
    8. If any of the 3 DTIs for the lot are found to be not acceptable, reject the DTI lot.

  4. Report. Report the following:

    1. Size, manufacturer and lot number for the bolt assembly used in the testing.
    2. Size, manufacturer and lot number for the DTI.
    3. Results of testing.

Last Document Correction:
December 14, 2007