What is Direct Tension Indicator (DTI) Connection? Explain in details step by step procedure to make a Direct Tension Indicator (DTI) Connection with example and application.

A Direct Tension Indicator (DTI) connection is a method used to achieve proper bolt tension in structural steel connections. It involves the use of specialized washers, called Direct Tension Indicators or Load Indicating Washers, to monitor and control the tension in high-strength bolts. DTI connections provide a visual indication of the bolt tension, ensuring that the bolts are properly preloaded and the connection is secure.

Here is a step-by-step procedure for making a Direct Tension Indicator (DTI) connection:

1. Design and Preparation:
   • Determine the required bolt tension and load-bearing capacity for the connection based on the structural requirements.
   • Select the appropriate high-strength bolts, nuts, washers, and other connection components based on the design specifications, considering factors such as material strength, size, and corrosion resistance.
   • Ensure that the surfaces of the steel components to be connected are clean, smooth, and free from any debris, rust, or paint.
2. Alignment and Positioning:
   • Position the steel components, such as beams, columns, or plates, in their designated locations, ensuring proper alignment and fit.
   • Use temporary clamps or tack welds to hold the components in place, preventing movement during the connection process.
3. Marking and Drilling:
   • Mark the positions for the bolt holes on the steel components, following the specified spacing and pattern.
   • Use a drill press or portable drilling machine to drill holes through the marked positions on the components. Ensure that the holes are aligned and perpendicular to the surface.
4. Deburring and Cleaning:
   • Remove any burrs or sharp edges around the drilled holes using a deburring tool or file.
   • Clean the holes and surfaces of the components to remove any debris, oil, or grease that may affect the connection’s integrity.
5. Inserting Bolts and DTI Washers:
   • Insert high-strength bolts through the holes in one of the components.
   • Place DTI washers onto the exposed ends of the bolts, ensuring that the raised projections on the washers are facing towards the nut.
6. Snug Tightening:
   • Use a suitable wrench or impact wrench to snugly tighten the nuts until they are in contact with the DTI washers and the joint is fully closed.
   • At this stage, the washers should be in their uncompressed state.
7. Initial Tensioning:
   • Begin tightening the nuts using an appropriate torque wrench or hydraulic tensioning device.
   • Gradually increase the tension in the bolts, while monitoring the rotation of the DTI washers.
8. Tensioning until Indication:
   • Continue tensioning the bolts until the DTI washers start to rotate.
   • The rotation of the washers indicates that the desired tension has been achieved in the bolts.
   • Follow the manufacturer’s specifications or design engineer’s instructions for the target rotation angle or displacement.
9. Final Inspection:
   • Inspect the connection to ensure that the bolts, nuts, and DTI washers are properly seated and tightened.
   • Check for any gaps, misalignment, or visible signs of damage or distortion.
   • Verify that the rotation or displacement of the DTI washers meets the specified indication requirements.

Example and Application: An example of a Direct Tension Indicator (DTI) connection is the connection between steel beams and columns in a building or bridge structure. DTI connections are commonly used in applications where accurate and controlled bolt tension is crucial for the structural integrity and safety of the connection.

Applications of DTI connections include:

• Building and bridge construction, where DTI connections are used to join steel components and ensure proper bolt tensioning.
• Heavy industrial structures, such as power plants or offshore platforms, where DTI connections are employed to connect critical steel elements subject to significant loads, vibrations, or dynamic forces.

The use of DTI connections provides several advantages, including accurate monitoring of bolt tension, prevention of under-tightening or over-tightening of bolts, and visual indication of proper tensioning. This results in enhanced structural performance, improved safety, and reduced maintenance requirements.