What is the design criteria of Direct Tension Indicator (DTI) Connection? Explain in details step by step procedure of a design of Direct Tension Indicator (DTI) Connection with required formula and an example of calculation.

Direct Tension Indicator (DTI) is a method used to achieve the desired tension in high-strength bolts by using special washers that indicate the level of bolt tension. The design criteria for a DTI connection include determining the required bolt tension, selecting the appropriate DTI washer, verifying the connection strength and safety, and interpreting the readings from the DTI washer. Here is a step-by-step procedure for designing a DTI connection:

Step 1: Identify the Connection Requirements Determine the specific requirements of the connection, including the type and size of the connected elements, the applied loads, and the desired level of performance and safety.

Step 2: Determine the Applied Loads Identify the loads that will be applied to the connection, such as shear forces, tension forces, and, if applicable, compression forces. Determine the magnitude, direction, and distribution of these loads.

Step 3: Select the Bolt Size and Material Select the appropriate bolt size and material based on the design requirements and specifications. Consider factors such as load capacity, corrosion resistance, and compatibility with the connected elements.

Step 4: Determine the Bolt Tension Calculate the required bolt tension based on the applied loads and the desired safety factor. The bolt tension provides the clamping force necessary to resist the applied loads. The formula to calculate the bolt tension is:

T = P x As

Where: T is the bolt tension P is the applied load As is the effective cross-sectional area of the bolt

Step 5: Select the DTI Washer Choose a suitable DTI washer based on the desired tension range and the bolt size. DTI washers are available in various designs and have markings that indicate the achieved tension level.

Step 6: Verify Connection Strength and Safety Perform a comprehensive design verification to ensure that the DTI connection meets the desired strength and safety requirements. This may involve additional checks for bolt shear strength, bearing strength, bolt spacing, edge distances, and other connection details as per the design code provisions.

Step 7: Interpret DTI Washer Readings Install the DTI washers on the bolts according to the manufacturer’s instructions. Apply the specified tension to the bolts and monitor the readings on the DTI washers. The markings on the washer indicate whether the desired tension has been achieved or if adjustment is needed.

Example: Consider a DTI connection joining two steel members subjected to a tension force of 100 kN. The bolt diameter is 20 mm, and the desired safety factor is 1.5.

Step 1: Identify the Connection Requirements The connection requires a DTI joint to transfer a tension force of 100 kN with a safety factor of 1.5.

Step 2: Determine the Applied Loads The applied load is a tension force of 100 kN.

Step 3: Select the Bolt Size and Material Assume a suitable bolt size and material based on the design requirements.

Step 4: Determine the Bolt Tension Calculate the required bolt tension using the formula: T = P x As

Assume the effective cross-sectional area of the bolt (As) is 157 mm² (for a 20 mm diameter bolt).

T = 100 kN x 157 mm² = 15,700 kN·mm (or N·mm)

Step 5: Select the DTI Washer Choose a DTI washer suitable for the desired tension range (15,700 kN·mm) and the bolt size.

Step 6: Verify Connection Strength and Safety Perform a comprehensive design verification considering other factors such as bolt shear strength, bolt bearing strength, bolt spacing, edge distances, and other connection details as per the design code provisions.

Step 7: Interpret DTI Washer Readings Install the DTI washers on the bolts and apply the specified tension. Read the markings on the DTI washers to ensure that the desired tension (15,700 kN·mm) has been achieved.

It is important to note that the actual design process for a DTI connection may involve additional considerations and checks depending on the specific requirements, design codes, and industry practices. It is recommended to consult the relevant design code or a qualified structural engineer for accurate and compliant design of DTI connections.