Post-installed Rebar Design III

Fire Limit State (FLS) Design

Calculation Approach

The calculation approach is based on the type of connection. Since the temperature is not constant in anchorage connection, the temperature is a function in terms of the depth (x). Therefore, the resultant bonding stress of adhesive  is a function in terms of x and the resultant force would be in the form of integration due to non-constant temperature. For parallel connection, constant temperature along the rebar implies same reduction on adhesive bond stress. Therefore, the resultant force of rebar can be obtained by substituting the reduced bond stress into Ultimate Limit State equations.

Please note that in both cases, a global safety factor  is applied in the calculation.

With two different approach in calculation, there are two forms of expression for rebar performance in HILTI’s research studies. A few parameters required in order to carry out Fire Limit State calculation, such as connection type, concrete cover, rebar diameter. Required fire resistance and design load should be verified based on your project requirement.

Anchorage Connection: How to extract useful information from the document?

For anchorage connection (Wall-to-slab and wall-to-beam connection), the performance of adhesive is presented in the form of maximum force, which is the resultant value from the integration. Select the right column according to fire resistance rating, the maximum force chosen must be greater than the design load and the rebar anchorage depth can be obtained. 

Parallel Connection: How to extract useful information from the document?

For parallel connection (Slab-to-Slab and Beam-to-Beam connection), the performance of adhesive is presented in the force of reduce bond stress. Select the correct bonding stress  according to fire resistance rating and concrete depth of rebar. The anchorage length will be obtained by substituting the parameter into the equation. 

After obtaining the anchorage length for FLS design, please do not forget to compare the result with ULS design. The larger value between ULS anchorage length & FLS anchorage length should be adopted to be the final anchorage length. Please note that FLS design may not be required.