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Post-Installed Reinforcing in Fire Conditions 2023 |
Existing |
Bond length |
New slab |
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The resulting determination of the temperature for calculation of the subsequent bond stress can be done in one of two ways .
1 ) The worst-case temperature based on the smallest cover distance can be used conservatively , or
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Temperature
Bond length
Figure 1 — Example of constant temperature over the bond length of a post-installed rebar .
For applications where the cover distance will vary along the length of the embedded rebar , the temperature will also vary along the length of the rebar . Figure 2 below shows an example of a concrete floor slab to wall connection with fire exposure on one side resulting in a variable temperature distribution over bond length of the of the post-installed rebar .
Existing
2 ) It is possible to use smaller increments , or segments , l seg
, and determine multiple temperatures along the length of the rebar . The designer should determine the value of l seg to be used for the application ( i . e . 10 mm ) and then record the worst case concrete temperature at each increment of l seg over the length of the rebar . The smaller the value of l seg will lead to more temperature checks in Figure 4.4.2.2.1a but will lead to a less conservative development length in the fire condition when larger values of l seg are used .
2.3 DETERMINE BOND STRESS RELATED TO TEMPERATURE
Once the temperature in the concrete , θ , at the rebar is determined , the next step is to determine what the bond stress is for the adhesive at that concrete cover temperature . The reduction in the bond stress under high temperatures is different for every adhesive anchor system and should be tested per the new fire provisions of AC308 .
Bond length
New slab
Hilti has two products tested to the new AC308 fire provisions . Refer to Section 3.0 of this document for the technical data for fire conditions for HIT-FP 700 R . Refer to Section 4.0 of this document for the technical data for fire conditions for HIT-RE 500 V3 which is also provided in ESR 3814 .
Temperature
Bond length
Figure 2 — Example of variable temperature over the bond length of a post-installed rebar .
For both products , a fire data curve is provided showing the relationship of temperature , θ , and bond stress , t fire ( θ )
. Refer to Figure 5 for HIT-FP 700 R and Figures 9 and 10 for HIT-RE 500 V3 . The figure below is from Figure 5 for HIT-FP 700 R .
May 2023
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