Post-Installed Reinforcing in Fire Conditions
With this information, and with the post-installed adhesive test data from the AC581( 24) or AC308( 24) fire tests in this document for either HIT-FP 700 R or HIT-RE 500 V3 the development length needed for the fire condition can be determined.
Determine Equivalent Bond Stress at Ambient Temperature
At ambient temperature( no fire consideration), development length for post-installed adhesives with rebar is calculated as follows:
For fire exposure on one side of a concrete wall, floor, or roof, refer to ACI 216.1 Figure 4.4.2.2.1a( a), Figure 4.4.2.2.1a( b), and Figure 4.4.2.2.1a( c), for carbonate aggregate, siliceous aggregate, and semi-lightweight aggregate respectively. The above noted figures are provided below for reference. Each figure shows concrete cover curves, with the Temperature( F) on left vertical axis and Temperature( C) on right vertical axis. The horizontal axis is the fire time in minutes( fire rating or duration). From the specific fire rating and concrete cover, the temperature at the location of the rebar, θ, can be determined.
Figure 4.4.2.2.1a( a). Temperatures within slabs during ASTM E119 fire tests— carbonate aggregate concrete
ACI 318 Chapter 25 Eq. 25.4.2.3:
l d = 3 40 × f y × ψ tψ e ψ s ψ g d λ f ′ c c b + k b( in) tr d b
CSA A23.3 12.2.2 Eq. 12-1:
l d = 1.15 k 1k 2 k 3 k 4 d cs + k tr f y f ′ c
A b
Refer to ACI 318, CSA A23.3, or the Rebar Tech Guide for more information on calculating development length with Hilti adhesive anchors including HIT-FP 700 R and HIT-RE 500 V3.
The development length calculated above is considered the ambient temperature development length. To determine an equivalent bond stress for the adhesive at ambient temperature, τ equiv, divide the yield capacity of the bar by the surface area of the rebar at the ambient temperature development length:
τ equiv = f y ⋅ A b π ⋅ d b ⋅ l d
The equation for τ equiv, is applicable for both ACI and CSA calculations.
Determine the Temperature in the Concrete Under Fire Conditions
The next step is to determine what the temperature in the concrete, θ, is based on the fire rating, the concrete cover, and knowing the type of concrete aggregates used. In the United States and Canada, typical fire exposure for buildings regulated by the IBC or NBC-C is based on a time to temperature curve established in ASTM E119. ACI 216.1 provides guidance on the temperature in the concrete based on the concrete cover, the fire test time( fire rating), and the aggregate type.
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