2.6 DESIGN EXAMPLE WITH VARIABLE TEMPERATURE ALONG REINFORCEMENT
Post-Installed Reinforcing in Fire Conditions 2024
• l d
= 21.6-inch → use 22-inch f
• t y
∙ A b equiv = = π ∙ d b
∙ l d
60,000 psi ∙ 0.44in 2 = 509psi π ∙ 0.750in ∙ 22in
Step 2: Determine temperature in concrete under fire conditions:
• Using ACI / TMS 216.1 Figure 4.4.2.2.1a( a) with 2-inch cover the temperature in the concrete is determined:
• θ ≈ 725 ° F
2.6 DESIGN EXAMPLE WITH VARIABLE TEMPERATURE ALONG REINFORCEMENT
The following design example is for a floor slab connected to a shear wall in 4,000 psi normal weight concrete with carbonate aggregate.
Existing
Bond length
New slab
Given:
• ASTM A615 Gr. 60 reinforcement, # 6 rebar installed with HIT-FP 700 R
• Concrete cover, c b
, starts at 2”( 50 mm) and then varies with embedment
• Non-seismic floor loads only
Step 1: Determine ambient temperature development length and equivalent bond stress:
Step 3: Determine the bond stress related to the concrete temperature in fire condition:
• From the equations of Figure 5 of Section 3.0 the bond stress at θ is determined:
• t fire( θ
= – 0.1990 ∙ θ + 834.4
• t fire( θ
= – 0.1990 ∙ 725 + 834.4 = 690 psi
Step 4: Determine the development length needed for the fire condition:
• l d, fire = t equiv
∙ l d = t fire( θ)
509 psi 690 psi
∙ 22in = 16.2in
• l d, fire < l d
∴ ambient temperature development length should be used
• l d, fire = l d
= 22-inch
• As a shortcut, since the value of t fire( θ) = 690 psi( where c b
= 50mm in Step 3) is greater than t equiv
= 509 psi, it could have already been determined that the ambient temperature development length controlled and no additional embedment depth is needed for the fire condition.
• From Table 3 of Section 3.0( or ACI 318 Chapter 25 Eq. 25.4.2.3) the development length for HIT-FP 700 R with # 6 rebar is determined:
• l d
= 21.6-inch → use 22-inch f
• t y
∙ A b equiv = = π ∙ d b
∙ l d
60,000 psi ∙ 0.44in 2 = 509psi π ∙ 0.750in ∙ 22in
Step 2: Determine temperature in concrete under fire conditions:
• Using ACI / TMS 216.1 Figure 4.4.2.2.1a( a) the temperature at various concrete cover depths needs to be determined as an iterative evaluation of temperature and bond will be performed. Since the new slab already has a 2-inch cover, start with 2-inch cover and use l seg
= 10mm to determine the temperature in the concrete at each segment, up to 180mm( 7-inch):
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