2.6 DESIGN EXAMPLE WITH VARIABLE TEMPERATURE ALONG REINFORCEMENT
Post-Installed Reinforcing in Fire Conditions 2023
• l d
= 21.6-inch → use 22-inch
• t equiv = f ∙ A y b = 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
• t equiv = f ∙ A 60,000 psi ∙ 0.44in 2 y b =
= 509psi π ∙ d b
∙ l d 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 ):
May 2023
7