- Crack Width Calculation As Per Aci 318 14 Online
- Crack Width Calculation As Per Aci 318 1400
- Crack Width Calculation As Per Aci 318 14 Free
Eurocode 2 part 1-1: Design of concrete structures 7.3 Crack control
wk = sr,max⋅(εsm - εcm) | (7.8) |
- sr,max
- is the maximum crack spacing
- εsm
- is the mean strain in the reinforcement under the relevant combination of loads, including the effect of imposed deformations and taking into account the effects of tension stiffening
- εcm
- is the mean strain in the concrete between cracks.
(7.9) |
see application for a rectangular section or application for a T-section
- Ecm
- the secant modulus of elasticity of concrete
fct,eff = fctm or lower, (fctm(t)), if cracking is expected earlier than 28 days
= (As + ξ1⋅A'p)/Ac,eff | (7.10) |
Crack Width Calculation As Per Aci 318 14 Online
ξ1 = | (7.5) |
- ξ
- the ratio of bond strength of prestressing and reinforcing steel, according to Table 6.2
- ΦS
- the largest bar diameter of the reinforcing steel
- ΦP
- the diameter or equivalent diameter of prestressing steel:
Φp = 1,6⋅√AP for bundles, where AP is the area of a prestressing steel,
Φp = 1,75⋅Φwire for single 7 wire strands,
Φp = 1,20⋅Φwire for single 3 wire strands, where Φwire is the wire diameter.
kt = 0,6 for short term loading,
kt = 0,4 for long term loading.
sr,max = k3c + k1k2k4Φ / ρp,eff | (7.11) |
k1 = 0,8 for high bond bars,
k1 = 1,6 for bars with an effectively plain surface (e.g. prestressing tendons).
k2 = 0,5 for bending,
k2 = 1,0 for pure tension.
Intermediate values of k2 should be used for cases of eccentric tension or for local areas:
k2 = (ε1 + ε2)/(2ε1) | (7.13) |
sr,max = 1,3(h - x) | (7.14) |
- h
- is the overall depth of the section (see Figure 7.1)
- x
- is the neutral axis depth of the section (see Figure 7.1).
FOR WATER TIGHT STRUCTURES
Crack width is a complex and tough topic. Most people still use 20 years old method defined in ACI 318-95. The situation becomes more complex if axial tension force and moment is combined to calculate crack width. One of the examples is large water tanks above ground. This tutorial aims at explaining details and methods in different ACI documents. Latest method defined in ACI 350-06 should be used. Given the variability and non-linear behaviour in long-term deflection and crack widths, it is NOT NEEDED to go for detailed sophisticated calculations for these effects. You can imagine this as calculating something non-linear (crack widths or long-term deflection) from linear-elastic analysis. You have to have some approximations for that. No matter how detailed are your calculations, you still can’t predict for certain the long-term deflection and crack widths.
- Table 4.1 is based on Nawy findings.
- The table is just a general guide line.
- The table gives w=0.004″ or 0.10mm for water retaining structures.
- It is expected that portion of cracks will exceed these values by a significant amount.
- No relationship between level of cracking & corrosion in long-term.
- More cover can be used even if it yields larger crack width, against corrosion.
- ACI methods deal only with conventional concrete for crack width.
- Crack width is directly proportional to dia of bar & fs and inversely to area of steel.
- Three reasons for limiting crack widths
1-Appearance
2-Corrosion
3-Water tightness
- For detailed calculations, find the N.A. depth but use ԑ at service loads. Strain diagram will be different from the one shown in figure above if axial load is included.
- Assume no strength from concrete due to axial tension load.
- Assume tension force acting at steel reinforcement level.
- Assume all the moment is resisted by top and bottom steel only.
- Tension at top steel; T1 = A’s / (A’s+As+As1+As1) x Total Tension Force
- Tension at bottom steel;T2 = As / (A’s+As+As1+As1) x Total Tension Force
- Tension at right steel; T3 = As1/ (A’s+As+As1+As1) x Total Tension Force
- Tension at left steel; T4 = As1/ (A’s+As+As1+As1 )x Total Tension Force
- Taking moment about top steel: