Crack Width Calculation As Per Aci 318 14

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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. 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. Eurocode 2: Crack width calculation; FREE VERSION OF RCsolver - Concrete Design with EC2, EC8, and ACI 318. Get full capabiltiies with our free version of RC-Solver once you signup for our newsletter. With the free version you will have to wait 30 seconds for advertisements. ACI 318 - 89, 99, Gergely-Lutz equation ACI requirements based on stress limits derived from the Gergely-Lutz equation: Code provisions for crack widths x)-x)/(d-(h 3 Adfz cs unitsmNzw 12 max 1011 Samirsinh P Parmar, Asst.Prof. DDU, Nadiad, Gujarat, India 15. 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.

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In ETABS, shell or area element has two types of stiffnesses i.e. inplane stiffness refers as f11, f22 and f12 and out-of-plane stiffness refers as m11, m22 and m12. Refer to the below Figure which shows the direction of local axes and their corresponding stiffnesses:

For shear wall (both piers and spandrels), the flexural and axial behavior is modified by either f11 or f22 depending on the orientation of the local axis and the shear behavior is controlled by f12. In column and code terms f11 or f22 would correspond to modifications of EI or EA and f12 would correspond to modifications to GAshear. The code recommendations in Section 10.10 of ACI 318 code are related to slenderness effects where flexural deformations govern so they have recommended modifying EI (corresponding to f11 or f22 for shear walls). There is no recommendation about reducing the GAshear. You should, however, note that some of our users use modifiers for f12 also, where they expect deterioration of shear stiffness and want to be realistic in their modeling.

The above discussion applies assuming the local axes 1 and 2 of the shear wall area object are either vertical or horizontal. This is under user control. When drawing in ETABS the default is to have the 1 axis horizontal and the 2 axis vertical. This means that the flexural modifier for EI should be applied to f22 for wall piers and to f11 for spandrels. If you apply the modifier to both f11 and f22 it hardly affects the results.

For slabs where bending is always in the out-of-plane direction, modifiers m11, m22 and m12 are required to model cracking behavior.

Crack Width Calculation As Per Aci 318 14 Free

Summary

Assuming beams and columns are modeled as frame then the stiffness modifier table is as follows:

ACI ETABS

Beams....................0.35*Ig I22 = I33 = 0.35

Columns..................0.70*Ig I22 = I33 = 0.70

Walls-Uncracked.........0.70*Ig modeled as shell – f11, f22 = 0.70

Walls-Cracked...........0.35*Ig similar to Walls-Uncracked (with modifiers of 0.35)

NOTE:

Walls are generally not designed for out-of-plane bending to avoid excessive longitudinal reinforcement. In this case, use a small modifier say 0.1 for m11, m22 and m12 so numerical instabilities could be avoided. However, use m11, m22, m12 = 0.70 (or 0.35) when considering the out-of-plane bending in wall.

Flat Plates & Flat Slabs..0.25*Ig modeled as membrane – f11, f22, f12 = 0.25 / modeled as shell – f11, f22, f12, m11, m22, m12 = 0.25 (for both cases fxx is not important if rigid diaphragm is assigned)

Width

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.

Three ACI documents for crack width; ACI 224R-01, ACI 350-01 & ACI 350-06

1. ACI 224R-01

Encarta 2000. Some notes:-

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  • 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

There are three methods mentioned in this document

A) ACI 318-95

Statistical method of Gergely & Lutz 1968

Covers up to 2.5″ only

z in any units

For two-way slabs see section 4.3 of ACI 224R-01

For shallow beams/thick one-way slabs: (w in inches)

Thick means L/D = 15-20

d used here will be distance to the center of bottom bar nearest to tension face.

ß=1.25 to 1.35 if cc≥1″

ACI 318-95 section 10.6 says use ß=1.20 & fs=0.6fy

ACI 340R has design aids for z

ACI 318-98 & earlier max z=175 kip/in for interior exposure based on 0.41mm probable crack width(0.016″)

ACI 318 max z=145 kip/in for exterior exposure based on 0.33mm probable crack width(0.013″)

B) ACI 318-99

No distinction for interior/exterior exposure

For beams & one-way slabs:

fs=0.6fy

Not for aggressive/water tight structures

C) EUROPEAN CODES

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2. ACI 350-01

Same concept like ACI 224R-01

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3. ACI 350-06

2 types of exposure:-

i)Normal

ii)Severe

can be taken = 25

where c is at service load

ß can be taken = 1.20 for h≥16″

Crack Width Calculation As Per Aci 318 14 Online

& 1.35 for h<16″

where appearance is of concern & cover exceeds 3″, also check equation 10-7

Exposure defined as

Previous codes (ACI 350-01) puts following limits on z:

Normal exposure: z=115 kip/in (w=0.010″ or 0.254mm)

Severe exposure: z= 95 kip/in (w=0.009″ or 0.229mm)

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EXAMPLE WITH AXIAL TENSILE LOAD AND MOMENT

  • 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:

M=Asfs(d-d’)+T2(d-d’)+0.5T3(h/4)+0.5T4(h/4)

T3=T4 so

M=Asfs(d-d’)+T2(d-d’)+T3(h/4)

Crack Width Calculation As Per Aci 318 14 Pdf

(where T is total axial tension force)

Crack Width Calculation As Per Aci 318 1400

From here calculate fs and compare with fsmax of ACI 350-06.