How are cracked sections analyzed in SAFE?
Answer: Two types of crackedsection analysis are available, including:
 Immediate cracked deflection
Crackedsection analysis is run in SAFE using either of the following two methods:
 All load patterns are applied in a single load case which uses either immediate or longterm cracked deflection, discussed as follows:
Immediate cracked deflection, in which all loads (DEAD + SDEAD + LIVE) are applied in a single load pattern, then analysis is run with the Crack Analysis option.
Longterm cracked deflection, in which analysis is divided into the following two categories: Nonsustained portion, in which crackedsection analysis considers only the nonsustained portion of LIVE load, solving for incremental deflection.
Sustained portion, in which longterm cracked analysis considers the sustained loading from DEAD, SDEAD, and a portion of the LIVE load. Creep and shrinkage are included only in this sustained portion of analysis because these effects are only applicable under sustained loading.
Info NOTE: Shortterm concrete modulus = Elastic concrete modulus Ec(to)
Info NOTE: Longterm concrete modulus = Ageadjusted concrete modulus Ec(t,to), given as:
For example, assume that 25% of the LIVE load is sustained. Analysis proceeds as follows: Case 1: Cracked analysis for shortterm load with shortterm concrete modulus is given as DEAD + SDEAD + Ψ_{s}LIVE, in which Ψ_{s} = 1.0
 Case 2: Cracked analysis for permanent load with shortterm concrete modulus is given as DEAD + SDEAD + Ψ_{L}LIVE, in which Ψ_{L} = 0.25 (Ψ_{L} = 0 if 100% of the LIVE load is nonsustained)
Case 3: Longterm cracked analysis (with creep and shrinkage) for permanent load with longterm concrete modulus is given as DEAD + SDEAD + Ψ_{L}LIVE, in which Ψ_{L} = 0.25
The value of total longterm deflection is then the combination of Case 3 + (Case 1 Case 2). The difference between Case 1 and Case 2 represents the incremental deflection (without creep and shrinkage) due to nonsustained loading on a cracked structure.
The procedure indicated above results on total long term deflection over time. Most engineers simply check this values against ACI 318 Table 9.5(b), since this will always result in safe and conservative design. In order to remove portion of dead load deflection occurring before attachment of nonstructural elements, the following procedure can also be used:
Case 4= Cracked analysis for permanent load with shortterm concrete modulus is given as DEAD + Ψ_{D}SDEAD, in which Ψ_{D} = percentage of super imposed dead load present before attachment of non structural elementsOr Case 4= Cracked analysis for permanent load with longterm concrete modulus creep and shrinkage is given as DEAD + Ψ_{D}SDEAD, in which Ψ_{D} = percentage of super imposed dead load present before attachment of non structural elements, and say using a creep factor for 3 months.
The value of total long term deflection to occur after attachment of nonstructural elements is then the combination of Case 3 + (Case 1 Case 2) Case 4.
We recommend this method, though an alternative is available, described as follows:
 Case 1: Cracked analysis for shortterm load with shortterm concrete modulus is given as DEAD + SDEAD + Ψ_{s}LIVE, in which Ψ_{s} = 1.0
 Nonsustained portion, in which crackedsection analysis considers only the nonsustained portion of LIVE load, solving for incremental deflection.
 A single load pattern is applied in a load case, then another case is set to continue From State at End of Nonlinear Case.
For example: Add a DEAD load case using the Nonlinear (Cracked) option, starting with a Zero Initial Condition.
 Add a SDEAD load case using the Nonlinear (Cracked) option, starting From State at End of Nonlinear Case DEAD.
 Add a LIVE load case using the Nonlinear (Cracked) option, starting From State at End of Nonlinear Case SDEAD.
The DEAD load case predicts cracking from a zero initial condition, in which no load is present, then computes cracking due to DEAD loadpattern application. Adding SDEAD then uses the stiffness at the end of DEAD load case, and contributes additional deflection. Deflection reports the total deflection from both DEAD and SDEAD cases, however, the increase in DEAD load deflection due to additional cracking from SDEAD load application is not recognized, therefore we do not recommend this method.
 Add a DEAD load case using the Nonlinear (Cracked) option, starting with a Zero Initial Condition.
Crackedslab deflection
SAFE can use userdefined reinforcement to compute crackedslab deflection. For this option, select Run > Reinforcing Option for Cracking Analysis, then select User Specified Rebars in Reinforcement Source. Select Draw Slab Rebar from the vertical menu on the left. Note that rebar must be added in both the tension and compression regions for the entire slab since the software will only use the userdefined reinforcement, and not use the reinforcement design.
Hidden content  

Related Incident:

References
Refer to watch and learn video: Cracked section analysis
During nonlinear crackedsection analysis, SAFE estimates deflection using a momentrotation curve as described in the reference which follows:
 Ghali, A., Favre, R., Elbadry, M. (2002).
(3rd ed.). London, England: Spon Press.Link in New Window linkText Concrete Structures: Stresses and Deformations: Analysis and Design for Serviceability href http://books.google.com/books/about/Concrete_Structures.html?id=1M3IlzKljMC  SAFE verification example 16 by going to Help > Documentation > verification> Analysis > Example 16Cracked Slab Analysis. Example 16.pdf
Hidden content  

Related Incident:

See Also
 Cracking article
 Soilstructure interaction section
 Cracking FAQ article