Combination for CDD

 

Automatic combination

Automatic generation of combination is used, if check box Automatic combination is ON) in command for calculation deflection, see "Command for Code dependent deflection"

Only the combination given for calculating the total deflection has been required as the user's input, the rest of the necessary sub-combinations to evaluate creep and the immediate part of the deflection are automatically generated by the program . Three type of load case/combination/class are used for calculation code dependent deflection

• load case/combination/class for calculation total deflection – this load case/combination/classes defined directly in command for calculation deflection (group Result case for deflection) ,see"Command for Code dependent deflection" . The envelope combination is exploded to dangerous (liner combination) , where these dangerous combination is based on local extreme values of

• 1D internal forces components N, M_y, M_z

• 2D internal forces components n_x, n_y, n_xy, m_x, m_y, m_xy

• longitudinal stresses s_x in 4 corners of idealized rectangular css of 1D members

• stresses s_x,s_y and t_xyat top and bottom face of 2D members

• global displacements u_x, u_y, u_z in each mesh node

• load case/combination/class for calculation immediate deflection - will be generated automatically in current version from each dangerous (linear) combination which is used for calculation total deflection., if means that for each dangerous total combination, new immediate combination is generated by removing variable load cases with duration =Medium, Short or Instantaneous.

• load case/combination/class for calculation deflection caused by creep - will be generated automatically in current version from each dangerous (linear) combination which is used for calculation total deflection, if means that for each dangerous total combination, new creep combination is generated by multiplying variable load cases by coefficient defined in Concrete stetting, see "Type of variable load coefficient for the automatic generation of a combination".

 

Manual input combinations

Manual input combination is used, if check box Automatic combination is OFF) in command for calculation deflection, see "Command for Code dependent deflection"

The user can define own combinations for calculation total deflection

• load case/combination/class for calculation total deflection – this load case/combination/classes defined directly in command for calculation deflection (group Result case: Total deflection) ,see"Command for Code dependent deflection" . The envelope combination is exploded to dangerous (liner combination) , where these dangerous combination is based on local extreme values of

• 1D internal forces components N, M_y, M_z

• 2D internal forces components n_x, n_y, n_xy, m_x, m_y, m_xy

• longitudinal stresses s_x in 4 corners of idealized rectangular css of 1D members

• stresses s_x,s_y and t_xyat top and bottom face of 2D members

• global displacements u_x, u_y, u_z in each mesh node

• load case/combination for creep deflection - this load case/combination is defined directly in command for calculation deflection (group Result case: Creep deflection), see"Command for Code dependent deflection". Only load case or linear serviceability combination cane be defined. It means, that the same creep combination will be used for each sub-combinations generated from total combination
• load case/combination for immediate deflection - this load case/combination is defined directly in command for calculation deflection (group Result case: Immediate deflection), see"Command for Code dependent deflection". Only load case or linear serviceability combination cane be defined. It means, that the same immediate combination will be used for each sub-combinations generated from total combination

The all sub-combinations for immediate and creep deflection are the same as input combination in case of manual input combination (Automatic combination is OFF)

Combination for determination cracked/uncracked section

These three types of combination (total, immediate and creep) are used for calculation deflection, but for determination if the section/element is cracked or uncracked new characteristic combinations is generated for all dangerous combinations:

• characteristic total combination - is generated from dangerous total combination
• characteristic immediate combination - is generated from dangerous immediate combination
• characteristic creep combination - is generated from dangerous creep combination

Generation characteristic combination depend on type of combination, which is input in command for calculation deflection (group Result case for deflection)

• for SLS Quasi permanent and SLS frequent combination - SLS characteristic combination is created from dangerous (total, immediate and creep) combination, it means that coefficient of variable load are changed:
  • for lead (master) variable load cases coefficient 1 is used
  • for other variable load cases y₀ factor is used

  

• for other combinations and load cases - SLS characteristic combination are the same as dangerous (total, immediate and creep) combination

If the more characteristic combinations are generated from one dangerous combination, then only characteristic combination which causes the biggest tensile stress, is taken into account

The combination for determination cracked/uncracked cross-section (characteristic combinations) for immediate and creep deflection in case of manual input combination (Automatic combination is OFF) are the same as input combination for creep and immediate deflection

Example of generation combination

Input load cases:

• LC1 - self weight (permanent load)
• LC2 - other permanent load
• LC3 - variable load case with long duration (load type =category A)
• LC4 - variable load case with short duration (load type = snow for Finland)

Input combination:

• SLS Quasi (type =EN-SLS Quasi-permanent) , content of combination: LC1+LC2+LC3+LC4
• SLS Creep (type = Linear serviceability), content of combination: LC1+LC2+0.3*LC3+0.3*LC4
• SLS Immediate (type = Linear serviceability), content of combination: LC1+LC2+0.5*LC3

1/Automatic combination

The following combination are generated for calculation code dependent deflection:

Type of combination	Combikey of all dangerous combinations
Total	1:LC1+LC2 2:LC1 + LC2 + 0.30*LC3 + 0.2*LC4
Immediate	1:LC1+LC2 2:LC1 + LC2 + 0.30*LC3
Creep	1:LC1+LC2 2:LC1 + LC2 + 0.30*LC3 + 0.2*LC4
Total characteristic	1:LC1+LC2 2a:LC1 + LC2 + LC3 + 0.70*LC4 2b:LC1 + LC2 + 0.70*LC3 + LC4
Immediate characteristic	1:LC1+LC2 2:LC1 + LC2 + LC3
Creep characteristic	1:LC1+LC2 2a:LC1 + LC2 + LC3 + 0.70*LC4 2b:LC1 + LC2 + 0.70*LC3 + LC4

2/Manual input combination

The following combination are generated for calculation code dependent deflection:

Type of combination	Combikey of all dangerous combinations
Total	1:LC1+LC2 2:LC1 + LC2 + 0.30*LC3 + 0.2*LC4
Immediate	1: LC1+LC2+0.5*LC3 2: LC1+LC2+0.5*LC3
Creep	1:LC1+LC2+0.3*LC3+0.3*LC4 2:LC1+LC2+0.3*LC3+0.3*LC4
Total characteristic	1:LC1+LC2 2a:LC1 + LC2 + LC3 + 0.70*LC4 2b:LC1 + LC2 + 0.70*LC3 + LC4
Immediate characteristic	1: LC1+LC2+0.5*LC3 2: LC1+LC2+0.5*LC3
Creep characteristic	1:LC1+LC2+0.3*LC3+0.3*LC4 2:LC1+LC2+0.3*LC3+0.3*LC4