Design parameters for longitudinal bars (concrete beam: EC2)
For each of these parameters, any user defined limits (as specified in Design Settings > Concrete > Castinplace > Beam > Reinforcement Layout) These are considered in addition to the EC2 or NA recommendations. 
Minimum diameter of reinforcement
The minimum diameters of reinforcement are set by the user in Design Settings, the initial default values being:  
Minimum longitudinal bar size 

12 mm 
Minimum side bar size 

16 mm 
Minimum link bar size 

8 mm 
If the design results in a bar size less than the user specified limits the checks fails. 
Maximum diameter of reinforcement
The maximum diameters of reinforcement are set by the user in Design Settings, the initial default values being: 

Maximum bar size 

32 mm 
Maximum link bar size 

16 mm 
If the design results in a bar size greater than the user specified limits the checks fails. 



In Section 8.8 of BS EN 199218:2004, additional rules are specified when "large diameter bars" are used in the design. A large diameter bar is defined as being a bar with a diameter larger than φ_{large} where φ_{large} is an NDP value.
For design in accordance with EC2 Recommendations, Finnish NA, Norwegian NA and Swedish NA; 

φ_{large} 

32 mm 
For design in accordance with UK NA, Irish NA, Malaysian NA and Singapore NA; 

φ_{large} 

40 mm 


In the current release the provisions of Section 8.8 are not implemented. If the design results in a bar size with φ > φ_{large} then a warning is displayed to this effect, advising that the user should take account of the provisions of Section 8.8 when preparing the final design. 

Note:
Clause 7.3.3 (2) indicates that cracking can be controlled either by restricting the bar diameter or the max spacing. Tekla Structural Designer adopts the latter approach using Table 7.3N  therefore the maximum bar diameters specified in Table 7.2N are not checked. 
Minimum distance between bars
The minimum clear horizontal distance between individual parallel bars, s _{cl,min}, is given by;^{1} 

s_{cl,min} 

MAX [k_{1}*φ, d_{g}+k_{2}, s_{cl,u,min}, 20 mm] 
where 

k_{1} 

the appropriate NDP 
k_{2} 

the appropriate NDP 
d_{g} 

the maximum size of aggregate 
φ 

the maximum diameter of adjacent bars, φ_{i} and φ_{j} 
s_{cl,u,min} 

user specified minimum clear distance between bars 
Note:
To allow you to make decisions regarding access for concrete compaction or size of aggregate, a value for the minimum clear distance between bars can be specified on the appropriate Reinforcement Settings page within Design Settings  separate values being set for bars in the top of a beam and for those in the bottom of a beam. 

The minimum clear vertical distance between horizontal layers of parallel bars, s_{cl,min}, is given by; 

s_{cl,min} 

MAX[k_{1}*φ, d_{g}+k_{2}, 20 mm] 


For design in accordance with EC2 Recommendations, UK NA, Irish NA, Malaysian NA, Singapore NA, Finnish NA and Swedish NA; 

k_{1} 

1.0 
For design in accordance with Norwegian NA; 

k_{1} 

2.0 
For design in accordance with EC2 Recommendations, UK NA, Irish NA, Malaysian NA, Singapore NA, Norwegian NA and Swedish NA; 

k_{2} 

5.0 mm 
For design in accordance with Finnish NA; 

k_{2} 

3.0 mm 
Maximum spacing of tension bars
The maximum centre to centre bar spacing for crack control, s_{cr,max}, is dependent on the maximum allowable crack width, w_{max}, specified in the beam properties from a menu of values which are: 0.20mm, 0.30mm or 0.40mm with a default value of 0.30mm. The service stress in the reinforcement, σ_{s}, is given by; 

σ_{s} 

(A_{s,reqd}/A_{s,prov}) * (f_{yk}/γ_{s})*R _{PL} 
where 

A_{s,reqd} 

area of reinforcement required for the maximum design Ultimate Limit State moment, M_{Ed } 
A_{s,prov} 

area of reinforcement provided 
R_{PL} 

permanent load ratio 
In the beam properties you are required to supply a value for the permanent load ratio, R_{PL}. A default of 0.65 has been assumed, but you are advised to consider if this is appropriate and adjust as necessary. The maximum allowable centre to centre bar spacing, s_{cr,max}, is then obtained from table 7.3N (shown below) by looking up the calculated value of the service stress in the reinforcement, σ_{s}, using interpolation between values of σ_{s} 
Steel Service Stress, σ_{s} (N/mm^{2}) 
Max Allowable bar Spacing for crack control, s_{cr,max}  
w_{max} = 0.40 mm  w_{max} = 0.30 mm  w_{max} = 0.20 mm  
≤ 160  300  300  200 
200  300  250  150 
240  250  200  100 
280  200  150  50 
320  150  100  Warning 
360  100  50  Warning 
>360  Warning  Warning  Warning 
Minimum area of reinforcement
The minimum area of longitudinal tension reinforcement, A _{s,min}, is given by;^{2} 

A_{s,min} 

MAX[k_{min1}*b_{w}*d*(f_{ctm}/f_{yk}), k_{min2}*b_{w}*d] 
where 

k_{min1} 

the appropriate NDP value 
k_{min2} 

the appropriate NDP value 
f_{ctm} 

mean value of the axial tensile strength of the concrete 
f_{yk} 

characteristic yield strength of the reinforcement 
For design in accordance with EC2 Recommendations, UK NA, Irish NA, Malaysian NA, Singapore NA, Finnish NA, Norwegian NA and Swedish NA; 

k_{min1} 

0.26 
k_{min2} 

0.0013 
Note:
There is no requirement to have a minimum area of compression reinforcement. 

The minimum area of longitudinal tension reinforcement for crack control, A_{s,min,cr} is given by;^{3} 

A_{s,min,cr} 

0.4*k*f_{ctm}*A_{ct}/σ_{s} 
where 

k 

1.0 when h ≤ 300 0.65 when h ≥ 800 
f_{ctm} 

mean value of axial tensile strength of concrete 
0.30*f_{ck} ^{(2/3)} for concrete grades ≤ C50/60  
2.12*ln(1+((f_{ck}+8)/10)) for concrete grades > C50/60  
σ_{s} 

the interpolated reinforcement service stress from appropriate for the bar spacing of the reinforcement provided 
A_{ct} 

area of concrete in tension just before formation of first crack 

b*y where y = the distance of the Elastic NA from bottom of beam  
The minimum area of longitudinal tension reinforcement required, A_{s,min,reqd}, is then given by; 

A_{s,min,reqd} 

MAX (A_{s,min}, A_{s,min,cr}) 
Maximum area of reinforcement
The maximum area of longitudinal tension reinforcement, A_{st,max}, is given by;^{4} 

A_{st,max} 

k_{max}*A_{c} 
The maximum area of longitudinal compression reinforcement, A_{sc,max}, is given by; 

A_{sc,max} 

k_{max}*A_{c} 
where 

k_{max} 

the appropriate NDP value 
A_{c} 

the cross sectional area of the beam 

h*b_{w}  
For design in accordance with EC2 Recommendations, UK NA, Irish NA, Malaysian NA, Singapore NA and Norwegian NA; 

k_{max} 

0.04 
For design in accordance with Finnish NA and Swedish NA; 

A_{st,max} = A_{sc,max} = unlimited 
Footnotes