Columns

Design Columns

Switch to turn on/off the design of all columns.

Fcu:

Characteristic strength of the concrete at 28 days in N/mm2 or cylinder/cube strength for EC design.

This is now better set in the Beam/Column Levels area as you can set different grades at different levels.

Minimum K Value:

The program uses BS 8110 equation 33 to calculate the K value for slender columns but allows you to conservatively set it to 1.  Allowing you to set the minimum value provides a flexible degree of safety.

X-X, Y-Y Braced:

The program needs to know whether the frame is braced or un-braced in each axis.

Fixed Bases are Deep:

When the program encounters a fixed support the program needs to know whether to consider this as a Deep or Shallow beam end condition.

Ignore Tension Gaps:

There are two schools of thought on whether BS 8110 requires you to check the tension steel gap in columns. When selected this check is ignored.

Symmetrical Reinforcement:

When selected the reinforcement on all 4 faces is identical. When de-selected the reinforcement on all opposite faces is identical.

Plane Frame Y-Y Restraints:

In 2-D frames you need to tell the program what the 'out of plane' YY restraint conditions are - deep, shallow or nominal.

Check for tie forces:

BS 8110 Pt1 - Cl 3.12.3.7 Vertical ties. 

When selected the tie force check will be carried out. It will look for a load case with 1.05D+0.35L or 1.05D+1.05L (storage &Industrial) cl_2.4.3.2.   If no suitable case is found then all ULS loading cases are checked and the maximum load divided by 1.333  = 1.4/1.05 conservative.  

EC2 - calc Lo using BS method:

Calc Lo in 'braced' columns using table 3.19 from BS 8110 Pt1 (see Concise EuroCode 5.6.1.2 table 5.1).

EC - Bi-axial bending to simplified eqn:

Use the simplified bi-axial bending formula eqn 5.39 in clause 5.8.9(4).

Aspect ratio limit:

Aspect ratio above which columns are not designed as they are considered to be walls.  

Pads

Design Pads:

Permit or omit the design of column supports as pads. You would turn this off if your frame was supported on piles.

No up-lift:

Size pads to prevent up-lift of the base. During AutoSizing only.

Ignore Shear:

Omit the horizontal shear force from the support reactions from the design of pad foundations. This reduces or omits applied bending on the pad. If you use this option you must be careful to remember to resist the horizontal forces by some other method. A typical example of this would be where the column leg is tied to the floor slab.

Ignore srv moment

If there are no Ultimate moments then ignore any service moments.

This applies to frames with “Nominally pinned” steel columns to BS 5950-1:2000 Cl 5.1.3.3 where 20% base fixity is allowed in service cases to reduce deflections.

Mass Concrete

Design all pads as mass concrete.

Estimate Serv Forces from Ultimate cases:

Where no matching service case is found, estimate the service forces from ultimate forces in corresponding ultimate case by reducing by an appropriate factor.

Fcu:

Characteristic strength of the concrete at 28 days in N/mm2.

SWP:

Safe Working Pressure in kN/m2 or the Un-Factored (Service) Bearing pressure used in sizing the pad. The program identifies a loading case as service case if all load factors are equal or less than 1.00.

Density:

Density of the concrete in kN/m3.

Style:

Style of reinforcement          

1 Straight Bars.  2 Bobbed Bars.  3 Full height U-Bars.

Surcharge:

Surcharge to top of base in kN/m2 applied to whole surface area of base.

Gk Service:

Partial safety factor on the Density and Surcharge in service load cases.

Gk Service:

Partial safety factor on the Density and Surcharge in ultimate load cases.

Mue %

Coefficient of friction between soil and concrete base as a percentage. 30% implies a mue of 0.30.

Cohesion

Cohesive shear resistance of base in kN/m2  10 to 140 kN/m2  for Soft to Stiff clays in Reynolds Table 17.   Use with caution.

Soil Density

If we have a soil density γs then we can increase your SWP by the overburden height H * γs.   H=top of plinth to underside of base. 

Height of soil Ho:

Height of soil in m above pad - used for calculating passive pressure & additional surcharge.

K Passive:

Set the K passive factor.