Design Code Options

Simple column bases can be designed to the following EC3 code versions:

• EC3
• EC3 Finland NA
• EC3 Ireland NA
• EC3 Malaysia NA
• EC3 Norway NA
• EC3 Singapore NA
• EC3 Sweden NA
• EC3 UK NA

Base plate steel grades

Base plates will use S235, S275, S355 and S460 family groups. Strengths greater than 460 are beyond scope. User defined grades ≤ 460 are allowed.

Design method and valid sections and forces for design

Base plate design uses the ‘Effective area’ method for axial compression loads, with horizontal major and/or minor shear allowed, but no moments i.e. pinned base design without uplift. Only I/H and hollow section steel columns are valid for design. Minor shear is a valid design force for base plates on all of these column sections except for Rectangular Hollow Sections.

Column position on the base plate

The column can only be concentric on the base plate.

Base plate position on the concrete foundation

The base plate can be eccentric on the concrete foundation along both the minor and major axes. Note, such eccentricities are achieved in the concrete foundation properties.

Concrete foundation design

Concrete foundation design is separate to, but cognizant of, the base plate design. Only isolated foundations are valid concrete foundations for base plate design checks in first release.

Tekla Connection Designer

Under EC head code there is no longer an option to export a base plate to Tekla Connection Designer from Tekla Structural Designer. For EC design checks, of moment bases for example, Tekla Connection Designer can still be used as a standalone product.

Design method

The ‘Effective area’ method is used for design. The principle steps in this method are as follows:

• Calculate the design bearing strength, f_jd

• Calculate the required plate area, A_reqd and the actual area provided, A_plate

• Compare A_plate and A_reqd (Note, A_plate must be greater than A_reqd to proceed)

• Calculate the stiff cantilever projection dimension, ‘c’

• Calculate the effective plate area, A_eff

• Compare A_eff and A_reqd (Note, A_eff must be greater than A_reqd to ‘pass’)

Clarification of the design bearing strength calculation

The design bearing strength, f_jd, between the underside of the base plate and the bedding material in the grout space is given by:

f_jd = β_j * α * fcd

Where

β_j = foundation joint material coefficient = (2/3)

α = a coefficient which accounts for diffusion of the concentrated force within the foundation

f_cd = design value concrete compressive strength = α_cc * f_ck / ɣ_c

α_cc = coefficient for long term effects

f_ck = concrete characteristic cylinder strength

ɣ_c = partial safety factor for concrete

Note that even where a concrete foundation is not modeled, the coefficient, α, is calculated from the concrete dimensions shown in the base plate properties. The plan dimensions of the concrete foundation must be larger than the base plate (plus an allowance for grout), and the depth of the concrete foundation must be larger than the embedded bolt length plus an allowance for bottom cover.

Welds

Weld resistance varies by section type and whether direct contact in bearing is flagged on or off in the base plate properties - when on, axial force on the weld is taken as zero.

• For I/H sections, flange welds resist the vector sum of axial force and minor shear force, while web welds resist major shear force. Forces and resistances are given in Force units.

• For RHS sections, flange welds (faces A & C) resist axial force, while web welds (faces B & D) resist major shear force. Forces and resistances are given in Force units.

• For CHS and SHS sections, an all around full profile weld resists the vector sum of axial force, major shear force and minor shear force. Forces and resistances are given in Force per length units.

Connection forces are established from a global analysis of the building as a whole. Column base plates in Tekla Structural Designer have a limited set of design forces for which they can be designed. Non-design forces are identified and, where their value is greater than a given limit, they are displayed to you in the results along with a Warning status. The given limits are defined on the Design Forces page of the Design Settings dialog available from the Design tab on the ribbon.

The forces from the global analysis are treated in the following manner:

• Simple column bases are designed for the positive axial force at the base of the column, the major shear (foundation reaction) in the plane of the column web (column section minor axis), and minor shear (foundation reaction) in the plane of the column flanges (column section major axis). Bases are orientated to the column’s major and minor axes and hence there is no requirement to resolve the force when the column is rotated. Columns can only be sloped in the plane of the web and the bottom stack axial force and shear are resolved into vertical and horizontal forces in the base.

Where the global analysis includes second-order (P-Delta) effects the Ultimate Limit State design forces will include these effects also. However, for column bases the design forces for soil bearing pressure calculations are taken from an elastic global analysis of the unfactored loadcases without second-order effects. Nevertheless, EQU and GEO load combinations are not considered in the base plate design i.e. these combinations do not appear in the results. All seismic (SEIS) combinations appear in the results. However, those deriving from ELF are considered for design while those from RSA result in Beyond Scope status.