Sections considered
NZS3101:2006 Concrete Structures Standard (incorporating Amendments 1, 2 and 3)
SECTION 1 GENERAL
1.1 SCOPE
1.1.1 Relationship to NZ Building Code
1.1.1.1 Minimum requirements
SECTION 2 DESIGN PROCEDURES, LOADS AND ACTIONS
2.3 DESIGN FOR STRENGTH AND STABILITY AT THE ULTIMATE LIMIT STATE
2.3.2 Design for strength
2.3.2.2 Strength reduction factors, ultimate limit state
(c) Flexure with or without axial tension or compression (φ = 0.85)
(e) Shear and torsion (φ = 0.75)
2.4 DESIGN FOR SERVICEABILITY
SECTION 5 DESIGN PROPERTIES OF MATERIALS
5.2 PROPERTIES OF CONCRETE
5.2.1 Specified compressive strength
5.2.2 Applicable density range
5.2.3 Modulus of elasticity
5.3 PROPERTIES OF REINFORCEMENT
5.3.2.3 Ductility class
5.3.3 Strength
SECTION 7 FLEXURE, SHEAR, TORSION AND ELONGATION OF MEMBERS
7.4 FLEXURAL STRENGTH OF MEMBERS WITH SHEAR AND WITH OR WITHOUT AXIAL LOAD
7.4.2.7 Equivalent rectangular concrete stress distribution
7.5 SHEAR STRENGTH OF MEMBERS
7.5.2 Maximum nominal shear stress, vmax
7.5.8 Design yield strength of shear reinforcement
7.5.10 Minimum area of shear reinforcement
7.6 TORSIONAL STRENGTH OF MEMBERS WITH FLEXURE AND SHEAR WITH AND WITHOUT AXIAL LOAD
7.6.1.2 Threshold torsional reinforcement, To
7.6.1.6 Torsional strength requirements
7.6.1.7 Torsional shear stress, vtn
7.6.3.2 Maximum stirrup spacing
SECTION 10 DESIGN OF REINFORCED CONCRETE COLUMNS AND PIERS
10.3 GENERAL PRINCIPLES AND DESIGN REQUIREMENTS FOR COLUMNS
10.3.1 Strength calculations at the ultimate limit state
10.3.1.1 Dependable section cross section
10.3.2 Slenderness effects in columns
10.3.2.3 Approximate evaluation of slenderness effects
10.3.2.3.4 Consideration of slenderness (short/slender classification)
10.3.2.3.5 Design actions including slenderness effects (moment-magnifier method)
10.3.4 Strength of columns in bending with axial force
10.3.4.2 Limit for design axial force, N*, on columns
10.3.8 Longitudinal reinforcement in columns
10.3.8.1 Limits for area of longitudinal reinforcement
10.3.8.2 Minimum number of longitudinal bars (Advisory only)
10.3.8.3 Spacing of longitudinal reinforcement
10.3.10 Transverse reinforcement in columns
10.3.10.2.1 Maximum permissible nominal shear force and effective shear area
10.3.10.5 Design of spiral or circular hoop transverse reinforcement for confinement of concrete and lateral restraint of longitudinal bars
10.3.10.5.1 Confinement and anti-buckling reinforcement
10.3.10.5.2 Spacing of spirals or circular hoops
10.3.10.6 Design of rectangular hoop and tie transverse reinforcement for confinement of concrete and lateral restraint of longitudinal bars
10.3.10.6.1 Confinement and anti-buckling reinforcement
10.3.10.6.2 Spacing of tie sets
10.3.10.7 Minimum diameter of transverse reinforcement
10.3.10.7.1 Minimum diameters for rectangular hoops and ties
Assumptions
This module designs reinforced concrete columns to NZS 3101:Part 1:2006. Design is for gravity (non-seismic) ultimate-limit-state load combinations using the nominally-ductile provisions of Section 10.3. The column cross-section must be a supported solid shape. Hollow sections (circular, rectangular and square tubes) are not supported.
Clause 5.2.3 - Concrete modulus of elasticity Ec is computed from Equation 5-1, using the specified concrete strength and density. This value (not the section material library's Young's modulus) is used by the column engine in the Euler buckling capacity and the moment-magnifier calculation. Where the library-specified Ec differs from the Equation 5-1 value by more than 5%, an informative warning is reported.
Clause 7.4 - Flexural and combined axial-flexural strength is computed by a full strain-compatibility solver that meshes the cross section and calculates the full 3d interaction diagram capacity surface. The equivalent rectangular stress block of Clause 7.4.2.7 is used as the stress-strain curve of the concrete.
Clause 10.3.2.3 - Slenderness is evaluated by the approximate moment-magnifier method (Eq 10-2 to 10-9). A rigorous second-order (P-delta) analysis to Clause 10.3.2.1 is not performed; the magnified-moment method is used in every case.
Clause 10.3.2.3(c) - The approximate method is only valid where the slenderness ratio kLu/r does not exceed 100. This limit is checked for both principal axes; a column exceeding it is reported as failing, since beyond kLu/r = 100 the Standard requires a second-order analysis that this module does not carry out.
Columns are assumed to be appropriately braced against sidesway.
Clause 10.3.2.3.5 - Cm is taken as 0.6 + 0.4·(M1/M2) with a floor of 0.4 (Eq 10-8), except that Cm is set to 1.0 where a transverse load acts between supports or where the minimum design moment of Eq 10-9 governs. The minimum design moment M2,min = N*(15 + 0.03h) (Eq 10-9) is applied about each axis (h is the section dimension in the plane of bending). The user may disable this floor, in which case a warning is reported.
Tie diameter, tie spacing for bar restraint and spiral clear spacing are always checked, independent of whether the user has enabled the shear or torsion checks.
Clause 10.3.10.6.3 - The support-of-longitudinal-bars requirement is not modelled and is surfaced as an advisory note for all columns.
Earthquake (seismic) design, prestressed concrete and fire resistance are not considered by this module. Seismic design and ductile detailing (NZS 3101 Sections 2.6, 6.9, 8.9, 9.4 and 10.4 - including potential plastic-hinge regions, ductile detailing and capacity-design overstrength actions) are not performed;