RC Column Concrete Jacketing

TN-RET-001 — ACI 318-19, ACI 562-16, ASCE 41-17, Mander et al. (1988) via fib Bulletin 14

Parametrization

Existing Column (as measured, not as drawn)

Width, bₑ (mm)

Depth, hₑ (mm)

f'c existing (MPa)

fy existing bars (MPa)

Bar diameter (mm)

Bars per face (width)

Bars per face (depth)

Cover to bar centre (mm)

Feed this from a condition assessment. ASCE 41-17 Table 10-1 multiplies lower-bound f'c by 1.50 and fy by 1.25 for expected values — decide which you are passing and stay consistent across the whole form.

Jacket

Faces enlarged

A partial jacket computes its geometry, axial strength and P-M interaction only. Confinement, shear, interface, stiffness and detailing have no model for it and are reported unavailable rather than estimated, and P·e is not added to Mu. Two adjacent faces are refused outright — that section's capacity is a biaxial surface, not a curve.

Thickness, t (mm)

f'c jacket (MPa)

fy jacket bars (MPa)

Bar diameter (mm)

Bars per face (width)

Bars per face (depth)

Clear cover to tie (mm)

Tie diameter (mm)

Tie spacing, s (mm)

Tie fyt (MPa)

Tie legs each way

Bars restrained per face

Bars restrained per face drives the Mander kₑ and is the input most often set wrong. A plain perimeter hoop restrains only the four corner bars — that is 2. Restraining every bar requires crossties (ACI 318-19 25.7.2.3); assuming full restraint when the detail is a plain hoop overstates f'cc by roughly 12%.

Transverse steel

Factored Demand on the Jacketed Column

Pu (kN, compression +)

Mu (kN-m)

Vu (kN)

Clear height, L (mm)

After jacketing the column is several times stiffer and attracts more force. If these came from a model of the un-jacketed structure, every result below is optimistic.

Construction

Jacket continuity

The single most consequential field. A jacket stopping at the slab soffit must push its entire axial share across the interface; one bearing on the foundation transfers it by direct bearing and the axial term vanishes.

P₀ at casting (kN)

P service (kN)

Creep coefficient

Interface surface

Dowel diameter (mm)

Dowels per row

Dowel row spacing (mm)

Dowel fy (MPa)

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RC Column Concrete Jacketing

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Figure 1 — P-M Interaction

Figure 2 — Jacketed Section