Seismic Design Criteria for Circular Lap-Spliced Reinforced Concrete Bridge Columns Retrofitted with Fiber-Reinforced Polymer Jackets

ACI Structural Journal, May/Jun 2005 by Elsanadedy, Hussein M, Haroun, Medhat A

3. The optimum computational tool in conjunction with the proposed safety factors were incorporated in a rigorous design methodology for circular lap-splice RC bridge columns upgraded with FRP jackets. In the proposed design approach, jacket thickness within the lap-splice zone will be the greater of: requirement for confinement of the compression concrete, anti-buckling constraint, and requirement for clamping on the lap-splice region. It is imperative to note that in addition to bridge columns, the proposed retrofit design criteria may be also applied to circular RC building columns in seismic regions.

NOTATION

A^sub b^ = area of longitudinal steel bar

A^sub g^ = gross area of column section

c^sub u(existing)^ = neutral axis depth at ultimate response of existing column

c^sub u(ret)^ = neutral axis depth at ultimate response of retrofitted column

D = diameter of circular column

d^sub bl^ = diameter of longitudinal steel bar

E^sub j(design)^ = design tensile modulus of FRP jacket

f'^sub ce^ = expected (most probable) concrete strength

f^sub ju(design)^ = design tensile strength of FRP jacket

f^sub ye^ = expected yield stress of reinforcing steel

L^sub c^ = column height

L^sub j^ = height of FRP jacket

L^sub p^ = length of plastic hinge

L^sub s^ = lap-splice length

M^sub u(existing)^ = moment capacity of existing column section

M^sub u(retrofit)^ = moment capacity of retrofitted column section

n^sub b^ = number of longitudinal steel bars within column section

P = axial force

t^sub j(conf)^ = thickness of FRP jacket within primary confinement zone

t^sub j(req)^ = required thickness of FRP jacket

t^sup ^ ^sub j(sh)^ = thickness of FRP jacket for shear enhancement within plastic end region

Δ^sub p^ = plastic displacement

Δ^sub u-exp^ = ultimate experimental displacement

Δ^sub u-th^ = ultimate theoretical displacement

Δ^sub y^ = idealized yield displacement

ε^sub cu^ = ultimate concrete compressive strain

ε^sub ju(design)^ = design ultimate tensile strain of FRP jacket

Φ^sub p^ = plastic curvature of column section

Φ^sub u^ = ultimate curvature of column section

φ^sub v^ = retrofit design factor for maximum lateral load

φ^sub µ^ = ductility knockdown factor

µ^sub Δ(demand)^ = demand ductility

µ^sub Δu-exp^ = ultimate experimental displacement ductility

µ^sub Δu-th^ = ultimate theoretical displacement ductility

µ^sup calc^^sub Δ(capacity)^ = calculated ductility capacity

µ^sup R^^sub Δ(capacity)^ = required ductility capacity

µ^sup Red^^sub Δ(capacity)^ = dependable (or reduced) ductility capacity

θ^sub p^ = plastic rotation at center of plastic hinge

ρ^sub j^ = volumetric ratio of FRP jacket

σ = standard deviation

τ'^sub bc^ = bond strength of confined concrete

τ'^sub bo^ = bond strength of unconfined concrete

τ^sub yield^ = bond stress at first-yield state

REFERENCES

1. Chai, Y. H.; Priestley, M. J. N.; and Seible, F., "Flexural Retrofit of Circular Reinforced Concrete Bridge Columns by Steel JacketingExperimental Studies," Report No. SSRP-91/06, UCSD, Oct. 1991.

2. Ma, R., "Seismic Retrofit and Repair of Reinforced Concrete Columns Using Advanced Composite Materials," PhD dissertation, University of Southern California, Los Angeles, Calif., Aug. 1999.