FRP REPAIR OF CHIMNEY

Repairs to concrete chimneys by concrete enlargement or steel sheathing have been carried out

for many years as a mean of extending the service life of deficient and deteriorated chimneys

(Pinfold and Scott, 1997). Steel sheathing has the advantage of lower additional weight in

comparison to concrete enlargement. However, the high cost of labor to install the usually heavy

steel plates, difficulties with splicing, and considerable maintenance costs to prevent corrosion

have limited the applications of this repair option. Fibers reinforced polymers (FRP), on the

other hand, have relatively high strength, are lightweight, and have a consistently lower cost.

Combining these factors with the relatively simple installation procedure and the immunity to

corrosion makes FRP the material of choice over steel sheathing for the repair of tall chimneys.


 

In the mid-eighties, Ohbayashi Co. and Mitsubishi Kasei Co. in Japan developed the concept of

strengthening and retrofitting existing RC chimneys using carbon fiber reinforced polymer

(CFRP) strands and tapes (Katsumata et al., 1990, ACI 440.R-96). In this repair method, CFRP

tapes were glued first to the concrete in the longitudinal direction to enhance flexural strength.

CFRP strands were then impregnated with resins and spiral-wound around the surface for

additional lateral reinforcement. The primary function of the spiral wound strand is to improve

shear capacity and ductility of the chimney (ACI 440.R-96). FRP installation using automated

wet winding drew considerable attention to the potential use of composites for the retrofit of

civil infrastructure and several chimney upgrade projects were completed using this technology.

A few years later, the automated wet winding method was completely replaced by the use of

carbon fiber sheet material, which is applied externally to the concrete using a manual lay-up

process. Between 1987 and 1994, Mitsubishi Kasei reported a total of 28 sites where retrofit had

been performed using either the tow winding or manual lay-up application processes (Emmons,

2008).

In the United States, Europe and Middle East, the use of composites for chimneys and smoke

stacks upgrade is still very limited, although increasingly gaining momentum. The reason for

the limited use, despite the significant construction savings in time and materials, is due in large

part to the lack of design guidelines and the limited experience of chimney designers with FRP

materials. This paper tries to overcome these limitations by a presenting a simple methodology

for the flexural strengthening of annular chimneys with FRP. A case study is used to

demonstrate the full scale application of FRP for increasing the seismic resistance of an existing

concrete chimney.