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1

CFRP Strengthening and Rehabilitation of Corroded Steel Pipelines under Direct Indentation

Mohamed Elchalakani1*, Ali Karrech1, Hakan Basarir1 and Sabrina Fawzia2

1School of Civil Environmental, and Mining Engineering, University of Western Australia, Australia, * Corresponding author: The School of Civil, Environmental and Mining Engineering at the Faculty of

engineering, computing and mathematics, the University of Western Australia, Email: [email protected]; Tel: (+614) 79199629.

2School of Civil Engineering and Built Environment, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia

ABSTRACT

A recent paper by the authors showed that the innovative technique of CFRP repair of severely corroded steel

circular pipes is promising. This paper presents further experimental results for two series of CFRP

strengthened and rehabilitated pipes under quasi-static large deformation 3-point bending and direct

indentation. The main parameters examined in this paper were the corrosion penetration in the wall thickness,

its extent along the pipe, the type and number of the CFRP sheets. The corrosion in the wall thickness was

artificially induced 3600 around the circumference and in the wall thickness by machining where four different

severity of corrosion were examined of 20% (mild), 40% (moderate), 60% (severe), and 80% (very severe).

The first series was for rehabilitation of 12 artificially degraded pipes with limited corrosion repaired using

externally wrapped sheets where the extent of corrosion along the pipeline was in the range of Lc/Dn=1.0 to

3.0, where Lc=length of corrosion and Dn is the nominal diameter of the pipe. The second series represents

strengthening of 4 degraded pipes with corrosion that extended along the full length of the pipe. The extent of

corrosion along the pipeline in this series was Lc/Dn =8.0. The section slenderness examined in this paper was

in the range of D0/t =20.32 to 93.6. The results show that the combined flexural and bearing strength of the

pipe can be significantly increased by adhesively bonding CFRP. The maximum gain in strength was 434%

which was obtained for the most severe 80% corrosion which extended along the full length of the pipe where

mailto:mohamed.elchalakani@

2

Lc/Dn =8.0. The average increase in the load carrying capacity was 97% and 169% for the rehabilitation and

strengthening series, respectively.

KEYWORDS: Steel, pipelines, CFRP strengthening, corrosion, retrofit, large deformation bending.

_________________________________

1. INTRODUCTION

1.1 General

Natural resources like oil and gas constitute the major share of global fossil fuel which is the dominant source

of energy of the world [1]. The advancement of human civilisation and scarcity of natural resources like oil,

natural gases and minerals lead to exploration deeper into the earth’s crust and to expand the venture in remote

locations; eventually increasing underground, high pressure ashore and subsea drilling activities. Metal

pipelines are the most efficient and safest ways to transport these natural resources over long distances. At

present, most of the pipeline systems consist predominantly of steel pipes due to their high strength, relative

simplicity of joints and low cost [2]. However, steel pipes that are laid underwater and underground can go

through adverse deterioration in the form of corrosion, crack, dents, wearing, buckling, gouging, spalling, leaks

and rupture. The most vulnerable weaknesses of steel pipe are corrosion and metal loss [3-4]. Steel pipes

carrying fluid, oil and gas are considerably susceptible to failure initiated by corrosion and due to its high

operating pressure under adverse atmospheric conditions. The severity is high when salt water and sulphur

ingress media are present. A general corrosion mechanism and initiation of corrosion in a pipe surface in the

presence of salt water. The hydroxide and chloride ions are contributing to the accelerated corrosion in

submerged and sea water conditions [3-4]. The degradation of the protective coating and formation of iron

hydroxide as a result of the corrosion [3-4].

A number of studies were carried out to study the corrosion of steel in saltwater and sulphur conditions and

subsequent performance degradations. Along with stress corrosion cracking resulted from high pH

environment, near-neutral pH as in groundwater was also found responsible for stress corrosion [5]. The

3

presence of CO2 in high temperature (400–6000 C) resulted in considerable corrosion of steel pipe and the

strong adsorption of sulphide anions blocked the development of a protective oxide film [6-7]. Hence,

corrosion and metal loss cause failures in pipelines and their rehabilitation is one of the prime interests of the

researchers all over the world.

Deterioration of metallic infrastructure including oil and gas pipelines is due to several causes but probably the

main factor is corrosion. Corrosion has a huge economic and environmental impact on virtually all facets of

the world’s infrastructure, from highways, bridges, and buildings to oil and gas, chemical processing, and water

and wastewater systems. In addition to causing severe damage and threats to public safety, corrosion disrupts

operations and requires extensive repair and replacement of failed assets. The annual cost of corrosion

worldwide is estimated to exceed $1.8 trillion, which translates to 3 to 4% of the Gross Domestic Product

(GDP) of industrialized countries. In the US, the annual cost of corrosion is estimated as $276B [8]. The annual

cost of corrosion to the Australian economy is estimated to be between $36B and $60B, whereas for the New

Zealand economy the cost lies between $5.5B and $9.2B [9]. Yet, governments and industries pay little

attention to corrosion except in high-risk areas like aviation and maritime industries.

In the UK, infrastructure asset including steel and composite bridges on the national trunk road network

managed by the Highways Agency are, in their majority, relatively new but a large number of old (over 100

years) wrought iron and early steel structures are to be found on the railway and canal network [10]. In the

USA, in according to the National Bridge Inventory compiled by the Federal Highway Administration, some

43% are made from steel and a considerable number of them suffers from different levels of corrosion. In

addition to corrosion, other problems relate to fatigue sensitive details, the need to increase the service load

and a lack of proper maintenance. In many cases, the deteriorated condition will be associated with certain

parts of the bridge and it would be more economical to consider repair and retrofit before a decision is made

to replace an entire bridge. Repair, upgrading and rehabilitation are invariably more economical than the

replacement alternative. Furthermore, in the case of bridges the strengthening (upgrading) and rehabilitation

4

takes less time and reduces service interruption. Strengthening and rehabilitation were traditionally

accomplished by attaching steel plates and more recently is performed by bonding Carbon fibre reinforced

polymer (CFRP) laminate [10-12].

1.2 CFRP Repair of Steel Structures

The superior mechanical, fatigue, high strength to density ratio and in-service properties of carbon fibre

reinforced polymer (CFRP) composites make them excellent candidates for strengthening and retrofitting of

steel girder bridges. However, to date only a limited amount of research appears to have been undertaken which

are related to rehabilitation although there is clear evidence that such studies are on the increase, particularly

those deal with rehabilitation of damaged steel structures. Despite its intrinsic cost, the possibility to shape the

CFRP lamina and to avoid the cumbersome work associated with the standard rehabilitation techniques, speed

of construction, reduced disturbance to the structure, minimizing economic losses due to the suspension of

services and finally the very low dead weight added makes the overall cost for strengthening to be reduced.

The raw materials of CFRP can be supplied in the forms of dry fibre/fabric sheets and impregnating resins for

the in-situ formation of FRP via the so-called wet lay-up process, which allows the use of CFRP on irregular

and curved surfaces where application of steel plates may be impossible or highly challenging [10-12].

In the past many of the research on CFRP strengthening and rehabilitation dealt with steel closed or open

sections. In regards to closed sections, examples included but not limited to Square Hollow Sections (SHS)

under static and dynamic axial load [13-15], Rectangular Hollow Sections (RHS) under bearing load [16,17],

Circular Hollow Sections (CHS) under axial and large deformation bending [18-19]. The failure modes

reported included local flange and or web buckling or yielding of the steel section associated with rupture or

the CFRP wraps (sheets) or debonding of the CFRP plates.

In regards to strengthening and or rehabilitation of open sections, much research focused on I-sections [20-22]

with some research dealt with other profiles such as T-sections by Harries et al. [23], struts under uniform

compression by Elchalakani et al. [24], and lipped channels by Silvestre et al. [25]. Experimental results have

5

shown the effectiveness of strengthening steel columns, steel beams and steel-concrete composite girders by

bonding a CFRP plate to its soffit [20-22]. A number of failure modes are possible in such CFRP strengthening

of steel beams: (a) in-plane bending failure [21]; (b) lateral buckling [22]; (c) plate end debonding [21]; and

(d) intermediate debonding due to yielding and the opening-up of a crack [22]. Additional but less likely failure

modes include: (e) local buckling of the compression flange; and (f) local buckling of the web. Out of the

debonding failure modes plate end debonding is likely to occur due to high stress concentrations at the plate

ends. Plate end debonding is a premature failure mode which often occurs before significant contribution from

the CFRP is made. The research has shown this type of failure mode can be prevented by using longer CFRP

plates thus placing the plate ends in lower bending regions [21-22]. Unlike to plate end debonding, intermediate

debonding initiates in a region where CFRP is highly stressed and move towards the plate ends. Often the

initiation of intermediate debonding is governed by the presence of cracks or steel yielding [22]. Experimental

research [26] has shown that the intermediate debonding is governed by the high interfacial shear stresses thus

depends strongly on the interfacial shear fracture energy of the bond joint. Recently the author examined the

CFRP strengthening and rehabilitation of welded Rectangular Hollow Sections (RHS) with sharp corners under

bending and bearing [27]. The main finding was that the web rehabilitation using CFRP wraps was the most

effective compared to the top and bottom flanges. The maximum gain in strength was 58% for two wraps of

CFRP around the RHS. Also, it was found that the capacity of the repaired specimens with 20% corrosion in

the wall thickness can be restored to the control un-corroded specimen. However, such capacity could not be

regained for repaired specimens with more severe corrosion with 40% and 60% in the wall thickness.

1.3 Scope

A related paper by the first author [28] presented the results for a series of tests on CFRP rehabilitated Circular

Hollow Sections (CHS) under quasi-static large deformation 3-point bending. This paper presents a summary

of such rehabilitation series in additional to a new strengthening series. The main parameters examined in this

paper were the corrosion penetration in the wall thickness, its extent along the pipe, the type and number of

6

the CFRP wraps. The corrosion in the wall thickness was artificially induced 3600 around the circumference

by machining where four different severity of corrosion were examined of 20% (mild), 40% (moderate), 60%

(severe), and 80% (very severe). New design equations for bare and repaired CHS are presented at the end of

the paper.

2. TEST PROGRAM

The main parameters examined in this paper were the corrosion penetration in the wall thickness, and its extent

along the pipe, and the type and number of the CFRP sheets. The corrosion was artificially induced 3600 around

the circumference and in the wall thickness by machining where four different severity of corrosion were

examined of 20% (mild), 40% (moderate), 60% (severe), and 80% (very severe). The first series was for

rehabilitation of 31 artificially degraded pipes with limited corrosion repaired using externally wrapped sheets

[28]. The extent of corrosion along the pipeline was in the range of Lc/Dn=1.0 to 3.0, where Lc is the length of

corrosion and Dn is the nominal diameter of the pipe. The second series represents strengthening of 4 degraded

pipes with corrosion along almost the full length of the pipe. The extent of corrosion along the pipeline in this

series was Lc=8Dn. The section slenderness examined in this paper was in the range of D0/t =20.32 to 93.6.

According to BS 5950 [29], the slenderness limits are 40ε2, 50ε2, 140ε2 to identify Class 1 (compact), Class 2

(non-compact), Class 3 (non-compact), Class 4 (slender) sections. The parameter ε=(275/ σys)0.5, where σys is

the measured yield stress of the CHS. It is seen that the control un-degraded specimens are classified as Class

1, the bare specimens with corrosion of 20% are Class 2, the bare specimens with corrosion of 40% and 50%

are all Class 3, whereas the bare specimens with corrosion of 80% are Class 4.

It is worth noting that the paper examined both bare tubes and composite tubes. The BS5950 method of

classification is suitable only for bare tubes. Adding the CFRP to the bare tube enhances the local buckling

behaviour of the tube considerably and thus the section slenderness limits will change. Thus using the

slenderness limits for the bare tubes is favourably conservative for design purposes. There is a need to establish

plate element section slenderness for composite tubes. To the author best knowledge, there is no well-

7

established cross section classification method available for bi-metallic composite tubes made of steel and

CFRP. However, there was an attempt to determine such slenderness in [19]. Also, at present there are no

design code available for such composite tubes.

The CFRP sheets were wrapped around the section in the longitudinal and transverse direction with a sufficient

overlap. Fig. 1 shows the 3-point bending test set up where the pipe specimen is subjected to bending and

bearing. The UTM had a capacity of 250 kN and the load was applied at a slow rate of 2.5 mm/min. Table 1

summarises the key mechanical properties and geometries of the specimens including: the span L; the inside,

outside and average diameters after corrosion Di and D0, and Dav; the mean radius after corrosion R; the

thickness remained after corrosion ts; the total thickness of the carbon fibre layers tf; the length and thickness

of corrosion tc and Lc; the applied protocol of repair i.e., 1T1L or 2T2L; the type and manufacturer of the

CFRP; the length of CFRP Lcfrp, the weight of specimen; the elastic modulus Zs; the plastic modulus Ss; the

elastic moment Mys; and the plastic moment Mps. All the 42 specimens were cut from CHS having

Doriginal=101.6mm and to=5.0mm.

The Structural Technology V-Warp C200 [30] was 610 mm in width with 0.28 mm nominal thickness and had

an overlap at 1/3rd of the span of 150mm. The Structural Technology V-Warp 700 was used as primer and

saturant while Structural Technology V-Warp 778 was used for putty fill. The nominal tensile elastic modulus

of this adhesive is 3.45GPa and the tensile strength to be 62MPa. The nominal elastic modulus of the carbon

fibre is 276 GPa with a tensile strength of 4820 MPa.

The Sika-Warp 300-C [31] were 500 mm width and 0.13mm nominal thickness and hence also had an overlap

at 1/3rd of the span of 150mm. Sikadur 330 adhesive was used where the nominal tensile elastic modulus of

this adhesive is 3.8GPa and the tensile strength to be 30 MPa. The nominal elastic modulus of the carbon fibre

is 230 GPa with a tensile strength of 3500 MPa. Table 2 summarises the key mechanical properties of the

CFRP system used in the strengthening series and also in the rehabilitation series. It is worth noting that, in the

rehabilitation series, 1T1L and 2T2L were examined whereas in the strengthening series the 2T2L and

8

4T4Lwere examined. The term “T” means fibre direction is transverse in the hoop direction, and “L” means

the fibre direction is parallel to longitudinal axis of the pipe.

The machining was performed by turning the tube specimen in a CNC machine to ANSI/ASME B46.1 [32]

with a surface roughness average rating value of 32 µin (micro-inch) which corresponds to 0.8µm (micro-

meter). Proper surface preparation of adherends (CFRP and steel) surfaces is an important step to achieve a

proper bond joint. The steel surface was prepared by using sand paper in the machined zone and light grinding

to remove oil and dirt within the Lcfrp zone. The CFRP sheets were wrapped around the section in the

longitudinal and transverse direction with a sufficient overlap. Fig.1 shows the geometry of the pipe specimen.

All the specimens were made of a nominal section with D0=101.6mm, ts=5.0 mm, and 1000mm end-to-end

length. Fig. 2 shows the machining of the specimen. After machining, the bare and strengthened sections had

a span of 900mm, except one specimen T5L0C0-02 had a span of 450 mm. The circular loading pin (indenter)

was 40 mm in diameter and 600 mm long. In the rehabilitation series, each specimen was given a unique ID,

where L0 refers to no corrosion, whereas L1, L2, and L3 refer to corrosion length of 100mm, 200mm, and

300mm, respectively. The term 1T1L refers to one wrap of CFRP in the transverse (circumferential) was used

and one wrap of CFRP was used in the longitudinal direction. The term 2T2L refers to two wraps of CFRP in

the transverse (circumferential) were used and two wraps of CFRP were used in the longitudinal direction. The

symbol C0 refers to no CFRP was used, where C2 refers to the corrosion length is 300mm and C4 refers to the

corrosion length is 400mm. For example for T4L1C2-1T1L, the symbol T4 refers to the remaining thickness

after corrosion ts=4mm, L1 means that the corrosion length is 100mm, C2 indicates the CFRP laminate length

is 300mm. In the strengthening series, all the symbols were kept the same except that the ID of the specimen

started with “ST” instead of “T”.

The material used to make the pipe specimens was mild steel grade ASTM A53 Schedule 30, grade B355JR

[33]. The nominal yield strength of such material is σyn=372.4 MPa, the nominal tensile strength is σun=532.7

MPa, and the nominal percentage elongation at fracture en=34%. Tensile coupons were prepared and tested

9

according to the American Standard ASTM A370 [34] to determine the actual yield strength (σyt), the tensile

strength (σut) and the percentage elongation (et) at fracture. Appendix A shows the geometry of the tensile

specimens. The tensile specimens were tested in a 1000 kN capacity Universal Testing Machine. The 0.2

percent proof stress was used as the yield stress (σyt) for all coupons since they all exhibited a rounded stress-

strain curve. It can be seen in Table 3 that the average measured yield stress (σyt/σyn) and ultimate strength

(σut/σun) are 30% and 3% larger than their nominal values. Also, the average ratio of the measured σut/σyt

=1.13, the average percentage elongation et=14.76% and the average yield stress σyt=482.63 MPa.

3. TEST RESULTS

3.1 Failure Modes

Table 4 summarises the test results, where Pu and ∆u are the ultimate load and its corresponding deflection.

Note, Pu/Pu,control is the normalised ultimate strength where Pu,control is the average ultimate load obtained for

the control bare un-degraded specimens T5L0C0-01 and T5L0C0-03. Note, T5L0C0-02 was not used to

determine Pu,control as it has smaller span of L=450mm. In Table 4, the damage of the specimen was presented

by the dimensions A C′ ′ and D1 as sketched in Fig. 4(a). Table 4 lists the failure modes in each specimen, i.e,

debonding between the steel surface and the CFRP, fibre rupture, or steel fracture.

In general, the bare, CFRP rehabilitated and strengthened specimens passed through three stages, initial

denting, denting and bending up to the peak load (Pu), and finally exhibited structural collapse due to the

formation of a plastic hinge at mid-span. These stages are similar to those found for box section strengthened

using CFRP plates under 3-point bending.

Fig. 3 shows the 43 specimens after testing. The bare specimens failed by local denting at mid-span

immediately under the loading rod. Specimens with 20% (Class 2), 40% corrosion (Class 3) to 60% (Class 3)

corrosion failed by forming a symmetric mode of buckling (see Fig. 4a) whereas the specimens with 80%

corrosion (Class 4) failed by anti-symmetric mode of buckling (see Fig. 4b). A number of the repaired

10

specimens in the rehabilitation series had fibre rupture at mid-span due to large hoop strains. Also had

intermediate plate debonding at the ends of the CFRP laminate length (Lcfrp) due to large interfacial

longitudinal stains. It appears that specimen, T2L1C2-1T1L-SIKA did not have noticeable intermediate plate

debonding as shown in Fig. 5(a). It is seen that the end preparation of tapering the adhesive was done very

carefully but this was not the case for T2L1C2-1T1L in Fig. 5(b). It can be concluded that the application of

the CFRP system has a considerable effect on the strength of the repair system. In the strengthening series,

plate end debonding did not occur as the length of the CFRP laminate was of the order of eight times the

diameter of the pipe, however still the fibres ruptured at mid-span for a number of specimens due to large

bearing strains in the hoop direction.

3.2 Strength Gain

Fig. 6 shows the gain in strength due to the repair and strengthening using CFRP. It is seen that the combined

flexural and bearing strength of the pipe can be significantly increased by adhesively bonding CFRP. The

percent increase in strength was mostly affected by the corrosion level where the maximum gain was obtained

for the most severe 80% corrosion in the wall thickness. In the rehabilitation series the minimal gain in strength

was 31.8% for T3L1C2-1T1L with 40% corrosion whereas the maximum gain was 282.3% for T1L2C4-2T2L

with 80% corrosion. In the strengthening series the minimum gain in strength was 40.8% ST4L8C8-2T2L with

20% corrosion whereas the maximum gain was 434.1% for ST1L8C8-4T4L with 80% corrosion. The average

increase in the load carrying capacity was 97% and 169% for the rehabilitation and strengthening series,

respectively [28]. The average gain in the strengthening series was 74% larger than that obtained for the

strengthening series as the number of CFRP layers used in the former system was double. It is worth noting

that, in the rehabilitation series, 1T1L was more effective than 2T2L and in the strengthening series the 4T4L

was much more effective than 2T2L. This indicates that more carbon fibre is better for strengthening.

Fig. 7 shows the gain in strength due to the repair of corroded pipes for two types of CFRP laminates, i.e.

STRUCURAL and SIKA at 40% and 60% corrosion penetration in the wall thickness. It is seen that only in

11

one instance out of three cases, the SIKA system provided larger gain in strength where T2L1C2-1T1L-SIKA

had 70% gain compared to 60% gain obtained for T2L1C2-1T1L . As noted earlier, the specimen repaired with

SIKA did not have intermediate plate debonding as shown in Fig. 5(a). It is seen that the end preparation of

tapering the adhesive was done very carefully but this was not the case for T2L1C2-1T1L in Fig. 5(b). In the

remaining three cases, STRUCURAL repair system provided larger gain in strength. For example, at 40%

corrosion with 1T1L wrapping where corrosion length is Lc=100mm, STRUCURAL repair system achieved

35%, whereas SIKA system provided only 31% gain. Also, at 40% corrosion with 1T1L wrapping where

corrosion length is Lc=200mm, STRUCURAL repair system achieved 62%, whereas SIKA provided only 49%

gain. In addition, at 60% corrosion with 1T1L wrapping where corrosion length is Lc=200mm, STRUCURAL

repair achieved 93%, whereas SIKA provided only 86% gain.

Fig. 8 shows the bare specimen ST1L8C8-0 with 80% corrosion after testing in the UTM and forming the anti-

symmetric mode of buckling (see Fig. 4b) within the corrosion length Lc=800mm. The bare specimen failed

by local denting at mid-span immediately under the loading pin. The specimens with 20% to 60% corrosion

failed by forming a symmetric mode of buckling whereas the specimens with 80% corrosion failed by anti-

symmetric mode of buckling. Fig. 9 shows the composite specimen ST1L8C8-4T4L (strengthened) after

testing, which also failed by forming the anti-symmetric mode of buckling (see Fig. 4b). A number of the

repaired specimens in the rehabilitation series had fibres rupture at mid-span due to large bearing stresses and

had intermediate plate debonding at the ends of the CFRP laminate length [28]. However, such failure modes

were not observed in the strengthening series because the CFRP laminate extended along the full length of the

pipe.

3.3 Effect of Corrosion Length

Fig. 10 shows the effect of the corrosion length (Lc) on the normalised strength Pu/Po where Pu is the ultimate

load obtained in the test and Po is the ultimate load for the control specimen without corrosion. Po was

determined as the average for T5L0C0-01 and T5L0C0-03. It is seen that increasing Lc induces significant

12

reduction in the strength up to Lc=100mm=Dn. Also it is seen that almost all the reduction in strength occurs

within Lc= 300mm=3Dn, where Dn is the nominal diameter. Increasing the corrosion length beyond 3D had a

negligible effect on the load carrying capacity. This phenomenon is similar to pitting corrosion, where the

capacity of the long pipe is controlled by the localised corrosion.

3.4 Load-deflection Curves

Figs. 11 (a) to (d) show the effect of the length of corrosion Lc on the load-deflection curve (P-∆ ) for the bare

CHS with 20% to 80% with a variable corrosion length in the range of Lc=100mm to 300mm. With increasing

corrosion length from Lc=100 to 300mm, the stiffness and load carrying capacity moderately decreased for

20% to 40% corrosion compared to the control specimen (T5L0C0-01). With increasing corrosion severity to

60% and 80%, the stiffness and load carrying capacity decreased very rapidly, for all values of Lc, compared

to the control specimen. In addition, both Fig. 13(c) for 60% corrosion and Fig. 11(d) for 80% corrosion show

that steel fracture occurred only for Lc=100mm where stress concentration is relatively high. Whereas, steel

fracture did not occur for Lc larger than 100 mm as the stress concentration factor was relatively small for all

corrosion levels. Stress concentration was due to the abrupt change in thickness from the original un-machined

thickness (to) to the machined thickness (ts).

Figs. 12(a) to (d) show the effect of CFRP repair on the on the P-∆ curve for the bare CHS with 20% to 80%

corrosion for the case of a relatively small corrosion length Lc=100mm. Fig. 12(a) shows that for 20%

corrosion, the stiffness and capacity of the control specimen (T5L0C0-01) were restored for both 1T1L and

2T2L protocols. Whereas in Fig. 12(b) to (d) such stiffness and capacity were not restored even for 2T2L

protocol. This later observation was true for both repair systems, i.e., Sika and Structural. Fig. 12(c) shows the

effect of CFRP repair on the load-deflection curve for the case of 60% corrosion where Lc=100mm. At the

peak load, local buckling occurred for all the bare and repaired specimens directly under the loading pin which

was followed by a drop in the load carrying capacity. The increase in stiffness and strength is evident for both

types of repair systems (SIKA and STRUCTURAL). It is seen that the ductility of SIKA specimen is lower

13

than the STRUCTURAL one due to fibre rupture which occurred after reaching Pu. This may have caused the

maximum displacement of the Sika’s specimen to be almost half of the STRUCTURAL one. In this latter

specimen, debonding was observed between the CFRP laminate and the CHS at the right and left ends of the

Lcfrp zone. The post-peak residual strength was larger for the specimen repaired with the Structural fibres. Fig.

12(c) also shows that the bare steel CHS fractured at the end of the corrosion length Lc due to high stress

concentration as discussed before.

Figs. 13(a) to (d) show the effect of CFRP on the on the P-∆ curve for the bare CHS with 20% to 80% corrosion

for the strengthening series where Lc=800mm. Fig. 13(a) shows that for 20% corrosion, the stiffness and

capacity of the control specimen (T5L0C0-01) were restored for 4T4L protocol. Whereas in Fig. 12(b) to (d)

such stiffness and capacity were not restored for both 2T2L and 4T4L protocols. Fig. 13(b) shows that for 40%

corrosion, the post peak strength of ST3L8C8-4T4L was larger than the corresponding one for the control

specimen. Note, only STRUCTURAL wrap was used in the strengthening series. Steel fracture did not occur

in the strengthening series for Lc = 800 mm because the stress concentration factor was negligible for all

corrosion levels.

4. STRENGTH OF COMPOSITE SECTION

It was observed during the test that a full bond remained between the steel and the CFRP laminate up to the

ultimate peak load. This observation will be used to derive the plastic bending capacity of the composite

section. Consider the bimetallic plate (shown in Fig. 14) consisting of fully adhering different materials of

thickness ts (for RHS steel plates) and tf for (=tCFRP for CFRP fibres) and corresponding yield stresses σys and

σyf, respectively. The ultimate strength of the CFRP fibres (σuf) reported in Table 2 by the manufacture will

be used in the present model instead of σyf, as CFRP laminate does not exhibit yield in the tensile coupon test.

Examining the full yielding of the composite cross section of overall thickness t = ts + tf with unit width, and

14

requiring the forces on the composite section to equal zero, we obtain the position of the plastic neutral axis x

from [11,12]

fyffysys ttxxt σσσ +−=− )()( (1)

ys

sysfys tttxσ

σσ2

)( −+= (2)

Only the thickness of the fibre layers parallel to the neutral axis was used in the calculations in Eq. 1. To

evaluate the full plastic moment per unit width to bend plastically the composite section Mp we take moment

about the neutral axis

)2

(2

)(2

)( 22 ffyf

fysysp

txt

txxtM −+−

+−

= σσσ (3)

Introducing the dimensionless ratios k=σyf / σys and tr = tf / ts, Eq. 3 can be written as

4)221(

4

2222

2sys

rrreqys

p

ttktktk

tM

σσ−++== (4)

From Eq. 4, the equivalent thickness ( eqt ) is given by

222221 rrrseq tkktkttt −++= (5)

By knowing the corrosion severity (tc/to), the extent of corrosion along the pipe (Lc/Do) and by using the

corresponding mechanical properties for the equivalent composite wall thickness (Eq. 5), the elastic and plastic

moment capacities of the composite CHS can be determined as

2yc c c ys c eq ysM Z R tα σ πα σ= = (6)

24pc c c ys c eq ysM S R tα σ α σ= = (7)

0

b

cc

LaD

α

=

(8)

Where R is the mean radius of the composite tube, σys is the yield strength of the steel, Zc and Sc are the elastic

and plastic section moduli of the composite tube. Nonlinear regression showed that the strength modification

15

factor αc varied nonlinearly with both the normalised corrosion length (Lc/Do) and with the normalised severity

of corrosion in the wall thickness (tc/to). Preliminary tests showed that the effect of αc becomes negligible at

about Lc/Do ≈8.0, i.e. αc ≈1.0. Also, for the control specimens without corrosion such as T5L0C0-01, αc =1.0.

Fig. 17 shows the variation of αc (αc= Pu/Pu,ref) versus Lc/Do for four different corrosion severity 20%, 40%,

60%, and 80% where Pu,ref is the strength of CHS with Lc/Do =8.0. Also the four curves resulted from the

regression analysis are shown in Fig. 15. It was found that the parameters a and b in Eq. 8 are both linearly

varying with the corrosion severity (tc/to) and are given by a=1.47(tc/to)+0.72, and b=-0.43(tc/to)+0.05. The

values of the parameters a and b are given in the inset of Fig. 15 and αc values are listed in Table 4 for bare

and composite CHS. Note, for design purposes, it is conservative to assume αc =1.0 to determine the combined

bending and bearing capacity for Lc/Do≤3.0, which assume that the corrosion is spread along almost the full

length of the CHS.

The bearing strength of bare CHS, in the present steel design codes [29,36,37,38] is not suitable for the 3-point

bending setup used in the present paper (Fig. 1). The design rules provided in the steel design codes are suitable

for the design of truss chord members with no bending moments. Therefore, the modified bearing strength of

the composite section Rbyc can be determined using the expression derived by Wierzbicki and Suh [35] for 3-

point bending and allowing for the corrosion severity (tc/to), and the extent of corrosion (Lc/Do) using αc:

204

4ys eq

byc ceq

t DRt

βσ

α π

= (9)

In Wierzbicki and Suh [35] the exponent β=0.5 was theoretically derived, and it was found suitable for the

present tests. In order to determine the bare CHS properties in Eqs. 6 to 8, the steel thickness ts was used

instead of the equivalent thickness teq.

16

5. INTERACTION OF BENDING AND BEARING

In the present steel specifications such as BS5950 [29], AS 4100 [36], Eurocode 3 [37], there are insufficient

design rules for the interaction of bending and bearing for bare CHS, in particular under 3-point bending.

ANSI-AISC-10 [38] provides separate design rules for bending and for bearing of truss chord members made

of bare CHS. The design equations for bare RHS provided in AS4100 [36] and Zhao et al. [39] will be modified

herein to be used for bare and composite CHS. The new design equations for the corroded bare and repaired

CHS specimens using CFRP tested in this paper can be derived as follows

1.0u ubyc pc

P MR M

+ ≤

for bare CHS where D0/ts ≤ 164ε2 and Lc/D0 ≤ 3.0 (10)

1.2u ubyc pc

P MR M

+ ≤

for repaired CHS using CFRP where D0/ts ≤ 164ε2 and Lc/D0 ≤ 3.0 (11)

Fig. 16 summarises the present test results where Mu/Mpc is plotted against Pu/Rbyc. Note, Mpc and Rbyc are

determined from Eqs. 7 and 9, respectively. For bare CHS in Eq. 10, the equivalent and bare thicknesses are

the same, i.e., teq=ts, thus Mpc=Mps and Rbyc=Rbys. The enhancement in both the bearing and bending strength

of CHS due to the CFRP reinforcement is evident in Fig. 16. It is seen that Eq. 10 provides a good lower bound

for the test results of the bare and corroded CHS. Also, Eq. 10 provides as a good lower bound for the corroded

CHS strengthened using CFRP. It is also seen that Eq. 11 serves as a good lower bound only for the corroded

CHS rehabilitated using CFRP [28]. Note, the load carrying capacity of the strengthened CHS is lower than

the repaired ones because the corrosion extended along the full length of the pipe in the former. The slenderness

limit of D0/ts =164ε2 in Eqs. 10 and 11 corresponds to the maximum diameter-to-thickness ratio examined in

this paper. Similar design equations were provided in [27] and [40] for Rectangular hollow Sections (RHS)

under combined bending and bearing.

It is worth noting that the design rules provided for CHS reinforced using CFRP in Zhao et al. [41] and that

based on the tests performed in [19] are only suitable for pure bending. Finally, Fig. 16 also shows the test

17

result of bare CHS subjected to pure bearing performed by Hou et al. [42] where a number of their specimens

with large D0/ts could not reach the bearing strength determined by Eq. 8.

6. CONCLUSIONS

This paper presented experimental results for two series of CFRP strengthened and rehabilitated pipes under

quasi-static large deformation 3-point bending. The main parameters examined in this paper were the corrosion

penetration in the wall thickness, and its extent along the pipe, and the type and number of the CFRP sheets.

The corrosion was artificially induced 3600 around the circumference and in the wall thickness by machining

where four different severity of corrosion were examined of 20% (mild), 40% (moderate), 60% (severe), and

80% (very sever). The first series was for rehabilitation of 31 artificially degraded pipes with limited corrosion

repaired using externally wrapped sheets. The extent of corrosion along the pipeline was in the range of

Lc/Dn=1.0 to 3.0, where Lc=length of corrosion and Dn is the nominal diameter of the pipe. The second series

represents rehabilitation of 12 degraded pipes with full corrosion along the length of the pipe. The extent of

corrosion along the pipeline in this series was Lc/Dn =8.0. The section slenderness examined in this paper was

in the range of D0/t =20.32 to 93.6. The CFRP sheets were wrapped around the section in the longitudinal and

transverse direction with a sufficient overlap. The results show that the combined flexural and bearing strength

of the pipe can be significantly increased by adhesively bonding CFRP. The percent increase in strength was

mostly affected by the corrosion level where the maximum gain was 434% which obtained for the most severe

80% corrosion in the wall thickness. The average increase in the load carrying capacity was 97% and 169%

for the rehabilitation and strengthening series, respectively. Two new lower bound design equations based on

the bare and composite section properties were derived to predict the strength of bare and repaired CHS using

CFRP under combined bending and bearing.

18

Acknowledgments

The authors would like to thank Anthony Miles of Sika in Perth for his continuous support towards our research

at UWA. Thanks are given to Dr. Tarek Alkhrdaji of Structural Technologies for providing the CFRP sheets

and Mr Chris Hill of Structural Middle East in Dubai in assisting the students to apply the CFRP.

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Thin-Walled Composite Steel-CFRP Square Tubes, International Journal of Impact Engineering, 2009,

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19. Haedir, J., M.R. Bambach, X.-L. Zhao, R.H. Grzebieta, Strength of circular hollow sections (CHS)

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beams reinforced by pultruded CFRP strips, 2006, Composites Part B: Engineering, 37(1), 64-73.

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CFRP plate, Composite Structures, 2007, 78, 232-242.

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strengthened lipped channel steel columns, Engineering Structures, 2008, 30(10), 2613-2630.

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Thesis, Hong Kong Polytechnic University, Kowloon, 2010.

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beams under combined bending and bearing, Thin-Walled Structures, 2014, Vol. 82(9), 278-295.

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design in simple and continuous construction: hot rolled sections, 2000, British Standards.

21

30. Structural Technology, Technical Product Manual, 2010, USA.

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32. ANSI/ASME B46.1, American National Standards Institute, Surface Texture: Surface Roughness,

Waviness and Lay, 2002.

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and seamless, 12th edition, 2012.

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of Mechanical Sciences, 30, No. 3/4, 229-248, 1988.

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1, February, 2005.

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Construction Inc., 2010, Chicago, December.

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Behaviour and Design, Elsevier, 2005.

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bending and bearing,” Thin-Walled Structures, vol. 77, no. 4, pp. 86–108, 2014.

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Experiments, Journal of Constructional Steel Research, Volume 83(4), 2013, 90-104.

22

NOTATION

a Coefficient in Eq. 8 b Exponent in Eq. 8 D0 Outside diameter of the tube Doriginal Outside diameter of the un-corroded bare CHS Di Inside diameter of the tube (Di=Do-2ts) E Elastic section modulus e % elongation of steel coupons h Width of loading pin = 40mm kf =σyf / σys kc =σyf / σyc L Span of tube specimen Lcfrp Length of CFRP Lc Length of corrosion M Moment Mu Ultimate peak moment Mps Full plastic moment of bare steel section Mys Yield moment capacity of bare steel section Mpc Full plastic moment of composite section Myc Yield moment capacity of composite section P Load at mid-span Pu Ultimate peak load Po Ultimate peak load of counterpart corroded bare CHS Pu,ref Ultimate peak load for a CHS with Lc/D0=8.0 Pu,control Average ultimate load for the control bare un-degraded specimens R Average radius of specimen Rbys Bare bearing yielding capacity Rbyc Composite bearing yielding capacity to Thickness of the un-corroded bare CHS (to=5.0mm) ts Thickness of CHS after corrosion tc Thickness of corrosion (tc=to-ts) teq Equivalent thickness of top flange of CHS tf Thickness of CFRP fibres (=tCFRP) tr Ratio of thickness Ss Plastic Section modulus of bare CHS Sc Plastic Section modulus of composite CHS Zs Elastic Section modulus of bare CHS Zc Elastic Section modulus of composite CHS αc Strength modification factor defined in Eq. 8. β Coefficient defined in Eq. 8. ε = (275/σys)0.5 εu Ultimate strain of CFRP fibres ∆ Vertical deflection at mid-span ∆u Ultimate deflection at peak load ∆max Maximum deflection in the test

23

σys Yield stress of steel plate σyn Nominal yield stress of steel σyt Measured yield stress of steel σyn Nominal ultimate stress of steel σut Measured ultimate stress of steel σyf Measured yield/tensile strength of CFRP (=σuf) θ Circumferential angle for corroded section 43.

(a) Test Set Up

(b) Section A-A within Lc before applying CFRP (c) Section A-A after applying CFRP outside Lc

Figure 1: Test Set Up and specimen geometry

1000 mmLc

Doriginal

Dc

toriginal ts32tc

Figure 2: Machining of the pipe specimen

250 kN Max Load

Loading Ram

Load Cell

Steel PipeTest specimen

Span (L)

Saddle Supports102 mm Diameter

1000 mm

D0

A

A

Loading Rod40 mm diameter

LcLcfrp

CFRP Wraps with length Lcfrpcover the corroded section of length Lc along the pipe

D

CFRP

t f

t s

Figure 3: The pipe specimens after testing (left: rehabilitation series [28], right: strengthening series

(a) Symmetric mode

(a) side view of anti-symmetric mode (c) plan view of anti-symmetric mode

Figure 4: Schematic representation of collapse modes under direct indentation and bending (a) symmetric mode, (b,c) anti-symmetric mode

Original Circular CrossSection at Saddle Support

D1 A'

C' Circular Region

Flattened Region

Ovalised Section at Central Hinge A'C'

Major CurvedPlastic Hinge

Central Hinge A'C'

S

(a)

(b)

Figure 5(a) T2L1C2-1T1L-SIKA (CFRP ruptured),

(b) T2L1C2-1T1L-STRUCTURAL (No CFRP rupture)

Figure 6: Gain in strength due to CFRP for rehabilitation and strengthening series

Figure 7: Gain in strength for Structural and SIKA laminates

due to CFRP for rehabilitation series

0

50

100

150

200

250

300

350

400

450

500

0% 20% 40% 60% 80% 100%

% In

crea

se in

Loa

d Ca

paci

ty

% All around 360 Deg Thickness Corrosin

20% Corrosion-Rehabilitation40% Corrosion-Rehabilitation60% Corrosion-Rehabilitation80% Corrosion-Rehabilitation20% Corrosion-Strengthening60% Corrosion-Strengthening40% Corrosion-Strengthening80% Corrosion-Strengthening

0

10

20

30

40

50

60

70

80

90

100

0% 20% 40% 60% 80% 100%

% In

crea

se in

Loa

d Ca

paci

ty

% All around 360 Deg Thickness Corrosin

40% Corrosion-Rehabilitation60% Corrosion-Rehabilitation

SIKA (70%, 86%)

Structural(60%, 93%)

SIKA(31%, 49%)

Structural(35%, 62%)

Fig. 8 Specimen ST1L8C8-0 (bare) after testing

Fig. 9 Specimen ST1L8C8-4T4L (strengthened) after testing

Fig. 10 Effect of the corrosion length (Lc) on the normalised strength (%Pu/P0) for both rehabilitation (100

(a) 20% corrosion (b) 40% corrosion

( c ) 60% corrosion (d) 80% corrosion

Fig. 11 Corroded bare pipe series- Effect of Lc on the load-deflection response for bare specimens (control specimen T5L0C0-01)

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

T5L0C0-01T4L1C0-0T4L2C0-0T4L3C0-0ST4L8C8-0

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250Lo

ad (k

N)

Deflection (mm)


0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)


Steel fracture

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Loa

d (

kN

)

Deflection (mm)


Steel fracture

( a ) 20% corrosion (b) 40% corrosion

( c ) 60% corrosion ( d ) 80% corrosion

Fig. 12 Rehabilitation series- effect of the CFRP repair protocol on P-∆ response for Lc=100 mm

(Control specimen T5L0C0-01, no corrosion)

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

T4L2C0-0

T4L1C2-1T1L

T4L1C2-2T2L

T5L0C0-01

Bare steel No fracture

2T2L

1T1L

control

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Loa

d (

kN)

Deflection (mm)

T3L1C0-0T3L1C2-1T1L-SIKAT3L1C2-1T1LT5L0C0-01

Bare steel No fracture

1T1L - SIKA

1T1L -Structural

control - local buckling

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

T2L1C2-1T1L-SIKA

T2L1C2-1T1L

T2L1C0-0

T5L0C0-01

local buckling

Bare steel fracture

1T1L - StructuralNo fibre rupture1T1L fibre

rupture - SIKA

controlLocal buckling

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Loa

d (

kN

)

Deflection (mm)

T1L1C0-0

T1L1C2-1T1L

T1L1C2-2T2L

T5L0C0-01

Bare steel fracture

2T2L

1T1L

Control

( a ) 20% corrosion (b) 40% corrosion

( c ) 60% corrosion (d) 80% corrosion

Fig. 13 Strengthening Series- effect of the number of CFRP sheets on P-∆ response

(control specimen T5L0C0-01, no corrosion)

0

20

40

60

80

100

120

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

ST4L8C8-0

ST4L8C8-2T2L

ST4L8C8-4T4L

T5L0C0-01

Control

4T4L

2T2L

Bare

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

ST3L8C8-0

ST3L8C8-2T2L

ST3L8C8-4T4L

T5L0C0-01

Control

4T4L

2T2L

Bare

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

ST2L8C8-0

ST2L8C8-2T2L

ST2L8C8-4T4L

T5L0C0-01

Control

Bare

4T4L

2T2L

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Load

(kN

)

Deflection (mm)

ST1L8C8-0

ST1L8C8-2T2L

ST1L8C8-4T4L

T5L0C0-01

Control

4T4L

2T2L

Bare

Fig. 14 equivalent thickness model

Neutralaxis

t st

t fx

o

o

ysσ

yfσ

ysσ

Fig. 15 Effect of the normalised corrosion length (Lc/D0) on the normalised strength (Pu/Pu,ref) where Pu,ref is the strength for a CHS with Lc/D0=8.0

αc = 1.0877(Lc/Do)-0.049

αc = 1.2065(Lc/Do)-0.101

αc = 1.9436(Lc/Do)-0.297

αc = 1.5783(Lc/Do)-0.221

1.00

1.20

1.40

1.60

1.80

2.00

0 2 4 6 8

αc,

Pu/P

u,re

f

Normalised Corrosion Length (Lc/Do)

20% Corrosion40% Corrosion60% Corrosion80% Corrosion

Fig. 16 Interaction diagram for bending and bearing of steel pipes with and without CFRP

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Mu/

Mpc

Pu/Rbyc

CHS-Bare Steel Properties [28]

CHS+CFRP Rehabilitation Series [28]

CHS+CFRP Strengthening Series [this paper]

Hou etal [42]-CHS Bearing Only

Equation 10 - Lower bound for bare CHS

Equation 11 - Lower bound for CHS+CFRP

Table 1: Mechanical properties of the specimens

Corrosion Corrosion ID Span Do Di Dav R ts tc Lc Lc/Do Do/ts Section θ CFRP t f CFRP Weight Zs Ss σys Mys MpsL Class to fibre Manufacturer

Level Level mm mm mm mm mm mm mm mm BS 5950 Deg. mm kg mm3 mm3 MPa kN.m kN.mT5L0C0-01 900 101.6 91.6 96.6 48.3 5 0 0 0 20.32 2 0 0 0 ST V-Wrap C200 12.065 3.66E+04 4.67E+04 482.6 17.69 22.52T5L0C0-02 450 101.6 91.6 96.6 48.3 5 0 0 0 20.32 2 0 0 0 ST V-Wrap C200 12.098 3.66E+04 4.67E+04 482.6 17.69 22.52T5L0C0-03 900 101.6 91.6 96.6 48.3 5 0 0 0 20.32 2 0 0 0 ST V-Wrap C200 12.082 3.66E+04 4.67E+04 482.6 17.69 22.52T4L1C0-0 900 99.6 91.6 95.6 47.8 4 1 100 1.004 24.9 3 360 0 0 N/A 11.898 2.87E+04 3.66E+04 482.6 15.06 19.17

T4L1C2-1T1L 900 99.6 91.6 95.6 47.8 4 1 100 1.004 24.9 3 360 1L1T 0.46 ST V-Wrap C200 12.488 2.87E+04 3.66E+04 482.6 15.06 19.17T4L1C2-2T2L 900 99.6 91.6 95.6 47.8 4 1 100 1.004 24.9 3 360 2L2T 0.92 ST V-Wrap C200 12.641 2.87E+04 3.66E+04 482.6 15.06 19.17

T4L2C0-0 900 99.6 91.6 95.6 47.8 4 1 200 2.008 24.9 3 360 0 0 N/A 11.640 2.87E+04 3.66E+04 482.6 14.56 18.53T4L2C4-1T1L 900 99.6 91.6 95.6 47.8 4 1 200 2.008 24.9 3 360 1L1T 0.46 ST V-Wrap C200 12.232 2.87E+04 3.66E+04 482.6 14.56 18.53T4L2C4-2T2L 900 99.6 91.6 95.6 47.8 4 1 200 2.008 24.9 3 360 2L2T 0.92 ST V-Wrap C200 12.586 2.87E+04 3.66E+04 482.6 14.56 18.53

T4L3C0-0 900 99.6 91.6 95.6 47.8 4 1 300 3.012 24.9 3 360 0 0 N/A 11.303 2.87E+04 3.66E+04 482.6 14.27 18.17T3L1C0-0 900 97.6 91.6 94.6 47.3 3 2 100 1.025 32.53 3 360 0 0 N/A 11.718 2.11E+04 2.68E+04 482.6 12.25 15.59

T3L1C2-1T1L 900 97.6 91.6 94.6 47.3 3 2 100 1.025 32.53 3 360 1L1T 0.46 ST V-Wrap C200 12.229 2.11E+04 2.68E+04 482.6 12.25 15.59T3L1C2-1T1L-SIKA 900 97.6 91.6 94.6 47.3 3 2 100 1.025 32.53 3 360 1L1T 0.26 SIKA 300C Wrap 12.120 2.11E+04 2.68E+04 482.6 12.25 15.59

T3L2C0-0 900 97.6 91.6 94.6 47.3 3 2 200 2.049 32.53 3 360 0 0 N/A 11.191 2.11E+04 2.68E+04 482.6 11.42 14.54T3L2C4-1T1L 900 97.6 91.6 94.6 47.3 3 2 200 2.049 32.53 3 360 1L1T 0.46 ST V-Wrap C200 11.297 2.11E+04 2.68E+04 482.6 11.42 14.54

T3L2C4-1T1L-SIKA 900 97.6 91.6 94.6 47.3 3 2 200 2.049 32.53 3 360 1L1T 0.26 SIKA 300C Wrap 11.752 2.11E+04 2.68E+04 482.6 11.42 14.54T3L3C0-0 900 97.6 91.6 94.6 47.3 3 2 300 3.074 32.53 3 360 0 0 N/A 10.777 2.11E+04 2.68E+04 482.6 10.96 13.96T2L1C0-0 900 95.6 91.6 93.6 46.8 2 3 100 1.046 47.8 3 360 0 0 N/A 11.509 1.38E+04 1.75E+04 482.6 10.38 13.21

T2L1C2-1T1L 900 95.6 91.6 93.6 46.8 2 3 100 1.046 47.8 3 360 1L1T 0.46 ST V-Wrap C200 12.047 1.38E+04 1.75E+04 482.6 10.38 13.21T2L1C2-1T1L-SIKA 900 95.6 91.6 93.6 46.8 2 3 100 1.046 47.8 3 360 1L1T 0.26 SIKA 300C Wrap 11.595 1.38E+04 1.75E+04 482.6 10.38 13.21

T2L2C0-0 900 95.6 91.6 93.6 46.8 2 3 200 2.092 47.8 3 360 0 0 N/A 10.697 1.38E+04 1.75E+04 482.6 8.90 11.34T2L2C4-1T1L 900 95.6 91.6 93.6 46.8 2 3 200 2.092 47.8 3 360 1L1T 0.46 ST V-Wrap C200 11.572 1.38E+04 1.75E+04 482.6 8.90 11.34

T2L2C4-1T1L-SIKA 900 95.6 91.6 93.6 46.8 2 3 200 2.092 47.8 3 360 1T1L 0.26 SIKA 300C Wrap 11.427 1.38E+04 1.75E+04 482.6 8.90 11.34T2L3C0-0 900 95.6 91.6 93.6 46.8 2 3 300 3.138 47.8 3 360 0 0 N/A 10.160 1.38E+04 1.75E+04 482.6 8.14 10.36T1L1C0-0 900 93.6 91.6 92.6 46.3 1 4 100 1.068 93.6 4 360 0 0 N/A 11.166 6.73E+03 8.57E+03 482.6 6.19 7.89

T1L1C2-1T1L 900 93.6 91.6 92.6 46.3 1 4 100 1.068 93.6 4 360 1L1T 0.46 ST V-Wrap C200 11.886 6.73E+03 8.57E+03 482.6 6.19 7.89T1L1C2-2T2L 900 93.6 91.6 92.6 46.3 1 4 100 1.068 93.6 4 360 2L2T 0.92 ST V-Wrap C200 10.336 6.73E+03 8.57E+03 482.6 6.19 7.89

T1L2C0-0 900 93.6 91.6 92.6 46.3 1 4 200 2.137 93.6 4 360 0 0 N/A 11.981 6.73E+03 8.57E+03 482.6 5.04 6.42T1L2C4-1T1L 900 93.6 91.6 92.6 46.3 1 4 200 2.137 93.6 4 360 1L1T 0.46 ST V-Wrap C200 11.307 6.73E+03 8.57E+03 482.6 5.04 6.42T1L2C4-2T2L 900 93.6 91.6 92.6 46.3 1 4 200 2.137 93.6 4 360 2L2T 0.92 ST V-Wrap C200 11.047 6.73E+03 8.57E+03 482.6 5.04 6.42

T1L3C0-0 900 93.6 91.6 92.6 46.3 1 4 300 3.205 93.6 4 360 0 0 N/A 9.352 6.73E+03 8.57E+03 482.6 4.47 5.69ST4L8C8-0 900 99.6 91.6 95.6 47.8 4 1 800 8.032 24.9 3 360 0 0 N/A 9.895 2.87E+04 3.66E+04 482.6 13.86 17.64

ST4L8C8-2T2L 900 99.6 91.6 95.6 47.8 4 1 800 8.032 24.9 3 360 2L2T 200 ST V-Wrap C200 11.486 2.87E+04 3.66E+04 482.6 13.86 17.64ST4L8C8-4T4L 900 99.6 91.6 95.6 47.8 4 1 800 8.032 24.9 3 360 4L4T 400 ST V-Wrap C200 13.454 2.87E+04 3.66E+04 482.6 13.86 17.64

ST3L8C8-0 900 97.6 91.6 94.6 47.3 3 2 800 8.197 32.53 3 360 0 0 N/A 8.131 2.11E+04 2.68E+04 482.6 10.18 12.96ST3L8C8-2T2L 900 97.6 91.6 94.6 47.3 3 2 800 8.197 32.53 3 360 2L2T 200 ST V-Wrap C200 9.963 2.11E+04 2.68E+04 482.6 10.18 12.96ST3L8C8-4T4L 900 97.6 91.6 94.6 47.3 3 2 800 8.197 32.53 3 360 4L4T 400 ST V-Wrap C200 11.286 2.11E+04 2.68E+04 482.6 10.18 12.96



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Table 2: Mechanical properties of the CFRP laminate [28]

Table 3: Tensile coupons results of pipe material grade ASTM A53 Sch 30 [34]

Manufacturer Item Type CFRP Laminate Width Thickness σu (ave) eu (ave) E (ave)mm mm Mpa % Gpa

CFRP fibres V-Wrap C200H Sheets 610 0.28 4820 1.70% 276

AdhsiveV-wrap 700 saturant+778 putty -- 0.92 62 -- 3.45

CFRP fibres Sika Wrap -Sheets 500 0.13 3500 1.50% 230Adhsive Sikadur 330 impregnation -- 0.10 30 -- 3.8

Structural 1

Sika 2

Testing Spec. Gauge Final width thk Area Py Pu ∆u σyn σun σyt σut σut/σyt σut/σun σyt/σyn eMachine ID mm mm mm mm mm2 kN kN mm MPa MPa MPa MPa %

TC1 200.00 233.92 39.82 5.08 202.29 103.01 116.79 33.9 372 532.7 509.23 577.35 1.13 1.08 1.37 16.96TC2 200.00 224.16 39.27 5.08 199.49 94.43 106.94 24.2 372 532.7 473.35 536.06 1.13 1.01 1.27 12.08TC3 200.00 220.10 38.72 5.08 196.70 88.39 100.15 20.1 372 532.7 449.37 509.16 1.13 0.96 1.21 10.05T1 200.00 240.00 38.44 5.10 196.04 98.88 112.36 40.0 372 532.7 504.36 573.14 1.14 1.08 1.36 20.00T2 200.00 246.00 38.30 5.10 195.33 92.21 104.79 46.0 372 532.7 472.09 536.47 1.14 1.01 1.27 23.00T3 200.00 253.00 38.33 5.10 195.48 95.27 108.27 53.0 372 532.7 487.37 553.83 1.14 1.04 1.31 26.50

Average 200.00 236.20 38.81 5.09 197.56 95.37 108.22 36.20 372.00 532.70 482.63 547.67 1.13 1.03 1.30 18.10

DCL

DMC

Table 4: Test Results for both rehabilitation series and strengthening series

Corrosion Corrosion Specimen Lc/Do αc Carbon fibre Adhesive teq Zc Sc Myc Mpc Pu ∆u A'C' D1 Mu Pu / Rbyc Mu/Mpc Pu/Pu,contol StrengthRupture or Debonding or Icrease

Level Level Steel fracture Steel fracture mm mm3 mm2 N.m N.m kN mm mm mm kN.m %T5L0C0-01 0.000 1.000 N/A N/A 5.00 3.66E+04 4.67E+04 17.69 22.52 63.040 33.38 143.22 37.43 14.18 ---- ---- 0.96 0.00T5L0C0-02 0.000 1.000 N/A N/A 5.00 3.66E+04 4.67E+04 17.69 22.52 102.600 40.78 151.36 22.39 11.54 ---- ---- 1.56 ----T5L0C0-03 0.000 1.000 N/A N/A 5.00 3.66E+04 4.67E+04 17.69 22.52 68.730 34.10 144.29 36.64 15.46 ---- ---- 1.04 9.03T4L1C0-0 1.004 1.087 N/A N/A 4.00 2.87E+04 3.66E+04 15.06 19.17 50.051 34.29 141.40 37.62 11.26 0.674 0.587 0.76 ----

T4L1C2-1T1L 0.987 1.088 No Rupture Debonding 4.86 3.55E+04 4.52E+04 18.63 23.72 70.074 38.25 152.37 43.93 15.77 0.699 0.665 1.06 40.01T4L1C2-2T2L 0.973 1.088 Rupture Debonding 5.58 4.14E+04 5.27E+04 21.74 27.68 71.375 40.91 155.00 47.89 16.06 0.574 0.580 1.08 42.60

T4L2C0-0 2.008 1.050 N/A N/A 4.00 2.87E+04 3.66E+04 14.56 18.53 47.621 33.73 143.91 34.02 10.71 ---- ---- 0.72 ----T4L2C4-1T1L 1.974 1.051 No Rupture Debonding 4.86 3.55E+04 4.52E+04 18.01 22.93 64.454 28.03 147.86 48.03 14.50 0.665 0.632 0.98 35.35T4L2C4-2T2L 1.946 1.052 Rupture Debonding 5.58 4.14E+04 5.27E+04 21.01 26.75 73.092 37.18 158.46 52.00 16.45 0.608 0.615 1.11 53.49

T4L3C0-0 3.012 1.030 N/A N/A 4.00 2.87E+04 3.66E+04 14.27 18.17 44.979 34.33 143.16 34.46 10.12 ---- ---- 0.68 ----T3L1C0-0 1.025 1.204 N/A N/A 3.00 2.11E+04 2.68E+04 12.25 15.59 40.716 32.16 135.39 46.18 9.16 ---- ---- 0.62 ----

T3L1C2-1T1L 1.007 1.206 Rupture Debonding 3.83 2.74E+04 3.49E+04 15.95 20.31 55.053 48.67 161.40 58.17 12.39 0.714 0.610 0.84 35.21T3L1C2-1T1L-SIKA 1.014 1.205 Rupture Debonding 3.50 2.48E+04 3.16E+04 14.44 18.38 53.656 29.13 155.34 68.54 12.07 0.802 0.657 0.81 31.78

T3L2C0-0 2.049 1.122 N/A N/A 3.00 2.11E+04 2.68E+04 11.42 14.54 34.454 34.72 141.66 43.10 7.75 ---- ---- 0.52 ----T3L2C4-1T1L 2.015 1.124 No Rupture Debonding 3.83 2.74E+04 3.49E+04 14.87 18.94 56.084 34.85 147.61 51.61 12.62 0.780 0.666 0.85 62.78

T3L2C4-1T1L-SIKA 2.029 1.123 Rupture Debonding 3.50 2.48E+04 3.16E+04 13.46 17.14 51.317 36.10 155.81 43.78 11.55 0.823 0.674 0.78 48.94T3L3C0-0 3.074 1.077 N/A N/A 3.00 2.11E+04 2.68E+04 10.96 13.96 34.423 31.72 139.36 35.95 7.75 ---- ---- 0.52 ----T2L1C0-0 1.046 1.562 Steel fracture Steel fracture 2.00 1.38E+04 1.75E+04 10.38 13.21 28.601 52.80 118.90 66.76 6.44 ---- ---- 0.43 ----

T2L1C2-1T1L 1.029 1.568 No Rupture Debonding 2.79 1.95E+04 2.49E+04 14.77 18.81 45.906 42.61 140.48 72.96 10.33 0.745 0.549 0.70 60.50T2L1C2-1T1L-SIKA 1.036 1.566 Rupture No Debonding 2.48 1.72E+04 2.19E+04 13.02 16.58 48.681 31.85 126.32 74.64 10.95 0.948 0.661 0.74 70.21

T2L2C0-0 2.092 1.340 N/A N/A 2.00 1.38E+04 1.75E+04 8.90 11.34 22.498 37.54 139.20 34.31 5.06 ---- ---- 0.34 ----T2L2C4-1T1L 2.058 1.345 No Rupture Debonding 2.79 1.95E+04 2.49E+04 12.67 16.14 43.529 39.82 140.54 56.84 9.79 0.824 0.607 0.66 93.48

T24L2C4-1T1L-SIKA 2.071 1.343 No Rupture Debonding 2.48 1.72E+04 2.19E+04 11.17 14.23 41.951 39.22 147.32 50.41 9.44 0.952 0.664 0.64 86.47T2L3C0-0 3.138 1.226 N/A N/A 2.00 1.38E+04 1.75E+04 8.14 10.36 22.461 39.62 124.31 27.79 5.05 ---- ---- 0.34 ----T1L1C0-0 1.068 1.906 Steel fracture Steel fracture 1.00 6.73E+03 8.57E+03 6.19 7.89 12.589 24.96 106.93 68.20 2.83 ---- ---- 0.19 ----

T1L1C2-1T1L 1.053 1.914 No Rupture Debonding 1.70 1.16E+04 1.48E+04 10.71 13.63 37.737 33.01 137.45 74.72 8.49 1.071 0.623 0.57 199.76T1L1C2-2T2L 1.042 1.920 No Rupture Debonding 2.16 1.49E+04 1.90E+04 13.85 17.63 40.742 25.25 135.10 76.23 9.17 0.795 0.520 0.62 223.63

T1L2C0-0 2.137 1.551 N/A N/A 1.00 6.73E+03 8.57E+03 5.04 6.42 10.032 31.54 135.41 33.25 2.26 ---- ---- 0.15 ----T1L2C4-1T1L 2.105 1.558 No Rupture Debonding 1.70 1.16E+04 1.48E+04 8.72 11.10 28.714 28.05 118.53 72.05 6.46 1.001 0.582 0.44 186.22T1L2C4-2T2L 2.085 1.563 Rupture Debonding 2.16 1.49E+04 1.90E+04 11.27 14.35 38.348 30.66 142.54 62.76 8.63 0.920 0.601 0.58 282.26

T1L3C0-0 3.205 1.375 N/A N/A 1.00 6.73E+03 8.57E+03 4.47 5.69 9.994 33.23 136.80 28.63 2.25 ---- ---- 0.15 ----ST4L8C8-0 8.032 1.000 N/A N/A 4.00 2.87E+04 3.66E+04 13.86 17.64 45.273 35.92 144.65 36.26 10.19 ---- ---- 0.69 ----

ST4L8C8-2T2L 7.785 1.000 Rupture No Debonding 5.58 4.14E+04 5.27E+04 19.97 25.43 63.767 41.60 166.62 51.57 14.35 0.558062 0.56 0.97 40.85ST4L8C8-4T4L 7.607 1.000 No Rupture No Debonding 6.78 5.16E+04 6.56E+04 24.88 31.68 100.977 47.15 153.35 58.77 22.72 0.651733 0.72 1.53 123.04

ST3L8C8-0 8.197 1.000 N/A N/A 3.00 2.11E+04 2.68E+04 10.18 12.96 32.418 36.26 144.85 31.63 7.29 0.49 ----ST3L8C8-2T2L 7.951 1.000 No Rupture No Debonding 4.51 3.27E+04 4.16E+04 15.78 20.09 48.424 49.18 151.61 52.51 10.90 0.589852 0.54 0.73 49.37ST3L8C8-4T4L 7.782 1.000 No Rupture No Debonding 5.60 4.16E+04 5.29E+04 20.06 25.54 62.717 61.98 149.68 58.99 14.11 0.545523 0.55 0.95 93.46

ST2L8C8-0 8.368 1.000 N/A N/A 2.00 1.38E+04 1.75E+04 6.64 8.46 15.039 39.54 143.91 21.80 3.38 ---- ---- 0.23 ----ST2L8C8-2T2L 8.132 1.000 No Rupture No Debonding 3.39 2.40E+04 3.06E+04 11.60 14.77 31.532 41.98 133.09 62.92 7.09 0.59514 0.48 0.48 109.67ST2L8C8-4T4L 7.979 1.000 No Rupture No Debonding 4.33 3.13E+04 3.98E+04 15.10 19.23 59.643 47.49 141.78 70.49 13.42 0.772942 0.70 0.91 296.59

ST1L8C8-0 8.547 1.000 N/A N/A 1.00 6.73E+03 8.57E+03 3.25 4.14 7.871 41.53 140.79 23.71 1.77 ---- ---- 0.12 ----ST1L8C8-2T2L 8.339 1.000 No Rupture No Debonding 2.16 1.49E+04 1.90E+04 7.21 9.19 23.961 32.09 135.73 53.65 5.39 0.89789 0.59 0.36 204.42ST1L8C8-4T4L 8.222 1.000 No Rupture No Debonding 2.85 2.00E+04 2.54E+04 9.64 12.27 42.036 45.59 138.56 51.23 9.46 1.035649 0.77 0.64 434.06

Str

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01_Text 01_3 April 2017ABSTRACT1. INTRODUCTION2. test program3. test results

02_Fig 01_3 April 201703_Table 01_3 April 2017

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