Numerical Studies on Corroded Steel Angle Members

Numerical Studies on Corroded Steel Angle Members Seminar Report - 2017
Department of Civil Engineering Thejus Engineering College1
1. INTRODUCTION
1.1 General
Because of high compressive strength as well as tensile strength nature, the
properties of structural steel differ from concrete. Further, because of various properties
like stiffness, and ductile properties, structural steel is used as building materials for
construction. The advantages of steel over other materials are:
 It has high strength per unit mass. Hence even for large structures, the size of steel
structures elements is small, saving space in construction and improving aesthetic
view.
 It has assured quality and high durability.
 Speed of construction is another important advantage of steel structure. Since
Standard sections of steel are available which can be prefabricated in the
workshop, they may be kept ready by the time the site is ready and the structure
erected as soon as the site is ready. Hence there is lot of saving in construction
time.
 Steel Structures can be strengthened at any later time, if necessary. Its needs just
welding additional Sections.
 By using bolted connections, steel structures can be easily dismantled transported
to other sites quickly.
 If Joints are taken care, it is the best water and gas resistant structure. Hence can
be used for making water tanks also.
 Material is reusable.
And the disadvantages are:
 It is susceptible to corrosion.
 Maintenance cost is high, since it needs painting to prevent corrosion.
 Steel members are costly.
Single steel angles section members are used in many various structures as bridges,
trusses and latticed transmission towers. Every structure is exposed to the effects of
different environmental influence. The circumstances, which include the inadequate
maintenance, lead to corrosion on the structures.

Corrosion is one of the most common problems of steel structures. The different
weather circumstances and the lack of the maintenance are leading to corrosion. The
corrosion influences both the material properties and the surface conditions. The
corrosion usually causes only surface changes; first the paint comes off in flakes and then
the element thickness is reduced. The appearance and rate of the corrosion can be various
therefore different parameters like thickness reduction, position and extension of
corrosion are to be defined to characterize the phenomenon. The knowledge of the
behavior and the resistance of the corroded elements are important to decide whether the
elements must be replaced or it is enough to strengthen it. Corrosion can occur anywhere
along the member length and has various size extensions and rarely extends to the whole
member. The corrosion is a significant problem in the world, therefore many researcher
analyze the effect of it on the various members of the structures. All of the studies deal
with the remaining capacity of the members and give recommendation how can be
assessed the influence of the corrosion.
Carbon fiber reinforced polymer (CFRP) is an extremely strong and light
fiber-reinforced plastic which contains carbon fibers. CFRPs can be expensive to produce
but are commonly used wherever high strength-to-weight ratio and rigidity are required,
such as aerospace, automotive, civil engineering, sports goods and an increasing number
of other consumer and technical applications. CFRP has become a notable material
in structural engineering applications; it has also proved itself cost-effective in a number
of field applications strengthening concrete, masonry, steel, cast iron, and timber
structures. Its use in industry can be either for retrofitting to strengthen an existing
structure or as an alternative reinforcing (or pre-stressing) material instead of steel from
the outset of a project.
Retrofitting has become the increasingly dominant use of the material in civil
engineering, and applications include increasing the load capacity of old structures
(such as bridges) that were designed to tolerate far lower service loads than they are
experiencing today, seismic retrofitting, and repair of damaged structures. Retrofitting is
popular in many instances as the cost of replacing the deficient structure can greatly
exceed its strengthening using CFRP.

CFRP is considered as suitable for structures in corrosive environment due to its
high-strength, light-weight, and anti-corrosive qualities. In recent years, a continuous
increase has been experienced in using carbon fiber reinforced polymer (CFRP) for
structural strengthening as well as repair works. In this paper, residual capacity of the
corroded members is evaluated by classifying the section according to the level of
corrosion.
In order to understand the behaviour of corroded and retrofitted angle
compression members, experimental and numerical studies were conducted. A numerical
study was performed by the finite element program ABAQUS. The results are intended to
achieve with the aid of both experimental tests and advanced numerical analyses. In
comparison with the experimental results the numerical study shows similar variation.
2. CORROSION
2.1 General
Corrosion is defined as a destructive degradation of metals in presence of any
medium which brings about the change in its chemical and physical appearance. The steel
structures are getting rust, when it is in contact with water. The rusting of iron is an
electrochemical process, which attacks at the anodic areas on the surface, where ferrous
ions go into solution. In solution, electrons are moving toward cathode sites on the
surface, where it combines with oxygen and water to form hydroxyl ions. The key
reaction in the electrochemistry of corrosion is the reduction of oxygen.
O2 + 4e-
+ 2H2O → 4OH
Because of the formation of hydroxide ions, the reduction process is strongly affected by
an acid. Another important reaction is the oxidation of iron.
Fe → Fe2+
+ 2e-
The overall equation is as follows
2Fe + 2H2O + O2 → 2Fe2+
+ 4OH-

Formation of Rust
Fe2+
+ 2OH-
→ Fe(OH)2
Fe(OH)2 + O2 → Fe(OH)3
Fe(OH)2 dehydrates to Fe2O3.nH2O (rust)
Figure 2.1: Corrosion of steel
Figure 2.2: Corroded angle section
2.2 Types of corrosion
Corrosion may appear in many forms. These forms are classified according to
how the corrosion attacks the metal. The types of metal corrosion which occur in
different types of steel structures are uniform corrosion, pitting corrosion, crevice
corrosion, stress corrosion, galvanic corrosion and corrosion fatigue.

Uniform corrosion is the formation of oxide, distributed uniformly over an
exposed surface. This is the most common form of the corrosion, which will lead to the
gradual thinning of members. Uniform corrosion is comparatively easy to measure,
predict and design. This type of attack is mostly found where a metal is in contact with an
acid, a humid atmosphere or a solution. The corrosion products produced may either form
a protective layer on the metal which would prevent further corrosion or may be readily
dissolved in the environment leading to further active corrosion. The rate of uniform
corrosion loss is highly variable, depending on conditions such as temperature, time of
wetness, and chemistry.
If the corrosion is concentrated in small area it may form a pit at the metal
surface. This form of corrosion can be serious in high-stress region because it can
penetrate into the metal showing little Pits will form imperfections on the metal surface
and these imperfections will act as stress concentrations, reducing the fatigue capacity of
the metal and increasing the metal’s sensitivity to cracking. Pitting is random in nature
and occurs quickly. Pitting may be initiated by external factors, e.g. where external
deposits such as debris and salts have settled on the metal surface. Pitting corrosion is
prone to occur in certain environments, particularly in the presence of salt.
Stressed corrosion is induced from the combined influence of tensile stress and a
corrosive environment. The impact of Stress Corrosion Cracking on a material usually
falls between dry cracking and the fatigue threshold of that material. The required tensile
stresses may be in the form of directly applied stresses or in the form of residual stresses.
Galvanic corrosion is the accelerated corrosion of a metal because of an electrical
contact with a more noble metal or non-metallic conductor in a corrosive electrolyte. It
occurs at the joint between the two dissimilar metals. Crevice corrosion is the localized
corrosion of a metal surface at, or close, to an area that is protected by another material.
Erosion corrosion is a conjoint action involving a corrosive flowing which leads to
accelerated loss of material.
Among the various forms of corrosion, present studies focus on uniform or
general corrosion. This is a surface phenomenon, which occur through uniform attack of

metal resulting from the contact with certain strongly acidic or alkaline electrolytes as
well as conditions of high humidity or moisture-laden atmosphere. This is the most
common form of the corrosion, which will lead to the gradual thinning of members,
accordingly for the greatest destruction of metal. As it occurs evenly over the entire
surface, the rate of corrosion is often presented as a weight loss. Uniform corrosion is
very predictable, and is the basis of most corrosion prediction equations. Also it has been
pointed out that this type of corrosion is the most serious form of corrosion observed on
steel structures.
3. EXPERIMENTAL TEST
To understand the behaviour of corroded, un-corroded and retrofitted angle compression
members, experimental studies were conducted. It is used to compare the results of
numerical studies. In the experimental part, out of the three specimens, one specimen was
kept as the control specimen while the other two were corroded.
3.1 Materials
The materials used in the experimental program are:
3.1.1 Steel Angle Sections
Single steel angles section members are used in many various structures as
bridges, trusses and latticed transmission towers. Three sets of steel angles are taken for
the experiment, out of the three set specimens; one specimen was kept as the control
specimen while the other two were corroded. Totally nine angle specimens were
considered, they are steel angle sections of 100 x 100 x 6 mm, 75 x 75 x 5 mm, 70 x 70 x
5 mm. Each set contains
a) Angle Un-corroded (AUC)
b) Angle corroded (AC)
c) Angle corroded and retrofitted (ARC)

The details of Corroded, Un-corroded and Retrofitted angle sections of size
100x100x6mm, 75 x 75 x 5 mm, 70 x 70 x 5 mm are shown in figure 3.1.
Figure 3.1: Details of the corroded, uncorroded and retrofitted angle specimens
3.1.2 Carbon Fiber Reinforced Polymer (CFRP)
Carbon fiber is defined as a fiber containing at least 92% carbon by weight.
Carbon fibers generally have excellent tensile properties, low densities, high thermal and
chemical stabilities in the absence of oxidizing agents, good thermal and electrical
conductivities, excellent creep resistance. Carbon fiber reinforced polymer (CFRP) is an
extremely strong and light fiber-reinforced plastic. Its use in industry can be either for

retrofitting to strengthen an existing structure or as an alternative reinforcing material
instead of steel. It is shown in Figure 3.2 and the properties are given below in Table 3.1
Figure 3.2: Carbon Fiber Reinforced Polymer
Table 3.1: Properties of CFRP used
Particulars Values
Modulus of Elasticity 295600 MPa
Tensile strength 378.2 N/mm2
Density 1.69 ton/mm3
Poisson’s ratio 0.33
3.1.3 Adhesive
The adhesive used for binding CFRP to steel angle section are Araldite AW 106
resin/Hardener HV 953Uepoxy adhesive. It is a multi-purpose, viscous material that is
suitable for bonding a variety of materials including metal, ceramic, and wood. Adhesive

and hardener are having different specific gravity and viscous properties. It is shown in
figure 3.3 and the properties are given below in Table 3.2.
Figure 3.3: Resin and hardener
Table 3.2: Properties of Adhesive
Property Resin Hardener
Colour /Appearance Creamy, viscous/ liquid Amber liquid
Specific gravity 1.17 0.92
Viscosity @ 25°C 50000 35000
3.2 Experimental Set-up
In order to understand the behaviour of corroded and retrofitted angle
compression members, experimental and numerical studies were conducted. In the
experimental part, out of the three set specimens, one specimen was kept as the control
specimen while the other two were corroded. Numerical results were validated with
experiments. Totally nine angle specimens were considered, with three sets.

The specimens were initially subjected to natural corrosion by immersing in 3.5%
NaCl solution for about three months. It is shown in figure 3.4. Meanwhile, the
specimens were subjected to alternate wetting and drying so that the specimens will be
undergoing chloride induced corrosion.
Figure 3.4: Initial condition of specimens during natural corrosion
The corrosion was then accelerated using Galvanostatic corrosion method.
Corrosion was allowed to occur only for a height of about one-third from the bottom base
plate. Galvanostatic corrosion method was used to induce corrosion where corrosion was
induced artificially by keeping the current constant during the entire corrosion process by
means of a galvanostat. The galvanostatic corrosion cell is shown in Figure 3.5.
Figure 3.5: The galvanostatic corrosion cell

In this study, structural member which was subjected to corrosion acted as the
anode and same steel was used as the cathode for obtaining continuity. The electrolyte
used was 3.5% of sodium chloride, i.e. 35 gms of NaCl was required for 1 litre of water
to get the desired salinity. By means of a galvanostat, the anode and cathode in the cell
were connected to an external supply of constant current. The anode was connected to the
positive terminal of the supply whereas the cathode was connected to the negative
terminal. When the external power supply was switched on, the structural member acting
as the anode got oxidized and the same metal used as the cathode got reduced resulting in
a corroded section at the anode. The test setup is shown in figure 3.6 and the Specimen
after subjected to accelerated corrosion is shown in figure 3.7.
Figure 3.6: Typical test setup for accelerated corrosion
Figure 3.7: Specimen after being subjected to accelerated corrosion

As a result of the corrosion the surface of metal is removed which leads to the loss of
weight and thickness. The thickness and weight measurements of specimens are tabulated
in Table 3.2.
Table 3.2: Thickness and weight measurement of Specimens
ID
Size of the
specimen
(mm)
Length
(mm)
Initial
thickness
Final
thickness
Initial
weight
(kg)
Final
weight
(kg)
Leg 1
(mm)
Leg 2
(mm)
Leg 1
(mm)
Leg 2
(mm)
AUC-100 100x100x6 1000 6.272 6.767 - - 16.55 16.55
AC-100 100x100x6 1000 6.456 6.334 5.59 5.27 16.49 15.87
ARC-100
100x100x6 (C) 1000 6.6 6.54 4.997 5.494 16.94 -
100x100x6 (R) - - - 8.22 8.165 - 16.61
AUC-75 75x75x5 1200 5.201 5.171 - - 15.65 15.65
AC-75 75x75x5 1200 5.277 5.254 4.091 4.152 16.51 15.75
ARC-75
75x75x5(C) 1200 5.276 5.331 4.44 4.537 16.56 -
75x75x5(R) - - - 6.895 6.863 - 16.26
AUC-70 70x70x5 1000 5.05 5.06 - - 13.91 13.91
AC-70 70x70x5 1000 5.071 5.099 4.294 4.406 13.55 12.05
ARC-70
70x70x5(C) 1000 5.007 5.034 4.648 4.572 13.51 -
70x70x5(R) - - - 8.405 8.51 - 13.31
AUC- Angle Uncorroded, AC- Angle Corroded, ARC- Angle Retrofitted after corrosion

Among the two corroded sections, one was retrofitted with one layer of CFRP
strip by using Araldite AW106 resin and HV 953U epoxy as hardener with a weight ratio
of 10:8. After achieving the desired amount of corrosion, the angle specimen to be
retrofitted was properly grounded and cleaned with acetone in order to have a proper
binding with CFRP. The resin and the hardener were then mixed in proportion and
applied with a spatula to the pretreated surfaces. Immediately after applying the
resin-hardener mix to the surface with a painting brush, CFRP was properly pasted to the
corroded portion of the specimen. After pasting CFRP to the corroded surface, one more
coat of the resin-hardener mix was applied over the CFRP in order to have proper binding
and to protect the fibers from getting damaged. The various steps involved in the
retrofitting techniques are shown in figure 3.7.
(a)
(b) (c)
Figure 3.8: a) application of resin hardener mix, b) Pasting of CFRP and c) application of
additional coat of resin hardener mix

Flange plates of diameter 200 mm and thickness 16mm were fixed at both the
ends of the angular member. They were then subjected to axial compressive forces. The
Compression tests were conducted under force control method using 500 kN
hydraulic jack in order to develop a stable post-buckling behaviour, the displacement in
axial in–plane buckling and out-of-plane buckling directions were measured during the
tests to observe the nonlinear behaviour of the angle members. The axial and lateral
direction displacements were measured using linear variable differential transducer
(LVDT). The strain was measured by using strain gauge and LVDT were placed at one
third of the overall length from the bottom flange i.e. (corroded region). At each load
stage, deflection measurements were recorded automatically using a data logger, which is
connected to a computer. The experimental test setup is shown in figure 3.8.
Figure 3.9: Experimental test set up

4. NUMERICAL STUDIES
Advances in the field of computer aided engineering during the last two decades
have been quite extensive and have led to considerable benefits to many engineering
industries. In the building industry, use of advanced finite element tools has not only
allowed the introduction of innovative and efficient building products, but also the
development of accurate design methods. High performance computing facilities and
advanced finite element programs are now available for research and development
activities. Advanced computing facilities results in safe and optimum solutions without
the need for expensive and time consuming laboratory testing.
The behaviors of corroded angle members under compression are numerically
modeled with ABAQUS finite element software. The Finite Element Analysis (FEA) is
used for solving the engineering problems. The Finite Element Method (FEM) is a
numerical technique to find approximate solutions of partial differential equations. It was
originated from the need of solving complex elasticity and structural analysis problems in
Civil, Mechanical and Aerospace engineering. In a structural simulation, FEM helps in
producing stiffness and strength visualizations. It also helps to minimize material weight
and its cost of the structures. FEM allows for detailed visualization and indicates the
distribution of stresses and strains inside the body of a structure. Many of FE software are
powerful yet complex tool meant for professional engineers with the training and
education necessary to properly interpret the results. The loadings, complicate geometries
and material properties results were obtained numerically through FEA and the results of
the properties, which were not obtained through analytically.
There are two major approaches to the analysis: Analytical and Numerical.
Analytical approach which leads to closed-form solutions is effective in case of simple
geometry, boundary conditions, loadings and material properties. However, in reality,
such simple cases may not arise. As a result, various numerical methods are evolved for
solving such problems which are complex in nature. For numerical approach, the
solutions will be approximate when any of these relations are only approximately

satisfied. The numerical method depends heavily on the processing power of computers
and is more applicable to structures of arbitrary size and complexity.
This study is aimed to simulate compression behavior of uniformly corroded and
retrofitted angle specimens. Uniform corrosion is modeled by thickness reduction. The
solid element used is element C3D8R (Continuum, 3D, 8 node, Reduced Integration)
shown in figure 4.1(a) and the properties are shown in Table 4.1. It is an eight noded
linear hexahedral brick element and is used for modeling because of the relatively small
leg thickness of the angular section compared to the other dimensions which results in
local buckling when subjected to axial compressive load. Meshing plays important role in
discretization technique as shown in Figure 4.1(b).
Table 4.1 Properties of 100 x100 x 6 mm specimen
Particulars Values
fu 360 N/mm2
fy 466 N/mm2
Modulus of elasticity 210000 N/mm2
Density 7850 kg/m3
(a) (b)
Figure 4.1: a) Discretized column model and b)Typical finite element model used

A kinematic coupling restraint is defined to constrain the motion of the top flange
plate to the regions below where all the translational and rotational degrees of freedom
are specified. Reference point is then established in the top flange plate which passes
through the centroid of the section under consideration. Boundary conditions are then
given with all translation degrees of freedom at top surface nodes except the vertical
displacement as fixed and all degrees of freedom restrained at bottom. Then axial loading
condition is simulated by applying load to the reference point. In this method, load
magnitude is considered as an additional unknown and thus loads and displacements are
solved simultaneously. The results of interest are the current displacements and the loads
which may be referred to a load proportionality factor. The ultimate load is obtained by
multiplying the load given with the load proportionality factor.
Traditional methods are having human error, costly and time consuming. Whereas
using computers, the error can be minimized, less time and costless, this can be attained
through running various multiple scenarios.
5. RESULTS AND DISCUSSIONS
The numerical and experimental studies were carried out in order to assess the
strength and behaviour of corroded steel angle members. The ultimate strength as well as
deflection for various specimens was studied. They were modelled using ABAQUS and
the results were compared with experiments. A comparison between the numerical and
experimental values of the load carrying capacities of the uncorroded, corroded and
retrofitted specimens were tabulated as shown in Table 5.1.

Table 5.1: Load bearing capacity of specimens
Specimen No.
Numerical method
(kN)
Experimental method
(kN)
AUC-100 338.04 327.470
AC-100 204.150 203.50
ARC-100 244.980 242.140
AUC-75 186.913 187.759
AC-75 117.709 111.839
ARC-75 180.981 184.564
AUC-70 168.397 172.153
AC-70 126.142 123.27
ARC-70 158.038 159.750
From the analysis, it was observed that the mode of failure in corroded members
was due to local buckling. It was because of higher compressive stresses caused due to
the reduction in the cross sectional area of the effected corroded region. Both numerical
and experimental results match well for un-corroded, corroded, and retrofitted specimens.
It was observed from load vs. axial displacement graph that, as the percentage of
corrosion increases, the ultimate capacity of the members decreases for 100 x 100 x 6, 75
x 75 x 5 and 70 x 70 x 5 and are shown in Figure 5.1 and 5.2.

Figure 5.1: Load vs. Axial Displacement behavior curves for 100x100x6 specimens
Figure 5.2: Load vs. Axial Displacement behavior curves for 70x70x5 and 75x75x5mm
specimens

Comparison of numerical and experimental failure modes were observed typically for the
retrofitted, corroded and uncorroded specimens are shown in figure 5.3.
ARC AC AUC
Figure 5.3: Comparison of numerical and experimental modes failure for the retrofitted,
corroded and uncorroded specimens

6. CONCLUSIONS
This paper presents numerical studies carried out on uncorroded, corroded,
corroded and retrofitted steel angle sections as compression members. The capacities of
corroded members were observed between 20% to 40% of their uncorroded capacities.
The study confirms that there is a drastic reduction in the load carrying capacity of the
corroded member compared to the uncorroded specimens. From the compression test
carried out on the specimens, it was concluded that corrosion has a major impact on the
failure mode of the member. For the uncorroded members, buckling was observed at mid
height whereas in the case of corroded members, the critical region of failure shifted
towards the location of minimum thickness region. Out of the six corroded specimens,
three was retrofitted with CFRP and tested under compression. From the study it was
found that 15% to 35% improvement in strength of the retrofitted specimens with CFRP
compared to the corroded specimen. Thus external bonding of CFRP has been clearly
established as a promising alternative strengthening technique for steel structures.

REFERENCES
1. Aparna Ben, Vikraman.R, Cinitha.A, Umesha.P.K, Eapen Sakaria, (2014)
“Compressive Strength of Uniformly Corroded Steel Angle Members Retrofitted with
CFRP”, International Journal of Emerging Technology and Advanced Engineering -
ISSN2250-2459, Vol. 4.
2. Cinitha. A, Umesha.P. K, and Nagesh R. Iyer, (2014) “An Overview of Corrosion and
Experimental Studies on Corroded Mild Steel Compression Members”, KSCE Jl. of
Civ. Engg., Vol. 18, pp 1735–1744.
3. Katalin Oszvald, (2014) “Behaviour of corroded steel angle compression members –
numerical study”
4. Katalin Oszvald, “Finite element analysis of corroded steel angles under
compression”, BME Department of Structural Engineering, Conference of Junior
Researchers in Civil Engineering.
5. Sharon John1, C. Banu Priya, Y. Preethy Dharanya, Meera Muthulakshmi, R. Suresh,
M. S. Dinesh Kumar and M. S. Hari Krishnan, (2016), “Numerical Investigation on
Corroded and Uncorroded Structural Steel Coupons”, Indian Journal of Science and
Technology, Vol 9

Numerical Studies on Corroded Steel Angle Members

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