1. AHSANULLAH UNIVERSITY OF SCIENCE
AND TECHNOLOGY (AUST)
Paper Title
“Investigation of axial capacity of RC columns made of
steel fiber reinforced concrete (SFRC)”
1
Presented by
Romana Akhter
Department of Civil Engineering
Ahsanullah University of Science
and Technology (AUST),
Dhaka 1208, Bangladesh
Co-Partners:
Kazi Shahriar Islam
Rufaka Tabasum
2. Presentation Outline
I n t r o d u c t i o n
O b j e c t i v e
E x p e r i m e n t a l P r o g r a m
a n d S t r a t e g y
E x p e r i m e n t a l D a t a
A n a l y s i s
F i n i t e E l e m e n t M o d e l i n g
a n d A n a l y s i s
V a l i d a t i o n o f F E r e s u l t s
E v a l u a t i o n o f F a i l u r e
P a t t e r n s
C o n c l u s i o n
2
5. Types of steel fiber
Introduction
According to ASTM A 820/A 820M – 06, five general types of
steel fibers are identified based upon the product or process
used as a source of the steel fiber material, these are,
Type I: cold-drawn wire,
Type II: cut sheet,
Type III: melt-extracted,
Type IV: mill cut,
Type V: modified cold-drawn wire
5
7. 7
Fibers distribute
randomly and act
as crack
arrestors.
changing concrete
from a brittle material
to a ductile one, in
addition to improving
toughness and
rigidity
Increases the
ductility by
arresting crack and
prevents the
propagation of
cracks by bridging
fibers.
zone a: Free area of
stress
zone b: Fiber bridging
area
zone c: Micro-crack area
zone d: Undamaged area
Introduction
8. Objective
8
To study the compressive behavior of SFRC RC columns
due to different aspect ratios of steel fiber, i.e. 40, 60 and
80
To investigate the compressive and tensile behavior of
SFRC RC columns of two different cross-sections
To examine failure patterns of RC columns made of
SFRC.
To construct FE models for plain concrete and SFRC in
the FE platform of ANSYS 11.0 and also to validate the
models with the experimental results.
9. 9
Important properties of steel fibers for fiber selection
Type of fiber
Shape of fiber
Aspect ratio (ratio of length to diameter, l/d)
Quantity of steel fiber (volume ratio in %)
Orientation of fiber
Experimental program and
strategy
10. 10
Selection of shape
Stress-strain curves for steel fiber
reinforced mortars in tension
(ACI 544.4R-88)
Experimental program and
strategy
11. 11
Materials
Sand
Stone
Cement
Water
Steel fiber
Experimental program and
strategy
Cement type OPC (Ordinary Portland Cement)
Coarse Aggregate Size 1 in passing and 3/4 in retain (50%)
3/4 in passing and 1/2 in retain (50%)
C:FA:CA 1:1.5:3
W/C 0.5
Slump 1in (25mm)
Fiber Volume 1.5%
Fiber Aspect ratio 40, 60 and 80
Fiber type End enlarged
Fiber Tensile strength 160000 psi (1100 MPa)
Fiber cross section Circular
Fiber diameter 1.18 mm
Concrete comp. strength 3700 psi (25.5 MPa)
Type of coarse aggregate Stone
12. 12
Testing and Data Acquisition
A digital universal testing machine (UTM) of capacity 1000 kN is
used in this experiment. This is a displacement controlled
machine. Load and displacement value can be measured from this
UTM.
In this experiment displacement rate of 0.5mm per minute is
applied.
Lateral displacements/strain are measured by analyzing the
image histories obtained from high definition video camera and
employing an image analysis technique which is called Digital
Image Correlation Technique (DICT).
Experimental program and
strategy
21. Finite Element modeling and
analysis
21
FE element
SOLID65 is used to model the concrete and also SFRC. The solid is
capable of cracking in tension and crushing in compression. The
element is defined by eight nodes having three degrees of freedom at
each node; translations in the nodal x, y, and z directions. The element
is capable of plastic deformation, cracking in three orthogonal
directions and crushing. In concrete applications, the element is also
applicable for reinforced composites, such as, fiberglass and in this
case fiber reinforced concrete (FRC). The geometry and node locations
for this type of element are as follows:
FE element
LINK8 is a spar. The 3-D spar element is a uniaxial tension-compression
element with three degrees of freedom at each node: translations in the
nodal x, y, and z directions. As in a pin-jointed structure, no bending of the
element is considered. Plasticity, creep, swelling, stress stiffening, and large
deflection capabilities are included. The geometry and node locations for this
type of element has shown below:
22. Finite Element modeling and
analysis
22
Properties for FE
model
Specimen
Unit
CSSCCON CSSC40 CSSC60 CSSC80
Elastic
Modulus
2200000 1936000 1936000 1936000 psi
Density 0.083 0.094 0.094 0.094 lb/in3
Ultimate uniaxial
tensile strength
558 884 1215 918 psi
Poisson’s
Ratio
0.3 0.3 0.3 0.3 -
Displacement
boundary
condition (-y
direction)
1.0 1.0 1.0 1.0 mm
Shear Transfer
Co-efficient for
Closed crack
0.5 0.5 0.5 0.5 -
Shear Transfer
Co-efficient for
Open crack
0.3 0.3 0.3 0.3 -
FE input data
Properties for FE
model
Specimen
Unit
CSCCCON CSCC40 CSCC60 CSCC80
Elastic
modulus
2200000 2200000 2200000 2200000 psi
Density 0.083 0.094 0.094 0.094 lb/in3
Ultimate uniaxial
tensile strength
558 884 1215 918 psi
Poisson’s
ratio
0.3 0.3 0.3 0.3 -
Displacement
boundary
condition (-y
direction)
1.0 1.0 1.0 1.0 mm
Shear Transfer
Co-efficient for
Closed crack
0.5 0.5 0.5 0.5 -
Shear Transfer
Co-efficient for
Open crack
0.3 0.3 0.3 0.3 -
Properties for FE model Reinforcement Unit
Density 0.283 lb/in3
Yield stress 72,500 psi
Teng. Modulus 3,000 psi
Poisson’s ratio 0.3
Elastic modulus 30000000 psi
23. Finite Element modeling and
analysis
23
Finite Element modeling requires optimum mesh size for better analysis.
A suitable mesh size helps to achieve sufficient accuracy and also saves
time.
FE mesh analysis
24. Finite Element modeling and
analysis
24
Geometry of FE models
Volume
With Reinforcement
Boundary Condition
32. Conclusion
32
It was observed that steel fibers, up to approximately 1.5% by volume, can
partially substitute for the transverse reinforcement in RC columns and
hence could result in improved constructability.
It was also observed that fibers transform the cover spalling from a sudden
mechanism to a gradual mechanism. The addition of fibers, however, did
not prevent bar buckling from occurring.
The FE models showed similar analyses result compared to experimental
outcomes which ensures good agreements
The failure patterns are also similar which validated the FE models.
The addition of steel fibers in reinforced concrete columns can lead to
improvements, including an increase in peak load-carrying capacity of the
column and a significant improvement in the post-peak response of the
column.
FE analyses have shown conservative results in most of the cases
compared to experimental result which indicate sufficient factor of safety
and also ensure a reliable FE model.
Hi everyone, thank you for having me here. Its an honor to be here. I have been chosen for giving you a presentation on
I’ve arranged the topic into some components which will help us to understand the subject clearly.
To understand a topic clearly one must know the answer of three important questions, What? Why? And How? The first question is, what?
It is a composite material, it means steel fiber reinforced concrete.
We can see some different shapes of steel fiber
In this slide we can see 5 types of steel fiber according to ASTM, based on their product or process by which these are produced. These are
Here are some pictures of SF. These are straight, hooked end, crimped, paddled, irregular, ordinary duoform.
Now we go to the next question. That is why? Why we will use SFRC instead of PC? Plain Concrete is a brittle material. It is weak in tension and SFRC has various advantages over PC. These are
When steel fibers are added to a concrete mix. Here we can see that at zone a….
the objective of the study are:
Above all to provide the construction industry of Bangladesh with reliable experimental data and validated FE modeling about this engineering material.
Now we r going to move to our last question. How? At first we have to select fiber. To select fiber there are some important properties. These are
Here we can see stress strain curve. The curve shows the tensile strength of mortars using different type of fibers and performance of end enlarged fibers are distinctly better compared to other fiber and according to ASTM classification we have chosen Type V: Modified cold drawn wire. For better handling and workability we have selected fibers with aspect ratios 40, 60, 80.
The materials we have used in this research are:
This is how we have collected data. With the help of utm of capacity 1000kN we have tested all specimens. It’s a displacement controlled machine. The rate is 0.5mm per min. to collect data we have used high definition video camera, this process is called DICT means...
This is the experimental strategy and reinforcement layout of this research. We have used only 4-8mm longitudinal rod and no tie bar is used.
There are some experimental works photos. This is how we work in the laboratory.
After testing specimens ,data analysis is necessary and This is how we test Compressive specimens
The compressive strength of SFRC made of steel fibers having aspect ratio 40 is found 17.6% increased with respect to control specimen (normal concrete without fiber). But in case of steel fiber aspect ratio 60 and 80 reduced compressive strength is observed. This is due to the length (original and effective) of these fibers are significantly larger and evenly distribution of concrete mix may not be accomplished. But in case of ductility which is one of the major concern of this investigation is increased about 5, 3.6 and 3 times for steel fiber aspect ratio 40, 60 and 80 respectively.
This is how we test tensile specimens
Compared to the plain concrete, the tensile capacity of steel fiber reinforced concrete with steel fiber of aspect ratio 40, 60 and 80 is increased 58%, 117.5% and 64.1% respectively. Beside this the ductility also enhanced 15, 9.2 and 13 times for steel fiber aspect ratio 40, 60 and 80 respectively. So it can be easily said that steel fiber is more effective to increase the tensile strength compared to compressive strength.
To investigate the axial capacity the square and circular columns are casted with only longitudinal rebars and no tie bars are used. The axial capacities are enhanced 6%, 12% and 21% for SFRC square RC columns with SFAR (steel fiber aspect ratio) 40, 60 and 80 respectively compared to control column (CON) and ductility enhanced 2, 3 and 4 times respectively
In case of SFRC circular RC columns axial capacities are enhanced 27%, 24% and 20% respectively and ductility enhanced 3, 4 and 2 times respectively.
Before start modeling we have to know the FE elements. We have used two elements. The 1st one is solid65 which is used to build model and it is capable of cracking in tension and crushing compression just like concrete. The another element is link8 which is a spar. It shows same behavior like steel.
To build FE model we have to give some input data. The in put data for solid65 in case of square column these are, in case of circular column these are and the in put data for link8 are
After building models we have to mesh them. Finite Element modeling requires optimum mesh size for better analysis.
Some geometry view of FE models.
FE analyses have shown similar stress strain pattern compared to experimental stress strain pattern.
From this graphical relationship it is seen that FE analysis by ANSYS 11.0 satisfactorily demonstrates the accuracy of the FE model of plain concrete as well as SFRC.
After analysis the cracks it is found that all cracks are vertical. It is observed that in case of plain concrete sudden spalling has occurred and pc specimens are splited out. And no. of cracks of SFRC RC columns are less than plain concrete RC column both in case of square column and circular column.
In the both cases square and circular columns the experimental failure pattern is quite similar to the ANSYS model failure pattern which validates the FE modeling and analysis. So there remains a good agreement as well as it can be used in future SFRC model of different fiber volume and different shape.
In this we can see the stress contour of square column and circular column for plain concrete as well as SFRC.
Based on the experimental investigation and FE analysis, the following conclusions can be made.
