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International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 5, May 2018, pp. 218–228, Article ID: IJCIET_09_05_025
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=5
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
INVESTIGATION OF HYBRID BEAM –
COLUMN JOINTS UNDER CYCLIC LOADING
A S. Srinivasan
M.Tech, Structural Engineering, SRM Institute of Science and Technology,
Kattankulathur, Kanchipuram, Tamil Nadu
S. Pradeep (O.G)
Assistant Professor, Civil Engineering Department, SRM Institute of Science and
Technology, Kattankulathur, Kanchipuram, Tamil Nadu
ABSTRACT
In this paper, the investigation is about the behavior of beam-column joints under
cyclic lateral loading. Where maximum stress at the joints is resisted by using steel -
profile mechanism for both external and internal beam-column joints. The behavior of
steel-profile is validated through Ansys 18.2 FEM software. Static analysis is carried
out to find the behavior of frame structure and the fatigue lifespan at the beam-column
joints is evaluated using constant amplitude method of cyclic loading. The frame
model is designed as per experimental parametric investigation and this study is
carried out for two frame specimens.
Keywords: Beam - Column Joints, Steel Profile, Fatigue, Cyclic Loading, Von-Mises.
Cite this Article: A S. Srinivasan and S. Pradeep (O.G), Investigation of Hybrid
Beam – Column Joints under Cyclic Loading, International Journal of Civil
Engineering and Technology, 9(5), 2018, pp. 218–228.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=5
1. INTRODUCTION
This research paper mainly is to ensure the joints strength under the lateral force. Due to
seismic force acting on the structures leads to failure at the beam-column joints. Normally
maximum shear bending in the structure will occurs at beam-column joints so; the life factor
is less at the joint area. To increase the strength at the joints many engineers implemented vast
area of research to enhance joint strength. By means of material replacement, mechanism
enhancement etc., in this paper introducing the steel-profile mechanism at beam-column joints
to increase stiffness at joints, also analytical investigation shows that the fatigue life of the
structure is improved when compared to the controlled specimen. Static analysis is carried out
to check the behavior of the steel-profile mechanism at the joints. Steel profile mechanism
mainly designed for practical implementation at the construction situations, where the steel
profile mechanism is placed at the both external and internal beam-column joints which are
used to reduce stress at that critical zone.
A S. Srinivasan and S. Pradeep (O.G)
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Figure 1 Behavior of frame due to lateral force.
Fig 1 shows the shear bending of the body due to lateral load. In this structure beam-
column joints having maximum shear force. So, these points are referred as the critical zone
to consider for the safety enhancement to the joints, this particular zone has to be more
stiffened than any other critical zone. So innovative design of steel profile is introduced at
those points to resist shear bending at the joint area. Also, steel profile is able to resist
maximum shear force acting at critical zone that shown as analytical representation in this
paper.
Figure 2 Shear force due to lateral loads.
Shear bending plot shows the maximum force is acting at the joint area shown in Fig 2,
this is due to lateral load causes heavy stress at beam-column joints resulting the joint zone
has minimum life factor. Here in the earthquake resistance design, the way is to reduce shear
bending is by increase in material strength, dimension of structure, and reinforcement area. In
this paper research proposed through reinforcement enhancement at maximum working stress
at the joints to resist stress by a reinforcement.
2. FRAME MODEL
Frame model is done through SolidWorks, CAD software for better designing. High-
performance CAD modelling tool is useful for dimension accuracy and better graphics
experience. Additional simulation for model is facilitated in solid works to perform the cross-
check for the model and its used to reduce errors in the model, which is more beneficial for
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designing a CAD model for an engineering research. Exported the model as (parasolid.exe)
format, then the file is imported into Ansys for numerical analysis.
2.1. Frame Parameters
Frame model is of one story with 2 bays in the structure, where this frame model is very
beneficial to find out the behavior at the both external and internal beam-column joints. This
framed model perfectly suits for lateral load deformation simulation and for designing
suitable reinforcement at beam-column joints. Concrete and Structural Steel material is
defined for the structure. Here for the applied lateral force, the stress will get transmitted to
the supports. Hence the failure begins at that support area first. So, to reduce the stress at the
supports, gradual increase in dimension at the base (1/3) of the column length. Therefore, for
applied lateral load the stress will take place first at the beam-column joints. Hence steel
profile mechanism is easy to validate at the joints.
Figure 3 SolidWorks CAD Model.
2.1.1. Beam Parameters
Sl. No. Parameters Descriptions
1 Clear Length 500mm
2 Width 90 mm
3 Depth 100 mm
4 Reinforcements Top & Bottom – 2nos of 6mm diameter bars
5 Stirrups 6mm diameter bar at 95mm C/C
6 Clear Cover 25 mm
2.1.2. Column Parameters
Sl. No. Parameters Descriptions
1 Clear Length 600mm
2 Width 100 mm
3 Depth 90 mm
4 Reinforcements 4nos of 6mm diameter bar
4 Stirrups 6mm diameter bar at 100mm C/C
5 Clear Cover 20 mm
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Figure 4 AutoCAD Reinforcement detailing.
Reinforcement solid body place inside the concrete body with the help of assembling tool
in the SolidWorks CAD Software. Removal of reinforcement volume from the concrete body,
were the steel area is subtracted from the concrete. Then again placing the reinforcement body
at the subtracted area.
3. ANSYS INPUTS
Ansys setup requires some information to proceed numerical analysis. Material properties are
the major inputs to consider for all the bodies, Structural steel material is applied for
reinforcement bodies and M25 Grade design is taken into account for the concrete body.
Contacts between the concrete and reinforcement are taken into consideration to cross check
the bonding between concrete and reinforcements. Fatigue data is needed for both concrete
and structural steel to evaluate the life factor of structural members for continuously applied
load. Constant amplitude method is adopted for cyclic loading.
3.1. Material Properties
Table 1 Concrete Properties
Parameters Value Units
Density 2300 Kg/m3
Elastic Modulus 25000 N/mm2
Poisons Ratio 0.17 -
Yield Tensile 2.25 N/mm2
Yield Compressive 25 N/mm2
Ultimate Tensile 2.5 N/mm2
Ultimate Compressive 31.2 N/mm2
Table 2 Structural Steel 250 Properties
Parameters Value Units
Density 7850 Kg/m3
Elastic Modulus 200000 N/mm2
Poisons Ratio 0.3 -
Yield Tensile 250 N/mm2
Yield Compressive 250 N/mm2
Ultimate Tensile 415 N/mm2
Ultimate Compressive 415 N/mm2
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Table 3 Structural Steel 415 Properties
Parameters Value Units
Density 7850 Kg/m3
Elastic Modulus 200000 N/mm2
Poisons Ratio 0.3 -
Yield Tensile 415 N/mm2
Yield Compressive 415 N/mm2
Ultimate Tensile 550 N/mm2
Ultimate Compressive 550 N/mm2
3.2. Body contacts
Bonded Contact is applied b/w Concrete and reinforcement in the model. Resulting both
behaves as a Single structural element in the Modal. Where Pre-Stressed Body Required
Frictional Contact between the elements due to frictional loss. Designing for normal RCC
structure doesn’t require frictional contacts between elements for analysis.
3.3. Fatigue data
Fatigue data is the collection of data for the material, which is subjected to repeated cyclic
load resulting data taken as total life of the material. It’s the progressive and localized
structural damage that occurs when a material is subjected to cyclic loading. Below data
analytically use to find out the total life of the materials.
Figure 6 Fatigue data for Structural Steel and Concrete
4. JOINT MECHANISM
The maximum shear force is acting at beam-column joints shown in fig 2, hence critical zone
taken into consideration for enhancing the joint strength. In this paper brief discussion is
about steel profile mechanism, Where Two-Types of steel profile is designed and provided at
joints, one is T- Shape provided at the external joint and the other is Cross-Shape provided at
the internal beam-column joint. Steel Profile mechanism reinforcement design is formulated
according to the structural variation. Design of steel profile is cost effective with more
beneficial enhancement at the both external and internal beam-column joints.
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Figure 7 Steel-Profile Mechanisms at Joints.
4.1. Formulation
• Area of reinforcement - Lesser than 0.5% of C.S (if >200mm).
• Area of Reinforcement - Equal to 0.5-0.55% of C.S (if <200mm).
Length of Steel Profile - User Defined According to Max Bending stress at joints. Should
not be more than 1/3 of the Clear length.
Total length of the bars along beam is 160mm and the column is 150mm, area of
reinforcement is 57 mm2
whereas 2nos of 6mm diameters bars are provided at the beam-
column joint. Same for external and internal joints, here in this analytical study shows that the
external steel profiles give more life to the joints than internal steel profile mechanism.
5. ANALYSIS
Static analysis is done for the Frame Specimens using Ansys FEM. Mesh for the concrete
body is 35mm and Steel Body is 10mm along longitudinal direction, Frame model divided up
to 450780 mesh elements. Various lateral loads were applied to the frame to find out the safe
load for the structure, where safe load processed for cyclic loading “constant amplitude
method” chosen to calculate the maximum life at the joints. Load concentrated on the body
varying from 5kN to 100kN. Ansys numerical result shows that the ultimate load carrying
capacity of the joints is around 50kN without any damage. Here its factor to 42.5kN for the
Uncracked Structural safe load to be considered for analysis of structure.
5.1. Static Structural Analysis
Figure 8 Loading Point and Boundary Conditions.
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A 50kN lateral load applied at the external beam-column joint, where the stress exceeds the
yield strength of the concrete material at joints area. Here concrete yield strength considered
as 25MPa, Material failure takes place when the applied load causes the stress at the joints
which exceeds yield strength of the material 25MPa. So, considering design load as 50kN, so
factored to 42.5kN for safe behavior at beam-column joints. Experimental load for heavy
destruction at beam-column joint load is around 75 to 80kN. Results evaluated by von mises
stress component is preferred by a designer, which represents the behavior of the structure due
to applied load and boundary condition. Von Mises stress shows that the failure occurrence at
the body point, when the stress exceeds the yield strength of the material. So, an engineer can
able to design a structure in the way to execute in the fields.
5.2. Fatigue Analysis
Linear and non-linear structural analysis do not show the fatigue life of the structure its shows
the behavior and evaluates components like stress, strain and deformation for applied load and
boundary conditions accordingly. If the analysis assumptions are observed and the calculated
stress are within the allowable limits, application concludes that the total fatigue life cycle of
the body which can withstand the maximum number of a cyclic load at each and every node
in the model. Static structural studies are used for numerical fatigue analysis. The maximum
number of cycles required for fatigue failure to occur at any location is depended on the
material and the yield stress acting on the body.
5.2.1. Stages of failure
Stage 1 Cracks development in the concrete is mainly due to honeycomb in the body which is
not visible for naked eyes. Irregular mix design will cause surface cracks in the concrete. Also due to human errors like material handling, transportation etc.
Stage 2 Cracks formation due to continuous cyclic loading in the structure. Which results in
breakage of material at certain cyclic loading?
Stage 3 The ability of the design to carry the maximum load applied continuously till failure
take place in the structure.
In this study fatigue, life cycle monitored at the starting point of the cracks at the beam-
column joints.
5.2.2. Correction methods
The fatigue analysis is programmed by using three different algebraic formulations which
designer should adopt as per field and requirement.
• For brittle material “Goodman method” is suitable for evaluating life.
• Ductile material “Gerber method” formulation shows accurate results.
• General adoption is “Soderberg Method” for conservative analysis.
Here in this paper, Goodman method is adopted to calculate total life cycle of Concrete
material which is brittle in nature.
5.2.3. Fatigue events
Two Types of fatigue events is carried out by using Ansys FEM: Constant amplitude method
and variable amplitude method. In this study, constant amplitude method is preferred because
the maximum load already designed for the structure to apply. Hence constant amplitude
method is adopted to find total life cycles at the joints.
Outputs: fatigue analysis shows components like life, damage, & factor of safety. The
Program based on the loading ratio determines a corrected alternating stress from the static
A S. Srinivasan and S. Pradeep (O.G)
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study stress value for each node can able to select or probe nodal value of specimen as shown
in figure 12&13.
Zero Based Analysis (LR=0): Here load is 42.5kN cyclically applied as shown in fig.
Where the load varies from 0 to 42.5kN then gradually reduced to “Zero” respect to time (t) in
Sec. Cyclic loading continuously applied till evaluation of material life of the structure.
Figure 9 Zero Based (LR=0) Constant Amplitude.
6. RESULTS AND DISSCUSSIONS
Here in this investigation, steel profile mechanism behavior is monitored exactly with the help
of Finite element analysis which is resulting over stiffening at the beam-column joints. Extra
reinforcement enhancement that is provided at joints is act as antilock mechanism at joints,
twisting of member at the joints area seems to be reduced at a certain level. The area around
the beam-column joints shows that the stress is reduced, were stress decreased around 1.5MPa
to 2MPa. The output results clearly show that the tensile performance at joints is increased.
Two types of results shown below 1) Static analysis results which shows the behavior of the
structure and 2) Fatigue analysis which shows the maximum life factor of the structure for
applied load and boundary conditions, zero based analysis is carried out for the frame, load is
applied continuously from “0” to “42.5kN” again to “0” as shown in fig 11.
6.1. Static analysis results
Figure 10 Von-Mises stress for concrete
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Figure 11 Von Mises stress for structural steel
Frame is stressed up to 95MPa, maximum stress inducing in structural steel and concrete
is stress up to 23MPa at joints for applied load. Normally in RCC structure the steel is always
has maximum stress than concrete, due to lateral force, tensile stress is maximum at structural
steel, shown in Fig 10 and 11.
6.2. Fatigue analysis results
Figure 12 total fatigue life at critical point (Frame without Steel-Profile)
Figure 13 total fatigue life at critical point (Frame with Steel-Profile)
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Hence the fatigue life at the joints is increased when compared to frame without steel-
profile. Here external joints life is increased from 1574 to 1804 cycles, Internal joints life is
increased from 1055 to 1205 cycles, shown in fig 12 and 13. Finally concluded that the steel
profile mechanism act as good load resistor at beam-column joints.
7. CONCLUSIONS
• Provision of steel profile is found to improve structural behaviour at beam-column
joints.
• Steel Profile reinforcement could able to resist the shear stress up to 47MPa at both
the joints. So, Reduction in Joint Shear deformation.
• Steel Profile Bars stressed up to 82MPa at the joints. Hence load-carrying Capacity of
the member is slightly increased.
• Stiffness at the beam-column joints increased which results in the improvement of
fatigue life at the joints, when compared to the controlled specimen.
• Initial Crack Formation due to yield stress is reduced. Hence life of the structure will
get increased.
• Steel-Profile reinforcement is cost effective and increase in mechanical behaviour at
joints.
• More research is required to validate steel profile mechanism for the future
construction applications.
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