I am Md. Sajjak Hosain. This is my undergraduate thesis program for retrofitting of existing structure with local material available in Bangladesh. This thesis highlights the behavior of RCC structure after and before strengthening.

1. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 95
CYCLIC LOAD TEST ON BEAM-COLUMN BEHAVIOR OF PORTAL FRAME
STRENGTHENING BY MICRO-CONCRETE
M. S. Hosain1
, Y. A. Khan2
and M. R. Ahsan3
ABSTRACT
Strengthening of concrete structures is very common for damage caused due to an earthquake or any natural
disasters. Studies show that reinforced concrete columns can experience a significant increase in the ultimate
capacity and ductility when strengthened by a micro concrete. This study investigates the effectiveness of
strengthening of half-scaled RC columns by Micro concrete jacketing. Among three physical models, one
simulates the existing structural condition and others simulate retrofitted behaviors. All specimens were
modeled to examine the seismic effect by cyclic loading. The concept of the weak beam-strong column was
also applied for the test. Micro-concrete was produced with the locally available materials. To investigate the
performance of retrofitted RC frames, the columns of two models were jacketed with micro-concrete by 50
mm widening and cyclic loading was applied with sustained gravity load. This test was a displacement control
test. Retrofitted specimens with 6.3 ksi micro concrete and 8.3 ksi showed higher stiffness and ductility than
the un-retrofitted specimen. The higher strength of jacketing material doesn’t affect the stiffness and the
lateral load carrying capacity significantly due to the anchorage failure of columns. All specimens were tested
by a hydraulic testing machine. Raw data were collected manually from displacement dial gauge and from a
computer database of video extension meter.
Keywords: Cyclic loading, Portal frame, Micro concrete, Jacketing, Strengthening, Stiffness, Horizontal
displacement, etc.
Introduction
The rapid growth of urban population in both developing and industrialized countries, reinforced concrete
has become a material of choice for construction because it’s cheaper compared to other materials. In the
construction of the reinforced concrete structure, it is very important to consider the earthquake provision.
Generally, most of the reinforced concrete structure has been constructed without seismic provision. To
facilitate such provision for the constructed structure it has been essential to strengthen the existing structure.
The stronger structure can be made by new technology but strengthening the existing structure needs
retrofitting of the structure by appropriate materials. For retrofitting RC structures micro concrete is now
being used. The various components of the existing structure are retrofitted. In this study, the column will be
retrofitted by micro concrete. The column of the existing structure will be widened by 50mm all around. The
aim of the present study is to investigate the strength improvement and performance of retrofitted RC portal
frame under incremental cyclic horizontal load with sustained vertical load. Most of the previous researches
were performed on behavior and response of structure by retrofitted with different material. Now it will be
studied with micro concrete.
Objectives of the Research
The main objective of this paper is to conduct experiments on two frames with retrofitted by micro-concrete
and one frame without retrofit to interpret the experimental findings. The terminal objectives of the
investigation are as follows: To investigate the ultimate lateral load carrying capacity and the maximum
lateral displacement of square RC columns strengthened using MC jacket
1. To study the effectiveness of the applied jacketing style in terms of ultimate lateral load carrying
capacity, failure patterns and to compare the obtained results with that of the columns of Control
specimen (CS)
2. To study the effect of jacket thickness on both the ultimate load carrying capacity and the lateral
displacement and to compare the obtained results with that of the columns of the CS
3. To observe the response of the specimens under the strength variation with different grain size
1
Post Graduate Student, Department of Civil Engineering, BUET, Dhaka-1000, Bangladesh
2
Graduate from Department of Civil Engineering, BUET, Dhaka-1000, Bangladesh
3 3
Professor, Department of Civil Engineering, BUET, Dhaka-1000, Bangladesh

2. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 96
4. To increase the factor of safety against lateral load carrying capacity by means of retrofitting.
Methodology
To investigate the behavior of reinforced concrete frame with varying retrofitted parameters, cyclic static
incremental horizontal load were provided to test the frames with sustained vertical load. Half scale RC model
frames were prepared, integral with a heavily reinforced concrete base. Frames were of 1.5 m height and 2.6
m span. Then the following parameters were considered for the study: A total of three frames were constructed
for the study:
1. All three frames were constructed with the same base beam cross section (300mm x 250mm)
2. All three frames were constructed with the same top beam cross section (125mm x 125mm)
3. All of three frames were constructed with column section by (125mm x 125mm) at first stage
4. After retrofitting the column section of two frames were (225mm x 225mm)
Finally, the load-deflection curves were compared for the considered different frames with retrofit and
without retrofit.
Material and Mix Proportions
Cement
Ordinary Portland cement (OPC) was used. Specification and composition of cement by the manufacturer:
28th days cube strength 42.5 N by ASTM C595, Clinker: 65-79%, Slag, Fly ash & Limestone: 21 - 35%
Gypsum: 0-5%, specific gravity 3.15 and unit weight 197 pcf.
Sand
Sylhet sand FM is 2.5. Sand was free from clay.
Reinforcement
Table 1: Material Properties Tested By Laboratory
Material Diameter Yield Strength MPa (Min) Ultimate Strength (MPa) Elongation %
420 W 10 mm 426 523 14
420 W 12 mm 440 685 14
420 W 16 mm 429 658 15
Concrete Mix Proportions
Highest compressive strength 7820 psi was achieved by a ratio of 1:1:1.5 (cement: fine aggregate: coarse
aggregate) with water cement ratio of 0.3 (Hassan and Ahmed, 2016). Two retrofitted specimen were prepared
by different strength to demonstrate the effect of strength on the retrofitting behavior. To make a variation of
strength, another mix ratio of 1:1.25:1.7 was used (6830 psi by Hassan and Ahmed, 2016).
Table 2. Volumetric Mix ratio for concrete for control and retrofitted specimen
Item Cement Sand: FM CA (mm) w/c Ratio
Cement: Sand: CA
Slump
(mm)
CS OPC 2.5 12.5
downgrade
0.46 1:1.5:3* 70
RS-1 OPC 2.5 6.0
downgrade
0.23 1:1:1.5** 250
RS-2 OPC 2.5 8.0
downgrade
0.28 1:1. 25:1.7 ** 200
* Conventional volumetric mix ratio which exhibits existing concrete ratio.

3. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 97
**Volumetric mix ratio for high strength concrete was suggested by Hassan and Ahmed, 2016.
Concrete Cylinder Strength
Item Cylinder size 7th
day f’c (psi) 14th
day f’c(psi) 28th
day f’c(psi)
Control specimen 100mmx200mm 1620 2150 2680
Retrofitted specimen 1 100mmx200mm 5800 N/A 8160
Retrofitted specimen 2 100mmx200mm 4610 N/A 6300
Admixtures
Water reducing admixture was used for reducing the water-cement ratio of dozes 9.0 ml/kg of cement.
Chemical Binder (Epoxy)
Chemical binder was used for proper binding between concrete and the steel reinforcement.
Methodology
To identify the effect of seismic loading on the retrofitted column, a one bay frame of the bottom story of a
six-storied building structure was selected. The model was designed in half scale of the original structure.
Frame Part Cross Section Reinforcement Detail
Base
Beam
Base Beam: B x D = 300mm x 250 mm
Main bar: 16-R16 ,Stirrup: R12 @100 with
135 degree hook, Clear cover = 20 mm
Column
of CS
Column: B x D = 125 mm x 125 mm
Main bar: 4-R12, Hoop: R8 @150 with
90 degree hook, L = 6d ,Clear cover = 20 mm
Column
of RSs
Column: B x D = 225 mm x 225 mm
Main bar: 4-R12, Hoop: R10 @150 with
90 degree hook, L = 6d, Clear cover = 20 mm
Beam Beam: B x D = 125 mm x 125 mm
Main bar: 4R10, Stirrup: R10 @150 mm with
90 degree hook, L = 6d, Clear cover = 20 mm
Specimen Preparation
First Stage
Three Frame specimens were prepared by casting horizontally (Figure 1). For time constraint it was chosen
to casting horizontally. But to reflect the existing condition of concrete it should be casted vertically.

4. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 98
Figure 1: Horizontal Concrete Casting Figure 2: Application of Epoxy
Chemical
Second Stage
In the second stage of the construction process, the two specimens were retrofitted by micro concrete of
different strength. One specimen was retrofitted by micro concrete of lower strength [6300 psi] and another
was retrofitted by higher strength micro concrete [8160 psi] to observe the response for the cyclic load. The
two specimens were extended by 50 mm on each side of the column only (Figure 3).
Figure 3. Formwork for a widening of column Figure 4. Micro-concrete placement
No surface epoxy was applied for bonding between existing and fresh concrete to reflect the worse effect of
retrofitting (Figure 4). Epoxy grouting agent was used for the insertion of new rebar into the control specimen
(Figure 2).
Figure 5. Control Specimen
(CS)
Figure 6. Retrofitted Specimen
(RS-1)
Figure 7. Retrofitted Specimen
(RS-2)
Test Set-Up, Instrumentation
The entire test was carried out in the hydraulic testing machine. The vertical hydraulic jacks were first loaded
to a combined force of 20 ton, 10 ton on each column top (Figure 10) (Fancy, 2014). The horizontal hydraulic
jacks were responsible for imposing the cyclic displacements to the specimen through complete cycles. The
test was displacement control.

5. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 99
Figure 8. Loading History for Control Figure 9. Loading History for Retrofitted Specimens
Age of Testing Specimens
Specimen Age of Specimen at Testing day (Days)
CS 67
RS-1 60 (after retrofitting)
RS-2 64 (after retrofitting)
Test Result for retrofitted specimens
All specimens were tested under Hydraulic Testing Machine (HTM). The loading was incremental static
cyclic loading with sustained gravity load. The load was applied at 0.5 ton interval to reach the desired
displacement (Fancy, 2014).
Test Result of Control Specimen (CS)
First loading was applied at the beam-column joint of the left side. The cracks marked by red colour were
during rightward loading (figure 11) and the cracks in black colour were for unloading (Figure.12). The test
of CS was accompanied with its very first crack at positive first cycle loading at the right column with 1 ton
load and corresponded to a displacement of 1.1 mm (Figure 11).
Figure 10. Final Crack Pattern of
CS
Figure 11: Crack in Right
Column after Failure
Figure 12.Failure cracks in
column- base beam joint at the
left column
Figure 13 (a). P-M Interaction diagram Figure 13 (b). Failure cycle of control speciment for
Left
Right

6. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 100
horizontal load
Test Result of Retrofitted Specimen-1 (RS-1)
The cracks marked in black were those that surfaced during rightward loading and unloading. The red marked
cracks represented the cracking that appeared during the leftward loading and unloading. The test of RS-1
was accompanied with its very first crack at positive first cycle loading at the left column and at base beam
near right column with 4.5 ton load and corresponded to a displacement of 2.8 mm.
Figure 14. The final crack pattern of
Retrofitted specimen-1
Figure 15. Load Vs. Displacement plot for all cycles
Figure 16. Crack Pattern
at Beam-Column Joint
Figure 17. Crack Pattern
at Beam-Column Joint
Figure 18. Crack Pattern
at Column-Base beam
Joint
Figure 19. Crack
Pattern at Column-
Base beam Joint
Test Result of Retrofitted Specimen-2 (RS-2)
The cracks marked in black were those that surfaced during rightward loading and unloading. The red marked
cracks represented the cracks that appeared during the leftward loading and unloading. During the test of RS-
2, its very first crack was found at positive first cycle loading at the joint of the base beam and left column
with 6 ton load and corresponded to a displacement of 4 mm.
Figure 20. Retrofitted specimen-2 under
Hydraulic testing Machine
Figure 21. Load Vs. Displacement plot for all cycles
Left Right
Left Right

7. Proceedings on International Conference on Disaster Risk Management,
Dhaka, Bangladesh, January 12-14, 2019
Page | 101
Figure 22. Crack
Pattern at Beam-
Column Joint
Figure 23. Crack
Pattern at Beam-
Column Joint
Figure 24. Crack Pattern
at Column-Base beam
Joint
Figure 25. Crack
Pattern at Column-Base
beam Joint
Conclusions
This research investigated the ultimate load carrying capacity and the maximum lateral displacement of RC
columns strengthened by micro-concrete. All fabricated frame specimens were subjected to successive cyclic
loading. Following conclusions are drawn based on the experiment and analysis of the results:
• Ultimate lateral load carrying capacity of RS-1 and RS-2 was found to be 175% greater than that of
CS
• Before the formation of the first crack, the RS-1 experienced 350% more lateral load than the
corresponding CS whereas RS-2 experienced 300% more lateral load than CS.
• Test results show that the CS suffered shear failure at the base of the column and significant
degradation of strength at relatively low lateral displacement.
• Although RS-2 [8160 psi] was stronger than RS-1 [6300 psi], it didn’t increase the load carrying
capacity and the stiffness of the RSs significantly.
• The failure mode of both RS-1 and RS-2 was anchorage failure. It indicates inadequate penetration
of longitudinal rebars during retrofitting.
• No hooks were provided in the longitudinal rebars during retrofitting of the columns. This resulted
cracking in the top of the column during the test.
• The results of this investigation indicated that the strengthening of a square reinforced concrete
column with micro concrete may be considered as successful.
References
Fancy, S. F., (2014) “Experimental Investigation on Performance of Beam-Column Frames with Column
kickers”.
Hassan, M. R., Ahmed, S., (2016) “Production of Micro-concrete Using Indigenous Materials”.