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Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 04 - 06 

4 

Bending Resistance Capacity of Steel Pile Caps Strengthened 

with Perfobond Shear Connectors 

Dae-Jin Kim
1,*

, Young-Ho Kim
2
 

1
Department of Architectural Engineering, Kyung Hee University, Yongin, Republic of Korea. 

2
Institute of R&D, Ji Seung Consultant Co., Ltc., Seoul, Republic of Korea. 

Received 31 March 2016; received in revised form 19 April 2016; accept ed 09 May 2016 

 

Abstract 

This study proposes a new perfobond shear 

connector, which can be  used to strengthen the 

steel pile  cap e mbedded into the structural 

foundation. The bending resistan ce capacity of 

the steel pile cap strengthened with the proposed 

perfobond connectors is evaluated by perform-

ing a test on seven specimens. Test parameters  

include the type of perfobond shear connectors, 

infilled concrete depths and number of L-shaped 

steel plates. The lateral load versus displacement 

curve is plotted for all specimens, and their 

failure  modes are identified. The effects of the  

test parameters on the bending resistance ca-

pacity of the specimen are e xa mined in this 

work. 

Keywor ds : steel pipe pile, perfobond shear 

connector, concrete foundation, 

bending resistance 

1. Introduction 

At the foundation to support an upper 

structure, there e xists a connection between piles 

and concrete footing. The integration of these 

two structural co mponents is very important to 

guarantee the safe load transfer fro m the upper 

structure to the supporting layer of rocks. In  

general, this can  be achieved by  the use of steel 

reinforc ing bars e mbedded into the co ncrete  

footing. In this case, the bond between the steel 

rebars and concrete is activated by the mechan-

ical bearing of bar ribs, and it is essential to 

retain a suffic ient level o f their bond strength. 

However, since their rib size  is limited and they 

have relative ly s mall cross -sectional area, their 

bond strength is also limited to a small value as 

indicated in various concrete design code pro-

visions such as ACI building code [1, 2].  

In order to handle this issue, we propose a 

new perfobond shear connector illustrated in Fig. 

1, wh ich can guarantee an excellent composite 

behavior among the structural components at the 

steel pile cap. Th is type of perfobond shear 

connector can guarantee an e xce llent co mposite 

behavior among the structural components at the 

steel pile  cap. This device  is basically  a steel 

plate with holes and embedded into concrete to 

ensure the perfect integration of steel me mbers  

and surrounding concrete. As external loads are 

applied, the dowel action of concrete inside the 

hole is activated and enables the load fro m the  

upper structure to be safely transferred to the 

steel pipe piles. 

  

(a) Pe rfobond shear 

connector with 

closed holes  

(b) Perfobond shear 

connector with 

open holes 

 Fig. 1 St rengthening of steel pile caps using the 

perfobond shear connectors  

This study experimentally investigates the 

structural performance of the steel pile cap  

strengthened with the proposed perfobond con-

nectors under lateral loading. A bending test is 

conducted on seven specimens by considering 

the type of perfobond shear connectors, infilled  

concrete depth and number of L-shaped steel 

* Corresponding aut hor. Email: djkim@khu.ac.kr 



Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 04 - 06 

5 Copyright ©  TAETI 

plates as test parameters. The failure character-

istics of the test specimens are e xa mined, and  

their load-displacement curves are analyzed. 

2. Experimental Program 

For this study, a total of seven specimens 

were manufactured and tested. Among the seven 

specimens, six were  strengthened with the newly  

proposed perfobond shear connectors, and the 

re main ing specimen with conventional steel 

reinforc ing bars. Fig. 2 illustrates the details of 

typical test specimens  with the perfobond con-

nectors , including their geometrical configura-

tions and infilled concrete depths. The pe r-

fobond shear connectors were connected to the 

outer surface of the steel pile cap by bolting. In 

addition, a number of L-shaped steel plates were 

connected to the inner surface of the steel pile  

cap by bolting. They play a role of shear keys 

and provide some additional shear resistance. 

The center of the steel p ile  cap co incided with  

that of the concrete block in all specimens. 

 
Fig. 2 Details of specimens with perfobond 

connectors 

The list of the seven test specimens are pro-

vided in Table 1. The main test parameters in-

clude the type of perfobond shear connectors, 

infilled concrete depths and number of L-shaped 

steel plates. Two types of perfobond shear con-

nectors were used in the test specimens. The first 

type (PO) has open holes while the other (PC)  

closed holes . The reference specimen strength-

ened with conventional steel rebars (SB) had the 

infilled concrete depth of 700 mm, which is 

greater than the diameter of the steel pile. In  

contrast, the specimens strengthened with the 

perfobond shear connectors had two different 

infilled concrete depths corresponding to the 

diameter (D10) and half dia meter (D05) of the 

steel pile, respectively. Three different numbers 

of L-shaped steel plates, which are 0 (NL), 3 (L3)  

and 6 (L6), were used in the specimens 

strengthened with the perfobond connectors . 

As shown in Fig. 3, lateral load was applied  

to the test specimen  by an actuator with  ma xi-

mu m capacity o f 500 kN, wh ich a llo ws dis-

place ment-based control. The rate of loading 

was 0.5 mm/ min., and its magnitude was meas-

ured by the load cell attached at the end of the 

actuator. The load-versus -displacement data 

were recorded throughout the entire loading 

history using a computer-aided data acquisition 

system. 

 Fig. 3 Test setup 

3. Results and Discussion 

Table 1 summarizes the test results such as 

peak loads  and displacements at peak loads. From 

these results, it can be seen that the specimens 

strengthened with the open-hole type perfobond 

connectors have higher bending resistance than 

those with the closed-hole type connectors, and 

almost equal strength to that of the reference 

specimen. For e xa mp le, the ratios of the peak 

strength of the open-hole type perfobond speci-

mens PO_D05_L3 and PO_D10_ L3 to that of the 

reference specimen are 93.3 % and 95.3 %, re-

spectively. This is remarkable considering that 

the concrete infilled depths of these specimens 

are only in the range of 200 mm and 400 mm, 

while that of the reference specimen is 700 mm. 

1
0
0
0

9
0
0

4
0
0

5
0
0

In
fi
ll
e
d
 c

o
n
c
re

te
 

d
e
p
th

406

1400

LVDT 5 LVDT 4

LVDT 3

A-1

C-1

B-1

A-4

C-4

B-4

C-2

B-2

LVDT 1

LVDT 2



Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 04 - 06 

6 Copyright ©  TAETI 

In addition, it can be noted from the test results 

that the peak strength of the specimen is  increased 

with increasing concrete infilled depth. For ex-

ample, in the case of PC_D10_L3 specimen, its 

peak strength is increased by 9.2 % due to the 

increase of concrete infilled depth from 200 to 

400 mm, while  that of PO_D10_L3 specimen  

only by 2.2 %. Therefore, the increase of peak 

strength due to increasing concrete infilled depth 

is more pronounced with closed-hole type per-

fobond specimens . 

Table 1 Summary of test results  

Specimen 

P eak load 
Displacement 
at  peak load 

(mm) 
Lat eral 

load (kN) 

Bending  

moment  
(kN∙m) 

SB_D10_NL 342 308 50.0 

P C_D05_NL 279 251 32.2 

P C_D05_L3 262 236 33.2 

P C_D10_L3 286 257 68.6 

P C_D10_L6 303 273 48.0 

P O_D05_L3 319 287 39.2 

P O_D10_L3 326 293 43.6 

4. Conclusions 

In this study, we performed an e xpe rimental 

investigation on the structural performance of 

the steel pile cap strengthened with the proposed 

perfobond connectors under lateral loading. A  

bending test is conducted on seven specimens by 

considering the type of perfobond shear con-

nectors, infilled concrete depth and number of 

L-shaped s teel plates as test parameters. Fro m 

the test results, it was found that the specimens 

strengthened with the open-hole type perfobond 

connectors have higher bending resistance t han 

those with the closed-hole type connectors, and 

almost equal strength to that of the reference 

specimen. In addition, it can be noted fro m the  

test results that the peak strength of the specimen  

is increased with increasing concrete infilled  

depth. 

Acknowledgement 

This work was supported by the Basic Sci-

ence Research Program through the National 

Research Foundation of Korea (NRF) funded by 

the Ministry of Science, ICT  & Future Planning  

(Grant number: 2013R1A1A1076011). 

References 

[1] ACI Co mmittee 318. “Building code re-
quire ments for structural concrete (ACI 

318-11) and commentary,” A me rican Con-

crete Institute. Farmington Hills: MI, 2011. 

[2] ASTM Standard C39/C39M-11. “Standard 
test method for co mpressive strength of cy-

lindrical concrete specimens ,” Ame rican  

Society for Testing and Material, 2011.