|Mulia Orientilize||Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, 16424, Indonesia|
|Widjojo A Prakoso||Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, 16424, Indonesia|
|Yuskar Lase||Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, 16424, Indonesia|
|Sidiq Purnomo||PT Wijaya Karya Beton Tbk, WIKA Tower 1 FL. 2-5, Jl. D.I. Panjaitan Kav. 9-10 Jakarta, 13340, Indonesia|
|Ignatius Harry Sumartono||PT Wijaya Karya Beton Tbk, WIKA Tower 1 FL. 2-5, Jl. D.I. Panjaitan Kav. 9-10 Jakarta, 13340, Indonesia|
|Winda Agustin||PT Wijaya Karya Beton Tbk, WIKA Tower 1 FL. 2-5, Jl. D.I. Panjaitan Kav. 9-10 Jakarta, 13340, Indonesia|
Experimental study was carried out on three low
confinement spun piles to pile cap connections.
The detail followed the typically fixed connection in Indonesia.
Reinforced concrete was filled to the spun pile to strengthen the connection region,
except SPPC01. Different concrete types were used, shrinkage and non-shrinkage
for SPPC02 and SPPC03, respectively. SPPC02 and SPPC03 could reach the targeted
drift of 3.5% whereas SPPC01 was stopped at a drift of 2.75%. There was no
shear failure detected during the test. The connection behaved as a fixed
connection indicated by the fracture failure of the prestressed bars near the
connection region. Analysis of the test results focused on displacement
ductility. Two definitions of yield and ultimate displacement were employed to
seek the possible ductility values. It varied from 3.05 to 6.04 for SPPC01 and
from 3.01 to 4.95 for SPPC02 and SPPC03. The non-shrinkage concrete did not
affect the strength of the connection but slightly improved the post-peak
behavior. The ductility is 6–12% higher than spun piles with ordinary
concrete. According to the limited
ductility referring to ATC 96, JRA 2002, and AASHTO 2011, all specimens could
achieve target ductility 3. Hence, it can be concluded that the low confinement
spun pile connections performed well in displacement ductility.
Displacement ductility; Experimental study; Low-confinement; Spun pile
connection of pile to pile cap in the foundation plays an important role to
transfer the force from the upper to the bottom structure and vice versa. This part is critical since the change of
area, stress, and stiffness occurs suddenly
Several methods have been
proposed to estimate the displacement ductility of the pile. Curvature
ductility is one of the main factors affecting it. To be ductile, the pile section should meet
the required curvature ductility demand
The spun pile is a precast prestressed pile that is massively used in bridges and wharves. Experimental and numerical studies of this pile and its connection to the pile cap have been performed by many researchers. In China, the study was performed on different connection details
In Indonesia, the spun pile is produced with a limited amount of transverse reinforcement and below the minimum requirement in accordance with
Indonesia should move forward to PBD for the bottom structure since based on the recent seismic risk map, where the ground acceleration tends to increase
full-scale spun pile connections were tested until failure to evaluate their
seismic performance. To represent the real condition, the pile was picked from
the stocking yard. A length of 220mm was
cut from the middle part which has less confinement according to the research
objective. The spiral pitch is 120mm
where the volumetric ratio is 0,113%.
To clarify the quantity of transverse reinforcement, the amount is
compared to three equations and presented in Table 1. As can be seen, the
equations result in different required quantities. The revised equation
Table 1 The requirement of transverse reinforcement
2.1. The Specimens
Figure 1 shows the DED of the specimens. The 450mm in diameter spun pile was chosen with a wall thickness of 80mm. The spun pile was made of 57Mpa of concrete strength, reinforced by a email@example.com PC bar, and confined by a spiral of 4mm in diameter. The connection between the spun pile and the pile cap was designed based on the common practice in Indonesia. The spun pile was embedded in the pile cap at a depth of 100mm. The required embedment length of the rebar was 620mm. To reduce the depth of the pile cap, the length was 500mm straight and the 200mm was bent 30 degrees as shown in Figure 1. SPPC01 was an empty spun pile, whereas SPPC02 and SPPC03 were filled with concrete and reinforced by 6D19 as shown in Figure 2.
1 The connection details (a) SPPC01; (b) SPPC02/3
and (c) the test set-up
SPPC02 represents the typical connection where for ease in construction the concrete infill was cast together with the pile cap. Additional rebar of 6D19 was added and embedded into the pile cap to improve the connection strength. Shrinkage of the concrete infill was a concern and therefore in the preceding research, non-shrink concrete was used
2 The cross-section of
SPPC01 and SPPC02
The pile cap was cast by 30Mpa of concrete strength and the actual strength of 28 days age was 34MPa. Due to the pandemic situation, the experimental test was delayed and the concrete age of SPPC03 was based on a 56-day test which was 36.5 MPa. The strength of steel employed in the experiment is presented in Table 1.
2.2. The Test Set-Up
Figure 1 shows the test setup. The specimen was attached to a strong floor and tied with 10 anchoring bolts. It was loaded vertically as 500kN which was equal to 0.1fc’Ag. A reverse cyclic lateral load was applied after the vertical force was fully applied. The horizontal loading protocol followed the ACI 437-07, where the test was conducted until a targeted drift of 3.5% was achieved or until the strength of the specimen was dropped by more than 25%. Seven and two transducers were employed to measure horizontal and vertical displacement, respectively. The concrete strain gauge was put on the spun pile and pile cap which was located 100mm from the connection. The strain of the reinforcement bar was measured through 6 strain gauges which were placed next to the connection in the loading plane. Meanwhile, four strain gauges were attached to the prestressed wire at a similar location.
3.1. The Hysteretic Curves
SPPC02 and SPPC03 were tested until they reached a drift of 3.5% whereas SPPC01 was stopped at a drift of 2.75% since its strength drop more than 50%. Figure 3 shows the hysteretic curve and the envelope of all specimens. As can be seen, the presence of the reinforced concrete infill in SPPC02 and SPPC03 changes the performance of the spun pile connection significantly. It improves strength and energy absorption. The envelope of SPPC02 and SPPC03 are very closed which indicates that different concrete type does not affect the strength of the connection.
3.2. The Crack Pattern
The crack pattern on the spun pile is shown in Figure 4. There was a slight shear-flexural crack was detected at several places. The crack initiated from the tensile face and propagated to the center of the spun pile. The majority of the crack was a result of flexural failure. The crack propagated until 650mm from the connection region of SPPC02 and almost 800mm of SPPC03. Meanwhile, the last crack of SPPC01 was detected at depth of 400mm above the connection.
Light damage was found on the pile cap of SPPC01. Concrete crushing of the pile at the connection region was observed when drift reach 2%. A similar failure mode occurred on SPPC02 and SPPC03. The first crack of the spun pile was at a drift of 0.35% and 0.5%. The pile cap suffered moderate damage where a crack was detected on its surface with a depth of less than 100mm. It started from the connection region and then it propagated to a radius of 150 to 180mm from the pile face.