| Summary: | The design of reinforced concrete must concern with the development length of the
steel reinforcement. The development length is a function of the yield stress of steel, diameter of
the reinforcing bar and the bond strength. This study aimed to determine the effect of length and
shape of reinforcing bar, embedded in several concrete qualities on pull out strength.
This study used 12 specimens in the form of concrete cubes with dimensions of 150
mm x 150 mm x 150 mm and the threaded steel bars of 10 mm diameter embedded with a length
of 100 mm and 150 mm. The number of test specimens was two for each concrete compressive
strength fc' of 15 MPa , 20 MPa , 25 MPa and 30 MPa . Pull out test was done by placing the
concrete cubes on the floor surface and let a hydraulic jack, with a hole at its longitudinal axis,
and a donut-type load cell be inserted over the embedded reinforcing bar. An LVDT was also
mounted to measure the displacement of the reinforcing bar.
Average yield strength of the reinforcing bar was 504.22 MPa . The average bond
strengths of concrete with compressive strength of 15 MPa, 20 MPa, 25 MPa and 30 MPa were
respectively of 5.90 MPa, 5.35 MPa, 5.34 MPa and 5.35 MPa with maximum strength of 8.51
MPa, 7.66 MPa, 6.95 MPa and 9.01 MPa respectively. The bond stresses are not closely
proportional to the compressive strengths of concrete . The pull out strengths obtained from this
study were smaller than that the pull out strength determined from the ACI 318 M - 1992 ,
SKSNI T - 15-1991-03 , and SNI - 03-2847-2002 , but more in line with Indonesian Concrete
Standard (PBI - 1971). Types of failure of the pull out test varied from specimen to specimen
(slippage of the reinforcing bar, broken of concrete and failure of reinforcing bar).
Keywords : development length, bond strength
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