Y-type perfobond rib shear connectors subjected to fatigue loading on highway bridges

Significance Statement

In order to realize the advantages of steel-concrete composite structures for construction of infrastructure and buildings, shear connector are installed to transfer the shear force between steel and concrete. The perfobond rib shear connector was developed to mitigate the fatigue problems the most common utilized type, stud shear connector offers.

Professor Sang-Hyo Kim and colleagues from Yonsei University in Republic of Korea studied the structural performance of Y-type perfobond rib shear connectors under cycling loading evaluated in terms of residual strength, stiffness and permanent plastic slip. The study published in Journal of Constructional Steel Research.

The Y-type perfobond rib shear connector proposed by Kim et al. (Journal of Constructional Steel Research, 2013) was modified to improve various aspects of performance such as shear resistance, vertical resistance, ductility and workability for transverse rebar placement.

Shear connectors of steel-concrete composite girder in bridges are subjected to high cycle fatigue loading under heavy traffic. Hence, many researchers have conducted cyclic push-out test to determine the fatigue strength of various types of shear connectors and it’s been found that that cyclic loading reduces shear strength, stiffness and plastic slip which has negative impact on fatigue performance.

The shear resistance under static loading due to local yielding and stress concentration in steel has been proven by several experiment and analysis. However, effect of cyclic loading on structural performance of shear connector composites has not been evaluated yet.

In order to determine load range of cyclic loadings, calculations were based on the shear force due to dead loads and live loads on highway bridges. With dimensions of bridges samples taken from guidelines in the Korean Highway Bridge Manual, design load was determined in accordance with the Korean Highway Bridge Specifications KHBS and the dead load and standard truck load (DB-24) recommended in KHBS was used. Minimum shear force of 20KN/m was generated by the secondary dead load while maximum shear force of 200KN/m was generated by summation of the live load and dead load. Ultimate conditions of minimum and maximum conditions were set to be 1.5 times the minimum and maximum shear forces respectively.

Cyclic loading test was conducted on three specimens (R1 to R3) for 650,000 cycles with constant load range of 30 to 300KN and the specimen with maximum plastic slip (R3) was subjected to 1,300,000 cycles to investigate the long-term behavior.

Results shown when evaluating plastic slip of the specimens revealed that plastic slip of specimen R1 increased for 70,000 cycles and then increased slowly to 500,000th. Plastic slip of specimen R2 increased for 100,000 cycles and remained unchanged thereafter. That of specimen R3 increased sharply after 70,000 cycles and then remained relatively constant up to 1,300,000 cycles. The stiffness ratio of three specimens (R1-R3) remained relatively unchanged over all cycles.

As push-out test was conducted on reference specimen (S1) that did not undergo cyclic loading, variations in residual strength of specimens R1, R2 and R3 that underwent cyclic loading were 0.43%, 0.79% and 1.40% respectively. Specimen R3 showed no changes in its residual strength which means that residual strength of the Y-type perfobond rib shear connector was found to be unaffected by number if repeated loadings.

When compared with stud shear connectors, specimens R1 and R2 experienced slight large plastic slip in early stage and permanent plastic slips were always less. For specimen R3, early-stage slip was greater than stud shear connectors and remained almost unchanged for 1,300,000 cycles but plastic slip stud shear connectors became longer than that of specimen R3 after 500,000 cycles. The residual strength of stud shear connector gradually decreased but that of R1 to R3 Y-type perfobond rib shear connectors did not. The results indicate that the Y-type perfobond rib shear connectors provide a suitable performance for steel-concrete composite structures.

Kim et al. (2016) experimental and numerical results show that the bridge examples with Y-type perfobond rib shear connector guaranteed sufficient shear connection to meet the criteria for the ultimate and serviceability limit states.