Research On The Short Rebar Shear Connectors Of Welded Structure Of The Light Composite Deck System Composed Of Orthotropic Deck And Ultra-thin UHPC Layer

In response to the problems such as easily damaged pavement layer and easy fatigue cracking of steel decks in the orthotropic steel deck,the author’s research team pioneered the use of steel-UHPC light composite bridge deck which successfully solved problems.In this structure,the short studs of 13×35mm(diameter×height)are used as shear connectors,and the UHPC layer of 45-60 mm thickness has been successfully used in dozens of Bridges.In consideration of the economy and the structural weight,the thickness of the UHPC layer needs to be further reduced(such as reducing the height to 35mm).At this circumstances,short studs is no longer suitable.Therefore,the research team proposed a new type of shear connectors-short rebar connectors.This paper conducted a preliminary study of the static and fatigue performances of short rebar connectors in steel-UHPC composite structure.The fllowing works have been done:(1)To study the static drawing performance of short rebar connections,fourteen static pull-out tests with different weld lengths(15,20,30mm),different interface,and different inclinations were performed.load-separation curves,failure modes and ultimate drawing bearing capacities were obtained.The test results indicate :there is only one failure mode-the connectors pulled out-in the short rebar pull-out specimens;inclinations can improve drawing capacity;both the weld length and the interface have no obvious influence on the drawing bearing capacity,but the interface oil can reduce short steel drawing stiffness of the specimens.(2)To study the static shear performance of short rebar connections,nine static push-out tests with different weld lengths(15,20,30mm)as well as different inclinations were performed.load-slip curves 、 failure modes and ultimate shear bearing capacities were obtained.The experimental results indicate: there are two failure mode-the connectors pulled out and the weld damaged-in the short rebar push-out specimens;the weld length can improve drawing capacity;the shear strength of the short steel reinforcement is higher than that of the stud connection and slightly lower than that of the reinforcement mesh.In the analysis of the push-out tests,the test results agree well with the calculated results which are simulated by using ABAQUS finite element software.(3)Fatigue tests were carried out on the pull-out specimens which connected byshort rebar connectors with weld length of 15 mm and a corner cut angle of 22.6°.The results indicate that under the 80 MPa shear stress amplitude,the three specimens were subjected to fatigue of 194.2,271.0 and 195.8 million times respectively.After removing the maximum value,the average fatigue life of the remaining two was 1.95 million times,which was slightly lower than the corresponding 2 million times of the specification.The Miner-Palmgren linear cumulative damage theory was used to transform the stress amplitude corresponding to different fatigue times.Considering the fatigue resistance partial coefficient of 1.15,the design shear stress amplitude of 2million fatigue was 69.2 MPa.Based on the nominal stress method,the fatigue assessment of short rebar connectors and the steel deck near the welding toe were carried out.The finite element model of the segment was built using ANSYS software based on the Runyang Yangtze River Bridge as the engineering background.The calculation results indicate that when the spacing between the longitudinal and transverse on bridges of the short rebar connectors is 200mm×200mm,both types of fatigue details meet the fatigue design requirements.