Once again DTSB has conducted a destructive shear test on a full scale DURA beam (i.e. TBG1325). The tested beam was 14.75 m in total length, and has a full depth of 1325mm. The web has a thickness of 100 mm and it does not have any conventional steel reinforcement or stirrup in the section. The beam was tested in three point load configuration and the shear span to effective-depth ratio of 2 is used in the shear test. The specimen was place in the 5000kN capacity stiff testing frame and the applied point load was placed at the centre of the beam. One end of the specimen was a pinned supported and the other end had a pin and roller support. The pins and rollers were greased to minimize friction and to give free rotation and horizontal translation, as required.
The experimental results shows the DURA TBG1325 beam has an experimental first shear cracking load of Vcr = 1125 kN (i.e. average shear stress of 8.5MPa) and an experimental ultimate shear capacity of Vu = 2186 kN (i.e. average shear stress of 16.5 MPa). The ultimate to first cracking shear capacity ratio is 1.9 which indicate after first shear cracking, the beam is able to resist extra 90% of loading before failure. This also further indicates the DURA material has superior shear capacity and ductility.
Tracing of the crack patterns of the tested beam shows diagonal shear cracking initiated in the web regions of each of the shear spans. The diagonal cracks then multiplied and propagated toward the top flange and smeared across the spans with increasing load. Finally, failure resulted from tensile fracture across a single, dominant crack or from a coalescence of cracks leading to the formation of a dominant crack. Numerous number of diagonal shear cracks was marked and it show the shear beam has superior ductility even with the absence of steel stirrups.
In a normal 30m span highway bridges where frequent traffic loading is considered, the worse scenario of the applied shear force that may subjected to these single bridge beam is approximately 440 kN at SLS loading and 60o kN at ULS loading. Once again it prove that the DURA beam has plenty of shear capacity over the required design forces of the bridge beam.