Design and Experimental Investigation of the Joints of Inclined Struts for the Widening of Bridge Deck Slabs

The widening of existing bridge deck slabs using inclined struts has been found to be an economical and aesthetically pleasing solution. The design of the joints linking the strut respectively to the deck slab and the web of the box with limited penetration or perforation of the existing structure is of particular interest. Five different original strut joint details were developed and experimentally investigated for three different strut inclinations. These joints were fabricated using fiber-reinforced mortar as well as steel plates and cylindrical studs and blades penetrating into the cover concrete. The test results showed that strut joint details with some penetration into the cover concrete provide significant strength and deformational behavior, and show much better structural performance than strut joint details relying only on friction at the interface surface. Also, the ultimate resistance decreases with the increasing joint inclination. Finally, it is shown that existing design criteria match the results obtained with the strut joint details relying on surface friction. However, as soon as the strut joint details penetrate into the cover concrete, the design criteria underestimate the strength and an improved design criterion is proposed.