2. Experimental Method 2.1. Experimental Beam Design To elucidate the internal force transmission mechanism and shear characteristics of narrow-width steel box-UHPC composite beams with partial filling under negative bending moments, a set of six composite beams was designed and constructed as simply supported structures, maintaining a shear span-to-depth ratio of 2.13. These beams were identified as SUCB-1 to SUCB-6. Figure 1 illustrates the test beams’ geometric layout.
