## 2 Concept Development
### Design of the \"Looney Bin\"
The clevises were designed to be attached to a 13 mm ball joint using a steel shank, and the ball joint would attach to the threaded rod. The ball joint size was chosen for its availability and had a tensile strength of 44 kN, which exceeds the anticipated peak load. ASTM A193 [25], Grade B7 threaded rods with a diameter of 13 mm were chosen to simplify the connection to the ball joint. The plinth height was set to 38 mm to allow for the bolts to thread 25 mm into the plinth, and two offset bolts were used to reduce the risk of rotating the plinths when tightening the connection bolts. A total of nine plinths and nine clevises were constructed to allow for the gluing and testing of three cubes during a single session. The American Institute of Steel Construction (AISC) Steel Construction Manual [26] was used to determine the capacities of the steel fixtures, and the yield stress was used to determine the axial capacity of the aluminum plinths to ensure they were adequately sized for the design force. The capacities are shown in Table 1.  
With the plinth sizes chosen, the specimen would have to be attached to a corner of the cube test setup, which provided the benefit of increasing the stiffness of the overall test since the load would be applied close to support (plate wall). The test apparatus was designed to have two plates that are inset on all four sides (labeled left and right plates), two plates that are inset on the top and bottom and directly supported by the left and right plates on the other two edges (labeled side plates), and the top and bottom plates would be directly supported on all four edges by the other four plates. The plates were attached together with three bolts on each edge to provide stability and stiffness. All edges that were inset had 25-mm-deep threaded holes that were centered in the plate thickness. All edges that were supported by a plate edge had 7 mm holes for the 6 mm-diameter bolts. With the plinth and clevis sizes determined, the interior dimensions required for the specimen and test fixtures could be determined. The length of each piece of the test setup in one direction was as follows: 38 mm plinth, 50 mm specimen, 54 mm clevis, and 38 mm shank thread length for the ball joint. The combined length (excluding epoxy thickness) was 180 mm, which would set the minimum interior dimension of the test setup to 205 mm to provide additional space for a load measuring device. However, fibers with up to 30 mm lengths have been tested in UHPC [18]. This fiber size would set the minimum cubic specimen dimension at 90 mm. Accounting for this new size, the fixture length would increase to 220 mm, with a minimum interior dimension of 245 mm. Aluminum plate stock \begin{table}
\begin{tabular}{c c c c} \hline
**Fixture** & **Material** & **Controlling Case** & **Capacity [kN]** \\ \hline Clevis Plate & ASTM A36 & Bolt Bearing (Equ. J3.6b [26]) & 73 \\ \hline Clevis Plate Weld & ASTM A36 & Base Metal (Equ. J2-2 [26]) & 145 \\ \hline Clevis Pin & ASTM A36 & Shear (J3-1 [26]) & 57 \\ \hline Plinth & Aluminum, Grade 6061 & Axial Tension & 547 \\ \hline Threaded Rod & ASTM A193, B7 & Bolt Tension (J3-1 [26]) & 56 \\ \hline \end{tabular}
\end{table} 
Table 1: Capacities of load application fixtures. with a 305 mm width was readily available at the time of fabrication and, using a 13 mm thickness would allow for an interior dimension of 280 mm with inset plate construction. Therefore, the interior dimension was set to 280 mm with an outside dimension of 305 mm. This width would provide a large enough interior section to house cubes with dimensions up to 100 mm without being overly bulky. A plate thickness was determined assuming the plate was simply supported on two edges, the 22 kN design force was applied directly in the center of the plate, and the material was only stressed to its yield stress, which were conservative assumptions. With these assumptions, a minimum plate thickness of 11 mm was determined, which is smaller than the 13 mm thickness assumed when determining the interior clearances.