# Ultra-High-Performance Concrete (UHPC) Piles and Splicing Options
## 3 U HPC Piles
### Previous Research on UHPC Piles  
UHPC pile research to date has mostly aimed at developing UHPC pile details to replace steel H-piles. A summary of the UHPC pile cross-sections that have been or are currently being investigated is shown in Figure 2[13; 43] and Figure 3. There is ongoing research by the Alabama Department of Transportation (ALDOT) and the Prestressed/Precast Concrete Institute (PCI) investigating prestressed UHPC H-piles; these works are investigating 12-inch (305 mm), 14-inch (355.6 mm), and 16-inch (406 mm) UHPC H-piles with high precompression. Figure 2b [43] shows the details of two of the UHPC H-pile sections. Figure 2a [13] shows a section of a completed research work conducted at Iowa State University.  
The Florida Department of Transportation (FDOT) is currently investigating several UHPC piles with different shapes. The configuration and shape of some of the UHPC pile sections are shown in Figure 3.  
[PERSON] et al. [13] developed a tapered H-shaped UHPC pile section aimed at replacing an HP 10 \(\times\) 57-inch (254 \(\times\) 1448 mm) steel pile, as shown in Figure 4[13]. The outside dimensions of the piles are almost identical, which allowed them to be driven using similar equipment.  
Figure 2: Summary of UHPC pile cross-sections investigated to date from (**a**) Iowa State University [13; 41; 44] and (**b**) the University of Alabama (unpublished work) [43].  
The section properties of the UHPC and steel H-piles used in their study are shown in Table 2. The UHPC piles had a much larger cross-sectional area and slightly heavier weight compared to steel H-pile.  
The moment-axial load interaction diagrams for these UHPC H-piles and HP 10 \(\times\) 57-inch (254 \(\times\) 1448 mm) steel piles are shown in Figure 5[13]. The axial load applied to generate 6 ksi (41 MPa) compressive stress in the piles is highlighted, as this was the axial stress limit used in the design in Iowa where the research was conducted. [PERSON] et al. [13] highlighted that although the moment capacity of the UHPC pile was less, the axial load at 6 ksi (41 MPa) axial stress is over three times greater for the UHPC pile compared to steel H-pile. They mentioned that the axial capacity is more significant since it typically controls the design.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **HP 10 \(\times\) 57 Steel Pile** & **UHPC Pile** \\ \hline Total Area (in\({}^{2}\)) & 16.8 & 56.8 \\ Weight (lb/ft) & 57.2 & 61.1 \\ Moment of Inertia (in\({}^{4}\)) & 294 & 795 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Properties of steel and UHPC pile section [13] (1 in = 25.4 mm, 1 lb = 4.45 N, 1 ft = 305 mm).  
Figure 4: Dimensions of (**a**) HP 10 \(\times\) 57 steel pile and (**b**) UHPC tapered H-shaped pile [13].  
Figure 3: Details of UHPC piles by FDOT: (**a**) 30-inch (762 mm) H-pile; (**b**) 24-inch (610 mm) octagonal pile; and (**c**) 18-inch (457.2 mm) square pile (unpublished work).  
[PERSON] et al. [41] also investigated the cracking performance of UHPC piles, as the piles would lose their long-term durability performance if cracking was to occur. They assumed a strain versus crack width relationship, as shown in Figure 6[13, 41]. Based on the results from [PERSON] et al. [13] for the strains when micro-cracking started, cracking started when cracks exceeded 0.012 in. (0.305 mm).  
They also compared the moment curvature analysis results for both UHPC and HP 10 \(\times\) 57-inch (254 \(\times\) 1448 mm) piles at strong and weak axis bending for four different axial load cases. They suggested that the service moment should be considered for UHPC pile design to ensure that cracking does not occur in UHPC piles in service [41].