# Predicting Tensile Strength for Prestressed Reinforced Concrete-Driven Piles
###### Abstract  
Reinforced concrete piles installed by impact hammers have been used as a common solution for deep foundations because they are cost effective and require less time for construction. Driven piles are often used in large volumes for infrastructure and industrial projects in rural areas. Unlike other installation methods, installing piles using impact hammers can generate tensile stress during construction, which can result in pile failures. Induced tensile stress occurs when piles are being driven through a hard soil layer to a softer soil layer, and transverse cracks happen when induced tensile stress exceeds the pile tensile strength. This issue is not explicitly stated in most standards; the rare code that mentions this issue is a AASHTO 2014. AASHTO 2014 uses correlations between the concrete tensile and compressive strengths to obtain the pile tensile strength. However, data collected from more than 1300 tests on the correlations between the concrete tensile and compressive strengths show that the concrete pile tensile strengths obtained using AASHTO 2014 are significantly conservative. This paper provides an adjustment in the correlation for the tensile strength based on previous data, and it proposes an approach to estimate the tensile strength for concrete-driven piles. A case study of the effects of pile failures on the tensile strength is also presented to verify the approach. The obtained tensile strength from the proposed approach agrees well with the measured field data. For the case study, the pile tensile strength obtained using the proposed approach is 38% and 59% higher than the tensile strength obtained using AASHTO 2014. These quantities are significant but may vary, depending on the compression strength of the concrete used and the pile configurations. The proposed approach better predicts the tensile strength of concrete piles and can lead to cost savings. p 2022  
mobilizes tensile strength from both of its material components: steel reinforcement (with or without prestressing) and concrete. When determining the tensile strength of prestressed concrete piles, some standards and guidelines take into account the tensile strength of the concrete component, such as AASHTO [5] and FHWA [6]. However, other standards do not [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]; in most cases, in practice, the concrete tensile strength is not taken into account. Neglecting concrete's tensile strength when determining the pile's tensile strength is safer, but not economical. [PERSON] and [PERSON] [1] suggest that it is necessary to include at least part of the concrete tensile strength in the calculation of the tensile strength of the pile. Different standards have different approaches for determining the concrete tensile strength, based on different testing methods, including direct tension, modulus of rupture, and split cylinder testing [6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Of these three standardized testing methods, modulus of rupture and split cylinder are more common, whereas the direct tensile test is only used in a few standards. ACI 543R-12 [21] states that the less commonly used direct tensile test is due to the difficulty of pure tensile loading on a plain concrete specimen. In practice, tensile-strength tests are not carried out as often as compressive-strength tests. Standards often allow for the conversion of the compressive strength to the tensile strength. The correlations between the modulus of rupture and the compressive strength of pile concrete in the standards are summarized in Table 1, where \(f_{t}f_{r}f_{c}\) and \(f_{c}{}^{\prime}\) are the tensile strength, flexural tensile strength, cube compressive strength, and cylinder compressive strength, respectively, of concrete at 28 days. As in Table 1, significant variation exists in the estimation of the tensile strength through the correlations, which not only affects the prediction of the tensile strength for prestressed driven piles, but also the overall cost of the piling work.