Helical Pile-to-Pile Cap Connections Subjected to Uplift Forces: Improving Future Practice-Paper

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The study examines how helical pile-to-pile-cap connection details affect the strength and failure behavior of concrete pile caps, particularly under uplift loads. Because connection failures have contributed to foundation problems and design guidance is limited, the authors aim to inform safer, more efficient design.<br /><br />The researchers conducted 108 nonlinear finite element simulations of pile caps supported by two piles. They compared single, double, and studded brackets while varying embedment depth, longitudinal reinforcement, shear span-to-depth ratio, and loading direction (uplift or compression).<br /><br />Under uplift, connection anchorage failure occurred in the shallow-embedment single-bracket configuration. This produced concentrated cracking near the connection and reduced load capacity by about 25% compared with more effective configurations. Increasing the single bracket’s embedment from shallow to intermediate raised capacity by an average of 29%; increasing it further to the deepest position provided little additional benefit. Double and studded brackets had uplift capacities comparable to single brackets with intermediate or deep embedment. Studded brackets performed better than single brackets when shallow embedment was required. Across bracket types, higher reinforcement and lower shear span-to-depth ratios generally increased capacity.<br /><br />Under compression, no anchorage failures were predicted, and embedment depth had little effect. Higher reinforcement and lower shear span-to-depth ratios improved capacity in all bracket types.<br /><br />The authors recommend explicitly checking connection capacity in addition to pile and pile-cap capacities. For uplift design, avoid shallow-embedment single brackets; use intermediate or deep embedment, or choose a double or studded bracket where appropriate. Higher reinforcement and lower shear span-to-depth ratios can improve resistance. The findings may also apply to micropile connections with similar details.

Keywords

helical pile

pile-cap connection

concrete pile cap

uplift load

anchorage failure

finite element simulation

embedment depth

reinforcement

double bracket

studded bracket