ratio (ρ ) percentages where the x increased system load capacity resulted in connection zone cracking in the bottom h position, such that the e connection zone starts to influence the response (see the deviation in dashed and dotted lines of Figure 4b). • The a/d ratio, which represents how thick a concrete pile cap or footing is, affects the system capacity significantly, with lower ratios (i.e., thicker members) providing exponentially higher system capacities (see bi-linear nature of lines in Figures 4a to 4c). • The double plate bracket has only one h position, which exhibits a good e performance since the connection zone does not influence the system capacity (see Figure 4c). • The tensile capacity of all bracket types increased significantly with higher ρ , x except for the bottom h , where the e connection zone failure prevents any significant capacity increase with higher ρ . x • The compression load results are presented in Figures 4d to 4f, where the overlapping, colored lines demonstrate that the compressive load resistance is independent of h changes for all bracket types examined. e Crack Patterns and Failure Modes The simulated deflected shapes, crack patterns and failure modes are presented in Figure 5 for the selected, representative specimens. Major connection zone cracking and failures are predicted for some of the specimens subjected to tensile loads. The bottom he of the single plate bracket exhibited the least favorable performance by sustaining connection zone failures, as shown in Figure 5a. While performing better, the bottom he of the studded bracket exhibi ted major connection zone cracking (see Figure 5b), which reduced, but did not govern, the system capacity. This type of cracking may be detrimental to the long-term durability of helical pile foundations. The double plate bracket (Figure 5c), the middle of he the single plate bracket (Figure 5d) and the middle he of the studded bracket (Figure 5e) performed satisfactorily with no major connection zone cracking. The double plate bracket may provide additional advantages, such as resilience to other types of loads and long-term durability, due to the top and bottom plates confining the entire depth of the pile cap. Subjected to pure compression loads, all specimens with all bracket types exhibited global failure modes of either flexure or shear, without exhibiting any major connection zone cracking, as shown in Figure 5f. Comparison with Sectional Analysis Methods Both the numerical simulations and the experimental tests include the influence and failure modes of connection zones. The traditional sectional analysis methods, on the other hand, consider the concrete foundation globally while neglecting the local influences such as how the load is introduced or how the supports and connection zones are detailed. To assess the significance of considering or neglecting the connection zone behavior, the experi- mental specimens were also analyzed with the sectional methods contained in the ACI 318-19 standard. It is clear from Figure 6 that the experimental capacities are much smaller than those predicted by the sectional analysis method. This result confirms that the connection capacity may govern the entire system response and that the use of the sectional analysis may overestimate the system capacity (by a factor of 2.2 on average in this study). Conclusions and Recommendations • The results demonstrate that helical pile-to-foundation connections may govern the entire system capacity for the load conditions incorporating net tension components. The traditional global analysis methods, which are not intended for the connection zones, may significantly overestimate the capacity of the helical pile systems, especially for the design configurations involving single plate terminations at the bottom embedment (h ) position. e • The tension load capacities of the concrete pile caps (all of which are doubly and symmetrically reinforced) are found to be 54% of their compres- sion load capacities. If analyzed with the traditional sectional analysis methods, which neglect the influence of the connection zones, their load capacities in tension and compression would be incorrectly calculated as equal. Figure 5. Representative failure modes and crack patterns 106 • DEEP FOUNDATIONS • MAR/APR 2020
