Failure Mode and Prediction of the Strength of Branch Attachments

Abstract

Predicting the strength of branch attachments is important for arborists and urban foresters because branch failure can cause damage and injuries. Previous studies have shown that the ratio of branch to trunk diameter is a better predictor of strength than the angle of attachment. Aside from these two factors, however, few other morphological measures of the attachment have been investigated with respect to predicting the strength of attachments. Many branch attachments from three species were broken on a testing machine and breaking stress was calculated. Prior to breaking, various morphological measures and ratios describing the attachment were made. Breaking stress varied by form of the attachment (u-shaped or v-shaped), failure mode, and the presence of included bark. The best predictor of breaking stress was the ratio of branch to trunk diameters. Results are discussed in the context of previous studies and with respect to tree risk assessment.

The Impact of Visual Defects and Neighboring Trees on Wind-Related Tree Failures

“…As might be expected given their location in the tree, weak branch attachments were associated with a smaller proportion of whole tree failures (Figure 3). Although many studies have quantified the reduced load-bearing capacity of weak branch attachments [48][49][50][51], they did not fail in 78% of trees in which they were the defect of primary concern. The comparatively low failure rate of weak branch attachment aligned with previous studies of tree failures following a hurricane [19] and a snowstorm [47], suggest that it may not be as serious a defect as considered.…”

Can Mechanical Strain and Aspect Ratio Be Used to Determine Codominant Unions in Red Maple without Included Bark

“…An inverse relationship between attachment stability and aspect ratio has been reported in red maple (Acer rubrum L.) [3,12]. Aspect ratio, the ratio of branch diameter divided by stem diameter (measured above the union), is considered an effective predictor of failure stress in static loading trials [3,[19][20][21]. While investigating branch unions from a hydraulic segmentation perspective, Eisner et al [22] suggested that aspect ratios of 0.75 or above indicate codominance.…”

“…While investigating branch unions from a hydraulic segmentation perspective, Eisner et al [22] suggested that aspect ratios of 0.75 or above indicate codominance. Kane et al [21] concluded that unions with aspect ratios greater than 0.70 are codominant, yet these trials include unions with and without included bark. They also found that the failure mode was ball and socket when aspect ratios were less than 0.70, and flat surface or imbedded branch failure when aspect ratio was greater than 0.70 [21].…”

“…Kane et al [21] concluded that unions with aspect ratios greater than 0.70 are codominant, yet these trials include unions with and without included bark. They also found that the failure mode was ball and socket when aspect ratios were less than 0.70, and flat surface or imbedded branch failure when aspect ratio was greater than 0.70 [21]. Yet it remains unclear from a mechanical perspective if the 0.7 threshold for codominant holds for branch unions without included bark.…”

“…Strain is a direct result of loading [24][25][26] and is increasingly being used in arboricultural studies [26][27][28][29][30][31][32][33]. While many practitioners suggest that branch attachment angle is a predictor of union stability, the literature has shown that attachment angle is not correlated with strength [10,11,13,21,34,35]. Kane et al [21] demonstrated that aspect ratio was a better predictor of attachment stability.…”