A CRITIC OF THE STATIC INTEGRATED ANALYSIS (SIA) METHOD

Abstract

Summary This report details a critical assessment of the Static Integrated Analysis SIA-method by the authors based on literature. The SIA-method (Wessolly and Erb, 1998) considers only four different shapes for the tree crown, which do not exist in cities showing such a low branch attachment. According to SIA, all trees in cities have the same wind load that is calculated based on a “proposal” for the drag coefficient. Required stem diameters and minimum wall thickness in hollow trees are derived from height measurements using bending theory. The effect of longitudinal shear cracks and cracks related to water hose kinking appear to be neglected in the SIA-method. For this reason, trees assessed by the SIA-method are theoretically allowed to be much more hollow than trees assessed by Visual Tree Assessment VTA-method, substantiated on extensive field studies performed for the VTA-failure criterion. The SIA-method is described by WESSOLLY and ERB (1998). It is surprising that SIA is actually the end of a tree assessment, i.e. the evaluation of the risk by failure criteria. The method does not include a catalogue of defect symptoms (warning signals in the body language of trees) as it is offered in VTA (MATTHECK and BRELOER, 1994). SIA tries to calculate maximum possible H/D-ratios and minimum wall thickness (hollow trees). This paper describes the process of the SIA-method based on our current knowledge and understanding. In WESSOLLY and ERB (1998) only the formal procedure is given. The reader is guided from diagram to diagram without pointing out the background of the theory.