Moment-less arches of constant axial stress: Implications for design

Abstract

The work discusses key features and advantages of optimal 2-pin arches shaped by statistically prevalent (permanent) load and a constant value of axial stress ensuring a moment-free action. A non-conventional design approach, known as analytical form-finding, is used to shape the arches, with guidance given for both symmetric and asymmetric forms. Previously discovered Design Space/existence of symmetric arches of constant axial stress is extended here to cover asymmetric forms. Minimum values of constant stress to be used in form-finding of constant stress arches made of various materials are given. Ultimate load analysis, using permanent and variable patch loads, show advantages of these structures over other arch forms. The work challenges structural optimisation approaches that assume arches of least weight to be optimal, while, in fact, they offer limited design options and are just a special case of constant stress arches. Conventional design approaches that minimise the weight of a structure, but within an imposed geometric configuration, produce non-optimal structures. By exhibiting a minimal stress response to loading, constant stress arches are analogous to highly optimised objects found in nature; this feature gives them the potential to address sustainability and durability issues facing our future infrastructure.