Steering of continuity stresses in beam structures by temperature induction

Abstract

Many statically indeterminate structures like multi-span bridges or girders are subjected to temperature variations that induce constraints. Associated sectional forces are usually unfavourable and might even accelerate the evolution of damage. However, active induction of further constraints through linear vertical temperature gradients provides the opportunity to counteract adverse loads and constraints.The paper recaps and extends the theoretical background of stresses due to temperature and provides a design chart to predict bending moments regarding position and length of induction. Due to the longitudinal thermal flow, the temperature affected length on-site turns out always longer than the theoretical length of induction which is resolved by a newly introduced effective length that works with constant temperature gradients. Required gradients are technically realised by insulated water tanks mounted on beam surfaces and water as a medium for heating and cooling. Measuring and comparison to target values in a closed-loop control system enables to control the temperature gradient in real time.The method is exemplified and experimentally verified joining two cantilevers to a continuous member while being pre-curved through a temperature gradient. Through coupling, continuity stresses are permanently inscribed. This procedure imitates the well-established construction method of cantilever bridges and significantly reduces the bending moments at the supports which usually remain from construction.