Differential axial shortening of concrete structures

Abstract

Non linear deformation of concrete has an adverse impact on high-rise buildings with complex
geometries due to differential axial shortening. These adverse effects are caused by time dependent
behaviour resulting in volume change known as “shrinkage”, “creep” and “elastic” deformation. These
three phenomena govern the behaviour and performance of all concrete elements during and after
construction. Reinforcement content, variable concrete modulus, volume to surface area ratio of
elements, environmental conditions and construction quality influence the performance of concrete
elements and differential axial shortening will occur in all structural systems. Their detrimental effects
escalate with increasing height and non vertical load paths resulting from geometric complexity. The
magnitude of these effects have a significant impact on building envelopes, building services,
secondary systems and the life time serviceability and performance
Analytical and test procedures available to quantify the magnitude of these effects are limited to a
very few parameters and are not adequately rigorous to capture the complexity of true time
dependent material response.
With these in mind, a research project has been undertaken to develop an accurate numerical
procedure to quantify the differential axial shortening of structural elements. The procedure has been
successfully applied to quantify the differential axial shortening of a high rise building and the
important capabilities available in the procedure have been discussed. Additionally, a new practical
concept based on the variation of vibration characteristic of structure during and after the construction
will be developed and used to quantify the axial shortening and to assess its performance.
Keywords: Axial shortening, Concrete buildings, Creep, Shrinkage, Elastic deformation, Vibration
characteristic of structure