Comparative Studies of Restraint Forces in Jointless Building Structures

The development of a seamless construction in reinforced concrete buildings leads to the increased occurrence of restrained stresses and thus to the formation of cracks when exceeding the tensile strength in the concrete. Eurocode 2‑1‑1 provides a general approach for determining a minimum reinforcement to limit the crack widths. After years of use, however, it has been shown due to unscheduled crack formation that more and more uncertainties occur when estimating the time of crack formation or the effective concrete tensile strength to be applied. The use of modern FEA software provides an alternative approach by a nonlinear calculation of reinforced concrete structures, taking into account the occurring restraint stresses.

Author	Marleen Eysel
University	Dresden University of Technology, Germany Institute for Concrete Structures

For this, it was first necessary to examine possible influencing parameters of the crack width limitation when using the nonlinear calculation methods, taking into account the concrete shrinkage on simple structural models. This allowed for proving that the realistic stiffness mapping of the structures is a decisive prerequisite for a reliable crack width estimation. Especially the crack width reducing effect due to the loss of stiffness with increasing building height is to be mentioned here. First of all, this leads to small crack widths on upper floors as a result of a late restraint, so the reinforcement quantities can be reduced at these locations. Furthermore, the findings of the parameter study were used to check the feasibility of such an approach at the planned construction project of the Dresden-Klotzsche High School. In a final comparison with the blanket approach of the standard, it was shown that it is possible to save concrete in this way when selecting the minimum reinforcement quantities.

Downloads

Complete Thesis (PDF - 16.5 MB)

16.52 MB

;