Cracking behavior of reinforced-concrete elements with multiple-layer reinforced cross sections when using large bar diameters

The formation of cracks is an inherent feature of reinforced-concrete construction. The width of any cracks occurring needs to be limited to a non-detrimental extent, however, in order to permanently ensure structural integrity, serviceability and an unimpaired exterior look. The relevant verification concepts are included in Eurocode 2.

The question arises, however, if cracks can be safely limited based on EC2 and EC2/NA in slab-type structural elements with multiple-layer, crosswise reinforcement used, for example, in highly stressed base slabs (also using large bar diameters). The doubts expressed above are essentially based on the fact that the design formulas underlying the verifications were primarily derived from and verified on (simple) concentrically reinforced test cross sections with “small” bar diameters (usually Ø 6 mm to Ø 14 mm). In order to clarify this question, numerous experimental and numerical tests were performed to determine the cracking behavior of structural elements with multiple-layer reinforcements of Ø 20 mm, 28 mm and 40 mm, thoroughly examining the factors influencing crack formation (bar diameter, transverse reinforcement, surface reinforcement). Based on these examinations, the experimental
values were compared with the results of a cross check performed
according to EC2 und EC2/NA, and the accuracy of the numerical prediction
was reviewed.
For the design concept according to EC2 and EC2/NA, one finding was that modifications of the design equations are recommended for cross-sectional approaches with multiple-layer, crosswise reinforcement to achieve a reliable numerical prediction of the crack widths to be expected. In addition, it is known that the crack width on the surface of a structural element is usually larger (possibly promoted by large concrete covers) than predicted
numerically. This controversy is also taken into account in the design proposal presented.

Related articles:

Issue 2019-02 Special aspects of crack width calculation

Recommendations for the building practice

Crack widths have a significant influence on the durability of reinforced concrete members. Therefore, the limitation of crack widths is an indispensable aspect of the design work, and is often...

Issue 2017-02 Innovative roof sandwich elements

Load-bearing behavior of sandwich elements with thin concrete shells and bar-shaped connectors

The presentation deals with an engineering model on the basis of tests regarding the load-bearing behavior of roof sandwich elements comprising 70 mm thin reinforced concrete shells each and a...

Issue 2020-02 Non-reinforced ultra-high performance concrete (UHPC)

A cover for sandwich wall panels

Multi-layer reinforced-concrete wall panels comprise a supporting and facing shell made of reinforced concrete as well as an interior insulating layer. The facing shell, which forms the façade, has a...

Issue 2021-11 Monday, 15th November ? Innovation workshop (5)

MasterFiber: The sustainable and efficient reinforcement for precast concrete

MasterFiber structural polymeric fibers have been established for a long time ago in flooring and pavement applications replacing steel mesh or steel fibers. In recent years they have been used as...

Issue 2014-02 On early and late restraint stresses

Designing cracks properly

Structural engineers are often uncertain about how to deal with the concept of restraint stress. Relevant codes and standards are of no help either. For relevant information, they have to refer to...