Part 2: Design and construction

The new DAfStb Guideline on UHPC

The design and construction part of the DAfStb Guideline on UHPC replicates the structure of EN 1992-1-1. The verification methods are based on the design principles for reinforced and prestressed concrete and, where necessary, account for the special structural behavior and high durability of UHPC. Modifications and amendments were required concerning, for instance, the stress-strain relationship, creep and shrinkage, required concrete cover, and maximum crack width. Extensions were also made to consider the contribution of the fibers in the design equations. The efficiency of the fiber reinforcement is expressed by the post-cracking tensile strength, which is defined as the nominal axial concrete tensile strength in the cracked state. This parameter is derived from the results of 3-point bending tests on notched beams.

In order to obtain sufficient robustness, a minimum value of post-cracking tensile strength, which depends on concrete compressive strength, is mandatory for structural components made from UHPC. The scope of the guideline thus includes structures exclusively reinforced with steel fibers as well as prestressed and conventionally reinforced structures both in combination with steel fibers.

The design value of the post-cracking tensile strength fcftd is directly used in the various verifications in the ultimate limit states. The figure exemplifies the aforementioned principle for the design for bending. The contribution of the fibers is considered by a stress block in the tensile zone. The stress-strain relationship in compression is assumed to be approximately linear-elastic, which results in a linear stress distribution in the compression zone, as shown in the figure. To account for the interaction between reinforcing bars and fibers, the tensile force of the reinforcing bars Fsd is determined using a modified stress-strain curve of the reinforcing steel (not depicted in the figure).

x

Related articles:

Issue 06/2022

New edition of the DAfStb guideline on steel fiber reinforced concrete – Latest regulations and developments

Steel fiber reinforced concretes have an enormous potential due to the elimination of labor-intensive and time-consuming reinforcement works. In addition to this, steel fiber reinforced concretes...

more
Issue 05/2024

Shear design of ultra-high-performance fiber-reinforced concrete girders

In [1], an approach for verifying the shear resistance of ultra-high-performance concrete (UHPC) girders is presented. This approach follows Eurocode 2 and the German DAfStb Guideline on „Steel Fiber...

more
Issue 02/2021

Punching shear behavior of steel fiber reinforced flat slabs in combination with punching shear reinforcement

The guideline “Steel Fibre Reinforced Concrete” published by the German Committee for Reinforced Concrete (DAfStb) in 2012 regulates the punching shear design of steel fiber reinforced flat slabs...

more
Issue 05/2024

Flexural design of ultra-high-performance fiber-reinforced concrete girders

In [1], an approach for determining the moment resistance of ultra-high-performance concrete (UHPC) girders with mixed reinforcement is presented. This approach considers the contribution of the steel...

more
Issue 10/2020

Compressive strength classes and performance classes of ultra-high-performance concrete (2)

3 Classification of UHPFRC in tension 3.1 Parameters and test method The axial post-cracking tensile strength (notation: fcft) is the most important material parameter of ultra-high-performance...

more