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2017-10-03

Displaying Curtailment of Longitudinal Reinforcement and Reinforcement Covering Line

In the case of a large amount of reinforcement, it might be useful to grade the longitudinal reinforcement of a beam, which means: curtailment. The grading corresponds to the tensile force distribution. Using RF-CONCRETE Members and CONCRETE, you can specify the curtailment of the reinforcement, which is considered in the automatically proposed reinforcement for the longitudinal reinforcement. When determining this reinforcement proposal, it is necessary to ensure that the envelope of the acting tensile force can be absorbed.

Curtailment of Longitudinal Tension Reinforcement

The design of the curtailment of the longitudinal tension reinforcement ensures that the envelope of the acting tensile force F_Sd can be absorbed by the provided reinforcement. 9.2.1.3(2) of EN 1992‑1‑1 [1] also requires considering the additional tensile force ΔF_td due to the shear force. For structural components with shear reinforcement, this additional tensile force ΔF_td can be calculated according to 6.2.3 (7) of EN 1992‑1‑1 [1]. The tensile force F_Sd is calculated from the following equation:

\begin{array}{l} F_{sd} = (\frac{M_{Eds}}{z} N_{Ed}) {ΔF}_{td} \\ where \\ {ΔF}_{td} = 0.5 \cdot V_{Ed} \cdot (\cot θ - \cot α) \end{array}

Formula 1

For structural components without shear reinforcement, the tensile force ΔF_td may be taken into account by shifting the tensile force curve from

(\frac{M_{Eds}}{z} N_{Ed})

Formula 2

about a distance of a_l = d in the unfavorable direction. This approach may also be used as an alternative to the approach for structural components with shear reinforcement mentioned above. In this case, this "shift rule" is determined according to the following formula:

a_{l} = 0.5 \cdot z \cdot (\cot Φ - \cot α)

Formula 3

Tension Cover Line from [1]

The resistant tensile force F_Rs of the provided reinforcement is determined within the anchorage lengths l_bd.

Graphical Display of Reinforcement Covering Line / Curtailment of Longitudinal Reinforcement

When the tensile force of the curtailment of longitudinal reinforcement is divided by the design stiffness f_yd of the reinforcing steel, a reinforcement covering line is obtained. In RF-CONCRETE Members and CONCRETE, the distribution of the required tension reinforcement A_s (first result diagram in Image 02) is shifted by the shift rule a_l in order to obtain the envelope of the required reinforcement (second result diagram in Image 02). You can display these shifted required reinforcement envelopes graphically by selecting "Detailed results" under "Provided Reinforcement" in the Results Navigator (see Image 02).

If the envelope of the required reinforcement (red), the shifted envelope of the required reinforcement (green), and the provided reinforcement (blue) are shown together graphically, a reinforcement covering line is obtained (third result diagram in Image 02) that corresponds to the curtailment of longitudinal reinforcement in Fig. 9.2 of EN 1992‑1‑1.

Reinforcement Cover Line/Tension Force Cover Line

Author

Mr. Meierhofer is the development leader of programs for concrete structures and is available for the customer support team in case of questions related to reinforced and prestressed concrete design.

Links

Structural Analysis & Design Software for Concrete Structures

References

Eurocode 2: Bemessung und Konstruktion von Stahlbeton- und Spannbetontragwerken – Teil 1-1: Allgemeine Bemessungsregeln und Regeln für den Hochbau; EN 1992‑1‑1:2011‑01

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Knowledge Base Articles

Fire Resistance Design with CONCRETE and RF-CONCRETE Members

The reinforced concrete design for fire situations is carried out according to the simplified method based on EN 1992-1-2, Clause 4.2. The "zone method" described in Annex B.2 is used: The cross-section is subdivided into a number of parallel zones of equal thickness, and their temperature-dependent compressive strength is determined. The reduced load-bearing capacity in the event of fire exposure is thus represented by a reduced structural component's cross-section with reduced strengths.

Minimum Reinforcement Reduction of Slow-Curing Concrete

In the case of using slow‑curing concrete (usually for thick components), you can reduce the calculated minimum reinforcement by a factor of 0.85 to apply the load due to restraint, according to EN 1992‑1‑1, Section 7.3.2. However, a precondition for reduction is that the characteristic value of the strength development r = f_cm2 / f_cm28 does not exceed 0.3. Other key requirements for the application of this reinforcement reduction are specified explicitly in the final planning documents.

Graphical Display of Full / Reduced Shear Force and Required Shear Reinforcement

For uniformly distributed loading according to EN 1992‑1‑1 (Eurocode 2), the design section for the shear reinforcement can be placed at the distance d from the front edge of the support. Thus for the shear reinforcement, the applied shear force is reduced to V_Ed,red. To analyze the maximum design shear resistance V_Rd,max, however, the total shear force is applied.

Subsequent Editing of Reinforcement Proposal

RF-CONCRETE Members for RFEM or CONCRETE for RSTAB propose an automatically created reinforcement to the user if the "Design the provided reinforcement" option is selected in Window 1.6 "Reinforcement".

Product Features

Transfer of Reinforcement from RFEM/RSTAB (Top) to Revit (Bottom)

The reinforcement proposal from RF-/CONCRETE Members can be exported to Revit. The rectangular and circular cross-sections are currently supported.

The reinforcement bars can be modified retroactively in Revit.

Feature 002801 | Punching Shear Design for All Section Shapes

Do you have individual column sections and angled wall geometries, and need punching shear design for them?

No problem. In RFEM 6, you can perform punching shear design not only for rectangular and circular sections, but for any cross-section shape.

Feature 002691 | Simplified Fire Resistance Design for Columns and Beams According to EN 1992-1-2, Sections 5.3.2 and 5.6

The Concrete Design add-on provides you with the option to perform the simplified fire resistance design according to EN 1992‑1‑2 for columns (Section 5.3.2) and beams (Section 5.6).

The following design checks are available for the simplified fire resistance design:

Columns: Minimum cross-sectional dimensions for rectangular and circular sections according to Table 5.2a as well as Equation 5.7 for calculating time of fire exposure
Beams: Minimum dimensions and center distances according to Table 5.5 and Table 5.6

You can determine the internal forces for the fire resistance design according to two methods.

1 Here, the internal forces of the accidental design situation are included directly into the design.
2 The internal forces of the design at normal temperature are reduced by the factor Eta,fi (ηfi), then used in the fire resistance design.

Furthermore, it is possible to modify the axis distance according to Eq. 5.5.

Feature 002670 | Fatigue Design According to EN 1992-1-1, Chapter 6.8

With the Concrete Design add-on, you can perform the fatigue design of members and surfaces according to EN 1992‑1‑1, Chapter 6.8.

For the fatigue design, you can optionally select two methods or design levels in the design configurations:

Design Level 1: Simplified design according to 6.8.6 and 6.8.7(2): The simplified design is performed for frequent action combinations according to EN 1992‑1‑1, Chapter 6.8.6 (2), and EN 1990, Eq. (6.15b) with the traffic loads relevant in the serviceability state. A maximum stress range according to 6.8.6 is designed for the reinforcing steel. The concrete compressive stress is determined by means of the upper and lower allowable stress according to 6.8.7(2).
Design Level 2: Design of damage equivalent stress acc. to 6.8.5 and 6.8.7(1) (simplified fatigue design): The design using damage equivalent stress ranges is performed for the fatigue combination according to EN 1992‑1‑1, Chapter 6.8.3, Eq. (6.69) with the specifically defined cyclic action Q_fat.

Frequently Asked Questions (FAQ)

I obtain different results when comparing the deformation analysis in the RF‑CONCRETE add-on modules and another calculation program. What could be the reason for this?

For the design, I can only select the surrounding reinforcement for a rectangular cross-section. Why?

I recently purchased RSTAB with the CONCRETE add-on module. Can I use it to perform the stability analysis of reinforced concrete columns?

Why do RF‑CONCRETE Members and CONCRETE determine a significantly higher provided reinforcement than the required reinforcement?

When calculating deformations in RF‑CONCRETE Members, I see inconsistencies in the deflection diagram. Why?

Why can I no longer display the intermediate results in RF‑CONCRETE Members?

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