FRILO at the Eurocode workshop in Brussels 2011 1

FRILO at the Eurocode workshop Brussels 2011

Preface The Friedrich + Lochner GmbH has been developing computer software for structural analysis and design for more than 30 years. With more than 80 applications we meet a wide range of demands in practice. GEO-Building is the central application for the geometrical input of a building. With its close to practice concept it offers a simple and comprehensible approach. Not the building model with all its details is in the focus of the approach but the simple and quick load determination and the preliminary design. The final design is performed in the individual Frilo design applications.

Fig 1: Overview on the application GEO-Building

As a subsidiary of the internationally active Nemetschek AG our mission is becoming increasingly the implementation of international design standards. In this context, we have already been concerned with the Eurocodes for several years now, beginning in the nineties. Nemetschek Frilo is a member of the relevant standard committees for concrete design, that were responsible for the development and testing the German national annex for EN 1992-1-1 (/2/). In addition to the original Eurocode and the German national annex also the national annexes of Austria , the Czech Republic, Belgium, the Netherlands, UK and Italy were implemented in our programs for reinforced concrete design as PLT for plates, DLT for continuous beams, B5 for columns, FD for isolated bucket foundation and B2 for cross-section analyses.

Fig 2: FEM Design for RC plates with application PLT

Fig 3: Application DLT for continuous beams with design for concrete, steel or timber

FRILO at the Eurocode workshop in Brussels 2011 2

Appropriate the FRILO program philosophy, to have a minimum of input effort but a maximum of output result, all necessary parameters of a national annex are set with one click when choosing the standard. Another advantage is the automatic load combination and the automatic determination of the relevant combination for each design check. The central GEO application mentioned above allows the customer to determine wind- and earthquake loads for different national annexes automatically and forwarding them to the design applications. The FRILO roof applications allow the same feature for wind- and snow loads. Eurocode Design modules are also available for steel-, masonry-, timber and composite structures. With the further development and marketing of our programs, we work closely together with Nemetschek SCIA. Through our participation in international activities such as workshops in Brussels 2008, in Prague in 2010 and this year in Brussels we try to ensure, that our programs always correspond to the latest state of knowledge.

Fig 4: Application B5 for RC Column Design

Fig 5: Design for isolated foundation with application FD

Fig 6: Design charts created with the B2 application

FRILO at the Eurocode workshop in Brussels 2011 3

EN 1992-1-1, a comparison of design results with different National Annexes The Worked Examples for concrete design were published in the year 2008 at the web-site of the European Concrete Platform (/7/). This is a very important precondition for testing our Eurocode software. In a special project we used these examples for a comparison of the design results between the national annexes, which we have implemented. We have analyzed the differences and find out that they are caused by the different defined national parameters and not by errors in the implementation (/4/).

Fig 7: Textbook of the ECP

Bending capacity The comparison of the curves for the absorbable internal forces of a symmetrically reinforced cross-section (Frilo application B2) clearly illustrates the effect on bending strength of the differences in the stress-strain curves resulting from the National Annexes. The differing national specifications of the long-term strength factor αcc result in deviations in the crest value fcd of the concrete stress-strain curve if αcc= 0.85, i.e. a 15% deviation from the original Eurocode that specifies αcc = 1. For precast components, this deviation increases to a maximum of 21% because of the varying acceptance of reduced partial safety factors in the NA documents.

Fig 8: Different bending capacity using the design parameters with αcc= 0.85 and αcc= 1.00

FRILO at the Eurocode workshop in Brussels 2011 4

Shear capacity When examining the change in the required stirrup reinforcement depending on the increase in the shear force, three segments can be clearly distinguished. Provided VEd <= VRd,s(ρmin, Θmin), a constant level results for the minimum reinforcement, followed by a linear increase in the reinforcement ratio. If VEd > VRd,max (Θmin), the upward slope of the curve is disproportionate due to the increase in the strut angle Θ until the strength Maximum is reached at Θ = 45 degrees. A comparison of the curves determined for a C25/30 concrete using various National Annexes reveals the following: due to the differing national specifications of parameters (limits of cot Θ, strut strength ν1*fcd), and because of a deviating method adopted in Germany for determining the smallest possible strut angle, significantly different curves are obtained for the individual National Annexes, showing strong deviations both for the required shear force and the maximum shear strength.

Comparison of shear capacity for different national annexes

0

0,2

0,4

0,6

0,8

1

1,2

1,4

0 1 2 3 4 5 6

vED (N/mm2)R

ho,w

(%)

EN2-0EN2-A-aEN2-UK / CZ / NL / A-bEN2-GEREN2-ITEN2-B

Fig 9

Limitation of crack with The magnitude of the crack width depends on the mean strain difference Δε and the crack spacing sr,max . Whereas differences between the national annexes are minor when determining Δε, significant deviations occur for sr,max, which are due to the nationally determined parameters k1, k2, k3 and k4. The crack formula is modified for determining the limit diameter

FRILO at the Eurocode workshop in Brussels 2011 5

s = (wk/Δε -sr1)/sr2, where sr,max is divided into the two components sr1 = k3*c and sr2 = k1*k2*k4/ρ.eff. The nationally determined parameters k1 and k2 have almost no influence on the calculated limit diameter, because their effects largely neutralize each other. Two different approaches to k3 and k4 are observed. Whereas, in the NAs for Austria and Germany, the term sr1 is zero because of k3 = 0, which has a favourable effect on s, the other NAs use k3 = 3.4, which results for sr1 in a minimum value of 85 mm, depending on the concrete cover. On the other hand, sr2 is more unfavourable due to k4 = 0.694 (other NAs: k4 = 0.5). The example shown at the right side is used to demonstrate the effect of this approach on the limit diameter as moments increase: For smaller loads, the NAs result in larger limit diameters if sr1 > 0. For greater loads, sr1 = 0 results in larger limit diameters. The influence of sr1 increases with Δε whereas the effect of sr2 decreases. (a cross-section of 20 cm * 100 cm is chosen, using a C25/30 concrete and wmax = 0.3 mm.)

Maximum bar diameter while increasing moment for As= 7,5 cm2

0

10

20

30

40

50

60

0 10 20 30 40 50 60

My in kNm

Ds

in m

m

NA_A

NA_GER

NA_UK=NL=B=CZ

NA_0

Fig 10: the effect of different use of sr1 on the limit diameter

FRILO at the Eurocode workshop in Brussels 2011 6

Load combination In another project (/6/) we analysed the influence of different parameters for load combination.

C25/30 b/h=30/80

10.00 4.0024 9.76 24 3.88

14.12

15.020.0

40.0

Fig 11: simple example for RC Beam

For the bending moment of a single-span beam with cantilever, shown at the right side, we obtained for the moment at the right support differences form +5 % (NA-D) until -12 % (NA-NL) relative to original Eurocode.

-800

-600

-400

-200

0

200

400

600

800

0 5 10 15

[m]

[kN

m]

NA-0 - Mf NA-0 Ms NA-NL Mf

NA-NL Ms NA_D Mf NA_D Ms

Fig 12: Different internal forces caused by different national

parameters for load combination

Overlaid with the differences in cross section design described above, the maximum of the differences for the required reinforcement increased from +8 % (NA-D) until –14 % (NA-NL) at this section. This is only partly offset by higher amounts of reinforcement to comply with the evidence of serviceability

Fig 13: Comparison pf bending design results

FRILO at the Eurocode workshop in Brussels 2011 7

EN 1992-1-2 fire design with Frilo-software Fire safety analyses in accordance with EN 1992-1-2 cannot be based only on the temperature profiles of Annex A any longer because of the different defined parameter in the national annexes.

The new FRILO TA (thermal analysis) application is used for the FEM based calculation of temperature fields in rectangular and circular concrete cross sections under fire exposure with the standard temperature-time curve as per EN 1991-1-2.

Temperature analysis TA is available as optional add-on feature and currently implemented with the following applications: Applikation B5 The preconditions for the use of the tabulated data in EN 1992-1-2 are not given for unbraced columns. Therefore this application provides a fire safety analysis with the general calculation method in EN 1992-1-2 with material properties depending on the different temperatures in each point.

The exact position of the reinforcement is of crucial importance for this method and a specially developed dialogue allows a convenient input. Applikation B2 This application allows inter alia a fire design for bending possibly with a longitudinal force. The determination off the stiffness in the accidental design situation of fire is interesting for the understanding of the complex results of a column analysis.

Fig 14: Screenshot of the TA application

Fig 15: dialogue for the input of the reinforcement

Fig 16: Graphic of the B2 application showing the

participation different sectors of the cross section

FRILO at the Eurocode workshop in Brussels 2011 8

Comparison of temperature profiles with the border conditions of various National Annexes (/5/) For a simple cantilever column, the effects of an 90 minute fire load (R90) on the temperatures in the bars and the required reinforcement are demonstrated.

C 30/37 BSt 500 S(A)Phi = 2.46Bewehrung in den Ecken

y

z

30

30

3.0

3.0

3.00

G = 132 kN

Ric_y Fig 17: simple example for RC Column

Compo-nent

moisture [%]

Density

[kg/m3]

Conductivity as per NA

Default in TA

application

Temper-ature [0C]

Req. As

[cm2]

Austria 1.5 2300 Standard l High strength u

l u

741 760

22.7 25.8

UK 1.5 2300 Standard l High strength u

l u

741 760

22.7 25.8

Netherlands 1.5

2300 Lime aggregate l Gravel aggregate u

l u

741 760

22.7 25.8

Belgium 1.5 2300 Lime aggr. l Gravel .aggr. m Lightweight u

l

u u

741 760 741

22.7 25.8 22.7

*1 *2

Czech Republic

1.5 2300 l … u l 741 *3

Germany 3 2400 u u 746 *1 According to the Belgian NA, a conductivity value m between the upper and the lower limit applies

with gravel aggregate. Currently, a thermal conductivity beyond the limits l and u cannot be taken into account. When using the upper limit, the results are on the safe side.

*2 According to the Belgian NA, a conductivity value u applies with lightweight aggregate.

*3 According to the Czech NA, the conductivity value is freely selectable within the limits of l and u. The default value is l in accordance with the assumptions of Annex A

Since specifications concerning the component moisture and the bulk density are not given in the code, the assumptions forming the basis of the temperature profiles of Annex A are used there with the exception of Germany. There the assumption of 3% component moisture and 2400 kg/m3 bulk density for the assessment of the design diagrams with the simplified method as per DIN EN 1992-1-2/NA Annex AA can be interpreted as a kind of recommendation for a practice-oriented approach. The obtained differences between the temperatures amount to 5 %, for the required reinforcement the obtained differences amount to 12 %.

FRILO at the Eurocode workshop in Brussels 2011 9

Preview According the Guidance Paper L, adopted by the European Commission 2003, all the Eurocode contradictory national standards should be withdrawn until March 2010. A study of Nemetschek SCIA /1/ shows, that more than 15 European countries have taken this step until the end of 2010/early 2011, including Austria, Great Britain, Germany, France, the Netherlands, Belgium, Czech Republic, Slovakia, Finland, Denmark, Sweden, Poland, Norway, Ireland and Iceland. In Austria, Great Britain, Italy, the Netherlands, Slovakia, Norway, Germany and Denmark the Eurocode can already be applied, at least in part. In some countries, the sole application of the Eurocodes is required (Austria, France, Czech Republic), in others the old national standard parallel is still valid and only its mandatory use in bidding and the requirements of the clients according to appropriate the state of the art planned buildings will lead to an increasing use of Eurocodes (UK, Netherlands, Germany).

Despite a design code that will be uniformly applied across Europe, the design results may vary significantly from country to country. Not all of these variances may be justified by diverging safety requirements. We believe that it is important to reduce these differences in order to create wide acceptance of the new code in the long term.

For our customers it is important to know, that the software development for the Eurocodes is of a great importance for our company. They get the new ability of the applications for Eurocode design (national annex of their home country and original Eurocode) as part of a software update. Other annexes can be purchased additional.

The development of the Eurocodes is therefore not complete. In the strategy of CEN TC250 to develop the code (->/3/) the priorities are called for further development: Further harmonization by the analysis so far about 1500 NDP and prepare proposals

for their reduction Development of the Eurocodes for fire safety Development of the Eurocodes for durability and sustainability of building Development of new codes for glass design and for strengthening of structural

components with fiber reinforced plastics (FRP) Pursue this process by developing appropriate software but also active participation in standardization work, is a challenge and an obligation for our company.

Literature / 1 / Scia's Eurocodes Explanatory Note http://www.scia-online.com/ / 2 / Abschlussbericht des DIBt-Forschungsvorhabens ZP 52-5-7.278.2-1317/09: „Eurocode 2 Hochbau – Pilotprojekte” / 3 / Jean-Armand Calgaro , “The strategy of CEN/TC250 for the future of the Eurocodes” http://eurocodes.jrc.ec.europa.eu/showpage.php?id=05 / 4 / Bert Ziems, Nemetschek Frilo; „Experiences with the implementation of

EUROCODE 2”, International Workshop at CTU Prague 2010 / 5 / FRILO-Aktuell Ausgabe 2/2011, Heißbemessung nach DIN EN 1992-1-2 / NA http://www.frilo.eu/de/service/publikationen/eurocode.html / 6 / Ziems, Seidel, Brendel; „Vergleich Stahlbetonträger nach Eurocode“; / 7 / Worked Examples for Eurocode 2 http://www.europeanconcrete.eu/publications/eurocodes