rcs validation examples part 1 - idea-rs.nl · 2018-03-09 · validation examples reinforced...
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IDEA RS s.r.o. South Moravian Innovation Centre, U Vodarny 2a, 616 00 BRNO tel.: +420 - 511 205 263, fax: +420 - 541 143 011, www.idea-rs.cz, www.idea-rs.com
Design of reinforced concrete sections
according to EN 1992-1-1 and EN 1992-2
Validation Examples
Brno, 21.10.2010
IDEA RS s.r.o. South Moravian Innovation Centre, U Vodarny 2a, 616 00 BRNO tel.: +420 - 511 205 263, fax: +420 - 541 143 011, www.idea-rs.cz, www.idea-rs.com
Foreword The introduction of European standards is a significant event as, for the first time, all design and construction codes within the EU will be harmonized. These Eurocodes will affect all design and construction activities. The aim of this publication, Design of reinforced concrete sections according to EN 1992-1-1 and EN 1992-2, is to illustrate how the Code is treated on practical examples. In order to explain the use of all relevant clauses of Eurocode 2, an example of a simply supported one-way rib-shaped slab and an example of column with high axial load and bi-axial bending is introduced.
Design of reinforced concrete sections according to EN 1992-1-1 and EN 1992-2 October 2010
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Contents
1. Rib T1 ................................................................................................................................. 4
1.1. Project details .............................................................................................................. 4
Actions and analysis of Rib T1 .............................................................................................. 5
1.1.1. Section forces ....................................................................................................... 7
1.2. Cross section ................................................................................................................ 9
1.3. Ultimate section resistance ........................................................................................ 10
1.4. Shear check ................................................................................................................ 13
1.5. Torsional check .......................................................................................................... 16
1.6. Interaction .................................................................................................................. 17
1.7. Crack width calculation ............................................................................................. 19
1.7.1. Crack width according to EN 1992-1-1 ............................................................. 19
1.7.2. Example - Calculation of crack width according to EN 1992-1-1 .................... 20
1.8. Calculating stiffness .................................................................................................. 22
1.8.1. Example - calculating the stiffness of the T-section according to EN 1992-1-1 22
2. Column ............................................................................................................................. 26
2.1. Project details ............................................................................................................ 26
2.2. Second order effects .................................................................................................. 28
2.2.1. Simplified method based on nominal stiffness .................................................. 29
2.2.1. Simplified method based on nominal curvature ................................................. 29
2.2.2. Biaxial bending .................................................................................................. 30
Validation Examples Reinforced Concrete Section
1. Rib T1
1.1. Project details
Example is taken from:
Ing. Miloš Zich, Ph.D. and othersposouzení betonových prvků dle Eurokódůhttp://www.stavebniklub.cz/konstrukcni
First floor slab
Validation Examples Reinforced Concrete Section
Project details
others, online publication "Konstrukční Eurokódy ů dle Eurokódů", nakl. Verlag Dashöfer s. r. o., 2010,
http://www.stavebniklub.cz/konstrukcni-eurokody-onbecd/
Figure 1.1 - Schematic layout of structure
October 2010
Page 4
ční Eurokódy - Příklady o., 2010,
Validation Examples Reinforced Concrete Section October 2010
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Section A
Section B
Figure 1.2 – Sections
Actions and analysis of Rib T1
Figure 1.3 –Static schema of Rib T1
Validation Examples Reinforced Concrete Section October 2010
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Figure 1.4 - Floor composition for the calculation of loads
Figure 1.5 - Permanent load calculation
Variable load: qk = 10 kN/m2 * 2.0m = 20 kN/m
quasi-permanent value: ψ� ∗ �� = 0,6 ∗ 20 = 12 ��/��
Factors defining the representative values of variable actions, ψ0, ψ1, ψ2 are shown in table. A1.1 of EN1990 (also in attachment A4 in this document)
Validation Examples Reinforced Concrete Section October 2010
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Actions for Serviceability limit states (SLS)
Loads for serviceability limit state are determined acc. to EN 1990 clause 6.5.3. There are 3 SLS-combinations:
Characteristic combination of loads (Unacceptable cracking or deformation) ∑ ��,�"+"�" + "��,�" + "∑ ψ�,���,�������
�,ψ� = 9,87 + 0 + 20 + 0 = 29,87 �� �⁄
Frequent load combination
���,�"+"�" + "ψ�,���,�" + "�ψ�,���,�������
�,ψ� = 9,87 + 0 + 0,7⋅ 20 + 0 = 23,87 �� �⁄
Quasi-permanent load combination
���,�"+"γ�" + �ψ�,���,�������
�,ψ� = 9,87 + 0 + 0,6⋅ 20 = 21,87 �� �⁄
Actions for Ultimate limit states (ULS)
It is considered as a persistent design situation for ultimate limit state where partial factors are: γG= 1,35, γQ = 1,50.
To determine the design load in Article 6.4.3.2 EN 1990 is prescribed the following equation marked as the equation (6.10)∑ γ,���,�"+"γ�" + "γ�,���,�" + "∑ γ�,�ψ�,���,�������
Substituting, we get the value of design load
� = 1,35⋅9,87 + 0 + 1,5⋅ 20 + 0 = 43,32 �� �⁄
Alternatively, load can be further reduced according to equation (6.10) and (6.10b) and consider the less favorable value of both terms:
�∑ γ,���,�"+"γ�" + "γ�,�ψ�,�" + "∑ γ�,�ψ�,���,�������∑ ξ ,���,�"+"γ�" + "γ�,���,�" + "∑ γ�,�ψ�,���,������� ,
� = 1,35⋅9,87 + 0 + 1,5⋅ 0,7⋅ 20 + 0 = 34,32 �� �⁄
� = 1,35⋅ 0,85⋅9,87 + 0 + 1,5⋅ 20 + 0 = 41,33 �� �⁄
1.1.1. Section forces
� ��� =1
2� �
����� =1
8� ��
Validation Examples Reinforced Concrete Section October 2010
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Combination/Value Loads [kN/m] Vz(a) [kN] My (b) [kNm]
SLS characteristic 29.87 96.33 155.33
SLS frequent 23.87 76.98 124.13
SLS quasi-permanent 21.87 70.53 113.73
ULS 41.33 133.29 214.93
Table 1.1 - Internal forces for individual SLS and ULS load combinations
The shear force is calculated at distance d from the face of the support. Estimated value of d is based on the assumption that the moment near the support will be positive. Value d = 458 mm. Values: VEd1 and MEd1 are calculated at distance lx = 0.225 + 0.458 = 0.683 m from the theoretical support.VEd1= 105,05 kN, MEd1 = 84,29 kNm.
Validation Examples Reinforced Concrete Section October 2010
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1.2. Cross section
Figure 1.6 – Cross section
Materials
Concrete C25/30 fck = 25 MPa
fcd = fck / γc = 25 / 1,5 = 16,66 MPa
fctm = 2,6 MPa
fctd = 0,7 fctm / γc = 0,7 2,6 / 1,5 = 1,213 MPa
Steel B500B fyk = 500 MPa
fyd = fyk / γs = 500 / 1,15 = 434,78 MPa
Validation Examples Reinforced Concrete Section October 2010
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1.3. Ultimate section resistance
The cross section resistance (capacity) is the calculation of stress, strain and internal forces status on the calculated cross section for its limit state. For concrete the stress-strain relation is assumed to bi-linear. For reinforcing steel the stress-strain relation is assumed to be bi-linear without strain hardening.
Bending moment at middle section from basic combination of loads.
Figure 1.7 - Response - given by program IDEA RCS
Input data, Plane of strain:
εx = 0,0005876εy =0,0 εz= - 0,01034961
Figure 1.8 - Resulted plane of strain calculated by IDEA RCS
Strain calculation in end fibers:
ε� = ε� + ε��� + ε �� = 0,00058758 + 0 ∗ 0 − 0,01034961 ∗ 0.131 = − 0,00076304
Figure 1.9–Strain in ultimate compression fiber (picture from program IDEA RCS)
Modulus of elasticity is calculated from stress-strain diagram ���� = ��/ε�� = −16,7/−0,00175 = 9,52 ���
Validation Examples Reinforced Concrete Section October 2010
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σ� = ε��� = −0,00076304 9,52 10� = −7,27 ���
Defining the depth of compression zone (depth to neutral axis) in concrete, follow from:
� = ���� +ε�ε
= 0,1305 +0,00058758
−0,01034961= 0,0737268 �
Concrete force in compression (as, the strain in concrete is outside the plastic branch, the stress along the section is linear in concrete) �� = �� �� 2 = 0,0737268 ∗ 1,85 ∗ 16,7 2 = −495,83 ��⁄⁄
Concrete lever arm in the compression �� = ���� − � 3⁄ = 0,1305 − 0,0737268 3⁄ = 0,1059244 �
Concrete moment in compression �� = ���� = −495,83 ∗ 0,1059244 = −52,52 ���
Strain in reinforcing steel
ε� = ε� + ε��� + ε �� = 0,00058758 + 0 ∗ 0 − 0,01034961 ∗ −0.327 = 0,0039769
Figure 1.10–Stress in reinforcing steel ( Diagram is taken from program IDEA RCS)
Calculating of stress in reinforcing steel (whereas, the section is loaded in the plane of symmetry and reinforcement is not in one layer, these layers can be replaced by one layer with an area equal to the sum of all areas of reinforcement)
σ� = ε�⋅ �� = 0,0039769 ∗ 200 = 559,34 > 434,78 ⇒ 434,78 MPa
Tensile force in reinforcement
Validation Examples Reinforced Concrete Section October 2010
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�� = ��σ� = 0,0011404⋅434,783 = 495,83 KN
Moment in tensile reinforcement
M� = F�z� = 495,83⋅ − 0.327 = −162,134 kNm
Figure 1.11 – Comparing with results calculated by IDEA RCS program
Equilibrium of forces �� + �� = �� = 495,83 − 495,83 = 0
Equilibrium of moments �� + �� = �� = -162,134 -52,52 = -214,654
Note: Due to coordination system that is used inside the program, the design moment My has opposite sign.
Validation Examples Reinforced Concrete Section October 2010
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1.4. Shear check
Resistance without shear reinforcement in zones without cracks under bending loads
Calculated in center of gravity of concrete section I = 1/12*1,85*0,083+ 1,85*0,08*0,0912+1/12*0,2*0,423+ 0,2*0,42*0,1592=
7,8933e-5+0,001225588+0,0012348+0,002123604= 0,004684m4 S = 1,85 * 0,08 * 0,091 + 0,2 * 0,051 *0,051/2 = 0,01373 m3 bw= 0,2 m σcp= 0,0 MPa αl= 1
���,� = � ��� ���� + �� ����� =
0,004684⋅0,2
0,01373!�1,213⋅10��� + 0 = 82,76��
���,� = 82,76�� < ���,� = 105,05��
Deriving from the above text, the concrete part does not carry all the shear force, hence shear reinforcement will be required.
Figure 1.12 - Comparing with results calculated by RCS program
Resistance without shear reinforcement in zones with cracks under bending loads
CRd,c= 0,18 / γc = 0,18 / 1,5 = 0,12
� = 1 + "200# = 1 + "200
458= 1,661
$� =�����# =
760
200 458= 0,008297 ≤ 0,02
k1= 0,15 σcp= 0,0 MPa bw= 0,2 m d = 0,458 m νmin = 0.035 k3/2 fck1/2 = 0.035 1,6613/2 251/2 = 0,3745 MPa
Validation Examples Reinforced Concrete Section October 2010
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���,� = %&��.�� (100 $���)� � + �� ��' ��#
= %0,12 1,661 (100⋅ 0,008297⋅ 25(3)� � + 0' 0,2⋅ 0,458 = 50,15��
Minimally
���,� = )*��! + �� ��+��# = �0,3745(3 + 0� ∗ 0,2 ∗ 0,458 = 34,30��
���,� = 50,15�� < ���,� = 105,05��
Deriving from the above text, the concrete part does not carry all the shear force, hence shear reinforcement will be required. Resistance without shear reinforcement ��� = min (���,� ,���,���) Asw= 2 * 0.0062 * PI /4 = 5,655e-5 m2 s = 0.24m z = 0.9*0.458 = 0.412 m exact value is 0,437 m fywd = fyd = 434,7MPa θ = 21,8°
���,� = ���, � ��� cot- =
2⋅2,827e − 5
0,24∗ 0,412 ∗ 434,78⋅10� ∗ ./021,8
= 105,70�� > ���,� = 105,05�� → &ℎ(.� 1, 23 αcw = 1,0 bw= 0,2 m z = 0.9*0.458 = 0.412 m exact value is 0,437m For calculation of strength reduction factor for concrete cracked in shear ν1must be checked if the design stress of the shear reinforcement is over the 80% of the characteristic yield stress
fywk, �� ="��
����
�#�$=
��%,%�⋅�����,����
�,� �,&�� �#���,'
434,74 ��� > 0.8 ∗ ��� = 400���
4� = 0.6⋅ 51 −(���%�6 = 0.6⋅ 51 −
�%�%�6 = 0,54.
���,��� = ��� �� � 4� ���cot- + tan-� =
1,0⋅ 0,2⋅ 0,412 ⋅ 0,54⋅ 16,66⋅10�
�cot 21,8 + tan 21,8�
= 255,76�� > ���,��� = 133,27�� → &ℎ(.� 1, 23
Validation Examples Reinforced Concrete Section October 2010
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Figure 1.13 – Comparison of results calculated by RCS program
Validation Examples Reinforced Concrete Section October 2010
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1.5. Torsional check
Section characteristics for torsional check
u = 2 * (1.85 + 0.5) = 4.7 m A = 2 * (1.85 + 0.5) = 0.232 m2
tef = A / u = 0.232 / 4.7 = 0.049 m
� =−7 ± √7� − 16�
−4=
−4.7 ± √4.7� − 16 ∗ 0.232
−4=
−4.7 ± 4.287
−4= m�.���
�.�&)
ℎ =�7 − 2b�
2= m�.�&)
�.���
�� = �0.103 − 0.049��2.247 − 0.049� = 0.1187 m�
7� = 2)�0.103 − 0.049� + �2.247 − 0.049�+ = 4.504m
Torsional capacity without shear reinforcement
9��,� = 2��0*(��� = 2⋅0.1187⋅0.049⋅ 1.213 10� = 14.11���
Torsional capacity with shear reinforcement ν = 0.6 αcw = 1,0 9��,��� = 2 4 �������0*( �+,$ �-�$
= 2 ∗ 0.6 ∗ 1,0 ∗ 16,66⋅10� ∗ 0,1187
∗ 0.049 ∗ sin 21.8 ∗ cos 21.8 = 36,09���
9��,� = 2��"���, ���
���7� ��= 2⋅ 0,1187"2,827e − 5
0,24434,78⋅10� 7,603e − 4
4,507434,78⋅10� = 14,59���
Figure 1.14 - Comparison of results calculated by RCS program
Validation Examples Reinforced Concrete Section October 2010
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1.6. Interaction
Combined shear and torsion "��
"��,�+
.��.��,�
=��%,�%%�,�% +
��&.�� = 2,09 > 1,0 => �/0 23
Shear reinforcement is not allowed to design according to detailing rules
Compression strut check for combined shear and torsion ������,���+
9��9��,���=
105,05
255,76+
0
36,09= 0,41 < 1,0 => 23
Shear reinforcement check for combined shear and torsion
����,��� = Σ������ =2,827e − 5
0,24434,78⋅10� = 51,21��
���� = :���;� � +9��
2 ��< tan- = :105,05
2 0,412+
0
2⋅ 0,1187< tan 21,8 = 50,99��
��������,���=
50,99
51,21= 0,99 < 1,0 => �/0 23
Longitudinal reinforcement check for shear, torsion and bending
����,��� = Σ����� =7,603e − 4⋅(434,78 − 253,9)⋅10� = 137,52��
���� =���
tan - +9��7�
2 �� tan - =105,05
tan 21,8+
0⋅4.504
2⋅ 0,1187 tan 21,8= 262,64��
��������,���=
262,64
137,52= 1,91 > 1,0 => �/0 23
Validation Examples Reinforced Concrete Section October 2010
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Figure 1.15 - Comparing with results calculated by RCS program
Validation Examples Reinforced Concrete Section October 2010
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1.7. Crack width calculation
1.7.1. Crack width according to EN 1992-1-1
Check is introduced at midsection of beam
My= 113,73 kNm
Plane of strain calculated by program IDEA RCS:
εx = 0,0002092938
εy= 0,0
εz = -0,00282806
Defining the depth of compression zone (depth to neutral axis) in concrete, follow from:
� = ���� +ε�ε
= 0,1305 +0,000209293
−0,002828058= 0,0565 �
Figure 1.16 - Strain-stress diagram on fully cracked cross section
Strain calculation in end concrete fibres:
ε�� = ε� + ε��� + ε �� = 0,000209293 − 0,002828058⋅ 0,1305 = − 0,0001598
Stress calculation in end concrete fibres:
σ�� = ε��⋅�� = −0,0001598⋅ 31 = −4,954 ���
Concrete force in compression:
�� =��σ�
2=
��⋅��σ�2
=�0,0565⋅1,85�⋅ − 4,954
2 = −0,259 kN
Concrete moment in compression:
M� = F�z� = F�⋅�z/01 − x 3⁄ � = −258937 − �0,1305 − 0,0565 3⁄ � = −28,92 kNm
Strain in reinforcing steel:
ε�� = ε� + ε��� + ε �� = 0,000209293 − 0,002828058⋅ − 0,32748 = 0,001135425
Validation Examples Reinforced Concrete Section October 2010
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Calculating of stress in reinforcing steel (whereas, the section is loaded in the plane of symmetry and reinforcement is in one layer, this layer can be replaced by one bar with an area equal to the sum of all areas of reinforcement)
σ� = ε�⋅�� = 0,001135425⋅ 200⋅10� = 227,1 ���
Tensile force in the bar: �� = ��σ� = 0,0011404⋅227085000 = 258,97 kN
Moment in tensile reinforcement:
M� = F�z� = 258,97 ⋅ − 0.32745 = −84,81 kNm
Equilibrium of forces: �� + �� = �� = 258,97– 258,97 = 0
Equilibrium of moments: �� + �� = �� = −84,81 − 28,92 = −113,725 kNm
1.7.2. Example - Calculation of crack width according to EN 1992-1-1
Effective ratio of reinforcement:
ρ�,*(( =����,*((
=11,40⋅102&
0,021= 0,05429
Maximal spacing of the cracks:
,3,��� = ��. + ������φ/ρ�,*((
,3,��� = 3,4⋅0,031 + 0,8⋅0,5⋅0,425⋅0,022/0,05649 = 0,1743 �
Factors:
k1= 0,8 in example is considered steel B500B
k2= 0,5 Cross section loaded by bending moment, pure bending
k3= 3,4
k4= 0,5
Effective height 7.3.2 (3) hc,ef:
ℎ�,*( = �1; =2,5�ℎ − #�;ℎ − �
3;ℎ
2> =
�1; =2,5�0,5 − 0,458�;0,5 − 0,05649
3;
0,5
2> =
�1;?0,105; 0,1478; 0,25@ = 0,105 �
Validation Examples Reinforced Concrete Section October 2010
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Effective area:
��,*(( = ℎ�,*(�� = 0,105 ∗ 0,2 = 0,021��
Mean strain in the reinforcement ε�� − ε�� =σ�2��
���,���
ρ�,���4�5α�ρ�,���6
��≥ 0,6
σ�
��
ε�� − ε�� =227,17 − 0,4
�,7�,�%&�� �1 + 6,45⋅0,05429�
200≥ 0,6
227,17
200
ε�� − ε�� = 0,0010065 > 0,0006815 →
ε�� − ε�� = 0,0010065
Mean value of the tensile strength of the concrete effective at the time
when the cracks may first be expected to occur:
��,*(( = ��� = 2,6 ���
factor: �� = 0,4, long term action
Crack width according to (EN 1992-1-1, clause 7.3.4) is :
A� = ,3,����ε�� − ε��� = 174,3 0,0010065 = 0,175 ��
Figure 1.17 - Comparison of values with IDEA RCS results
Validation Examples Reinforced Concrete Section October 2010
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1.8. Calculating stiffness
1.8.1. Example - calculating the stiffness of the T-section according to EN 1992-1-1
Considering the strain, stress and internal forces in the previous examples are already calculated, the plane of strain is computed for a cracked section loaded by internal forces at the time when the cracks may first be expected to occur from the quasi-permanent combination. To calculate, for short-term stiffness, the difference in the calculation of short-and long-term stiffness is only taking into account the effective modulus of elasticity:
��,*(( =���
�5ϕ89,��:
where: ϕ(∞,t0) is the final value of creep coefficient
Calculation will be carried out at mid-span section of quasi-permanent combination
My = 113,73 kNm
εx = 0.0002092938,
εy = 0.0,
εz = -0.00282805826
Figure 1.18 - Strain – stress diagram on cracked concrete cross section
Sectional characteristics of transformed concrete section without cracks
Cross sectional area of transformed cross section (steel area is transformed to concrete)
�� = �� + �� ���� = �ℎ − �� − ���)ℎ − ℎ(+ + ��α* =
1,85⋅0,5 − �1,85 − 0,2��0,5 − 0,08� + 11,40⋅102& 210
31= 0,239357 ��
Center of gravity of transformed cross section
��� =��α*��� =
11,40⋅102&⋅6,4516⋅ − 0,327
0,239357= −0,01005 �
Validation Examples Reinforced Concrete Section October 2010
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Moment of inertia of original cross section
��� = 1
12�ℎ� + �ℎ ����� − ℎ 2⁄ �� −
1
12�� − ���)ℎ − ℎ(+�
− �� − ���)ℎ − ℎ(+)���! + )ℎ − ℎ(+ 2⁄ +� =
1
121,85⋅0,5� + 1,85⋅0,5⋅�0,1305 − 0,5 2⁄ �� −
1
12�1,85 − 0,2��0,5 − 0,08��
− �1,85 − 0,2��0,5 − 0,08�)−0,3274 + �0,5 − 0,08�+� = 0,0046628 �&
Moment of inertia of transformed cross section
��� = ��� + ������ + ��α*�� =
0,00468631 + �1,85 − 0,2��0,5 − 0,08� + �−0,01005�� + 11,40⋅102&⋅6,4516⋅ − 0,3274�
= 0,00542541 �&
Sectional characteristics of transformed concrete section with cracks
Compression zone:
� = ���� +ε�ε
= 0,1305 +0,000209293
−0.002828058= 0,0565 �
Cross sectional area of transformed cross section (steel area is transformed to concrete)�� =� � + ��α* = 1,85 0,0565 + 11,40 102&6,4516 = 0,111901 ��
Center of gravity of transformed cross section
��� =�⋅�(���� − � 2⁄ )��α*��� =
1,85⋅0,0565⋅�0,1305 − 0,0565 2⁄ � + 11,40⋅102&⋅6,4516⋅ − 0,327
0,239357= 0,07401�
Moment of inertia of original cross section
�� =1
12��� + ������� − � 2⁄ �� =
1
121,85 0,565 + 1,85 0,565�0,1305 − 0,565 2⁄ �� =
I; = 0,001909 m&
Moment of inertia of transformed cross section
��� = ��� + ������ + ��α*�� =
0,0565⋅1,85⋅0,07401� + 11,40⋅102&⋅6,4516⋅−0,327� = 0,00129725 �&
Validation Examples Reinforced Concrete Section October 2010
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Rematk: Current IDEA RCS version calculates cross sectional characteristics related to original center of gravity of cross section
Since the same assumptions for calculating the limit state and stiffness and width of cracks were used, we assume the stress in the reinforcement from the example of the calculation of crack width:
σ� = 227,1���
Now we calculate the tensile force from ultimate load on the cracked section immediately prior to cracking. This plane is taken over from program IDEA RCS.
εx = 0.00007225525,
εy = 0.0,
εz = -0.0009763408
Strain in reinforcing steel:
ε�� = ε� + ε��� + ε �� = 0,000072255 − 0,00097634⋅ − 0,32748 = 0,000392
Stress in reinforcing steel σ�3 = ε⋅�� = 0,000392⋅ 200 = 78,3 ���
Reduction factor/distribution coefficientξ = 1 − β5σ��σ�6� = 1 − 1 5 )',�
��),�6� = 0,8808
bending stiffness of uncracked cross section:
���,< = ��<�� = 0,00542541⋅31⋅10� = 169 ����
Validation Examples Reinforced Concrete Section October 2010
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bending stiffness of fully cracked cross section:
���,<< = ��,<<�� = 0,00129725⋅31 = 40,215 ����
Stiffness is interpolated according to following expresion (Interpolation is done on level of stiffnesses) α = ξα<< + �1 − ξ�α< = ξ��<< + �1 − ξ���<
α = 0,88 ⋅ 40 + �1 − 0,88�⋅169 = 55,48 ����
Validation Examples Reinforced Concrete Section October 2010
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2. Column
2.1. Project details
Square cross section 0.4 x 0, 4 m2 reinforced in four corners by bars of 25 mm , stirrup with diameter 10 mm. Material C35/45, Reinforcements B 500B, concrete cover 25 mm, creep coefficient in infinity φ (∞, t0) = 1,68.
Column 5 m, one- Laterally fixed in the XY plane, and both-sidedly fixed in the plane XZ. It is stand-alone element that is unbraced perpendicular to the Y-axis and braced to the Z axis .
Figure 2.1 - Cross section and column geometry
The internal forces obtained by calculating a linear structure in the investigated section:
Combination for the ultimate limit state:
��� = −800 ��,
���,� = 50 ���,
���, = 0 ���.
Quasi-permanent combination for the serviceability limit state:
���,=� = −700 ��,
���,=�,� = 45 ���,
���,=�, = 0 ���.
First order end moments:
At the beginning: At the end:
���,� = 60 ���, ���,� = 0 ���,
���, = 0 ���. ���, = 0 ���.
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Calculating geometrical imperfections:
Effective length l0 ��,� = 2 ∙ � = 2 ∙ 5 = 10 �,
��, = 0,5 ∙ � = 0,5 ∙ 5 = 2,5 �.
Reduction factor for length:
�>,� = �>, = 2/√� = 2/√5 = 0,894, 2/3 ≤ 0,894 ≤ 1.
Reduction factor for number of members
��,�, = !0,5�1 + 1/�� = !0,5�1 + 1/1� = 1.
Inclination-�,�, = -� ∙ �> ∙ �� = 1 200 ∙ 0,894 ∙ 1⁄ =0,00447.
Eccentricity:
(�,� = -���,�/2 = 0,00447 ∙ 10/2 = 0,02235 �,
(�, = -���, /2 = 0,00447 ∙ 2,5/2 = 0,0055875 �.
Total eccentricity including effects of geometrical imperfections:
(��!,� + (�,� = ���,�/��� + (�,� = 50/800 + 0,02235 = 0,0625 + 0,02235 = 0,08485 �,
(��!, + (�, = ���, /��� + (�, = 0/800 + 0,0055875 = 0,0055875 �.
Minimum eccentricity according to paragraph 6.1 (4):
(�,�, = max�ℎ/30; 0,02� = max�0,4/30; 0,02� = max�0,0133BBBB; 0,02� = 0,02 �,
(���,� = max)(��!,� + (�,�; (�,�+ = max�0,08485; 0,02� = 0,08485 �,
(���, = max)(��!, + (�, ; (�, + = max�0,0055875; 0,02� = 0,02 �.
The first order moment with geometrical imperfections:
����,� = ��� ⋅ (���,� = 800 ⋅ 0,08485 = 67,88 ���,
����, = ��� ⋅ (���, = 800 ⋅ 0,02 = 16 ���.
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2.2. Second order effects
Slenderness and limit slenderness:
Slenderness ratioC� =��,�
��=
���,��%% = 86,6, C =
��,�
��=
�,%�,��%% = 21,65,
1�, = � ��� ℎ� = � �
�� 0,4� = 0,1155 �.
Necessary values for calculating the limit slenderness:
End moments ratio:
D�,� = 1, because member is unbraced perpendicularly to Y axis,
D�, = 1, because end moments are equal (��, ,� = ��, ,�).
Relative normal force; =?��
@�(��=
'��∙����,�7×�%∙�� �,%⁄ = 0,214.
Mechanical reinforcement ratioE =@�(��@�(��
=�,����7×%��∙�� �,�%⁄
�,�7×�%∙�� �,%⁄ = 0,229.
• The effect of creep may be ignored, if the following free conditions are metF(9,��) =
1,68 ≤ 2
• C� = 86,6 ≰ 75, C = 21,65 < 75
• B���,�
?��=
7),'''�� = 0,08485 ≱ ℎ = 0,4,
B���,�
?��=
�7'�� = 0,02 ≱ ℎ = 0,4.
Conditions are not fulfilled, the effect of creep must not be ignored
Effective creep ratio:
F*(,� = F89,��:B��,��,�
B���,�= 1,68
7�,7%7),'' = 1,501,
F*(, = F89,��:B��,��,�
B���,�= 1,68
�,���7 = 0,411, the moment from the quasi-permanent
combination, including the effects of the first order we received from the same calculation as for the design moment, only difference is we are not taking account the condition for minimum eccentricity.
�� =�
C�5�,�D��,�E=
�8�5�,�⋅�,%��: = 0,769, � =
�8�5�,�⋅�,&��: = 0,924,
G = √1 + 2E = √1 + 2 ⋅ 0,229 = 1,207,
&�, = 1,7 − D�,�, = 1,7 − 1 = 0,7
Limit slenderness:
C���,� = 20 ⋅ �� ⋅ G ⋅ &�/√; = 20 ⋅ 0,769 ⋅ 1,207 ⋅ 0,7/√0,214 = 28,09,
C���, = 20 ⋅ � ⋅ G ⋅ & /√; = 20 ⋅ 0,924 ⋅ 1,207 ⋅ 0,7/√0,214 = 33,75,
Slenderness criterion:
C� = 86,6 > C���,� = 28,09 slender column,
C = 21,65 < C���, = 33,75 non-slender column, 2nd order effects can be neglected.
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2.2.1. Simplified method based on nominal stiffness
Necessary factors:
H = ��/�� = 0,00196/0,16 = 0,01225 > 0,002, method can be used.
�� = !��/20 = !35/20 = 1,323,
��,� = ; ⋅ C�/170 = 0,214 ⋅ 86,6/170 = 0,109,
3� = 1, 3�,� = ����,�/(1 + F*(,�) = 1,323 ⋅ 0,109/(1 + 1,501) = 0,0577,
��� =���F��
=�&,�))�,� = 28,397 ���,
I = J�/.� = J�/9,6 = 1,028
Nominal stiffness:
��� = 3�,������,� + 3�����,�= 0,0577 × 28,397 ⋅ 10� × 2,133 ⋅ 102� + 1 × 200 ⋅ 10� × 4,566 ⋅ 102%
= 12,631 ����.
Euler critical load:
�G,� =J������,�
� =J� × 12,631 ⋅ 10�
10� = 1246,63 ��
Second order moment:
��,� = ����,�I�)�G,�/���+ − 1
= 67,881,028�1246,63/800� − 1
= 124,99 ���,
Total design moment including second order moment:
���,� = ����,� + ��,� = 67,88 + 124,99 = 192,87 ���,
���, = ����, = 16 ���.
2.2.1. Simplified method based on nominal curvature
Necessary factors:
;� = 1 + E = 1 + 0,229 = 1,229,
;��� = 0,4,
33 = �;� − ;�/�;� − ;���� = �1,229 − 0,214�/�1,229 − 0,4� = 1,31 ≰ 1,
I� = 0,35 +(����� −
H��%� = 0,35 +
�%��� −
'7,7�%� = −0,052,
3D,� = 1 + I�F*(,� = 1 + −0,052 ⋅ 1,501 = 0,921 ≱ 1.
Effective depth:
# = (ℎ/2) + 1� = 0,3525 m,
K�� =(����
=
���
�,��
������ = 0,00217,
1/D� = K��/(0,45 #) = 0,00217/(0,45 ⋅ 0,3525) = 0,0137,
Validation Examples Reinforced Concrete Section October 2010
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1/D� = 33 ⋅ 3D,� ⋅ 1/D� = 1 ⋅ 1 ⋅ 0,0137 = 0,0137.
Deflection:
(�,� = L1D�M ��,�� /. = 0,0137 ⋅ 10�/10 = 0,137 �.
The nominal second order moment:
��,� = ���(�,� = 800 ⋅ 0,137 = 109,6 ���.
Total design moment including second order moment:
���,� = ����,� + ��,� = 67,88 + 109,6 = 177,48 ���,
���, = ����, = 16 ���.
2.2.2. Biaxial bending
No further check is necessary if the slenderness ratios satisfy the following conditions
H�H�
='7,7��,7% = 4 ≰ 2, first condition is not fulfilled, biaxial bending must be taken account
according to paragraph 5.8.9 (4).