Investigation on cold-formed steel lipped channel built-up I beam with intermediate web stiffener
Abstract
The aim of the present study is to examine the behaviour of cold-formed steel (CFS) lipped channel built-up I-section with edge and intermediate web stiffeners under bending. Initially, the section dimension of length, width of the flange and depth of the sections are optimized numerically and finally, it is validated with the test results. All the select cross-section dimensions have satisfied the pre-qualified beam dimensions. Numerical analysis is carried out using the software ABAQUS. Totally, four section geometries are tested experimentally. After validation, a total of 75 parametric studies are carried out using the verified finite element model. All the results are compared with the direct strength method specifications for CFS structures and the suitable design modifications are detailed.
Keywords
Bending ABAQUS Edge stiffener Intermediate stiffener Two-point loadingList of symbols
- b
Breadth of flange
- CFS
Cold-formed steel
- H
Depth of the section
- L
Length of the section
- d1
Lip size
- d1
Size of return lip
- S
Size of intermediate stiffener
- t
Thickness of the section
- PFEA
Ultimate load from FEA
- MEXP
Ultimate moment from experiment
- MFEA
Ultimate moment from FEA
- MDSM
Ultimate moment from DSM
- My
Yield moment
Subscripts
- DSM
Direct strength method
- FEA
Finite element analysis
- FEM
Finite element model
- EXP
Experimental result
Introduction
Cold-formed steel (CFS) members have become ready for the action of building products in modern building construction due to their inherent constructive uniqueness over conventional hot-rolled steel members. The reason is that, the CFS members provide enormous advantages such as high strength-to-weight ratio, high structural efficiency and so on over hot-rolled members. The load capacity of CFS beam depends on buckling mode like local buckling (LB), distortional buckling (DB), lateral torsional buckling (LTB), flexural buckling (FB) or interactions among them.
Experimental and numerical investigations on CFS C-section flexural member were carried out by Wang and Zhang (2008). An experimental study on laser-welded CFS built-up beams was conducted by Landolfo et al. (2008). Paczos and Wasilewicz (2009) have investigated the buckling studies on lipped CFS I-shaped beam with anti-symmetrical bends, which increase the load capacity, and while designing, special attention needs to be paid to their size. Magnucka-Blandzi (2010) has studied the behaviour of CFS channel beams with double-box flange beams. Magnucka-Blandzi and Magnucki (2010) have investigated the global–local buckling behaviour of thin-walled channel beams. The LTB behaviour of CFS lipped channel beams under bending was examined by Kankanamge and Mahendran (2010). Anapayan and Mahendran (2010) have presented the behaviour and capacity of light steel flexural members subject to LTB. Numerical investigation of CFS members subjected to bending and compression of built-up double Z-members has been discussed by Georgieva et al. (2011).
Similarly, Madulia et al. (2012) have developed the new design rules for in-elastic bending capacity of CFS channel sections. Haidarali and Nethercot (2012a, b) have investigated the true buckling behaviour of beam with both edge and intermediate stiffeners in their compression flanges on the post-buckling of laterally restrained CFS Z-section beam. Manikandan et al. (2014, 2015, 2016) have investigated the behaviour of thin-walled built-up I beams in pure bending. Experimental and numerical studies on the flexural behaviour of CFS built-up section were performed by Alex and Iyappan (2016), Yang et al. (2017) and Hassan et al. (2017).
There are only a minimal amount of studies available on the behaviour of the CFS built-up section under bending and it is observed that studies on built-up beam with intermediate stiffener are almost nil. Hence, in the current study, the lipped channel built-up sections with intermediate web stiffeners are chosen. Totally, four section geometries are tested and the results are validated numerically. A total of 75 parametric studies were carried out using finite element analysis (FEA) software ABAQUS. The aim of the study is to examine the behaviour of CFS built-up I-section with edge and intermediate stiffeners under bending. All the parametric results are compared with the DSM specifications for CFS structures and a suitable design modification is proposed.
Experimental investigation
Totally, four types of built-up cross-section are tested: first is the simple lipped channel (SLC), second is the simple lipped channel with intermediate web stiffener (SLC-I), third is the complex lipped channel (CLC) and fourth is the complex lipped channel with intermediate web stiffener (CLC-I). Material properties of the specimens are determined by conducting tensile tests on steel coupons as per the IS standard (IS 1608 -2006).
Average results of coupon test
Yield stress (Mpa) | Young’s modulus (Mpa) | Ultimate stress (Mpa) | Elongation |
---|---|---|---|
276 | 2.05 × 105 | 350 | 13% |
Stress–strain curve
Dimension of the section
S.No | Specimen ID | Dimension of the section (mm) | ||||||
---|---|---|---|---|---|---|---|---|
H | b | d 1 | d 2 | S | t | L | ||
1 | SLC | 140 | 50 | 20 | – | – | 1.6 | 1200 |
2 | SLC-I | 140 | 45 | 20 | – | 20 | 1.6 | 1200 |
3 | CLC | 140 | 50 | 20 | 20 | – | 1.6 | 1200 |
4 | CLC-I | 140 | 45 | 20 | 20 | 20 | 1.6 | 1200 |
Section geometries with labels
Experimental set-up
Finite element modelling
The finite element model (FEM) is developed using the numerical analysis software ABAQUS. In this study, material and geometric non-linearities are incorporated, whereas residual stress and cold-forming process are not incorporated (Xu et al. 2009). For defining the material non-linearity, multi-linear stress–strain behaviour is adopted. The numerical investigation involves two types of analysis. One is linear and the other one is non-linear. In the linear analysis, the sections are considered to have a perfect geometry to determine the probable buckling behaviour. In the non-linear analysis, both geometric and material non-linearities are incorporated (Manikandan et al. 2014; Manikandan and Sukumar 2015, 2016, Kankanamge and Mahendran 2012).
Details of FE model
Selection of section dimensions
For arriving at the section dimensions, initially, 33 FEMs are analysed. To minimize the LB, in the entire study, the dimension of the lips (d1), flange width of the section (b), depth of the section (H), length of the member (L), bolt spacing and thickness of the section are taken as 20, 40, 75, and 1200 mm, respectively, and the variations of these dimensions are specified in the appropriate places.
Buckling plot
Effect of variations of section dimensions of SLC
Effect of variations of section dimensions
S. no | Specimen ID | Section dimensions (mm) | Ultimate load PFEA (kN) | Failure mode | |||||
---|---|---|---|---|---|---|---|---|---|
H | b | d 1 | t | L | S | ||||
1 | L900 | 75 | 40 | 20 | 1.6 | 900 | 100 | 21.14 | LT |
2 | L1200 | 75 | 40 | 20 | 1.6 | 1200 | 100 | 24.93 | LD |
3 | L1500 | 75 | 40 | 20 | 1.6 | 1500 | 100 | 16.89 | LT |
4 | L1800 | 75 | 40 | 20 | 1.6 | 1800 | 100 | 13.27 | LT + F |
5 | L2100 | 75 | 40 | 20 | 1.6 | 2100 | 100 | 11.73 | LT + F |
6 | H50 | 50 | 40 | 20 | 1.6 | 1200 | 100 | 18.24 | LT |
7 | H55 | 55 | 40 | 20 | 1.6 | 1200 | 100 | 18.99 | LT |
8 | H60 | 60 | 40 | 20 | 1.6 | 1200 | 100 | 19.81 | LT |
9 | H65 | 65 | 40 | 20 | 1.6 | 1200 | 100 | 20.28 | LT |
10 | H70 | 70 | 40 | 20 | 1.6 | 1200 | 100 | 21.50 | LT |
11 | H75 | 75 | 40 | 20 | 1.6 | 1200 | 100 | 24.93 | LT |
12 | H80 | 80 | 40 | 20 | 1.6 | 1200 | 100 | 21.32 | LT |
13 | H85 | 85 | 40 | 20 | 1.6 | 1200 | 100 | 20.75 | LT |
14 | H90 | 90 | 40 | 20 | 1.6 | 1200 | 100 | 20.52 | LT + F |
15 | H95 | 95 | 40 | 20 | 1.6 | 1200 | 100 | 20.24 | LT |
16 | H100 | 100 | 40 | 20 | 1.6 | 1200 | 100 | 20.19 | LT + F |
17 | H125 | 125 | 40 | 20 | 1.6 | 1200 | 100 | 18.80 | LT + F |
18 | H150 | 150 | 40 | 20 | 1.6 | 1200 | 100 | 18.25 | LT + F |
19 | b20 | 75 | 20 | 20 | 1.6 | 1200 | 100 | 17.50 | LT + F |
20 | b30 | 75 | 30 | 20 | 1.6 | 1200 | 100 | 20.35 | LT + F |
21 | b40 | 75 | 40 | 20 | 1.6 | 1200 | 100 | 24.93 | LT + F |
22 | b50 | 75 | 50 | 20 | 1.6 | 1200 | 100 | 21.40 | LT + F |
23 | b60 | 75 | 60 | 20 | 1.6 | 1200 | 100 | 21.00 | LT |
24 | d10 | 75 | 40 | 0 | 1.6 | 1200 | 100 | 18.97 | LT + F |
25 | d15 | 75 | 40 | 5 | 1.6 | 1200 | 100 | 20.95 | LT + F |
26 | d110 | 75 | 40 | 10 | 1.6 | 1200 | 100 | 21.20 | L + F |
27 | d115 | 75 | 40 | 15 | 1.6 | 1200 | 100 | 22.50 | L + F |
28 | d120 | 75 | 40 | 20 | 1.6 | 1200 | 100 | 24.95 | LT |
29 | d125 | 75 | 40 | 25 | 1.6 | 1200 | 100 | 21.07 | LT |
30 | S20 | 75 | 40 | 20 | 1.6 | 1200 | 20 | 13.30 | LT + F |
31 | S30 | 75 | 40 | 20 | 1.6 | 1200 | 30 | 16.50 | LT + F |
32 | S50 | 75 | 40 | 20 | 1.6 | 1200 | 50 | 24.40 | LT + F |
33 | S100 | 75 | 40 | 20 | 1.6 | 1200 | 100 | 20.71 | LT + F |
34 | S150 | 75 | 40 | 20 | 1.6 | 1200 | 150 | 18.96 | LT + F |
35 | S200 | 75 | 40 | 20 | 1.6 | 1200 | 200 | 17.45 | LT + F |
Result and discussion
Comparison of test and FE analysis result
S.no | Specimen ID | Flexural strength (kN.m) | MEXP MFEA | Failure mode | |
---|---|---|---|---|---|
MEXP | MFEA | ||||
1 | SLC | 5.06 | 5.23 | 0.97 | L + LT |
2 | SLC-I | 7.88 | 8.00 | 0.99 | L + LT |
3 | CLC | 7.38 | 7.58 | 0.97 | L + LT |
4 | CLC-I | 10.21 | 10.40 | 0.98 | L + LT |
Mean | 0.98 | ||||
Standard deviation | 0.01 |
Comparison of load–deformation between experiment and (a) SLC (b) SLC-I (c) CLC (d) CLC-I
Comparison of failure modes (a) SLC (b) SLC-I (c) CLC (d) CLC-I
Comparison of stiffness evaluation (a) SLC and CLC (b) SLC-I and CLC-I (c) SLC and SLC-I (d) CLC and CLC-I
Parametric study
Results of the parametric study
Specimen ID | Section dimensions (mm) | MFEA (kN.m) | MDSM (kN.m) | MFEA MDSM | Failure modes | |||||
---|---|---|---|---|---|---|---|---|---|---|
H | b | d | t | s | L | |||||
SLC-L900H140 | 140 | 50 | 20 | 1.6 | 0 | 900 | 7.10 | 8.30 | 0.86 | LT |
SLC-L1200H140 | 140 | 50 | 20 | 1.6 | 0 | 1200 | 6.10 | 7.02 | 0.87 | L + LT |
SLC-L1500H140 | 140 | 50 | 20 | 1.6 | 0 | 1500 | 5.57 | 6.50 | 0.86 | L + LT |
SLC-L1800H140 | 140 | 50 | 20 | 1.6 | 0 | 1800 | 5.29 | 5.46 | 0.97 | L + LT |
SLC-L2100H140 | 140 | 50 | 20 | 1.6 | 0 | 2100 | 5.04 | 5.21 | 0.97 | L + LT |
SLC-L2400H140 | 140 | 50 | 20 | 1.6 | 0 | 2400 | 4.65 | 4.93 | 0.94 | F + LT |
SLC-L2700H140 | 140 | 50 | 20 | 1.6 | 0 | 2700 | 3.95 | 4.03 | 0.98 | F + LT |
SLC-I-L900H140 | 140 | 45 | 20 | 1.6 | 20 | 900 | 11.06 | 12.26 | 0.90 | LT |
SLC-I-L1200H140 | 140 | 45 | 20 | 1.6 | 20 | 1200 | 9.51 | 10.71 | 0.89 | L + LT |
SLC-I-L1500H140 | 140 | 45 | 20 | 1.6 | 20 | 1500 | 8.68 | 9.88 | 0.88 | L + LT |
SLC-I-L1800H140 | 140 | 45 | 20 | 1.6 | 20 | 1800 | 8.24 | 7.94 | 1.04 | L + LT |
SLC-I-L2100H140 | 140 | 45 | 20 | 1.6 | 20 | 2100 | 7.86 | 7.56 | 1.04 | F + LT |
SLC-I-L2400H140 | 140 | 45 | 20 | 1.6 | 20 | 2400 | 7.26 | 6.96 | 1.04 | F + LT |
SLC-I-L2700H140 | 140 | 45 | 20 | 1.6 | 20 | 2700 | 6.16 | 5.86 | 1.05 | F + LT |
CLC-L900H140 | 140 | 50 | 20 | 1.6 | 0 | 900 | 12.20 | 13.40 | 0.91 | LT |
CLC-L1200H140 | 140 | 50 | 20 | 1.6 | 0 | 1200 | 11.93 | 12.98 | 0.92 | L + LT |
CLC-L1500H140 | 140 | 50 | 20 | 1.6 | 0 | 1500 | 11.41 | 11.45 | 1.00 | L + LT |
CLC-L1800H140 | 140 | 50 | 20 | 1.6 | 0 | 1800 | 10.31 | 9.89 | 1.04 | F + LT |
CLC-L2100H140 | 140 | 50 | 20 | 1.6 | 0 | 2100 | 9.02 | 8.56 | 1.05 | F + LT |
CLC-L2400H140 | 140 | 50 | 20 | 1.6 | 0 | 2400 | 7.42 | 7.12 | 1.04 | F + LT |
CLC-L2700H140 | 140 | 50 | 20 | 1.6 | 0 | 2700 | 5.57 | 5.05 | 1.10 | F + LT |
CLC-I-L900H140 | 140 | 45 | 20 | 1.6 | 20 | 900 | 16.88 | 18.33 | 0.92 | LT |
CLC-I-L1200H140 | 140 | 45 | 20 | 1.6 | 20 | 1200 | 16.50 | 17.12 | 0.96 | L + LT |
CLC-I-L1500H140 | 140 | 45 | 20 | 1.6 | 20 | 1500 | 15.78 | 16.22 | 0.97 | L + LT |
CLC-I-L1800H140 | 140 | 45 | 20 | 1.6 | 20 | 1800 | 14.25 | 16.01 | 0.89 | F + LT |
CLC-I-L2100H140 | 140 | 45 | 20 | 1.6 | 20 | 2100 | 12.48 | 13.23 | 0.94 | F + LT |
CLC-I-L2400H140 | 140 | 45 | 20 | 1.6 | 20 | 2400 | 10.26 | 11.45 | 0.90 | F + LT |
CLC-I-L2700H140 | 140 | 45 | 20 | 1.6 | 20 | 2700 | 7.71 | 8.56 | 0.90 | F + LT |
Mean | 0.96 | |||||||||
Standard deviation | 0.07 |
Load–deformation curve for specimen (a) SLC- series (b) CLC- series
Theoretical investigation
As per the DSM (22) for CFS structures, the nominal flexural strength (MDSM) is the minimum of lateral–torsional buckling (Mne), local buckling (Mnl) and distortional buckling (Mnd) as given below.
Comparison of results between FEA and DSM (a) SLC series (b) SLC-I series (c) CLC series (d) CLC-I series
Variability of results between FEA and DSM
Correlation between FEA and DSM
Conclusion
The FEM using ABAQUS software is perfect in predicting the strength and the behaviour of the beams. Therefore, the FEM developed can be used with a high level of assurance in predicting the capacity of the beams. Design of CFS built-up I beam with and without intermediate web stiffeners requires the consideration of FB and interaction of FB and LTB. Keeping the length and cross-sectional area the same by adding the intermediate web stiffeners has a considerable effect on the strength and the behaviour of the beam, which is due to minimizing the LB and the increase in the moment of inertia about a symmetrical axis and the increase in resistance against torsional buckling. Adding the complex edge stiffener at the flange has a considerable result in terms of the strength and behaviour of the beams. This study has shown that the provision of intermediate web stiffeners and edge stiffeners improves the behaviour and increases the strength of the section.
Notes
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