Cold-Formed Steel Panel and Stud Design

This article describes the use of StatiCAD’s cold-formed (light-gauge) steel shear wall panel module. The module performs two main checks: the panel’s sheathing shear capacity (TBDY 2018) and the studs in the panel frame under axial compression plus out-of-plane wind bending (Effective Width Method — EWM in the layout of HCBTİE Chapter 4; LRFD or ASD). The forces are taken from the program’s analysis solution; results are presented in the analysis warnings and in the Turkish/English calculation reports.

Related articles: Cold-Formed Steel Beam and Column Design, Code Requirements, Anchorage and Foundation, Theoretical Basis, Verification.

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Which editions? Cold-formed steel calculations are available in the StatiCAD Ultimate edition. Panel data is stored with the project in every edition.

1. General workflow

1. Draw the wall as usual and open the Wall Properties window.
2. Select the “Panel in Cold-Formed Steel” option as the design type.
3. Enter the sheathing and stud inputs in the Cold-Formed Steel Panel tab (Section 2) and save with OK.
4. For panels on the exterior façade, tick the appropriate edge-axis box in Wall Properties (On Top/Bottom/Left/Right Edge Axis); wind bending is calculated only for these walls (Section 5).
5. In Project General Settings, check the design method (LRFD/ASD), the wind velocity pressure and the stud deflection limit (Sections 5 and 6).
6. Run the analysis. Panel shear capacity and stud checks are calculated automatically during the analysis; inadequacies appear in the warning list at the end of the analysis (Section 8).
7. In the tree on the Report tab of the Report Selection window, tick the “Cold-Formed Steel Member Reports” group and its sub-reports and generate the report (Section 9).

2. Inputs of the “Cold-Formed Steel Panel” tab

Input	Description	Default
Left/Top Panel Sheathing Present	Whether there is a sheathing board on the left (top) face of the panel	Present
Right/Bottom Panel Sheathing Present	Whether there is a sheathing board on the right (bottom) face of the panel	Present
vc,left, vc,right (kN/m)	Characteristic shear strength of the sheathing per unit length (depending on board type, screw diameter and spacing; the note in the tab gives the typical values of TBDY Table 10.5)	10.2 (11 mm OSB)
Stud Profile (C / Sigma)	Cold-formed section to be used for the panel studs; the list is filled from the profile table that comes with the installation	Empty (selected by the user)
Stud spacing s (mm)	Centre-to-centre spacing of the intermediate studs	600
Number of end studs n	Number of studs at each end of the panel; the overturning force is shared among these studs	2

note

Older project files that do not contain these inputs open without any change; the fields come with their default values.

3. Panel shear capacity (TBDY 2018)

The shear capacity of the sheathed face(s) is calculated for each cold-formed steel panel:

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Vc = 0.6 · vc · L (L: wall length)

• In the range 2 ≤ h/L ≤ 4 the capacity is reduced by the factor 2L/h; if h/L > 4 or L < 0.30 m, the panel does not contribute to the shear capacity.
• If only one face is sheathed, the capacity of that face is used; if both faces are sheathed, the sum is used for equal sheathing, and the rule max(2·smaller, larger) is used for different sheathing.

The result is taken into account as the lateral capacity of the panel in the storey shear distribution and is listed panel by panel in the report.

3.1 Unsheathed panel

If the sheathing ticks on both faces (Left/Top Panel Sheathing Present and Right/Bottom Panel Sheathing Present) are cleared in the Cold-Formed Steel Panel tab, the panel is considered unsheathed:

• The shear capacity of the panel is zero, because the shear capacity comes from the sheathing. The panel is not included in the gypsum-board share calculation either.
• The studs are designed with the unsheathed buckling lengths: Ly = Lz = h, or h/(n+1) with n rows of bridging (Section 4.2).
• If the shear distribution is carried out with the finite element method, the panel practically receives no shear while the stiffness type is Capacity. With the Classical Stiffness type it receives shear in proportion to its stiffness; if this shear exceeds one thousandth of the panel shear of the storey in the same direction, an error is given. In the classical shear distribution the panel receives no shear.
• An information line reporting the unsheathed panels appears in the analysis warnings.

If the panel is actually sheathed, check the face ticks.

3.2 Storey with no panel with shear capacity

If all the panels in one direction (X or Y) on a storey are unsheathed or short (h/L > 4 or L < 0.30 m), no panel remains to carry the lateral load in that direction. In this case the analysis gives the error “kat, X/Y doğrultusu: kesme kapasiteli panel yok” (storey, X/Y direction: no panel with shear capacity) and writes it in the project checklist. Solely so that the storey shear can be distributed, it is assigned to these panels on the assumption that both faces are sheathed; since their capacities remain zero, the panel checks turn out inadequate. Sheathe or lengthen some of the panels. Panels with steel strap cross-bracing are not supported.

4. Stud check (EWM — HCBTİE Chapter 4)

4.1 Demands

For each panel, the analysis extracts the envelope of the wall’s in-plane shear (V) and vertical axial force (N) over all load combinations; the name of the governing combination is shown in the report. The stud demands are derived from this envelope:

Member	Axial demand	Description
Intermediate stud	Nint = N · s / L	Share of the vertical load according to tributary width
End stud	Nend = max[ N·(s/2)/L + (V·h/L)/n ; Cd ]	Tributary share plus the end force from the overturning moment divided by the number of end studs. Cd is the same distribution calculated combination by combination with the earthquake effect magnified by the overstrength factor D (TBDY 10.4.1.1(a)); the larger one governs. In the report, “(D ile)” (with D) or “(zarf)” (envelope) is written next to the demand.

4.2 Capacity

For the selected section, the axial compression capacity (Pd) is found with EWM: the smallest of the local buckling (effective widths), distortional buckling and flexural–torsional (global) buckling rows governs. Buckling lengths:

• Strong axis: Lx = panel height h.
• If at least one face is sheathed, Ly = Lz = stud spacing s is taken for the weak axis and torsion, and lateral–torsional buckling is assumed to be restrained; if there is no sheathing, Ly = Lz = h (h/(n+1) if n rows of bridging are defined; see Code Requirements, Anchorage and Foundation in Cold-Formed Steel Buildings).

The gross section properties (A, Ix, Iy) are the manufacturer’s catalogue values in the profile table; the torsion constant, shear centre and warping constant are calculated automatically from the section geometry. In sheathed panels the governing row is mostly distortional buckling; the distortional critical stress is calculated with the general method of HCBTİE 4.10.3.3 or, if selected, with the finite strip method (see Theoretical Basis).

For each panel, the end stud and the intermediate stud are checked as separate rows. Two ratios are calculated, and the larger one is the governing ratio that gives the Adequate / YETERSİZ (inadequate) decision:

• Axial ratio = PEd/Pd (envelope of all load combinations),
• Wind combination ratio = P/Pd + M/Md (only on exterior walls; HCBTİE Eq. 4.8.4).

5. Out-of-plane wind bending and deflection

The studs of walls marked with an edge axis (exterior walls) bend like simple beams under wind pressure perpendicular to the wall face:

• w = max(0.8 · q ; 0.5) kN/m² (0.8: TS 498 pressure coefficient; 0.5 kN/m²: lower limit of the HCBTİE characteristic wind load)
• M = γW · w · b · h² / 8 (b: s for an intermediate stud, s/2 for an end stud; second-order magnification is applied)

q is the “Wind Load” box in the Project General Settings → Load Combinations tab; a value appropriate to the building height according to TS 498 must be entered (0–8 m: 0.5; 8–20 m: 0.8; 20–100 m: 1.1 kN/m²). The snow load in the same tab contributes to the axial force in the wind combination. Wind combinations — LRFD: 1.2G + 1.0Q + 0.5S + 1.6W and 1.2G + 1.6S + 0.8W; ASD: G + 0.75Q + 0.75S + 0.45W and G + 0.6W.

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If no cold-formed steel panel in the project is marked as an exterior wall, a line stating this appears in the analysis warning list; wind bending is not skipped silently. A warning is also given if q has not been entered or is lower than the TS 498 value corresponding to the height of the panel’s top level (q is not changed by the program).

Deflection check: In exterior wall studs, the out-of-plane deflection is calculated with the characteristic value of the wind and δ ≤ h/K is checked. The deflection is calculated with the effective moment of inertia at the service moment (HCBTİE 4.9.5); for slender sections it may come out larger than the one calculated with the gross moment of inertia. K is selected from the Stud deflection limit list of the “Cold-Formed Steel Member Design Method” box in the Project General Settings → Code Selection tab (h/120, h/200, h/240 default, h/300, h/360). Since HCBTİE gives no stud-specific limit, the selection should be made by engineering judgement according to the type of finish: h/120 is common for flexible cladding, h/240 for gypsum or OSB sheathing, and h/360 for plaster or ceramic finishes. The result is written in a separate “Sehim” (Deflection) row in the report; if it is exceeded, the stud is considered inadequate.

6. Design method: LRFD / ASD

It is selected from the “Cold-Formed Steel Member Design Method” box in the Project General Settings → Code Selection tab (visible when the building type is cold-formed steel or when the project contains a cold-formed steel panel) and is saved with the project:

Option	Strength	Load combinations
LRFD (default)	φc = 0.85, φb = 0.90 (HCBTİE)	The program’s combinations; 1.2G instead of G in combinations containing earthquake; in addition, the HCBTİE 4.3.1 vertical combinations (1.4G; 1.2G + 1.6Q + 0.5S; 1.2G + 1.6S + Q) are generated from the plain G/Q/S results and added to the envelope.
ASD	Ωc = 1.80, Ωb = 1.67 (AISI S100)	The program’s combinations are converted to their ASD counterparts; in addition, G + Q, G + S, G + 0.75Q + 0.75S and the G + 0.7E form of the combinations with earthquake are added to the envelope.

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HCBTİE defines only LRFD; the ASD option is for comparison and preliminary sizing. Use LRFD in official calculations. Older projects open with LRFD.

7. Rotational restraint of the sheathing (kφ)

OSB or plywood sheathing restrains the flanges of the stud against rotation and thereby increases the distortional buckling strength (HCBTİE 4.10.3.3, AISI S240). If no data is entered, kφ = 0 is assumed.

• In the “Sheathing rotational restraint to the stud” box of the Wall Properties → Cold-Formed Steel Panel tab, the board type (Undefined / Gypsum board / OSB / Plywood / User kφ), the board bending stiffness (0 = default of the type), the screw spacing and, only for “User kφ”, kφ are entered for the left and right faces. The smaller of the two faces is used in the calculation: if one of the faces is gypsum board, undefined or unsheathed, kφ = 0.
• Conditions: screw spacing ≤ 305 mm and stud spacing ≤ 625 mm; otherwise kφ = 0 is taken and the reason is written in the report.
• In the stud note of the report, the kφ value of each face, or the reason for zero, and the value used are written.

8. Analysis warnings

Warning	Meaning / action
“… hafif çelik panel dikme hesabı yapılamadı: Dikme profili seçilmedi” (… cold-formed steel panel stud calculation could not be performed: Stud profile not selected)	No stud profile has been selected in the panel’s tab. Select a profile in the Wall Properties → Cold-Formed Steel Panel tab.
“… hafif çelik panel KENAR/ARA dikmesi yetersiz (oran=…)” (… cold-formed steel panel END/INTERMEDIATE stud inadequate (ratio=…))	The governing ratio of the stud concerned exceeds 1. Select a larger or thicker profile, reduce the stud spacing, or increase the number of end studs.
“Hafif çelik panellerde bina kenar aksı (dış duvar) işaretli duvar yok …” (There is no wall marked with a building edge axis (exterior wall) among the cold-formed steel panels …)	Wind bending was not calculated because no panel is marked as an exterior wall. For façade panels, tick the edge-axis boxes.
“… hafif çelik panel dikme sehimi fazla (rüzgâr: sehim=… mm > h/K=… mm)” (… cold-formed steel panel stud deflection excessive (wind: deflection=… mm > h/K=… mm))	The out-of-plane deflection of the exterior wall stud exceeds the selected limit. Select a stiffer profile, reduce the stud spacing, or review the limit if appropriate for the type of sheathing.
“Rüzgâr basıncı q girilmemiş …” / “… TS 498 yükseklik kademesinin altında …” (Wind pressure q has not been entered … / … below the TS 498 height step …)	Enter the Project General Settings → Load Combinations → Wind Load value appropriate to the building height.
Unsheathed panel information line	Panels marked unsheathed on both faces are listed; these panels carry no shear (Section 3.1). If the panel is sheathed, correct the face ticks.
“… kaplamasız … katılamaz ancak analizde V=…” (… unsheathed … cannot participate, but in the analysis V=…)	With the Classical Stiffness type, an unsheathed panel received more than one thousandth of the panel shear of the storey in the analysis. Sheathe the panel or use the Capacity type.
“kat, X/Y doğrultusu: kesme kapasiteli panel yok” (storey, X/Y direction: no panel with shear capacity)	There is no panel able to carry lateral load in that direction (Section 3.2). Sheathe or lengthen some of the panels.

9. Reports

In the tree on the Report Selection → Report tab there is the “Cold-Formed Steel Member Reports” group (visible if the project contains a cold-formed steel panel):

• Cold-Formed Steel Panel Design: Panel by panel, the sheathing information, h, L, vc inputs and the sheathing shear capacities.
• Cold-Formed Steel Stud Design (EWM): Storey by storey, panel by panel — panel name and profile, geometry (h, L, s, n), design method and wind pressure, envelope forces (with the name of the governing combination), demand, capacity, axial ratio, governing ratio and status for the end and intermediate studs; for exterior walls the wind combination row and deflection; anchorage and panel shear rows; bottom and top track and bridging rows (demand, tension and compression strength, ratio, collector, bridging force and HCBTİE 6 detail warnings); a note on calculation assumptions.
• Cold-Formed Steel Beam Design (EWM) and Cold-Formed Steel Column Design (EWM): If the project contains such members (see Cold-Formed Steel Beam and Column Design).

Reports are produced in Turkish or English according to the program language setting; after the analysis is completed they are obtained with “Generate All Selected Reports” and can be exported as PDF/DOCX.

10. Frequently asked questions

The panel shear capacity is shown as 0. h/L may be > 4 or L < 0.30 m, or sheathing may not be ticked on either face (unsheathed panel, Section 3.1). In older projects the sheathing strength may come with the old default (2.7 kN/m); check it in the tab.

The stud profile list is empty or shows only Sigma profiles. The profiles are loaded from the HafifCelikProfil.txt file (527 profiles) in the installation folder. If this file cannot be found, the backup HafifCelikSigma.txt (90 Sigma profiles) is used; if neither exists, the list stays empty. Reinstall the update.

The stud profile comes up empty in a new cold-formed steel wall. The profile is selected by the user: Wall Properties → Cold-Formed Steel Panel → Stud Profile. If it is not selected, the analysis gives a warning.

There is no wind combination row in the report; it says “iç duvar” (interior wall). The wall has not been marked with any of the edge-axis boxes. If it is a façade wall, tick the relevant edge axis in Wall Properties and repeat the analysis.

“(D ile)” (with D) is written next to the end stud demand. According to TBDY 10.4.1.1(a), the end stud demand is also calculated from the earthquake combinations magnified by the overstrength factor D; in a multi-storey building the overturning moment accumulated from the upper storeys is also taken into account. If the ratio is inadequate, increase the number of end studs or the profile.

There is a note “Kenar rijitleştirici (HCBTİE 4.9.3)” (Edge stiffener (HCBTİE 4.9.3)) in the report footnote. The lip is not sufficient to fully stiffen the flange; the flange plate buckling coefficient and the effective widths have been reduced according to the code. If a profile with a thicker wall or a longer lip is selected, the reduction becomes smaller.

Why is the governing row always distortional buckling in a sheathed panel? The sheathing limits weak-axis and torsional buckling to the stud spacing; in thin-walled sections the lowest strength in this case is usually given by distortional buckling. Entering the rotational restraint of the sheathing (Section 7) and the finite strip option (for Sigma sections) calculate this strength more realistically.