CLT floor panel: bending and rolling shear
Checks a cross-laminated timber (CLT) floor panel spanning one way at the ultimate limit state: bending on the layers that run along the span, and rolling shear in the cross layers. SIA 265 has no provisions for CLT; the partial factor and the modification factor k_mod come from EN 1995-1-1. Every step shows its formula and where it comes from.
Pro EN 1995-1-1
Part of the Pro plan
This module is included in the Pro plan and above, with its calculation note.
About this check
clauses, worked example and questions
Checks a cross-laminated timber (CLT) floor panel spanning one way at the ultimate limit state: bending on the layers that run along the span, and rolling shear in the cross layers. SIA 265 has no provisions for CLT; the partial factor and the modification factor k_mod come from EN 1995-1-1. Every step shows its formula and where it comes from.
What it checks
- Net section of the panel: only the layers running along the span are credited with bending stiffness (A0,net, I0,net, W0,net); the cross layers carry the rolling shear.
- Bending: σm,d = Md / W0,net ≤ fm,Rd = kmod · fm,k · ksys / γM.
- Rolling shear: τv,R,d = 1.5 · Vz,d / (b · h) ≤ fv,R,Rd = kmod · fv,R,k / γM; ksys does not apply to rolling shear.
- Modification factor kmod from EN 1995-1-1, table 3.1, by load duration and humidity class.
What you enter and what you get
You enter the lay-up (3, 5 or 7 layers, each thickness, numbered from the exposed face), the width considered (usually 1 m), the load duration and humidity class, the characteristic bending strength fm,k and rolling shear strength fv,R,k of the product, the system factor, the partial factor γM, and the design moment and shear force.
You get the net section properties, both checks with their utilisations, and every intermediate value with its source. With the Pro plan, it prints as an A4 calculation note.
Assumptions and limits
- Panel spanning one way; the layers along the span carry bending, the cross layers are given no bending stiffness.
- Rolling shear is taken over the full thickness of the panel.
- The characteristic strengths of the CLT product are entered by you.
- The deflection and vibration of the panel (its own module) and the fire situation (its own module) are separate.
Worked example
A five-layer panel 40-20-20-20-40 mm (140 mm), one metre wide, permanent actions in humidity class 2, f_m,k = 24 N/mm², f_v,R,k = 1.1 N/mm², k_sys = 1.1, γ_M = 1.25, with M_d = 12.09 kN·m and V_z,d = 12.09 kN. These are the module's own results for its worked example, computed when this page was built.
| Input | Value | Ref. |
|---|---|---|
| Number of layers | 5 | |
| Layer 1, along the span d1 | 40 mm | |
| Layer 1–2, across the span d12 | 20 mm | |
| Layer 2, along the span d2 | 20 mm | |
| Layer 2–3, across the span d23 | 20 mm | |
| Layer 3, along the span d3 | 40 mm | |
| Width considered b | 1000 mm | |
| Load duration kmod | Permanent | EN 1995-1-1 t.3.1 |
| Humidity class | 2 | EN 1995-1-1 t.3.1 |
| Characteristic bending strength fm,k | 24 N/mm² | |
| Characteristic rolling shear strength fv,R,k | 1.1 N/mm² | |
| System factor ksys | 1.1 | |
| Partial factor γM | 1.25 | EN 1995-1-1 |
| Design bending moment Md | 12.09 kN·m | |
| Design shear force Vz,d | 12.09 kN |
| Step | Value | Ref. |
|---|---|---|
| Modification factor | kmod = 0.50 | EN 1995-1-1 t.3.1 |
| Total thickness of the panelthe sum of every layer | h = 140.0 mm | |
| Net area of the layers along the spanonly the layers running along the span are counted | A0,net = 100,000 mm² | |
| Position of the neutral axiszs = h / 2 for a symmetrical lay-up | zs = 70.0 mm | |
| Net second moment of areaΣ over the parallel layers of [b·d³/12 + b·d·(z − zs)²]. The cross layers are given no bending stiffness at all. | I0,net = 211,333,333 mm⁴ | |
| Net section modulusW0,net = I0,net / zs | W0,net = 3,019,048 mm³ |
| Step | Value | Ref. |
|---|---|---|
| Design bending strengthfm,Rd = kmod · fm,k · ksys / γM | fm,Rd = 10.560 N/mm² | EN 1995-1-1 |
| Bending stressσm,d = Md / W0,net | σm,d = 4.0046 N/mm² | |
| Bendingσm,d ≤ fm,Rd | η = 0.379 · Pass38 % of the capacity used |
| Step | Value | Ref. |
|---|---|---|
| Design rolling shear strengthfv,R,Rd = kmod · fv,R,k / γM. ksys does not apply to rolling shear. | fv,R,Rd = 0.4400 N/mm² | EN 1995-1-1 |
| Rolling shear stressτ = 1.5 · Vz,d / (b · h), taken over the full thickness | τv,R,d = 0.1295 N/mm² | |
| Rolling shearτv,R,d ≤ fv,R,Rd | η = 0.294 · Pass29 % of the capacity used |
How this module is verified
Verified step by step against the factors of EN 1995-1-1 and against independent calculations used on real projects, before release.
Questions
Why not SIA 265?
SIA 265 has no provisions for cross-laminated timber. The module uses the partial factor and the modification factor kmod of EN 1995-1-1, and says on each step where a value comes from.
Why does rolling shear govern CLT?
The cross layers are loaded across the grain in both directions at once. Their rolling shear strength is roughly a tenth of the shear strength along the grain.
Which plan includes this module?
The Pro plan, with its calculation note.
Related
- CLT floor panel — deflection and vibration
- CLT floor panel — fire situation
- EN 1995: modules and checks
Norm: EN 1995-1-1 · Page updated: 20 October 2026