Free Online Plate Analysis Software
Analyse slabs, walls, panels, diaphragms, and mat-style surfaces directly in your browser. AutoCalcs supports quadrilateral and triangular shell elements, surface pressure loads, plate result contours, and mixed frame-and-plate models - no signup or download required.
Build structural FEA models in the browser, run analysis, and inspect plate, frame, and mixed-model results
Plate and Shell Elements in AutoCalcs
Plate analysis is for surface structures where load spreads through a two-dimensional area. A flat slab supported by columns, a shear wall, a tilt-up panel, a diaphragm, or a stiffened plate behaves differently from a line-member frame. The solver needs shell elements that carry both membrane action in the plane of the surface and bending action out of the plane.
AutoCalcs uses flat Mindlin-Reissner shell elements with six degrees of freedom at every node, matching the frame elements. Plate corners can snap to existing nodes and member endpoints, so plates and surrounding beams or columns connect through the same model geometry instead of a separate manual constraint workflow.
Shell Elements
- Four-node MITC4 quadrilateral shells
- Three-node MITC3 triangular shells
- Membrane, plate bending, and transverse shear action
- Concrete stiffness modifiers for cracked slabs and walls
Modelling Tools
- Draw quad plates with a three-click rectangle flow
- Draw triangle plates for irregular areas
- Set material, thickness, and target mesh size
- Re-mesh plate groups as the model changes
Loads and Analysis
- Local normal pressure on plate surfaces
- Global X, Y, or Z area loads per plate surface area
- Plate self-weight from material density
- Linear static analysis plus supported modal and buckling workflows
Plate Results
- Deflection contours and deformed shape
- Mx, My, Mxy, M1, and M2 bending moments
- Qx, Qy transverse shear and membrane stresses
- Von Mises and Wood-Armer demand moments
Quads, Triangles, and Mixed Meshes
Use quadrilateral plates where the geometry is regular and a structured mesh makes sense. The MITC4 quad is the default workhorse for slabs, walls, diaphragms, and rectangular panels because it gives efficient two-way plate bending with a clean local x-y frame.
Use triangular plates where a rectangle cannot represent the shape cleanly - skewed panels, transition zones, non-rectangular wall pieces, or filler regions around irregular geometry. The MITC3 triangle exposes the same degrees of freedom and the same result quantities, so triangle and quad shell elements can be mixed in one model.
What Results Can You Read?
Plate contours can be displayed as smooth gradients or colour bands. You can inspect deflection, local bending moments, twisting moment, principal moments, transverse shear, membrane direct stresses, membrane shear, principal membrane stresses, von Mises stress, and concrete Wood-Armer demand moments.
The bending moment display is sagging-positive, so a typical simply supported slab shows positive midspan moment for bottom-face reinforcement demand and negative hogging moment over supports. For concrete plates, Wood-Armer top (+local z face) and bottom (-local z face) demand contours help turn the twisting moment into orthogonal reinforcement demand directions.
Try the Slab Panel Sample
The sample model opens a meshed slab panel with 12 nodes, perimeter line supports, and a ready-to-run load setup. Open it, run Linear analysis, then switch the results display to plate contours to inspect deflection and slab moment patterns across the mesh.
Engineering Interpretation
Plate FEA gives analysis demands, not automatic final slab detailing. Peaks near columns, supports, openings, mesh corners, and beam tie-ins are mesh-sensitive, so design should use engineering judgement, mesh refinement, section-averaged values, or code-specific checks where local punching, one-way shear, or reinforcement detailing governs.
Why Choose AutoCalcs?
- Plate and Frame Models - Combine shell elements with beams and columns in the same 3D model.
- Quad and Triangle Meshes - Use structured quads where practical and triangles where the geometry needs them.
- Useful Result Contours - View deflection, bending, shear, membrane stress, von Mises, and Wood-Armer demand fields on the model.
- Instant Access - No installation, no signup. Open a sample or start a blank model in the browser.