MPCO File Format

The .mpco file is an HDF5 container that stores the model definition and all result data from an OpenSees analysis.

Top-level structure

/
├── MODEL_STAGE[1]/
│   ├── MODEL/
│   │   ├── NODES/
│   │   │   ├── ID                    (N,) int
│   │   │   └── COORDINATES           (N, 3) float
│   │   ├── ELEMENTS/
│   │   │   ├── 203-ASDShellQ4[201:0] (M, 5) int  [eid, n1, n2, n3, n4]
│   │   │   ├── 204-ElasticTimoshenkoBeam3d[202:0]  (K, 3) int  [eid, n1, n2]
│   │   │   └── ...
│   │   └── SECTION_ASSIGNMENTS/
│   │       ├── SECTION_0/
│   │       │   ├── ASSIGNMENT         (P, 2) int  [elem_id, fiber_index]
│   │       │   └── FIBER_DATA         (F, 3) float [x, y, weight]
│   │       └── ...
│   └── RESULTS/
│       ├── ON_NODES/
│       │   ├── DISPLACEMENT/
│       │   │   ├── ID                 (N,) int
│       │   │   └── DATA/
│       │   │       ├── STEP_0         (N, 3) float  [Ux, Uy, Uz]
│       │   │       ├── STEP_1
│       │   │       └── ...
│       │   └── REACTION_FORCE/
│       │       └── (same structure)
│       └── ON_ELEMENTS/
│           ├── section.fiber.stress/
│           │   ├── 203-ASDShellQ4[201:0:0]/
│           │   │   ├── ID             (M,) int
│           │   │   ├── META/
│           │   │   │   ├── GAUSS_IDS      (n_gp,) int
│           │   │   │   ├── MULTIPLICITY   (n_gp,) int  [= num_fibers]
│           │   │   │   ├── NUM_COMPONENTS (n_gp,) int
│           │   │   │   └── COMPONENTS     (1,) string
│           │   │   └── DATA/
│           │   │       ├── STEP_0     (M, n_gp * n_fib * n_comp) float
│           │   │       └── ...
│           │   └── 203-ASDShellQ4[201:0:1]/
│           │       └── (same structure, different section)
│           └── section.fiber.strain/
│               └── (same structure)
├── MODEL_STAGE[2]/
│   └── (same structure, different step keys)
└── ...

Element keys

Format: {geom_id}-{ElementType}[{section_id}:{property_id}]

Examples: - 203-ASDShellQ4[201:0] -- ASDShellQ4 elements with geometry 203 - 204-ElasticTimoshenkoBeam3d[202:0] -- beam elements with geometry 204

The element type name is extracted with regex: \d+-(\w+)\[.

Element result data layout

Each row in a DATA/STEP_N dataset has all Gauss points, fibers, and components flattened into columns:

col = gp * (n_fibers * n_components) + fiber * n_components + component

For example, with 4 GPs, 8 fibers, and 5 components (= 160 columns): - Column 0: GP0, Fiber0, Component0 - Column 1: GP0, Fiber0, Component1 - ... - Column 5: GP0, Fiber1, Component0 - ... - Column 40: GP1, Fiber0, Component0 - ...

META/COMPONENTS string

Format: 0.1.2.3.4.Name0,Name1,Name2,Name3,Name4;...

One semicolon-separated block per Gauss point (all identical in practice). Each block has dot-separated component indices followed by comma-separated names. The parser extracts names from the first block.

When "Unknown" appears as a component name, ops-post falls back to generic labels (C0, C1, ...).

What the .mpco does NOT store

The HDF5 file contains node coordinates, element connectivity, section fiber data, and all result arrays. However, it does not store:

• Element local axes (shell normal direction, beam orientation)
• Beam cross-section profiles (for 3D visualization)

This information is derived from the TCL model files and stored in the .mpco.postdata companion file. See Postdata Format for details on how this file is generated and structured.

Section thickness detection

Fiber layer y-coordinates encode the through-thickness position:

thickness = (y_max - y_min) / (num_fibers - 1) * num_fibers

For a single-fiber section, the thickness is 2 * abs(y).