{
  "revision": "lightweight-comparison-1",
  "brief": {
    "revision": "lightweight-brief-2",
    "date": "2026-10-19",
    "status": "Requirements fixed for concept comparison; neither concept is selected, load-rated or approved for fabrication",
    "objective": "Reduce the installed weight of the dance-floor and sheep-support systems while preserving the shared functional requirements",
    "requirements": {
      "people": 20,
      "person_allowance_lb": 225,
      "total_people_allowance_lb": 4500,
      "use": "Dancing while the bus moves at up to 5 mph",
      "maximum_event_speed_mph": 5,
      "deck_footprint_m": [
        11.396,
        2.6984
      ],
      "deck_surface_height_m": 3.4004,
      "deck_geometry_basis": "Preserve current modeled footprint and height for both concepts; donor geometry remains unmeasured",
      "exterior_panel_count": 206,
      "road_width_maximum_in": 102,
      "road_requirement_source": "project-constraints.json",
      "road_retained": "Donor bus, all permanent supports and every retained fitting",
      "road_removed": "Roof deck/removable frame, sheep panels, projecting support assemblies, speakers and event equipment",
      "removable_connections": true
    },
    "variables": [
      "Station count and positions, subject to actual attachment access",
      "Member geometry, material specification and wall thickness",
      "Floor joist arrangement and deck construction",
      "Truss layout and available depth without changing the deck height",
      "Transverse bracing, removable connections and module sizes",
      "Panel subframes and dedicated equipment supports"
    ],
    "concepts": [
      {
        "id": "six",
        "name": "Optimized six-station frame",
        "station_ids": [
          "A",
          "B",
          "C",
          "D",
          "E",
          "F"
        ],
        "status": "Concept; existing v5 is a mass and geometry reference only"
      },
      {
        "id": "four",
        "name": "Four-station frame with longitudinal trusses",
        "station_ids": [
          "A",
          "C",
          "D",
          "F"
        ],
        "status": "Concept; retained positions are a first comparison, not optimized or field-verified"
      }
    ],
    "deferred_measurements": [
      "Actual exterior and rub-rail width and clearances along uprights",
      "Chassis rail dimensions, spacing, condition and accessible attachments",
      "Scale weights, axle loads, GVWR and axle/tire ratings",
      "Equipment weights and locations, including speakers and head"
    ],
    "unresolved_engineering": [
      "Acceleration, braking, cornering, bumps, synchronized dancing, wind and fatigue loads",
      "Floor vibration, crowd distribution and frame reactions",
      "Transverse stability and removable joint stiffness/strength",
      "Chassis attachment uplift, bearing, torsion and body/chassis movement",
      "Whole-vehicle stability and complete road configuration"
    ],
    "not_adopted": [
      "Rub-rail cutting or welding uprights to the bus body",
      "Using the existing body as an assumed dance-floor support",
      "Treating a 2x live-load sensitivity as a validated dancing factor",
      "Any final member sizes, connection details or fabrication drawings"
    ],
    "interior_investigation": {
      "page": "interior-supports.html",
      "data": "interior-support-study.json",
      "basis": "User confirms BAAAHS has individual cabin posts, not paired wall portals. Exact structure unknown.",
      "trials": "Three and four individual posts; centerline, over one rail, or near one wall. Illustrative positions only.",
      "status": "Supplementary concept investigation; no final sections, mass, capacity or road-envelope acceptance."
    }
  },
  "reference": "subframe-study-v5",
  "mass_basis": "Current schedule: nominal sharp-corner steel at 7850 kg/m\u00b3; plywood at 600 kg/m\u00b3. Rounded source member masses. No structural adequacy implied.",
  "excluded_mass": [
    "connections and fasteners",
    "guardrails",
    "panels and panel subframes",
    "head",
    "speakers and other equipment"
  ],
  "categories": [
    {
      "id": "stations",
      "label": "Posts, lower beams, caps & headers",
      "lb": 1572.380946355857
    },
    {
      "id": "joists",
      "label": "37 floor joists",
      "lb": 1219.4870032763274
    },
    {
      "id": "floor",
      "label": "Plywood floor",
      "lb": 774.8885766138333
    },
    {
      "id": "longitudinals",
      "label": "Longitudinal roof beams",
      "lb": 556.711304469562
    },
    {
      "id": "bracing",
      "label": "Side & roof diagonals",
      "lb": 342.2676620422125
    }
  ],
  "baseline_lb": 4465.735492757793,
  "concepts": [
    {
      "id": "six",
      "name": "Optimized six-station frame",
      "station_ids": [
        "A",
        "B",
        "C",
        "D",
        "E",
        "F"
      ],
      "status": "Concept; existing v5 is a mass and geometry reference only",
      "station_x_m": [
        -4.75,
        -3.0719,
        -0.85,
        2.3861,
        4.45,
        5.55
      ],
      "spans_m": [
        1.6781000000000001,
        2.2218999999999998,
        3.2361,
        2.0639000000000003,
        1.0999999999999996
      ],
      "maximum_span_m": 3.2361,
      "removed_station_ids": [],
      "gross_removed_station_mass_lb": 0.0
    },
    {
      "id": "four",
      "name": "Four-station frame with longitudinal trusses",
      "station_ids": [
        "A",
        "C",
        "D",
        "F"
      ],
      "status": "Concept; retained positions are a first comparison, not optimized or field-verified",
      "station_x_m": [
        -4.75,
        -0.85,
        2.3861,
        5.55
      ],
      "spans_m": [
        3.9,
        3.2361,
        3.1639
      ],
      "maximum_span_m": 3.9,
      "removed_station_ids": [
        "B",
        "E"
      ],
      "gross_removed_station_mass_lb": 524.126982118619
    }
  ],
  "span_sensitivity": {
    "moment_ratio": 1.4523970132564057,
    "deflection_ratio": 2.1094570841161278,
    "basis": "Simply supported beam, same uniform line load and unchanged section/EI. This is a span sensitivity, not a truss analysis or whole-frame response."
  },
  "diagram": {
    "donor_length_m": 12.446,
    "donor_height_m": 3.2004,
    "deck_length_m": 11.396,
    "deck_width_m": 2.6984,
    "deck_height_m": 3.4004,
    "station_base_m": 0.5277625,
    "axles_x_m": [
      -3.81,
      3.1242
    ],
    "stations": [
      {
        "id": "A",
        "x_m": -4.75,
        "purpose": "Behind door / head-support interface",
        "verify": "Stepwell, front suspension and head load transfer"
      },
      {
        "id": "B",
        "x_m": -3.0719,
        "purpose": "Just behind front wheelwell",
        "verify": "Actual arch, suspension, luggage bay and speaker brackets"
      },
      {
        "id": "C",
        "x_m": -0.85,
        "purpose": "Ahead of generator envelope",
        "verify": "Tank, driveshaft, generator service and body mounts"
      },
      {
        "id": "D",
        "x_m": 2.3861,
        "purpose": "Just ahead of rear wheelwell",
        "verify": "Actual arch, suspension and rear speaker brackets"
      },
      {
        "id": "E",
        "x_m": 4.45,
        "purpose": "Rear deck / rump interface",
        "verify": "Rear engine, cooling and service access"
      },
      {
        "id": "F",
        "x_m": 5.55,
        "purpose": "Rear deck edge / rump interface",
        "verify": "Rear engine, cooling, service hatch and stair interface"
      }
    ]
  },
  "budget_basis": "User-controlled mass targets only. Shared reductions apply equally to both concepts. Four-station extra steel/joints is a NET allowance relative to the retained v5 members, including all reinforcement, replacements and differential fittings. Unlisted common systems remain excluded. No resulting value is a sized design or total vehicle weight."
}