Balanced roof reach
About 4.4 ft to either roof edge. Posts occupy the middle of the cabin; bases need a bridge between the chassis rails. The two clear paths around a post must be checked against the real interior.
Structure study / 02 · Individual interior supports
Bring the supports
inside the sheep.
Keep the side envelope of the bus. Explore a few interior posts, an overhead frame that spreads the roof loads, and foundations that carry those loads into the chassis.
DESIGN STATUSInvestigating
Geometry and load-path study. No final sections, capacity or weight saving established.
01 / What we now know
Individual posts. A different frame.
You report three individual posts inside BAAAHS. That makes an interior support system worth investigating. Their precise positions, roof framing, attachments and capacity are unknown; these drawings are our own trials.
The shared brief stays fixed: 20 people at 225 lb, dancing while moving up to 5 mph; 206 panels; 102-inch maximum road width. Keep the current deck footprint and height. Event deck/frame, skin, projecting mounts and speakers remain removable.
02 / Try the interior tradeoff
Where could the posts live?
Loading the interior layouts…
Individual posts / foundationRemovable roof frameChassis rails / load
Scroll the drawing sideways on a small screen. Connections and bracing are unsized and incomplete. The diagrams explain the load path; they are not fabrication details.
Post size controls space only, not steel strength. Dashed boxes add 1 inch per side for finish/access; foundations, gussets and cabinetry need additional space. The 30-inch centered aisle band is a layout test, not a code requirement. Actual doors, seats and equipment still need mapping.
Longest support span—
Post to far roof edge—
Peak allocated static load / post—
Centered aisle-band overlap—
Over a chassis rail
Loading placement comparison…
Closer to the chassis
About 5.8 ft to the far roof edge. A post can sit above a rail, but roof eccentricity still needs a resisting system. Local rail reinforcement, cross-ties and connections remain to be designed.
More usable cabin space
About 7.9 ft to the far roof edge at the default dimensions. Larger sideways roof reach and an outboard foundation transfer can consume the weight saved by fewer posts.
03 / Same load scenario, fewer supports
Count the load, not just the posts.
| Concept | Total posts | Longest span | Peak static allocation / post |
|---|---|---|---|
| Loading the comparison… | |||
Illustrative 13,000-lb uniform static scenario: 8,500 lb assumed dead load + 4,500 lb people. Load is allocated by midpoint tributary lengths, with equal sharing within each exterior pair. This is not a solved roof frame or a capacity check. It excludes crowd clustering, dancing, vehicle accelerations, wind and eccentric equipment. Dead load is held constant for comparison, not recalculated from these unsized concepts.
The three-post trial uses evenly spaced locations between the current front and rear supports; it does not reproduce BAAAHS. The four-post trial retains A/C/D/F longitudinal positions. Both require checks for wheel housings, driver space, exits, tanks and underfloor access.
04 / What the physical connection needs to do
A continuous path into the chassis.
Above the roof
Deck → transverse beams and longitudinal frame → removable bolted interfaces → individual posts. Keep transfer framing above the existing roof where the fixed deck height permits. Bracing or moment-resisting joints must stabilize the frame in both directions.
Through the cabin
Posts pass through detailed roof and floor openings. Preserve body/chassis movement and weather sealing. Do not assume the floor sheet or existing roof bows can take the new loads. Interior trim must allow access to the joints.
Below the floor
Post base → designed transfer assembly → verified chassis attachments. Check concentrated bearing, bending, uplift and torsion in the rails and connections. A post directly above a rail still needs this design.
The sheep skin: lighter removable regional panel frames attach to the primary roof frame and designed lower mounts. Their wind and handling loads belong in the analysis. Speakers and the head need dedicated load paths.
Road mode: interior posts and their retained fittings stay within the existing exterior. All projecting event assemblies come off. Retained post tops need their own stability check with the removable roof assembly absent.
05 / Width benefit, with an honest status
No exterior posts to add side width.
Interior supports can avoid increasing the donor’s width if every permanent fitting stays within its existing exterior envelope. That resolves the geometric source of our exterior-post problem; it does not establish the donor’s measured width, registration eligibility or complete road compliance.
The existing exterior v5 model still fails at approximately 103.35 inches. The interior concept has no complete retained-hardware model or road-width audit yet. The 102-inch invariant remains unchanged.
Existing geometry audit ↗Project width requirement ↗06 / Turn the concept into a lighter design
Develop four.
Keep three in the comparison.
We can develop the load model and connection concepts now. Final positions, member selection and fabrication release depend on the donor measurements that are currently deferred.
- Reserve interior routesMap four candidate posts against furniture, exits and chassis access. Check whether a slightly offset aisle preserves the cabin; the default over-rail case overlaps the centered test band by about 1.1 inches.
- Design roof and foundations togetherCompare three versus four individual posts, load distribution, transverse restraint, vibration and removable joints under the same moving-dance-floor requirements.
- Count the complete weightInclude roof framing, floor, posts, bases, joints, bracing and panel/equipment mounts. Compare against the 4,466-lb current frame/floor subtotal on an equivalent basis.
- Reconcile and reviewVerify the donor, retained road envelope, axle loads and vehicle stability; then produce reviewed member schedules and assembly drawings.
Evidence & assumptions
Blue Bird’s family manual describes two main chassis rails and body mounts with rubber pads to reduce vibration and fatigue. That supports treating the chassis interface and body movement as explicit design work; it does not rate this conversion. Chassis manual. The body manual describes the original structure, not dance-floor capacity.
Study data & assumptions ↓ · Shared brief · Earlier exterior-frame comparison
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