Bamboo Restaurant in Trancoso, Brazil

Project 01 · Trancoso, BAStructural design and optimization

Aerial view: the piassava thatch roof in four lobes over the light floor, on the lawn — From above: the piassava thatch roof in four lobes.

Under the roof: rings, rafters and the bamboo crown — Under the roof: rings, rafters and the crown.

The crown seen from below, with the radiating rafters.

The four bamboo culm clusters opening up to the eave — The four culm clusters open from the pedestal to the eave.

The base of a culm cluster: strapped culms on the steel plate and the concrete pedestal — The base of a culm cluster: strapped culms on the steel plate.

The bamboo structure without the piassava, against the sky — The structure before the piassava: arches, rings and rafters.

The crown oculus and the steel hub at the center, seen from below — The crown oculus and the steel hub at the center.

Bamboo arches and rings crossing, held by straps and bolts — Arches and rings cross, held by straps and bolts.

The open hall, without walls, under the piassava thatch roof — The open hall, without walls, under the roof.

Four culm clusters hold up the sky.

Each support is a bundle of culms that opens into arches, columns and rafters up to the crown.

The roof wraps around the central kitchen and rests on just four points. From each culm cluster spring diagonal arches, columns and rafters that rise to the rings and the crown, at almost 7 m. We developed the structural design and the optimization of this form: the calculation, the sections and the detailing of every connection and foundation.

That is 369 culms up to 6 m long, so they reach the site whole, and 234 m² of shade without a single wall.

Wind and structureFig. 01 to 03

Fig. 01 — CFD streamlines (OpenFOAM, k-ε) of the project, in the section through the center; behind, the structure beyond the section. East, where the wind comes from, is on the left. Hover to see the air move.

The sea breeze passes over and under.

East–west section through the center, east wind of 10 m/s at 10 m height.

Over the crown the air speeds up, from 9.6 to 11 m/s. Underneath, at table height, it flows at almost the same speed as outside: the hall stays in the shade and remains ventilated.

wind speed (m/s) · by quantiles06,48,810,012,8

White model of the structure, without the roof, seen from above — **Fig. 02** — *Without the piassava: culm clusters, arches, rings and rafters.*

White model of the structure: the crown oculus seen from below — **Fig. 03** — *The crown oculus, seen from below. Rhino model.*

“Under wind, the culm clusters swayed more than the code allows.”

The challenge: bracing the culm clusters.

In the previous version, the top of the culm clusters drifted 1.29 % of their height under wind. X-bracing on the sides and a collar 2.71 m above the ground braced the columns: drift fell to 0.84 %, and all 2,054 members of the model pass ISO 22156.

Each culm cluster gathers 23 culms that meet at the base and open into arches, columns and rafters. Steel straps keep the bundle working as a single element.

White model of the structure: a cluster of strapped culms opening under the roof — **Fig. 04** — *A culm cluster: the strapped culms open under the roof. Rhino model.*

Structural analysisFig. 05

The load path to the ground.

Karamba3D, under the south-west wind, the most unfavourable direction.

Under the south-west wind, the roof is sucked upwards and the windward lobe is pushed: the rafters on that side are the most stressed elements, with a utilization of 0.97.

The four culm clusters carry everything to the bases without uplift. The greatest compression at a base is 38 kN.

Fig. 05 — Karamba3D member model of the final version: deformation under self-weight and under wind, axial force and bending moment.