ST RAFQA BASILICA, JRABTA, LEBANON

Built on the mountainside at Jrabta in Lebanon, this imposing structure is designed to give the impression of a ship – its roof appearing to form a continuation of the surrounding hillside. 

The challenging design of the roof, as a one-way slab resting on concave beams, included spans that averaged around 32 m and a concave shape with variable sectional geometry. As a consequence, the weight of the beams would have proved to be problematic and would have yielded large flexural effects.

The CCL design team responded to these challenges with a series of innovative solutions. Voided sections allowed the reduction of the beam self-weight while providing efficient inertia. Pot bearings were used at beam-column joints to act as a pinned connection without transferring any moment to the column, while temporary sliding bearings let the beams displace under post-tensioning (PT), shrinkage, and self-weight deformation. The locking of the bearing for the final stage secured the beams laterally.

The PT tendons were stressed prior to casting the slab, in order to maximise pre-compression in the beam, the sequencing of the post-tensioning within the beam itself. The other beams helped to introduce the post-tensioning in a gradual manner. Displacement monitoring was carried out to allow validation of design equations in the case of complex slab geometry.

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