Stair for New U.S. Consulate Nuevo Laredo

The Project

The monumental stair at the new US Consulate in Nuevo Laredo is two stories tall, 525 SF, with two intermediate landings at each level. It consists of curved, built-up steel box beams supported at levels 1, 2, and 3 without intermediate support. The stairs are clad with stone treads and wood soffit sheathing. The guardrails are clad with wood paneling.

The Design/Build contractor is B.L. Harbert International, and the Architect of Record is Page Southerland Page. The bridging team included Moore Ruble Yudell as the design architect and Thornton Tomasetti/Weilinger Associates as the structural engineer.

Challenge

Design challenges included the lack of vertical support at intermediate landings, large mass from the stone treads and cladding, curved geometry yielding unbalanced bending, and meeting vibration constraints to ensure user comfort.

Solution

The stair’s structural system consists of 20” deep by 4” wide built-up box beans consisting of ½” thick plates (in lieu of HSS tubes to achieve the necessary curvature). The box beams were rigidly connected to levels 1, 2, and 3 to stiffen the structure. Given the large bending moments and forces associated with the challenging geometry, concrete piers and footings support the bottom of the stair at level 1 rather than the slab on grade. Large, embedded connections supported by concrete beams connect the stringers to levels 2 and 3. The inner stringer was supported at level 2 by an outrigger tube because the box beam curved sharply at level 2 before reaching the concrete beam. Complex and heavy embedded systems were needed to rigidly attach the stringers at each level and the concrete beams were designed for the resulting forces, moments, and torsion.