Engineering the Q’eswachaka: structural analysis of a historic suspension bridge rebuilt with natural fibres

The 29-metre-long Q’eswachaka suspension bridge, located in the Cusco region of Peru, is annually rebuilt by local communities using traditional techniques and natural fibres, and is recognised by UNESCO as Intangible Cultural Heritage. Although previous studies have documented its cultural significance, construction process, and selected material or structural aspects, few have integrated the traditional rope-making system, rope mechanical behaviour, and global structural response within a single engineering framework. This study addresses this gap by documenting the fabrication of ropes made from Festuca dolichophylla fibres, locally known as Q’oya, conducting tensile tests, performing an in situ static load test, and calibrating a three-dimensional finite element model based on measured deflections. The results showed clear differences among rope types: twisted ropes exhibited higher stiffness and strength, whereas braided ropes showed greater deformation capacity. The calibrated model reproduced the measured deflections and estimated tensile safety factors of approximately 15 and 20 for the upper and lower main cables, respectively, under the analysed single-person static load condition. Overall, the study provides a conservation-oriented structural assessment framework for natural-fibre heritage suspension bridges.