Valencia has experienced a surge in its cultural development during the last thirty years, exemplified by exhibitions and performances at such iconic institutions as the Palau de la Música, the Palacio de Congresos, the Metro, the City of Arts and Sciences (Ciutat de les Arts i les Ciències), the Valencian Museum of Enlightenment and Modernity (Museo Valenciano de la Ilustracion y la Modernidad), and the Institute of Modern Art (Instituto Valenciano de Arte Moderno). The various productions of Santiago Calatrava, a renowned structural engineer, architect, and sculptor and of the architect Félix Candela have contributed to Valencia's international reputation. These public works and the ongoing rehabilitation of the Old City (Ciutat Vella) have helped improve the city's livability and tourism is continually increasing.

Answer this question, if possible (if impossible, reply "unanswerable"): Which structural engineer's work has helped Valencia's reputation?
Santiago Calatrava