Abstract

Elmina Castle, built in 1482 by the Portuguese, was the first of a series of European trading bases along the west coast of Africa and served as a commercial outpost for over four centuries of trade. The structure was captured by the Dutch in 1637 and became a major hub for the Atlantic Slave Trade. The castle is currently a UNESCO World Heritage Site and a Ghanaian national museum. The building is constructed from a combination of mud- and lime-mortared rough-hewed sandstone masonry. The primary focus of the analysis is the western curtain wall, which faces the only side of the castle accessible by land. A flaring at the base of the curtain wall points to the likely presence of an additional tower located approximately midway along the length of the wall in early Portuguese times. Using a pushover analysis with nonlinear 3D FE under Abaqus/CAE explicit formulation, we assess the stability of the tower-wall system to determine if a historical earthquake could have caused the tower to collapse. During the Dutch occupation, a two-story building, brick vaulted at the ground level, was added along the entire curtain wall. Using 2D plane strain nonlinear models, we evaluate the structural capacity of this vaulted system, considering its sensitivity to the density and the thickness of the loose material above the vault as well as the compressive strength of the rough-hewed sandstone masonry in the walls.

Abstract

Elmina Castle is the first of a series of European trading bases along Africa’s west coast, and it is the oldest and best preserved early European building in Sub-Saharan Africa. The structure shows a combination of mud-mortared and lime-mortared sandstone masonry macro elements and has undergone reconstructions and modification throughout time under Portuguese and Dutch occupation. This study focuses on the structural analysis of Elmina Castle’s east curtain wall, which features two massive masonry buttresses built only alongselected portions of the wall. The hypothesis that these buttresses were built in correspondence of deep voids in the foundation bedrock platform is numerically evaluated using pushover analysis. The lateral capacity is determined based on energy considerations using nonlinear FE models in Abaqus/CAE Explicit and concrete damaged plasticity. Results indicate that, at a later Dutch stage of structural modification, loose soil filling might have caused rotational instability of the curtain wall, requiring the addition of the buttresses.