Final answer:
The 'bi-polar structure' is likely related to the urban design and organization during Fort Lamy's colonial period, but the question lacks sufficient context to provide a definitive answer.
Step-by-step explanation:
The existing bi-polar structure of the colonial city Fort Lamy refers to the town's urban design and how it was organized during the colonial period. The question hints at the specific design patterns or urban planning schemes used, possibly concerning the manner in which colonial and indigenous spaces were delineated within the city. However, to accurately determine what the 'bi-polar structure' specifically refers to in the context of Fort Lamy, it would be necessary to look at historical urban planning documents or studies pertaining to that city during the period in question, such as those by Candilis-Josic-Woods, which might outline the dichotomy of urban zones within the city.