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I I I I I I I I I I I I I I I I I I I ~. . ;.a: Figure 1 Structural Implications this option would cross very close to the existing residential building and would occupy large areas of private property. It is unlikely that this alternate would fit within the anticipated easement. r-I I A more likely scenario would result if the easement was assumed to follow the north-south line between properties, but did not include any access along the north side of the Porto Bellagio Building. In this scenario, the bridge structure would have to skew at a greater angle to stay-off shore before sweeping back to align with the north easement. As a result, this alignment would result in a longer bridge structure and would have greater impacts to the mangrove fringe. It is our opinion that this represents the most likely scenario for approximate alignment of the project. We have added a plan view of this projected layout as Figure 1. For discussion sake, we have chosen this option for further development. The structural implications of this project increase dramatically as the degree of the skew and the severity of the reverse curve increases. Various assumptions of alignment will result in vastly different structural design criteria. First of all, as the skew increases, the length of the structure needed to make the crossing increases as well. Secondly, the increased skew exacerbates the curves needed at each end resulting in an increasingly odd shaped bridge structure. Various degrees of length and structure distortion will require differing approaches to the design. For the sake of discussion, we will consider the layout shown in Figure 1 as the probable alignment. This configuration results in a total structure length of approximately 165 feet. The distortion of the bridge structure shape is evident at the northern end where the alignment curves back to the north. From early discussions, it was apparent that the City felt that this crossing needed to be a clear span structure without any intermediate piers. A single span bridge presents two major challenges related to alignment. First of all, the single span will need to be adapted to fit the distorted structure shape above without the advantage of intermediate piers to better fit the alignment. The second major issue involves the vertical alignment of the corridor. With the longer span length, the structure depth would increase dramatically resulting in bridge deck elevation much higher than existing elevations at the embankments. There are two approaches to solving this problem. The most traditional approach would utilize the embankments on either side of the canal to gradually slope the alignment back down to grade. Due to the space constraints, this would need to be done with traditional or MSE retaining Page 2 of 7