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what is the difference between progressive placement(balanced cantileve) and span by span construction method

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in progressive placement(balanced cantilever, precast segments are placed on both sides of the pier until it reaches the mid of span and closure is made with segments from another pier as shown in figure 1. For progressive placement, temporary stays with temporary tower are placed on the pier to limit the cantilever stresses and deflections.
Figure 1









The segments are placed from one pier or abutment until it reaches the next pier or abutments for span by span construction method, figure 2 shown span by span construction method. placing segments alternatively at both side of the same pier in progressive placement method will help in counteracting hogging moment at the pier, this differs from span by span method, in span by span method the hogging moment at pier will be bigger than in progressive placement method.
Figure 2







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