When planning railway structures, it is imperative to be mindful of the factors that
frequently control design and construction. Many in the railway industry would agree,
that the driving factor of design and construction is track time. Operations are key,
and with greater traffic demands on an ever-aging infrastructure, track time is at a
premium. It is important for railways to balance time for operations,
maintenance/repair and new construction. The designer is challenged with producing
plans and specifications that will yield the best structure in the shortest amount of time.
Many times the design efficiency is sacrificed for a shorter construction period. Lets
briefly examine one simple scenario: the superstructure replacement of a short, singlespan
bridge. In its nearly 100-year life span, the steel superstructure had been raised
while being converted from a ballasted deck to an open deck. This conversion
included the use of what is known as a grillage. A grillage (also known as cribbing) is a
temporary steel support, usually in the form of short sections of steel H-piles, welded
together side-by-side to form a shallow (1-2 foot) bearing seat.
The steel is subsequently encased in concrete. This technique is most common to
rehabilitation projects. When replacing this superstructure, the most efficient design
might include cutting the backwall, removing the grillage (thus lowering the beam seat)
When planning railway structures, it is imperative to be mindful of the factors that
frequently control design and construction. Many in the railway industry would agree,
that the driving factor of design and construction is track time. Operations are key,
and with greater traffic demands on an ever-aging infrastructure, track time is at a
premium. It is important for railways to balance time for operations,
maintenance/repair and new construction. The designer is challenged with producing
plans and specifications that will yield the best structure in the shortest amount of time.
Many times the design efficiency is sacrificed for a shorter construction period. Lets
briefly examine one simple scenario: the superstructure replacement of a short, singlespan
bridge. In its nearly 100-year life span, the steel superstructure had been raised
while being converted from a ballasted deck to an open deck. This conversion
included the use of what is known as a grillage. A grillage (also known as cribbing) is a
temporary steel support, usually in the form of short sections of steel H-piles, welded
together side-by-side to form a shallow (1-2 foot) bearing seat.
The steel is subsequently encased in concrete. This technique is most common to
rehabilitation projects. When replacing this superstructure, the most efficient design
might include cutting the backwall, removing the grillage (thus lowering the beam seat)
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