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31
on Use of Self-Propelled Modular Transporters to Remove and
Replace Bridges (2007).
Note that simpler means than SPMTs can be used to trans-
port whole spans where space and conditions permit. These
include sliding, skidding, launching, and crane placement.
Such schemes have been used in a number of applications,
including bridges in Utah, Washington State, and California.
These approaches work best with a partnering arrangement
between the designer and contractor to ensure that the sys-
tem is designed to handle the erection stresses and deforma-
tions. The same design considerations apply for SPMT use
(Park 2011, Khaleghi 2011).
Figure 21. Prefabricated superstructure installed Time Savings
using SPMTs (Utah DOT).
The distinguishing characteristic of the bridge bent systems
considered in this study is speed of construction, so some way
of measuring it was necessary to evaluate the systems. Because
ponents (because these are no longer on the critical path).
of the wide variety of systems reviewed, a sophisticated
Other advantages of SPMTs include better control by the
method for evaluating the required construction time was
contractor over the environment at the work site, lower life-
deemed impractical. The method chosen is described in
cycle costs, and public favor for fewer disruptions to traffic.
Chapter 2, and consisted of comparing the construction time
Constructing the entire span in a controlled environment
of the precast system with that needed for a conventional CIP
adds benefits of reduced maintenance and improved quality.
system. A mini-workshop was arranged to obtain estimates of
The technology should be considered for all bridge replace-
construction time from professional design and construction
ment projects where reduced onsite construction time is a
personnel.
priority and a nearby space is available for constructing the
As the project developed, it became clear that most of the
bridge.
connection technologies could be applied in several locations
The SPMT process requires considerable coordination bet-
within the bridge. Thus, the decision was made to base the
ween the engineer of record, the contractor, a heavy lift con-
tractor, and multiple disciplines, including traffic control, evaluations of performance, TRL, and so forth on connection
roadway and geotechnical engineering, as well as utilities and technology rather than on connection location.
right of way. A test bed structure was needed to make comparisons
SPMTs are versatile devices that can be used to transport between the connection technologies. For that purpose, a
either a complete bridge or parts of one, depending on which bridge bent was selected that had dimensions typical of a free-
approach is the most efficient and what equipment is avail- way overpass in Washington State. The bent is shown in
able. For example, the interior bridge piers and end abutments Figure 22. The results of the time savings workshop are pre-
can be constructed at the final bridge site, without blocking sented in Appendix H.
traffic, while the superstructure is constructed off site at the The major conclusions from the time savings study are as
bridge staging area and brought in on SPMTs when the sup- follows:
porting structure is ready.
Seismic isolation techniques can be integrated fairly simply · The required curing time before construction may progress
with bridges where the entire superstructure is moved into has an important influence on the total construction time.
place. Isolation bearings may be used to support the superstruc- · In the precast systems, the majority of the time savings
ture, thereby providing a place to attach the superstructure, arises from precasting the cap beam, leading to 9 to 10 days
although connections that are appropriate to the ABC construc- savings for bar coupler, grouted duct, and socket-type con-
tion would need to be developed for each application. nections used to facilitate the placement of a cap beam.
SPMTs provide additional means for handling large weights Pocket-type connections saved about half that time due to
of precast and/or preassembled bridge elements. This advan- the curing time of concrete in the pocket.
tage has great potential for SABC because seismic connectivity · Precast columns provide significant time savings only under
requirements lead to larger and heavier elements. For more special circumstances, such as a bridge with a large number
information regarding SPMTs, refer to the FHWA Manual of columns.
