La producción simbólica en el taller narrativo

Early in the development stage it was recognized that transportation limitation will play

an important role in determining the modular unit configuration and the maximum span

length. Also, the number and details of the transverse and longitudinal joints would have

a marked effect on the durability of the new systems. These limitations played an

important part in the choice of the new concept. In addition to achieving the goal of

accelerated construction, it is important to limit or eliminate any type of forming and

shoring; in other words, all construction work needs to be performed “from the top”.

The research team studied several concepts before arriving at the concept presented in Figures 4.2 to 4.5. The new concept combines the traditional steel girders and deck system with some features of the railroad flat car system. Figure 4.2 shows the basic components of the proposed system. The new system relies on a wide interior unit with depth varying between 9 and 12 ft and a variable width exterior unit. These units are fabricated to create a self contained stay-in-place steel pan form. A cold formed steel plate or corrugated metal form are welded to the top of the steel girders under factory controlled conditions followed by welding a welded wire mesh to the plate as shown in Figures 4.2(b). As seen in Figure 4.2(a) the steel pan depth is only 4 inches, the welded steel mesh is welded to the top of the steel pan. The depth of cast-in-place concrete deck will vary between 6 to 8 inches and will provide sufficient concrete cover to the steel mesh.

The welded wire mesh is designed to provide the necessary deck reinforcement. The stay-in-place steel pan form eliminates the need for forming or shoring and allows all construction work to be performed “from the top”.

Figure 4.2(a) Exterior and Interior Units Details

Figure 4.2(b) Adding Deck Reinforcement

The units are transported using traditional methods of transportation to the construction site and erected in place to form the bridge system as illustrated in Figure 4.3. Each unit is tied to adjacent units using steel bolts spaced at predetermined distances. Once the units are assembled and tied together, sections of steel mesh for lap-splicing are placed on top of the longitudinal joints and tied to the welded steel mesh as shown in Figure 4.4.

As stated earlier, the steel pan depth is only 4” and the wire mesh sections are welded at the manufacturer.

It should be pointed out that while Figure 4.2 shows a unit width of 12 feet which is later used in the optimization work presented in Chapter 6, it is anticipated that the practical width limit will be between 9 to 10 feet to facilitate transportation of the units without requiring special permits.

The concrete is then placed in the stay-in-place steel pan forms to form the bridge deck,

as shown in Figure 4.5. The use of fast setting concrete will allow traffic on the bridge

within three days. The welded wire fabric placed on top of the joints are tied to the

existing steel mesh using common wire ties. The cast-in-place concrete depth is 8” deep

which places the welded wire fabric approximately at mid depth of the slab.

Figure 4.3 Erection and Assembly

Figure 4.4 Installation of Steel Mesh Over Transverse Joints

Figure 4.5 Placement of Concrete Deck

To facilitate construction and simplify the field work for forming and casting the exterior

unit the exterior unit can be prefabricated and partially filled with concrete as shown in

Figure 4.6. Block outs are fabricated during the construction of the unit to facilitate

connecting and bolting the unit to adjacent interior units. The exterior unit is placed and

tied to the interior unit as shown in step 1 of Figure 4.6. The welded wire fabric sections

are then placed over the joints as earlier described. The cast in place concrete is then

placed to form the deck as shown in Figure 4.6 (step 2).

If desired, continuity for live loads could be easily achieved by providing negative moment reinforcement over the support area prior to casting the deck concrete.

Figure 4.6 Exterior Unit Details

It is envisioned that a simple joint detail as shown in Figure 4.7 will provide the

necessary durability and performance of the proposed system. Joint details and the

optimum number of bolts required to develop monolithic behavior will be established through research and testing of the proposed modular bridge system.

Figure 4.7 Transverse Joint Details

The method described above will allow accelerated bridge construction, while eliminating all the construction joints, typical in modular bridge systems. Long term durability could be achieved through applying durable coatings to the interior and exterior of the modular units at the factory or through using high performance steel.

The proposed concept solves many of the problems associated with transverse and

longitudinal joints. Though a very significant amount of concrete must still be poured

to construct the bridge deck, the work can be performed without much intrusion to

whatever is going on below the bridge. Once the units are up, the deck form plates

provide a safe work platform while also adding some stability (note that these plate

should probably be corrugated to ensure their own stability). The system achieves all