The Implementation of Full Depth UHCP Waffle Bridge Deck Panels

APPENDIX A: WAFFLE DECK PANEL FABRICATION

Prototype Bridge

A full–scale single–span, two–lane, prototype, full–depth bridge system was designed as a replacement of an existing bridge in Wapello County, Iowa, and the details of this structure are shown in Figure 1. The prototype bridge is 33 ft wide and 60 ft long and it consisted of prefabricated, full–depth, precast concrete panels installed on five standard Iowa "B" girders placed at a center–to–center distance of 7ft 4 inches.

The bridge cross section consists of two 16'-2" long panels on a 2 percent slope away from the crown. The panels are jointed at the crown with UHPC infill and are bearing on five 3'-3" tall Iowa "B" girders placed at a center-to-center distance of 7'-4". The 60' length of the bridge is made up of seven 8'-0" wide pieces jointed transversely with UHPC infill.

Figure 1: Plan and cross section details of the proposed UHPC Waffle Deck Bridge in Wapello County.

The waffle deck is expected to be made fully composite with girders using the following connections:

Shear pocket connection: This connection is formed between the girder and the waffle deck using shear pockets. In this connection, the shear pockets in the waffle deck are filled with UHPC and a shear hook extended from the girder is embedded into the UHPC fill (see Figure 2). This will cause the girders and the waffle deck to act in a composite manner.

Figure 2: Shear pocket connection details between girder and the waffle deck
Waffle panel to girder longitudinal connection: This connection is formed between the central girder and the waffle deck. In this connection, the dowel bars from the panels and the shear hook from the girder are tied together with additional reinforcement along the girder length and the gap between the panels is filled with UHPC (see Figure 3). This connection will provide a positive moment connection between the girder and the panels.

Figure 3: Connection details between the central girder and the waffle deck

The bridge consisted of waffle deck panels which were 16 ft wide (full width) and 8 in. thick. They are connected across the length of the bridge using a transverse joint connection shown in Figure 4. In this connection, the dowel bars from the panels are tied together with additional transverse reinforcement and the gap between the panels is filled with UHPC (see Figure 4). This connection will provide continuity between the panels and facilitate load transfer between the panels.

The dowel bars from the panels are tied together with additional transverse reinforcement and the area is cast with UHPC.

Figure 4: Connection details between the waffle deck panels

Panel Details and Prefabrication

The UHPC waffle panels were designed with conventional mild steel reinforcement primarily to resist the transverse flexural moments (i.e., for moments induced about the bridge longitudinal axis) in accordance with the current AASHTO slab deck design provisions (AASHTO, 2007). This resulted in Grade 60 No. 7 (db = 0.875 in, where db is diameter of the bar) and No.6 (db = 0.75 in.) mild steel reinforcement located at 1¼ inches from the bottom surface and at 1 5/8 inches from the top surface of the panel, respectively. In the longitudinal direction, the panels were detailed with Grade 60, No. 7 and No.6 mild steel reinforcement at 2 1/8 inches from the bottom surface and at 2 3/8 inches from the top surface, respectively. All the reinforcement was provided along panel ribs in both directions. Figure 5 shows the cross–section and reinforcement details of a typical waffle deck panel designed for the prototype bridge.

For the experimental investigation, a waffle deck region between two adjacent girders as identified in Figure 1 was chosen. Accordingly, two waffle deck panels with dimensions of 8 ft (length) by 9 ft 9 in. (width) were fabricated by Coreslab Structures (Omaha) Inc. in September 2009. Commercially available standard Ductal® mix was used as the UHPC mix design.

Table 1. Strength gain of UHPC in the waffle deck panels
Traffic Occurring During Total Roadway Closure Hours		Traffic Normally Occurring During Those Hours
Time (hours)	Strength (psi)	Time (hours)	Strength (psi)
22	1800	20	850
24	4500	26	5000
26	6250	44	10650
44	11650	52	13800
52	13400	–	–
28 days (post–steam cure strength)	21843	28 days	22120

After curing, the panels were transported to the Iowa State University's (ISU) Structures Laboratory. Both the deck panels exhibited a very smooth surface on all sides that were in contact with the formwork. Other surfaces, especially the underside of the panels appeared somewhat rough.

The Form View shows reinforcing and rib spacing of 2'-1" at all locations along the length of the panel except the shear pocket over the beam which is 1'-1". Across the width of the panel the spacing is 2'-2" for all ribs. Section A shows the view across the width of the panel, the dowel bars for the transverse joint, and the reinforcing layout top and bottom. Section B show the view along the length of the panel, the keyway for the longitudinal joint, and the reinforcing top and bottom. Detail 1 shows the typical rib and deck dimensions. Detail 2 shows the longitudinal keyway dimensions. Detail 3 shows the transverse joint dimensions and reinforcing locations. Detail 4 shows the opposite transverse joint dimensions and reinforcing locations. Detail 5 shows the shear pocket dimensions and block out location.

Figure 5: Reinforcement details of the UHPC waffle deck test panels

a.) Mild steel reinforcing is placed in the form work. b.) A specially designed 8’ wide concrete placing bucket was used to pour the UHPC into the form. c.) The bucket was moved along the length of the form. d.) The form was filled to a predetermined level of approximately 5" e.) The voids that form the ribs of the panel were placed into the fresh UHPC and displaced the concrete to form the final shape.

Figure 6: Construction sequence of the UHPC Waffle deck panel at the precast plant.