Design of Ultrahigh-Performance Concrete Waffle Deck for Accelerated Bridge Construction Sriram Aaleti and Sri Sritharan the delays and disruptions to the community (2). However, the transverse connections used between precast bridge deck panels have exhibited various serviceability challenges as a result of cracking and poor construction of connections (3). Therefore, it is imperative that durable and efficient field connections be developed to implement precast deck panels successfully in practice. These connections can use high-performance materials such as ultrahigh-performance concrete (UHPC) to ensure improved performance. Although these materials may adhere well to the precast components, it is important to design these connections to prevent cracking and leakage along the connection interfaces between precast elements. UHPC is a newly developed concrete material that exhibits high compressive strength, dependable tensile strength, and excellent durability properties, including very low permeability. The superior structural characteristics and durability of UHPC are perceived to provide major improvements over ordinary concrete and highperformance concrete in long-term structural efficiency and durability, and possibly in cost-effectiveness. Thus, the construction of new bridges and the renewal of aging highway bridges using UHPC have been explored for improving construction efficiency, enhancing bridge performance, and reducing maintenance and lifecycle costs. Previous use of UHPC for bridge applications (mostly in bridge girders) in the United States has proven to be efficient and successful (4–7). A prefabricated UHPC waffle deck system with field-cast UHPC connections was developed as part of the FHWA Highways for LIFE program that combined the advantages of UHPC with those of precast deck systems. An integrated experimental and analytical study was performed to evaluate the performance of the precast UHPC waffle deck system and UHPC connections under laboratory (8) and field (9) conditions. The UHPC waffle deck system performed extremely well under service and ultimate and fatigue loading, with the latter two tests completed under laboratory conditions. The ultimate capacity tests revealed that the UHPC waffle deck system had significantly higher capacity than the required design level capacity, suggesting potential improvements to the design of the UHPC waffle deck system and reduction in construction costs (10). Given the success of the precast UHPC waffle deck system and increased interest in full-depth precast deck panels for accelerated bridge construction, a design guide was developed to increase the awareness, improve efficiency, and broaden the use of UHPC waffle deck systems for new and replacement bridges. This guide provides the technical and practical information necessary to allow future bridge owners to consider the use of UHPC waffle slabs in a wide
As part of an innovation project funded by the FHWA Highways for LIFE program, a full-depth precast, ultrahigh-performance concrete (UHPC) waffle deck panel and appropriate connections suitable for field implementation of waffle decks were developed. After a successful full-scale validation test on a unit consisting of two panels with three types of connections under laboratory conditions, the waffle deck was installed on a replacement bridge in Wapello County, Iowa. The subsequent load testing confirmed the desirable performance of the UHPC waffle deck bridge. With lessons from the completed project and outcomes from a series of simple and detailed finite element analyses of waffle decks, a design guide was developed to help broaden the design and installation of the UHPC waffle deck panel cost-effectively in new and existing bridges. This paper describes the waffle deck design introduced in the guide as it is applied to new bridges. To minimize the cost of this new bridge deck system, information on maximum rib spacing and simplified connections, along with the design of the deck panel for positive and negative moments, is presented.
The combination of aging infrastructure, increasing numbers of structurally deficient or obsolete bridges, and increasing traffic volume in the United States demands both rapid improvements to the nation’s bridge infrastructure and increases in bridge longevity. The increased emphasis on work zone safety, user costs associated with traffic delays, and the environmental impacts of the construction process requires development of technologies and structural details suitable for accelerated construction. In consideration of these challenges, FHWA has been promoting accelerated bridge construction methods using prefabricated bridge elements. Precast concrete deck panels are being increasingly used by departments of transportation (DOTs) in several states for both bridge deck replacements and new structures to decrease construction time (1). The use of prefabricated, full-depth precast concrete deck systems can accelerate the construction and rehabilitation of bridge decks significantly while extending the service life and lowering the life-cycle costs of the bridge decks and minimizing S. Aaleti, Department of Civil, Construction, and Environmental Engineering, University of Alabama, South Engineering Research Center Building, 2037C, Tuscaloosa, AL 35487. S. Sritharan, Department of Civil, Construction, and Environmental Engineering, Iowa State University, Town Engineering Building, Room 376, Ames, IA 50011-3232. Corresponding author: S. Aaleti,
[email protected]. Transportation Research Record: Journal of the Transportation Research Board, No. 2406, Transportation Research Board of the National Academies, Washington, D.C., 2014, pp. 12–22. DOI: 10.3141/2406-02 12
Aaleti and Sritharan
variety of bridge types. This paper focuses on the recommendations developed for the design of the waffle deck slab and a suitable set of connections as applicable to new bridges. Ultrahigh-Performance Concrete UHPC is an advanced, highly engineered, cementitious material consisting of typical portland cement, fine aggregate made of sand, silica fume, crushed quartz, steel fibers, super plasticizers, and high water reducers. A few notable differences in UHPC composition compared with high-performance concrete are the lack of coarse aggregate, addition of steel fibers, high proportions of cementitious materials, and a low water–cement ratio. The use of powder and well-graded constituents helps to achieve a high packing density for UHPC, leading to significantly improved mechanical properties, such as increased compressive strength and considerable tensile strength, as compared with high-performance concrete and normal-strength concrete. The use of steel fibers in UHPC improves the material’s ductility as well its tension capacity. Recommendations based on an extensive literature review of UHPC research done in the United States for the material behavior as applicable in the design of structures are presented in the design guide (11). A selected set of recommendations critical in the design of precast waffle deck system are presented below: • In precast environments, UHPC is commonly subjected to heat treatment at 194°F at 95% humidity conditions to accelerate the full development of its strength and durability properties. However, this is not a requirement. Ambient or air curing of UHPC is also appropriate depending on the constraints set forth by the specific application (e.g., field cast joints between deck panels). • The compression behavior of UHPC is linear up to a strain of 0.0032. The design compressive strength of UHPC can be taken as 24 and 18 ksi for heat-treated and air-cured (ambient curing) conditions, respectively. • The tension behavior of UHPC can be represented with an elastic–perfectly plastic curve. The design tension strength of the UHPC can be taken as 1.2 ksi. • The elastic modulus of UHPC can be approximated to 46,200 f c′ (compressive strength, psi). In the absence of exact concrete strength, a modulus value of 7,500 ksi can be used for design purposes. • The unit weight of UHPC is 157 lb/ft3. • The minimum concrete cover for unprotected mild steel reinforcement in UHPC shall be 0.75 in. because of the excellent durability properties of UHPC. UHPC Waffle Deck System Analogous to the typical full-depth precast deck systems currently used in practice and developed in previous research, the waffle deck system consists of a series of UHPC waffle deck panels that are full depth in thickness (as required by the structural design) and connected to the supporting girders with robust connections (12). A UHPC waffle deck panel consists of a thin slab cast integrally with concrete ribs spanning in the transverse and longitudinal directions. This system is similar to the two-way joist system used by the building industry. A schematic of the waffle deck system is shown in Figure 1. The transverse ribs along the
13
deck panel act as T-beams, distributing wheel load effects to the adjacent bridge girders. The longitudinal ribs help to distribute the wheel load to the adjacent panels through the panel-to-panel connections. The reinforcement needed to resist the wheel loads is provided in the ribs along both directions. The spacing of the ribs in both directions is determined on the basis of the girder-to-girder spacing, panel dimensions, and minimum detailing requirements for panel-to-panel connections. As a result of the improved structural properties of UHPC, a UHPC waffle deck system for a given thickness has the same or higher capacity and is 30% to 40% lighter than a comparable solid precast fulldepth panel made of normal-strength concrete. The decreased weight of the UHPC panel has significant benefits, including increase in span length for a given girder size, increase in girder-to-girder spacing, improvement in bridge ratings when used for deck replacement projects, and reductions in seismic, substructure, and foundation loads when compared with solid precast deck panel systems. The presence of steel fibers in UHPC and the very minimal shrinkage of UHPC after steam curing of the precast elements also decrease the reinforcement requirements when compared with traditional precast deck panels. Design of Waffle Deck Panels The design of the waffle deck panels consists of two main steps: geometrical design and structural design. In geometrical design, critical dimensions of the waffle deck panel are determined primarily on the bridge functional requirements. The structural design phase consists of the design of the primary deck reinforcement (both transverse and longitudinal) to resist AASHTO design loads. Geometrical Design Several recommendations to arrive at the dimensions of the UHPC waffle deck panel are provided: • Thickness of the waffle deck panel. Considering the minimum thickness requirements of Article 9.7.5 of AASHTO 2010 and structural capacity requirements, an 8-in.-thick panel was found to be structurally sufficient for most cases. • Length and width (dimensions perpendicular and parallel to the direction of the traffic). The length and width of the panel depend on the handling requirements of the panels at the precast plant and at the job site, along with the transportation constraints. If the roadway width is more than 24 ft, the use of waffle panels with lengths equal to half the roadway width is recommended. The width of the panel will depend on the bridge geometry and is thus left to the designer’s judgment. However, 8- to 12-ft-wide precast panels are appropriate for practical use. • Thickness of slab. The thickness of the slab connecting the ribs on top in the UHPC waffle deck panel is dictated by the punching shear capacity of the plate between the ribs, the cover requirements of the top transverse and longitudinal reinforcements, and any anticipated surface wearing over time. On the basis of an experimental test completed at Iowa State University (9) and the limited data available on punching shear capacity of UHPC (8, 13), a flat plate thickness of 2.5 in. is recommended. • Dimensions of the longitudinal and transverse ribs. On the basis of the side cover requirements for the reinforcement, as well as previous studies completed by FHWA (14) and Iowa State University
14
Transportation Research Record 2406 Overlay (optional) Panel-to-center girder connection (longitudinal connection) filled with UHPC
Waffle deck panel
Shear studs
Open railing system Shear Pockets (filled with UHPC)
Panel-to-panel connection (transverse connection) filled with UHPC Shear hooks
Dowel bars
Steel girder Concrete girder
(a) Overhang region (solid section) CL of girder Traffic direction
Transverse rib spacing
Support rib spacing
CL of girder
Traffic direction
Panel length
Transverse rib
Girder spacing
Longitudinal rib Support ribs (at girder locations)
(b)
Longitudinal rib spacing
Deck panel width (typically varies from 8 to 12 feet)
(c) FIGURE 1 Waffle deck: (a) components of a bridge with UHPC waffle deck system and (b) top and (c) bottom views of precast waffle deck panel.
(9), the width of transverse and longitudinal ribs was set at 3 in. at the bottom with a gradual increase to 4 in. at the top of the ribs at the rib-to-plate interface (see Figure 2b). • Spacing of the longitudinal and transverse ribs. The spacing between the transverse and longitudinal ribs will depend on the girder-to-girder spacing, width of the panel, and minimum number of dowels required for establishing sufficient panel-to-panel connections as the dowels are located within the longitudinal ribs. On the basis of the limited available data on punching shear behavior and the results from detailed three-dimensional finite element analyses in ABAQUS (15) of waffle deck panels with
different rib spacing, a maximum allowable rib spacing of 36 in. is suggested to control the extent of flexural panel cracking under service loads and limit the extent of local damage to the flat slab at ultimate loads. • Support rib spacing. The support longitudinal ribs, which are located at the girder lines (see Figure 1b), provide an enclosure for the girder-to-panel connection referred to as the shear pocket connection, making the support rib spacing dependent on the top flange width of the girder. It is recommended that the support rib spacing is limited to a value less than the beam top flange width, with a minimum value of 12 in. (see Figure 2c).
Aaleti and Sritharan
15
B
A
Shear pocket spacing (2 to 4 ft)
B
Longitudinal ribs Support ribs (longitudinal)
18 in. < S lr < 36 in. 12 in. minimum
A (a)
(b)
2.5 in. Flat plate (2.5 in. thick) Transverse rib spacing
8 in. Panel-to-panel connection
4 in. 3 in. Transverse ribs
Panel 1
Panel 2 8 in.
S tr
18 in. < S tr < 36 in.
3 in. (rib width at bottom) 8 to 12 feet (c)
FIGURE 2 Recommended geometric dimensions for waffle deck panels: (a) schematic of bridge with UHPC waffle panel with (b) longitudinal (Section BB) and (c) transverse (Section AA) section details.
• Shear pockets. Shear pockets facilitate the connection to achieve full composite action between the precast waffle panels and supporting systems (concrete girders, steel girders, stringers, and so forth). If the shear studs and hooks are positioned uniformly along the girder length (typical in concrete girders), the shear pocket spacing should be equal to the transverse rib spacing. However, if a group configuration is used for the shear studs, the shear pockets can be placed 2 to 4 ft apart, in agreement with the maximum shear stud group spacing allowed by AASHTO guidelines (16) and recent studies on shear stud group spacing (17). Flexural Design The experimental testing of waffle deck systems at Iowa State University demonstrated that the wheel load is distributed to the supporting girders in a similar fashion to the traditional cast-in-place deck system (9). The extent of distribution of the wheel load among the transverse ribs of the waffle panel is dependent on the rib spacing and girder spacing. Therefore, the waffle deck panel system can be designed conservatively with the strip method described by the current AASHTO LRFD Bridge Design Specifications (16). The transverse strip, whose width is estimated according to Article 4.6.2.1.3 in the AASHTO specifications, is analyzed as a continuous beam supported by bridge girders that are considered as nonsettling rigid supports (16). The transverse strip width depends on the location of the critical section along the length of the panel in the positive
moment (M+), negative moment (M−), or overhang regions. The transverse strip width for the waffle deck system can be determined by using AASHTO specifications and is given by Equation 1. The entire transverse strip is designed to resist the dead load and live load effects with appropriate load factors at different limit states. 26 + 6.6 S Wts = 48 + 3.0 S 45 + 10.0 X
for M+ for M−
(1)
for overhang
where Wts = transverse strip width (in.), S = girder-to-girder spacing (ft), and X = distance of critical location from centerline of exterior girder (ft). Design Loads Design loads include the dead load due to self-weight of the waffle panel and wearing surface (if used), live load (design truck load), and collision loads. Design moments are determined at three regions along the panel cross section: the section at the center of the span between the girders, the sections over interior girders, and the overhang section. As detailed in the AASHTO guidelines, the interior spans between
16
Transportation Research Record 2406
girders are investigated for positive bending at the Strength I limit state. Sections over interior girders are examined for negative bending at the Strength I limit, and the overhang region is investigated for different combinations of dead, live, and collision loads for the Strength I and Extreme Event II limit states. The deck system should be designed to satisfy the serviceability requirements of AASHTO Article 5.7.3.4. The previously established geometric details and the following design parameters are used to determine the loads on the deck panels:
The positive and negative design moments due to the live load LL LL (M u+ and M u− , respectively) can be arrived at by using AASHTO LRFD Bridge Design Specifications Table A4-1. The maximum positive and negative moment demand varies from 8.29 to 13.17 kip-ft/ft and 3.81 to 13.41 kip-ft/ft, respectively, with the girder spacing changing from 4 to 10 ft. Design moment values for different girder spacing can be found in Aaleti et al. (11).
• The longitudinal and transverse rib spacings vary between 18 and 36 in. • A girder centerline spacing of 4 to 10 ft, which was established on the basis of an extensive review of frequently used standard details used by several state DOTs (including Alabama, Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Nebraska, New Jersey, New York, Ohio, Oklahoma, Virginia, and Wisconsin), is used.
Flexural Capacity Calculation
Dead Load Dead load on the waffle panel includes the self-weight of the panel and the weight of any future wearing surface or overlays (if used by the DOT). The weight of the waffle deck panel will depend on the rib spacing and is given by Equation 2: wwaffle
( )
S b h γ uhpc = hslab + 1 + tr w w Slr Str 12
The moment capacity of the waffle deck panel in the positive and negative bending directions can be estimated by using a transverse strip along the deck panel (see Figure 3a). As shown in Figure 3b, the equivalent strip width contains a number of ribs depending on the girder span and rib spacing in the waffle deck panel. The cross section of the transverse strip can be further divided into a combination of T-beams with a cross section, as shown in Figure 3c. The flange width for positive bending (b+f ) or negative bending (b−f ) can be estimated with Equation 5. The moment capacity for the T-beam cross section can be estimated by using the strain compatibility approach as shown schematically in Figure 4. b +f =
(2)
+
Wts 1 + integer value of Str
and
where 2
wwaffle = weight of waffle deck panel (lb/ft ), hslab = thickness of top slab (2.5 in.), Str = transverse rib spacing (in.), Slr = longitudinal rib spacing (in.), bw = rib width (in.), hw = rib height (in.) or hdeck − hslab (8 in. − 2.5 in. = 5.5 in.), and γuhpc = unit density of UHPC (157 lb/ft3).
b −f =
Wts− −
Wts 1 + integer value of Str
(5)
where W +ts and W −ts are the transverse strip widths for M+ and M− regions, respectively.
Deck Reinforcement
The design dead load is given by Equation 3: wudead = 1.25wwaffle i Wts + 1.5wws i Wts
Wts+
(3)
where wudead is the design dead load and wws is the weight of any future wearing surface or overlays. Live Load The precast deck panel is designed for HL-93 truck loading. More details of the HL-93 truck loading can be found in Section 3.6 of the AASHTO LRFD Bridge Design Specifications (16).
From the observations from the experimental testing of waffle deck panels and a detailed three-dimensional finite element model, two configurations for deck reinforcement in transverse ribs using No. 6 and No. 7 bars are proposed. The nominal positive and negative bending moment capacities of waffle deck panels for different girder spacing and transverse rib spacing configurations can be estimated by using the strain compatibility approach (Figure 4). The cross-section configurations are shown in Figure 5 and denoted by UWD6T6B and UWD6T7B. To simplify the design process, the estimated nominal moment capacities of the two cross sections with different girder and transverse rib spacings are presented in Table 1 and Table 2.
Design Moment The moment demand for the deck panel between the girders (M+ region) and at the interior girder locations (M− region) is estimated by the Strength I limit state. The positive and negative design DL moments due to the dead load (M u+ and M DL u− , respectively) can be estimated with Equation 4: DL MuDL + = Mu− =
Wudead S 2 10
(4)
Overhang Design The overhang region is designed for different combinations of dead, live, and collision loads for the Strength I and Extreme Event II limit states as required by AASHTO guidelines (16). An F-shape standard concrete railing is used for designing the overhang region for collision loads. In addition, based on the suggestions from Iowa DOT designers, using a solid cross section for the overhang region instead of a waffle configuration is recommended. The solid section
Aaleti and Sritharan
17
A Transverse strip for M–
Transverse strip for M+ +
W
–
Flange width = bf or bf
– ts
2.5 in. +
W ts
tire-load
4 in.
1.1875-in. clear cover
5.5 in. 1-in. clear cover Girder spacing
3 in. A
(b)
CL of girder
Overhang (typically less than 4.5 feet)
(a) +ve
Transverse strip (M+) W ts
– ve
Transverse strip (M–) W ts
1.1875 in.
2.5 in. 4 in. 5.5 in. 1 in.
Reinforcement in longitudinal ribs
3 in.
Transverse reinforcement
Transverse rib spacing
Longitudinal rib
(c) FIGURE 3 Cross section of equivalent strip for positive and negative bending: (a) three-dimensional view of waffle deck bridge, (b) rib cross section, and (c) cross section at Section AA. εtop = 0.007 c (h-c)
bf
C
c
d2
hf
fc = EUHPC εtop
Tst2
A st d1
h hw A st
d1 = location of tension steel from top of beam d 2 = location of compression steel from top of beam h = height of beam bw = rib width bf = flange width hf = flange thickness hw = rib height strain = 0.007
TUHPC
Tst1 1.2 ksi
h FIGURE 4 Strain and stress profiles for estimating positive nominal moment capacity of T-shaped UHPC beam ( A st 5 area of steel; « top 5 strain in extreme compression fiber; f c 5 stress in extreme compression fiber; E UHPC 5 Young's modulus of UHPC; T UHPC 5 tension force of UHPC; c 5 compression force; T st 5 force in steel).
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Transportation Research Record 2406
+ve
Flange width = bf
–ve
+ve
or bf
Flange width = bf
2.5 in.
–ve
or bf
2.5 in. 1.25-in. clear cover
1.25-in. clear cover
5.5 in.
5.5 in. 1-in. clear cover
1-in. clear cover
3 in.
3 in.
(a)
(b)
FIGURE 5 Reinforcement details recommended for transverse rib for (a) UWD6T6B and (b) UWD6T7B.
TABLE 1 Nominal Moment Capacities of UWP6T6B Bending Capacity (kip-ft/ft) by Transverse Rib Spacing (in.) Positive
Negative
Girder Spacing
36
33
30
27
24
21
18
36
33
30
27
24
21
18
4 feet 0 in. 4 feet 3 in. 4 feet 6 in. 4 feet 9 in. 5 feet 0 in. 5 feet 3 in. 5 feet 6 in. 5 feet 9 in. 6 feet 0 in. 6 feet 3 in. 6 feet 6 in. 6 feet 9 in. 7 feet 0 in. 7 feet 3 in. 7 feet 6 in. 7 feet 9 in. 8 feet 0 in. 8 feet 3 in. 8 feet 6 in. 8 feet 9 in. 9 feet 0 in. 9 feet 3 in. 9 feet 6 in. 9 feet 9 in. 10 feet 0 in.
12.00 11.79 11.59 11.39 11.21 11.04 10.88 10.73 10.59 10.45 10.32 10.19 12.63 12.46 12.29 12.13 11.98 11.84 11.70 11.57 11.44 11.32 11.20 11.09 10.98
12.00 11.79 11.59 11.39 11.21 11.04 10.88 10.73 10.59 13.19 12.99 12.81 12.63 12.46 12.29 12.13 11.98 11.84 11.70 11.57 11.44 11.32 11.20 11.09 10.98
12.00 11.79 11.59 11.39 11.21 14.08 13.84 13.61 13.40 13.19 12.99 12.81 12.63 12.46 12.29 12.13 11.98 11.84 11.70 11.57 11.44 11.32 11.20 13.13 12.98
12.00 15.19 14.89 14.61 14.34 14.08 13.84 13.61 13.40 13.19 12.99 12.81 12.63 12.46 12.29 12.13 11.98 11.84 13.95 13.77 13.60 13.44 13.28 13.13 12.98
15.52 15.19 14.89 14.61 14.34 14.08 13.84 13.61 13.40 13.19 12.99 12.81 15.18 14.95 14.73 14.52 14.32 14.13 13.95 13.77 13.60 13.44 13.28 13.13 12.98
15.52 15.19 14.89 14.61 14.34 14.08 13.84 16.49 16.20 15.92 15.66 15.41 15.18 14.95 14.73 14.52 14.32 14.13 13.95 13.77 15.75 15.55 15.35 15.16 14.98
15.52 18.59 18.19 17.81 17.45 17.11 16.79 16.49 16.20 15.92 15.66 15.41 17.72 17.43 17.16 16.90 16.65 16.42 16.19 15.97 15.75 15.55 15.35 17.20 16.98
24.65 24.57 24.46 24.39 24.29 24.19 24.10 24.04 23.95 23.86 23.78 23.70 23.63 23.55 23.48 23.39 26.62 26.52 26.41 26.31 26.22 26.16 26.06 25.97 25.89
24.65 24.57 24.46 24.39 24.29 24.19 24.10 24.04 27.51 27.37 27.28 27.16 27.04 26.92 26.84 26.73 26.62 26.52 26.41 26.31 26.22 26.16 26.06 25.97 25.89
28.55 28.42 28.26 28.14 27.99 27.88 27.74 27.60 27.51 27.37 27.28 27.16 27.04 26.92 26.84 26.73 26.62 26.52 26.41 26.31 26.22 26.16 26.06 25.97 25.89
28.55 28.42 28.26 28.14 27.99 27.88 27.74 27.60 27.51 27.37 27.28 27.16 27.04 26.92 26.84 26.73 26.62 26.52 26.41 26.31 26.22 26.16 26.06 25.97 25.89
28.55 28.42 28.26 28.14 27.99 27.88 27.74 27.60 27.51 27.37 27.28 27.16 27.04 26.92 26.84 26.73 29.80 29.71 29.58 29.45 29.32 29.20 29.08 28.96 28.85
28.55 28.42 28.26 28.14 31.64 31.45 31.32 31.14 30.97 30.81 30.69 30.53 30.38 30.23 30.08 29.94 29.80 29.71 29.58 29.45 29.32 29.20 29.08 28.96 28.85
32.33 32.17 31.97 31.83 31.64 31.45 31.32 31.14 30.97 30.81 30.69 30.53 30.38 30.23 30.08 29.94 32.98 32.80 32.67 32.50 32.33 32.21 32.05 31.90 31.79
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TABLE 2 Nominal Moment Capacities of UWP6T7B Bending Capacity (kip-ft/ft) by Transverse Rib Spacing (in.) Positive
Negative
Girder Spacing
36
33
30
27
24
21
18
36
33
30
27
24
21
18
4 feet 0 in. 4 feet 3 in. 4 feet 6 in. 4 feet 9 in. 5 feet 0 in. 5 feet 3 in. 5 feet 6 in. 5 feet 9 in. 6 feet 0 in. 6 feet 3 in. 6 feet 6 in. 6 feet 9 in. 7 feet 0 in. 7 feet 3 in. 7 feet 6 in. 7 feet 9 in. 8 feet 0 in. 8 feet 3 in. 8 feet 6 in. 8 feet 9 in. 9 feet 0 in. 9 feet 3 in. 9 feet 6 in. 9 feet 9 in. 10 feet 0 in.
14.06 13.79 13.52 13.28 13.05 12.83 12.62 12.42 12.23 12.05 11.88 11.72 14.87 14.65 14.44 14.23 14.04 13.85 13.68 13.50 13.34 13.18 13.03 12.88 12.74
14.06 13.79 13.52 13.28 13.05 12.83 12.62 12.42 12.23 15.60 15.34 15.10 14.87 14.65 14.44 14.23 14.04 13.85 13.68 13.50 13.34 13.18 13.03 12.88 12.74
14.06 13.79 13.52 13.28 13.05 16.75 16.44 16.14 15.86 15.60 15.34 15.10 14.87 14.65 14.44 14.23 14.04 13.85 13.68 13.50 13.34 13.18 13.03 15.52 15.33
14.06 18.18 17.79 17.43 17.08 16.75 16.44 16.14 15.86 15.60 15.34 15.10 14.87 14.65 14.44 14.23 14.04 13.85 16.57 16.35 16.13 15.91 15.71 15.52 15.33
18.60 18.18 17.79 17.43 17.08 16.75 16.44 16.14 15.86 15.60 15.34 15.10 18.16 17.87 17.58 17.32 17.06 16.81 16.57 16.35 16.13 15.91 15.71 15.52 15.33
18.60 18.18 17.79 17.43 17.08 16.75 16.44 19.85 19.48 19.13 18.79 18.47 18.16 17.87 17.58 17.32 17.06 16.81 16.57 16.35 18.90 18.64 18.39 18.14 17.91
18.60 22.56 22.04 21.55 21.09 20.66 20.24 19.85 19.48 19.13 18.79 18.47 21.44 21.07 20.72 20.39 20.07 19.76 19.46 19.18 18.90 18.64 18.39 20.76 20.48
24.55 24.48 24.38 24.28 24.19 24.10 24.01 23.93 23.85 23.77 23.69 23.62 23.55 23.45 23.39 23.33 26.51 26.41 26.32 26.23 26.13 26.01 25.93 25.84 25.76
24.55 24.48 24.38 24.28 24.19 24.10 24.01 23.93 27.37 27.25 27.13 27.05 26.94 26.83 26.72 26.61 26.51 26.41 26.32 26.23 26.13 26.01 25.93 25.84 25.76
28.42 28.26 28.15 28.01 27.86 27.76 27.63 27.50 27.37 27.25 27.13 27.05 26.94 26.83 26.72 26.61 26.51 26.41 26.32 26.23 26.13 26.01 25.93 25.84 25.76
28.42 28.26 28.15 28.01 27.86 27.76 27.63 27.50 27.37 27.25 27.13 27.05 26.94 26.83 26.72 26.61 26.51 26.41 26.32 26.23 26.13 26.01 25.93 25.84 25.76
28.42 28.26 28.15 28.01 27.86 27.76 27.63 27.50 27.37 27.25 27.13 27.05 26.94 26.83 26.72 26.61 29.68 29.55 29.43 29.30 29.19 29.07 28.96 28.81 28.70
28.42 28.26 28.15 28.01 31.49 31.32 31.15 30.98 30.82 30.67 30.51 30.36 30.22 30.08 29.94 29.81 29.68 29.55 29.43 29.30 29.19 29.07 28.96 28.81 28.70
32.19 32.00 31.81 31.67 31.49 31.32 31.15 30.98 30.82 30.67 30.51 30.36 30.22 30.08 29.94 29.81 32.81 32.69 32.52 32.35 32.19 32.04 31.88 31.78 31.64
for the overhang will not only help to address the variability in the types of railings and their capacities as used by DOTs, but will also provide adequate space to include the necessary details for attaching the railing to the precast deck. The negative moment capacity of the solid overhang for the UWP6B6T and UWP6T7B configurations was found to vary between 37.6 and 41.83 kip-ft/ft, depending on the transverse rib spacing. Connection Details The short-term and long-term performance and durability of bridges constructed with these deck panels will be influenced by the quality of the connections among the panels (i.e., panel-to-panel connections in both longitudinal and transverse directions) and of panels to girders. Panel-to-panel connections are subjected to bending moments and vertical shear forces under vehicular loading. In recent decades, a wide variety of deck-level connection designs have been deployed in bridge projects involving full-depth precast panels with substantial variance in observed performance under traffic loads. Several of these connection details are provided in the design guide (11). The connections that perform well typically consist of match-cast shear keys with epoxy adhesive or grouted
female-to-female joints with discrete reinforcement combined with field-cast concrete or grouted together with quality construction. A few connection details appropriate for the waffle deck panel-to-panel connection are shown in Figure 6. By realizing the superior durability and bond characteristics of UHPC, all the connection regions are designed with field casting of UHPC. The connection details presented in Figure 6, b to d, were developed for solid deck panels. However, these connections can be adopted for waffle deck panels by making the cells solid that are adjacent to the connections. The deck panels are made to act compositely with the girders by connecting them according to recommended connection details, as shown in Figure 7. These connections were developed as part of the Highways for LIFE program, and their performance was extensively tested under service, ultimate, and fatigue loads (8, 9). Figure 7a shows a longitudinal panel-to-panel-to-girder connection detail using dowel bars extending from the panels and shear hooks protruding from the girder, which are tied together with additional reinforcement placed longitudinally (along the girder length). The void between the panels is subsequently filled with UHPC. The deck panels are also supported between the edges by bridge girders. To provide a connection between the panel and girder, shear pockets are provided at intervals along the deck panel, and
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(a)
(b)
(c)
(d)
FIGURE 6 Recommended panel-to-panel connection details: (a) panel-to-panel connection detail tested as part of Highways for LIFE project and (b) headed, (c) straight, and (d) hairpin reinforcements (8, 18).
clusters of horizontal shear connectors are left protruding from the supporting girder at these locations. In this connection, shown in Figure 7b, shear hooks extending from the girder are embedded into UHPC that is poured to fill the shear pocket. When panels are connected to steel girders, shear studs instead of shear hooks may be used as per the AASHTO guidelines. Figure 7, c and d, show the details used in the Wapello County Bridge in Iowa, which was built with UHPC waffle deck panels.
(a)
Conclusions After a successful laboratory validation and field implementation and evaluation of a UHPC precast waffle deck system in Iowa, a design guide to broaden the applications of UHPC waffle deck panels to new bridges and deck replacement projects was developed. To minimize the cost of this new bridge deck system, information on maximum spacing of ribs and simplified connections is presented,
(b)
FIGURE 7 Recommended panel-to-girder connection details: (a) panel-to-girder connection (at centerline of bridge) and (b) shear pocket connection. (continued)
Aaleti and Sritharan
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(d) (c) FIGURE 7 (continued) Recommended panel-to-girder connection details: (c) panel-to-panel-girder connection at center girder and (d) shear pocket connection used in Wapello County Bridge.
along with design of the deck for positive and negative moments. The conclusions from this design study are as follows: • For broader applications, an 8-in.-thick UHPC waffle panel deck is recommended. This waffle deck is to have the ribs in both directions with recommended rib spacing of 18 to 36 in. • Two configurations for transverse rib reinforcement, which are applicable for different girder spacing, are proposed (Figure 5). The first configuration (UWD6T6B) consists of No. 6 bars at the top and bottom of the transverse rib. The alternate configuration (UWD6T7B) consists of a No. 7 bar at the bottom and a No. 6 bar at the top of the transverse rib. In both configurations, No. 6 bars are provided in the longitudinal ribs at top and bottom. • The UWD6T6B configuration can be used for waffle deck panels with any rib configuration (rib spacing < 36 in.) in bridges with a maximum girder spacing of 8.25 ft. This configuration can be used for bridges with a girder spacing of 8.5 to 10 ft if the transverse rib spacing is limited to 21 in. • The UWD6T7B configuration can be used for waffle deck panels with variable transverse and longitudinal rib spacing in bridges with a maximum girder spacing of 9.25 ft. For girder spacing of 9.5 to 10 ft, the transverse rib spacing is limited to 30 in. • To establish robust connections between waffle deck panels and girders, three connections including their details are presented. Their adequate performance under various loads has already been verified. Acknowledgments The authors are indebted to the FHWA Highways for LIFE program. The authors thank Julie Zirlin, Highways for LIFE Technology Partnerships coordinator, for her advice and suggestions and Ahmad
Abu-Hawash of the Iowa DOT Office of Bridges and Structures for his valuable input. Valuable feedback was received during the design guide development process from a number of people, including Benjamin Graybeal of the FHWA Turner–Fairbank Highway Research Center; Dean Bierwagen, Kenneth Dunker, Ping Lu, and Michael Nop of the Iowa DOT; Mathew Royce of the New York State DOT; Bruce Johnson of the Oregon DOT; Claude Napier of the Virginia DOT; and Brian Moore of Wapello County, Iowa. References 1. Issa, M. A., A. A. Yousif, and M. A. Issa. Experimental Behavior of Full-Depth Precast Concrete Panels for Bridge Rehabilitation. ACI Structural Journal, Vol. 97, No. 3, May–June 2000, pp. 397–407. 2. Berger, R. H. Full-Depth Modular Precast Prestressed Bridge Decks. In Transportation Research Record 903, TRB, National Research Council, Washington, D.C., 1983, pp. 52–59. 3. Issa, M. A., V. Cyro do, H. Abdalla, M. S. Islam, and M. A. Issa. Performance of Transverse Joint Grout Materials in Full-Depth Precast Concrete Bridge Deck Systems. Precast/Prestressed Concrete Institute Journal, Vol. 48, No. 4, July–August 2003, pp. 92–103. 4. Bierwagen, D., and A. Abu-Hawash. Ultra-High Performance Concrete Highway Bridge. Proc., 2005 Mid-Continent Transportation Research Symposium, Ames, Iowa, 2005, pp. 1–14. 5. Keierleber, B., D. Bierwagen, T. J. Wipf, and A. Abu-Hawash. Design of Buchanan County, Iowa Bridge Using Ultra-High Performance Concrete and Pi-Girder Cross Section. Proc., Precast/Prestressed Concrete Institute National Bridge Conference, Orlando, Fla., 2008. 6. Wipf, T. J., B. M. Phares, S. Sritharan, E. B. Degen, and T. M. Giesmann. Design and Evaluation of a Single-Span Bridge Using Ultra-HighPerformance Concrete. IHRB Project TR-529 report. Iowa State University, Ames, 2009. 7. Rouse, J. M., T. J. Wipf, B. Phares, F. Fanous, and O. Berg. Design, Construction, and Field Testing of an Ultra-High-Performance Concrete Pi-Girder Bridge. IHRB Project TR-754 report. Iowa State University, Ames, 2011.
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8. Aaleti, S. R., S. Sritharan, D. Bierwagen, and T. J. Wipf. Structural Behavior of Waffle Bridge Deck Panels and Connections of Precast Ultra-High-Performance Concrete: Experimental Evaluation. In Transportation Research Record: Journal of the Transportation Research Board, No. 2251, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 82–92. 9. Aaleti, S., S. Sritharan, D. Bierwagen, and P. B. Moore. Precast UHPC Waffle Deck Panels and Connections for Accelerated Bridge Construction. 2011 PCI National Bridge Conference, Salt Lake City, Utah, 2011. 10. Rouse, M., E. Honarvar, S. Aaleti, S. Sritharan, and T. J. Wipf. The Structural Characterization of UHPC Waffle Bridge Deck Panels and Connections. IHRB Project TR-614 report. Iowa State University, Ames, 2012. 11. Aaleti, S., B. Peterson, and S. Sritharan. Design Guide for Precast UHPC Waffle Deck Panel System, Including Connections. Report No. FHWA-HIF-13-032. FHWA, Washington, D.C., 2013. 12. Badie, S. S., and M. K. Tadros. NCHRP Report 584: Full-Depth Precast Concrete Bridge Deck Panel Systems. Transportation Research Board of the National Academies, Washington, D.C., 2008.
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13. Harris, D. K., and C. L. Roberts-Wollmann. Characterization of the Punching Shear Capacity of Thin Ultra-High Performance Concrete Slabs. Final report. VTRC 05-CR26. Virginia Department of Transportation, Richmond, 2005. 14. Graybeal, B. Analysis of an Ultra-High Performance Concrete TwoWay Ribbed Bridge Deck Slab. TECHBRIEF, FHWA-HRT-07-055. FHWA, McLean, Va., 2007. 15. ABAQUS User’s Manual, Version 6.11. Dassault Systèmes Simulia Corp., 2012. 16. LRFD Bridge Design Specifications, 6th ed. American Association of State Highway and Transportation Officials, Washington, D.C., 2010. 17. Badie, S. S., A. Morgan Girgis, M. Tadros, and N. Nguyen. Relaxing the Stud Spacing Limit for Full-Depth Precast Concrete Deck Panels Supported on Steel Girders (Phase I). Journal of Bridge Engineering, Vol. 15, No. 5, 2010, pp. 482–492. 18. Graybeal, B. Behavior of Field-Cast Ultra-High Performance Concrete Bridge Deck Connections Under Cyclic and Static Structural Loading. FHWA-HRT-11-023. Office of Infrastructure Research and Development, FHWA, McLean, Va., 2011. The General Structures Committee peer-reviewed this paper.
