Abstract
This research develops design provisions for partial-depth precast deck panels for California. Based on a literature review, including AASHTO LRFD Bridge Design Specifications (2012), the Precast/Prestressed Concrete Institute Bridge Design Manual, as well as Caltrans Semi-Standard XS Sheets, Bridge Memo to Designers, Amendments, and other specifications, a design methodology for precast deck panels (PDPs) was established. A parametric analysis was then performed for three California girder types: Bulb-Tee Girder, Wide Flange Girder, and I Girder. Strand spacing in PDPs was studied for each girder type with several variables: precast deck panel thickness, cast-in-place (CIP) topping thickness, concrete compressive strength at release (𝑓′𝑐i) and 28 days (𝑓′𝑐), and girder spacing. Five combinations of PDP thickness and CIP topping thickness were chosen to study the influence of the variables on the strand spacing in PDPs: 3½” PDP with 4¼” CIP topping, 3¾” PDP with 4” CIP topping, 4” PDP with 4” CIP topping, 4” PDP with 4½” CIP topping, and 3½” PDP with 5” CIP topping. A minimum PDP thickness of 3½” and minimum total deck thickness of 7¾” were used. Parametric study results show that the design of PDPs is always governed by one of two conditions: the bottom flexural tensile stress in the PDP due to permanent and transient loads in vi service (LRFD Service III load combination) or the minimum flexural reinforcement requirement. The minimum flexural reinforcement requirement governs the design when the distance between girders is relatively short (i.e., “short span” condition with girder spacing under approximately 10’-0” for Bulb-Tee and Wide Flange girders and under 8’-6” for 8’-6” for I girders). The bottom tensile stress at Service III condition governs the design when the distance between girders is relatively long (i.e., “long span” condition with girder spacing from approximately 10’-0” to 12’-6” for Bulb-Tee Girder/Wide Flange Girder and 8’-6” to 10’-3” for I Girder). An investigation of the influence of concrete compressive strength revealed that the compressive strength has minor influence in the PDP strand spacing, not exceeding ¾”. The girder spacing and the total deck thickness for the PDP and CIP topping slab have the greatest influence on strand spacing. For the thickness combinations investigated (including a minimum 3½” PDP and 7¾” total deck thickness), a strand spacing of 6” always satisfies LRFD design requirements for the three girder types and for girder spacing associated with the “short span” condition. For the “long span” condition, strand spacing decreases linearly from approximately 6” to approximately 3½” at the maximum girder spacing. Equations representing this behavior are presented. The results of the parametric analysis were used to develop two design tables for PDPs used on: 1) Bulb-Tee Girders or Wide Flange Girders, and 2) I Girders. The tables specify the required minimum strand area as well as the minimum area of reinforcement at the negative moment section over interior girders based on a practical range of combination thicknesses for the PDP and CIP topping. vii A table was also developed to compare the required flexural reinforcement in CIP topping slab at the critical negative moment section for exterior girders vs. interior girders. Due to the extra design requirements including collision, the required reinforcement in the CIP topping for an exterior girder was 40% to 80% larger than that required for an interior girder. This table additionally compares the required reinforcement in the CIP topping slabs to reinforcement for a full-depth CIP slab design per Caltrans Bridge Memo to Designers, Table 10-20.1(c). The CIP topping was approximately larger 10% than that the required for a full-depth CIP slab per Caltrans. Lastly, the conclusions are made based on the parametric study, demonstrating the viability of PDPs in bridge deck design.