Development of a precast UHPC seat-type abutment for seismic applications
Date
2024-12
Authors
Karki, Anisha
Major Professor
Advisor
Sritharan, Sri
Shafei, Behrouz
Ashlock, Jeramy
Committee Member
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Abstract
About 50% of bridges in the USA are more than 50 years or older and a significant number
(47000 bridges) are deemed structurally deficient. Compounded by continuously increasing traffic
demands, these bridges face accelerated deterioration, necessitating more frequent maintenance,
partial rehabilitation, or even complete replacement. However, the partial or total closure
required for such activities poses significant disruptions to the traveling public and impacts local
economies, given the critical role bridges play in daily societal operations. This situation
underscores the necessity for Accelerated Bridge Construction (ABC) methods that seek
innovative ways to hasten onsite construction. Various ABC methodologies, such as the use of
structural precast elements and modular bridge systems, have been developed and implemented
across the United States. Focusing largely on superstructures, these efforts aim to streamline
onsite construction processes, thereby enhancing overall transportation efficiency. For
substructures, the ABC methods are primarily in the experimental stage, with most projects
presenting one innovative idea after another but lacking in standardization.
The significant challenge within ABC in substructures lies in handling heavy precast elements,
introducing transportation challenges, and requiring large cranes for on-site assembly. Thus, this
thesis proposes innovative solutions for precast elements in the foundation by addressing the lack
of standardization and the need for reducing the number of robust connections among
components transported in pieces. To reduce costs and improve transportability, the concept of
hollow precast substructures was proposed in this study, focusing on investigating the ABC design
of seat-type bridge abutments frequently used in seismic regions utilizing ultra-high-performance
concrete (UHPC). By employing UHPC, it becomes feasible to reduce the sectional dimensions,
enabling the transportation of the main abutment component as a single, sizable unit that would
require a reduced number of connections in the field. The proposed abutment stem adopts a hollow section with a 6-inch thickness, incorporating a hammer head at the top to meet the
30-inch seat width requirement outlined in California Department of Transportation (Caltrans)
Seismic Design Criteria (SDC). The precast abutment cap features corrugated steel pipe sockets
filled with UHPC cast-in-place closure pours to ensure rigid connections with steel H piles. The
performance of the new system and its components will be validated by a half-scale experimental
test unit. It is anticipated that Caltrans will implement this detail in constructing standard
ordinary bridges with two or three spans.
This study also explores another hybrid approach to implementing ABC in substructures
through the experimental use of thin, open-hollow precast UHPC shell members. These
lightweight elements are designed to improve handling and mobility both before and during
assembly. Serving as stay-in-place (SIP) formwork, these shells eliminate the need for onsite
formwork installation—a process that is time-consuming and dependent on labor availability at
the bridge site. The experimental arrangement included straight and battered steel piles for the
foundation, with an open hollow precast thin shell unit used for the pile cap, the primary
substructure component tested. A top-loading block shell was also incorporated to apply loads to
the system, along with rebar cages for each component. Another lateral load block was
constructed directly at the top of the pile cap. The test unit was subjected to combined vertical
and lateral loads that simulated both normal operating conditions and extreme events for
two-lane bridges in Iowa and California. Despite these demanding conditions, the battered and
vertical pile-pile cap system demonstrated exceptional resilience, maintaining its integrity and full
elasticity even under unrealistic severe loads. The employment of UHPC SIP formwork played a
critical role in preventing microcrack development and widening within the regular concrete,
thereby enhancing the system’s elasticity and structural integrity. Additionally, the connections
between the piles and the pile cap showed excellent structural stability, with no evidence of
pullout, pile yielding or buckling. The observed load-displacement behavior was mostly linear,
and the slight nonlinearity was primarily due to gap formation in the surrounding soil. This
paper provides an extensive overview of the outdoor test setup and its pivotal findings, highlighting the effectiveness battered steel piles in the foundation serving to perform much
adequately than anticipated under extreme seismic loading and the role of UHPC SIP formwork
in improving the performance and durability of bridge foundations.
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