Date of Award

2025-08-01

Degree Name

Master of Science

Department

Civil Engineering

Advisor(s)

Jeffrey Weidner

Abstract

Cantilever overhead sign support (COSS) structures are one of the most common features of transportation systems, providing navigational information to motorists. The slender geometry, lightweight design, and welded connection at the base make COSS structure susceptible to fatigue cracking under long term cyclic loading from wind-induced galloping, truck-induced gust pressure and so on. COSS structures are traditionally designed considering nominal wind conditions. However, rising incidents of seismic activity in regions like Dallas-Fort Worth related to industrial injection wells in the Permian Basin have created a serious concern regarding the seismic performance of potentially fatigued-damaged COSS structure. The interaction between already existing fatigue cracks and newly emerging high intensity ground motion from seismic activity remains largely unknown and may cause a serious threat to infrastructure safety. This study addressed the gap, providing a numerical framework considering fatigue damage and seismic fragility. Finite element models were developed in Abaqus for round and multisided pole to simulate the fatigue crack development and stress concentration hot spot. All the loads including dead loads, galloping loads, natural wind gust and truck induced gust loads were applied following AASHTO provisions. To account for the earthquake effect, near field seismic demand was characterized by using ten ground motion records observed with high peak ground accelerations and velocity pulses. Incremental Dynamic Analysis (IDA) was performed for each configuration by gradually increasing the spectral acceleration to understand the progressive nonlinear response behavior of COSS structure up to failure. The findings suggest that base plate thickness of the COSS has major impact in stress concentration factors and seismic fragility. It was found that stress propagation is the result of amplified local stress linked to the thinner base plate substantially reducing the structural capacity. A comparative study between round and multisided pole suggested that multisided pole exhibited higher displacement and fragility threshold with 50% exceedance at Sa ? 1.4g. A similar range of exceedance was observed for the round pole at Sa ? 0.95g. While multisided pole reached displacement limit at higher intensity of ground motion, it exhibited greater uncertainty compared to round pole due to geometric discontinuity and resulting stress irregularity under dynamic loading. In contrast, the round pole displayed smooth stress distribution and predictable IDA response, while reaching displacement threshold at small seismic intensities. Thus, it is imperative to examine the trade-off between deformation capacity and response predictability linked when choosing pole geometry for design of COSS structure. The study provided a comprehensive numerical framework for examining seismic vulnerability of COSS structure examining the influence of geometric properties on stress concentration and stress intensification in addition to failure behavior under seismic loading. The study highlights the need for a holistic approach for evaluation of COSS structure integrating the effects of fatigue damage and near-field seismic demand and provides a pathway forward for informed decision-making and enhancing infrastructure safety.

Language

en

Provenance

Received from ProQuest

File Size

107 p.

File Format

application/pdf

Rights Holder

Yeasin Ahmed

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