Daniel J. Getter

Equivalent Static Analysis Method for Barge Impact-Resistant Bridge Design

In the United States, barge impact-resistant bridge design typically involves static application of code-prescribed impact loads. However, the existing static analysis procedure neglects crucial dynamic effects in the impacted bridge. Recent experimental and analytical studies have uncovered important impact-related dynamic amplification of pier member demands, primarily stemming from superstructure inertial effects. These studies have focused on the use of dynamic structural analysis as a means of accounting for dynamic amplification. Although time-domain dynamic analysis techniques are capable of accurately predicting amplified member design forces, such techniques may not be warranted during preliminary design iterations when detailed structural parameters have not yet been established. In this paper, a static analysis procedure is developed that emulates pier response modes that arise during dynamic barge impact events. The proposed method provides a simplified means of approximating dynamic amplification effects and is shown to produce conservative predictions (in relation to dynamic analysis) of both pier and foundation design forces.

Dynamic Amplification of Pier Column Internal Forces Due to Barge–Bridge Collision

In the United States, bridge design provisions for waterway vessel collision typically involve static application of code-prescribed impact loads. However, results from full-scale experimental impact tests have revealed that significant mass-related inertial forces can develop in affected piers because of the overlying superstructure. In part on the basis of these findings, a dynamic (time history) analysis technique was previously developed; it predicts both impact load and structural response. In the current research, the dynamic analysis technique is combined with recently developed barge force–deformation relationships and a simplified bridge modeling technique to conduct a detailed investigation of collision-induced dynamic amplification phenomena. Design forces are quantified for a wide range of bridge types by using dynamic and static analyses. For each bridge considered, dynamic amplifications are numerically quantified by comparing dynamic to static predictions of pier column demand. Significant amplification effects are consistently found among the barge–bridge collision simulations conducted, indicating that dynamic phenomena should be accounted for in bridge design.

Probability of Collapse Expression for Bridges Subject to Barge Collision

Accounting for waterway vessel collision is required in the structural design of bridges spanning navigable waterways. During collision events, massive waterway vessel groups such as barge flotillas are capable of dynamically transmitting horizontal forces to impacted bridge components. Furthermore, collision-induced forces can be sufficient to collapse piers or roadway spans in the vicinity of the impact location. If collapse takes place, economic loss is suffered because of subsequent traffic rerouting and bridge replacement costs. Additionally, fatalities may occur if the roadway is occupied during or shortly after collapse. This paper focuses on the development of a probability of collapse expression for bridge piers subject to barge impact loading, where the relationship can be readily integrated into existing bridge design methodologies. The expression is developed by employing probabilistic descriptions for a multitude of random variables related to barge traffic characteristics and bridge structures in conjunction with nonlinear dynamic finite-element analyses of barge-bridge collisions. Highly efficient, advanced probabilistic simulation techniques are necessarily incorporated into the barge-bridge collision analysis framework to allow feasible estimation of structural reliability parameters. These parameters facilitate the formation of an expression that, in turn, bridge designers can use to estimate probabilities of structural collapse attributable to barge collision, without performing probabilistic analyses.

Relationships of Barge Bow Force-Deformation for Bridge Design

Loads generated during vessel collisions with bridges are inherently dependent on force–deformation characteristics of the impacting vessel. Currently in the United States, barge impact forces used in bridge design are computed with a force–deformation (crush–curve) model proposed by AASHTO. A recent study uncovered important limitations in the AASHTO barge-crushing model, and a revised procedure for developing barge force–deformation relationships was developed. However, relationships developed in this previous study were based on the assumption that impact occurred directly head on to the impacted pier; the scenario was unlikely. Impact more likely occurs at some oblique angle. This paper shows that barge impact forces on flat-faced pier surfaces (i.e., rectangular columns or waterline pile caps) are typically less severe when collisions occur at even small oblique angles. Thus, the current study focused on updating the prior crushing model to account probabilistically for reduced forces associated with oblique impact. In this paper, oblique impact forces were quantified by means of a series of high-resolution simulations of finite element barge bow crushing. Results obtained from these simulations were used in a probabilistic study to develop a force prediction model that implicitly accounted for the relative likelihood of impact occurring at particular angles. Findings from the current study were then integrated into the previously developed barge-crushing model to produce a design-oriented calculation framework that would permit bridge designers to account easily for force reductions that arise in oblique impact scenarios.

An Improved Equivalent Static Analysis Method for Barge-Bridge Collision Design

In the United States, barge impact resistant bridge design typically involves static application of code-prescribed impact loads. However, recently conducted full-scale experimental collision tests led to the discovery of significant inertial effects not accounted for in existing design provisions. Subsequent to the experiments, a numerically efficient dynamic (time history) analysis procedure was developed to quantify transient impact loads and load effects. While this technique is capable of accurately predicting member design forces, a time-domain dynamic analysis may not be warranted for the design of certain structures, or during preliminary design iterations when detailed structural parameters cannot be adequately estimated. In this paper, common modes of dynamic pier response arising during barge impact loading are characterized for a wide range of bridge configurations. Dynamic amplifications of pier member design forces are quantified by comparing forces obtained from time-history dynamic simulations to those obtained from static analyses. As a means of capturing dynamic amplification effects, an equivalent static analysis procedure is developed that mimics pier response during dynamic barge impact events. The proposed static method is shown to produce conservative predictions of both pier and substructure design forces, relative to dynamic analysis.