Abstracts:Progressive collapse alternate path scenarios are often characterized by restrained beam configurations that provide resistance to structural collapse after column removal. While various methods have been presented to model the behavior of restrained beams, opportunities exist for mechanics-based estimation of the complete static and dynamic load-deflection curves. This paper presents an axially restrained beam (ARB) model that incorporates axial–flexural interaction throughout the entire static load-deflection curve including the elastic material range, the plastic flexural dominant range, the range beyond plastic flexure with increasing catenary effect, and the full catenary range. Energy methods are applied to static load-deflection curves to determine dynamic load-deflection relationships. A parametric study was conducted to assess the accuracy of the ARB method compared to nonlinear, dynamic time history finite-element (FE) analyses. The model compares favorably to results of FE models with average estimates of dynamic deflection within 2.1% for ideal moment connections and 7.7% for configurations combining simple and moment resisting connections.

Abstracts:Concrete-filled steel tubular (CFST) piers have been applied in bridge structures due to their high bearing capacity, good ductility, and light weight. During their service life, CFST piers may suffer vehicle collision. Nevertheless, there is still a lack of a performance evaluation method for CFST piers subjected to vehicle impact. Therefore, this paper presents a residual deformation-based method to evaluate the performance of CFST piers under truck impact. Before that, a numerical model was developed to simulate responses of CFST piers under truck collision and validated by reported impact tests. Then, the performance levels of 6- and 12-m high CFST piers under 20 and 40 ton and 60, 100, and $140\mathrm{km}/\mathrm{h}$ truck collisions were numerically investigated. Afterwards, a residual deformation-based performance evaluation method was proposed based on the numerical investigations. In this method, the ratio of the residual lateral deflection at the mid-height to half of the pier height was first selected as the evaluation index. Then, threshold values of the evaluation index at different performance levels were determined. Finally, an analytical model for the evaluation index was developed. Comparisons indicate that the analytical performance levels are in good agreement with the numerical results. The proposed residual deformation-based performance evaluation method can be used for design and accident analysis of CFST piers subjected to truck collision.

Abstracts:Eight low-profile arch corrugated metal culverts were recently annexed by the city of Anniston, Alabama. These structures are nearly 80 years old and have never been load rated. To satisfy federal requirements, load rating of the culverts was required. Attempts to rate these structures using methods developed by the corrugated steel pipe industry implied that the culverts require posting due to low soil cover, without any consideration for structural integrity. Guidance for load rating of steel and concrete bridges and cast-in-place concrete culverts is well established, while the guidance for corrugated metal culvert structures is limited. The objective of this study was to examine the contemporary practice of load rating corrugated metal culverts with shallow cover and use diagnostic load testing to demonstrate the capacity and overcome the shortfall of the current rating methods. To verify the load-carrying capacity of these structures and improve the load rating, diagnostic load tests were therefore carried out to assess the load response of two of the culverts using a $381.3\text{-}\mathrm{kN}$ ( $85.7\text{-}\mathrm{kip}$) test truck. The load testing program featured a very simple instrumentation package that was easy to install, recover, and reuse. The instrumentation plan consisted of displacement transducers and electrical resistance strain gauges. Load, displacement, and strain data collected in the field load tests were analyzed, which showed satisfactory performance with a maximum deflection of less than 0.1% of the span length and a maximum strain that corresponds to approximately 24% of the estimated yield stress. Following standard procedures, the test response data were used to improve the analytically derived rating factors, and challenges associated with the approach are discussed.

Abstracts:A combined experimental and analytical investigation was conducted at the University of Ottawa to assess the performance of blast-resistant window retention anchors to generate design information. The experimental phase of research involved 46 full-scale window tests with different parameters. The analytical investigation included numerical modeling and dynamic analysis of windows to expand the experimental results and to assess the significance of design parameters. Computer software LS-DYNA was selected for the analyses. Analytical models of selected test windows with aspect ratios of 1.0 and 3.0 anchored on structural steel, reinforced concrete, concrete block masonry, and stone masonry substrates were modeled. The models were validated against experimental data. Additional windows with aspect ratios of 1.5 and 2.0 were also modeled for investigation. The models were used to conduct a parametric investigation with the parameters consisting of substrate flexibility, anchor fixity conditions, window size and aspect ratio, frame rigidity, number and spacing of anchors, and the threat level as defined by reflected pressure-impulse combinations. The significance of each parameter is illustrated with emphasis placed on the magnitude of anchor shear and tension design forces. The distribution of anchor forces is obtained numerically. Anchor forces and distributions are compared with those observed experimentally. Design force distribution along the perimeter of window frames is recommended for use in design. The paper provides the results of numerical simulations illustrating the significance of design parameters on anchor design force levels and their distributions.

Abstracts:For through tied-arch bridges, the corrosion and degradation of the cable’s load-bearing capacity are the main external causes of cable breakage and subsequent structural failure; nevertheless, the progressive collapse after cable breakage is primarily attributed to the weak structural robustness, which makes a huge potential risk of bridge operation and maintenance (O&M). Whereas, as the basis of O&M, current condition evaluation method has not yet taken into consideration the influence of different consequences of cable breakage, resulting in unscientific conclusions for O&M decisions frequently. In this study, a robustness-based condition evaluation framework for the overall structure of the through tied-arch bridge is presented, consisting of three stages: (1) structural robustness assessment associated with tie-bar and suspender failure respectively; (2) classification of evaluation process by the results of robustness assessment, within which the overall structure is either evaluated using the code method or evaluated directly as unqualified (Condition I and II), or the structural member weightings are adjusted according to the robustness weightings (Condition III); and (3) condition evaluation of entire bridge. The evaluation processes of three conditions are further presented in accordance with the tied-arch structure and suspended deck system. To establish the robustness weightings in Condition III, the safety redundancy indexes of through tied-arch structures as well as the suspended deck system are calculated separately, combined with robustness assessment result. Applying the proposed framework to evaluating the condition of a through tied-arch bridge with different structures, the analysis and comparison indicates that, due to the robustness of the through tied-arch structure and suspended deck system, the variation in the potential risk of accidents induced by cable failure is shown intuitively through the evaluation results, which better meets the needs of guiding bridge O&M decisions consequently.

Abstracts:This paper introduces an innovative technology based on an actual corrugated steel arch bridge project. The design of steel-concrete composite structure in which concrete arches are poured around the corrugated steel plate arch ring is proposed to improve its mechanical performance. Field tests and numerical simulations were conducted. In the field test, the load was applied to the structure by loading a heavy truck, and the strain and displacement of different positions of the corrugated steel arch ring section were tested. Two models of corrugated steel arch bridges with and without concrete arch protections were established through finite-element software to study the effect of concrete arch protections on the mechanical properties of corrugated steel arch bridges and verify the test results. The model calculation results showed that when a concrete arch protection was applied, the stress and displacement of each position of the corrugated steel plate arch ring were reduced to varying degrees. The calculated values of the numerical model were also compared with the measured values of the field trials, and it was found that the calculated value is generally slightly higher than the measured value. This study showed that the mechanical performance of corrugated steel arch bridges could be effectively improved by applying concrete arch protection on the corrugated steel arch ring.

Abstracts:Semi-integral abutment bridges are integral abutment bridges with a flexible interface at the abutment to reduce the force transferred to the foundation. Past research has investigated the uplift forces from the drill shafts using finite-element analysis, while insufficient experimental data exist to validate this hypothesis. Therefore, a semi-integral abutment bridge in Ohio supported on drilled shafts was monitored for a long-term to investigate the performance of semi-integral abutment with drilled shafts and abutment walls under environmental conditions. During the construction of the bridge, vibrating wire strain gauges were placed in three drilled shafts, footing, and the abutment wall above. Strain and temperature were collected from the installed sensors. It was found that the seasonal and daily temperature changes significantly affect the changes in the strain in the substructure. The behavior of the abutment wall significantly affects the behavior of the footing and drilled shafts. The behavior of the abutment was irreversible, and the top of the abutment wall and the top of the drilled shaft induced higher strain than the bottom. Cracks were noticed at the front face of the abutment wall, and the extremely cold weather conditions induced tensile strain higher than the allowable strain at the top corner of the front face of the abutment wall. In addition, a three-dimensional finite-element model was created and calibrated with the field data. The FEM results were used to investigate the maximum stress magnitudes and locations under temperature variation.

Abstracts:Precast prestressed concrete (PPC) deck girders are among the most common types of structural systems used for bridges with short-to-medium spans. Although this bridge system is known to experience longitudinal (reflective) cracking, there is little information on the impact of transverse cracking on the structural integrity of these bridges. Transverse cracking of PPC girders can significantly compromise the safety and serviceability of these girders. This study focuses on better understanding the impact of transverse cracks on the residual capacity and load rating analysis of in-service PPC deck girder bridges. To obtain a realistic assessment of the condition of in-service cracked girders, a PPC deck girder with transverse cracks is extracted from a bridge in the field and tested under four-point bending until failure. Finite element analysis is also performed to investigate the capacity of the as-built PPC girder. Finally, decompression stresses in the prestressing steel are predicted from the measured crack width using different crack width models that are recognized in the literature. A transverse crack is found to reduce the load rating capacity of the girder by almost 34% which subsequently reduced the capacity-based load rating factor by 22% under the HS-20 truck load. Although serviceability-based load rating from crack width conservatively provided a negative rating, the flexural testing indicated that the girder could carry over 50% of its nominal and residual capacities while remaining in the elastic range.