Bridge Load Testing: State-of-the-Practice Alampalli, Sreenivas; Frangopol, Dan M; Grimson, Jesse ...
Journal of bridge engineering,
03/2021, Letnik:
26, Številka:
3
Journal Article
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Abstract
Bridge load testing can answer a variety of questions about bridge behavior that cannot be answered otherwise. The current governing codes and guidelines for bridge load testing in the ...United States are the 1998 NCHRP Manual for Bridge Rating through Load Testing and Chapter 8 of the AASHTO Manual for Bridge Evaluation. Over the last two decades, the practice of load testing has evolved, and its intersections with other fields have expanded. The outcomes of load tests have been used to keep bridges open cost-effectively without unnecessarily restricting legal loads, when theoretical analyses cannot yield insights representative of in-service performance. Load testing data can be further used to develop field-verified finite-element models of tested bridges to understand these structures better. In addition, structural reliability concepts can be used to estimate the probability of failure based on the results of load tests, and noncontact measurement techniques capturing large surfaces of bridges allow for better monitoring of structural responses. Given these developments, a new Transportation Research Board (TRB) Circular, Primer on Bridge Load Testing, has been developed. This document contains new proposals for interpreting the results of diagnostic load tests, loading protocols, and the determination of bridge load ratings based on the results of proof load tests. In addition, included provisions provide an estimation of the resulting reliability index and the remaining service life of a bridge based on load testing results. The benefit of load testing is illustrated based on a cost–benefit analysis. The current state-of-the-practice has demonstrated that load testing is an effective means for answering many important questions regarding bridge behavior that are critical to decisions on bridge maintenance or replacement. Load testing has evolved over its history, and the newly developed TRB Circular reflects this evolution in a practical way.
For the assessment of existing slab-between-girder bridges, the shear capacity and failure mode are under discussion. Previous research showed that the static and fatigue punching capacity of the ...slabs is sufcient as a result of compressive membrane action. The girders then become the critical elements. This research studies the shear capacity of prestressed concrete bridge girders. For this purpose, four (half) girders were taken from an existing bridge that was scheduled for demolition and replacement and tested to failure in the laboratory. Two loading positions were studied. The results show that there should be a distinction between the mode of inclined cracking and the actual failure mode. In addition, the results show that for prestressed concrete girders, the influence of the shear span-depth ratio should be considered for shear span-depth ratios larger than 2.5. These insights can be used for the assessment of existing slab-between-girder bridges in the Netherlands. Keywords: bridge assessment; concrete bridges; flexure-shear; large-scale testing; prestressed concrete; shear; shear-compression; shear-tension.
Parents in academic careers face notable challenges that may go unrecognized by university management and/or policy makers. The COVID-19 pandemic has shed light on some of these challenges, as ...academic parents shifted to working from home while simultaneously caring for children. On the other hand, many parents found that the shift to working from home offered new opportunities such as working more flexible hours, development of digital skillsets, and increased involvement in the education of their children. In this article we explore the work-related challenges and opportunities experienced by academic parents as a result of the COVID-19 pandemic and offer potential long-term solutions for academic parents and their universities. We use the following methods: (1) a literature review focused on identifying the work-related challenges academic parents faced prior to the pandemic, as well as the impact of the pandemic on scientists and working parents and (2) administer a world-wide survey with the goal of identifying the challenges and opportunities associated with parenting and academic work through the COVID-19 lockdown (304 total responses; 113 complete). Moving forward these findings have enabled conclusions to be drawn in order to shape a new normal. Our aim is to offer university administrators, policy makers, and community service providers with ways to provide additional support for academic parents as well as provide tools for academic parents to learn successful strategies directly from their peers.
For the assessment of existing slab-between-girder bridges, the shear capacity and failure mode are under discussion. In particular, preliminary assessment calculations showed that the critical ...failure mode of the girders is shear-tension. In this paper, four girders taken from a demolished bridge that were tested in the lab are analyzed according to existing codes. The comparison between the experiments and the analysis shows that the Dutch RBK provisions are conservative and the ACI 318-19 provisions result in good predictions of the shear capacity at inclined cracking and at ultimate. These observations are then combined into recommendations for the assessment of prestressed concrete girders in existing slab-between-girder bridges for shear cracking and the ultimate shear capacity. Keywords: bridge assessment; concrete bridges; flexure-shear; large-scale testing; prestressed concrete; shear; shear-compression; shear-tension.
AbstractA 55-year-old bridge showed large cracking in the approach bridge caused by restraint of deformation and support settlement. After repair, it was uncertain at which crack width the traffic ...loads on the bridge should be further restricted. The shear capacity was calculated by counting on the aggregate interlock capacity of a supposedly fully cracked cross section. An aggregate interlock relationship between shear capacity and crack width based on an unreinforced section was used to find the maximum allowable crack width. Limits for crack widths at which load restrictions should be imposed were found. The large structural capacity of the cracked concrete section shows that the residual bearing resistance based on the aggregate interlock capacity of reinforced concrete slab bridges with existing cracks is higher than expected. This expected capacity could be calculated with the inclined cracking load from the code provisions. The procedure outlined in this paper can thus be used for the shear assessment of fully cracked cross sections of reinforced concrete bridges.
Depending on the support conditions (hence the questions in Point 1), the width of the specimen might play a role,31 and change the shear-carrying mechanism from the twodimensional (2-D) behavior of ...beams to the three-dimensional (3-D) behavior seen in slabs under concentrated loads failing in one-way shear. For a more complete comparison, the authors are encouraged to take into account the self-weight of the specimen and take this into account when defining the maximum load on the structure or the maximum sectional shear.
In a proof load test, a load corresponding to the factored live load is applied to a bridge, to directly demonstrate that a bridge fulfils the code requirements. The case of viaduct De Beek, a ...four-span reinforced concrete slab bridge that did not fulfil the requirements for bending moment after an inspection survey is studied. The middle spans, located above highway lanes, which could not be tested in the field, are the critical spans of this structure. Therefore, the observations from the field are used to check the finite element model, and improve the rating of the critical middle spans. The proposed method can be applied and further extended for proof load tests where the access to the site and the critical position of the viaduct is limited. This improvement will allow for an optimized combination of field testing and modelling, reducing the costs of field tests.
In a proof load test, a load corresponding to the factored live load is applied to a bridge, to directly demonstrate that a bridge fulfils the code requirements. This chapter discusses viaduct De Beek, an existing reinforced concrete slab bridge in the Netherlands with insufficient flexural capacity and significant cracking. Finite element models are not directly used after the proof load test for the assessment of the bridge. Only when the assessment needs to be improved with more accurate restrictions for the passing traffic, further studies are needed. In traditional approaches for proof load testing, linear finite element models are used to determine the most unfavourable position of the load during the field test, and the required magnitude to show that the tested bridge fulfils the code requirements. Since it is found that the section at the mid support does not fulfil the requirements when a linear finite element analysis is used, a nonlinear analysis is carried out.
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