E.O.L. Lantsoght
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Proof load testing on bridges requires high magnitude loads. Stop criteria are used to avoid irreversible damage or failure during proof load testing. These stop criteria are thresholds to measurable parameters during the test. After reaching a stop criterion, the proof load test needs to be terminated. While in the past, stop criteria have been identified as a single level, this research proposes to use a traffic light system for stop criteria: green light (related to the serviceability limit state), yellow light (as an intermediate level) and red light (further testing is not permitted). The green light relates to the development of cracking, whereas the yellow and red light relate to the failure modes of flexure and shear. To develop stop criteria for the brittle failure mode of shear, thresholds are derived from mechanical models, based on strain measurements and crack widths, as well as using acoustic emission measurements. To validate the stop criteria, three series of experiments are analyzed: reinforced concrete slab strips, straight slabs, and skewed slabs. While field validation of the traffic light system is pending, the developed tool is a step forward to safely test concrete bridges without shear reinforcement.
Size Effect of Slender and Thick Reinforced Concrete Members Without Transverse Reinforcement Failing in Shear
Parameter Analyses and Code Predictions
The shear strength of reinforced concrete members without transverse reinforcement remains a critical design issue, particularly for thick and slender structural members where pronounced size effects may significantly reduce the nominal shear strength. This study investigates the combined influence of member depth, concrete compressive strength, and longitudinal reinforcement ratio on the shear capacity of beams without stirrups through nonlinear finite element analyses (NLFEA). Beam depths ranging from 1000 mm to 4000 mm and concrete strengths between 30 MPa and 50 MPa were considered, together with variations in different longitudinal reinforcement ratios. The numerical results confirmed a clear deterministic size effect, with nominal shear stresses decreasing systematically as the effective depth increased, while the influence of compressive strength was found to be secondary. The depth-dependent response was successfully represented using Bažant’s energetic Size Effect Law (SEL Type II), and the calibrated parameters provided an excellent fit to the numerical database. Furthermore, the numerical predictions of shear capacity were compared with major design provisions, including ACI 318 (2014 and 2019), Eurocode 2 (EN 1992-1-1:2005 and EN 1992-1-1:2023), and fib Model Code approaches with levels of approximation (LoA) 1 and 2. The results highlight that older formulations such as ACI 318-2014 and EN 1992-1-1:2005 tend to be unconservative for deep members, whereas EN 1992-1-1:2023 offers significantly improved agreement with reduced scatter. Among the evaluated expressions, fib Model Code LoA1 was the most conservative, while LoA2 provided the most accurate overall predictions. The findings emphasize the importance of incorporating size-effect considerations in modern shear design models, particularly for large reinforced concrete structures such as bridge decks, thick slabs, and dam walls.
Bridge load testing for assessment
Recent advances in application, collaboration, codes, and research
As infrastructure continues to age and traffic levels intensify, there is a growing need for efficient methods to verify the reliability of many existing structures. Field testing offers the possibility to assess the current condition of a structure. Specifically, in a proof load test, substantial loads are applied to evaluate the structure's resistance to future loads that could compromise structural safety. However, to prevent excessive test loads and their potential damage, it is desirable to assess structural reliability by monitoring the response under more moderate loads. This study merges laboratory and in-situ testing results through a Bayesian update of the structural reliability after each successful load application. Two case studies are presented where laboratory testing on structurally similar elements and analytical modelling provide ample evidence to justify test load reductions of 20 % and 25 %. The proposed method offers a systematic framework to link the structure's response during testing to structural reliability and address the uncertainties in resistance, loads and measurements. Nonetheless, the representativeness of the data in terms of structural similarity and uncertainties related to measurements continue to be significant factors. Despite these challenges, incorporating monitoring data during proof load testing is expected to reduce target loads in most cases.
As the construction industry shifts toward more sustainable solutions, bio-based materials are emerging as promising alternatives to conventional building components. This work explores two primary categories: supplementary cementitious materials (SCMs) derived from agricultural byproducts, and natural fibers used to reinforce cement-based composites. Materials such as rice husk ash and sugarcane bagasse ash can partially replace Portland cement, lowering carbon emissions while maintaining structural performance. At the same time, plant and animal-based fibers like jute, sisal, coconut, and wool enhance mechanical properties such as tensile strength and crack resistance. The use of renewable biopolymers and bio-based phase-change materials further improves workability, insulation, and energy efficiency. While challenges such as durability and material variability remain, bio-based materials offer a compelling pathway toward greener, eco-efficient construction.
Proof load testing (PLT) offers a valuable and sustainable alternative to analytical approaches for improving knowledge on the safety level of existing bridges, providing an in-situ measurement of structural bearing capacity under actual traffic loads by reducing resistance uncertainties and associated probability of failure if the test is passed. The present paper investigates the influence of the PLT on the structural reliability of prestressed concrete I-type simply-supported decks representing the most common type of existing bridges in Italy. By supplying data on the lower-bound of the capacity distribution, the PLT turns into an updated estimation of the bridge reliability. A fully-probabilistic analysis is developed combining random uncertainties on both materials and load effects with epistemic uncertainties. A traffic load model variable based on Eurocode Load Model 1 effects is calibrated to provide consistent modelling with code-prescribed safety levels. Structural capacity of the edge girder is considered both in terms of ultimate limit state for flexure and shear and serviceability limit state in terms of cracking load which could affect long-term bridge durability. The manuscript main contribution lies in developing a reliability-based approach to PLT that accounts for both prior (before test) and posterior (after test) structural reliability, incorporating conditioning on the success of the test. A sensitivity analysis according to the partial safety factor method is presented to investigate the impact of different proof loads assuming different Capacity-to-Demand Ratios (CDR). A case-study bridge is investigated where a proof load was executed recently demonstrating the benefit of the PLT in case of CDR lower than unit. The case study also showcases the possibility to significantly reduce the failure probability during the test when the target level is imposed with a number of intermediate levels of load steps.
The authors regret that the original publication of this paper did not assign the correct affiliations to R.D.J.M. Steenbergen. The authors would like to apologise for any inconvenience caused.