Proof Load Research Articles

Calibrating resistance factors of pile groups based on individual pile proof load tests

Pile load tests have been utilized to reduce the uncertainty of pile resistance, thus leading to a higher resistance factor used in the Load and Resistance Factor Design (LRFD). Previous studies have primarily focused on calibrating resistance factors for single piles based on load tests. This calibration hinges upon the resistance bias factor of single piles, defined as the ratio of measured resistance to predicted resistance. Due to the redundancy in the pile group system, it is conventionally assumed that if the individual piles within the group achieve a lower reliability index (e.g., 2.0–2.5), the pile group as a whole attains the target reliability index of 3. However, the approach is empirical as it does not consider system redundancy directly. Moreover, this empirical approach disregards the correlation between resistance bias factors of individual piles, which is inherently influenced by the spatial variability of soils. In this study, the random finite difference method (RFDM) is employed to evaluate the correlation between resistance bias factors of individual piles in spatially variable soils. The resultant correlation matrix is subsequentially employed in Bayes’ theorem to update resistance bias factors using individual pile load test results and their corresponding test locations. The updated resistance bias factors are then used for the direct calibration of resistance factors for pile groups within the framework of LRFD. A pile group subject to vertical loading in undrained clays is adopted for illustration. Comparative analyses between the proposed approach and the empirical approach demonstrate that the latter tends to overestimate the resistance factor. Furthermore, the proposed approach enables the determination of optimal locations for conducting subsequent load tests based on previous test results.

Dynamics of bridges during proof load tests and determination of mass-normalized mode shapes from OMA

Modal shapes derived from Operational Modal Analysis (OMA) lack normalization with respect to masses, hindering direct estimation of effective mass or modal participation factors. The mass-change method is suitable to solve this issue since it proposes an experimental derivation of scaling factors for modes based on OMA results in different load conditions. However, in the case of bridges, the method application is challenging, as significant static masses are required on the deck for OMA in loaded conditions. To address this challenge, trucks can be used as added masses during standard static proof load tests for bridges, making the mass-change method feasible. However, the presence of trucks introduces dynamic coupling effects among bridge and vehicles, potentially complicating the dynamic identification. This paper proposes a methodology to exploit data obtained from OMA on bridges loaded with stationed trucks within the framework of the mass-change method in order to get the modal scaling factors for the mass normalisation of mode shapes and taking into account possible effects of the dynamic coupling between the two systems. To this purpose, the bridge dynamics with added stationed trucks is studied by introducing a finite element model to address the bridge-vehicles dynamic coupling. Then, a simple but effective 2-degree of freedom system is introduced to develop a parametric investigation in a non-dimensional manner in order to provide a practical tool for engineers to account for the bridge-truck dynamic coupling effects. Finally, numerical applications are proposed to derive some conclusions about the effectiveness of the proposed procedure and its suitability in real applications.

Acoustic emission measurement during the proof loading of the new bridge over Odra river in Wrocław

The acoustic emission method is applied for damage monitoring through the analysis of internal events within the material. Sensors were placed at the cantilever joint during the proof loading. Signal analysis revealed potential damages. Signal values were compared against criteria for assessing the condition of reinforced concrete structures. Regular measurements detect potential damages, and combining this technique with other methods enhances its efficiency

Rebuilding Bailey Bridge to Bridge With Bascule Span – A Case Study

The structural analysis of a road foldable prefabricated steel Bailey- type bridge located over the Tuga River in Żelichowo, Poland is performed in this paper. Interesting and untypical bridge redevelopment performed made it possible to lift the middle foldable bridge span by approximately 4.0 m concerning the existing state. The paper begins with a survey of literature carried out on the investigations of foldable Bailey-type bridge subject matter. A description of the numerical modelling of foldable prefabricated bridges is performed. The comparison of the proof load test results with the FEM numerical model results has shown very good compatibility. This paper can provide scientists, engineers, and designers the basis for structural analysis in the field of foldable Bailey-type bridge constructions and numerical simulations.

SHEAR EXPERIMENTS ON STRAIGHT REINFORCED CONCRETE SLABS

As the existing bridge stock is aging, assessment of existing bridges becomes increasingly important. In the Netherlands, the shear capacity of reinforced concrete slab bridges is found to be insufficient. In particular, the shear and punching shear capacity of reinforced concrete slab bridges subjected to concentrated loads from the design tandem or truck is subject to discussion, as the shear behavior is situated in between one-way and two-way shear. Currently, an experimental program is being conducted at Delft University of Technology to determine the shear capacity of straight and skewed reinforced concrete slabs under point loads near to the support. This paper presents the results of the 25 tests conducted on six straight slabs of 5m × 2.5 m × 0.3 m subjected to a proof load testing loading protocol. The failure load and modes of the slabs are described in detail. Reinforced concrete slabs under concentrated loads can fail in shear, punching, and flexure, as well as a combination of these failure modes. The results of the experiments are compared to strength predictions obtained by using current design models and current methods for assessment. These experiments demonstrated that the Dutch guidelines, which are based on previous slab experiments, are an improvement as compared to the Eurocode for the assessment of existing reinforced concrete slab bridges. Ultimately, this work provides recommendations for bridge engineers tasked to assess reinforced concrete skewed slab bridges.

Evaluation of bridge load capacity using proof-load tests

A proof-load test is often necessary to accurately measure the field behavior of a bridge structure. A new segmental steel bridge has been constructed over the Tisza River in Hungary. The bridge comprises of two independent steel box girders assembled by a welding system. Engineers performed proof load tests before opening the structure to evaluate its load-carrying capacity and deck deflection. This paper presents several aspects of the load testing and evaluation of the bridge structure under static and dynamic loads using a rating factor (RF) approach compared to a baseline finite element model. The load test results helped to calibrate the model and verify the method. The study reveals that the tested bridge has an elastic behavior, a high capacity, and adequate dynamic performance.

Temporary Structural Health Monitoring of Historical Széchenyi Chain Bridge

A temporary monitoring system was installed on the 175-year-old historical Széchenyi Chain Bridge during its reconstruction. The bridge is in the downtown area in the capital city of Hungary and plays a significant role in the city life of Budapest. Six-month-long measurements were conducted during the reconstruction process of the bridge, yielding crucial insights into the structural behaviour of the historical structure. The measurement results were evaluated; the findings encompass the rotation capacity of the pins between the chain elements and the structural response to temperature changes. This information helped the decision-making between 2021 and 2023 by the designers and construction company during the reconstruction. For instance, daily temperature fluctuations resulted in increased bending moments in the chain elements, rising up to 158% compared to the values observed during a proof load test in 2018. Furthermore, the measurements reveal an approximate 42% increase in normal forces compared to the proof load test, which highlights the high sensitivity of chain bridges to temperature fluctuations, where geometric stiffness plays a crucial role. Reconstruction, namely reducing self-weight, notably intensifies the impact on normal forces and bending moments. These outcomes strongly emphasize the dominance of the dead load and self-weight in the case of chain bridges.

Optimized finite element analysis and strengthening assessment of the I-39 Kishwaukee bridge utilizing proof load testing

Optimized finite element analysis and strengthening assessment of the I-39 Kishwaukee bridge utilizing proof load testing

Time-dependent reliability assessment of existing concrete bridges with varying knowledge levels by proof load testing

In the evaluation of existing bridges and viaducts, relying solely on a desk study is often inadequate for determining their structural reliability. Performing a proof load test provides valuable field data that offers detailed information about the structural integrity. However, the relation between the magnitude of the load and the structural reliability is not immediately clear. This study addresses the challenges associated with determining the target load and highlights the uncertainties that play a key role. A case study is presented that shows the time-dependent character of the structural reliability and the influence of an informative and a weakly informative prior distribution in a Bayesian context. It is shown how both past traffic loads and a proof load test may contribute to the proven strength of a structure. The described method provides a starting point towards a flexible approach for proof load testing in which structure-specific knowledge levels and requirements are considered.

Assessment of existing concrete bridges by load testing: barriers to code implementation and proposed solutions

As the existing bridge stock is aging, the task of assessing these bridges becomes increasingly important. One of the assessment methods for existing bridges is load testing. Improvements in the field of diagnostic load testing are related to the use of numerical models. Improvements in the field of proof load testing focus on the safety of the execution of the test as well as the required load in the test. What is still lacking is a reflection of these recent advances in the codes and guidelines used for load testing of bridges. Two approaches are proposed to address this lack. The first approach attempts to answer fundamental questions with regard to bridge load testing through research. The second approach is to coordinate efforts and facilitate collaboration and exchange of ideas internationally through the IABMAS Technical Committee on Bridge Load Testing. In conclusion, it is expected that these efforts will form the basis of improved recommendations for the assessment of concrete bridges by load testing to be included in codes and guidelines and to serve the community of engineers faced with the task of assessing ageing infrastructure.

Numerical investigation of the keying process of a new type of expandable plate anchor

High efficient anchors are increasing demanded to moor floating structures with oil and gas and renewable energy developments move into deeper water. One effective way to increase efficiency is by maximizing the bearing area of the anchor during operation. Along this line of design, a new high efficiency plate anchor composed of two pieces of fluke plates, which are expandable after installation under preloading, is proposed in this paper. The keying process plays a significant role in the anchor's bearing performance. To gain insights into the keying process and optimize the geometry design of this anchor, a series of Large Deformation Finite Element (LDFE) analyses are carried out. From the comprehensive LDFE analysis, this proposed anchor with optimal padeye eccentricity has lower loss of embedment compared with traditional upright anchor and the accompanying higher holding capacity. Besides, the newly proposed expandable anchor also has a much stiffer response, the anchor can bear 3 times the keying load (proof loading) without losing much embedment during operation stage. This has an important implication for saving offshore cost, where the proposed anchor could be keyed using small vessel with limited winch capacity.

Load Testing of Cultural Heritage Structures and Sculptures: Unconventional Methods for Assessing Safety

The paper presents the results of static and dynamic experimental tests conducted on historical heritage structures and sculptures. In recent years, there was an increasing need to address the behaviour of these types of structures due to several reasons. Diagnosing the actual condition of a historical structure involves not only identifying the cause of a detected defect, but also determining its impact and assessing whether the structure can continue to perform safely. This article utilises unconventional loading methods to generate measurable mechanical responses. In one case, a lifting procedure is employed to study strains in a composite structure, while in another example, the mass and movement of people are used as a form of loading. Proof load tests conducted on a monumental sculpture allowed for the determination of load distribution among its heterogeneous structural components, namely a bronze shell and an iron reinforcing frame. Furthermore, the static and dynamic loading of a ceiling supported by a masonry vault demonstrated its ability to withstand anticipated loads resulting from unconventional use as a temporary exhibition space.

Experimental and analytical approaches for load rating reinforced concrete slab bridge

Load testing of bridges is often used as a reliable method for assessing the capacity of in-service bridges with low analytical load rating factors. This paper presents a detailed load rating study of an 82-year-old concrete slab bridge with an unusually large aspect ratio of 3.73 by performing non-destructive diagnostic and proof load tests. The test-based modified rating factor is evaluated based on the American Association of State Highway and Transportation Officials (AASHTO) approach and the structural effective strip width approach which is then compared with the analytical rating factor from a simplified 1-D beam-line model. Field data is also used to evaluate the impact of the rotational stiffness of the bridge on its global response and load rating factor. The field test results based on the AASHTO approach reveal that the rating factor improves by up to 53% compared to the analytical rating factor. Monitoring the rotational residual response at the bridge supports is proven to be an effective method for assessing the global response of the bridge during field testing. The study shows that adding a rotational spring with a field-calibrated rotational stiffness to the 1-D analytical model of the bridge can significantly increase the load rating factor.

Multisection Optimization–Based Target Proof Load Determination Method for Bridge Load Testing

Multisection Optimization–Based Target Proof Load Determination Method for Bridge Load Testing

Development of an Integrated Powered Hip and Microprocessor-Controlled Knee for a Hip-Knee-Ankle-Foot Prosthesis.

Hip-knee-ankle-foot prostheses (HKAF) are full lower-limb devices for people with hip amputations that enable individuals to regain their mobility and move freely within their chosen environment. HKAFs typically have high rejection rates among users, as well as gait asymmetry, increased trunk anterior-posterior lean, and increased pelvic tilt. A novel integrated hip-knee (IHK) unit was designed and evaluated to address the limitations of existing solutions. This IHK combines powered hip and microprocessor-controlled knee joints into one structure, with shared electronics, sensors, and batteries. The unit is also adjustable to user leg length and alignment. ISO-10328:2016 standard mechanical proof load testing demonstrated acceptable structural safety and rigidity. Successful functional testing involved three able-bodied participants walking with the IHK in a hip prosthesis simulator. Hip, knee, and pelvic tilt angles were recorded and stride parameters were analyzed from video recordings. Participants were able to walk independently using the IHK and data showed that participants used different walking strategies. Future development of the thigh unit should include completion of a synergistic gait control system, improved battery-holding mechanism, and amputee user testing.

Proof Load Testing Method by the American Association of State Highway and Transportation Officials and Suggestions for Improvement

Because of the aging of infrastructure, methods are explored by which the reliability of existing bridges and viaducts can be assessed. In cases in which limited information of the structure is available or its condition is of concern, proof load testing may be used to demonstrate sufficient live load carrying capacity. Proof load tests in the U.S.A. are typically performed using the Manual for Bridge Evaluation (MBE) published by the American Association of State Highway and Transportation Officials (AASHTO). The proof load is expressed by the regular live load model magnified by the target proof load factor. The level of reliability obtained using the target proof load factor is not explicitly stated in the MBE, but is of particular interest. In this article, relevant background documents are investigated to uncover the underlying calculations, assumptions, and input data. Current challenges in proof load testing are described in which the considerations of time dependence, stop criteria, available information, and system-level assessment are highlighted. Subsequently, improvements to the MBE proof load testing background are suggested. An example calculation using traffic data from the Netherlands shows that the HL93 load model and Eurocode LM1 provide a reasonably constant proof load factor with span length for bending and shear. However, the HS20 load model does not scale well with increasing span length. It is found that the magnitude of the target load as specified through the proof load factor is directly related to the desired level of reliability. Although the MBE proof load testing method is practical, several challenges remain.

Reliability-Based Proof Load Factors for Assessment of Bridges

Advanced reliability assessment can be required when evaluating existing bridge structures through proof load testing. The target load of a proof load test typically requires input from resistance models; however, bridges with a low documentation level are often the most relevant for proof load testing, and resistance models thus involve significant uncertainties. This paper presents a different approach to proof loading and target proof load, in which the resistance model is not included in the determination of this load. Instead, the target proof load is determined based on load models coupled to the desired target failure probability, thus ensuring sufficient safety of the existing bridge. The method is in line with the proposal for a new Eurocode on assessment of existing structures and is deemed to be superior to existing approaches. An essential assumption of the method is that monitoring systems can identify stop criteria before irreversible damage occurs. The approach was applied in a case study, where an OT-slab bridge with a span of 6.5 m was proof-load-tested and reclassified for capacity upgrading of a road stretch in Denmark.

Decision analytic approach for the reclassification of concrete bridges by using elastic limit information from proof loading

Decision analytic approach for the reclassification of concrete bridges by using elastic limit information from proof loading

Experimental characterization and numerical modeling of the influence of a proof load on the fatigue resistance of welded structures

The influence of a proof load, or an initial overload, on the fatigue resistance of welded structures is investigated in this study. Arc welded stiffeners made of S355 steel are considered and fatigue-tested in as-welded and proof-loaded conditions. X-ray diffraction analyses are carried out to evaluate the influence of a proof load on the residual stress field. To better understand the role of a proof load on the mechanical fields in the stress concentration zones, a numerical approach based on elasto-plastic finite element analyses is proposed. The methodology includes a non-local multiaxial fatigue criterion, which integrates a strain hardening contribution, that makes it possible to estimate the number of cycles to failure. The comparison between experimental and numerical results indicates that the beneficial effect of a proof load on the fatigue resistance can be mainly attributed to residual stress and strain hardening effects. The final result is a master SN curve adapted to the fatigue design of stiffener structures, tested under different loading conditions.

Proof load testing and shear assessment of kishwaukee I-39-river bridge using the modified compression field theory

Proof load testing and shear assessment of kishwaukee I-39-river bridge using the modified compression field theory