Controlled Load Tests Research Articles

Prestressed concrete bridge tested to failure: the Alveo Vecchio viaduct case study

The number of bridges approaching or exceeding their initial design life has been increasing dramatically. Meanwhile, bridges are withstanding an ever-increasing traffic volume, both in number and weight of vehicles. Analytical and numerical models can predict bridges’ response to traffic loads and their ultimate capacity with low uncertainties; however, such uncertainties increase as bridges age due to deterioration mechanisms. Non-destructive tests of material specimens and full-scale load tests allow for updating structural models and predicting bridges’ responses with higher accuracy. On-site load tests with different load levels provide different information on the bridge behaviour (e.g., elastic response, first-crack load, and ultimate capacity), which impact the model updating differently. This paper compares the observed response of the Alveo Vecchio viaduct, a prestressed concrete (PC) bridge subjected to a controlled load test up to its failure, with its predicted response provided by four structural models. The observed response is measured by an extensive structural health monitoring system, while the structural models are developed with different levels of refinement and uncertainty in the input parameters. This study gives an insight into the ultimate load-carrying capacity of existing PC bridges and their behaviour during a whole load test to failure. The results show that the load-carry capacity of the Alveo Vecchio viaduct is almost four times higher than the design load; likely, many other Italian highway bridges with similar structural characteristics have a similar capacity.

Model calibration of a long-span concrete cable-stayed bridge based on structural health monitoring data: Influence of concrete variability

Structural Health Monitoring (SHM) systems, in combination with controlled load tests, can provide valuable data for calibrating high fidelity bridge models, which can then be used for evaluating the long-term performance of the bridge, improved load ratings, and permit vehicle evaluation. The objective of this research was to calibrate a 3D model of the Indian River Inlet (IRIB) cable-stayed bridge, using strains recorded by the bridge SHM system during a controlled load test. The bridge was modeled in STAAD-Pro and calibrated using a pre-commercialized software platform that uses a Generic Algorithm to minimize the error between the measured and predicted strains. The calibration parameters were the elastic modulus of groups of the main longitudinal edge girder/deck elements, which once calibrated, could be related to the measured concrete strength of the members. Four different models were investigated, using 6, 10, 14, and 18 parameter element groups of the edge girder members. Of the different models, the 14 and 18 parameter models yielded the best results. The “design” model yielded errors as high as 42% when compared to the measured strains; the error was less than 10% for the majority of measurements for the 14-parameter model. Including the effect of the traffic barriers in the model, the weighted average concrete strength of the calibrated model was within 4% of the measured weighted strength. The calibration was shown to be insensitive to measurement noise and was validated using several unique single and multi-vehicle load cases that were heavier and more offset from the centerline of the bridge. The calibration procedure was able to capture the variability in flexural stiffness of the edge girders due to the variability of the concrete, resulting in significantly better agreement between the live load measured strains and the model predicted strains.

Experimental Strain Measurement Approach Using Fiber Bragg Grating Sensors for Monitoring of Railway Switches and Crossings.

Railway infrastructure plays a major role in providing the most cost-effective way to transport freight and passengers. The increase in train speed, traffic growth, heavier axles, and harsh environments make railway assets susceptible to degradation and failure. Railway switches and crossings (S&C) are a key element in any railway network, providing flexible traffic for trains to switch between tracks (through or turnout direction). S&C systems have complex structures, with many components, such as crossing parts, frogs, switchblades, and point machines. Many technologies (e.g., electrical, mechanical, and electronic devices) are used to operate and control S&C. These S&C systems are subject to failures and malfunctions that can cause delays, traffic disruptions, and even deadly accidents. Suitable field-based monitoring techniques to deal with fault detection in railway S&C systems are sought after. Wear is the major cause of S&C system failures. A novel measuring method to monitor excessive wear on the frog, as part of S&C, based on fiber Bragg grating (FBG) optical fiber sensors, is discussed in this paper. The developed solution is based on FBG sensors measuring the strain profile of the frog of S&C to determine wear size. A numerical model of a 3D prototype was developed through the finite element method, to define loading testing conditions, as well as for comparison with experimental tests. The sensors were examined under periodic and controlled loading tests. Results of this pilot study, based on simulation and laboratory tests, have shown a correlation for the static load. It was shown that the results of the experimental and the numerical studies were in good agreement.

Fatigue Behavior of Hybrid Components Containing Maraging Steel Parts Produced by Laser Powder Bed Fusion

This investigation concerns about of fatigue behavior under controlled loading and under strain control for hybrid specimens with parts produced with conventional processes in steel AISI H13 and the stainless steel AISI 420 and the rest part produced by laser powder bed fusion in AISI 18Ni300 steel. The controlled loading tests were performed in constant and variable amplitude. Fatigue failure of hybrid samples occurs mostly in laser-melted parts, initiated around the surface, in many cases with multi-nucleation and propagated predominantly between the deposited layers. Fatigue strength of hybrid parts, tested under displacement control is similar, but for specimens tested under load control the fatigue strength the fatigue strength of hybrid specimens is progressively lesser than laser powder bed fusion samples. Despite a tendency to obtain conservative predictions, Miner’s law predicts reasonably the fatigue lives under block loadings. The interface between materials presented an excellent joining and fatigue strength because the fatigue failure of hybrid samples occurred mostly in laser melted parts out of the interface.

Probabilistic fatigue assessment of monitored railroad bridge components using long-term response data in a reliability framework

Fatigue is a primary concern for railroad bridge owners because railroad bridges typically have high live load to dead load ratios and high stress cycle frequencies. However, existing inspection and post-inspection analysis methods are unable to accurately consider the full influence of bridge behavior on the fatigue life of bridge components. Reliability-based fatigue analysis methods have emerged to account for uncertainties in analysis parameters such as environmental and mechanical properties. While existing literature proposes probabilistic fatigue assessment of bridge components, this body of work relies on train parameter estimates, finite element model simulations, or controlled loading tests to augment monitoring data. This article presents a probabilistic fatigue assessment of monitored railroad bridge components using only continuous, long-term response data in a purely data-driven reliability framework that is compatible with existing inspection methods. As an illustrative example, this work quantifies the safety profile of a fracture-critical assembly comprising of six parallel eyebars on the Harahan Bridge (Memphis, TN). The monitored eyebars are susceptible to accelerated fatigue damage because changes in the boundary conditions cause some eyebars to carry a greater proportion of the total assembly load than assumed during design and analysis; existing manual inspection practices aim to maintain an equal loading distribution across the eyebars. Consequently, the limit state function derived in this article accounts for the coupled behavior between fatigue and relative tautness of the parallel eyebars. The reliability index values for both the element (i.e. individual eyebars) and system (i.e. full eyebar assembly) reliability problems are assessed and indicate that under the conservative assumption that progressive failure is brittle, first failure within the parallel eyebar system is generally equivalent to system failure. The proposed method also serves as an intervention strategy that can quantify the influence of eyebar realignment on the future evolution of the reliability index.

Technology for condition and performance evaluation of highway bridges

Today, bridge owners must consider increasing traffic demands (in both volume and weight) and also face concerns related to sustainability, resilience and liveability which were virtually unknown in the 1950s. Furthermore, legislators demand data-driven asset management decisions based on objective, quantitative and reliable bridge condition and performance evaluation. To explore the current state-of-the-art in objective performance and condition evaluation of constructed systems by leveraging technology, a 30-year old freeway bridge in New Jersey, exhibiting multiple complex performance deficiencies, was transformed into a field laboratory. To identify the root causes of performance concerns, Visual Inspection, Operational Monitoring, Forced Excitation Testing, Controlled Load Testing, Non-destructive Probes, Long-term Monitoring, Finite Element Modelling and Parameter Identification were conducted within a Structural Identification framework. The results showed that root causes of some performance deficiencies of the test bridge were identified definitively only through the application of field measurements and analyses integrated by following a scientific approach—i.e. Structural Identification. Controlled Proof-Load Testing was especially useful in demonstrating the location and impacts of damage and the remaining capacity although such an approach can only be considered for the most critical cases due to its high cost and disruption to operations. Operational monitoring was shown as a sufficient and much cheaper alternative for structural identification permitting the development of a 3D digital twin of the bridge, which proved critical in identifying the root causes of its deficiencies and formulating meaningful interventions. Without an a-priori model used for designing the experiments as well as a model (i.e. a digital twin) calibrated by parameter identification and used for simulations, it was not possible to offer options for corrective measures confidently. The study demonstrated the challenges in relying only on visual inspection when a multitude of interdependent mechanisms lead to damage and deterioration, and the information value of different experimental methods such as vibration testing, proof load testing, wide-area NDE scans and multi-year SHM in being able to understand the root causes of various damages.

Evolution of Bridge Diagnostic Load Testing in the USA

Driven by advancements in technology, along with the ever-growing demands of our aging infrastructure, structural evaluation through testing has progressed from a number of research endeavors to a full-fledged industry. Guidelines for Non-Destructive Evaluation (NDE) methods, diagnostic load testing, and proof load testing were published by the American Association of State Highway and Transportation Officials (AASHTO) in 2003 and were largely shaped by the technologies that were available in the 1990s. While specifications in subsequent AASHTO bridge evaluation manuals have remained relatively constant over the last 15 years, commercial applications have sprung forth in all areas of field-based bridge assessment. Much of the development has revolved around inexpensive high-speed data acquisition, high-speed wireless communications, and the surge of cloud-based data management. The market of equipment and services has developed around three main camps; NDE, Controlled Load Testing, and Structural Health Monitoring (SHM), with each field having a variety of subcategories. For example, Diagnostic Load Tests and Proof Load Tests are the two primary forms of controlled load testing. Selection of the appropriate tools and methods to solve any bridge assessment is a function of what information is available and the required functional serviceability of the structure. In many cases, a combination of methods must be employed to achieve a complete assessment. As such, the lines between NDE, Testing, and SHM have blurred and have become increasingly integral gears of a larger machine. This article provides a history of the primary field bridge evaluation techniques and includes the driving forces in commercial development. Focus is placed primarily on diagnostic load test methodology; however, a variety of testing methods are outlined to illustrate the best tool for the job, along with the several pros and cons of various testing and monitoring methods. Finally, a glimpse into the future of bridge evaluation is provided based on current trends and emerging technologies.

Identification of Composite Action Through Truck Load Testing

The continual increase of truck weights on our transportation system is a growing concern among bridge engineers. The load carrying capacity of the structures within the system must withstand this ever-growing demand. For multi-girder steel bridges, the load carrying capacity is heavily influenced by the presence of composite action between the girders and the concrete deck slab. While detailing to ensure reliable composite action is typically included in new designs, for many existing structures, the owner may not fully know the level of composite action. This may be due to administrative issues like insufficient original construction drawings or mechanical issues like breakdown of the shear transfer components. Even in situations where composite action was not intended there exists some partial interaction due to chemical bond and friction. Clearly understanding the presence and reliability of composite action in multi-girder structures is key to managing these structures effectively. This paper explores how load testing has been utilized to identify the level of composite action for existing bridges. The challenges associated with field identification of composite action are presented. In addition, three case studies of truck load testing are discussed. The first case utilized uncontrolled ambient truck measurements of an instrumented structure to field determine the composite behavior. The second and third cases perform a controlled load test with variations in truck weights and positions. Overall, the paper illustrates the advantages and disadvantages of truck load testing for identification of composite action and provides recommendations for future studies.

Influence of tyre inflation pressure on measured pavement strain responses and predicted distresses

The Federal Highway Administration conducted controlled loading tests on the US Route 23 Test Road under hot weather conditions in 1998. The testing was conducted using three tyre inflation pressures (TIPs) for four tyre types in two configurations on two asphalt concrete pavement sections. The pavement response data were collected from strain rosette sensors glued to the existing surface pavement layer and were adjusted to common temperature, lateral offset distance and speed for comparison purposes. The comparisons of the adjusted strain responses revealed the impact of the TIP on pavement strain responses and distress prediction. Mechanistic-Empirical Pavement Design Guide fatigue cracking and rutting models were used to predict the damage influenced by TIPs to the experimental pavement sections. The most road-friendly inflation pressure is recommended for each tyre configuration based on the resulting pavement service life, with pavement thickness influencing distress predictions. The two pavement sections with different thicknesses are compared based on their predicted performance as an additional study.

Deflection monitoring and assessment for a suspension bridge using a connected pipe system: a case study in China

Summary This paper discusses the application of a connected pipe system (CPS) to a suspension bridge in China for the purpose of vertical deflection monitoring and assessment. The CPS mainly consists of three main parts: the pressure transmitters to detect the height change of liquid, the pipes to connect the reference point and measurement points, and the liquid to fill the connected pipes. Multiple pressure transmitters, taken as the measurement point, were mounted inside of the girder. A reference transmitter was mounted inside of a tower, taken as a fixed point. To verify the performance and reliability of the CPS, a controlled load test after the completion of the bridge construction and an uncontrolled load test under the actual traffic loading were carried out. The results showed that the CPS exhibited excellent capability in real-time measurement of vertical deflection of the suspension bridge. With the long-term deflection data monitored by the CPS, the extreme deflections with respect to vehicle loads were predicted by extreme value analysis. The generalized extreme value distribution was adopted to establish the probability models of the daily maximum and minimum deflection sequences, and then the extreme deflections within the design reference period of 100 years were determined based on the probability models. Comparison of the extreme deflections and the deflection thresholds was carried out. The deflection monitoring and assessment method proposed in this paper have shown high potential of applicability in the practice of health monitoring for long-span bridges. Copyright © 2015 John Wiley & Sons, Ltd.

Structural monitoring and 8-year load test on Europe's first fibre-reinforced polymer highway bridge

In October 2002 the first all-fibre-reinforced polymer (FRP) composite bridge on the public highway network in Europe, West Mill Bridge, UK, was installed. The design and construction of this bridge was the culmination of a 4-year EU research project called Asset, to develop a heavy-duty FRP bridge decking system for use in repairing, upgrading and new civil infrastructure. As part of this project, a monitoring system was installed on the bridge during fabrication. In addition to an initial controlled load test on installation of the bridge, further controlled load tests using a 30 t lorry have been undertaken after 3 years and 8 years. The results from these load tests confirmed the medium-term structural behaviour to be essentially unchanged from the original structural behaviour. In particular, a high level of composite action between the glass fibre reinforced polymer deck, FRP main beams, and concrete parapet beams was still present after 8 years of service.

Influence of tyre configuration on pavement response and predicted distress

The Federal Highway Administration conducted controlled loading tests on the U.S. Route 23 Test Road in hot weather conditions in Ohio, including two dual and two wide-base configurations. This paper is to reveal the influence of tyre configuration on pavement and provide some suggestions on tyre configuration from the perspective of reducing pavement damage. The raw strains were adjusted to common temperature, lateral offset distance and nominal speed for consistent comparison. MEPDG fatigue cracking and rutting models were used to predict damage brought by different tyres to pavement sections. The results indicate that newer generation of wide-based tyres with wider interface with pavement could be road-friendly, inducing similar or even less damage than the conventional dual tyres. At the same time, certain conventional dual tyres, which are commonly used in the current market, might cause larger damage to the pavement than other tyres in certain environmental and loading conditions.

An Investigation into Wheel Sinkage on Soft Sand

ABSTRACT Sinkage is an empirically significant factor in vehicle performance as it can result in an immobile vehicle or significant environmental damage. Bernstein first proposed a pressure-sinkage relationship in 1913, and subsequent work by Janosi and Hanamoto and Hedegus concluded that longitudinal wheel slip also plays a role in sinkage. Shinone, Nakashima, Takatsu, Kasetani, and Matsukawa identified a linear relationship between slip and sinkage on a lightly loaded tire (980 N). In this study, the effects of vertical wheel load, longitudinal wheel slip ratio, and tire inflation pressure on wheel sinkage on loose sand were investigated to relate sinkage to a vehicular operating condition. The test program in this study was conducted using the Cranfield University Single Wheel Tester (SWT) on loose, desert-like sand in the Cranfield Off-Road Dynamics facility soil lane. The SWT uses a closed loop servo-controlled hydraulic actuator to actively control vertical wheel load and twin hydraulic motors to actively control wheel speed. The SWT apparatus is mounted on an independent prime mover tractor unit, which controls forward speed. True forward speed is continuously measured against a fixed reference point and used to calculate the required wheel speed in real time to give the desired slip profile. A series of controlled load tests were conducted using a Goodyear G90 tire on a dry desert sand material. Four discrete inflation pressures (0.69, 1.38, 2.07, and 2.76 bar [10, 20, 30, and 40 psi] and four vertical wheel loads (1, 2, 3, 4, and 5 kN) were chosen to represent the operating range of the tire. Each test run consisted of a continuously decreasing sweep of longitudinal wheel slip ratio (the slip ratio was controlled to decrease linearly from 85% [driven] to −15% [braked]). Although a near-linear increase in sinkage was identified for wheel slip ratios greater than 10%, as Shinone et al. also found, the overall relationship between slip ratio and sinkage was found to be nonlinear.

Development of Load Rating Procedure for Railroad Flatcar Bridges through Use of Field Instrumentation. I: Data Collection and Analysis

Because of budget constraints, many state and county highway agencies are often forced to develop innovative and economical replacement strategies for deteriorated bridges. One such option is to use a retired railroad flatcar (RRFC) for a bridge superstructure. Many states have found RRFCs to be successful and economical alternatives to more traditional structural systems. Although the performance of RRFCs has been satisfactory, there is little to no guidance in the AASHTO specifications for load rating these structures. Such inexperience has led some to take overly conservative approaches when rating these bridges. This paper, the first of two companion papers, presents the use of field instrumentation and controlled load testing on seven RRFC bridges located in Indiana. Stress data were used to gain an understanding of the in situ response of these structures, including global bending, secondary bending, and lateral load distribution. Proposed load rating guidelines presented in the second companion paper were developed using data from these load tests as well as other data found in the literature.

Development of Load Rating Procedure for Railroad Flatcar Bridges through Use of Field Instrumentation. II: Procedure Development

Many state and county highway agencies are often forced to develop innovative and economical replacement strategies for deteriorated bridges. One such option is to use a retired railroad flatcar (RRFC) for a bridge superstructure. Many states have found RRFCs to be successful and economical alternatives to more traditional structural systems. Although the performance of RRFCs has been satisfactory, there is little to no guidance in the AASHTO specifications for load rating these structures. This inexperience has led some to take overly conservative approaches when rating these bridges for strength and fatigue. This paper, the second of two companion papers, presents the development of proposed load rating guidelines for RRFC bridges. The guidelines were developed based on previous research found in the literature and through the use of controlled load testing of RRFC bridges as presented in the first companion paper.

The performance of different adhesives for archaeological ceramics under mechanical stress

The influence of environmental conditions, in particular temperature, on the performance of adhesives joining different archaeological ceramic fabrics is assessed in laboratory conditions. Different types of model ceramic fabrics were manufactured and joined with commercially available adhesives, which are commonly employed in the conservation of archaeological ceramics, and a series of systematic tests on the various adhesive–ceramic systems was conducted. The response of joins to static mechanical stress was assessed in controlled loading tests. Results of those tests as well as failure mechanisms observed are discussed.

Structural monitoring of a strengthened orthotropic steel bridge deck using strain data

Orthotropic steel bridges have experienced early fatigue cracks at several welded connections in the steel deck plate. One of the possible strengthening systems to enlarge the fatigue life of the existing decks consists of bonding a second steel plate to the existing deck. This renovation technique was for the first time applied on the orthotropic deck of the movable bridge Scharsterrijn. This article describes the results of the structural monitoring carried out to evaluate the short-term and long-term performance of the strengthening system. Static and dynamic controlled load tests were carried out using a calibrated truck. Strain history measurements were recorded continuously during 1 year from the normal traffic running on the bridge. The short-term measurements show significant decrease of the stress level at the bridge deck after the renovation, especially at the deck plate details. The stresses at the welds between the deck plate and the stiffener web reduce approximately 55% at the deck plate side and 35% at the stiffener web side. Due to this reduction, the fatigue life of these welds is expected to increase 11 times at the deck plate side and 3.6 times at the stiffener side. The long-term measurements do not show significant changes in the stress level at the bridge deck during the year of monitoring. The strengthening system has demonstrated good performance reliability to prolong the life span of the movable orthotropic bridges.

Pavement Shear Strain Response to Dual and Wide-Base Tires

FHWA conducted controlled loading tests on the US-23 test road in hot weather conditions in Ohio. The tests used four tire types in both dual and wide-base configurations, which were fitted on a single unit two-axle truck, maintaining a constant gross vehicle weight. Two pavement sections, one 8 in. (200 mm) and one 4 in. (100 mm) thick, were instrumented with strain gauge rosettes oriented vertically to measure strain traces induced from the passing wheel loads at three speeds and tire inflation pressures. Pavement temperature was monitored with depth during testing as well as wheel track offset distance from the strain sensors. Because of time constraints, only the sensors in the plane parallel to the direction of loading were analyzed, and response data were compared only with linear elastic pavement response models. The as-measured data were processed and evaluated for all rosettes oriented in the direction of loading. Stress relaxation modulus data were used to adjust the pavement modulus to a common temperature and loading time so all measured data could be compared at the same loading conditions. The WinLEA linear elastic model was used to determine the relationship of structural modulus to strain. Lateral offset distributions were determined from measured data to adjust all strains to the offset where maximum strain response is observed in the as-measured data. The adjustments were then applied to the as-measured strain data to make consistent comparisons between tires. Three of the four tire configurations produce nearly equivalent pavement response, which was attributed to similarities between the tire footprint widths.

Field stress/displacement monitoring and fatigue reliability assessment of retrofitted steel bridge details

This paper presents the field stress and displacement measurements in controlled load tests and long-term monitoring to investigate the performance of two retrofitted details, which were used to alleviate the cracking problems of an existing steel bridge. Effectiveness of the retrofit schemes is demonstrated by comparing the displacements of the retrofitted details with those of the non-retrofitted ones. Based on the field monitored data and the AASHTO Specifications, time-dependent fatigue reliability assessment is made, in which S– N curves are used to consider the influence of variable amplitude loading on the propagation of initial defects and fatigue damage. Effective stress ranges are derived from daily stress range histograms, and lognormal probability density functions (PDFs) are used to model the uncertainties in the effective stress range with the aid of regression analyses. It is observed that stress ranges in the instrumented details are all below the corresponding constant amplitude fatigue limits. Consequently, high fatigue reliabilities of these retrofitted details are expected. However, the reliability indices decrease significantly as time goes on, and this deterioration process may be accelerated with the increase in traffic volume. The analysis results provide references to bridges with similar fatigue cracking problems.

Behavior of instrumented prestressed high performance concrete bridge girders

A comprehensive monitoring of the behavior of four prestressed high performance concrete (HPC) bridge girders, with higher compressive strength, during construction and while in-service, is presented. The monitoring program covered instrumentation and monitoring of a series of four girders during the casting operation, after construction, under the effects of traffic and thermal loads, as well as under controlled load conditions. Information regarding transfer length, prestress loss, heat of hydration, compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR), creep, shrinkage, coefficient of thermal expansion, and chloride permeability of the concrete used is obtained and presented. Furthermore, the in-service monitoring and controlled load tests and details regarding thermal expansion, bridge stiffness, and load distribution factors are also presented. This paper provides details of testing of the concrete properties and field instrumentation of the bridge girders as well as a discussion of service level monitoring and controlled load testing. Comparisons are made between experimental and theoretical results.