Nondestructive Testing Evaluation of Drying Process in Flooded Full-Scale Masonry Walls

After an investigation on the most recent floods occurred in Italy that damaged the Cultural Heritage masonry buildings, an experimental research started on-site on full-scale masonry models exposed to the environmental agents in Milan. The masonry materials used for the full-scale models were largely investigated in the past and the models were subjected to decay caused by the capillary rise and by the crystallization of sodium sulfate coming from the foundations. These walls can actually simulate the state of naturally contaminated walls before a flood and represent a construction where the main parameters are known. A flood has been simulated by adding water for several days to the walls of the full-scale models previously contaminated by salts, then the walls were left to naturally dry. The objective is to check the effectiveness of nondestructive (ND) techniques in detecting the presence of water and the drying process and also the influence of surface treatments presence. Radar tests, thermography tests, sonic tests, as well as the minor destructive powder drilling tests were applied successfully to evaluate the moisture distribution in the masonry after flooding and during natural drying.     

Condition Assessment of a Deteriorated Cement Works

This paper describes the condition assessment of a 30 year old cement works, where some of the structures were clearly deteriorated. It was carried out for the purpose of obtaining material properties needed for evaluating strength and integrity, and for establishing durability. This was done by sampling the structures using the nondestructive techniques of visual inspection, perusal of drawings, ultrasonic pulse velocity measurements, covermeter surveys, and core testing. Core testing gave information not only about strength but also about sorptivity, carbonation, chlorides, and sulfates, and about the variation of some of these properties with depth from the concrete surface. Some new approaches were used to estimate the grade of concrete and the partial safety factor for reinforcement. The use of “twin cores” (surface and internal) indicated that the surface quality of the concrete was actually better than the internal quality. Recommendations for repair and maintenance dealt with (1) accumulated cement dust; (2) concrete deterioration; (3) areas experiencing elevated temperatures; and (4) waterproofing of the concrete surface.     

Bridge Management and Nondestructive Evaluation

The City and County of Denver (CCD) Public Works Department owns, inspects, and maintains 531 bridges in its inventory of which 264 are considered major structures spanning over 6.1?m in length. In this paper, a methodology using the CCD major bridge network for the application of nondestructive evaluation (NDE) methods in bridge inspections is explained. The methodology, called Bridge Evaluation using Nondestructive Testing (BENT) helps systematically integrate NDE methods and conventional bridge management systems by using a Markovian deterioration model. Although the BENT method can be applied to timber, steel, and concrete bridges, in this paper the application of the method will be restricted to concrete bridges. The BENT system is part of a comprehensive geographic information system whereby database queries can be completed using a map interface. The database contains a wide array of information in the CCD infrastructure inventory including bridges, pavements, alleys, and street subsystems.     

Experimental Response of Externally Retrofitted Masonry Walls Subjected to Shear Loading

Recent earthquakes have produced extensive damage in a large number of existing masonry buildings, demonstrating the need for retrofitting masonry structures. Externally bonded carbon fiber is a retrofitting technique that has been used to increase the strength of reinforced concrete elements. Sixteen full-scale shear dominant clay brick masonry walls, six with wire-steel shear reinforcement, were retrofitted with two configurations of externally bonded carbon fiber strips and subjected to shear loading. The results of the experimental program showed that the strength of the walls could be increased 13–84%, whereas, their displacement capacity increased 51–146%. This paper presents an analysis of the experimental results and simple equations to estimate the cracking load and the maximum shear strength of clay brick masonry walls, retrofitted with carbon fiber.     

Detection of Ungrouted Cells in Concrete Masonry Constructions Using a Dielectric Variation Approach

In this study, a new technique for detecting ungrouted cells in concrete block masonry constructions was developed. The concept, based on detecting the local dielectric permittivity variations, was employed to design coplanar capacitance sensors with high sensitivities to detect such construction defects. An analytical model and finite element simulations were used to assess the influence of the sensor geometrical parameters on the sensor signals and to optimize the sensor design. To experimentally verify the model, the dielectric properties of various materials involved in concrete masonry walls were measured. In addition, a masonry wall containing predetermined grouted and ungrouted cells was constructed and inspected using the developed sensors in a laboratory setting. Moreover, different capacitance sensors were designed and compared with respect to their sensitivity, signal-to-noise ratio, and coefficient of variation of the inspected measurements. Excellent agreements were found between the experimental capacitance signal response parameters and those predicted by the analytical and finite element models. The proposed sensor design, coupled with a commercially available portable capacitance meter, would facilitate employing this technique in the field for rapid inspection of masonry structures without the need for sophisticated data analyses usually required by other more expensive and time consuming methods.     

Detection of Common Defects in Concrete Bridge Decks Using Nondestructive Evaluation Techniques

The transportation infrastructure in the United States is deteriorating and will require significant improvements. Consequently, innovations in the area of transportation infrastructure maintenance and rehabilitation are keys to the health and wellness of this valuable national asset. A major component of maintenance and rehabilitation is the ability to accurately assess the condition of the transportation infrastructure. This can be accomplished in part by using nondestructive evaluation techniques. Several nondestructive techniques have been used on concrete bridge decks and have proven to be efficient and effective. This paper aims at studying the different nondestructive evaluation techniques used in the assessment of concrete bridge deck conditions. An experimental investigation to evaluate the ability of infrared thermography, impact echo, and ground penetrating radar to detect common flaws in concrete bridge decks is developed and discussed. Results from this study showed the ability of these methods to detect defects with varying precision. Capabilities of the methods were verified and comparisons among the methods were made.     

Superload Evaluation of the Bonnet Carré Spillway Bridge

The passage of overloads that require special permitting is a common occurrence. Prior to the passage of such an overload, a simplified computer analysis is generally conducted to predict the expected behavior of the bridge. This paper addresses the field evaluation of three superloads that crossed the Bonnet Carré Spillway Bridge in Louisiana. Emphasis is placed on comparisons between the expected and actual behavior due to rotational restraint, live load distribution, the stiffening effect of bridge rails, and other factors. Finite-element modeling was conducted and the approach taken along with the results obtained are described. One important conclusion was that the longitudinal configuration of the axle loads supplied by the hauler was configured differently than indicated on the permit. While the gross load was accurate, the distribution between sets of axles varied considerably from those assumed in the permitting process. To minimize the potential for damage to bridges it is therefore recommended that axle loads be weighed prior to the passage of such overloads.     

Nondestructive Assessment of Damage in Concrete Bridge Decks

Impact-echo tests were performed on a precast, reinforced concrete bridge slab that was removed from a maintenance bridge built in 1953 in South Carolina. Impact-echo tests were first performed to nondestructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. It was found that the velocity varied by as much as 900?m/s throughout the slab. After the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slab that were not visible from the surface. Areas with preexisting damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.     

Inspection of Quebec Street Bridge in Denver, Colorado: Destructive and Nondestructive Testing

Nondestructive testing techniques have been historically and commonly used to evaluate the quality of existing concrete structures. Several traditional nondestructive testing techniques were applied to the pier caps of the Quebec Street Bridge over Air Lawn Road, constructed in 1971, which is located in Denver, Colorado. The techniques utilized included visual inspection, hammer sounding, Schmidt hammer rebounding, and ultrasonic pulse velocity testing, including tomographic imaging. Results of the nondestructive tests were used to determine areas to be tested with local destructive tests. These tests included concrete compressive strengths, chloride testing, and petrographic testing. This paper presents the application and interpretation of common nondestructive testing techniques and the consequent repair, rehabilitation, and maintenance decisions. The overall results indicate that inside cores of all the pier caps are healthy, sound concrete. On all of the pier caps, extensive exterior concrete layer rehabilitation needed to be completed.     

Response of Slab Bridges Before, During, and After Repair

Continuous reinforced concrete slab bridges rely on reinforcing steel bars near the top of the deck over the piers to carry negative moment. Transfer of forces in these bars may be jeopardized by deterioration and repair procedures that involve variable depth removal of deteriorated concrete around the bars. Partial or full loss of continuity could overstress the bottom reinforcement. Truckload testing of three bridges with various levels of damage was conducted before, during, and after repair in an attempt to quantify the level of loss of continuity and to examine the effectiveness of repair in terms of increasing the load transfer and enhancing the overall stiffness. Test results show loss of stiffness during repair but increased stiffness after completion of repair. The continuity was found to be lost during repair, and the slab dead load positive moments may be increased by as much as 50%. After repair, the continuity was restored, and the live-load distribution was essentially unaltered. For the test bridges, the redistribution of dead-load moment to the positive-moment zones did not appreciably affect the overall bridge rating factor. The amount of moment redistribution may be controlled through planning of repair steps.     

Monitoring and Repair of the Milwaukee City Hall Masonry Tower

The Milwaukee City Hall was built between 1893 and 1898 and is located in downtown Milwaukee, one block east of the Milwaukee River. The 300?ft (91.4?m) long building, nine stories high over its main portion, is a trapezoid in plan. On the south side, there is a 393?ft (119.8?m) tall South Tower located above the main entrance to the building. On three sides, the South Tower rises from the street level to the 13th level and the roof above, and on the north side, it is connected to the rest of the building up to the ninth floor. The South Tower is a hybrid steel and masonry structure consisting of masonry perimeter walls and a central core, four-sided steel truss supporting the floors and roof. The building is a perimeter-load-bearing masonry structure supported on wood piles. The city of Milwaukee had been aware of distress, in the form of cracks and loose masonry, in the South Tower for a number of decades. In 2002, the city took action to investigate the causes and significance of distress, and to develop a repair program. The scope of our work included review of the available structural drawings and documents, inspection of the tower, measurement and monitoring of movements, monitoring of thermal response, structural analyses of the hybrid steel and masonry structure, and development of repair recommendations. The repair program presently is under construction. This paper describes the monitoring program, analyses of the causes for distress, and the implemented repair concepts for the observed distress in the South Tower of the Milwaukee City Hall.     

Fatigue Behavior and Nondestructive Evaluation of Full-Scale FRP Honeycomb Bridge Specimen

An experimental investigation was performed to assess the projected fatigue performance of a fiber-reinforced polymer honeycomb bridge that has recently been completed in Troupsburg, N.Y. The laboratory specimen was representative of a 305-mm-wide strip of the completed bridge. The specimen was first subjected to fatigue loading. Load, displacement, and strain were measured every 25,000 cycles. The data indicated minimum signs of degradation after 2 million cycles of fatigue loading, as reflected in slightly increased values of vertical deflection and strain at midspan. After completion of the fatigue loading, the specimen was evaluated with acoustic emission. Load was statically applied and increased incrementally until failure occurred at a load level exceeding 16 times the fatigue level loading. The results of the static testing also indicated that only minor damage occurred due to fatigue. Field load testing of the actual bridge has been completed by the New York State Department of Transportation, and the results are discussed as they pertain to the fatigue and static load testing programs described.     

Evaluation, Rehabilitation Planning, and Stay-Cable Replacement Design for the Hale Boggs Bridge in Luling, Louisiana

The Hale Boggs Bridge opened to traffic on October 5, 1983. At the time, it was the first U.S. cable-stayed crossing over the Mississippi River. The PE (polyethylene) protective sheathing was damaged in many of the cables before and during installation, and after the opening of the bridge to traffic. Repairs were attempted to correct the defects in cable sheathing. Many of the repairs performed poorly and failed to protect the main tension element. The condition of 39 out of 72 cables indicated a critical need for repair and timely action was recommended. To address these damages, and to assure the structural integrity of the bridge structure, several strategies involving a range of repair and replacement options were evaluated using life cycle cost analysis. It was concluded that the strategy to replace all cables presents the best value among evaluated alternatives. The design of the complete 72 cable array replacement is the first occasion on which this process is attempted in North America. The final design of the replacement cables is heavily influenced by the geometric restrictions of the existing anchorage locations. The replacement cables are being designed for a 75-year design life and incorporated with the latest advancements in corrosion protection and vibration control. Maintenance of traffic design is an essential part of the project. The bridge is a critical regional link and constitutes a hurricane evacuation route. Traffic maintenance during cable replacement was designed to be as unobtrusive to the public and commerce as practical. This paper describes efforts associated with cable condition assessment, rehabilitation strategy, and design considerations and concepts, undertaken by the writers since 2002 to improve the condition of this major river crossing.     

Nondestructive Evaluation of the I-40 Bridge over the Rio Grande River

A nondestructive strength evaluation of the I-40 Bridge over the Rio Grande River in Albuquerque, N.M. was completed for the New Mexico Department of Transportation (NMDOT). The I-40 Bridge is a precast, prestressed concrete girder bridge located within 3?mi. of the “Big I” interchange carrying Interstates I-40 and I-25. Because of its location, the I-40 Bridge is subjected to large amounts of heavy truck traffic. The primary objective of the study reported herein was to determine a more accurate capacity rating for the I-40 Bridge and thus, reduce the number of overweight vehicle permit denials. To achieve this objective, a conventional rating analysis is first performed based on American Association of State Highway and Transportation Officials (AASHTO) guidelines. A diagnostic load test and a finite-element analysis are then completed. Details of the AASHTO rating analysis as well as the approach by which measured girder strains from the load test and finite-element results were considered in the capacity rating of the I-40 Bridge are discussed. Findings from the study confirmed that the capacity ratings of the I-40 Bridge could be safely increased by a factor of 1.7.     

In-Plane Lateral Response of a Full-Scale Masonry Subassemblage with and without an Inorganic Matrix-Grid Strengthening System

A full-scale unreinforced masonry (URM) wall with an opening was tested under in-plane lateral loading. The wall was first subjected to monotonically increasing displacements until a moderate damage level was reached. The damaged specimen was then cyclically tested up to almost the same maximum drift attained during the monotonic test to investigate the effects of previous damage on its nonlinear response. Finally, the masonry wall was repaired with inorganic matrix-grid (IMG) composites and subjected to a cyclic displacement-controlled test up to a near-collapse state. Most of the observed damage developed in the spandrel panel affecting both lateral resistance and strength degradation. Rocking of piers governed lateral stiffness and hysteretic response, which was characterized by low residual displacements and recentering behavior. The comparison between the experimental force-displacement curves demonstrated that the IMG strengthening system was able to provide energy dissipation capacity to the spandrel panel, restoring load-bearing capacity of the as-built wall, and delaying strength degradation that was indeed observed at larger displacements. Bilinear idealizations of force-displacement curves allowed the identification of displacement ductility, global overstrength, and strength reduction factor of the tested wall systems.     

Ultrasonic Pulse Velocity in Nondestructive Evaluation of Low Quality and Damaged Concrete and Masonry Construction

This paper discusses applications of ASTM C 597 “Standard Test Method for Pulse Velocity Through Concrete” technique to field detection of damage to concrete in service and field quality assessment of cast-in-place concrete and masonry under construction. Four unique field investigation and validation studies are discussed in this paper. The first part includes field assessments of concrete members under construction with questionable quality. Case studies include detection of zones of high air content and low strength concrete in a cast-in-place, posttensioned structure and detection of voids and honeycombs in poorly consolidated cast-in-place beams. The third case study pertinent to construction involves detection of poorly consolidated collar joints in a masonry rehabilitation project. In addition to assessments during construction and rehabilitation, this paper also discusses assessment of damage to concrete structures in service. The case study included in the paper involves exposure to elevated temperatures during a fire at a precast, double tee concrete parking structure. Nondestructive evaluation (NDE) testing findings were validated by subsequent laboratory testing or selective demolition to confirm NDE findings. This paper should be of value to practicing engineers interested in application of pulse velocity testing technique in field assessments similar to ones discussed. This paper should also be of value to researchers interested in applicability of pulse velocity to research concerning properties of concrete subjected to the damage mechanisms associated with elevated temperatures.     

Nonlinear Behavior of a Masonry Subassemblage Before and After Strengthening with Inorganic Matrix-Grid Composites

Past experimental tests on a full-scale masonry wall with an opening evidenced the key role of the spandrel panel in the in-plane nonlinear response of the system. Recent seismic codes do not provide specific criteria to assess and to strengthen existing masonry spandrel panels with inorganic matrix-grid (IMG) composites. Numerical finite-element (FE) analyses are used to deepen the knowledge about the nonlinear response of masonry walls and the role of the IMG strengthening system. The comparison of experimental and numerical results contributes to the development of a simplified analytical model to assess the influence of the external reinforcement system on the in-plane seismic response of masonry wall systems. Some hints about the strengthening design that could change the failure mode from brittle shear to ductile flexure are given. Finally, a further enhancement of the IMG strengthening system is proposed to avoid the undesirable splitting phenomena attributable to compression forces and to exploit the full compressive strength of masonry against bending moments.     

Nondestructive Testing of GFRP Bridge Decks Using Ground Penetrating Radar and Infrared Thermography

As glass fiber-reinforced polymer (GFRP) bridge decks are becoming a feasible alternative to the traditional concrete bridge decks, an innovative methodology to evaluate the in situ conditions are vital to GFRP bridge decks’ full implementation. Ground penetrating radar (GPR) typically performs well in detecting subsurface condition of a structural component with moisture pockets trapped within the material. On the other hand, infrared thermography (IRT) is traditionally known for its ability to detect air pockets within the material. In order to evaluate both nondestructive testing methods’ effectiveness for subsurface condition assessment of GFRP bridge deck, debonds of various sizes were embedded into a GFRP bridge deck module. A 1.5 GHz ground-coupled GPR system and a radiometric infrared camera were used to scan the deck module for condition assessment. Test results showed that both GPR and IRT retained their respective effectiveness in detecting subsurface anomalies. GPR was found to be capable of detecting water-filled defects as small as 5×5?cm2 in plan size, and as thin as 0.15 cm. Furthermore, tests on additional specimens showed that the GPR system offers some promise in detecting bottom flange defects as far down as 10 cm deep. IRT, on the other hand, showed that it is capable of finding both water-filled and air-filled defects within the top layers of the deck with solar heating as main source of heat flux. While test results showed IRT is more sensitive to air-filled defects, water-filled defects can still be detected with a large enough heating mechanism. The experiments showed that a more detailed and accurate assessment can be achieved by combining both GPR and IRT.     

Underwater Fiber–Reinforced Polymers Repair of Prestressed Piles in the Allen Creek Bridge

This paper presents an overview of a demonstration project in which corroding prestressed piles located in tidal waters were wrapped underwater using carbon and glass fiber-reinforced polymer material. An innovative instrumentation scheme was developed to allow assessment of the prewrap and postwrap corrosion state using linear polarization. This system is simple to install and eliminates the need for wiring or junction boxes. The underwater wrap used a unique water-activated urethane resin system that eliminated the need for cofferdam construction. Linear polarization measurements taken before and after wrapping indicate that the corrosion rate in the wrapped specimens is consistently lower than those in its unwrapped counterpart. These preliminary findings are encouraging and suggest that underwater wrapping without cofferdam construction may provide a cost-effective solution for pile repair.     

Bridge Health Index for the City and County of Denver, Colorado. II: Denver Bridge Health Index

Current bridge health index (BHI) in Pontis bridge management system applied to assess the bridge health conditions for 615 bridges in the city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. Both the calculation results and the computing methodology of the current BHI reveal that it is subjective to a municipality’s often imprecise cost data. This paper focuses on developing an alternate BHI. In order to understand the principle and procedure of the BHI calculation, the element weighting point was developed as a new concept in the analysis. The study concluded that the weighting point should reflect the effect of element damage on bridge health and function instead of a percentage of element value. Based on this conclusion, the current BHI was modified. The Denver BHI, a new diagnostic tool, was developed. It has already been adopted in the Pontis bridge management system of the CCD public works department.