Destructive and Non-Destructive Testing of Bridge J857 Phelps County, Missouri : Strengthening and Testing to Failure of Bridge Piers

Many of the existing reinforced concrete (RC) bridge piers constructed in the first half of this century were designed as gravity piers with minimal flexural reinforcement and no consideration to seismically induced lateral forces. When considered in earlier designs, the seismic lateral forces were typically low. The potential risk of failure of columns on these piers under a moderate earthquake is becoming a growing concern for the transportation management agencies. In addition, flexural strength deficiency in RC columns may arise from the loss of reinforcement due to corrosion, premature termination of the main reinforcement, or inadequate splicing. One method for retrofitting columns with flexural strength deficiencies consists of the addition of a RC or steel jackets. However, these systems may not be very practical due to undesirable section enlargement or construction constraints. Fiber Reinforced Polymers (FRP) have suitable mechanical properties for structural applications such as corrosion resistance and high strength-to-weight ratio. Although a properly designed FRP jacket can improve column compression strength, shear strength, and ductility, it may not sufficiently improve flexural capacity. Near-surface mounted (NSM) FRP rods is another technique that could be used to improve the flexural capacity of RC columns. This strengthening technique consists of FRP rods embedded in grooves made on the surface of the concrete and bonded in place with epoxy. To investigate the applicability and effectiveness of this technique, a research program was carried out in which bridge columns originally designed to carry gravity loads were upgraded and then tested to failure. Flexural strengthening was achieved by mounting carbon FRP (CFRP) rods on two opposite sides of the columns. In addition, the strengthened columns were wrapped with carbon and glass composites to satisfy seismic detailing requirements. The columns were tested to failure by applying lateral load cycles. The behavior of strengthened columns and their failure modes are discussed and conclusions are drawn. Test results indicate that the proposed strengthening is feasible and effective for improving the flexural capacity of RC columns. The capacity of the strengthened sections could be predicted using classical methods of analysis. Full investigation of the upgraded structure should be made to ensure that the deficiency is not shifted to other structural components. The final report consists of three volumes. Volume I depicts the strengthening and testing to failure of the three bridge decks. Volume II focuses on the laboratory and field dynamic tests. Volume III presents the strengthening and testing to failure of the bridge piers

Destructive and Non-Destructive Testing of Bridge J857 Phelps County, Missouri : Strengthening and Testing to Failure of Bridge Decks

Concrete bridges are conventionally reinforced with steel bars and/or prestressed with steel tendons. When subjected to aggressive environments, corrosion of the reinforcing and prestressing steel occurs and eventually leads to premature structural deterioration and loss of serviceability. In addition, the increasing service loads as well as seismic upgrade requirements result in a need to strengthen many of these bridges. The use of externally bonded steel plates for flexural and shear strengthening of concrete members is well established. However, corrosion related problems have limited the use of this technique for outdoor application. Fiber reinforced polymer (FRP) composites are corrosion resistant and exhibit several properties that make them suitable for repair/strengthening of reinforced concrete (RC) structures. However, the database for performance of FRP strengthened RC members is based on small-scale specimens that do not account for the variation of boundary conditions of a real structure. Fullscale field tests can demonstrate the actual behavior of a structure and can lead to a better understanding of the performance of the system and therefore strengthening design requirements. This part of the research program aimed at demonstrating the feasibility and effectiveness of strengthening bridge RC decks with two systems of externally bonded FRP reinforcement to increase their flexural strengths as well as verify design methodology and capacity improvement. Two of the three simply supported decks were strengthened and tested to failure. One span was strengthened using near-surface mounted (NSM) CFRP rods while the second span was strengthened using externally bonded CFRP strips. The objective of the strengthening scheme was to increase the flexural capacity by approximately 30%. Each of the three spans was tested to failure by applying quasi-static load cycles. Test results indicate that the actual capacity of the bridge decks were higher than anticipated due to higher actual material strengths. In addition, the decks had end fixities that were estimated by comparison of experimental and theoretical results. The experimental moment capacities compared well with theoretical values based on the actual material properties obtained from laboratory testing and the determined end fixity. Strengthened decks exhibited ductile behavior prior to FRP failure. The short-term behavior of FRP strengthening system applications has been experimentally evaluated. Research into longterm performance should be conducted even though FRP used in highway bridges is expected to perform for a long time. The final report consists of three volumes. Volume I depicts the strengthening and testing to failure of the three bridge decks. Volume II focuses on the laboratory and field dynamic tests. Volume III focuses on the strengthening and testing to failure of the bridge piers

Assessing the effectiveness of embedding CFRP laminates in the near surface for structural strengthening

The authors of the present work wish to acknowledge the support provided by the S&P, Bettor MBT Portugal, Secil, Nordesfer, Ferseque, Casais, Solusel, VSL, Unibetão (Braga) and the colaboration of Cemacom.Near Surface Mounted (NSM) is a recent strengthening technique based on bonding Carbon Fiber Reinforced Polymer (CFRP) bars (rods or laminate strips) into pre-cut grooves on the concrete cover of the elements to strength. To assess the effectiveness of the NSM technique, an experimental program is carried out involving reinforced concrete (RC) columns, RC beams and masonry panels. In columns failing in bending the present work shows that the failure strain of the (CFRP) laminates can be attained using the NSM technique. Beams failing in bending are also strengthened with CFRP laminates in order to double their load carrying capacity. This goal was attained and maximum strain levels of about 90% of the CFRP failure strain were recorded in this composite material, revealing that the NSM technique is also very effective to increase the flexural resistance of RC beams. The effectiveness of externally bonded reinforcing (EBR) and NSM techniques to increase the flexural resistance of masonry panels is also assessed. In the EBR technique the CFRP laminates are externally bonded to the concrete joints of the panel, while in the NSM technique the CFRP laminates are fixed into precut slits on the panel concrete joints. The NSM technique provided a higher increase on the panel load carrying capacity, as well as, a larger deflection at the failure of the panel. The performance of EBR and NSM techniques for the strengthening of RC beams failing in shear is also analyzed. The NMS technique was much more effective in terms of increasing the beam load carrying capacity, as well as, the beam deformability at its failure. The NSM technique was easier and faster to apply than the EBR technique.The first author wishes to acknowledge the grant SFRH/BSAB/291/2002-POCTI, provided by FCT and FSE

Flexural Strengthening of Bridge Piers Using FRP Composites

The effectiveness of FRP jackets for increasing the shear capacity and the flexural ductility of reinforced concrete (RC) columns was demonstrated in many studies. However, for smaller axial loads, the contribution of FRP jackets to flexural strength is minimal. Using FRP sheets in the direction of a column with end anchorage to improve its flexural capacity at the base is not easily achieved. This paper reports on a research project aimed at upgrading the flexural capacity of RC piers using near-surface mounted (NSM) FRP rods. Flexural strengthening and testing to failure of the piers were carried out on a bridge that was scheduled for demolition during the Spring of 1999. Three of the four piers of the bridge were strengthened with different configurations using FRP rods and jackets. The flexural strengthening was achieved using NSM carbon FRP rods that were anchored into the footings. The piers were tested under static push/pull load cycles. An analytical model was developed to determine the net forces acting on a bridge pier at a given load level based on the measured response. Strengthening techniques, test results, modes of failure, and sample analytical results of tested bridge piers are described and the effectiveness of this technology is demonstrated

Experimental investigation of the shear flow zone in torsional members

In this study an attempt was made to examine experimentally the shear flow zone in reinforced concrete members subjected to pure torsion. The strain distribution through the shear flow zone was measured using a special concrete-embeddable strain gage units that were especially developed for this purpose. The performance and the reliability of the embeddable units were assessed experimentally prior to their application. The units were used to measure the shear flow zone in four full-size beams. It was found that the actual shear zone is smaller than the prediction of the ACI 318-95. The strain distribution through this zone was rather parabolic [sic] which indicated that reinforcement can affect the strain distribution. A rational definition of the shear flow centerline was introduced. Furthermore, discripancy with tests results were discussed. The ACI 318-95 formula for predicting the cracking torque was assessed and found to underestimate the cracking torque, a more accurate approach was proposed. Finally, an attempt was made to investigate the softening of diagonals concrete under torsion --Abstract, page iii

Assessment of Existing Structures Using Cyclic Load Testing

When a building is renovated for a change of use, the load-carrying capacity of the structural system must be established. The cyclic load test (CLT) method requires the application of multiple cycles of loading and unloading (typically six). Two case studies are presented. In both of the described cases, the CLT method efficiently verified the capacities of the existing structures. The method was also used to evaluate structural behavior after members were strengthened using externally bonded fiber-reinforced polymer reinforcement alone or in conjunction with a reinforced concrete topping course