John J. Myers

CONCRETE ROUGHNESS CHARACTERIZATION USING LASER PROFILOMETRY FOR FIBER-REINFORCED POLYMER SHEET APPLICATION

The failure of a reinforced concrete member strengthened with fiberreinforced polymer (FRP) laminates may be caused by crushing of concrete, rupture of FRP laminates, or delamination of the FRP sheet. Therefore, the effectiveness and failure mode of FRP sheets applied to beams and columns is related to the degree of adhesion of the epoxy to the concrete surface. When a peeling or delamination failure can be avoided, a more effective engagement of the FRP sheet occurs, which results in more efficient use of the material. One of the principal factors affecting the bond behavior between the concrete and epoxy is the roughness of the concrete substrate. To prepare the bond surface, sand blasting or grinding is typically used to roughen the concrete. To that end, a portable device has been developed to measure the roughness of concrete surfaces. This device can be used as a quality-control tool to characterize surface roughness and identify when an adequate surface preparation has been attained. The method uses laser striping and image analysis. The method was tested on six slabs of sandblasted concrete, which were sandblasted to varying degrees of surface roughness, and a series of nine plastic model concrete surface profiles.

LIVE-LOAD TEST RESULTS OF MISSOURI'S FIRST HIGH-PERFORMANCE CONCRETE SUPERSTRUCTURE BRIDGE

For its significant economical savings and greater design flexibility, high-performance concrete (HPC) is becoming more widely used in highway bridge structures. High-performance bridges with HPC and large-diameter prestressed strands are becoming attractive to designers. Bridge A6130 is the first fully HPC superstructure bridge in Missouri. The bridge has HPC cast-in-place deck and high-strength concrete girders reinforced with 15.2-mm (0.6-in.) diameter strands. The bridge was instrumented with embedded strain gauges and thermocouples to monitor the early-age and later-age behavior of the structures from construction through service. To investigate the overall behavior of the bridge under live load, a static live-load test was developed and carried out. During the live-load test, 64 embedded vibrating wire strain gauges and 14 embedded electrical-resistance strain gauges were used to acquire the changing strain rate in the bridge caused by the varying live-load conditions. Girder deflections and rotations were also recorded with external sensors and a data acquisition system. Based on the test results, the load distribution to the girders was studied. The AASHTO specifications live-load distribution factor recommended for design was compared with the measured value and found to be overly conservative. The AASHTO load and resistance factor design live-load distribution factors recommended for design were found to be comparable to measured values. Two finite element models were developed with ANSYS and compared with measured values to investigate the continuity level of the Missouri Department of Transportation interior bent detail.

Shear and Flexural Strengthening of Masonry Infill Walls with FRP for Extreme Out-of-Plane Loading

Unreinforced masonry (URM) walls have a low resistance against out-of-plane blast loading due to their low flexural capacity and their brittle mode of failure. Failures of URM walls were identified by The Masonry Society (TMS) and the Federal Emergency Management Agency (FEMA) as one of the major causes of material damage and loss of human life due to blast loads. This led to an urgent need in developing effective retrofitting techniques in lieu of more impractical conventional approaches to upgrade masonry members to resist blast loads. An alternative method is using Fiber Reinforced Polymer (FRP) composites adhered to the surface of the wall to resist high flexural stresses. However, this is a new approach to blast resistant design and there is little available test data to use as a basis for the design of wall upgrades. Two series of walls, reflecting twelve un-grouted URM walls with different strengthening schemes using FRP composite materials were tested in this study. The walls were subjected to uniform loading along their height using high-pressure bags where the applied pressure could be controlled and monitored through failure. FRP composites in the form of rods and laminates were used as strengthening materials. Retrofit connections were evaluated at the top and bottom using two innovative boundary connections. The tests caused a well-distributed range of damage levels. Under a pilot field study [El-Domiaty, Myers, and Belarbi (2002)] the shear capacity controlled the blast behavior of the strengthened walls, a shear retrofit connection was also studied in the two series of tests. An analytical analysis using a single degree of freedom (SDOF) approach was used to predict the behavior of masonry walls strengthened with FRP.

Shear Behavior of High-Volume Fly Ash Concrete versus Conventional Concrete

AbstractThe production of portland cement—the key ingredient in concrete-generates a significant amount of carbon dioxide. However, due to its incredible versatility, availability, and relatively low cost, concrete is the most consumed manufactured material on the planet. One method of reducing concrete’s contribution to greenhouse gas emissions is the use of fly ash to replace a significant amount of the cement. An experimental investigation was conducted to study the shear strength of full-scale beams constructed with both high-volume fly ash concrete (HVFAC)—concrete with at least 50% of the cement replaced with fly ash—and conventional concrete (CC). This experimental program consisted of 16 beams (12 without shear reinforcing and four with shear reinforcing in the form of stirrups). Additionally, three different longitudinal-reinforcement ratios were evaluated within the test matrix. The beams were tested under a simply supported four-point loading condition. The experimental shear strengths of the b...

Field evaluation of unreinforced masonry walls strengthened with FRP composites subjected to out-of-plane loading

Unreinforced masonry (URM) walls at a decommissioned building in St. Louis, Missouri were tested to failure. The walls belonging to the present experimental program were subjected to out-of-plane loading. Previous work on URM and reinforced masonry walls strengthened with FRP laminates has shown remarkable increases in capacity and ductility. However, most of this research has been conducted under laboratory conditions, where, many times, it is a difficult task to represent real field conditions. In this context, this experimental program offered a singular opportunity for performing field experimentation on URM walls strengthened with Glass, Aramid and Carbon Fiber Reinforced Polymers (GFRP, AFRP and CFRP, respectively), as well as Glass Near Surface Mounted Rods. Parameters such as the type of composite system, strip width, and FRP installation methods were evaluated. A mechanism of failure caused by a shear-compression effect lead to the fracture of either the upper or lower boundary masonry units. Due to this failure mode, the walls were not able to develop a higher capacity compared to the control specimen.

An Assessment of In-Situ FRP Shear and Flexural Strengthening of Reinforced Concrete Joists

This study examines the in-situ shear performance and modes of failure of reinforced concrete (RC) T-beams (joists) strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets. The experimental program consisted of testing a series of nine structural components at the Malcom Bliss Hospital, in St.Louis, Missouri. The members were tested to validate the different systems and techniques of strengthening. In particular, this paper covers cases of U-Wraps with and without end-anchors. The experimental results clearly indicate the contribution of externally bonded CFRP sheets in increasing the shear capacity of the system. The experimental and theoretical shear strength of the reinforced concrete members (RC) under investigation is presented with and without anchorage.

Research Agenda for Transportation Infrastructure Preservation and Renewal: Conference Report

Many elements of the nation’s surface transportation infrastructure are deteriorating as a consequence of aging and increasing stresses. The American Recovery and Reinvestment Act of 2009 the stimulus package provided an initial infusion of funds for transportation infrastructure renewal and restoration, but these resources are not sufficient for rebuilding and sustaining the condition and performance of that infrastructure. Under these circumstances, it is particularly important to develop and deploy the best methods and technologies to support effective management of transportation infrastructure. To respond to this challenge, the U.S. DOT Research and Innovative Technology Administration sponsored a conference organized by the Transportation Research Board that brought infrastructure owners and decision makers together with researchers to consider problems, needs, and achievements and to define the directions for essential research to manage and preserve the nation’s surface transportation infrastructure. Participants at the November 2009 conference outlined the challenges and opportunities facing the highway, public transit, and rail systems and

Finite-Element Modeling of Hybrid Composite Beam Bridges in Missouri

AbstractThree bridges were recently constructed in Missouri using a new type of hybrid composite beam (HCB) incorporated within traditional RC deck systems. These HCBs are comprised of three main subcomponents: a composite shell, compression reinforcement, and tension reinforcement. The compression reinforcement is a self-consolidating concrete (SCC) arch that is tied at the ends by high-strength galvanized steel strands. The compression and tension reinforcements are encapsulated in a glass fiber–reinforced polymer (GFRP) box, and the voids are filled with polyisocyrunate (polyiso) foam. This unique configuration aims to optimize the structural performance of the HCB constituents, hence optimizing the overall performance of the beam. However, because of the novelty of the HCB, its structural behavior is not yet completely understood. Consequently, the finite-element (FE) modeling of this new type of beam is crucial for providing deeper insight into its structural behavior and validating the current desig...

Flexural and Shear Behavior of Reinforced Concrete Members Strengthened with a Discrete Fiber-Reinforced Polyurea System

Recent research has been conducted to evaluate the benefits provided by externally-applied discrete fiber-reinforced polyurea (DFRP) coating systems. This coating was proposed to allow for ease of construction in repair-retrofit situations and to provide multihazard benefits, ranging from blast or impact fragmentation mitigation to seismic reinforcement and general strengthening. This phase of research investigated the flexural and shear reinforcement capabilities of the systems. Testing parameters included type of structural failure, polyurea, and fiber volume fraction. Additionally, the effects of the thickness of the composite system were considered. Concrete beam specimens were fabricated and coated per the designed test matrix and subjected to four-point bending. Analysis was based on ultimate capacity, deflection, overall ductility, and the qualitative observations of coating adhesion and fragmentation confinement. In addition, a theoretical model was developed and validated to describe the flexural behavior of the polyurea-coated beams and to normalize the test data for comparison. Results presented in this paper suggest measurable strengthening for both flexural and shear capacity provided by the coating system and substantial gains in ductility. DOI: 10.1061/(ASCE)CC.1943-5614.0000308.

Nondestructive Evaluation of RC Structures Strengthened with FRP Laminates Containing Near-Surface Defects in the Form of Delaminations

Fiber reinforced polymer (FRP) composites are being utilized in a wide range of application areas in structural rehabilitations because these materials are less affected by corrosive environmental conditions and known to provide longer life with less maintenance. However, there are still some concerns about FRP strengthened reinforced concrete (RC) structures, such as the presence of near-surface defects. Currently limited data exists regarding this issue. The presence of near-surface defects in the form of delaminations between the fiber reinforced polymer (FRP) laminate and concrete substrate can significantly affect the structural integrity and stiffness of the structural section. These defects should be properly detected and accurately located to access if injection or replacement is warranted. The control and assessment of these defects still require improvements in detection techniques and standardization in these assessment methods. The latest advances in non-destructive evaluation (NDE) techniques including technologies in microwave, acousto-ultrasonic, impact-echo and thermography are providing promising results in detecting such defects and are discussed in further detail in this paper. 1 Senior Evaluation Specialist, International Code Council-Evaluation Service, 5360 Workman Mill Road, Whittier, California, 90601 mekenel@icc-es.org (Corresponding Author) 2 Associate Professor, Department of Civil, Arch. & Env. Engineering, University of Missouri-Rolla, Rolla, Missouri, 65401 jmyers@umr.edu Ekenel, M. and Myers, J.J. 2