Showing papers by "Antonio Nanni published in 2008"

FRP Composites for Reinforced and Prestressed Concrete Structures: A Guide to Fundamentals and Design for Repair and Retrofit

Abstract: Chapter 1: Introduction Chapter 2: Constituent Materials Chapter 3: Fabrication Techniques Chapter 4: Common Repair Systems Chapter 5: Flexure: Reinforced Concrete Chapter 6: Flexure: Prestressed Concrete Chapter 7: Shear in beams Chapter 8: Columns Chapter 9: Load Testing

Review of Design Guidelines for FRP Confinement of Reinforced Concrete Columns of Noncircular Cross Sections

Abstract: Current international design guidelines provide predictive design equations for the strengthening of reinforced concrete (RC) columns of both circular and prismatic cross sections by means of fiber-reinforced polymer (FRP) confinement and subjected to pure axial loading. Extensive studies (experimental and analytical) have been conducted on columns with circular cross sections, and limited studies have been conducted on members with noncircular cross sections. In fact, the majority of available research work has been on small-scale, plain concrete specimens. In this review paper, four design guidelines are introduced, and a comparative study is presented. This study is based on the increment of concrete compressive strength and ductility and includes the experimental results from six RC columns of different cross-sectional shapes. The observed outcomes are used to identify and remark upon the limits beyond the ones specifically stated by each of the guides and that reflect the absence of effects not consi...

Performance of Two Anchor Systems of Externally Bonded Fiber-Reinforced Polymer Laminates

Abstract: In regard to concrete-based transportation and civil infrastructure upgrades, fiber-reinforced polymer (FRP) composite materials have been proposed and used. While the effectiveness of this technology has been proven, there have been concerns over issues related to premature peeling, end anchorage, and bond length when strengthening structures in flexure or shear. Two different FRP-based anchor system are presented in this study, namely, a spike anchor and a near surface mounted end anchor. In an attempt to prevent or delay the above listed problems, each has been tested. To check the end anchor system's effectiveness, a total of 16 specimens were tested to failure, and to the spike anchor system's effectiveness, a total of 19 specimens were tested. The study's focus is on the influence of: 1) for the first system, the anchor bar size, groove size, and location; and 2) for the second system, the spike anchors' location and embedment. That each of these systems in highly effective in increasing strengthened member capacity by delaying FRP material delamination has been shown through test results. When using these anchors for flexural and shear strengthening applications, it is recommended that bond-dependent coefficients be 0.90 (K sub m) and 0.25 (K sub v) after comparing design guidelines and experimental results.

Distributed Strain Measurement in Steel Bridge with Fiber Optic Sensors: Validation through Diagnostic Load Test

Abstract: Fiber optic sensing technologies are emerging as valid alternatives for the health monitoring of civil structures. Distributed sensors based on Brillouin scattering add the unique capability of measuring strain and temperature profiles along optical fibers. Measurement is performed by establishing the correlation between fiber strain and temperature, and the frequency shift of the Brillouin backscattered light induced by a monochromatic light pulse. The technology holds potential for use on large structures and integrated transportation infrastructure. Its effectiveness has been assessed through scaled laboratory experiments, whereas field validation is limited to very few demonstration projects conducted to date. This paper presents a pilot application of Brillouin optical time domain reflectometry to measure strain profiles along the steel girders of a continuous slab-on-girder bridge subjected to diagnostic load testing. One of the exterior continuous girders required heat-straightening after falling during construction due to wind. The significance of applying a distributed measurement technique lies in the potential to assess the global girder response, which would be impractical and uneconomical using discrete measurement techniques. A 1.16 km long sensing circuit was installed onto the web of four girders. The circuit comprises bare optical fiber sensors, and a novel adhesively bonded fiberglass tape with embedded sensing fibers for strain measurement and thermal compensation. The strain profiles were first converted into deflection profiles and validated against discrete deflection measurements performed with a high-precision total station system. Structural assessment based on comparison of the strain profiles with the results of three-dimensional finite-element analysis of the bridge superstructure, and with specification mandated criteria, indicated that the response of the girder under investigation was within the design limits, and did not pose serviceability concerns. Factors that may affect measurement accuracy are finally discussed on the basis of the experimental and numerical results.

In-Situ Evaluation of Two Concrete Slab Systems. II: Evaluation Criteria and Outcomes

Abstract: The primary objective of in-situ load testing is to evaluate the safety and serviceability of an existing structural system with respect to a particular load condition and effect. In light of technological advances in construction methods, analytical tools and monitoring instrumentation, new different evaluation criteria are being proposed in addition to different in-situ load test methods. Some criteria may be more appropriate than others based on the expected damage and failure mechanisms of the structure being considered. The companion paper describes the rationale and application of both a consolidated and an alternative approach to the determination of load level, loading procedure and instrumentation requirements for two case studies. This paper discusses in detail the evaluation criteria and outcomes of these two field projects consisting of a posttensioned concrete slab with structural deficiencies due to tendon and mild reinforcement misplacement and a floor bay of a two-way reinforced concrete slab showing cracking at the positive and negative moment regions. After discussing the relative merits of the evaluation methodologies and the significance of their respective acceptance thresholds, concepts for the development of a new global criterion are discussed.

Monte Carlo Simulation of Shear Capacity of URM Walls Retrofitted by Polyurea Reinforced GFRP Grids

Abstract: A model proposed in the literature for the evaluation of the in-plane shear capacity of unstrengthened and strengthened concrete and clay brick unreinforced masonry (URM) walls was modified and calibrated following the results from an experimental research program. The tested walls were strengthened with grids made from glass fiber-reinforced polymer (GFRP) embedded within a rapid-setting sprayed polyurea. Various GFRP grid reinforced polyurea layouts were investigated, and consisted of strips oriented in either the vertical or horizontal direction and installed on one or both faces. The prediction models proposed in this paper were subsequently evaluated using a probabilistic Monte Carlo simulation (MCS) by considering the uncertainty and variability of the independent variables, which were assumed to follow a truncated normal distribution. Corroborated by the MCS, test results clearly show that the failure modes of the strengthened URM walls were affected by the strengthening scheme. Experimental and simulation results are presented and discussed in this paper.

Scaling of strength of FRP reinforced concrete beams without shear reinforcement

Abstract: Among the unresolved issues in the design of structural concrete reinforced with fiber reinforced composite (FRP) bars, the understanding of size effect in the reduction of the shear strength of deep beams without shear reinforcement is of fundamental and practical sig- nificance. Size effect accrues primarily from the larger width of diagonal cracks as the effective depth is increased, and has been extensively documented in the case of steel reinforced concrete (RC) through a number of laboratory tests. In FRP RC, the lower longitudinal elastic modulus of the flexural reinforcement results in deeper and wider cracks. Yet, the calibration of any of the current semi-empirical design algorithms is based on test results of beams and one-way slabs with maximum effective depth of 360 mm, which is not representative of relevant large-scale applications. This paper presents and discusses the results of laboratory testing of large-size and scaled FRP RC beams without shear reinforcement, having maximum effective depth of 147, 294 and 883 mm, and effective reinforcement ratio of 0.12% and 0.24%. It is shown that the shear strength of the large-size specimens with less flexural reinforcement decreases on average by 55% compared with the smaller specimens. However, the conservativeness of the current de- sign algorithms generally offsets the size effect. The provisions of the UK Institution of Struc- tural Engineers (ISE) and the Italian National Research Council (CNR) provide the most accu- rate estimates, where the former yields more conservative and consistent results.

In-Situ Evaluation of Two Concrete Slab Systems. I: Load Determination and Loading Procedure

Abstract: The primary objective of in-situ load testing is to assess the safety and serviceability of an existing structural system with respect to a particular load effect At this time, the most appropriate loading level and procedure, as well as the associated evaluation criteria are being reconsidered in light of technological advances in construction methods, analytical tools, and monitoring instrumentation The in-situ load test method for reinforced concrete systems described in the ACI Building Code Requirements for Structural Concrete, namely the 24–h load test method and its evaluation criteria, has been in use for several decades, but may no longer serve the needs of contemporary construction and engineering practices As a result, other load test methodologies and associated evaluation criteria are under development This paper and a companion paper describe the rationale and application of an alternative approach to the determination of load level, loading procedure, instrumentation requirements, evalu

Flexural Strength of Reinforced Concrete Beams Strengthened with Prestressed Carbon Fiber-Reinforced Polymer Sheets - Part II

Abstract: In an accompanying paper in the same issue of this journal, the development of a prototype mechanical device for prestressing carbon fiber-reinforced polymer (CFRP) sheets was described. To investigate the feasibility of using this device, seven reinforced concrete (RC) beams were strengthened with prestressed CFRP sheets. This paper describes theoretical and experimental results related to prestressing levels that can lead to debonding of the sheets immediately after transfer and during flexural testing. An investigation regarding the increase in the flexural capacity that results from prestressing and anchoring the CFRP sheets at the beam ends with U-wraps is also discussed. Analytical and experimental results suggest that values of the tensile strength of concrete are likely to be higher than suggested by ACI. The predominant premature failure mode in RC beams prestressed with CFRP sheets is by concrete cover separation unless the CFRP sheets are effectively anchored with U-wraps. For the prestressed sheets anchored with U-wraps, concrete cover separation was averted and the predicted theoretical capacity was achieved. Results also showed that the addition of prestressed and non-prestressed sheets increased the cracking load by nearly 3 to 6 times, respectively compared with the control beam. The yield and ultimate loads were increased by nearly 25%, but displacement ductility capacity of the system was reduced by nearly 5 times.

Recommended Construction Specifications and Process Control Manual for Repair and Retrofit of Concrete Structures Using Bonded FRP Composites

Abstract: This report presents recommended construction specifications to facilitate highway agencies' use of bonded fiber-reinforced polymer (FRP) composites for the repair and retrofit of concrete structures. These specifications cover the construction of FRP systems used as externally bonded or near surface-mounted reinforcement to enhance axial, shear, or flexural strength of a concrete member. These specifications are supplemented by a construction process control manual that provides a program for assuring a consistent and uniform control of quality and regulatory requirements. The material contained in this report will be of immediate interest to engineers, inspectors, contractors, suppliers, and others involved in the repair and retrofit of concrete structures using FRP composites.

Description of a Mechanical Device for Prestressing of Carbon Fiber-Reinforced Polymer Sheets - Part I

Abstract: A mechanical device for prestressing carbon fiber-reinforced polymer (CFRP) sheets was developed, and its application for the flexural strengthening of reinforced concrete (RC) beams was investigated in this research program. Significant features of this mechanical device are 1) the CFRP sheets are directly anchored to the device itself; 2) prestressing is easily achieved while the device is not yet attached to the RC beam; 3) the prestressing is applied with a manual torque wrench without the need for power-operated hydraulic jacks; 4) fiber-reinforced polymer (FRP) U-wraps can be easily attached to the end of the prestressed CFRP sheets; and 5) the prestressing transfer is accomplished under slow strain rates. This paper describes in detail the main features and the application procedures for this mechanical device. To investigate the feasibility of using this device for flexural strengthening, the experimental program consisted of testing seven RC beams under a four-point bending test setup. Test results indicate that the device was efficient in applying prestressing to the CFRP sheets and, as predicted, in comparison with the control beams, the flexural capacity and serviceability of the beams were increased after strengthening with the prestressed CFRP sheets. In a second accompanying paper, the experimental and analytical results obtained from the flexural program are discussed in further detail.

Experimental Evaluation of Non-Circular Reinforced Concrete Columns Strengthened with CFRP

Abstract: This paper presents the results of an experimental investigation on the axial behavior of medium and large scale Reinforced Concrete (RC) columns of circular and non-circular cross-sections, which were strengthened with unidirectional Carbon Fiber Reinforced Polymer (CFRP) wraps. A test matrix was developed to investigate the effect of different variables, such as the geometry of the specimen cross-section (circular, square, and rectangular), the side aspect ratio, and the area aspect ratio. A total of 22 specimens were divided into six series of three specimens each and two series of two specimens each. The largest and smallest columns featured cross-sectional areas of 0.8 m2 (9 ft2) and 0.1 m2 (1 ft2), respectively. All the specimens were subjected to pure axial compressive loading. The experimental results are compared with available data on RC specimens with one minimum dimension of the cross-section of 300 mm (12 in.). This evaluation allowed confirming that among circular and non-circular specimens of the same cross-sectional area and FRP volumetric ratio, the level of confinement effectiveness decreases as the side aspect ratio increases. Additionally, size effect within specimens of circular cross-section does not appear to be significant; however, for the case of noncircular specimens, scatter and limitation of data-points does not allow at the present time to draw a definite conclusion. A new analytical method that allowed estimating the confining pressure in noncircular cross-sections from the transverse strains at the corners is proposed. The obtained confining pressures and experimental results from this study allowed calibrating a strength model, which was validated with the available experimental data in the literature. Finally, the predictions of this strength model were compared to the ones by the model of Lam and Teng yielding close agreement.

Accelerated Construction of Bridge 14802301, Greene County, Missouri, with Prefabricated Stay-in-Place Glass Fiber Reinforced Polymer Reinforcement

Abstract: In the two-year project reported herein, a new prefabricated stay-in-place (SIP) glass fiber reinforced polymer (GFRP) reinforcing system for the accelerated construction of bridge decks was developed and implemented in the reconstruction of Bridge 1482301 in Greene County, Missouri, USA. The owner opted for the replacement of the 70-year old bridge due to the severe corrosion-induced deterioration of the superstructure. A significant joint effort was required for the concept development, design, analysis, detailing, full-scale laboratory validation, development of project special provisions, and construction planning and execution. Related tasks were completed in coordination between Missouri University of Science and Technology and the University of Wisconsin-Madison, FRP reinforcement manufacturers, the Greene County Highway Department (owner), the engineer-of-record, and the designated contractor. The project demonstrated a technology that combines the superior durability of internal FRP reinforcement for concrete, and the substantial constructability advantages that derive from the use of lightweight advanced composite systems engineered in an innovative, integrated stay-in-place form.