Showing papers by "Antonio Nanni published in 2015"

RC beams shear-strengthened with fabric-reinforced-cementitious-matrix (FRCM) composite

Abstract: The interest in retrofit/rehabilitation of existing concrete structures has increased due to degradation and/or introduction of more stringent design requirements. Among the externally-bonded strengthening systems fiber-reinforced polymers is the most widely known technology. Despite its effectiveness as a material system, the presence of an organic binder has some drawbacks that could be addressed by using in its place a cementitious binder as in fabric- reinforced cementitious matrix (FRCM) systems. The pur- pose of this paper is to evaluate the behavior of reinforced concrete (RC) beams strengthened in shear with U-wraps made of FRCM. An extensive experimental program was undertaken in order to understand and characterize this composite when used as a strengthening system. The labo- ratory results demonstrate the technical viability of FRCM for shear strengthening of RC beams. Based on the experi- mental and analytical results, FRCM increases shear strength but not proportionally to the number of fabric plies installed. On the other hand, FRCM failure modes are related with a high consistency to the amount of external reinforcement applied. Design considerations based on the algorithms proposed by ACI guidelines are also provided.

Experimental Study of a Large-Scale Ground Anchor System with FRP Tendon and RPC Grout Medium

Abstract: The poor performance and durability of traditional steel tendon and cement grout have become serious constraints to the development of ground anchor systems, especially when these systems are permanent features in large-scale projects such as ground anchors with capacities of more than 4,000 kN in Aizhai Bridge, China. This paper presents a large-scale ground anchor system with carbon fiber-reinforced polymer (CFRP) tendon and reactive powder concrete (RPC) grout as the bonding media in both above-ground and below-ground parts. Two full-scale ground anchor specimens named GA12-20 and GA12-9 were designed and installed at the construction site, and their behavior was systematically studied through monotonic and cyclic load testing. The two systems displayed acceptable displacements under both monotonic load testing with maximum tension twice the design lock-off load and in cyclic load testing under about 90% of its bearing capacity, with residual displacements all less than 5 mm. Furthermore, the b...

Acoustic Emission Assessment of Through-Thickness Fatigue Crack Growth in Steel Members

Abstract: The understanding of crack behavior under fatigue remains a critical issue in addressing the performance of steel bridges. Single edge notches in general provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM-E647 SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. Acoustic emission (AE) has been increasingly used for assessment and prediction of fatigue cracks in steel bridge members. In steel bridge members, AE transducers are commonly attached to the surface of the plate from which the crack is initiated, hence producing a through-thickness crack growth monitored by the transducer. A modified version of the SE(T) specimen was developed in order to maintain similitude with the field crack propagation orientation and to provide a small-scale specimen with improved AE characteristics while maintaining accuracy of fatigue crack growth rate (da/dN) versus stress intensity factor range (∆K). The specimen simulates fatigue cracks in flanges or early stage of crack growth in webs of steel bridge members. Effects of load ratio (R) and material on AE data recorded during the crack growth was addressed. Applicability of AE to capture, locate and predict the behavior of the growing crack was positively verified. R ratio showed to have a significant effect on evolution of AE data captured during the test.

Behavior of Full-Scale Porous GFRP Barrier under Blast Loads

Abstract: This research paper is part of the SAS (Security of Airport Structures) Project funded by the European Programme for Critical Infrastructure Protection, whose objective was to develop and deploy a fiber reinforced polymer (FRP) fencing system intended to protect airport infrastructures against terrorist acts. In the paper, the efficacy of the proposed glass FRP discontinuous (porous) barrier under blast loads is presented by showing the results of the blast test campaign conducted on full-size specimens with a focus on the reduction of the blast shock wave induced by the barrier. A simplified model predicting the reduction of the shock wave beyond the barrier is proposed and validated via the experimental data obtained in the project.

Condition Assessment of Prestressed Concrete Beams Using Cyclic and Monotonic Load Tests

Abstract: Eight prestressed T-shaped beams were tested using the cyclic load test (CLT) method as proposed by ACI 437-12 followed by the ACI 318-11 monotonic (24-hour) load test method. The objective of the study is to assess the ability of these methods to evaluate damage in prestressed concrete (PC) beams. The test matrix included both pristine beams (subjected to no prior loading) as well as beams that were cracked and artificially predamaged using accelerated corrosion techniques, impressed current, and wet/dry cycles, prior to load testing. Deflections, crack widths, and slipping of the prestressing strands were recorded during the load tests. The load at which the monotonic test was conducted was chosen to be greater than the service load of Class U PC members, which does not allow cracking. This ensured that at the time of the monotonic load test the specimens were significantly damaged. However, the acceptance criteria associated with this test methodology were still met. Only one index in the CLT acceptance criteria (deviation from linearity) identified the condition of the specimens. The deviation from linearity index is found to correlate to the opening and widening of cracks.

FRCM and FRP Composites for the Repair of Damaged PC Girders

Abstract: Fabric-reinforced-cementitious-matrix (FRCM) and fiber-reinforced polymer (FRP) composites have emerged as novel strengthening technologies. FRCM is a composite material consisting of a sequence of one or more layers of cement-based matrix reinforced with dry-fiber fabric(s). Conversely, FRP consists of a sequence of one or more plies of unidirectional fibers embedded in organic resin. The primary objective of this project was an extensive material characterization of two pre-selected FRCM and FRP systems in order to investigate their basic constitutive behavior and durability. Material characterization is performed in compliance with established Acceptance Criteria (AC434 and AC125). Results from the characterization yield material properties that are considered in determining experimental, theoretical, and design ultimate capacities of strengthened members. FRCM and FRP were used for the strengthening of intentionally damaged American Association of State Highway and Transportation Officials (AASHTO) Type III prestressed concrete girders taken from I-81 overpass near Arcadia, Virginia. Experimental and theoretical analyses were performed to demonstrate the ability of these two repair methods to restore moment capacity compromised by the loss of four and eight 9.5-mm (3/8-in.) diameter prestressing tendons. All experimental work was conducted at Virginia Tech and reported in details elsewhere. This document presents some of the experimental findings and shows additional and original analytical considerations on the performance of the repaired girders. In particular, it offers a comparison between theoretical results according to AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications (2010) and experimental tests. Finally, design methodology including ACI 318 (2011), ACI 549.4R (2013) and ACI 440.2R (2008) are used to calculate design values that are compared to experimental values.