Search

Corrosion of reinforcing steel in concrete is one of the most prevalent deterioration mechanisms affecting reinforced concrete structures. While there have been significant advances in modeling the initiation stage of corrosion, corrosion kinetic models for predicting the rate of corrosion after depassivation of steel are scarce, and models with experimental corroboration under controlled experimental conditions are virtually nonexistent. Furthermore, the sensitivity of corrosion kinetic models to the uncertainty of their input parameters is not understood. The objective of the present work is to model active corrosion of steel in synthetic solution, experimentally corroborate the modeling approach under controlled conditions, and study the effect of uncertainty of the input parameters on the model predictions. To this end, a two-dimensional finite element method is used to solve the coupled system of Poisson-Nernst-Planck (PNP) equations subjected to electroneutrality constraint. To corroborate the modeling approach, the results of computations are compared against one-dimensional and two-dimensional galvanic corrosion of stainless/carbon steel in dilute and non-dilute NaCl electrolytes as well as two synthetic concrete pore solutions. The modeling parameters, including electrode polarization behaviors and electrolyte properties, are obtained experimentally. Monte Carlo simulations are used to understand the effect of uncertainty of polarization parameters on the predicted corrosion rate.

This paper presents design and installation details and full-scale test results for a prestressed mechanically fastened fiber-reinforced polymer (MF-FRP) retrofit solution that restores the...

Large inelastic tensile strains and wide horizontal cracks primarily caused by in-plane loading, may lead to local out-of-plane deformations of the end regions of reinforced concrete (RC) walls within a buckled zone that comprises the plastic hinge length. Critical parameters that influence the onset of this failure mode have been studied through past experimental tests on RC prisms subjected to axial loading, which simulates the response of end regions of RC walls under in-plane demands. Missing from those studies is the effect of bidirectional loading protocols and the effect of the longitudinal reinforcement ratio on the hysteretic response. Therefore, 12 RC prisms with 3 longitudinal steel ratios representative of prototype boundary elements of typical special RC walls and piers walls were tested. The experimental results showed that the longitudinal steel content and the in-plane loading demands mainly govern the onset of out-of-plane buckling instability of planar RC walls.

The seismic performance of reinforced concrete-filled steel tube (RCFST) drilled shafts, also known as RCFST pile-columns, was examined based on experimental tests conducted on twelve half-scale RCFST specimens at the soil-structure interaction facility at the North Carolina State University, Constructed Facilities Laboratory (NCSU-CFL). The specimens consisted of steel tubes with diameter-to-thickness (D/t) ratios ranging from 48 to 95 that were filled with reinforced concrete. Spirally welded steel tubes with outer diameters (D) of 12″ (305 mm) and 12–3/4″ (324 mm) were utilized. The specimens were tested with aboveground-to-diameter (La/D) ratios of 5.5 and 7.5, and they were embedded 14′ (4270 mm) into poorly graded sand (SP). Different levels of soil stiffness were induced in the sand by using a soil-sandwich approach, which allowed for modifying the soil stiffness profile by means of applying a surcharge on the soil surface. Cyclic lateral load was applied by a 100-kip (445 kN), 70-in. (1780 mm) stroke hydraulic actuator, supported on a braced steel frame, and pin-connected to the pile-column head ensuring that the plastic hinge developed below ground. The failure mechanism was controlled by the tensile strain in the steel tube and it was caused by a combination of tube local buckling and tube fracture. First, tube local buckling developed outward at the extreme compression fiber of the section. Tube fracture then occurred in the section with the largest buckle and it extended around about half of the section perimeter. The plastic hinge developed at depths of 2D to 4D. Onset of tube local buckling was observed at higher displacement ductility levels (µ = 3) for specimens using thicker tubes (D/t = 48) than for those using thinner tubes (D/t = 95). The force-displacement response, tensile strain distribution, and hysteretic equivalent viscous damping are discussed in this paper.

This paper presents an study on the rupture strain of cylindrical fiber-reinforced polymer (FRP) jackets under internal ice pressure. A total of 45 cylindrical FRP jackets were prepared using three unidirectional carbon, glass, and basalt fabrics in three different internal diameters, namely 60, 114, and 216 mm, and one-, two-, and three-plies. Three jackets for each combination were typically tested and the average hoop rupture strains were obtained and compared to the rupture strain of flat coupons in the form of a strain efficiency factor. It was found that the strain efficiency factor ranged from 0.53 to 1.05 with an average of 0.77. A new analytical model was also developed based on the bi-axial state of stress in a cylindrical FRP jacket to obtain the rupture strain and strain efficiency factor of the FRP jacket using a closed-form solution. The model engaged four major parameters, namely: diameter, thickness, axial/transverse strength ratio, and Poisson’s ratio of the FRP jacket. The two latter parameters were eliminated after a parametric study to propose a simplified formula. The analytical and simplified models predicted the experimental strain efficiency factors with an average error of −3.4% and −4.6%, respectively.

This paper examines the results of material testing of hybrid carbon and glass fiber-reinforced polymer (FRP) plates for use in prestressed mechanically fastened applications. The small-sca...

The paper presents a combined experimental and numerical investigation of the bending response of lap welded joints in pressurized steel water pipelines. It is motivated by the structural performance of large-diameter steel pipelines used for water transmission in seismic and geohazard areas, where the pipeline may be subjected to severe permanent ground-induced actions. A series of large-scale four-point bending experiments on lap welded joints has been performed, and rigorous finite element numerical models have been developed for conducting extensive numerical simulations. The numerical models account for the bell forming process and the corresponding residual stresses, as well as the presence of initial geometric imperfections on the pipeline wall. A very good comparison has been found between experimental results and numerical simulations in terms of both global response and local strains developed at the vicinity of the weld. The finite element models are also employed for elucidating some interesting features of lap welded joint behavior under severe bending deformation, towards determining the joint strength, its deformation capacity and the evolution of strain at different deformation stages. The experimental and numerical results indicate that lap welded joints, can sustain a significant level of bending deformation and strain, without loss of pressure containment, and can be used in geohazard areas, where severe permanent ground-induced strains on the pipeline wall are expected to develop.

In this paper, the mechanical performance of pretensioned concrete girders manufactured with ultra-high performance fibre reinforced concrete (UHPFRC) and carbon fibre reinforced polymer (CFRP) tendons is explored both experimentally and analytically. For the experimental investigation, four UHPFRC beams with either steel or CFRP tendons are tested under four point bending to failure. Digital image correlation is used to monitor the development of cracks. These results are then used to validate a rational analysis technique based on the modelling of concrete cracking and crushing through the application of partial interaction mechanics which is then compared to that suggested by codes of practice

This paper presents several advancements in the use of fiber reinforced polymer (FRP) materials for the precast concrete industry. Precast concrete members are commonly selected for reasons such as the high level of quality control used in their production, the durability of the finished structure, reduced labor costs and shorter construction schedules, and the economics of scale achieved with mass-production of components. The environmental durability, high strength to weight ratio, and ease of installation of FRP reinforcements an attractive alternative material for the precast industry. This paper presents several advancements in the use of FRP grid as flange reinforcement for precast double-tee members, as a shear transfer mechanism for thermally efficient composite and partially-composite load bearing wall panels, as reinforcement for precast architectural cladding panels. Each of these applications highlights the advantages of using FRP materials to achieve significant enhancement of the structural, thermal and architectural performance. The innovative use of the FRP materials and the unique construction techniques described have resulted in the development of safe and functional structures, as demonstrated by the research conducted by the authors and others in collaboration with the precast industry.

This paper summarizes the results of an analytical research program undertaken to develop a rational design procedure for normalweight precast concrete slender spandrel beams. The analytical and rational models use test results and research findings of an extensive experimental program presented in the companion paper "Development of a Rational Design Methodology for Precast Concrete Slender Spandrel Beams: Part 1, Experimental Results," which appeared in the Spring 2011 issue of PCI Journal. The overall research effort demonstrated the validity of using open web reinforcement in precast concrete slender spandrel beams and proposed a simplified procedure for design. The webs of such slender spandrels, particularly in their end regions, are often heavily congested with reinforcing cages when designed with current procedures. The experimental and analytical results demonstrate that open web reinforcement designed according to the proposed procedure is safe and effective and provides an efficient alternative to traditional closed stirrups for precast concrete slender spandrel beams.

This paper describes the structural behavior of precast, prestressed concrete sandwich wall panels reinforced with carbon-fiber-reinforced polymer (CFRP) shear grid to achieve composite action. Use of CFRP as a shear transfer mechanism was intended to increase the thermal insulation efficiency, enhance the service life, and increase the overall structural capacities of the panels. This study included testing of six full-scale sandwich wall panels, each measuring 20 ft x 12 ft (6.1 m x 3.7 m). The panels consisted of two outer prestressed concrete wythes and an inner insulation wythe. The study included two types of insulation and several shear transfer mechanisms with different CFRP reinforcement ratios to examine the degree of composite action developed between the two concrete wythes. All panels were simultaneously subjected to applied gravity and lateral loads. Reverse-cyclic lateral loads simulated the effects of wind pressure and suction. All panels were subjected to approximately 4000 cycles of lateral loading with the presence of factored gravity load. Following each fatigue regime, the lateral loads were increased until failure was achieved. Test results of the experimental program were compared with theoretical predictions of fully composite and noncomposite actions to evaluate the percent composite action and to assess the optimum panel configuration.

This paper summarizes test results of an extensive experimental program undertaken to develop a rational design procedure for precast concrete slender spandrel beams. Experimental research findings presented in this paper are used to propose a rational design procedure that will be presented in a forthcoming companion paper. The research introduced significantly simplified detailing requirements for the end regions of precast concrete slender spandrel beams. Such regions are often congested with heavy reinforcing cages when designed according to current procedures. In total, 16 full-scale precast concrete spandrel beams were tested to failure to study the limit state behavior. Each specimen was loaded through full-scale double-tee deck sections to mimic typical field conditions. Three of the specimens were designed and detailed with closed stirrups, according to current practice, and served as controls for the experimental program. The remaining thirteen specimens were designed with various configurations of open web reinforcement. Several specimens were specially configured with flexural, ledge/corbel, and hanger reinforcement in excess of what would be provided in a normal design. The enhanced reinforcement helped to delay typical midspan and local failure modes and allowed for observation and study of failure modes in the end region. The experimental results, combined with the analytical results and rational modeling in the companion paper, demonstrate that properly designed open web reinforcement is a safe, effective, and efficient alternative to traditional closed stirrups for precast concrete slender spandrel beams that have an aspect ratio of 4.6 or greater.

This paper presents results from full-scale testing conducted on 4 precast, prestressed concrete L-shaped spandrels. The 4 L-shaped spandrels were each loaded through 12-ft-long, prestressed double tees that rested on the spandrel ledge at one end and on an independent support at the other. None of the beams were constructed with closed stirrups of mild-steel reinforcement. Rather, different arrangements of transverse L-shaped bars, welded-wire reinforcement, and longitudinal bars were provided to resist the shear and torsion induced in the spandrels. Shear and torsion forces were created by the double-tee reaction forces that were loaded eccentrically to the spandrels. The transverse and longitudinal reinforcement resisted the combined effects of vertical shear and out-of-plane bending of the web and satisfied minimum vertical hanger reinforcement requirements for ledge-to-web attachment. All beams sustained loads in excess of their factored design loads. Eliminating the need for closed reinforcement in slender spandrels would be of significant benefit to the precast concrete industry. This design approach would enhance constructability of slender members, which could increase plant productivity and reduce overall costs. Behavior of all 4 spandrels at various limit states is presented, including crack patterns and failure modes. Researchers used these test results to better understand the fundamental mechanism developed in the L-shaped spandrels to resist shear and torsion.

This paper presents results of nonlinear finite element (FE) analyses conducted to model the behavior of L-shaped, precast, prestressed concrete spandrels built with open web reinforcement. The FE model was calibrated using experimental results from recent tests of slender, L-shaped, precast, prestressed concrete spandrels. Detailed correlative studies between analytical and experimental results are provided, demonstrating the capability of the FE program to describe the observed experimental behavior. The feasibility of using open web reinforcement in compact, L-shaped, precast, prestressed concrete spandrels to achieve a more construction-friendly reinforcement scheme is also examined. Five different web reinforcement configurations for the compact spandrels were studied in order to evaluate the contribution of closed stirrups to the spandrels' shear-torsion behavior. The behavior, ultimate load-carrying capacity, and mode of failure of both the slender and compact L-shaped precast, prestressed concrete spandrels are presented. For loading values near the ultimate, the out-of-plane bending behavior of compact, L-shaped, precast, prestressed concrete spandrels is strongly influenced by the web-reinforcement configuration. Results from the analysis show that for long-span, compact spandrels, open web reinforcement can be used effectively to resist torsional forces throughout the member.

The results of an experimental program conducted to study the splice strength of large diameter, high strength reinforcing bars, either No. 20 (63.5 mm diameter) or No. 9 (28 mm diameter), are presented. The parameters included in the experimental program are the bar size, splice length, concrete compressive strength, and the amount of transverse reinforcement provided within the splice zone. The ability of several models including the current ACI 318 Building Code, to predict the maximum steel stresses at the onset of splitting failure was examined for these high strength, large diameter bars. The influence of the moment of inertia of the bar on the induced splitting stresses was evaluated numerically using finite element analysis. Test results showed that the presence of transverse reinforcement has a more pronounced effect for large diameter spliced-bars compared to regular size bars. It is also shown that the current ACI 318 Building Code provided more conservative bond strength predictions for regular bars compared to large diameter bars.

This paper presents the use of distributed fiber optic sensing to achieve centimeter level resolution strain data along the entire length of a large composite beam. A 6.5 meter long composite beam, designed for use in a corrosive flue gas desulfurization (FGD) unit, was instrumented. A section of optical fiber was embedded into a fiberglass rope, which in turn was embedded into the composite beam during the manufacturing process. The beam was experimentally tested in four-point bending at the North Carolina State University Constructed Facilities Laboratory, and the strain profile along the entire length was measured using the embedded optical fiber. Strains of up to 6500 microstrain were measured at over 300 unique positions along the span by monitoring changes in the spectral shift of the Rayleigh scatter in the optical fiber using optical frequency domain reflectometry (OFDR). The fiber used in this test was optically equivalent to standard telecommunication fiber, allowing for low-cost, high-density strain measurements on large structures. The experiment confirms the potential of embedded fiber optic distributed sensing to be used for real-time health monitoring, or as a process feedback in an instrumented structural system. Benefits of employing distributed fiber optic sensing in structures such as the composite FGD unit include the ability to monitor and detect deterioration and damage, minimize the chance of unplanned downtime or failure, and limit exposure to consequences such as environmental contamination.

This paper describes the behavior of concrete bridge decks reinforced with newly developed high-perfonnance (HPJ steel that is charac­ terized by its high stren gth mId en hanced corrosion-resistance in comparison with conventionaL ASTM A6JS-06 Grade 60 steel. The study presented herein included testing of three full-scale bridge decks with a span-depth ratio of 12.5. The first and second decks were constructed with the same reinforcement ratio using HP and Grade 60 steel, respectively. The third deck was reinforced with HP steel using 33% less reinforcement in an attempt to use its high strength. A nonlinear finite elemen t model was used to predict the mode offailure alldfailure loads. Test results demollstrate that the use of HP steel at a reduced reinforcement ratio is viable as flexural reinforcemellt in concrete bridge decks. The paper also presents the test results of specially-designed specimens to study the effect of bending of HP steel bars on their tensile strength.

Corrosion of steel reinforcement is considered to be one of the leading causes of deterioration of concrete bridges. This fact has led to the development of numerous technologies such as corrosionresistant steel that attempt to mitigate this expensive problem. The recent development of highstrength, high corrosion-resistant steel, commercially known as Micro-composite Multi-Structural Formable (MMFX) steel, is a promising technology. MMFX steel offers its high corrosion resistance without the use of the coating technologies. This characteristic was achieved by proprietary alteration of the steel composition and microstructure. In addition, the control of MMFX steel’s morphology of its microstructure has resulted in its higher strength. Use of MMFX steel could lead to potential savings through using less reinforcement ratios due to its higher strength characteristics and longer service life of structures because of its high corrosion resistance. Recently, many state transportation departments have begun to use MMFX steel as a direct replacement for regular Grade 60 steel in concrete bridge decks. However, despite these field applications, there is insufficient information about the behavior of such concrete bridge decks utilizing MMFX steel as main reinforcement. This paper evaluates the use of MMFX steel as main flexural reinforcement in concrete bridge decks in light of test results. Assessment of the effect of the arching action on the strength of bridge decks due to the use of this new steel is also presented.