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BACKGROUND The efficacy of treatments in vineyards largely depends on the necessary balance between leaf coverage and spray drift and, therefore, knowledge about droplet size is of major importance, but scarce scientific information is available on pneumatic spraying, often adopted in this crop. The objective of this work was to obtain the relationships between the droplet size spectra characterization parameters and the main affecting factors in pneumatic nozzles. RESULTS Three liquid flow rates (LFR) and four air speeds (AS) were combined in laboratory conditions to assess their influence on the droplet size spectra (D10, D50 and D90), homogeneity (Relative Span Factor, RSF) and driftability (V100 ) in two different air shear nozzles (cannon-type and hand-type nozzles). The droplet size parameters were significantly affected by LFR and AS, and a model was fitted to predict droplet size in every spout type. The droplet V100 was also affected by both factors. The RSF was similar in both cases but did not follow regular trends. CONCLUSIONS The findings obtained can help vineyard farmers and technicians to effectively increase the efficiency and, therefore, the efficacy of the pesticide treatments reducing at the same time the spray drift risk by selecting appropriately the optimal values of the main operational parameters: LFR and AS. © 2018 Society of Chemical Industry.

Several studies have been conducted to investigate early age Portland cement hydration using acoustic emission technique, with different mechanisms attributed by different authors. In the proof-of-concept research presented in this paper, acoustic emission (AE) was employed to explore relationships between recorded signals associated with elastic stress waves and potential mechanisms associated with cement hydration. Ordinary Portland cement paste samples having water/cement ratio of 0.3 and 0.5 were monitored during the first 72 h of curing using broadband AE sensors. The acoustic emission signals were analyzed using unsupervised and supervised pattern recognition algorithms to address limitations of acoustic emission parameter analysis. Wavelet analysis was utilized as a complementary method, which can be considered as a map for identification of patterns in the signal set. Unsupervised methods are useful when there is no history or background data concerning the pattern of a phenomenon such as the hydration process.

Temperature-controlled experiments are performed to characterize the viscoelastic response of materials commonly used in asphalt roofing shingles, including both creep compliance master curves and shear retardation spectra. Material systems characterized in this study include polymer modified bitumen (PMB) and bitumen impregnated fiberglass mat (BIFM). BIFM experiments are conducted using 3-point bend specimens in a TA instruments RSA III DMA, whereas PMB results are obtained from torsional loading of two cylindrical specimens in a MARS II controlled stress rheometer. Short term (duration of 1000 s) isothermal creep experiments are conducted at temperatures above the bitumen glass transition (T g = −42 °C) (a) on BIFM specimens in the range −30 °C ≤ T ≤ 30 °C and (b) on PMB specimens in the temperature range −30 °C ≤ T ≤ 20 °C. Using the time-temperature superposition principle (TTSP), creep compliance master curves for both materials are obtained at a reference temperature of 0 °C. The results are then used to obtain the shift factors and develop both Williams-Landel-Ferry (WLF) and Arrhenius models. Results show that BIFM has ≈ 2.2X lower creep compliance than PMB at T = 0 °C, with the difference increasing at higher temperatures. Furthermore, beyond the early, short-term creep times, significant deviations between the retardation spectra of BIFM and PMB are observed.

Since presentation of the 2013 Murray Lecture focusing on developments in digital image correlation (DIC), the methods have continued to expand internationally and their use has begun to grow in fields where there was less activity in the past. First, a brief history of digital image correlation methods is presented from the perspective of the first author, followed by a discussion of recent trends associated with the use of digital image correlation methods in academics, governmental laboratories and industrial settings. In the remainder of the article, new results are provided in three areas where DIC methods have seen rapid growth; application of StereoDIC or three-dimensional DIC (3D-DIC) to the study of wall structures in civil engineering; the use of Volumetric DIC or Digital Volume Correlation (DVC) to quantify the internal response of a specially-designed composite material and in the area of model validation for another application in civil engineering; transfer length measurements in pre-stressed concrete beams.

The authors regret that they have identified a miscalculation in the original article that required the authors to provide corrective additions that are listed below. Specifically the authors determined that the shingle uplift pressure, p 1 = 12.5 Pa, used in the original article (Croom et al., 2015) is associated with a 40 km/h (25 mph) wind velocity instead of 145 km/h (90 mph). A miscalculation of pressure values due to inaccurate unit conversion was the source of the misstatement. The corrected interior uplift pressure is p 1 = 183 Pa for a 145 km/h (90 mph) wind velocity and p 1 = 507 Pa for a 241 km/h (150 mph) wind velocity. Additional simulation results have been performed for the corrected pressures and the results are reported in this Corrigendum.

Glass fiber-reinforced polymer (GFRP) bars are a viable corrosion-resistant reinforcement for concrete bridge structures. This technology is becoming increasingly attractive, especially in aggressive environments as coastal areas or cold-weathered regions where de-icing salts are used.The development of a bridge-comprehensive national standard is crucial to foster the deployment of durable GFRP-RC structures. To respond to this demand, a task force of researchers and practitioners has developed a draft for the second edition of the AASHTO LRFD Bridge Design Specifications for GFRP-RC (AASHTO GFRP-2). The draft was submitted to AASHTO Subcommittee T6 and approved for publication by AASHTO Committee on Bridge and Structures in June 2018.Compared to the first 2009 edition of the guidelines, changes were introduced to reflect the current state-of-the-art. The goals included making the provisions more rational, offsetting some over- conservativeness, and harmonizing the design philosophy with that of authoritative national and international guides and standards.This paper illustrates the salient contents of the document, with a focus on flexural design. The GFRP-RC deck of the Anthony Wayne Trail Bridge over Norfolk Southern Railroad (OH) is presented as an example of a common application for GFRP bars in cold-weathered regions. The design with GFRP bars according to AASHTO GFRP-2 is compared to an equivalent design performed according to the first edition of the specifications. Furthermore, the design is compared to traditional and non- corrosive steel-RC alternatives. Economic considerations are included.

The efficacy of treatments in vineyards largely depends on the necessary balance between leaf coverage and spray drift and, therefore, knowledge about droplet size is of major importance, but scarce scientific information is available on pneumatic spraying, often adopted in this crop. The objective of this work was to obtain the relationships between the droplet size spectra characterization parameters and the main affecting factors in pneumatic nozzles.Three liquid flow rates (LFR) and four air speeds (AS) were combined in laboratory conditions to assess their influence on the droplet size spectra (D10, D50 and D90), homogeneity (Relative Span Factor, RSF) and driftability (VThe findings obtained can help vineyard farmers and technicians to effectively increase the efficiency and, therefore, the efficacy of the pesticide treatments reducing at the same time the spray drift risk by selecting appropriately the optimal values of the main operational parameters: LFR and AS. © 2018 Society of Chemical Industry.

The accuracy and spatial resolution of full-field deformation measurements performed through digital image correlation are greatly affected by the frequency content of the speckle pattern, which can be effectively controlled using particles with well-defined and consistent shape, size and spacing. This paper introduces a novel toner-transfer technique to impress a well-defined and repeatable speckle pattern on plane and curved surfaces of metallic and cement composite specimens. The speckle pattern is numerically designed, printed on paper using a standard laser printer, and transferred onto the measurement surface via a thermo-mechanical process. The tuning procedure to compensate for the difference between designed and toner-transferred actual speckle size is presented. Based on this evidence, the applicability of the technique is discussed with respect to surface material, dimensions and geometry. Proof of concept of the proposed toner-transfer technique is then demonstrated for the case of a quenched and partitioned welded steel plate subjected to uniaxial tensile loading, and for an aluminum plate exposed to temperatures up to 70% of the melting point of aluminum and past the melting point of typical printer toner powder.

An analytical model based on beam-on-elastic foundation (BOEF) principles is formulated and employed to simulate the structural response of a realistic asphalt shingle-sealant system under high wind loads. The system consists of individual three-tab shingles that are discretely bonded to the underlying shingles and subjected to differential out-of-plane pressures that are associated with high wind loads. Relevant mechanical properties for a typical modern asphalt shingle and sealant were determined experimentally and input in the proposed structural model. The model was then used to estimate the applied energy release rate, G, for the sealant strip as a function of length, location, and applied uplift pressures on the shingle. Results indicate that the G values are highly sensitive to sealant strip location and sealant length, where sealant length is defined to be along the perpendicular direction between the nail line and leading edge of the shingle, and that the sealant strip location in typical modern shingles is roughly optimized to ensure a balanced value of G at the inner and outer sealant strip edges. However, predictions also indicate that G could be further reduced by using longer sealant strips that are slightly shifted towards the leading edge of the shingle, thereby decreasing the potential for failure. Additional BOEF model simulations were performed using full-field shingle uplift displacements as input to determine the potential for estimating the average uplift pressures imparted on asphalt shingles under high wind loading conditions. Promising results were obtained regarding the suitability of the proposed BOEF-based inverse analysis technique to estimate shingle uplift pressures. In addition, G values that are scaled for high pressures associated with extreme wind conditions, and resulting in sealant separation, are in qualitative agreement with an estimate of critical energy release rate, Gc, based on the results of standard direct tensile tests reported in the literature.

This paper discusses the effect of pre-processing image blurring on the uncertainty of two-dimensional digital image correlation (DIC) measurements for the specific case of numerically-designed speckle patterns having particles with well-defined and consistent shape, size and spacing. Such patterns are more suitable for large measurement surfaces on large-scale specimens than traditional spray-painted random patterns without well-defined particles. The methodology consists of numerical simulations where Gaussian digital filters with varying standard deviation are applied to a reference speckle pattern. To simplify the pattern application process for large areas and increase contrast to reduce measurement uncertainty, the speckle shape, mean size and on-center spacing were selected to be representative of numerically-designed patterns that can be applied on large surfaces through different techniques (e.g., spray-painting through stencils). Such “designer patterns” are characterized by well-defined regions of non-zero frequency content and non-zero peaks, and are fundamentally different from typical spray-painted patterns whose frequency content exhibits near-zero peaks. The effect of blurring filters is examined for constant, linear, quadratic and cubic displacement fields. Maximum strains between ±250 and ±20,000 µe are simulated, thus covering a relevant range for structural materials subjected to service and ultimate stresses. The robustness of the simulation procedure is verified experimentally using a physical speckle pattern subjected to constant displacements. The stability of the relation between standard deviation of the Gaussian filter and measurement uncertainty is assessed for linear displacement fields at varying image noise levels, subset size, and frequency content of the speckle pattern. It is shown that bias error as well as measurement uncertainty are minimized through Gaussian pre-filtering. This finding does not apply to typical spray-painted patterns without well-defined particles, for which image blurring is only beneficial in reducing bias errors.

Cement-based composites have been used as reliable materials in building and civil engineering infrastructure for many decades. Although there are several advantages, some drawbacks such as premature cracking may be problematic for sensitive applications such as those found in nuclear power plants or associated waste storage facilities. In this study, acoustic emission monitoring was employed to detect stress waves associated with damage progression during uniaxial compressive loading. Acoustic emission data resulting from loading of plain cement paste prisms and cement paste prisms amended with carbon nanotubes are compared. Unsupervised pattern recognition is employed to categorize the data. Results indicate that increased acoustic emission activity was recorded for the plain cement paste prisms when compared to prisms amended with carbon nanotubes.

Earthen masonry made of compressed and stabilized earth blocks (CSEBs) is emerging as a sustainable and locally appropriate construction material for affordable high-quality dwellings. Compelling features include the local availability and affordability of suitable soils, thermal insulation and humidity control properties, and small embodied energy compared with fired clay masonry. The mechanical properties of CSEBs have been the subject of several investigations. However, the research on the response and design optimization of CSEB masonry building structures is in its infancy, and a significant knowledge and technological gap exists with regard to resistance to extreme loads due to natural hazards (e.g., high winds and earthquakes). It is necessary to address this gap to understand whether engineered earth masonry can be enlisted to respond to the growing demand for hazard-resistant dwellings that are also affordable and sustainable. This paper discusses the feasibility of using earth masonry in low-rise dwelling structures to withstand extreme winds. Hurricanes and tornadoes periodically scourge vast areas in Central and North America and the Caribbean where low-income families live, and where the demand for sustainable construction meets that for structural resistance and affordability. Feasibility is studied based on the structural analysis of the main wind force resisting system (MWFRS) of a typical one-story single-family dwelling subject to wind pressures resulting from 3-s gust speeds up to 90 m/s (324 km/h). The output consists of parametric curves that relate wind speed with masonry compressive, tensile and shear strength demand for wall thicknesses ranging from 203 to 508 mm. The structural adequacy of the MWFRS is assessed for the cases of flat and 15° gable roof. The design implications are discussed vis-a-vis strength reduction factors and design strength demands, and sustainable reinforcement options. It is concluded that it is feasible to design one-story CSEB masonry dwellings that can withstand winds loads from Category 4 hurricanes and EF3 tornadoes, provided that a rigid horizontal diaphragm is used. Grouted steel reinforcement may be used in safety shelter CSEB masonry structures to be designed for more extreme wind loads.

Five large-scale concrete specimens reinforced with bonded seven-wire steel strands and representative of portions of bridge piles were exposed to salt water wet/dry cycles for 1 year, simulating tidal action. Corrosion of multi-wire steel strands was facilitated by minimizing the concrete cover. Half-cell potential and polarization resistance measurements were routinely performed to assess early corrosion. Supporting visual evidence of pitting and crevice corrosion was collected from strands removed from decommissioned specimens. It is shown that corrosion can be assessed based on polarization resistance thresholds. Tafel slopes were numerically estimated for passive and corroding strands from ±20 mV polarization curves, and used to gain a preliminary insight into the evolution of the Stern–Geary parameter and the associated corrosion intensity. These results suggest that the Stern–Geary parameter increases upon depassivation of the strands, different from deformed bars in reinforced concrete.

This paper reports on a project aimed at understanding whether acoustic emission (AE) data can be used to detect and classify corrosion in PC piles exposed to saltwater, ranging from steel depassivation to concrete cracking caused by the formation of expansive surface oxides. Experimental results are presented from three specimens representing portions of PC piles, which were directly exposed to saltwater through wet/dry cycles mimicking tidal action for up to 790 days. Corrosion activity was monitored continuously using AE sensors. Half-cell potential and polarization resistance were measured periodically to serve as benchmarks to detect steel depassivation and corrosion. Visual evidence of naturally-occurring corrosion at different stages was collected from strands that were extracted from decommissioned specimens.

SUMMARY Prestressed concrete (PC) piles in marine environments are vulnerable to corrosion damage especially at their tidal zone because of the concurrent exposure of steel reinforcement to moisture, chlorides, and oxygen. Early detection of corrosion in prestressed strands is desirable to enable the effective planning and prioritizing of maintenance operations. This paper reports on experiments aimed at testing the hypothesis that acoustic emission (AE) monitoring is suitable to recognize and classify early corrosion damage in PC piles exposed to saltwater. In fact, AE is sensitive to the formation and growth of microcracks in both steel and concrete, which may develop upon depassivation of reinforcement and buildup of corrosion by-products. In addition, the influence of AE signals produced through flexural cracks in the concrete is of less concern for PC piles as such cracks are seldom produced under service loads. Five specimens representative of full-scale portions of PC piles were designed to accelerate corrosion and subjected for 1 year to wet/dry cycles in saltwater simulating tidal action. The specimens were monitored continuously with AE sensors. Benchmark electrochemical measurements were routinely performed to understand when depassivation of the steel strands occurred. Visual evidence of early corrosion was collected from strands removed from two decommissioned specimens. It is shown that AE intensity analysis is more effective than AE signal strength and cumulative signal strength analysis in recognizing corrosion damage. Intensity analysis-based criteria for the assessment of early corrosion damage are proposed, complementing previously developed criteria for more severe corrosion damage in steel strands. Copyright © 2014 John Wiley & Sons, Ltd. Received 22 May 2014; Revised 15 September 2014; Accepted 2 November 2014

The understanding of the load-resistance mechanisms and failure modes of large-scale concrete and masonry structures relies on accurate measurements of surface motions and deformations, and faithful crack maps. Measurements are typically taken using surface-mounted point-wise sensors (PWSs), and crack maps are hand-drawn based on visual inspection. It is impractical to obtain detailed displacement and deformation maps that describe the complex response of large structures based on PWS measurements. In addition, manual crack drawing is difficult, time-consuming, and prone to human errors, which makes it challenging to consistently produce faithful crack maps. This paper reports on a pilot study to test the use of three-dimensional digital image correlation (3D-DIC) as a non-contacting method to measure surface deformation fields on full-scale masonry walls, and produce detailed crack maps. Three confined masonry walls were tested under horizontal in-plane reverse-cycle loads. The specimens were designed to attain different levels of strength and deformability through different load-resistance mechanisms. Representative 3D-DIC measurements of drift, diagonal deformations, and interface slip between the reinforced concrete tie columns and the masonry infill were evaluated vis-a-vis benchmark PWS measurements, showing a comparable accuracy. Strain maps based on 3D-DIC measurements were enlisted to visualize the development of the fundamental strut-and-tie resisting mechanism in confined masonry walls subjected to horizontal in-plane loads, and illustrate practical structural analysis and design implications. More detailed crack maps compared with traditional hand-drawn maps were obtained based on 3D-DIC maximum principal strain contours.

Acoustic emission (AE) was used to monitor eight prestressed concrete (PC) T-shaped beams that were tested per the ACI 437 cyclic load test (CLT) method. Limited research has examined the validity of this test method for PC structures. The study aims to explore the use of AE for damage evaluation as a supplement to conventional measurements used to assess the condition of a structure based on the CLT acceptance criteria. The beams had different initial conditions: five specimens were pre-cracked and corroded to different corrosion levels while the remaining unconditioned beams served as control specimens. AE enabled to monitor the accumulation of damage during the load tests and damage quantification charts based on AE data are presented. These charts allowed determining load test failure with better sensitivity than the existing ACI 437 evaluation criteria. The charts enabled the assessment of damage regardless of the specimens’ initial condition. In addition, it is shown that accurate damage source location and crack mapping can be achieved by using suitably filtered AE data.

Evidence from load tests on concrete beams internally reinforced with corrosion-resistant glass fiber-reinforced polymer (GFRP) bars, and without shear reinforcement, shows that the sectional shear stress at failure drastically decreases at increasing effective depths. An important implication is that the strength and failure mode of typical laboratory-scaled specimens can be misleading if such results are used to extrapolate the response of larger members. In addition, the most accurate nominal shear strength algorithms are based on fundamentally different hypotheses on the governing shear-resisting mechanisms, namely aggregate interlocking and shear-compression fracture. Advanced computational modeling and simulation tools can aid with understanding the underlying mechanics of size-dependent shear response. This paper demonstrates the practical selection of the parameters of a Lattice Discrete Particle Model (LDPM) for a concrete for which only uniaxial compression test results are available, which is a typical case for specimens in existing databases. The LDPM was enlisted as it represents the physical heterogeneity of concrete, and incorporates constitutive laws (e.g., tension-softening and shear-compression fracture) that are critical to realistically simulate meso-scale friction and fracture damage mechanisms. The calibrated LDPM was used to build numerical models of slender GFRP RC beams with effective depth of 146 and 292 mm, for which evidence from actual load tests highlighted a size effect in the range 48–62%. The computational simulations yielded accurate estimates of strength, failure mode and load-deflection response irrespective of beam size. The output of the numerical simulations using the LDPM-based models was used to gain new insight into the contribution of different shear-resisting mechanisms to strength and size effect.

This paper discusses the crashworthiness of prototype steel post-and-beam barriers [Ministry of Transportation of Quebec (MTQ) Type 210] whose concrete curb-to-bridge deck connection is reinforced with corrosion-resistant glass fiber-reinforced polymer (GFRP). Experimental evidence is obtained from proof tests on five full-scale barrier and overhang subassemblies. The text matrix includes three GFRP RC and two steel RC specimens. The steel RC benchmark system is currently used as specified in the Canadian Highway Bridge Design Code (CHBDC). The objective is to verify whether (1) the resistance to out-of-plane quasi-static loads and the associated transverse deflection of the GFRP RC curb and steel barrier system are comparable to those of the steel RC counterparts; (2) the transverse strength exceeds the CHBDC equivalent static load demand; and (3) failure at the curb-deck connection is attained at safe transverse loads, and premature failure at the curb-deck connection is prevented. The GFRP and steel RC systems exhibit comparable strength, with the former undergoing greater deformations. For both systems, premature brittle failure of the curb-deck connection is prevented, and the equivalent static load requirements are satisfied. A larger capacity is attained when closed GFRP stirrup connectors are used at the curb-deck connection in lieu of C-shaped stirrups. An analytical model is used to predict the lower-bound strength of the GFRP RC curb-deck connection, and relevant design implications are discussed. It is recommended that the adoption of the proposed GFRP RC design relies on conclusive evidence from crash testing to verify safety against vehicle rollover because of the greater deformations compared with steel RC systems having the same amount of reinforcement.

Steel degradation due to corrosion in prestressed concrete bridges has been of major concern as it presents a threat to the integrity of structures adjacent to marine environments or where deicing salts are regularly used. To assess the potential for monitoring of the corrosion process, an accelerated corrosion testing program has been conducted. A series of specimens with dimensions 114×114×508 mm (4.5×4.5×20 in.) were subjected to constant potential application through the embedded steel strand while being continuously monitored with acoustic emission (AE). Depassivation of the strand was detected by monitoring the fluctuations in applied anodic current. Half-cell potential measurements assessed the probability of corrosion, and all results obtained were compared to acoustic emission data. The mass loss of the corroded strands was correlated to acoustic emission intensity analysis to quantify the degree of damage. Results show that acoustic emission is as sensitive as half-cell potential for d...

Weld seams are critical points for the initiation of fatigue cracks in steel structures subjected to cyclic loads. Semi-elliptical surface cracking at the toes of a fillet weld is not easily found when it is partially through the thickness and subcritical. In this study the acoustic emission (AE) method is used to detect crack propagation in cruciform fillet welded joints that are representative of typical fatigue sensitive details in steel bridge superstructures. The effect of geometry and fatigue load on the AE data is investigated by varying the width of the base plate and the stress ratio. AE data filtering based on load pattern, source location, and waveform feature analysis was implemented to minimize noise-induced AE signals and false indications due to wave reflections. AE time domain features such as amplitude ( b -value), counts, signal strength, and absolute energy are employed to study the influence of geometry and fatigue load on the AE data.

This paper discusses the calibration of a concrete lattice discrete particle model (LDPM), and its preliminary validation for the case of shear failure in scaled glass fiber reinforced polymer (GFRP) reinforced concrete (RC) beams without stirrups. First, the model parameters were defined based on: (a) the design of the concrete mixture that was used to fabricate scaled beam specimens; and (b) a literature database of meso-scale concrete parameters. Second, the calibration was refined to reach satisfactory agreement between numerical and experimental compression stress-strain curves as obtained by testing concrete cylinders in accordance with ASTM C469. The calibrated model was then used for the numerical simulation of four-point bending load tests on two slender GFRP RC beams without stirrups, and having an effective depth of 146 and 292 mm, respectively. The beam computational models are discussed vis-a-vis experimental data based with respect to elastic response, post-cracking stiffness degradation and damage progression, ultimate strength, and failure mode. The proposed model accurately approximates the preand post-cracking flexural stiffness, and holds promise to predict the shear strength of scaled GFRP RC slender beams without stirrups, provided that a suitable rebar-concrete bond stress-slip law is implemented.

This paper reports on a feasibility study to develop a reversible and potentially fire-resistant fiber reinforced cement-based matrix (FRC) composite system for concrete confinement applications. The first part of this study aimed at selecting a candidate FRC system from different fiber (including glass and basalt) and inorganic matrix combinations on the basis of: constructability, by verifying the workability and ease of installation on concrete cylinders; structural performance, by evaluating strength and deformability enhancement in confined concrete cylinders tested under uniaxial compression; and compatibility, by examining the quality of the concrete–FRC interface and the level of fiber impregnation using scanning electron microscope images. In the second part of this study, the selected FRC system was further assessed through compression tests of additional concrete cylinders confined using different FRC reinforcement ratios, where both axial and in-plane (radial) deformations were measured to assess confinement effectiveness. The feasibility of making the application reversible was investigated by introducing a bond breaker between the concrete substrate and the composite jacket in a series of confined cylinders. The prototype FRC system produced a substantial increase in strength and deformability with respect to unconfined cylinders. A superior deformability was attained without the use of a bond breaker. The predominant failure mode was loss of compatibility due to fiber–matrix separation, which points to the need of improving fiber impregnation to enable a more efficient use of the constituent materials. Semi-empirical linear and nonlinear models for compressive strength and deformation in FRC-confined concrete are also presented.

The external confinement of RC columns by means of externally bonded fiber-reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated American Concrete Institute (ACI) 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity. The discussion of the results includes a comparison with the values obtained using existing constitutive models.

Large amounts of rice husk ash (RHA) are produced every year worldwide, and difficulties related to its disposal may cause this product to become an environmental hazard. Owing to its high amorphous silica content, RHA has shown to be a valid supplementary cementing material in the production of concrete. This paper presents the physical and chemical properties of a new generation RHA that is off-white in color, is carbon neutral, and has no crystalline SiO2 and toxic metals. The effects on mechanical properties of a mixture using off-white rice hull ash (OWRHA) as partial replacement of white cement were also investigated. The OWRHA-blended concrete has higher compressive and splitting tensile strengths at various ages compared with the control mixture. It is shown that up to 15% of OWRHA could be advantageously blended with white cement to enhance white concrete performance without modifying the aesthetics of the final product.

Externally post-tensioned steel tendons have long been an attractive option for increasing the design loads or correcting strength and serviceability problems in bridge and building structures. More recently, alternative solutions have been developed and implemented that use straight post-tensioned carbon fiber reinforced polymer (CFRP) tendons, ideally enlisting their high-strength to failure, small relaxation, corrosion resistance, and light weight. In this paper, a novel CFRP system for external post-tensioning is presented. The solution consists of unbonded CFRP bars connected to dead- and live-end steel anchors by means of couplers that allow the bar to develop the full tensile strength. Intermediate deviators can be extended vertically to impart additional post-tensioning (PT) force and achieve a profiled bar configuration. The required uplift forces for deflection control of a flexural member are provided by modifying the number, position and extended height of the deviators, similarly to commercially available systems that use steel wire strands. The structural efficiency of such approach in controlling deflection is analyzed and discussed for single-span one-way members on the basis of a parametric study that considers the influence of member geometry, flexural stiffness, boundary conditions, and PT system layout. A design example is also provided.

In the aftermath of the 2010 Haiti earthquake, households were often reluctant to reoccupy their dwellings due to concerns about the safety of damaged structures. If feasible, structural repair (to complement to temporary sheltering) is a realistic option for rapid reoccupancy as reconstruction poses greater barriers of cost and time. Considering the economic and technological limitations found in developing regions, this paper addresses the question of whether it is feasible to repair a severely damaged substandard CM wall in a context-sensitive fashion, that is, using: (a) materials that are locally available and commonly used and often substandard (e.g., low-strength concrete and mortar); and (b) construction and installation practices that are familiar to local workers, without the need for additional training. Two full-scale CM wall specimens were subjected to cyclic quasi-static in-plane load test till failure, and retested after repair by means of reinforced plaster made of low-strength mortar and steel welded wire mesh. Three-dimensional digital image correlation was used to provide full-field strain maps to describe the load-resistance mechanisms and damage evolution. It is shown that the failed CM walls can be transformed into walls with acceptable strength and deformability. In addition, it is shown that only the repaired specimens qualify as earthquake-resistant structures based the acceptance criteria set forth in Mexico City Building Code for Masonry Structures (NTCM 2004). It is concluded that it is feasible to repair a highly-damaged substandard CM wall in a context-sensitive fashion and make it safe, comparable to a CM wall built with acceptable materials and details.

The use of adhesively bonded carbon fiber reinforced polymer (CFRP) laminates is increasingly being considered for the rehabilitation of metallic structures. The effective structural monitoring of steel/CFRP adhesive joints is of critical importance to assess the design service performance of the system, which ultimately depends on the bond damage tolerance at the load transfer regions. In the present study laboratory static and fatigue tests were conducted on steel/CFRP skin doubler and double strap joint specimens, which were monitored using the acoustic emission (AE) technique. The characteristics of the AE signals were correlated with the mechanical response of the samples, in order to understand the AE response associated with the accumulation of bond damage. One-dimensional source location was also performed to examine the initiation and the development of the disbond. The results show that AE parameter-based analysis is an effective nondestructive evaluation tool for bond damage detection and area location.

This paper describes research on the evolution of a cost-effective, structural stay-in-place (SIP) formwork bridge deck system with an integrated modular three-dimensional fiber-reinforced polymer (FRP) reinforcement cage. Recent research conducted at the University of Wisconsin is reviewed to show the evolution of the reinforcing system to include an integral FRP SIP form. The evolution occurred through laboratory testing, which was followed by the design and construction of two bridge structures owned by the State of Wisconsin. Each structure used different FRP reinforcement and formwork. These projects pointed out the need for a competitive SIP formwork to be used in conjunction with FRP reinforcement. Two specimens with different FRP reinforcement and SIP formwork arrangements were tested. Full-scale deck slab specimens were tested by applying a simulated wheel design load to investigate the static response, ultimate capacity, and failure mechanism. The most economical FRP reinforcing system has been implemented in a superstructure replacement project in Greene County, Missouri.

There is a growing need for the development and implementation of new methods for the rapid and cost-effective rehabilitation of deteriorating steel structural components to offset the drawbacks related to welding and/or bolting in the field. Carbon fiber reinforced polymer (CFRP) composites provide a potential alternative as externally bonded patches for strengthening and repair of metallic structural members for building and bridge systems. This paper describes results of an investigation of tensile and fatigue response of steel/CFRP joints simulating scenarios of strengthening and crack-patching. It is shown that appropriately designed schemes, even when fabricated with levels of inaccuracy as could be expected in the field, can provide significant strain relief and load transfer capability. A simplified elasto-plastic closed form solution for stress analysis is presented, and validated experimentally. It is shown that the bond development length remains constant in the linear range, whereas it increases as the adhesive is deformed plastically. Fatigue resistance is shown to be at least comparable with the requirements for welded cover plates without attendant decreases in stiffness and strength.

Compressed and stabilized earthen masonry (CSEM) offers a sustainable, affordable, and locally appropriate alternative to traditional residential construction. In a National Science Foundation funded project carried out by the authors, the suitability of engineered earthen construction in high-wind climates as the main wind force resisting system (MWFRS) is investigated. The fundamental research program includes experimental investigations on the material properties of cement stabilized earth blocks, mortars, and assemblies. However, the particular subject of this paper is the remaining research gap with respect to available design processes and construction details in material-specific and general design codes and guidelines. In this project, this gap in knowledge is addressed by using the experimentally determined material characteristics and traditional reinforced masonry design methods to develop high-wind resistant wall systems using CSEM. Various reinforced double wythe CSEM wall system alternatives are proposed with roof-to-wall and wall-to-foundation connections and wall section details. Also, due to CSEM assemblies not meeting minimum strength requirements, bond beam designs made of CSEB units and CMU are proposed.

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.

This paper reports on research aimed at investigating the reinforcing effects of graphene nanoplatelets (GNPs) in cement composites. Nanoreinforced cement mortar cubes were prepared using surfactant-coated GNPs. The dispersion and embedment of GNPs in the cement matrix were verified based on evidence from compression strength tests and scanning electron microscopic imaging. Results from fracture mechanics tests on notched beams were then used to evaluate the effect of incorporating well-dispersed, surfactant-coated GNPs on the flexural strength and stiffness of cement paste. 3D digital image correlation measurements were used to study the morphology and evolution of the fracture process zone in plain and GNP-reinforced cement paste.

Understanding of deformations and the progressive failure mechanisms of asphalt shingles under wind loads is key to develop wind-resistant roofing systems, as well as standard test methods to characterize strength under representative wind loads. In fact, failure of shingles rated as resistant to winds up to 150 mph have been reported at speeds below 115 mph. Damage associated with failure of roof shingles continues to be a major source of insurance claims. Though pressure measurements can be taken at discrete points using pressure taps, no technology has been successfully deployed to measure full-field deformations on roof shingles subjected to wind loads. This paper reports on a feasibility study of three-dimensional digital image correlation (3D-DIC) as a non-contacting technique to measure full-field displacements of roof shingles under high wind loads. Feasibility is assessed based on evidence from load testing of three-tab shingles mounted on a full-scale roof panel specimen that was subjected to straight winds with speed up to 155 mph. Uplift displacements were measured on a target shingle tab. The natural color variations on the shingle exposed surface were used to provide a suitable speckle pattern for 3D-DIC measurements. It is shown that consistent 3D-DIC uplift displacement maps can be obtained up to failure. The evidence gained also highlights the importance of understanding the influence of time-dependent shingle material deformations, together with the progressive physical damage along the sealant strip.

This paper reports on the fracture behavior of MWCNT-reinforced cement paste based on evidence from three-point bending tests of single-edge notched beam samples. Digital image correlation (DIC) was used to measure full-field displacements at different stages of fracture in reinforced and unreinforced samples. Strain maps extracted from displacement data were used to characterize the morphology of the fracture process zone (FPZ). The DIC principal tensile strain maps from nanoreinforced samples consistently highlighted the development of a larger FPZ prior to failure. Evidence from scanning electron microscopy analysis of fracture surfaces further supports the hypothesis that highly-dispersed and well-bonded MWCNTs contribute to toughness through crack-bridging.

Corrosion of steel strands in prestressed concrete (PC) bridges may lead to substantial damage or collapse well before the end of the design life. Acoustic Emission (AE) is a suitable nondestructive technique to detect and locate corrosion in reinforced and prestressed concrete, which is key to prioritize inspection and maintenance. An effective tool to analyze damage-related AE data is intensity analysis (IA), which is based on two data trends, namely Severity (average signal strength of high amplitude hits) and Historic Index (ratio of the average signal strength of the most recent hits to the average of all hits). IA criteria for corrosion assessment in PC were recently proposed based on empirical evidence from accelerated corrosion tests. In this paper, AE data from prestressed and non-prestressed concrete pile specimens exposed to salt water wet-dry cycling for over 600 days are used to analyze the relation between Severity and Historic Index and actual corrosion. Evidence of corrosion is gained from the inspection of decommissioned specimens. The selection of suitable J and K parameters for IA is discussed, and an IA chart with updated corrosion criteria for PC piles is presented.

Acoustic emission was used to monitor the cracking mechanisms leading to the failure of scaled concrete beams having Glass Fiber Reinforced Polymer (GFRP) longitudinal reinforcement and no shear reinforcement. Dimensional scaling included that of the effective depth of the cross section, which is a key parameter associated with the scaling of shear strength; and maximum aggregate size, which affects the shear-resisting mechanism of aggregate interlock along shear (inclined) cracks. Five GFRP reinforced concrete (RC) beams with effective depth up to 290 mm and constant shear span-to-effective depth ratio of 3.1 were load tested under four-point bending. Two types of failures were observed: flexural, due to rupture of the GFRP reinforcement in the constant moment region; and shear, due to inclined cracking in either constant shear region through the entire section depth. Acoustic emission (AE) analyses were performed to classify crack types occurring at different points in the load history. The results of this study indicate that appropriate AE parameters can be used to discriminate between developing flexural and shear cracks irrespective of scale, and provide warning of impending failure irrespective of the failure mode (flexural and shear). In addition, AE source location enabled to accurately map crack growth and identify areas of significant damage activity. These outcomes attest to the potential of AE as a viable technique for structural health monitoring and prognosis systems and techniques.

The main cause of degradation for reinforced concrete (RC) structures is the corrosion of the steel reinforcement. Laboratory tests aimed at studying durability are typically accelerated to provide usable results within a reasonable period of time, and well-established electrochemical techniques are used for the assessment of corrosion. However, because these techniques are not suitable for continuous monitoring and are often intrusive, nondestructive testing (NDT) techniques are also suitable for monitoring. Acoustic emission (AE) is one of the NDT techniques used to detect the onset and progression of corrosion. This paper presents an accelerated corrosion test setup and AE monitoring methodology based on the historic index, H(t), for laboratory experiments on RC specimens. Accelerated corrosion is attained by increasing the capillarity suction of RC exposed to chlorides. The frequency spectrum of the AE signals before and after the initiation of corrosion is investigated to isolate the frequency components associated with corrosion. It is shown that the AE signals generated by early corrosion excite a well-defined narrow band of the frequency spectrum.