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Reinforced concrete (RC) diaphragms play a fundamental role in seismic resistance of RC buildings. In addition to transferring the gravity loads to the beams and columns, diaphragms need to be sufficiently rigid with high shear capacity to resist and distribute the earthquake loads to the lateral force resisting system. Despite the large building inventory with under designed diaphragms to resist the shear loads from earthquakes, the number of studies investigating possible approaches to increase the in-plane shear capacity of diaphragms is limited. External equally distributed narrow strips of fiber-reinforced polymers (FRP) providing additional shear strength for RC diaphragms is proposed in this study. Five full scale RC diaphragms with overall dimensions of 4.5 m long by 1.5 m wide by 0.1 m thick were built and tested under cyclic shear loading. One out of the five specimens was tested as a reference with no strengthening, while the remaining four were strengthened with external glass or carbon fiber-reinforced polymer (GFRP or CFRP) composites. The test results showed that the FRP strengthening system effectively enhances the in-plane shear capacity of the RC diaphragms. Compared to the reference specimen, the FRP layout used for testing increased the shear capacity by up to 40%. This paper presents the test specimens, strengthening systems, and in-plane shear response of tested diaphragms in terms of failure modes, strength, and deformation. The experimental results were also compared to theoretical values determined according to the evaluation criteria in the International Code Council (ICC)-Evaluation Services (ES), Acceptance Criteria (AC) 125.

Cu-Al-Mn (CAM) shape memory alloys (SMA) are cost effective, have a high low-cycle fatigue life and superelastic limit, and a wide temperature application range compared to other types of SMAs. These characteristics of CAM SMAs have resulted in an increased research interest in their use in civil engineering applications, particularly as reinforcement in concrete structures, and dampers in steel structures. However, these applications could require machining of the CAM SMA bars for connecting with other structural elements. This study presents the methods and results of the first systematic research on the machinability of CAM SMAs. The key machinability characteristics of CAM SMAs, such as chip formation, cutting temperature, tool wear, workpiece surface roughness and diameter deviation were studied and compared with conventional NiTi SMAs, and commonly used steel: mild steel (MS) and 304 stainless steel (SS). Effects of a wide range of cutting parameters, such as cutting speed ranging from 15 to 120 m/min, feed rate ranging from 0.1 to 0.2 mm/rev, and depth of cut ranging from 0.5 to 1.5 mm, were investigated. The results from this study demonstrated that the tool wear from machining CAM SMAs was close to that of SS and slightly higher than that from machining MS but much lower than of that from machining NiTi SMAs. In all the cases considered here, the tool wear from machining CAM SMAs was found to be 0.6 to 1.8 times that from machining SS, 0.8 to 2.4 times that from machining MS, and 1/7 to 1/21 times that from machining NiTi SMAs. After a continuous machining test with a total cutting length of 4.5 m, the nose wear of machining CAM SMAs was found to be 1.6 times that of machining MS, and the average flank wear of machining CAM SMAs was found to be three times that of machining MS; the diameter deviation (relative diameter difference with the first sample) of CAM SMAs was only 10 mm larger than that of MS.

In this paper, the influence of brick masonry infill walls on the seismic performance of reinforced concrete (RC) frames is investigated. The presence and the location of a door opening are conside...

Highway bridge beams are subjected to aggressive environments, temperature fluctuations, and millions of loading cycles throughout their service life. The combi­nation of these effects can result in the reduction of the service life of structural components. In the past decades, more-durable composite materials, such as carbon-fiber-reinforced polymers (CFRPs) have been implemented in concrete structures to address problems related to environmental durability. To date, prestress­ing applications of CFRP in beams have been mostly investigated for rectangular cross sections, which are not representative of the geometry used in modern highway bridges. In addition, the construction and detailing aspects of CFRP prestressed concrete beams have not been investigated outside of laboratory conditions. This paper describes an experimental investigation conducted on eight 40 ft (12 m) long AASHTO Type I prestressed concrete beams with 3 ft (0.9 m) wide composite con­crete decks and detailed identically to highway bridge beams in practice. Three beams were pretensioned with carbon-fiber-composite cables, four beams with CFRP bars, and one with prestressing steel. The beams were tested under monotonic and fatigue loading. All CFRP prestressed concrete beams were designed to fail due to the rupture of the prestressing CFRP. The CFRP prestressed concrete beams exhibit several desirable features of the typical steel prestressed concrete beams in terms of serviceability and strength.

Superelastic alloy (SEA) bars are widely used in structures subjected to moderate and strong earthquakes. Compared with conventional nickel-titanium (NiTi) SEAs, Cu–Al–Mn (CAM) SEAs has received increasing attention recently due to their cost-effectiveness and easier machinability. The authors’ previous research showed that despite their lower strength and limitations in the maximum length, the CAM SEAs have comparable superelastic strain recovery, a wider temperature range, and superior strain rate stability compared to NiTi SEAs. However, the previous research was limited to a few specimens and only conducted to a few hundred cycles without considering the full deterioration in the material properties. Besides, the existing research on CAM SEA was only limited to small sample sizes at room temperature, while the fatigue performance of large diameter CAM SEAs under low and high temperatures relevant for civil engineering structures has not been reported. To fill this knowledge gap, low-cycle fatigue performance of 20 mm diameter CAM SEAs was studied at room temperature 25 °C, low temperature, −40 °C, and high temperature, 50 °C. Both single crystal and polycrystal CAM SEAs were investigated to determine their feasibility as concrete reinforcement under repeated high strain loading cycles expected during an earthquake. Strain cycles up to 50 000 have been applied at a tensile strain amplitude of 5%. Variations in the superelastic properties were observed and analyzed, including the stress–strain curves, elastic modulus, transformation stresses, damping ratio and recovery strain. Stable hysteresis has been observed for cycles exceeding tens of thousands at all temperatures demonstrating the suitability of CAM SEAs for seismic applications in civil engineering structures.

In this study, an investigation of the shear behavior of full-scale reinforced concrete (RC) beams affected from alkali–silica reactivity damage is presented. A detailed finite element model (FEM) was developed and validated with data obtained from the experiments using several metrics, including a force–deformation curve, rebar strains, and crack maps and width. The validated FEM was used in a parametric study to investigate the potential impact of alkali–silica reactivity (ASR) degradation on the shear capacity of the beam. Degradations of concrete mechanical properties were correlated with ASR expansion using material test data and implemented in the FEM for different expansions. The finite element (FE) analysis provided a better understanding of the failure mechanism of ASR-affected RC beam and degradation in the capacity as a function of the ASR expansion. The parametric study using the FEM showed 6%, 19%, and 25% reduction in the shear capacity of the beam, respectively, affected from 0.2%, 0.4%, and 0.6% of ASR-induced expansion.

Structural performance of nuclear containment structures and power plant facilities is of critical importance for public safety. The performance of concrete in a high-speed hard projectile impact is a complex problem due to a combination of multiple failure modes including brittle tensile fracture, crushing, and spalling. In this study, reinforced concrete (RC) and steel-concrete-steel sandwich (SCSS) panels are investigated under high-speed hard projectile impact. Two modeling techniques, smoothed particle hydrodynamics (SPH) and conventional finite element (FE) analysis with element erosion are used. Penetration depth and global deformation are compared between doubly RC and SCSS panels in order to identify the advantages of the presence of steel plates over the reinforcement layers. A parametric analysis of the front and rear plate thicknesses of the SCSS configuration showed that the SCSS panel with a thick front plate has the best performance in controlling the hard projectile. While a thick rear plate is effective in the case of a large and soft projectile as the plate reduces the rear deformation. The effects of the impact angle and impact velocity are also considered. It was observed that the impact angle for the flat nose missile is critical and the front steel plate is effective in minimizing penetration depth.

This article investigates the effect of alkali–silica reaction (ASR) damage on the structural performance of reinforced concrete (RC) dry casks for spent nuclear fuel (SNF) storage. Dry cas...

Post-earthquake functionality of bridges is mainly affected by the residual deformations and damage level of the bridge columns. Recent earthquakes have shown that the bridge columns constructed based on current design regulations suffer large permanent deformations. Using high-performance materials such as super-elastic alloys (SEA) and engineered cementitious composites (ECC) has recently been proposed to address these issues. In this study, the performance of an innovative bridge column design incorporating ECC and Cu-Al-Mn (CAM) SEA bars is investigated under seismic loads. The behavior of ECC is simulated by introducing an experimentally calibrated constitutive model for concrete with smeared reinforcement. Additionally, a one-dimensional constitutive model is implemented to simulate the behavior of CAM SEA bars. A total of five different column configurations are modeled and the results are compared with the corresponding experimental data for validation purposes. The results are analyzed to understand the seismic behavior of these innovative columns in terms of lateral strength, post-peak degradation, permanent deformation, and shape of the hysteresis curves. Through numerical modeling, data are obtained and interpreted regarding the salient aspects of the structural behavior of these columns that could not be obtained through experiments.

Vertical concrete dry casks, which provide an interim solution for the storage of spent nuclear fuel, are vulnerable to tip-over due to lateral loads. This paper explores the probabilistic structural response of a representative dry cask subjected to tip-over impact loads and aging effects. Considering concrete and soil material properties, thickness of the pad, angular velocity at the onset of tip-over, and age of the cask as variables, 200 configurations of the tip-over problem are generated by Latin Hypercube Sampling. To consider aging and the associated temporal variations, material properties of the steel parts vary in the generated configurations due to temperature variations. The generated tip-over scenarios are analyzed by numerical models developed and validated in a commercial finite element analysis program. Machine learning algorithms such as polynomial response surface models, multivariate adaptive regression splines, regression trees, support vector machines, Gaussian processes and neural networks are trained on datasets provided by the finite element analysis to develop metamodels for the maximum strain of the canister and maximum acceleration of the concrete overpack. These metamodels offer statistical approximating functions that enable efficient impact fragility analysis and evaluation of the sensitivity of the fragility to age, concrete material properties of the cask and pad, and pad thickness. The effect of aging due to alkali-silica reaction on the strain fragility is also studied, and recommendations regarding the design of vertical concrete dry casks are provided. Risk analysis is performed to estimate the dry storage cask’s risk of failure (i.e., probability of limit state exceedance) and to uncover the effect of age and design parameters on the probability of strain and acceleration exceeding predefined limits. The risk analysis shows that the probability of canister failure in the tip-over event is negligible. That is, despite expected cracks in the concrete overpack, the structural integrity of the dry cask system subjected to the tip-over impact loads is retained.

Recently, single-crystal Cu-Al-Mn (CAM) superelastic alloy (SEA) bars have been developed to address the shortcomings of traditional Ni-Ti SEA bars, i.e., high cost, low workability, and la...

This paper investigates the dynamic characteristics of a multilevel structure for the transportation and storage of spent nuclear fuel (SNF) from commercial power plants. The nuclear fuel is stored in slender rods that are grouped together into fuel assemblies (FA). In a sealed cylindrical container called “canister”, the FA are inserted into a honeycomb basket. The objective of this paper is to develop a computational model that accurately represents the structural dynamics of the canister as seen from its external surface, such that this computational model can be used in the context of structural integrity assessment of the internal components (FA and fuel rods) based on external vibration measurements. The numerous components lead to a large finite element model, and correspondingly, vibration modes and eigenfrequencies. Nevertheless, the localized connections between components enable an efficient domain decomposition with few interface coordinates. Craig–Bampton (CB) substructuring is thus used to perform the modal analysis. However, the high modal density yields a large-scale CB eigenvalue problem that necessitates a sparse solver. A block factorization by Schur complement that exploits the sparsity of the CB matrices allows an efficient calculation of the numerous eigenpairs. Many local vibration modes contribute little to the dynamics of the SNF canister. The main contribution of this paper is the development of an efficient methodology for determining the importance of each of the substructural modes of the CB model. The removal of the least dominant substructural modes allows for reducing the CB model. Using a 75% filtering, a significant speed-up is obtained, without noticeable loss of accuracy.

This study focuses on two separate investigations of the main aging mechanisms: alkali&ndash, silica reactivity (ASR) and the corrosion of reinforcing steel (rebar) concrete, both of which may result in a premature failure to meet the serviceability or strength requirements of a concrete structure. However, these processes occur very slowly, spanning decades. The impact of direct chemical additives to fresh concrete to accelerate ASR and the corrosion of reinforcing steel on the fresh and hardened properties of the ensuing material are investigated to inform the potential use of chemicals in large-scale studies. The deterioration of reinforced concrete (RC) is determined by means of expansion, cracking, bulk diffusivity and surface resistivity measurements, and compressive, split tensile and flexural strength tests. The results indicate that the addition of sodium hydroxide and calcium chloride can effectively accelerate the crack formation and propagation in concrete due to ASR and the corrosion of rebar, respectively. The ASR-induced cracks maintained a constant crack width from 0.05 mm to 0.1 mm over the measurement period regardless of the intensity of aging acceleration. Adding 4% chloride by weight of cement for accelerating rebar corrosion resulted in an average crack that was 82% larger than in the case of ASR accelerated with the addition of sodium hydroxide. The addition of alkali resulted in an increase in early-age (7-day) strength. At a total alkali loading of 2.98 kg/m3, 3.84 kg/m3 and 5.57 kg/m3, the 28-day compressive strength of concrete decreased by 3%, 10% and 24%, respectively. Similarly, a higher early-age strength and a lower later-age strength was observed for the concrete in the presence of corrosive calcium chloride. The results from this research are expected to inform future studies on the long-term performance of RC structures under accelerated ASR and corrosion.

Special moment resisting frames (SMF) are commonly used in low- and medium-rise buildings located in regions of high seismicity. Although adequate performance of this seismic force resisting system was observed in prior earthquakes in terms of protecting buildings from collapse, the formation of plastic hinges in the beams and columns causes irreparable damage to the beam-column connections. Recently, interest in using fiber-reinforced concrete (FRC) has been growing to enhance energy absorption capacity and damage tolerance of beam-column connections and other components in reinforced concrete (RC) buildings. Prior research has mostly focused on the application of steel FRC (SFRC) in 2-D beam-column connections. However, little is known about the performance of exterior beam-column connections that are usually subjected to more complex loading during an earthquake, involving bi-directional bending and torsion of the column. In addition to the loading, the geometry of the connection requires a more involved test setup (i.e., with an out-of-plane beam and proper boundary conditions). In this research, the use of engineered cementitious composites (ECC) in 3-D exterior beam-column connections is investigated experimentally to improve building seismic performance. ECC is a special class of high-performance fiber-reinforced cementitious composites (HPFRCC) that, compared to conventional concrete, exhibits higher tensile ductility, energy absorption and shear resistance, in addition to improved bond performance with reinforcing steel (rebar). To understand the performance of exterior beam-column connections under complex loading conditions, scaled 3-D specimens were constructed and tested under simulated seismic loads. To improve the performance of the connections, conventional RC was replaced with reinforced ECC (RECC) that extends from the panel zone to the adjoining beams and columns to cover the potential plastic hinge regions. This paper discusses the loading protocols, the test setup for 3-D exterior beam-column connections, and the improvement in the joint behavior with the application of RECC as compared to conventional RC. The results suggest that the efficient use of ECC in the potential plastic hinge regions can improve the capacity and damage tolerance of beam-column connections under realistic seismic loading conditions.

Low-rise metal buildings are used in all geographic locations, including high seismicity regions. In the design of low-rise metal building systems, column base connections are commonly modeled as pinned supports with no rotational stiffness or moment capacity. However, past studies have indicated that base connections, which are designed as pinned supports, exhibit a non-negligible level of rotational stiffness and strength. Neglecting the rotational stiffness of the base connection may result in a significant overestimation of the lateral displacement of the frames. This additional displacement is addressed by increasing the flexural stiffness of the frame members thereby increasing the cost of low-rise metal buildings. The moment capacity may similarly be exploited for strength design. However, there is a lack of design guidelines to support the use of rotational stiffness or moment capacity at the pinned column bases. This study evaluates the applicability of existing code-formulations to pinned colum base-plate connections. Both the rotational stiffness and the moment capacity from past experiments are compared with those calculated based on the provisions of the European and American design codes. It was found that the Eurocodes do not accurately estimate the rotational stiffness of the connections. A modification to the Eurocodes is recommended to capture the characteristics of pinned connections. It was also observed that the moment capacity of the connections was conservatively estimated by the existing codes.

The structural integrity of concrete dry storage systems under an impact loading caused by a simulated commercial airplane engine crash is evaluated in this study. A finite element model of a generic vertical dry storage system including the concrete overpack, multi-purpose canister, spent nuclear fuel (SNF) basket, and SNF assemblies was developed using a commercial finite element analysis software. The strain rate effect was considered for the steel parts of the cask via a rate dependent and nonlinear constitutive model. The modeling approach was first validated using experimental data available in literature on projectile impact of concrete and steel/concrete composite (sandwich) panels. Then, a comprehensive comparison in terms of strains, damage and deformations was performed for two configurations of reinforced and sandwich cask overpacks commonly used in the industry. Critical impact height was identified by an examination of the strains and accelerations in the SNF assemblies. Furthermore, the effect of boundary conditions for the two cases of free-standing and anchored configuration was investigated. The maximum deformation and stress as well as the peak acceleration were identified in the SNF basket to assess safety of the SNF assemblies. The minimum impact velocity causing tip-over from aircraft engine impact was determined.

Prestressing concrete bridge beams with composite materials has been investigated extensively within the last two decades. The outcomes of these research efforts, however, emerged only in a limited number of representative applications in the United States. This is partly due to a lack of comprehensive design guidelines for use by bridge engineers, especially in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design format. An extensive review of literature related to the prestressing of concrete bridge beams with carbon fiber–reinforced polymer strands was conducted. A database of the beams prestressed with carbon fiber–reinforced polymer was established, and the existing design methods along with the required parameters were reviewed. Based on the collected data, the flexural and shear capacity of beams was calculated and compared with the experimentally obtained capacity and that obtained from selected design guidelines. Variables related to the design of carbon fiber–reinforced polymer prestressing that need calibration with dedicated material properties were examined, and the effects of carbon fiber–reinforced polymer on long- and short-term losses were identified.

The performance of vertical concrete casks (VCC) for storage of spent nuclear fuel (SNF) under hypothetical accident conditions is of particular importance given the planned extensions of service-lives of such structures in the absence of a permanent disposal solution. Numerical models are created in this paper to simulate the structural response of a generic VCC in the cases of end-drop (handling drop) and tip-over considering material degradation. A concrete damage plasticity model (CDP) was calibrated using standard material tests to capture the non-linear behavior of concrete. Similarly, the steel properties and the properties of the soil supporting the cask foundation were based on material test data. The finite element models (FEM) were validated using experimental data from end-drop and tip-over tests of a 1/3-scale VCC performed by the same authors and reported elsewhere. The numerical results are compared with the experimental measurements in terms of velocity, acceleration, damage, and failure modes to gain confidence in the numerical results. Thereafter, a push-over analysis method was proposed and performed on the VCC for the first time to investigate the effect of different levels of material degradation on the structural response of VCC. The reduction in the concrete reinforcing steel area and bond degradation due to corrosion, and concrete strength reduction due to effects such as alkali-silica reactivity were considered as the variables for the parametric analysis. The results are interpreted to understand the changes in the performance of VCC in the long-term when subjected to hypothetical accident conditions in comparison to intact as built conditions.

Safety of dry-cask storage structures, containing spent nuclear fuel, has always been an important concern for the nuclear industry. Detailed investigations of the mechanical response of these important composite structures due to hypothetical accident conditions have been the subject of many studies. In this paper, a tip-over induced impact of a dry cask is numerically analyzed at two different dimensional scales, i.e., a full-scale “prototype” and a 1/3-scale “model cask”. The latter is considered to study the accuracy of similitude laws because most experiments are done at the reduced scale. The added mass technique is applied to the model cask using the dynamic similitude concept in order to represent the behavior of the prototype cask. The effects of this added mass are also studied in terms of damage parameters, time histories of strains, stresses and accelerations to compare these two models. The results demonstrate that the added mass is able to predict the behavior of the model cask compared to that of the full-scale prototype.

Dry storage casks are the most common form of spent nuclear fuel (SNF) storage in the United States. An explosion near a spent nuclear storage facility poses a serious public risk due to the potential of radioactive leakage. In this study, for the first time, the structural performance of vertical steel–concrete-steel sandwich (SCSS) and reinforced concrete (RC) casks under blast loading scenarios is studied using explicit finite element simulations considering material and geometric nonlinearity and strain rate effects. The response of the cask is investigated in terms of stress levels, deformations, and peak accelerations. The conventional weapons (CONWEP) model was used to induce a blast load on the structure at varying blast charges. The accelerations experienced by the canister and the fuel assemblies, which are critical for design are estimated. The inherent vibration damping characteristics of the cask are evaluated, and a novel damper configuration is proposed to improve the energy dissipation capacity of the system. The results showed that the general integrity of the cask could be preserved in the presence of a thick reinforced concrete layer. However, due to the lack of a damping mechanism, the blast wave can propagate through the system and result in very large accelerations in the canister and the fuel assemblies. Results also revealed that the SCSS configuration has a more ductile response compared to the RC design. The results of this study could be used for the safety evaluation and design optimization of current casks in service and other cylindrical composite containment structures.

This paper presents the results of high-cycle fatigue testing of high-mast illumination poles (HMIPs) with pre-existing cracks at the pole-to-base plate connection detail. Resonant bending fatigue tests were conducted on five pairs of HMIP base specimens at nominal stress ranges of 41.4 MPa (± 20.7 MPa), 27.6 MPa (± 13.8 MPa), 20.7 MPa (± 10.3 MPa) and 6.9 MPa (± 3.4 MPa). The length and depth of pre-existing cracks was measured and the propagation of the individual crack was monitored throughout the testing using an ultrasonic inspection technique. The experimental results suggested that the fatigue lives of the tested specimens can exceed the predicted life for AASHTO fatigue category E details and approach category D details even in the presence of pre-existing cracks. The results provide insight into the fatigue response of HMIP with pre-existing cracks at the base connections at very low stress ranges and high cycle counts. The findings suggest that the pre-defined constant amplitude fatigue limits for AASHTO details may not strictly apply to HMIP details with pre-existing cracks.

Vertical concrete dry storage systems (or dry casks) are circular containers made of steel and/or reinforced concrete, specifically developed for storing spent nuclear fuel (SNF). In the United States, dry casks have an intended life of 40 years; however, in the absence of a permanent repository for storage of SNF, it is expected that dry casks will remain in service for a significantly longer period of time. Tipping-over is considered as one of the hypothetical accident conditions. The consequence of such an incident may be more severe if the structural integrity of the dry cask is compromised during the extended service life due to steel corrosion and related material degradation. In this study, structural performance of a 1/3-scale vertical concrete cask is evaluated under combined corrosion-induced damage and tip-over impact. The results are compared with those from a control cask, which is only subjected to impact but no corrosion-induced damage. The impact response of both casks in terms of acceleration, velocity, and strain was measured and compared. The damage after testing is investigated in terms of cracking and deformation to identify the failure modes for each cask and the effects of aging on the structural performance.

This paper presents a new analytical formulation to predict the bending stiffness of multilayered spiral strands. The effect of interwire contact forces and slip between wires have been ful...

A growing number of critical concrete infrastructure are affected by alkali-silica reaction (ASR) damage such as the Seabrook Nuclear Power Plant in New Hampshire, Parker arch-gravity dam in Arizona, and several highway bridges in California and Texas. ASR causes expansion and cracking and degrades the concrete mechanical properties. Despite a wealth of material level studies there is still limited large-scale experimental data regarding the effects of ASR on reinforced concrete (RC) members. Due to the brittle nature of the shear failure in RC structures, this study focuses on the shear response of full-scale ASR damaged RC beams with minimum shear reinforcement. Six RC beams were built with different levels of ASR susceptibility and conditioned in different environments during which continuous expansion monitoring was performed. The beams all contained reactive fine aggregate (sand) and two of them had additional alkali, 1.25% by weight of cement, to accelerate ASR. The highest expansion rate of the beams happened during the first 150 days and the expansions stayed constant after 240 days and 330 days for beams conditioned in outdoor and laboratory conditions, respectively, until the last measurement at 575 days. The highest expansion, 0.4%, was seen in the beams with additional alkali and conditioned outside with regular water spray. Out of the six beams, three were selected at different levels of ASR damage and two shear tests were performed on the minimally reinforced spans close to the ends of each beam. Results indicated that beams gain shear strength from ongoing cement hydration in the presence of moisture for ASR expansions less than 0.2%. Compared to one of the beams with 0.2% ASR expansion, one of the other samples with 0.4% expansion lost 6% of its shear strength, 25% of its shear stiffness, and showed about two times larger shear cracks and shear deformations at peak load. Additionally, the shear reinforcement yielded at 20% less load in the beam with 0.4% expansion compared to the beam with 0.2% expansion.

In this paper, chloride (Cl−) binding isotherms are developed for cement hydration compounds, specifically, calcium-silicate-hydrates (CSH) and AFm phases including mono-sulfate aluminate, hydroxy-AFm, monocarbonate-AFm, and hemicarbonate-AFm, in simulated concrete pore solutions to account for the effect of pH and the presence of other ions. pH and the presence of other ions have a strong influence on the Cl− binding capacity of cement compounds, which have not been taken into consideration in previous research. A novel experimental technique is developed to characterize the binding capacity from very low (1 mM) to very high concentrations (5 M). To overcome the existing challenges of measuring both low and high Cl− concentrations without significant dilution and in the presence of SO42− and OH− ions, a potentiometric method was used. The amorphous CSH in the hydrated cement paste; thus, the heterogeneity of the hydrated components of the cement paste was also quantified and accounted for in this study.

The objective of this research is to evaluate the influence of column base-plate connection rotational stiffness on the design of low-rise metal building systems. Currently, low-rise metal buildings are designed based on a zero rotational stiffness (pinned connection) assumption at the column-bases. Although prior research indicates that the assumption of zero rotational stiffness of the column base-plate connection could result in a significant underestimation of the overall lateral stiffness of horizontally loaded moment frames (leading to less economical designs), there has been no systematic study to investigate this issue. This paper first presents the details of an experimental research program that was conducted to quantify the rotational stiffness of “pinned” column base-plate connections that are commonly used in the low-rise metal building industry. Eight full-scale column base-plate connections with varying base-plate dimensions, numbers of anchor rods, anchor rod diameters, and gage distances were tested. Then, the data obtained were used to investigate the reduction in the total weight of gabled frames used in metal building construction. Finally, a piecewise nonlinear spring model was fitted to the test data to represent the rotational stiffness of the joints beyond the elastic range. Analyses of example frames indicate that consideration of the rotational stiffness of the pinned connections reduces frame deflections between 11 and 67% and has the potential to make metal building systems more economical by decreasing the frame weight between 0 and 12%, which is considered a substantial cost saving for the metal building industry where profit margins are relatively low.

In this paper, an efficient numerical procedure is proposed, which is adapted to the modal analysis of a fully-loaded spent nuclear fuel canister exhibiting distinct structural levels associated with a hierarchy of components. On the one hand, the fully-loaded spent nuclear fuel canister is constituted of a repetition of identical components, resulting in a pseudo-periodicity; and the components of a given level are separated from each other and only connected to their upper level through localized attachments. This gives rise to an advantageous structural connectivity that can be exploited for efficiency. On the other hand, the necessary fine mesh resolution of the small levels leads to a high-dimensional computational model and, in addition, the independent resonant vibrations of each of the components produce a very large number of vibration eigenmodes. The aforementioned opportunities and difficulties are respectively leveraged and tackled by an adapted method that combines domain decomposition, shift–invert Lanczos eigenvalue solver, and Craig–Bampton substructuring technique. A parallel eigensolution via spectrum slicing is facilitated by an efficient block factorization by Schur complement due to the sparsity of the Craig–Bampton matrices. A computational gain of four orders of magnitude is obtained, at the expense of negligible errors that are exactly characterized. The proposed methodology enables a high-fidelity vibration analysis of the sealed fully-loaded spent nuclear fuel canister, useful for non-intrusive inverse identification of the structural integrity of the internal structural levels holding the nuclear material.

An experimental study is carried out in this paper to evaluate the corrosion performance of mild steel reinforcing bars (MS), high strength steel reinforcing bars (HS), epoxy-coated steel reinforcing bars (EC), and high-chromium steel reinforcing bars (HC) under harsh environmental conditions. Reinforcing bars (rebar) of 16 mm diameter and 310 mm length were embedded in cylindrical concrete samples of 60 mm diameter and 350 mm length, and subjected to a Southern Exposure test for sixteen months. The open circuit potential (OCP) was monitored during the exposure period until corrosion initiation. The linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and Tafel plot techniques were employed to assess the corrosion rates on the rebar surfaces. The macrocell corrosion current was monitored by connecting the corroding rebar with an external stainless steel bar of the same size. The polarization resistance of the HC was found to be 1.5 times higher than that of the MS. The EIS technique showed that EC, even with damaged epoxy coating, has the highest resistance to chloride attack. The macrocell current of HC rebar was 48% less than that of MS during the active corrosion state. The LPR, EIS and Tafel plots analysis provided the current densities, which were close to each other; indicating the validity of these techniques to study the problem at hand. The corrosion rates from electrochemical methods were compared against the ones calculated by gravimetric methods. The quantitative results from this research may be used in service life prediction of concrete structures with different types of rebar. Extensive analysis of the results indicates that the corrosion resistance of the evaluated steels was in the following decreasing order: EC, HC, MS, and HS.

This paper reports the results of an investigation carried out to understand the influence of two different diatomaceous earths on the service life of natural fibers in cement composites. D...

This paper presents the results of a field study carried out on three reinforced concrete (RC) structures built in the 1960s, 1970s, and 1980s to determine the main load (environmental) and the resistance (for example, the concrete quality and clear cover) factors affecting the durability of the infrastructure in the harsh environmental conditions of the Arabian Gulf region. The effects of degradation, such as the carbonation depths and chloride concentration profiles, in the columns, beams and slabs were determined from concrete core samples. To determine the durability factors, the concrete resistivity to electrical charge, the rapid chloride permeability, and the sorpitivity were measured. Digital image processing was performed to estimate the cement contents and the proportions of other ingredients used in the concrete samples. In most of the structural members, the chloride threshold for steel depassivation had been surpassed and the carbonation had reached the steel surface. The spalling of the concrete cover was observed with severe corrosion damage to the reinforcing bars. It is expected that this study will help understand the degradation phenomena in RC structures in the Gulf region and similar hot, humid, and saline environments. The results will help to establish the input parameters for the chloride diffusion and carbonation models in aggressive environmental conditions. Because the concrete quality directly impacts the initiation of many deterioration processes such as corrosion of the steel reinforcement and carbonation, the results could be used to predict the remaining service life of existing RC structures with similar concrete properties. The funding for this research was provided by the National Priorities Research Program of the Qatar National Research Fund (a member of the Qatar Foundation) under the award NPRP 7-410-2-169. Scopus