Laboratory Specimens Research Articles

Determining the Optimal Frequency and Perturbation Amplitude for AC Electrical Resistance Measurements of Cement-Based Materials Using Harmonic Analysis

Abstract Measuring electrical resistivity is becoming a desirable method for evaluating the material property in cement-based materials. As a rapid nondestructive technique, measurement of resistivity is frequently performed both in laboratory specimens and on-site structures. Alternating current/potential (AC)-based methods are common approaches to measure the resistivity in cement-based materials. The alternating perturbation amplitudes applied range from several millivolts to even volts. However, how the perturbation amplitude influences the results, and what are the optimal frequency and perturbation amplitude are still in question. In the present study, AC resistance measurements using electrochemical impedance spectroscopy were performed on cement-based specimens with different compositions. To investigate the effect of perturbation amplitude on the measured resistance, different amplitudes of potential perturbation varying from 5 mV up to 1,000 mV were applied. The reliability of data was evaluated by the harmonic analyses. Results indicated that, as the resistivity of specimens increased, a slight decrease in the fR (i.e., the frequency at which the ohmic resistance is measured) was observed. Noticeably, significant scatter in fR was demonstrated by applying different potential perturbations, especially for amplitudes lower than 50 mV. In terms of the perturbation amplitude, the results of resistivity were generally maintained in a relatively small variation when the potential perturbation was higher than 100 mV. Based on harmonic analyses, the appropriate frequency and perturbation amplitude for measuring the resistance of cement-based materials were determined.

Undrained shearing behaviour of oil sands tailings

The instability of coarse oil sands tailings (CST) is investigated in this study by conducting a series of monotonic direct simple shear tests. Laboratory specimens were prepared using moist-tamping, dry deposition, and slurry deposition techniques to investigate the effect of sample reconstitution method and tailings fabric on CST's instability behaviour. CST specimens were then subjected to constant volume (CV), and constant vertical stress (drained) shearing at three different consolidated relative densities corresponding to loose, medium-dense, and dense conditions. The effects of consolidation vertical stress and void ratio on the instability and post-liquefaction strength of the CST specimens were examined. Shear wave velocity (VS) of the specimens were also measured using a pair of bender elements attached to the top and bottom caps of the simple shearing apparatus. The VS measurements were subsequently used to establish practical relationships with undrained strength ratios and yield friction angle of CST.

Optimization of Laboratory Molding Techniques for Nordic Dry Deep Mixing

Abstract The dry deep mixing method is a widely used stabilization method in the Nordic countries to improve the strength and deformation properties of soft clays. In engineering practice, laboratory tests normally precede in situ stabilization; however, previous studies have shown considerable differences between field and laboratory stabilization. The type of laboratory molding technique will determine how representative the specimen is compared with field conditions. A key property is the amount of entrapped air in the stabilized clay, which is shown to be very low in field stabilization. This paper presents a study of two different Norwegian molding techniques, including different optimizations to reduce the amount of entrapped air. The specimens are tested for density and strength, and it is shown that the strength increases with increasing density of the stabilized clay. Consequently, there is an inverse relationship between the amount of entrapped air and the strength, showing the importance of reducing the amount of entrapped air in laboratory specimens as much as possible. It is also shown that the wet mixing method does not necessarily give the same strength development as dry deep mixing given the same water to binder ratio.

Seismic Response of Slab Column Connection with Pyramid Shaped Drop Panel

Both experimental and finite element analysis (FEA) was used to study the seismic response of reinforced concrete (RC) interior slab-column connection made with pyramid-shaped drop panel subjected to vertical and horizontal loads. The dimensions of the models at “¼ ” linear scale for laboratory testing and FE Analysis (FEA) are derived from rules for dimensions of column drops, given a prototype “9.60m” grid and a slab thickness of “320mm”. Lab specimens were tested with the drops (flat slab, rectangular and pyramid-shaped) facing up, with loadings (vertical down and horizontal in grid direction) applied by jacks towards the top of a central projecting “150mm” square column. One flat slab (“80mm” thick no drop), tested to failure under vertical load (80kN), provided values for setting variables used in the FEA. The remaining 5 lab specimens (1 flat and 1 each rectangular and pyramid-shaped 40mm and 30mm drop thicknesses), under a fixed vertical load (40kN), were tested to failure by increasing a moment at the column slab junction applied by a horizontal load to the column “500mm” above the slab. FEA results for the same conditions compared closely with experimental results. The pyramid-shaped drop models, with equal thickness to the rectangular drop models at the column faces (drops of “40mm” and “30mm”), exhibit similar maximum force resistances to the rectangular drop models. However, these resistances were achieved in the pyramid drops at higher maximum deflections – deflections being measured downwards at column centerline one half of slab thickness away from the face. A parametric study was conducted by FEA, at constant load, in vertical steps (10kN; 25kN 55kN), calculating deflections under increasing horizontal load. Calculations were made on the following definitions: Energy absorption is represented by the area under the deflection vs horizontal load curves; Ductility is the ratio of deflection at maximum to deflection at yield, and Stiffness and Overstrength factors are the slopes of the deflection load diagrams in the elastic and plastic zones respectively. Both drop type models exhibit significantly improved performance compared to the models without drops. The pyramid-shaped drop models exhibited improved energy absorption, ductility, and stiffness and overstrength compared to the rectangular drop models of the same column face thickness.

A clinical study of the hemodynamic and metabolic effects of Zone 3 REBOA for sacral and pelvic tumor resections

BackgroundResuscitative endovascular balloon occlusion of the aorta (REBOA) is a key procedure in sacral and pelvic tumor resection that provides hemorrhage control. However, few studies have been performed to capture the effects of REBOA in a nonshock condition and provide a detailed description of the changes occurring with prolonged occlusion time. This study aimed to examine the hemodynamic and metabolic effects of Zone 3 REBOA for sacral and pelvic tumor resections following different periods of REBOA.MethodsIn total, 121 patients who underwent surgical tumor resections of the pelvis and/or the sacrum with the use of aortic balloon occlusion were prospectively enrolled from October 2020 to December 2021. All cases were divided into Group A (occlusion time ≤ 60 min, n = 57) and Group B (occlusion time ≥ 90 min, n = 64). Physiologic parameters were continuously recorded, and laboratory specimens were obtained at regular intervals.ResultsBalloon inflation resulted in a significant increase in SBP from 106 to 120 mmHg and decreased to 96 mmHg immediately following balloon deflation. With the application of REBOA, the median blood loss was only 1200 ml (range, 400–7900). When deflating the REBOA, the arterial pH was lower than baseline (7.36 vs. 7.41, p < 0.01), the arterial lactate concentration increased from 0.9 to 1.4 mmol/L (p < 0.01), serum potassium measurements increased from 3.99 to 4.12 mmol/L, serum calcium measurements decreased from 2.31 to 2.04 mmol/L, and blood creatinine decreased from 64 to 60 µmol/L. The operating time of Group B was longer than that of patients in Group A, and the patients in Group B needed more blood units to be transfused. Although laboratory measurements, including pH, potassium, calcium, and blood creatinine, were at the same level in two groups comparison, the lactate was significantly higher in Group B after deflation (p = 0.01).ConclusionsThe results of this study showed that acceptable hemodynamic and metabolic stability can be attained when the occlusion time of REBOA is more than 90 min, although the long duration of occlusion caused relatively higher lactate levels.

Quality Analysis of Tuberculosis Specimens Transported by Drones versus Ground Transportation

There are many challenges that impact the current referral network for Tuberculosis (TB) sputum specimens in Mozambique. In some cases, health facilities are remote and the road infrastructure is poor and at times impassable, leading to delays in laboratory specimen transportation and long turn-around times for results. Drone transportation is a promising solution to reduce transportation time and improve access to laboratory diagnostics if the sample quality is not compromised during transport. This study evaluated the impact of drone transportation on the quality of TB sputum specimens with suspected Mycobacterium tuberculosis. 156 specimens were collected at five (5) health centers and sent to the Instituto Nacional de Saúde (INS) National TB Reference Laboratory. Specimens were then equally divided into two aliquots; one to be transported on land and the other by air using a drone. Control and study group specimens were processed using the NALC-NaOH method. Agreement between sample and control specimens was acceptable, indicating that drone transportation did not affect the quality of TB specimens. The authors recommend additional studies to validate drone transportation of TB specimens over a longer period of time to give further confidence in the adoption of drone delivery in Mozambique.

Infection Prevention Resources to Respond to the Initial Coronavirus Disease Pandemic at an Academic Medical Center

BackgroundInfection prevention specialists (IPS) are relied on as subject matter experts, providing guidance and support within healthcare facilities. During the coronavirus disease (COVID-19) pandemic, infection prevention (IP) department resources were heavily taxed, creating an increased IP staffing need. The objective of this study is to quantify the additional IP resources needed to support pandemic response at a large, academic medical center.MethodsPre-pandemic, our IP department included 12 full-time IPS, providing support to a 1315-bed hospital, 138 outpatient clinics, and 2 ambulatory surgery centers. The increased level of organizational support needed for the COVID-19 pandemic response required more full-time employees (FTE) to assist in managing additional duties. Duties included: conducting employee cluster investigations and contact tracing; reviewing positive COVID-19 lab specimens reported each shift to ensure appropriate isolation and bed placement; developing and reviewing COVID-19 related protocols across multiple hospital areas; and instituting a clinical case review process with infectious disease (ID) physicians to respond to call questions about testing, isolation requirements, and discontinuation criteria in complex patients.ResultsThe first known COVID-19 positive patient was admitted on 3/17/2020. Department call volumes peaked between May 2020 and end of June 2020. Calls during that time frame totaled 2,825 with an average of 202 calls daily. In response our IP department added 6 additional FTE. These FTE consisted of 2 reassigned bedside nurses and 4 contract nurses, supporting the 24/7 on-call service from 3/31/2020- 4/6/2021. Physician support increased to 2 dedicated epidemiologists managing COVID-19 guidance and IPS escalation needs, and a 24/7 on-call clinical review team, involving 16 ID physicians was implemented.ConclusionsA pandemic response effort can have a major impact on infection prevention staffing resources. Repurposing and/or onboarding non-IP staff and training them to support concrete IP processes can be an effective strategy to reduce strain on department resources.

Nondestructive assessment of local microcracking degree in orthoclase and plagioclase feldspars using spectral analysis of backscattered laser-induced ultrasonic pulses

The laser-ultrasonic method for nondestructive assessment of a microcracking degree in laboratory specimens of orthoclase and plagioclase feldspars is proposed. The influence of the local concentration of microcracks on the spectral efficiency of backscattering of pulses of longitudinal ultrasonic waves in the studied specimens (the so-called “structural noise power”) is studied. A specially designed laser-ultrasonic transducer used in experiments combines laser excitation of probe broadband ultrasonic pulses in a black polyethylene film and piezoelectric detection of both probe pulses and that scattered in the specimen. We study specimens of a potash feldspar and soda-calcium plagioclase with nonuniformly distributed local microcracks. The cracking domains were identified by optical microscopy as well as using the attenuation coefficient of longitudinal ultrasonic waves measured in these domains. The increase in the ultrasonic attenuation coefficient was associated with a higher concentration of microcracks, which efficiently scatter acoustic waves. At the same time, the domains with a higher ultrasonic attenuation exhibited an increased structural noise power. The direct correlation between the growth of the structural noise power and a higher local concentration of microcracks can be used as a basis of a system of nondestructive ultrasonic monitoring of occurrence and evolution of local microcracks in rocks and geomaterials under external loads of different nature.

Typical strength of asphalt mixtures compacted by gyratory compactor

Abstract Design of asphalt mixes and quality testing is influenced by the laboratory compaction procedure. Laboratory specimens must be manufactured in a way that suitably resembles field compaction for a performance test to give reliable mechanical properties. The internal structure of the mixture, which is referred to in this article as the spread of aggregate and air voids, provides the basis for the simulation. Gyratory compaction uses a kneading effort to produce cylindrical specimens. The goal of the present article is to determine the required strength for asphalt mix compaction of 40–50 per surface. This look was achieved with three distinct types of filler material and two kinds of sand. The asphalt mixture’s compressibility was tested. By adding the cumulative energy expended during gyratory specimen compaction to the compression data, the force applied to the sample during gyrations may be calculated. The relation between the number of gyrations and forces demonstrates pressure resistance. The measured fore force vs number of gyrations for combinations containing limestone, cement, and fly ash as fill materials was presented. The force required to compact the six bituminous materials was found to be influenced by the filler content. As the number of gyrations increases, its compaction properties change until it achieves a steady state. Except for the asphalt–cement mixture, compaction strength in mixes containing river sand requires less strength than compaction strength in mixes containing crushed sand.

Surface-strength approach for concrete monitoring using sensors and shock-pulse method

There are many methods used for temperature-strength control of reinforced concrete structures globally. Their majority is associated with the significant challenges of being time-consuming, costly and prone to errors. Therefore, this study investigated the potential applicability of the surface-strength approach of specimens using non-destructive testing methods to derive temperature-strength relationships as an alternative approach to the currently widely used methods. The studies were carried out by comparing the surface strength of small laboratory specimens (SS) and large specimens (LS), imitating building structures, obtained by the shock-pulse method and the strength obtained by the destructive method; and the obtained calibration dependencies were adapted to the results of specimens’ thermal control. The temperature-strength dependence was corrected by comparing the strength and temperature parameters of SS and LS. The obtained nomograms make it possible to correct changes in the temperature regime of hydration of structures curing in real climatic conditions. The final adaptation of the temperature-strength dependence to the real erected structures showed a significant potential of this method in the construction industry. The difference between the actual strength of the drilled cores and the predicted strength of concrete at 28 days was only 1.02%.

HIV-1 drug resistance genotyping success rates and correlates of Dried-blood spots and plasma specimen genotyping failure in a resource-limited setting

BackgroundHIV-1 drug resistance genotyping is critical to the monitoring of antiretroviral treatment. Data on HIV-1 genotyping success rates of different laboratory specimen types from multiple sources is still scarce.MethodsIn this cross-sectional study, we determined the laboratory genotyping success rates (GSR) and assessed the correlates of genotyping failure of 6837 unpaired dried blood spot (DBS) and plasma specimens. Specimens from multiple studies in a resource-constrained setting were analysed in our laboratory between 2016 and 2019.ResultsWe noted an overall GSR of 65.7% and specific overall GSR for DBS and plasma of 49.8% and 85.9% respectively. The correlates of genotyping failure were viral load (VL) < 10,000 copies/mL (aOR 0.3 95% CI: 0.24–0.38; p < 0.0001), lack of viral load testing prior to genotyping (OR 0.85 95% CI: 0.77–0.94; p = 0.002), use of DBS specimens (aOR 0.10 95% CI: 0.08–0.14; p < 0.0001) and specimens from routine clinical diagnosis (aOR 1.4 95% CI: 1.10–1.75; p = 0.005).ConclusionsWe report rapidly decreasing HIV-1 genotyping success rates between 2016 and 2019 with increased use of DBS specimens for genotyping and note decreasing median viral loads over the years. We recommend improvement in DBS handling, pre-genotyping viral load testing to screen samples to enhance genotyping success and the development of more sensitive assays with well-designed primers to genotype specimens with low or undetectable viral load, especially in this era where virological suppression rates are rising due to increased antiretroviral therapy roll-out.

Retrospective identification of key activities in Uganda's preparedness measures related to the 2018-2020 EVD outbreak in eastern DRC utilizing a framework evaluation tool.

Uganda has engaged in numerous capacity building activities related to outbreak preparedness over the last two decades and initiated additional just-in-time preparedness activities after the declaration of the 2018-2020 Ebola Virus Disease (EVD) outbreak in eastern Democratic Republic of Congo (DRC). When Uganda faced importation events related to the DRC outbreak in June-August 2019, the country's ability to prevent sustained in-country transmission was attributed to these long-term investments in preparedness. In order to help prepare countries for similar future scenarios, this analysis reviewed evidence from Uganda's response to the June-August 2019 importation events to identify preparedness activities and capacities that may have enabled Uganda to identify and isolate infected individuals or otherwise prevent further transmission. Content from 143 grey literature documents gathered via targeted and systematic searches from June 6, 2019 to October 29, 2019 and six interviews of key informants were utilized to inform a framework evaluation tool developed for this study. A conceptual framework of Uganda's preparedness activities was developed and evaluated against timelines of Uganda's response activities to the June-August 2019 EVD importation events based on the applicability of a preparedness activity to a response activity and the contribution of the said response activity to the prevention or interruption of transmission. Preparedness activities related to coordination, health facility preparation, case referral and management, laboratory testing and specimen transport, logistics and resource mobilization, and safe and dignified burials yielded consistent success across both importation events while point of entry screening was successful in one importation event but not another according to the framework evaluation tool. Countries facing similar threats should consider investing in these preparedness areas. Future analyses should validate and expand on the use of the framework evaluation tool.

Use of a Modified Preexposure Prophylaxis Vaccination Schedule to Prevent Human Rabies: Recommendations of the Advisory Committee on Immunization Practices - United States, 2022.

Human rabies is an acute, progressive encephalomyelitis that is nearly always fatal once symptoms begin. Several measures have been implemented to prevent human rabies in the United States, including vaccination of targeted domesticated and wild animals, avoidance of behaviors that might precipitate an exposure (e.g., provoking high-risk animals), awareness of the types of animal contact that require postexposure prophylaxis (PEP), and use of proper personal protective equipment when handling animals or laboratory specimens. PEP is widely available in the United States and highly effective if administered after an exposure occurs. A small subset of persons has a higher level of risk for being exposed to rabies virus than does the general U.S. population; these persons are recommended to receive preexposure prophylaxis (PrEP), a series of human rabies vaccine doses administered before an exposure occurs, in addition to PEP after an exposure. PrEP does not eliminate the need for PEP; however, it does simplify the rabies PEP schedule (i.e., eliminates the need for rabies immunoglobulin and decreases the number of vaccine doses required for PEP). As rabies epidemiology has evolved and vaccine safety and efficacy have improved, Advisory Committee on Immunization Practices (ACIP) recommendations to prevent human rabies have changed. During September 2019-November 2021, the ACIP Rabies Work Group considered updates to the 2008 ACIP recommendations by evaluating newly published data, reviewing frequently asked questions, and identifying barriers to adherence to previous ACIP rabies vaccination recommendations. Topics were presented and discussed during six ACIP meetings. The following modifications to PrEP are summarized in this report: 1) redefined risk categories; 2) fewer vaccine doses in the primary vaccination schedule; 3) flexible options for ensuring long-term protection, or immunogenicity; 4) less frequent or no antibody titer checks for some risk groups; 5) a new minimum rabies antibody titer (0.5 international units [IUs]) per mL); and 6) clinical guidance, including for ensuring effective vaccination of certain special populations.

Development of sustainable prefabricated housing system by small-scale experimental model

Utilisation of unused industrial wastes and the need for rapid volumetric construction led to the evolution of sustainable prefabricated housing elements, particularly for urban slums. An agro-industrial by-product as raw material and waste expanded polystyrene beads as the insulation material are chosen to develop a lightweight prefabricated construction element. This bio-ash is used as a partial replacement, 20 and 10%, for fine aggregates to prepare concrete and a lightweight mix, respectively. A small-scale model of one-third scale is conceptualised according to standards. This model includes precast columns and beams as framed structure and prefab panels as walling and roofing elements. These elements are developed according to the desired mix proportions of the identified raw materials. The respective laboratory specimens are evaluated for physico-mechanical, durability and thermal properties. The developed walling end product is found to be 27% lighter, 8% stronger, 24% less water absorbent and 62% less conductive when compared with the properties of commercially available fly-ash brick. A solar photovoltaic panel embedded into the pitch roof of the model can provide 71% of its generated energy to necessary electrical appliances. The material properties are found to be satisfactory for its on-site application. Also, the model’s erection is 20% faster than the conventional method.

Antifouling Mortars for Underwater Restoration.

This research has focused on the assessment of the compositional features and mechanical and antifouling performances of two different mortars formulated for an underwater setting, and which contain Mg(OH)2 as an antifouling agent. Regarding the mechanical characterization, the uniaxial compressive strength and flexural strength were measured. The composition of the materials was explored by differential thermal/thermogravimetric analysis (DTA-TG), X-ray diffraction analysis (XRPD), and scanning electronic microscopy (SEM) coupled with EDS microanalysis. The assessment of the biological colonization was evaluated with colorimetric analysis and image analysis. The results suggest that both mortars have good mechanical resistance once set underwater. Moreover, the adding of Mg(OH)2 improves the resistance toward biofouling; this was observed both in laboratory and sea-exposed specimens.

Effect of the Thermal History on Macrostructure and Microstructure Development in High-Strength Steel Welds

The present work addresses the microstructural and macrostructural development in multipass welded joints. It focuses on multiple thermal cycles induced by successive deposition of welding passes. The local welding-related thermal history was related in detail to the evolution of austenite grains during the manufacturing of two high-strength low alloy steel welds. The analytical Rosenthal thermal model was used to identify the thermal cycles experienced within typical weld metal regions. Selected heat cycles were applied to laboratory specimens, taken from the same weld metal, to investigate microstructural evolution during the welding process. Heat cycle experiments, involving full austenitization, showed the persistence of columnar zones resulting from a memory effect of the prior austenite grains during the reverse transformation. Intercritical heat cycles led to white etching, softer regions with high fractions of retained austenite. They also showed that the memory of austenite grains was actually stored in elongated retained austenite particles that remained after complete welding. This memory effect vanished under high peak temperatures (typically, 130 °C higher than Ac3); this was linked to a competition between growth and merging of elongated, intragranular retained austenite particles, and growth of equiaxed, intergranular austenite particles. Finally, a low peak temperature promoted refined, harder final microstructures.

The comparative energetics of the cephalopods: they neither grow nor reproduce fast

The Add-my-Pet (AmP) collection of data on energetics and Dynamic Energy Budget (DEB) parameters currently contains 92 of the 800 extant species of cephalopods. Growth data, as reconstructed from statolith-, beak- or shell-readings, show a rather large scatter, whereas that from laboratory specimens with known age, does not. This implies that food availability varies under field conditions and/or age-determination is uncertain. We compare DEB parameter values and traits of cephalopods with those of other molluscs (Polyplacophora, Bivalvia, and Gastropoda). All cephalopods appear to start accelerating their metabolism at birth, quite few even up till puberty. As a consequence, length-at-age initially shows a clear up-curving at constant temperature and food, which is not clearly linked to morphological changes. They have a high acceleration factor, specific somatic maintenance, surface area-specific assimilation and maximum reserve density. The energy conductance, which controls reserve mobilisation, is typical for molluscs, and age at death is low. The investment into reproduction, in terms of specific offspring mass production per life span, is typical for molluscs. The negative effects that a short life span would have on reproductive output is compensated by a large allocation fraction to maturation or reproduction. Mass at birth is larger than that of gastropods, which, in turn, is much larger than that of bivalves and polyplacophorans. Cephalopod reproduction in terms of number of offspring per life time is, therefore, smaller than that of other molluscs. Although cephalopods are reputed to grow fast, gastropods grow equally fast per gram at maximum rate, while bivalves and polyplacophorans grow quite a bit slower. We conclude that 79% of the cephalopod species do not survive thinning of their populations in the long run, while this holds for some 20% of other animal species. This underscores their vulnerability for this type of harvesting.

Experimental and analytical investigation of drilled flange connections (DFCs) with radial drilling patterns

The capability of reduced beam sections (RBS) to improve the seismic behavior of rigid connections leads to their notable application in steel moment-resisting frames. However, they may encounter shortcomings such as local buckling and lateral-torsional buckling. To resolve such problems, the idea of utilizing perforated beam flanges instead of cut-out flanges as reduced beam sections was presented. These type of connections can reduce the potential for local and lateral-torsional buckling of conventional RBS connections and improve their seismic performance. Achieving such advantages requires special care to geometrical specifications and drilling patterns (DPs). Appropriate arrangement of holes reduces the stress concentration around the beam flange-to-column Complete Joint Penetration (CJP) groove weld and, consequently, prevents the groove weld and inter-hole area from tearing and fracturing in early cycles of loading. The present study investigated the hysteretic performance of the drilled flange connections (DFCs) of various drilling arrangements through an experimental program.It should be noted that the box-shaped columns were considered in this study to target the 3D moment resisting frames (MRFs) that all their axes participate in the lateral force-resisting system. The most appropriate drilling patterns were selected using remarkable numbers of numerical analyses. Four laboratory specimens with different drilling arrangements of top and bottom flanges were fabricated based on preliminary numerical analyses. The laboratory specimens were subjected to cyclic loading. To evaluate the specimens' seismic performance, moment-rotation hysteresis curves were compared, and the stress distribution at the connection CJP groove welds. The results of the experimental tests revealed that those DFCs with combined DP with notches and holes (DFC1), radial DP (DFC2), semi radial DP with notches (DFC3), and semi radial DP (DFC4) could increase the rotational capacity of the DFCs up to 50% of the required rotation of the special moment-resisting connections. Moreover, semi radial DP (DFC4) may increase the connection's rotational capacity up to 75% of the special moment-resisting connections. Also, Based on the analytical results, conventional RBS connections may increase the 0.04 radians, needed rotational capacity up to 37.5% for a pre-qualified moment-resisting connection. It was also shown that no lateral-torsional buckling and smaller degradation in stiffness and strength took place in plastic hinge zones at the relative deformation of 0.04 radians. The plastic strain at the center of the CJP groove weld line in the beam longitudinal direction was more significant than those corners of the groove weld line in the same direction. In all specimens, the minimum plastic strain of the CJP groove weld took place in central parts of the weld in the transverse direction. In DFC1, DFC2, DFC3, and DFC4 specimens, the contribution of panel zone rotation in the overall plastic rotation of the connection is negligible.

Suppression of Sulfate-Induced Expansion with Lime-Silica Fume Blends.

Sulfate-induced expansion resulting from the formation of ettringite in sulfate-bearing soil stabilised with calcium-based stabilisers is a problematic issue with technical and economic implications. Thus, this research examines the viability of the co-addition of lime (L) and silica fume (S) at varying binder dosages (4, 6, and 10 wt%), with a view of establishing the optimum blend of L–S for suppressing the ettringite-induced expansion of artificially high sulfate-dosed soil (kaolinite-K and gypsum-G). To do so, a series of laboratory specimens, designed using different gypsum and lime concentrations, were investigated using unconfined compression strength (UCS), linear expansion, and derivative thermo-gravimetric analysis (DTG) as the main criteria for the examination. The research outcomes indicated that the increasing substitution of L with S induces a gradual reduction on the UCS and linear expansion at binder levels of 4 and 6 wt%, while its usage in a high binder level (10 wt%), can yield an expansion reduction, with no compromise on the UCS performance. Therefore, silica fume has the potential for restricting ettringite formation and suppressing the expansion, of which 3L7S is the optimum blending ratio for suppressing the expansion.

Simulation of mechanical behavior of carbonate gravel with hybrid PSO–SVR algorithm

Large-scale testing is one of the common methods used to study the mechanical behavior of carbonate gravels. However, due to the huge workload of larger-scale tests and a dimensional limitation of laboratory specimens, there are only a limited number of large-scale tests, and the mechanical behavior of carbonate gravels is not fully understood. In this study, a hybrid algorithm combining two techniques of artificial intelligence – particle swarm optimization and the support vector regression technique – are used to simulate soil behavior using on a dataset obtained from large-scale direct tests of carbonate gravels. Three types of single-output models have been developed, results show that the models developed by the proposed hybrid algorithm are highly accurate. In addition, one of the models used is to predict the shear strength of carbonate gravel under different normal stress. The results show that when the normal stress is larger than 600 kPa, the nonlinear shear strength model is more suitable for carbonate gravel with high particle breakage. Modeling the mechanical behavior of soil with artificial intelligence is thus a useful method to evaluate the mechanical properties of gravel economically and conveniently.