Efficiency of shape memory alloy seismic restrainers for several conditions of bridge joints

Movement joints are needed in bridges to accommodate longitudinal expansion and contraction. Enough joint width needs to be available to accommodate not only longitudinal expansion but also expected movements of joints during earthquakes. This may result in excessive joint openings. Devices that can dissipate energy have been suggested to reduce joint displacements. Shape memory alloy (SMA) is one of these energy dissipation devices, which is well known for its ability to return to its natural shape after being deformed. Several cases of bridges and different conditions of seismic events are modeled and tested using developed software programs in MATLAB to show the efficiency of using SMA inside bridge joint openings. These models include the case of two adjacent frames with SMA inside them (2�frames), the case of multi�frames with constant hysteretic SMAs between every two of them (N�frames), the case of multi�frames with constant hysteretic SMAs taking the delay of seismic forces between frames into consideration (delay), and the case of variable masses of bridge frames. Also, parametric studies are performed to show the impacts of all parameters of bridge frames and SMA retrofit devices on seismically joint openings. The results show that the superelastic SMA device plays a huge role in controlling bridge opening and enables limiting the joint width of all models during earthquakes with different values reaching 60% in some cases depending on bridge frame properties, ground motion characteristics, and the hysteretic properties of SMA devices

Factors Affecting Outcomes of COVID-19 Infection among Older Adults with Type 2 Diabetes: A Single Center, Cross-Sectional Study

Objective: COVID-19 infection and the factors affecting it are major concerns worldwide. This retrospective study aimed to investigate clinical, laboratory and radiological characteristics associated with disease severity and hospitalization among older adults with type 2 diabetes mellitus (T2D) with COVID-19. Materials and methods: A retrospective case series study was conducted to review the records of older adults with T2D infected with COVID-19. Sociodemographic, COVID-19-related data, laboratory tests at the time of COVID-19 diagnosis and CT findings were collected. Bivariate and multivariate regression analysis were done to determine the predictors of the studied outcome, either hospitalization or complete recovery. Results: A total of 343 patients’ records were reviewed, with a mean age of 73.6 ± 6.4 years. Most of patients had fever and cough at the time of diagnosis and ground glass opacities was found on CT in 62.1% of patients. Hospitalized patients had higher duration of diabetes, suffered more from dyspnea, body aches and chest pain, had higher HbA1c, CRP and ferritin and lower lymphocytes and hemoglobin. Fasting plasma glucose and HbA1c positively affected the duration from onset of symptoms till resolution, while hemoglobin level negatively affected it. Logistic regression analysis revealed that duration of diabetes, HbA1c, ferritin and dyspnea were significant predictors of hospitalization. Conclusions: Among older adults with T2D infected with COVID-19, poor glycemic control is associated with higher risk of hospitalization and longer duration till recovery of symptoms. Longer duration of diabetes, high serum ferritin and the presence of dyspnea are associated with higher risk for hospitalization among these patients

Theoretical Study on the Flexural Behavior of Structural Elements Strengthened with External Pre-Stressing Methods

This study aims to strengthen the flexural behavior of structural elements with external pre-stressing tendons, thereby improving their load-carrying capacity and increasing their resistance against the external load. Different techniques were used to apply external pre-stressed strengthening to RC beams and RC frames. Seven identical RC frames were analyzed: an original sample without an external tendon, two strengthened samples with external tendons at the positive bending zone, two strengthened samples with external tendons at the beam–column connection zone, a strengthened sample with external straight line tendons along the beam and, finally, a strengthened sample with external U-shape tendons along the beam of the frame. The analysis and the results were obtained using ANSYS WORKBENCH finite element (FE) program. Comparisons were performed between these techniques to determine which technique is better for strengthening. The failure mode, vertical deflection, column stress, load-carrying capacity, and ductility of the samples were listed and analyzed under four-point vertical loading. The results show that using external tendons significantly increases the load capacity and the stiffness of structural frames. Moreover, the tendon in the beam zone is more effective than the tendon in the column zone

Wood sawdust waste-derived nano-cellulose as a versatile reinforcing agent for nano silica cement composites: a systematic study on its characterization and performance

Abstract The development of sustainable construction materials is a pressing concern for researchers worldwide, as the cement industry is a major contributor to environmental degradation. The incorporation of nano-materials with cement composites has emerged as a promising solution to sustainable materials production. In this study, the effect of the addition of nano cellulose produced from wood sawdust waste on the performance of cement-based nano-silica composite was investigated. The nano-materials were incorporated at low concentrations and in gel form to eliminate the need for any advanced dispersion techniques. The results indicated that the addition of even low concentrations of nano cellulose significantly enhanced the compactness and mechanical properties of the cement matrix. The crack propagation was observed to be arrested with better adherence to the cement hydration product, which resulted from the presence of nano-silica. The nano cellulose fibers were found to bridge the calcium silicate hydrate products, arresting the propagation of cracks at their initial condition. The high pozzolanic reactivity of nano-silica ensured a minimal amount of calcium hydroxide, which is a significant contributor to the carbon footprint of cement production. Overall, the findings of this study suggest that the incorporation of nano cellulose from wood sawdust waste with cement-based nano-silica composite can lead to the development of sustainable and high-performance building materials with improved mechanical properties and reduced environmental impact

New insight into the pathogenesis of insulin resistance in hyperthyroidism and hypothyroidism

Background and aim Thyroid hormones are linked to the different metabolic processes in the body.We evaluated the association of metabolic syndrome and different thyroid diseases. Patients and methods Eighty female patients were enrolled in this study; 40 hypothyroid (group I) and 40 hyperthyroid (group II) as well as 40 healthy females as control group. Waist circumference, BMI, fasting blood glucose, fasting insulin, HOMAIR index, adiponectin, free T3, freeT4, TSH, total cholesterol and HDL were measured in all patients. Results Adiponectin was lower in hypothyroid group (3.68 ± 0.63 ng/dl) and higher in hyperthyroid group (7.52 ± 0.68 ng/dl) than the control group (5.11 ± 0.67 ng/dl) P = 0.0001. The HOMAIR was higher in both hypothyroid (3.56 ± 0.57 ng/dl) and hyperthyroid groups (1.68 ± 0.27) compared to control group (1.33 ± 0.25) P = 0.0001. The cholesterol was also higher in both hypothyroid (161.22 ± 12.98 mg/dl) and hyperthyroid (147.02 ± 8.7 mg/dl) compared to control group (134.74 ± 6.34 mg/dl) P = 0.0001. The HDL was low in both hypothyroid group (35.86 ± 3.55 mg/dl) and hyperthyroid group (40.34 ± 3.17 mg/dl) compared with the control group (41.64 ± 3.12 mg/dl) P = 0.04. The adiponectin was positively correlated to free T3, free T4 and negatively correlated to TSH (r = 0.8, P = 0.0001; r = 0.9, P = 0.000; r = -0.9, P = 0.0001) respectively. HOMAIR was significantly correlated to the thyroid parameters (r = -0.8, P = 0.0001; r = -0.9, P = 0.0001; r = 0.8, P = 0.0001) respectively. The total cholesterol was negatively correlated with the free T3 and T4 (r = -0.5, P = 0.0001; r = -0.5, P = 0.0001) and positively correlated with the TSH (r = 0.5, P = 0.0001), It was also negatively correlated with adiponectin (r = -0.5, P = 0.0001), and positively correlated with HOMAIR (r = 0.5, P = 0.0001). The HDL was negatively correlated with TSH (r = -0.5, P = 0.000) and HOMAIR (r = -0.5, P = 0.0001), it was positively correlated with free T3, T4 (r = 0.6, P = 0.000; r = 0.5, P = 0.000) and adiponectin (r = 0.5, P = 0.0001). Conclusion Both hypo and hyperthyroidism were associated with insulin resistance and disturbances in lipid profiles

Effect of External Tendon Profile on Improving Structural Performance of RC Beams

The objective of the research is to improve the structural behavior of reinforced concrete (RC) T–beams by applying various techniques of external pre-stressing tendons, thus enhancing the load-carrying capacities and raising the resistance to applied forces. Seven identical RC T–beams were subjected to four-point loading to study the influence of the deviator number, tension mechanism, and tendon profile on flexural behavior. Of these, one beam was an original specimen without any tendons. The other six beams were strengthened with external tendons: two identical specimens with straight–line tendons but with a different number of inner deviators; two identical specimens with V–shaped tendons but with a different tension direction; and finally, two identical specimens with U–shaped tendons but with a different tension direction. The results and discussion were achieved using finite element (FE) software, ANSYS WORKBENCH. The results from all specimens were listed and analyzed for the failure mechanism, load-carrying capacity, deflection, and ductility. According to the FE results, external tendons greatly enhance the load-carrying and stiffness of RC beams. In addition, strengthening beams with external pre-stressing techniques can delay the early cracking load, yield load, and ultimate load by approximately 250%, 570%, and 30%, respectively, when compared to an unstrengthened beam. Moreover, the straight-line tendon with inner deviators was obtained to be the most effective technique for simple beams

Performance of RC frames strengthening by external post-tensioning tendons under vertical and lateral loads

In this study, the structural performance of reinforced concrete frames strengthened with external post-tension tendons was investigated. An experimental study was performed to investigate the failure modes and generate the data required to validate the numerical model. The experimental study includes a reinforced concrete (RC) frame control specimen without strengthening and three strengthened specimens under vertical loads. The specimens were strengthened using external post-tensioning with three different tendon layouts, including a straight tendon in the beam-positive moment zone, straight tendons in the beam-positive and column-negative moment zones, and U-shape tendons along the frame beam. The numerical model was built for the four specimens, validated using the experimental results, and used to analyze the lateral load performance. Results showed that the most effective strengthening technique for the vertical load was the beam U-shape tendons, and for the lateral load, it was the beam and column strengthening. It can be concluded from this case study that strengthening frames with external post-tensioning techniques can enhance the first crack load, yielding load, and ultimate load by 80–100 %, 180–250 %, and 35–70 %, respectively

Natural Radioactivity Assessment and Radiation Hazards of Pegmatite as a Building Material, Hafafit Area, Southeastern Desert, Egypt

Sixty-seven sites of Hafafit pegmatite from the Southeastern Desert of Egypt were investigated radiometrically in the field using an in situ γ-ray spectrometer to determine eU, eTh, and K contents. The obtained results ranged from 0.4 to 6 ppm for eU with a mean value of 2.5 ppm, from 0.2 to 32 ppm for eTh with a mean value of 6.7 ppm, and from 0.7% to 5.4% for K with a mean value of 3.3%. Consequently, the radiological effects from these rocks were estimates by determination of the environmental parameters: gamma activity concentration index Iγ, external hazard index Hex, internal hazard index Hin, external absorbed dose rates in outdoor, and external absorbed dose rates in indoor air. The results obtained in this study showed that values U, Th, and K lie in the range of the acceptable world values. In addition, the calculated radiation hazard parameters (Iγ, Hex, and Hin) have values lower than the world values, while the calculated external absorbed dose rates (Dair) have values higher than the world and Egyptian permissible levels

Optimal hysteresis of shape memory alloys for eliminating seismic pounding and unseating of movement joint systems

Bridge structures adapt to movement through the addition of joint systems that accommodate anticipated movement due to temperature variations or earthquakes, thereby relieving stress on the bridge structure. Shape memory alloys (SMAs) have been proposed to limit joint displacements because of their ability to dissipate seismic energy and restore their original shape. A parametric study is conducted in this study using computer simulations of some advanced MATLAB programs to show the effects of all hysteretic parameters of SMA retrofit devices on seismic joint openings. The results show that SMA hysteretic parameters have a huge effect on SMA efficiency as a restrainer, which is compatible with energy dissipation philosophy, but there are some reversible impacts of some hysteretic parameters in some cases due to the resonance problem and their dependence on other parameters such as natural time period, period ratio, mass ratio, and seismic records. As a result, some design charts are created in this study after more than 200 million trials, taking into account the variation of all key parameters of the structure and the SMA under a suite of historical ground motion records. Moreover, bridge designers can choose optimal SMA hysteresis for a desired opening width, a desired time period, and desired period/mass ratios between adjacent frames with the help of these charts to overcome the two bridge problems of pounding and unseating of bridge decks

Strengthening of hollow core precast prestressed reinforced concrete slabs using different techniques

AbstractHollow-core precast prestressed reinforced concrete (HCPPRC) slabs have been widely available since the 1980s in different structures due to many advantages. Since no shear reinforcement is arranged in HCPPRC slabs before casting, concrete itself provides the shear resistance, especially in the zones close to the supports, which are the most popular regions for shear failure. This experimental study aims to investigate some shear strengthening techniques for HCPPRC slabs, including using carbon fiber reinforced polymer (CFRP) sheets, concrete topping, filling 50% of the slab voids in shear zones with concrete, filling all shear zone voids with concrete, steel through anchors in shear zones, and mixing between filling 50% of the slab shear zone voids in addition to using steel anchors. The experimental program consists of two control specimens and six shear-strengthened specimens that were tested using two-line loads up to failure. Cracking load, cracking deflection, ultimate load, maximum deflection, and failure mode are recorded and discussed for all specimens. The results show that filling 50% and 100% of shear voids with concrete increases slab concrete strength by about 79% and 61.45%, respectively, while using steel through anchors decreases slab concrete strength. Moreover, filling 50% of the shear voids is the best technique for strengthening the shear capacity of HCPPRC slabs due to increasing the cross-section area of the slab’s shear strength. In contrast, using screws with nuts only is not preferred for shear strengthening of HCPPRC slabs