Experimental Investigation of Connection Details on the Cyclic Performance of All-steel Tubular Buckling Restrained Braces

To eliminate the geometrical defects and to reduce the damage caused by out-off-plane rotation of the end portion of the conven-tional buckling restrained braces, as well as introducing a new way to facilitate the construction and installation process, the exper-imental behavior of 5 proposed specimens as new type of all-steel tubular buckling restrained braces (AST-BRB) under cyclic axial loads was studied.The proposed specimens consist of a steel tube as a load bearing member (core), which is placed inside a larger tube as a buckling restraining member (pod). At the two ends of the core member, different end details and connection (compared to the common BRBs) are provided as the elastic transitional region. The performance of the specimens were evaluated based on indices, such as damage mode, repeatable behavior, adjusted strength factors, load-bearing capacity, and cumulative inelastic displacement.The evaluation of the results indicated that, the specimens, which welded variable cross-section steel lids at both ends of the core, have superior seismic performance. The superior specimens, for all cycles with larger displacements of the yielding displacement, exhibited a stable hysteresis behavior in bearing of cyclic loads. The bearing pressure was about 1.07 times greater than the tensile load. The cumulative inelastic axial displacements of these specimens is at least 209 times of their yield displacement. Meanwhile, they can tolerate at least 140 % compressive load and 10 % greater tension loads relative to the nominal capacity of the core individual

Selection of ground motion prediction equations for probabilistic seismic hazard analysis based on an improved fuzzy logic

The fuzzy logic method has been used widely in civil and earthquake engineering, but there is no comprehensive point of view for utilizing fuzzy approach in order to obtain ground motion prediction equations (GMPEs) for probabilistic seismic hazard analysis (PSHA). Hence, fuzzy magnitude–distance method as a new approach for choosing GMPEs in the process of PSHA, is developed in this research through the selection of the ruling peak ground acceleration (PGA) of each common cell (the combined cell of earthquake intensity and site to source distance). The presented method reduces the need for engineering judgments in seismic analysis based on a newly developed benchmark. It enables designers to not only determine the range of acceptable fuzzy results but also introduces a concept which ensures the selection of initial well-suited GMPEs for the analysis

Investigation of fling-step effect on the selected structures subjected to the simulated Fandoqa near source strong motion

This study is intended to investigate the contribution of fling step to seismic demands of the selected structures. Due to the scarcity of real data recorded at the two sides of the causative fault including fling step effects, Fandoqa scenario (Iran, 1998) is simulated using a theoretical Green’s function. The three components of the seismograms at Sirch station are simulated using the developed Multi-Objective Particle Swarm Optimization algorithm (MO-PSO) algorithm. The model is calibrated by incorporating the obtained optimal model parameters. The seismograms at four stations close to and located both sides and the causative fault are generated and used as the input data. The fling step contributions are removed from the synthetic data thus providing the seismograms without fling effects. Two structures, a 3D-30 story steel structure dual system (MRF and X-brace) and a 2D-20 story special R/C frame are selected. These two structures are dynamically analyzed under synthetic waveforms with and without fling step contributions. The nonlinear seismic demands over the height of the selected structures with and without fling step contribution are calculated and assessed. It is concluded that in general, fling step may increase or decrease the seismic demands and is not a predictable problem

Estimation of Corrosion Occurrence in RC Structure Using Reliability Based PSO Optimization

In this study, meta-heuristic approach of two types of Particle Swarm Optimization (PSO) method is used to calculate corrosion occurrence probability, due to chloride ions penetration and carbonation. The models' eciency is verified by comparing with available examples in technical literature and results of Monte Carlo analysis. According to the analyzes performed, using different probabilistic distributions regardless of probabilistic moments based on real distribution, lead to diverse results. In addition, influence of each eective parameter on corrosion occurrence varies by changing other parameters and by time The eect of concrete cover (d) reduces at corrosion initiation and the corrosion threshold (Cth) slightly increases over time. Almost, the concrete cover is the most important factor, and the corrosion threshold is also the least important factor. The influence of chloride concentration amount at surface (Cs) increases over time, in a way that, it becomes the most important parameter in low-quality concretes after several years. Thus, the precise amount of Cs is of great importance in exact estimation of corrosion and durability design

Best-fit probability models for wind loads and its effect on the structural reliability

Wind loads are very important in the design of buildings as the load combinations, including the wind load, often govern the design. Compared to other loads, such as gravity load, wind loads are more uncertain and therefore bring about a lower safety index as the ratio of wind to gravity loads increases. Wind load, which is evaluated in terms of wind pressure, is a product of several factors. Wind speed is the main parameter. Other factors depend on the structural shape and geometry. In order to perform a realistic and accurate reliability analysis, it is important to find a suitable model for wind pressure. Previous studies have used Extreme Type I for modeling the wind load. In this study, based on wind speed data for 105 stations located in non-hurricane regions, this wind pressure model is evaluated and then modified. The best-fit models investigated were Lognormal and Extreme Type I. For these, the probability distribution parameters were averaged and general models were then obtained. Results show that lognormal probability distribution could better model wind pressure, although the Extreme Type I model is also close to Lognormal. It is shown that using lognormal probabilistic distribution leads to more conservative reliability indices than those from Extreme Type I

Strength of Different Fiber Reinforced Concrete in Marine Environment

In this paper, the compressive strength, tensile strength and growing rate of compressive strength in 3, 7, 28 and 90 day ages for steel, polypropylene and hybrid steel-polypropylene fiber reinforced concrete with different water to binder ratios (0.4 and 0.5) in a real marine condition and tidal zone were determined. Moreover, regarding a large number of gathered data from the other researches, new equations between compressive strength, tensile strength and elasticity modulus for different types of steel fiber reinforced concrete were proposed. Finally, proposed equations were compared and verified for a marine environment. Based on marine environment results, compressive strength of polypropylene and hybrid steel-polypropylene fiber reinforced concrete were about 18 % and 5 % greater than plain concrete in 90 day ages, respectively and steel fibers had not meaningful effect on compressive strength in 90 day ages. By increasing the water to binder ratio, the compressive strength of plain concrete and steel fiber reinforced concrete was decreased about 18 % and 25 %, respectively. Also in 28 and 90 days, steel fiber reinforced concrete tensile strength was increased about 15 % in 0.4 water to binder ratio and 20 % in 0.5 water to binder ratio rather than plain concrete. Effect of steel fiber in increment of plain concrete tensile strength in 0.5 water to binder ratio was higher than 0.4. Steel fiber reinforced concrete elasticity modulus was lower than related plain concrete and with increasing the compressive strength, the difference between elasticity modulus of steel fiber reinforced concrete and plain concrete was decreased. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.17909</p

Effect of zinc oxide nanoparticles on viability of human spermatozoa

Background: The extensive use of different nanoparticles has raised great concerns about their occupational and biological safety. Objective: The aim of this study was to evaluate the cytotoxic effect of zinc oxide nanoparticles (ZnO NPs) on viability of spermatozoa. Materials and Methods: Semen samples were obtained from 15 healthy persons, and were analyzed using WHO guidelines. Each semen sample was separately incubated with different concentrations of ZnO NPs (10, 100, 500, and 1000 μg/mL) at 37PoPC for 45, 90, and 180 minutes. Then, the cell death percentage of spermatozoa was measured by MTT assay. Mann-Whitney test was used for comparison of different times and concentrations. Results: The maximum cell death percentage was 20.8%, 21.2%, and 33.2% after 45, 90, and 180 minutes, respectively. In case of concentration, the highest concentration (1000 μg/mL) of ZnO NPs led to the highest toxicity for all incubation times. Statistically, there were significant differences in cell viability after 180 minutes vs. 45 and 90 minutes. Conclusion: This study indicated that cytotoxicity of ZnO NPs is dose and time dependent

Effect of Steel Fiber and Different Environments on Flexural Behavior of Reinforced Concrete Beams

The main kind of deterioration in marine Reinforced Concrete (RC) structures and other infrastructures is steel bar corrosion due to cracks in concrete surfaces, which leads to the reduction of the load carrying capacity, ductility, and structural safety. It seems that steel fibers can reduce and delay the cracking, and increase the flexural strength and ductility of marine RC structures. To do so, in marine atmosphere and the tidal zone of the Oman Sea and fresh water, the flexural behavior of beams containing Plain Concrete (PC), Concrete with Steel fiber Reinforcement (SFRC), RC, Concrete with Steel fiber, and bar Reinforcement ((R+S)C) at 28, 90 and 180 days were determined. Beams were 99 un-cracked and pre-cracked beams, with dimensions of 200 × 200 × 750 mm. Based on results and at 180 days, the flexural strength and toughness of pre-cracked (R+S)C beams were 22%–43% higher than the pre-cracked RC beams. The effect of steel fiber on the increment of load capacity and the toughness of pre-cracked RC beams were approximately the same. By addition of steel fiber to un-cracked RC beams, load capacity and toughness were increased up to 20%. The load capacity and toughness in marine atmosphere and tidal zone were approximately 15% lower than the fresh water condition

Risk Perception of Nonspecific Low Back Pain among Nurses: A Qualitative Approach

Background:Low back pain (LBP) is a common medical problem among nurses. A better understanding of nurses’ experiences about LBP may help to develop preventative approaches. The study aimed to explore risk perceptions of nonspecific LBP among nurses in Bandar Abbas City, southern Iran. Methods: This qualitative study conducted as directed content analysis in 2013. Private semi-structured interviews were conducted with a convenience sample of 30 nurses with minimum of 1-year working experience in hospital. The interview questions were based on perceived severity and vulnerability structures of Protection Motivation Theory. All interviews were transcribed and analyzed using thematic analysis. Results: Perceived Severity had the following sub-themes: developing disorders in one’s own life and profession, psychical and mental consequences, conflicts and problems in family life, and financial problems. Two sub-themes (problems and limitations in hospital’s working system, nature of nursing profession) were identified in relation to perceived vulnerability. Conclusion: Nurses reflected their concerns about the impact of LBP on their job security and their considerations about how their back pain might be interpreted by their employers and co-workers. Importance of transparent medical diagnostic procedure and clinical evidence to justify degree of LBP and its burden on the nurses’ performance was also addressed