فهرست مطالب mohammadhossein mahmoudi

A significant number of engineering structures around the world are exposed to fire on a daily basis. The most important effect of fire on the structure is elevated temperatures, which may reach more than 1000 degrees Celsius and cause not only thermal stresses and deformations but also diminished mechanical properties of materials comprising the structure. Fire-related collapses have been observed in numerous structural fires. However, many reinforced concrete structures exposed to fire do not demonstrate notable apparent damage and survive despite having experienced elevated temperatures before the fire is put out. Estimating the residual strength of such structures is of critical importance when deciding whether such structures can be safely used after fire. Moreover, in many industrial applications, there is a need to concrete that can withstand repeated long-term cycles of elevated temperatures without diminished mechanical properties. The objective of this paper is to investigate the effects of silica fume and fly ash as two widely used supplementary cementitious materials on the residual strength of concrete exposed to elevated temperatures and evaluate while such materials can be of benefit in improving the strength retention in case of heat exposure. Using 19 mix designs, a series of 570 concrete cylinders was fabricated using different water to cement ratios (0.35, 0.5, and 0.65), silica fume replacement ratios (0, 10, and 15 percent), and fly ash replacement ratios (0, 10, 20, and 30 percent). The specimens were cured in water for 56 days, after which they were placed in a rate-controlled large-scale electrical furnace, and their residual compressive and tensile strengths were measured before heat, and after heat exposure for 2-, 12-, and 24-hour heating cycles with temperatures reaching 200, 400, and 600 degrees Celsius. To eliminate the risk of explosive spalling, all specimens were preheated at a temperature of 100 degrees for 24 hours before the main heating cycle. Results showed that the compressive and tensile strengths did not reduce noticeably after exposure to 200 degrees but demonstrated a significant drop after exposure to 400- and 600-degree cycles. In many cases, the residual compressive and tensile strengths of specimens were found to be smaller than those predicted in previous studies. The square root equation widely used in the literature was found to provide a reasonable lower-bound estimate of the residual splitting tensile strength of concrete from the residual compressive strength; however, a linear trend was identified to provide a more accurate estimate for the results of this study. Moreover, due to less scatter, the splitting tensile strength was found to be a better indicator of heat damage in the structure than the compressive strength. The use of silica fume did not result in a meaningful trend in the residual compressive strength but reduced the residual tensile strength of specimens. Fly ash, on the other hand, could increase the residual compressive strength of the specimens but reduces the residual tensile strength. The results suggest that generally, and with few exceptions, these two supplementary cementitious materials are not recommendable choices for improving the strength retention of concrete in case of heat exposure.

Assessing the workability of employees is very important, and firefighting is one of the critical jobs. Therefore, the aim of this study was to evaluate the work ability index (WAI), and identify some effective factors among firefighters.

This cross-sectional study was carried out with participation of 101 firefighters in Zahedan, Iran in 2018. Subjects were included in the study by census method. Data were collected using a two-part questionnaire (demographic information and WAI items), and data analysis was performed using SPSS 24.

The mean of age and work experience of the subjects were 34.18±6.70 and 8.47±6.79 years, respectively. Only 18 individuals (17.8%) were single, and most of them exercised at least once a week. The mean score of WAI was 44.33±3.56 and most of the subjects were in the excellent range. With increasing age and work experience, WAI decreased, and there was also a significant relationship between marital status and weekly exercise with WAI.

In general, the condition of the firefighters was favorable in terms of workability. However, due to the relationship between personal characteristics and WAI, it is necessary to adjust the duties of older people with more work experience.

Background and Both hypothermia and Decompressive craniectomy (DC) have been shown to reduce ischemic injury in experimental middle cerebral artery occlusion (MCAO). This study was designed to evaluate the effect of delayed combination of DC and Local Hypothermia (LH) on infarct size, neurological outcome and blood brain barrier (BBB) disruption in a rat model of stroke. MCAO was induced in 36 Wistar rats assigned to three groups of control, Decompressive Craniectomy (DC) and combination of Hypothermia and Craniectomy (HC). Infarct size and BBB disruption were measured 48 hour after ischemia insult. Neurological deficits were assessed at 24 and 48 hours after stroke using sticky tape test, hanging-wire test and Bederson’s scoring system. BBB disruption was measured by Evans blue dye leakage. Compared to the control group, infarct size reduced significantly in DC and HC groups (P<0.001), however, combination therapy was more neuroprotective compared to craniectomy alone (P<0.01). Compared to the control group, BBB disruption was significantly reduced in DC (P<0.05) and HC (P<0.01).While compared to the control group sticky tape test (P<0.05 at 24 h; P<0.001 at 48 h) and hanging-wire test (P<0.05) showed better behavioral performance only in HC, and Bederson test showed improved behavioral functions of HC animals (P<0.01). At the same time neurological deficits also decreased in HC group (P<0.05 at 24 h; P<0.01 at 48 h) compared to the DC group. According to this study although both delayed local hypothermia and craniectomy are protective after stoke, combination therapy of them is more neuroprotective than given alone.