نشریه مهندسی عمران فردوسی
سال سی و ششم شماره 2 (تابستان 1402)

The occurrence of urban accidents depends on many human and environmental factors, so identifying the important factors influencing accidents and their spatial effects on each other is of great importance. The main goal of this study is to evaluate the spatial effects of environmental factors on the frequency of accidents in the city of Shiraz, Iran at the TAZ level. In the first step of the study, using component analysis models, important environmental factors affecting the accident were identified and composite indicators were produced as independent variables. In the second step, in order to control the effect of correlation and heterogeneity of model variables, spatial statistical models based on Euclidean distance such as geographically weighted Poisson regression (GWPR), geographically weighted negative binomial distribution (GWNBR) as well as Poisson and distribution models Negative binomial based on neighbor distance is used in spatial Bayes method with INLA approach. The results of the study showed that models based on distance and contiguity in order to evaluate the spatial effects of accident data and the factors affecting it at the TAZ level have higher accuracy than geographic weighted regression models, as well as indicators of land use diversity and access to The public transportation system is effective and in TAZs where this index is high, there is a higher probability of an accident.

In this research, the progressive collapse of braced frames with knee braces in steel structures under fire load was investigated based on the software modeling method. In order to carry out the research 3, 6 and 9-story steel frames with coaxial and off-axis knee bracing systems were considered in the shape of inverted-V and were analyzed and analyzed using the software method and ABAQUS and SAP software. In this regard, at first, the frames were analyzed and designed by modeling the frames in SAP software, and the sections of the frames were determined. In the following, the frame was analyzed in ABAQUS software under the fire load. the frame without and with the removal of the critical elements was analyzed successively under the fire load in the SAP software to check and compare the energy of the frame samples in each case based on the results obtained from the analysis. Based on the study conducted on the frame with off-axis and coaxial knee bracing, it was determined that the bracing type of off-axis had a significant effect on reducing the energy of the frame compared to the coaxial bracing system. The 3,6 and 9-storyframes with off-axis knee bracing had 35%, 50% and 65% less energy than the frames with coaxial knee braces during the fire and in the entire time period.

Isolators and dampers are devices that dissipate energy and reduce the seismic response of structures during strong earthquakes. Lead Rubber Bearings (LRBs) and Tuned Mass Dampers (TMDs) are two common types of these devices. Studying non-linear behavior and seismic properties of structural systems equipped with this type of isolators and dampers can significantly enhance understanding of their behavior against lateral forces caused by strong earthquakes. In this study, a 9-story steel structure was analyzed using the Endurance Time Analysis (ETA) method in SAP2000 software with fixed and isolated bases, along with a tuned mass damper with different mass ratios and without a tuned mass damper. The analysis results indicate that the tuned mass damper is highly effective in reducing the displacement of the isolator level, drift ratio, and story shear forces. This effect is more significant with higher mass ratios of the TMD. This effect is more pronounced with higher mass ratios of the TMD. However, reducing the absolute acceleration response of the structure has not been effective, and increasing the mass ratio of the TMD only reduces the performance of the control system in improving the absolute acceleration response compared to the isolated state.

Traffic accidents are one of the main causes of death in the world and the resulting damages have an important effect on the economy of any country that the need to identify factors affecting accidents that lead to a reduction in the frequency or severity of accidents is understandable. Since the outbreak of Covid-19, travel restriction policies have been widely adopted by cities around the world that it played a profound role in changing the shape of urban travel patterns. One of the factors that influenced traffic behavior in recent years was the epidemic of Corona disease in the world. Therefore, new driving rules and regulations were established for urban and suburban traffic, and traffic behaviors were affected by those rules. It is possible to investigate the effect of each factor on the severity of accidents by using accident severity models according to the effective parameters. In this article, urban accidents due to lack of attention during the corona epidemic were analyzed using logistic regression and information related to intra-urban accidents in Rasht city. The final model shows that the independent variables of working day, at-fault male drivers over 60 years of age, front-to-front collision and the at-fault vehicle Pride increase the probability of a fatal or injury accident compared to a damage accident. Variables with negative coefficients (6:00 a.m. to 9:00 p.m., dry road surface conditions, clear weather, and daylight conditions) reduce the probability of fatal or injury accidents compared to damage accidents.

Control of structures in order to prevent serious damage to structures has become a prominent issue in earthquake engineering. In traditional structural control systems, wires were used to communicate between sensors, actuators, controllers and integrate the entire system as a single network. Using of wireless sensors for measurement, communication and control in structures has increased with the advancement of technology. The use of this technology has attracted the attention of engineers due to the reduction of installation costs and flexible system. In this article, the benchmark nonlinear three-story structure with magnetorheological damper (MR) equipped by wireless sensor network is investigated. The seismically excited building is combined with a wireless sensor network simulated by TOSSIM in the MATLAB simulator environment. For real network simulation, noise and wireless signals collected from a real structure have been used. In this network, a time division multiple access protocol (TDMA) is used. This protocol assigns a specific time to each sensor to send information. The benchmark structure is trained by a fuzzy-genetic controller. Then, the structure equipped with wire and wireless sensors was evaluated under the various earthquakes. Examining the evaluation criteria and time history charts shows the proper performance of the wireless system in reducing structural responses. At the same time, the wireless system has caused a slight increase in the average displacement and acceleration of floors compared to the wired mode.

In recent decades, shells made of composite materials have been used in modern structures under impact load. Multi-Layer Composites (MLC) and Functionally Graded Materials (FGMs) are the upgrades of composites that have been considered due to their suitable mechanical properties such as high resistance to weight ratio, flexibility and impact resistance. In this research, geometric nonlinear dynamic behavior on multilayer composite cylindrical shells with FGM core under impact load has been analyzed; Because it is necessary to know how structures made of these materials behave under such loads. For this purpose, the effect of FGM core volume fraction index and the effective parameters of multi-layer composites such as the angles of the layers and the number of layers have been investigated. The results of this study show that by increasing the volume fraction index, the maximum displacement of the shell decreases. The maximum displacement occurs in the CFC (CFRP/FGM/CFRP) shell with pure metal FGM and the minimum displacement occurs in the GFG shell with pure ceramic FGM. Evaluation of the different positions of the layers shows that selecting a 15-degree positioning angle causes less displacement and also decreases the displacement as the number of layers increases.