فصلنامه رویکردهای نوین در مهندسی عمران
سال هفتم شماره 3 (پاییز 1402)

Concrete is the most widely used material in the construction industry of the country. Porous concrete has always been the focus of researchers due to its special properties such as high permeability. The present article has determined the design of porous concrete mix with specific strength based on the laboratory program and modeling by using artificial neural network. The experiment program in this research started with 200 mixing plans in the field of porous cylindrical concrete and preparing a database and it was modeled by using different types of multilayer perceptron neural network (MLP). Evaluation indices including regression coefficient and mean square error have been used to check the efficiency of artificial neural network structures. The results showed that the regression coefficient in most of the structures used was above 85% and in the neural network with the optimal structure it was 95%. Also, the evaluated error index in the neural network with optimal structure is determined to be 0.121.

The application of seismic isolators at the base or mid stories by employing the mechanism of tuned mass dampers (TMDs) in structures provides an effective seismic control method for buildings. In this study, three prototypes of 10-story steel moment-resisting frame structures with intermediate ductility that are designed in accordance with second and fourth editions of Iranian Seismic Design Code (Standard No. 2800) as well as the second edition with one story on seismic isolator at the last floor were designed and modelled using nonlinear static pushover and nonlinear dynamic time history analyses under three far-fault earth‎quakes. The results were presented in the form of pushover curves and time history of roof displacement, base shear, maximum drift and roof acceleration of stories to compare the seismic enhancement of roof-level isolating technique and the effectiveness of the seismic criteria of Standard No. 2800. The results of research indicated that adding on isolated story at roof level had a significant effect on decreasing the drift of the stories. This reduction for the designed structure based on the second edition of Standard No. 2800 is down to an average maximum of 25%. In addition, using seismic isolators reduces the base shear by 30%. The decrease in the amount of roof displacement is also 40%. Also, the results showed that the efficiency of isolated story application as the last story to reduce the damage.

Natural disasters often bring about wide-ranging catastrophic consequences. The post-crisis assessment of different regions generally indicates poor crisis management, evacuation routing, and planning performance, leading to incoordination and wasting time and network capacity. Therefore, this study presented an integrated solution to determine evacuation routes in a short time using an algorithm based on network analysis and the definition of safe nodes and arcs based on crisis conditions. The proposed flow optimization model employs the MCNFP method to find the shortest evacuation routes from each node to the safe zone and guide the maximum possible flow through this route. The model's efficiency was controlled using 12 small networks with different combinations of nodes and vehicles and 10 medium networks with different numbers of nodes and similar demands. Then, the running times of each MCNFP algorithm and the proposed model (P-M) were compared. The results showed that the evacuation time increased by increasing the number of nodes and the routing expanse and complexity. In addition, increasing the number of vehicles in limited and local networks increased the evacuation time. Generally, the research results confirmed the optimal speed of the proposed algorithm in network evacuation.

The theory of beams on elastic foundation occupies a prominent place in contemporary structural mechanics. The governing equations of motion of dynamic systems are generally partial differential equations that are difficult to solve in mathematical terms. This work is facilitated through the use of matrix methods and modern computational techniques. The matrix methods are based on the concept of replacing the actual continuous structure by an equivalent model made up of discrete structural elements having known elastic and inertial properties expressible in matrix form. The purpose of the present paper is to expand the dynamic stiffness matrix of a Timoshenko beam-column on two-parameter elastic foundation. So, first, a brief review of the literature related to soil-structure interaction is presented. Then, the method of dynamic analysis of the structures with distributed mass and elasticity is discussed. In the discussion, the procedure of derivation of dynamic matrices using exact differential equation of vibration is studied. Afterward, the Timoshenko beam theory which takes into account the effect the rotary inertia of mass and shear distortion can be modeled is presented. Furthermore, foundation model including two-parameter models of elastic foundation are studied, and the governing differential equation of vibration of each presented model is derived. Then, the differential equation of the model is solved in order to derive the dynamic stiffness matric of a Timoshenko beam-column on two-parameter elastic foundation. Then, expansion of the obtained dynamic matrix is carried out using power series. We use program Mathematica for this purpose. The result of this expansion is a two-variable power series of some useful matrices in terms of vibration frequency and axial force which its coefficients are the relevant first, second and higher order stiffness, geometrical and mass matrices.

Investigation of seismic behavior and seismic safety evaluation of concrete dams has been the focus of many researchers due to the importance of dam safety during an earthquake. Because the destruction of these structures due to an earthquake can have negative economic and social effects. In the present study, the nonlinear dynamic analysis of gravity concrete dams has been done considering the effect of dam-reservoir interaction. In fact, the minimum and maximum principal stresses for the U-shaped dam and reservoir have been measured via ANSYS. Also, the present study seeks to investigate the evaluation of V-shaped dams in seismic conditions. The results show that the static analysis with non-linear behavior in the rock mass with medium and weak layers has more stability compared to the weak homogeneous system. But it is more possible to concentrate plastic strains in weak layers. Other results of this study showed that the compressive stresses in the safety check of the dam were not critical and the maximum tensile arc stresses were obtained mainly in the upper levels of the middle blocks and also in the vicinity of the contact surface with the side supports.