Scientia Iranica
Volume:28 Issue: 6, Nov-Dec 2021

The dynamic behavior of structures has always received considerable attention. The dynamic behavior of structures requires the suitable numerical modeling method in order for the behavior of structures under dynamic loads to be illustrated. In this study, the response of two identical unreinforced masonry walls to the underground blast was examined. The experimental variables were the horizontal distance from the explosion point and depth in which the explosives were located. After examining the behavior of the masonry walls under high-frequency dynamic loads, different numerical models were applied to simulate the dynamic behavior of these two walls against the underground blast experiments. Thus, a number of different factors, including yield criterion, types of meso and macro modeling for the masonry wall, and topography of the site were investigated. Finally, due to the degree of accuracy required, it was concluded that each of the methods can be used; however, the most appropriate and accurate modeling method for the unreinforced masonry wall is the frictional-cohesive zone material and modified Mohr-Coulomb model, which provided accurate and precise responses.

Endurance Time (ET) method is a time history-based analysis procedure that applies special intensifying acceleration functions for estimating the seismic performance of structures at different excitation levels in every single analysis, and therefore, remarkably reduces the computational time, effort, and cost. For some structures with complicated models, such as dams, performing multiple seismic analyses are impractical. In such cases, it is recommended that researchers pay conscious attention to choose appropriate and compatible Endurance Time excitation functions (ETEF) considering the basic properties of their structure. However, in this study, it is observed that selecting and using various ETEFs for analyzing an intermediate concrete moment frame structure subjected to individual earthquake ground motions will lead us to obtain false and unreliable responses. In other words, different ETEF series have significantly different accuracies (over 26 percent error) in predicting the responses of the mentioned structure subjected to individual earthquake ground motions. This problem mainly arises due to the turbulent nature of the spectrum of a single ground motion which is in contrast to the smoothed shape of spectra of the ETEFs. One solution to avoid this problem might be to produce a specific ETEF.

By using the vehicle-track interaction model and the wear calculation model, the development characteristics of rail profile wear and the longitudinal characteristics of rail wear development of the track-vibration-absorber fastener tangential track at different passing speeds were analyzed. The results of rail profile wear analysis show that with the increase of iteration times, the wear ranges and wear depths of left and right rails at the corrugation trough/crest position are close. Meantime, the wear depths of rail profile and wave depth amplitudes at the corrugation trough/crest position in discrete passing speed modes are significantly lower than those in constant passing speed mode. The results of rail longitudinal wear analysis show that with the increase of vehicle running times, the characteristic frequencies of corrugation do not change under different passing speed modes, which reflects the fixed frequency feature of corrugation, and the irregularity levels corresponding to characteristics frequencies of rail longitudinal wear under the three passing speed modes show a decreasing trend in turn. Compared with the constant passing speed mode, the discrete passing speed modes can significantly decrease the rail profile wear and the development degree of rail wear at the characteristic frequencies.

An experimental program was conducted to investigate the effects of curing time and curing temperature on shear behavior of a sand-bentonite mixture. The specimens were cured at temperatures of 40°C, 60°C and 80°C for 1, 3 and 5 days under 100kPa, 500kPa and 1000kPa confinements. The results of consolidated undrained triaxial shear tests showed that an increase in temperature from 40°C to 80°C at 1, 3 and 5 days of curing increased the shear strength by 25%, 24% and 23%, respectively. Also, the increase in curing time from 1 to 3 and from 1 to 5 days at 80°C increased the shear strength of samples 12% and 24%, respectively. The failure of pre-cured samples occurred in lower strains as a result of more induced brittleness. Moreover, the secant modulus as well as the size of yield loci and critical state line’s slope increased by pre-curing. The application of thermal cycles resulted in increasing shear strength and experiencing a negative pore water pressure which shows a transition towards the quasi-structured behavior. The results of scanning electron microscopy (SEM) studies confirmed the increase in void ratio during thermal curing.

Fiber-reinforced foamed urethane (FFU) synthetic sleeper is used in ballasted track with the potential problem of insufficient lateral resistance due to lower weight and smooth surface compared with concrete sleepers. In this paper, the lateral resistance of prototype and modified FFU synthetic sleepers was investigated by single tie push tests and DEM analysis, where the real shape of ballast particles was created using 3D scanning technique. Results indicate that due to the smooth surface of sleeper facets, the lateral resistance of prototype FFU sleepers is reduced by 10-15% and governed by the interactions of shoulder ballast and sleeper ends. On the other hand, modification of the sleeper shape by adding FFU strip block along sleeper base and sides increased lateral resistance up to 19 % of prototype sleepers with higher interlocking ability between ballast and sleeper sides. Results could be used to develop modified FFU sleepers for application in various ballasted tracks.

An extension of the slip line theory to unsaturated soils is presented and applied to the problem of stability of slopes in unsaturated soils. The matric suction is then introduced and implemented in governing equations by the well-known Bishop effective stress concept. In this regard, the van Genuchten model is utilized to estimate the effective stress parameter required for the computation of the effective stress. The influence of the soil matric suction on the stability of slopes has been investigated for a variety of soils under steady state evaporation and infiltration, i.e., the distribution of the matric suction was assumed to remain constant with time. In addition, a measure of stability in terms of some factor of stability has been introduced.

The physical and chemical properties of cohesive sediments have been determined. The consolidation mechanism was also investigated in various scenarios by changing the initial sediment concentration from 50 to 150 gr/lit. In the experiments, cohesive sediment samples of the Karkheh dam reservoir were tested using settlement columns. The initial sediment concentration, initial settlement height, and temperature are among the effective parameters on the settlement of cohesive sediments. In addition, the effects of the bed elevation of reservoir, as well as the scale effects on the settlement of cohesive sediments, were also studied. The results showed that the initial free settlement process and the hindered settlement phase take more time than self-weight consolidation settlement stages by increasing initial sediment concentration. Therefore, at an initial sediment concentration of 25 g/l and 150 g/l, the samples began self-weight consolidation after 1.5 h and 17.5 h respectively. The results also showed that the final average concentration increased linearly by the initial concentration. The concentration of the settled sediments decreased with a nonlinear trend by the initial height. In addition, under the same initial conditions, by increasing the diameter of the settlement column, the final concentration of the settled sediments first decreased and then increased.

Under impact loads, it may be a challenge to analyze reinforced concrete (RC) sandwich plates with hollow structures in terms of crushing, punching, cracking, and crack trajectories via static and dynamic equations.In the literature, the finite element solutions were conducted after determining the behaviors of the materials according to test results.Therefore,it is required to conduct experiments to determine the behaviors of RC plates to investigate their behaviors.In this study, the behaviors of sandwich plates under impact loads were analyzed experimentally.The sandwich plates were manufactured by cutting polyester foams (PF) into hexagonal prisms, square prisms, I-type, and S-type, and installing them inside the reinforced concrete plates.The newly manufactured sandwich plates are 27% lighter than the full plate.A weight of 320 kg was dropped freely from 2.5m, and the load was implemented on the center of the plate at a velocity of 7.5 m/s.Similar implementations were also conducted for filled plates, and the maximum displacements were measured in both types of plate tests.By comparing the measurements obtained from each test,the sandwich plate with core geometry that provided the highest absorption, namely, the lowest displacement, was determined. In the analyses, the S-type core geometry demonstrated more absorption compared to other core geometries.

The non-linear response of steel plate shear walls (SPSWs) with perforated infill plates are studied by considering the interaction effect between the frame and the infill plate. A number of single and 14-stories SPSWs with solid and perforated infill panels with different perforation ratios are studied numerically. The results are utilized to discuss (a) the influence of perforated ratio and placement of the holes on system behavior (b) changes in system strength, stiffness, damping ratio and ductility due to the introduction of perforation in infill panels, and (c) evaluate the change in behavior of low and high-rise structures by the introduction of perforations. The results reveal that the perforation ratio is not the only controlling factor in strength and ductility of the shear wall specimens, and the strength and ductility of SPSW also depend upon the placement array of the perforations in the infill plate. The ultimate strength, ductility ratio and initial stiffness of the perforated SPSWs have been reduced to 28, 29 and 33.5% compared to the reference specimen, respectively. Also, the values of normalized CHE and LHE and equivalent viscous damping ratio in perforated specimens reduced to about 28, 26 and 10%, respectively.