Journal of Numerical Methods in Civil Engineering
Volume:7 Issue: 2, Dec 2022

The outrigger arm system and belt truss with braced core in the center of the structure surrounded by belts truss, is an efficient and reliable system for high-rise buildings against severe lateral forces such as earthquake and wind. The purpose of this research is investigating the outrigger arm system and belt truss with the braced core under lateral loads. Another purpose of this research is to reduce the drift and displacement of the roof against these loads with deformation and finding the optimal location for the outrigger arm by/through various methods. Analysis of nonlinear time history and spectral analysis of the site with a high relative risk for the three models of 30, 45, and 60 floors have shown that the optimum location of the outrigger arm and belt truss with the proposed method in this research has been better more noteworthy than the previous methods and caused decreasing as it has induced/brought about a decrease in absolute roof displacement and maximum relative displacement of floors. The suggested deformation for outrigger arm in addition to reducing the stress concentration in the floors where outrigger arm are is installed, has caused a significant reduction in the absolute change in the roof of the building and the maximum relative displacement of the floors.

The seismic safety levels provided by the three most recent editions of ACI and ASCE regulations for new moment frame structures are determined. Five special RC moment frames having 3, 5, 10, 15, and 20 stories are designed separately based on ACI 318-99, ACI 318-05, and ACI 318-11, and the associated seismic regulations of UBC 97, ASCE 7-05, and ASCE 7-10. A suit of 10 consistent earthquake records is selected for non-linear dynamic analysis of buildings. Incremental dynamic analysis is conducted, and the corresponding fragility curves are calculated. The comparison of results shows that seismic safety of special moment frame buildings has considerably improved from ACI 318-99 to ACI 318-11, and from UBC 97 to ASCE 7-10, owing its larger part to the improvements made in the two latter versions of the mentioned building codes. However, the safety enhancement is not uniform and is much less for buildings with larger fundamental periods, especially for periods larger than 1.0 sec. For structures with fundamental periods smaller than 1 sec, the collapse ratio has increased up to more than 70%. For larger fundamental periods, the increase is less than 20%. Changes in ASCE7 with regard to the R-factor and coefficients of the load combination equations and its introduction of stricter requirements for the allowable story drift are pinpointed to be the most important factors. For the ACI codes, stricter requirements regarding the confinement of the plastic hinges and configuration of the longitudinal reinforcement are recognized to be the most influential changes.

In this study, the effects of some geotechnical parameters on the surface settlement curves due to mechanized tunneling and the corresponding risk on surface buildings are investigated through numerical analysis. The advanced constitutive law of Plastic Hardening is utilized to accurately reflect the Soil behavior in unloading. Using the surface settlement curves obtained from numerical analysis, the risk category of surface buildings are calculated and the effectiveness of each parameter on the risk level is investigated. The results show that the cohesion and friction angle do not have a remarkable effect on surface settlement and the corresponding risk. However, the amount of overburden and the soil elastic modulus considerably affect the surface settlement and the risk level subjected to the surface buildings. Recognizing the role of each parameter makes it possible to predict the potential risk on surface buildings and to optimize the approaches for mitigating these risks.

The forward solution of dislocation on the fault plane is one of the most important issues for earthquake source slip inversion. The dislocation on the fault plane, explained by the Burgers vector which is called slip, plays a fundamental role in estimating displacement patterns in the whole medium. In addition, obtaining displacement values in any point of a medium is possible by using the slip function on the fault plane and Green’s function as medium properties. This study shows that various assumptions for earth materials result in significant differences in displacements. Therefore, due to the realistic ground motion simulations caused by future earthquakes, considering the properties of earth materials requires more attention. By implementing the elastostatic Green’s functions and based upon line integral representations due to an arbitrary Volterra dislocation loop, elastic displacements and strains due to finite fault dislocations in a functionally graded transversely isotropic (FGTI) half-space material is presented. Also, numerical examples are provided to demonstrate the effect of material anisotropy on the internal and surface responses of the half-space.

This research uses a nonlinear finite element analysis to evaluate and validate two experimental specimens. The Hognestad stress-strain model is used to express the uniaxial compressive behavior of concrete to define three-dimensional concrete in the ABAQUS software, and the linear model is utilized to introduce its tensile behavior. Furthermore, a bilinear model with kinematic hardening is used to simulate the behavior of the steel. Both corner and knee joints, including transverse beams and slabs, are investigated using experimental results from different aspects, including force-displacement hysteresis diagram, the effect of stiffness deterioration, fractural mode, energy absorption rate, and the contour of fracture, and von Mises stress. This study examines two different models which present the predictive modeling, so it is shown that the current model has remarkable power and high reliability by taking into account some important effective parameters in the modeling, such as vulnerable regions, design codes defects, the impact of concrete confinement in large plastic strains, and local buckling. To sum up, this research not only provides a reliable model with the lowest inaccuracy in the study of concrete corner beam-column under seismic load but also presents a simplification in the modeling process that highly reduces analysis time.

This paper numerically investigates the fire resistance of HSC columns under the ISO-834 standard fire curve. Due to its complexity, concrete behavior is mainly evaluated using experimental testing. Because of the limitations of experimental studies, this study uses the finite element method to model concrete behavior under fire conditions. The effects of various parameters such as concrete cover, loading rate, concrete strength, aggregate type, and axial load on the behavior of concrete columns, including temperature and displacements, are investigated. The results showed that concretes with high cover, low preloading, siliceous aggregates, and lower compressive strength exhibit a higher fire resistance than other types.

This paper addresses a reliability-based multi-objective desgin method for spatial truss structures.The uncertainties of the applied load and the resistance of the truss members have been taken into account by generating a set of 50 random numbers. The failure probability of each truss member have been evaluated and consequently the failure probability of the entire truss system have been calculated considering as a series system. A multi-objective optimization problem has been defined with objective functions of truss weight and failure probability of the entire truss structure. The cross sectional area of the truss members have been considered as the design variables. The limitations of nodal displacements and allowable stress of the members have been defined as constraints. A 25-bar benchmark spatial truss has been considered as the case study structure and has been optimally designed using the non-dominated sorting genetic algorithm II (NSGA-II). The results show effectivness and simlicity of the proposed method which can provide a wide range of optimal solutions through Pareto fronts. These optimal solutions can provide both safety and reliability for the truss structure. Also, the results indicate that the failure probability of the truss structure reduces by increasing the uncertainty level of load and resistance.

Leachate recirculation in bioreactor landfills provides appropriate conditions for rapid decomposition of waste. On the other hand, this operation increases the pore water pressure and consequently increases risk of bioreactor failure, especially on the side slopes. In the present study, according to the waste conditions, a two-dimensional (2D) model was proposed through GeoStudio software for investigating the effects of leachate recirculation (by considering vertical injection pipes in two areas A1 and A2 at distances of 20 and 40 m from the side slope of the landfill, respectively) in a bioreactor landfill with a slope of 3:1 H: V at a height of 20m from the base and at two injection pressures (150 and 200 kPa) on stability of bioreactor. Also, six different waste layers with various charecteriastics (including different cohesion, internal friction angle, specific gravity, and hydraulic conductivity were considered.  The results revealed that Factor of Safety (FS) values were lower when the leachate injection was located at the area A1 in comparison to the area A2. This could be due to the higher pore water pressure generated when leachate injection was located at A1. Moreover, the higher values of injection pressure (200 kPa) and greater distance from the side slope (A2) cause more areas to be affected by the leachate recirculation and provide stable conditions for bioreactor landfills in a shorter time. The findings of the current research help to better understandthe influence of leachate recirculation on the FS value and enhance the design of biorector landfills.