Journal of Engineering Mechanics

The seismic behavior of a representative medium-rise building of Mexico City is evaluated using the capacity spectrum method. This method is widely used in the seismic assessment of buildings because it allows obtaining fragility curves which permit evaluating the ability of a building to resist earthquakes. A real full-height multistory model is proposed to test the capabilities of the algorithm exhibited. The model is outlined through structural drawings sized and structured in accordance with building code regulations for masonry structures in Mexico City. Computational requirements for the analysis of large structures are indicated in addition to improvements to a nonlinear computing code for better performance in terms of memory management and execution times. Finally, a comparison of obtained results and building code regulations is carried out, highlighting differences in the obtained results. The need to handle meshes with a high number of finite elements (FEs) led to development of a new layered finite element that can reproduce the nonlinear behavior of its constituent materials when there are out-of-plane stresses without having to introduce additional degrees of freedom. The proposed FE is compared with the standard FE, presenting different kinematics, and excellent results are obtained. This work emerges from the need to combine and improve existing technologies in the field of finite-element analysis. One such technology is the numerical simulation of the behavior of composite materials. Therefore, it was also necessary to develop a computing program capable of reading both finite-element meshes and patterns of fibers to calculate the information of the composite materials, such as volumetric participation and fiber’s orientation.

This paper presents a constitutive model for sand based on the framework of generalized plasticity and the concept of critical state soil mechanics. In order to model the nonlinear relationship between the critical void ratio and the pressure level more precisely, an enhanced version of the critical void ratio curve is proposed and included in a pressure and density dependent state parameter. In contrast to previous versions, the constitutive relation for the critical void ratio can be adjusted more accurately to a wider range of pressures. The new state parameter is embedded in the plastic modulus, loading vectors, and plastic flow direction vectors of a generalized plasticity model originally developed by Pastor, Zienkiewicz, and Chan. The simulation of a series of drained and undrained triaxial compression tests were used to validate the performance of the modified model under monotonic loading. The comparison between the results of numerical calculations with experimental data shows that the modified model can simulate the stress-strain characteristics of cohesionless sand in a wide range of initial densities and confining pressures with a single set of constitutive parameters.

Material stress-strain behaviors and system load-displacement responses characterized with the origin-crossing input-ouput feature under repetitive loading and unloading conditions can be modeled efficiently by mem-spring models. Mem-springs are from a new family of state-space hysteresis constitutive and component models recently introduced to engineering mechanics by building on analogy with the recent concepts of the memristor, memcapacitor, and meminductor in electrical engineering. In this study, the modeling capability of mem-springs was explored, first by relaxing the continuity condition in the original definition to allow switching, and second, by leveraging a hybrid dynamical system approach as a framework for the switching. State variables were employed in a systematic manner, including the absement (i.e., the time integral of strain or displacement) or momentum (i.e., the time integral of stress or restoring force), and, when needed, internal variables that capture long- and/or short-term memory. Secant rather than tangent stiffness of the input-output pair was a signature of the data analysis. In this manner, mem-springs were constructed as parsimonious and physically meaningful hysteresis models at a constitutive and component level. Mem-springs incorporated into the simplest hybrid dynamical system can render rich hysteretic behaviors and responses, which have the potential to be very useful in engineering mechanics applications. Both rate-dependent and rate-independent hysteresis can be captured by mem-spring models. A partial model for concrete and qualitative models for rubber and the Mullins effect are presented as illustrative examples.

This study investigates the effect of encapsulating a golden fullerene (${\mathrm{Au}}_{32}$) cluster on the mechanical properties of a single-walled carbon nanotube (SWCNT) and a boron-nitride nanotube (BNNT). First, the geometrical parameters of the nanopeapods were optimized using the density functional theory (DFT) method. The DFT results demonstrated that the strength of interaction between the ${\mathrm{Au}}_{32}$ cage and a BNNT was stronger than that between the ${\mathrm{Au}}_{32}$ cage and SWCNT. The molecular dynamics (MD) method was then applied to calculate mechanical properties such as Young’s modulus, failure stress, and failure strain using a stress–strain plot. The mechanical results indicated that encapsulating the ${\mathrm{Au}}_{32}$ cluster reduced the Young’s modulus and failure stress of both a SWCNT and BNNT, whereas the failure strain did not observably change. To validate these results, a ${\mathrm{C}}_{60}$ cage was inserted inside an SWCNT in the most exothermic situation. The MD calculation indicated that, similar to the effect of ${\mathrm{Au}}_{32}$ in the ${\mathrm{Au}}_{32}$-nanotube peapod, ${\mathrm{C}}_{60}$ reduced the mechanical properties of the SWCNT.

Low submergence is usually observed over a channel bed of a steep slope. It is equivalent to large-scale roughness characterized by high ratios of grain diameter to flow depth, $d_{50}/h$. This study shows that the critical Shields stress ${\theta }_c$ for incipient sediment motion can be theoretically formulated either as a function of $d_{50}/h$ or the channel bed slope $S$ for fully rough beds. Different from previous studies, the derivation is conducted by involving the friction factor that applies for open-channel flows subjected to large-scale roughness. The analysis also takes into account other factors including grain density, sediment uniformity, and intergrain friction. The results show that for natural gravel beds, if $d_{50}/h<1$ or $S<0.6$, the incipient sediment motion is controlled by the bed resistance and therefore ${\theta }_c$ increases with increasing $d_{50}/h$ or $S$. Otherwise, the incipient motion is dominantly driven by the streamwise component of the grain gravity, which causes a reduction in ${\theta }_c$ with increasing $d_{50}/h$ or $S$. The theoretical formula agrees reasonably with experimental data collected from eight sources in the literature.

This paper presents a new analytical formulation to predict the bending stiffness of multilayered spiral strands. The effect of interwire contact forces and slip between wires have been fully considered, with the emphasis on the fretting fatigue behavior over individual interwire/interlayer contact patches, where wire fractures have mostly been found to occur. After extensive theoretical parametric studies on a variety of strand constructions, it is shown that the overall effective bending stiffness varies from an upper bound (fully stuck, with no interwire/interlayer slippage) to a lower bound (full slip), with the difference between two limiting values depending on the assumed friction coefficient and cable geometry. Furthermore, wire lay angles in different layers of the strand are shown to play an important role in overall strand deformations and contact forces. To validate the theory developed in this paper, the theoretical predictions regarding contact forces, deformations, and bending stiffness are compared with the previously published, full-scale experimental data in the literature. In all cases, a very close agreement is found between theoretical predictions and full-scale experimental data for multilayered strands of 39-, 41-, and 164-mm-diameter, respectively.

A major consideration in the seismic design of unanchored tanks and equipment and sliding isolation systems is estimation of the peak sliding displacement, which is typically controlled by ground motions with near-fault directivity pulses. Closed-form solutions to the sliding response of a rigid block, subjected to an idealized acceleration pulse, demonstrate that the peak sliding displacement is primarily a function of the area under the acceleration pulse and the coefficient of sliding friction. The solution also shows that the displacement is not strongly dependent on the shape of the acceleration pulse. Based on these observations, an expression is developed to determine the peak sliding displacement as a function of peak acceleration of the ground motion pulse, the pulse duration, and the interface coefficient of friction. A simplified ground motion intensity parameter, termed the effective incremental ground velocity (EIGV), is then proposed to estimate the peak sliding displacement as a function of the ratio of the peak ground acceleration to the friction coefficient and the pulse duration. Comparisons to numerical solutions demonstrate that the EIGV provides a reliable estimate of peak sliding displacement for rigid structures subjected to pulse-like ground motions. EIGV is particularly effective for sliding systems with high-friction coefficients (greater than 0.1), where the sliding response is generally controlled by a single sliding excursion resulting from a dominant ground motion pulse.

The phenomena of soil arching is frequently encountered in geosyntheic-reinforced and pile-supported embankments (GRPSE). This study emphasizes a complicated issue of interactions integrating the embankment soil and geosynthetic-reinforced granular layer (GRL), as well as foundation soil reinforced with piles, on the performance of the GRPSE system. In this modeling, the GRL layer was treated as a reinforced Timoshenko beam that suffers from arching loads, and the mobilization of arching loads would depend upon the differential settlement between piles and soft soils. In addition, the equivalent bending stiffness of GRL, accounting for the tensionless behavior of the granular layer, was also developed, and a correlation of the arch height and differential settlement was investigated by parametric study. The results indicate that the growth of arch height in the embankment would be promoted by pile–soil differential settlement, pile spacing, and pile diameter but inhibited by the shear strength of embankment soil.