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Finite element analysis of dynamic foundation problems requires the use of transmitting boundaries to model the radiation of waves from the finite element mesh into the far field. Problems involving inelastic behavior of the soil in the near field are most readily solved in the time domain. The standard viscous boundary is widely used in such situations. However, in axisymmetric situations this boundary is inappropriate. This paper develops plane strain boundary equations for axisymmetric shear and dilation waves based on an approximation of the form of the outward traveling waves. These boundary equations are shown to be equivalent to mechanical systems with frequency independent components. The complex stiffnesses of the new boundaries are compared with the equivalent viscous and plane strain boundary stiffnesses, and the new boundaries are found to agree closely with the plane strain boundaries. The response of an extended axisymmetric finite element mesh subjected to a transient force of the type generated by pile hammers is computed and compared to the responses of the same mesh truncated with various transmitting boundaries.

In most soil types, it is generally assumed that the shaft capacity of a pile is identical under both tensile and compressive loading. However, there is widespread experimental evidence that in sand the shaft capacity is significantly lower for tensile loading, or uplift, than for compressive loading. This paper describes the results of a parametric study that was conducted to explore the theoretical basis for such differences. It is shown that the primary cause of lower tensile capacity is due to a Poisson's ratio effect, and that the ratio of tensile to compressive shaft capacity may be expressed as a function of the relative compressibility of the pile and the slenderness ratio. Design recommendations are proposed, and corroborated with results from high-quality field tests.

The piled raft is a geotechnical composite construction, consisting of the three elements piles, raft, and soil, which is applied for the foundation of tall buildings in an increasing number. In a parametric study, 259 different piled raft configurations have been analyzed by means of three-dimensional elastoplastic finite element analyses. In the study, the pile positions, the pile number, the pile length, and the raft-soil stiffness ratio as well as the load distribution on the raft has been varied. In the scope of this paper, the results of the parametric study are presented and design strategies for an optimized design of piled rafts subjected to nonuniform vertical loading are discussed. DOI: 10.1061/(ASCE)1090-0241(2004)130:1(1) CE Database subject headings: Foundation design; Pile foundations; Raft foundations; Vertical loads; Numerical analysis; Finite element method; Differential settlement, Bending moments.

The majority of periprosthetic joint infections occur shortly after primary joint replacement (<3 months) and require the removal of all implant components for the treatment period (~4 months). A clinically relevant animal model of periprosthetic infection should, therefore, establish an infection with implant components in place. Here, we describe a joint replacement model in the rat with ultrahigh molecular weight polyethylene (UHMWPE) and titanium components inoculated at the time of surgery by methicillin‐sensitive Staphylococcus aureus (S. aureus), which is one of the main causative microorganisms of periprosthetic joint infections. We monitored the animals for 4 weeks by measuring gait, weight‐bearing symmetry, von Frey testing, and micro‐CT as our primary endpoint analyses. We also assessed the infection ex vivo using colony counts on the implant surfaces and histology of the surrounding tissues. The results confirmed the presence of a local infection for 4 weeks with osteolysis, loosening of the implants, and clinical infection indicators such as redness, swelling, and increased temperature. The utility of specific gait analysis parameters, especially temporal symmetry, hindlimb duty factor imbalance, and phase dispersion was identified in this model for assessing the longitudinal progression of the infection, and these metrics correlated with weight‐bearing asymmetry. We propose to use this model to study the efficacy of using different local delivery regimens of antimicrobials on addressing periprosthetic joint infections. Statement of clinical significance: We have established a preclinical joint surgery model, in which postoperative recovery can be monitored over a multi‐week course by assessing gait, weight‐bearing, and allodynia. This model can be used to study the efficacy of different combinations of implant materials and medication regimens. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1101‐1112, 2020 [ABSTRACT FROM AUTHOR]