Selection criteria for pile diameter in seismic areas

According to modern seismic codes such as Eurocode 8, pile foundations in earthquake-prone areas must resist two different, yet simultaneous bending actions resulting from kinematic and inertial interaction. Due to the different nature of the two demands, pile must resist seismic actions following different patters, thus leading to different design requirements. In this work, analytical solutions are presented to define maximum and a minimum pile diameters required to resist kinematic and inertial effects in an essentially elastic manner, respectively. It is shown that the range of admissible diameters decreases with decreasing soil stiffness and with increasing design acceleration, collapsing into a single admissible diameter for certain problem configurations. Regions where no pile diameter can guarantee elastic response during strong seismic shaking are identified

An exponential matrix method for the buckling analysis of underground pipelines subjected to landslide loads

Abstract Due to their dimensions, long pipelines often cross areas that are highly susceptible to landslides. In Italy, this problem requires special attention, as many slow-moving landslides interact with buried pipelines. The paper analyzes such interaction problem with particular reference to buckling analysis, tackling the solution of the governing equations by an exponential matrix method. In the paper the basic equation, its computational aspects and numerical analysis options are outlined. Representative results of the proposed methodology and potential applications on buckling analysis of buried pipes are presented

A new three object triangulation algorithm based on the power center of three circles

peer reviewedaudience: researcher, professional, popularizationPositioning is a fundamental issue in mobile robot applications that can be achieved in multiple ways. Among these methods, triangulation is a proven technique. As it exists for a long time, many variants of triangulation have been proposed. Which variant is most appropriate depends on the application because some methods ignore the beacon ordering while other have blind spots. Some methods are reliable but at a price of increasing complexity or special cases study. In this paper, we present a simple and new three object triangulation algorithm. Our algorithm works in the whole plane (except when the beacons and the robot are concyclic or colinear), and for any beacon ordering. Moreover, it does not need special cases study and has a strong geometrical meaning. Benchmarks show that our algorithm is faster than existing and comparable algorithms. Finally, a quality measure is intrinsically derived for the triangulation result in the whole plane, which can be used to identify the pathological cases, or as a validation gate in Kalman filters

A simple method for N-M interaction diagrams of circular reinforced concrete cross sections

A novel analytical method is derived for the ultimate capacity interaction diagram (i.e., axial compression, N - bending moment resistance, M) of reinforced concrete (RC) columns with circular cross section. To this aim, the longitudinal rebar arrangement is replaced with a thin steel ring equivalent to the total steel area; moreover, according to modern design approaches, simplified stress–strain relationships for concrete and reinforcing steel are used. Illustrative applications demonstrate that the ultimate capacity computed by the proposed analytical approach agrees well with the results obtained by rigorous methods based on consolidated numerical algorithms. The new solution allows for a rapid, accurate assessment of circular cross section capacity by means of hand calculations; this is especially useful at the conceptual design stage of various structural and geotechnical systems. The method can be easily extended to more general configurations, such as multiple steel rings and composite concrete-steel sections

Size Limitations for Piles in Seismic Regions

A novel theoretical study exploring the importance of pile diameter in resisting seismic actions of both the kinematic and the inertial type, is reported. With reference to a pile under a restraining cap, is shown analytically that for any given set of design parameters, a range of admissible pile diameters exists, bounded by a minimum and a maximum value above and below which the pile will yield at the top even with highest material quality and amount of reinforcement. The critical diameters depend mainly on seismicity, soil stiffness and safety factor against gravity loading, and to a lesser extent on structural strength. This scale effect is not present at interfaces separating soil layers of different stiffness, yet it may govern design at the pile head. The work at hand deals with both steel and concrete piles embedded in soils of uniform or increasing stiffness with depth. Closed-form solutions are derived for a number of cases, while others are treated numerically. Application examples and design issues are discussed

Axial kinematic response of end-bearing piles to P waves

Kinematic pile-soil interaction under vertically impinging seismic P waves is revisited through a novel continuum elastodynamic solution of the Tajimi type. The proposed model simulates the steady-state kinematic response of a cylindrical end-bearing pile embedded in a homogeneous viscoelastic soil stratum over a rigid base, subjected to vertically propagating harmonic compressional waves. Closed-form solutions are obtained for the following: (i) the displacement field in the soil and along the pile; (ii) the kinematic Winkler moduli (i.e., distributed springs and dashpots) along the pile; (iii) equivalent, depth-independent, Winkler moduli to match the motion at the pile head. The solution for displacements is expressed in terms of dimensionless transfer functions relating the motion of the pile head to the free-field surface motion and the rock motion. It is shown that (i) a pile foundation may significantly alter (possibly amplify) the vertical seismic excitation transmitted to the base of a structure and (ii) Winkler moduli pertaining to kinematic loading differ from those for inertial loading. Simple approximate expressions for kinematic Winkler moduli are derived for use in applications. © 2013 John Wiley & Sons, Ltd

Failure envelopes of pile groups under combined axial-moment loading: Theoretical background and experimental evidence

Abstract The problem of failure envelopes of pile groups subjected to vertical and eccentric load is investigated both theoretically and experimentally. A critical review of literature works on failure envelopes for pile groups under combined axial-moment loading is first provided. Emphasis is placed on a recent, exact solution derived from theorems of limit analysis by idealizing piles as uniaxial rigid-perfectly plastic elements. The application of the relevant equations over a practical range of problems needs only the axial capacities in compression and uplift of the isolated piles. An intense program of centrifuge experiments carried out along with different load paths on annular shaped pile groups aimed at validating the equations pertinent to the above solution is presented and discussed. The endpoints of the load paths followed in the centrifuge lie approximately above the analytical failure envelope, giving confidence that the reference equations can be reliably adopted to assess the capacity of a pile group under combined axial-moment loading. Finally, the kinematics of the collapse mechanism observed experimentally is compared to that determined from the application of the reference theory

Malignant otitis externa in the antibiotic resistance era: key to successful treatment

Malignant otitis externa in the antibiotic resistance era: key to successful treatment. Objective: Malignant otitis externa (MOE) is a rare aggressive, necrotizing infection of the external auditory canal and the temporal bone. MOE may have a poor prognosis when it is not treated promptly and adequately. It is most commonly reported in males, older individuals, patients with diabetes, or patients that are immunocompromised. Pseudomonas aeruginosa is the main pathogenic agent involved. This study aimed to evaluate a clinical series of patients with MOE and discuss the current literature on the topic. Methodology: This retrospective study included 8 patients with MOE that were evaluated and treated, medically and/ or surgically, at the University Hospital of Ferrara between January 2012 and December 2016. We retrieved data from medical records on the clinical history, imaging, and treatment. Results: In all cases, a microbiological examination disclosed the presence of P. aeruginosa. The infection was eventually controlled in all cases, after a median of 6 months of therapy. All patients were followed-up for an average of 12 months after infection resolution. Conclusion: Currently, no specific guidelines for MOE treatment are available in the literature. Based on our findings, we proposed a diagnostic and therapeutic flow-chart for managing this infection

Size Limitations for Piles in Seismic Regions

A novel theoretical study exploring the importance of pile diameter in resisting seismic actions of both the kinematic and the inertial type, is reported. With reference to a pile under a restraining cap, is shown analytically that for any given set of design parameters, a range of admissible pile diameters exists, bounded by a minimum and a maximum value above and below which the pile will yield at the top even with highest material quality and amount of reinforcement. The critical diameters depend mainly on seismicity, soil stiffness and safety factor against gravity loading, and to a lesser extent on structural strength. This scale effect is not present at interfaces separating soil layers of different stiffness, yet it may govern design at the pile head. The work at hand deals with both steel and concrete piles embedded in soils of uniform or increasing stiffness with depth. Closed-form solutions are derived for a number of cases, while others are treated numerically. Application examples and design issues are discussed