D.D. Theodorakopoulos

Dynamic analysis of a poroelastic half-plane soil medium under moving loads

The dynamic response of a poroelastic half-plane soil medium subjected to moving loads is studied analytically/numerically under conditions of plane strain. The material is idealized as a uniform, fully saturated poroelastic layer of soil obeying Biots dynamic poroelastic theory. Hysteretic damping in the soil skeleton may also be present. The loading function is presented by a Fourier series expansion allowing the analysis to handle different types of load such as uniform pressures and multiple loads. The parameters examined include mainly the poroelastic material properties such as porosity, permeability, shear modulus, compressibility of fluid and the velocity of the moving load. The response quantities include the vertical displacement of the solid skeleton, the fluid pressure and the solid vertical effective stress. It is concluded that the effect of porosity and permeability on response is more pronounced in soft materials, especially at high load speeds. Some of the results of the parametric study are qualitatively well compared with theoretical results obtained by other investigations.

ULTIMATE PUNCHING SHEAR STRENGTH ANALYSIS OF SLAB-COLUMN CONNECTIONS

Abstract A simple analytical model is presented to predict the ultimate punching shear strength of slab–column connections. The model is based on the physical behavior of the connections under load, and is therefore applicable to both lightweight and normal weight concrete. The model assumes that punching is a form of combined shearing and splitting, occurring without concrete crushing, but under complex three dimensional stresses. Failure is then assumed to occur when the tensile splitting strength of the concrete is exceeded. The theory is applied to predict the ultimate punching shear strength of 60 slab–column connections reported recently in literature, and designed to fail in shear, involving a large number of variables, such as type of concrete, concrete strength, tension steel ratio, compression reinforcement and loaded area. The results show very good agreement between the predicted and experimental values. The uniqueness of the model is that it incorporates many physical characteristics of the slabs and their failure behavior, and this is reflected by its ability to predict extremely well the results of tests conducted by researchers other than the authors.

Flexural vibrations of poroelastic plates

SummaryThe governing equations of flexural vibrations of thin, fluid-saturated poroelastic plates are derived in detail. The plate material obeys Biots theory of poroelasticity with one degree of porosity, while the plate theory employed is the one due to Kirchhoff. These governing equations are compared with the corresponding ones for thermoelastic plates and a poroelastic-thermoelastic analogy for flexural plate dynamics is established in the frequency domain. The dynamic response of a rectangular, simply supported, poroelastic plate to harmonic load is obtained analytically-numerically and the effects of inertia as well as of porosity and permeability on the response is assessed.

A SIMPLE CONCRETE DAMAGE MODEL FOR DYNAMIC FEM APPLICATIONS

A simple damage model for concrete is presented. The basic version of the model is a combination between the elastic-damage part of the elastoplastic-damage model of Faria & Oliver and the damage theory of Mazars. This basic version of the model takes into account most of the basic traits of concrete under monotonic static and dynamic loading, like the different response under compression and tension, the stiffness reduction with the increase of external loading and the appearance of softening behavior. This model is further enhanced with a sensitivity to the rate of loading and the ability to simulate cycling behavior, characteristics which are necessary for general cases of dynamic loading. The main advantages of this model are the employment of only one damage parameter and the investigation of the damage state in concrete under static or dynamic loading. The model is implemented into a general three-dimensional finite element program capable of treating static and general dynamic problems. The validation and performance of the proposed model is demonstrated by characteristic numerical examples.

Dynamic pressures on rigid cantilever walls retaining poroelastic soil media. Part II. Second method of solution

The problem of the determination of the dynamic pressures and the associated forces on a rigid, vertical cantilever wall retaining a semi-infinite, uniform, fully-saturated poroelastic (with or without hysteretic damping) layer of soil under conditions of plane strain is considered. The rigid wall and the base of the soil layer are both excited by an acceleration harmonically varying with time and spatially invariant. The method of solution is based on the theory of Mei and Foda and considers the total field to be approximated by the superposition of an elastodynamic problem with modified elastic constants and mass density for the whole domain and a diffusion problem for the pore fluid pressure confined to a boundary layer at the free boundary (top) of the soil layer. Both problems are solved analytically in the frequency domain. Extensive parametric and comparison studies are conducted in order to assess the range of values of the various parameters (frequency, shear modulus, Poissons ratio, porosity and permeability) for which the accuracy of the present method against the direct one, reported in a companion paper, is satisfactory.

A knowledge-based system for maintenance planning of highway concrete bridges

This paper presents a knowledge-based system that is used for maintenance planning of highway concrete bridges. The system includes functions for maintenance priority setting among bridges, feasible treatment assessment in each case, and maintenance planning for a bridge stock. Maintenance priorities are set using a scoring model with decision parameters appropriately weighted. Feasible treatments are determined based on bridge condition and other factors that accelerate deterioration. Decisions for maintenance planning result from a linear programming model and are based on priority ranking, cost and effectiveness characteristics of feasible treatments, and existing budget constraints. The system has been successfully evaluated with actual and simulated data.

Dynamic pressures on a pair of rigid walls retaining poroelastic soil

This work deals with the evaluation of the dynamic pressures and the associated forces on a pair of rigid vertical cantilever walls retaining a uniform, fully saturated poroelastic layer of soil. Hysteretic damping in the soil skeleton may also be present. Wall pressures and forces are induced by horizontal ground shaking harmonically varying with time and spatially invariant. The problem is solved analytically under conditions of plane strain. The governing partial differential equations of motion, after separation of variables and the simplifying assumptions of zero vertical normal stresses and zero horizontal variation of vertical displacements, reduce to a system of two ordinary differential equations for the amplitudes of the solid skeleton horizontal displacement and the pore water pressure, which are easily solved. The parameters examined include the ratio of the distance between walls to the height of the retained soil material and the soil material properties such as porosity, permeability and damping. The comprehensive numerical data presented indicate that the displacements, wall pressures and resultant forces are highly dependent on the distance between the walls for any values of porosity and permeability.

Analytical Model to Predict Punching Shear Strength of FRP-Reinforced Concrete Flat Slabs

The use of fiber-reinforced polymer (FRP) reinforcement in practice, especially where the corrosion of steel bars is a concern, is very much hampered by the absence of a rational theoretical method of analysis to predict the ultimate strength of structural elements, especially flat slabs and bridge decks, made with FRP-reinforced concrete. This study aims to evaluate the punching shear capacity of internally FRP-reinforced slab-column connections without shear reinforcement. The method is based on a simple analytical model developed by the authors for concrete slabs reinforced with conventional steel. The effects of the FRP elastic modulus, ultimate tensile strength, and bond characteristics, which are sufficiently different from those of steel, are incorporated in the existing model. The predictions of the proposed model for FRP-reinforced slabs are then compared with test results obtained from 28 slabs recently reported in the literature. The comparisons show excellent agreement between the predicted and experimental values. It is concluded that the proposed predictive equation presented in this study provides a convenient and reliable framework for the punching strength analysis of slabs reinforced with FRP bars or grids.

Dynamic pressures on a pair of rigid walls experiencing base rotation and retaining poroelastic soil

Abstract The dynamic response of a pair of rigid retaining walls to horizontal harmonic ground shaking is studied analytically. The two walls are elastically constrained against rotation at their base. The retained material is idealized as a uniform, fully saturated poroelastic layer of soil of constant thickness obeying Biot’s dynamic poroelastic theory. In the analysis, emphasis is given to the calculation of the wall rotation angle. The parameters examined include mainly the rotational flexibility of the wall constraint, the properties of the retained medium and the distance between the walls. The response quantities considered include the displacement of the wall, the wall pressures, and the associated forces. It is shown that, for a system experiencing base rotation, the maximum wall forces are much lower than those obtained for fixed-based rigid walls for any combination of the soil permeability and porosity and any distance between the walls.

Flexural vibrations of fissured poroelastic plates

SummaryThe governing equations of flexural vibrations of thin, fluid-saturated, poroelastic plates are derived in detail. The plate material obeys the Aifantis-Beskos theory of poroelasticity with two degrees of porosity, while the plate theory employed is the one due to Kirchhoff. The dynamic response of a rectangular, simply supported, poroelastic plate with two degrees of porosity to harmonic load is obtained analytically-numerically and the effects of porosities and permeabilities on the response are studied. A comparison between the single and double porosity material models is also made. The quasi-static problem is analysed as as special case of the dynamic one.ÜbersichtEs werden die Gleichungen, die die Biegeschwingungen von dünnen, mit Flüssigkeit gefüllten, poroelastischen Platten beschreiben, im einzelnen hergeleitet. Das Materialverhalten der Platte wird durch die Poroelastizitätstheorie von Aifandis und Beskos für Materialien mit doppelter Porosität beschrieben, während für die Platten die Kirchhoffsche Plattentheorie angewandt wird. Man erhält auf analytisch-numerischem Weg das dynamische Verhalten einer rechteckigen, einfach gestützten, poroelastischen Platte mit doppelter Porosität bezüglich einer harmonischen Belastung. Der Einfluß der Porosität und Permeabilität auf das dynamische Verhalten wird untersucht. Weiterhin werden die Modelle für Materialien mit einfacher und doppelter Porosität miteinander verglichen. Das quasi-statische Problem wird als Spezialfall des dynamischen Problems analysiert.