Milos Novak

Nonlinear analysis for dynamic lateral pile response

An analysis of pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behavior, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. Furthermore, the effect of neighbouring piles is taken into account for piles in a group. The validity of the approach was examined and a reasonable agreement with field tests and more rigorous solutions was found. Equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are presented.

Nonlinear lateral interaction in pile dynamics

Abstract A model for pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behaviour, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. The approach is used to establish equivalent linear stiffness and damping parameters of single piles as well as dynamic interaction factors for approximate nonlinear analysis of pile groups. The applicability of these parameters to the pile-group analysis was examined, and a reasonable agreement with the direct analysis was found. The superposition technique may be used to analyze the response of small pile groups. Also, the dynamic stiffness of pile groups is greatly affected by both the nonlinear behavior of the soil and the slippage and gapping between the pile and soil. For a basic range of soil and pile parameters, equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are provided.

Free convection heat transfer in multiple vertical channels

Abstract Free convection heat transfer in multiple parallel vertical channels with isothermal walls is considered in this paper. Systems consisting of two, three and an infinite number of channels located side by side and with aspect ratios (the ratio of channel height to its width) ranging from 5 to 20 and for Grashof numbers, based on the channel width, up to 10 5 were investigated numerically. Results show that the heat transfer in a channel is affected by its interaction with the neighboring channels. This interaction depends upon the number of participating channels; it increases with an increase of the Grashof number and decreases with an increase of the distance between the channels. Compared with a single isolated channel, the Nusselt number in the case of a two-channel system increases by up to 5% on the channel inner wall (wall closer to the other channel) and decreases by up to 5% on the channel outer wall. When an infinite number of channels is present (periodic configuration), the Nusselt number increases by up to 18%. When heat transfer only in the entrance region of the channel is considered (the first 10% of the channel total length), the interaction between the channels increases the corresponding Nusselt number by up to 38% on the channel inner wall and decreases it by up to 33% on the channel outer wall for a two-channel system and increases it by up to 48% for the periodic configuration. Correlations permitting quick determination of the Nusselt numbers for both configurations are given.

Wind tunnel studies of cable roofs

Abstract Behaviour of large cable roofs in turbulent wind is studied in the wind tunnel using both rigid and aeroelastic models. The similarity requirements are reviewed with special attention being paid to the effect of the air enclosed under the roof. A similarity law for the modeling of this enclosure is presented and its role in free vibration as well as wind induced vibration is investigated. A wind tunnel study of a large tension roof is described.

Structural response to wind with soil-structure interaction

Abstract The effect of soil-structure interaction on structural response to wind is theoretically investigated. Excitation due to gusting wind and vortex shedding is considered for structures supported by flexible foundations in the form of mats (raffs) or piles. Effect of foundation flexibility on modal properties is discussed and examples of response of buildings to gusting wind and of chimneys to vortex shedding are given.

Damping of structures due to soil-structure interaction

Abstract Structures resting on flexible foundations can derive a significant amount of damping from energy dissipation in soil. This damping can sometimes be exploited to reduce structural response to wind and particularly response to vortex shedding. Methods of evaluating the effect of soil-structure interaction on damping are described and compared. A few examples are given.

Vibration of hammer foundations

Abstract Hammer foundations are often deeply embedded and highly damped. Yet, in the prediction of vibration amplitudes, damping is usually neglected. In this paper, two methods are proposed which make it possible to incorporate damping in the analysis. One method, suitable for hand calculations, is based on an energy consideration and the other, suitable for computer analysis, utilizes the notions of the complex eigenvalue problem. It is shown that damping derived from soil may reduce foundation amplitudes very significantly, e.g. 50%, particularly for large, embedded foundations. Methods for the evaluation of foundation stiffness and damping which are needed in the analysis are outlined.

Response of hammer foundations to pulse loading

Abstract The response of hammer foundations to the blows of the head can be considered either as caused by the initial velocity imparted to the anvil or as a pulse. This paper presents a solution based on the latter assumption. The approach is based on the notion of complex eigenvalues, incorporates damping in a rigorous way and is particularly suitable for more complex types of hammer foundations featuring more than one degree of freedom.

Effect of leakage and acoustical damping on free vibration of light roofs backed by cavities

Abstract Free vibration of light roofs backed by cavities with wall openings is investigated both theoretically and experimentally. The interaction between the roof and the outside air as well as the air enclosed by the cavity is considered and the air leakage through wall openings is accounted for. Approximate formulae for natural frequencies and modal damping are presented. The experimental program comprises one model with a membrane roof and one with a flexible plate roof. Comparison of theoretical results with experimental data is made.

Vertical partitions in slender rectangular cavities

Abstract Two-dimensional laminar natural convection heat transfer in slender rectangular cavities equipped with two small vertical partitions, located in the middle of horizontal walls, is studied numerically. The evaluations are carried out for cavity aspect ratios up to 45 and for Grashof numbers, based on the cavity height, up to 5 × 10 8 . As shown, for this range of aspect ratios and Grashof numbers, two small vertical partitions of the same length, made of glass and located in the mid-plane of the cavity, may reduce the cavity mean as well as peak Nusselt numbers by up to 6 and 27 percent, respectively.