Zbigniew Zembaty

Spatial response spectra and site amplification effects

A simplified analysis of local site amplification effects on the seismic response of multi-support structures is presented. The site effects are modeled by considering reflections and transmission of vertically propagating shear waves from bedrock to the surface through a soil layer. A random vibration-based response spectrum of a simple oscillator on two supports, one of which is founded on rock outcrop and the other on soil layer, is formulated in order to study the influence of non-uniform excitations on multi-support structures. Joint inertial and pseudo-static effects in the overall response are studied in detail. The resulting response spectra are formulated as displacement and force spatial seismic coefficients, convenient for sensitivity analyses. Numerical analyses of the response spectra as affected by various soil parameters are included.

Tutorial on Surface Rotations from Wave Passage Effects: Stochastic Spectral Approach

This article presents a concise review of the methods to obtain spectral densities of the rotational components of seismic ground motion from the spectral densities of both the translational components and wave propagation parameters. The rotational components are obtained by decomposing ground motion at the site into body and surface wave contributions with random amplitudes. To obtain rotation the resulting stochastic fields of body and surface waves are differentiated with respect to spatial coordinates. Assumption of plane waves radiating from a point source leads to two rotational components: rocking around a horizontal axis perpendicular to the source-site direction and torsion around a vertical axis. Construction of the rocking acceleration spectral density from P -, SV -, and Rayleigh-wave contributions as well as torsional spectral density from SH and Love waves (in terms of translational spectral densities and wave parameters) are discussed in detail. A short numerical analysis illustrates the proposed approach. A shift of the rotational spectra into higher frequencies compared to respective translational spectra is observed.

On the sensitivity of bridge seismic response with local soil amplification

The paper presents a numerical sensitivity study of the local site effects on structural response. Following a recently developed model of spatial coherency and a concept of a simple site coefficient the local site effects are modelled as filtrations of excitation processes with a frequency shift. An analysis of a bridge response with supports founded on different soils is carried out. The joint effects of dynamic response and pseudostatic motion are considered. Two types of response are analysed: longitudinal and transverse. The differences between dynamic displacements and force responses are pointed out.

Assessment of seismic resistance of masonry structures including boundary conditions

The paper is devoted to the investigation of seismic response of the masonry structure and describes experiences with modelling of boundary conditions during the test of large heavy model on 6DOF shaking table. The main aim of the research was how to increase dynamic resistance capacity of old masonry buildings including the medium and strong seismic effects. The results of theoretical and numerical analyses are compared including initial forecasting calculations made before any test started. The emphasis is given to the boundary conditions reached during the excitation of the large masonry model via shaking table. Strengthening and retrofitting procedures and their effects are discussed when special fibre mortar is used for repair and strengthening of masonry parts of structure.

Application of rotation rate sensors in an experiment of stiffness ‘reconstruction’

Preliminary results of an application of rotation rate sensors in dynamic identification of a vibrating beam are reported. Three rotational sensors, measuring the response of a cantilever beam to kinematic harmonic excitations are applied in the reconstruction of its stiffness. A successful reconstruction of 15% stiffness drops is demonstrated. With the development of angular sensors and the decrease in their cost one can expect further progress of this new area of vibration-based damage detection. (Some figures may appear in colour only in the online journal)

Rotational Ground‐Motion Records from Induced Seismic Events

Surface rotational ground‐motion records that were collected by a network of deep mining exploration monitoring in the Polish region of the Upper Silesian Coal basin are reported. A set of 51 rotation records acquired during the first two months of the recording program is analyzed. The three strongest records are discussed in detail in this article. Thus far, the maximum measured rotation velocity has reached 0.03°/s, whereas the respective maximum rotational acceleration was equal to 2.53°/s2. Based on the maximum horizontal ground velocity of 2  cm/s, this corresponds to the modified Mercalli intensity (MMI = IV). The recorded “time history” records of ground rotations have similar durations to those of their respective translational records. However, their Fourier spectra are shifted to higher frequencies in a characteristic way, as predicted by earlier, theoretical considerations. The long‐term objective of the research program is to acquire robust surface rotation records that correspond to MMIs VI or even VII, since mine tremors with a magnitude of 4 or higher are expected to occur in this area in the near future.

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s.

Stochastic modeling of seismic surface rotations

In this paper, a stochastic analysis of surface rotations during earthquakes is presented. The surface motion is modeled by a spacetime random field. A method to obtain rotation based on direct differentiation of the random field is proposed with a reference to a second method based on wave decomposition. The first method leads to a spectral density of surface rotations in terms of point translation spectral density, coherence function and apparent waves velocity, while the second method formulates the rotational spectrum in terms of point translation spectral density and wave parameters. The advantages and disadvantages of both methods are discussed in detail.

Application of Rotation Rate Sensors in Measuring Beam Flexure and Structural Health Monitoring

This paper presents a new approach to measure and monitor structural vibrations in civil and seismic engineering which uses new rotational sensors which can measure flexural vibrations of a beam axis. First a rotation rate sensor (measuring rotational velocity) is tested with respect to its ability to follow changes of strains in a beam during its vibrations. Next a system of rotation rate sensors is applied to effectively reconstruct stiffness variations of a simple, cantilever beam. It is demonstrated that the rotation rate sensors can be used to effectively reconstruct three unknown stiffness drops of a cantilever beam under harmonic vibrations. Both experiments are carried out using small plexi beams in laboratory scale. At this moment the rotational sensors are still rather expensive and with limited range and accuracy. However with the time passing by, their quality will improve and prices decrease making them very effective instruments in seismic engineering and health monitoring of structural systems.

Estimation of Rotational Ground Motion Effects on the Bell Tower of Parma Cathedral

The purpose of this paper is to present results of calculations of seismic response of the old Parma Bell Tower with and without the rotational, rocking seismic effects as modeled in the European seismic code: Eurocode 8 (part 6: Towers, Masts and Chimneys). A detailed, finite element model of the tower was prepared, which led to the solution of its eigen problem and to conventional dynamic, response modal analysis. Next a simplified rod model, equivalent to the detailed finite element model was prepared, taking into account soil compliance as well as the rocking excitation effects. The results of computations show rather substantial, 30–40 % contribution of the rocking excitations in the overall seismic response.