The possibility of the use of a layer of natural material under foundations for seismic base isolation was investigated. The dissipation of seismic energy of a low-cost natural material with adequate thickness, bearing capacity, and lateral and vertical stiffness, which can serve as an optimal solution for seismic base isolation under the foundations of many structures, was tested. This paper presents the results of a brief experimental study to determine the effectiveness of ordinary limestone sand under the foundation of a cantilever concrete column to increase its seismic resistance. The behavior of small-scale columns with three substrates below the foundation (rigid base, the thin layer of limestone sand, and the thick layer of limestone sand) was investigated by the shake table. The column was exposed to a set of horizontal base accelerations until structure collapse. It was concluded that a layer of limestone sand of appropriate thickness and compressibility can serve as the means a seismic base isolation. The nonlinear numerical model for the dynamic analysis of planar concrete structures coupled with soil is briefly presented and verified by the performed experimental tests.

Using a shake-table, the effects of several stone pebble layer parameters (the layer thickness, the fraction of pebbles, the pebble compaction, the pebble moisture, the vertical contact stress below the foundation, and the effect of repeated excitations) on layer aseismic efficiency were investigated. For each considered parameter, a model of a rigid building on an aseismic layer was exposed to four different accelerograms, with three levels of peak ground acceleration (PGA), while all other layer parameters were kept constant. For each test, the characteristic displacements and accelerations were measured. Based on the test results, the main conclusions regarding the effect of the considered parameters on the effectiveness of the adopted aseismic layer are given.

The results of a shake table study of the efficiency of a seismic base isolation using a layer of natural stone pebbles are presented. Models of stiff and medium-stiff buildings were tested. Case studies were conducted with the foundation of model on the rigid base and on four different layers of pebbles (thin and thick layer with small and large pebbles). Four different horizontal accelerograms were applied, and the characteristic displacements, accelerations, and strains were measured. Strains/stresses of the tested models remained in the elastic area. It was concluded that the effectiveness of the stone pebble layer under the foundation, i.e., the reduction in the seismic forces and stresses in the structure compared to the classical solution of foundation, significantly depends on the type of the applied excitation and depends relatively little on the layer thickness and pebble fraction. The results of the study showed that a layer of pebbles can significantly reduce the peak acceleration and strains/stresses of the model, with acceptable displacements. Further research is expected to confirm the effectiveness of this low-cost and low-tech seismic base isolation and to pave the way to its practical application.

The paper presents the testing results of a small scale model of cantilever concrete columns on a shake table, with varying stirrup spacing. During the test, earthquake accelerations were gradually increased. Displacements and accelerations at the top of the earthquake‐like columns, as well as the strains in the concrete, vertical bars and stirrups in characteristic points, were measured during each shake table excitation. It was concluded that the distance between stirrups in the concrete column has a significant effect on the size of the cracking zone in the concrete, as well as on the number, location, spacing and width of cracks. By reducing the distance between the stirrups, columns becomes stiffer. That leads to smaller displacements and slightly larger inertial forces under excitation with low accelerations. Maximum displacements at the top of the column with denser stirrups are slightly smaller and the crack zone and crack width in concrete is therefore significantly reduced.

First, the basic characteristics of macro and micro masonry models in numerical analyses of masonry structures are discussed. Afterwards, developed numerical macro and micro masonry models, intended for the nonlinear static and dynamic analysis of unreinforced and confined masonry walls, as well as of masonry-infilled frames, are briefly presented. The models are tested on previously performed experimental tests of masonry-infilled steel frame under horizontal static force and masonry-infilled steel frame on a shaketable. The precision of both models is compared. It is concluded that both numerical models can provide reliable results. However, the macro model has more advantages for wide practical application.

Firstly, a discussion about the application of beam-column (1D) and plane (2D) finite elements in the numerical analysis of the planar concrete frames is presented. Then, briefly are presented two numerical models for nonlinear static analysis of planar concrete frames, first based on beam-column (1D) elements and second on plane (2D) finite elements, which can simulate their main nonlinear effects. The presented models are verified on two experimental test results. Good agreement was obtained between the experimental and the numerical results, which confirm the possibility of practical application of both presented numerical models. However, their further verifications are necessary.

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Prikazani su rezultati eksperimentalne studije efikasnosti seizmičke izolacije pomoću sloja od prirodnih kamenih oblutaka. Ispitivani su modeli krute i srednje krute zgrade. Razmatrani su slučajevi oslanjanja modela na krutu podlogu te na četiri različite podloge od oblutaka (tanka i debela podloga sa sitnom i krupnom frakcijom oblutaka). Aplicirana su četiri različita horizontalna akcelerograma i mjereni karakteristični pomaci, ubrzanja i deformacije na testiranim modelima. Sve deformacije/naprezanja modela ostala su u elastičnom području. Zaključeno je da efikasnost sloja od kamenih oblutaka ispod temelja, u odnosu na klasično rješenje s krutom podlogom, značajno ovisi o tipu apliciranog akcelerograma i relativno malo o razmatranim debljinama sloja i frakcijama oblutaka. Rješenje se pokazalo vrlo efikasnim, uz smanjenje potresnih sila čak do oko 70 %. Ključne riječi: potresna platforma, seizmička izolacija, prirodni kameni oblutci