Matija Gams

Shaking table study and modelling of seismic behaviour of confined AAC masonry buildings

The response of autoclaved aerated concrete confined masonry buildings to seismic ground motion has been studied. Three 1:4 scale models of residential buildings with the same distribution of walls in plan but different types of floors and number of stories have been tested on a uni-directional shaking table. Lightweight prefabricated slabs have been installed in the case of the three-storey model M1, whereas reinforced concrete slabs have been constructed in the case of three-storey model M2 and four-storey model M3. Model M1 was subjected to seismic excitation along the axis of symmetry, whereas models M2 and M3 were tested orthogonal to it. Typical storey mechanism, characterised by diagonal shear failure mode of walls in the ground floor in the direction of excitation has been observed in all cases. Taking into consideration the observed behaviour, a numerical model with concentrated masses and storey hysteretic rules has been used to simulate the observed behaviour. Storey resistance curves calculated by a push-over method and hysteretic rules, which take into account damage and energy based stiffness degradation hysteretic rules, have been used to model the non-linear behaviour of the structure. Good agreement between the experimentally observed and calculated non-linear behaviour has been obtained.

Strengthening Brick Masonry by Repointing – An Experimental Study

The results of an experimental study aimed at seismic strengthening of brick masonry walls by the use of repointing and reinforcing bed joints are presented. Within the testing campaign eight walls were tested by cyclic shear. Two of the walls were used as control walls, whereas the other six walls were strengthened. Two kinds of mortar were used for repointing and steel and GFRP materials were used for reinforcement. In case of one wall, reinforcement was laid into a flexible polymer in order to distribute the stresses in the steel bar to a larger area. The tests indicate that repointing can be a very successful strengthening technique. Best results were obtained in case of repointing by mortar with low elastic modulus and steel reinforcement.

Strengthening of stone masonry walls with composite reinforced coatings

The efficiency of strengthening traditionally built three-leaf stone masonry walls with different types of composite reinforced coating has been investigated. Glass fibre grid in single component fibre reinforced mortar and glass fibre fabric in epoxy resin matrix were used as coating materials. Four different coating types have been applied, with coating placed on one or both sides of the walls, anchored or not anchored to the masonry at the corners of the walls. Ten walls have been tested by subjecting them to cyclic shear loading at constant precompression, among them two walls in the original state as the control specimens. Four walls have been first tested up to the occurrence of the first significant damage, strengthened and then re-tested up to collapse, whereas four walls have been strengthened undamaged and tested up to collapse. All walls failed in shear. Significant increase in lateral resistance with regard to control walls was observed in all cases, up to 2.5–4.0-times the resistance of the control walls. The degree of improvement did not depend on the type of coating but on the technology of application. Although the coating increased the rigidity of the walls, displacement and energy dissipation capacities have been also improved.

Seismic strengthening of brick masonry by composite coatings: an experimental study

In this paper an extensive experimental study is presented in which the efficiency of seismic strengthening of brick masonry walls, typical in Slovenia and wider region, is analyzed. The results of cyclic shear tests of 24 walls are presented. The walls were strengthened using different materials and different layouts of the reinforcement. Externally bonded glass and carbon composites were used for strengthening and were applied to the wall by either cementitious mortar or epoxy resin. 12 walls were first tested up to the point where repair was still feasible and then strengthened and retested until collapse to study the efficiency of repair/strengthening. The rest were strengthened in the undamaged state. In addition to cyclic shear tests, the tests of the composite-masonry bond in double shear lap configuration were also performed. Results of cyclic shear tests show significant differences between different types of strengthening with shear strength resistance improvements of up to 130%. The displacement capacity was barely increased, except for one type of strengthening, thus confirming the importance of correct strengthening layout and anchoring. The observed failure mechanisms were characterized by debonding of coating which resulted in sudden resistance and stiffness degradation, leading to brittle collapse of the walls. The performance of composite-to-masonry bond in double shear lap test was significantly better than in cyclic shear tests. Finally, the resistance of strengthened walls is estimated using simple numerical models based on measured bond strength.

Preliminary study on the influence of fibre orientation in fibre reinforced mortars

The influence of steel fibres in fibre reinforced mortars is considered in the paper. Fresh mortar samples with randomly distributed fibres are placed in a spiral coil and exposed to electromagnetic filed so as to achieve orientation of fibres. The location and orientation of fibres is defined by x-ray images. The bending strength testing with deflection checking using the ICS system (Digital Image Correlation System) is conducted. Considering the fibre orientation and load applied, the results exhibit better energy dissipation and greater energy at fracture in case of samples with oriented fibres.

Seismic behaviour of masonry buildings built of low compressive strength units

Seismic behaviour of masonry buildings, built of low compressive strength units, is discussed. Although such materials have already been tested and approved for use from mechanical and thermal insulation point of view, the knowledge regarding their structural behaviour is still lacking. In order to investigate the resistance and deformation capacity of this particular type of masonry construction in seismic conditions, a series of eight walls and model of a two-storey full scale confined masonry building have been tested by subjecting the specimens to cyclic shear loads. All tests were conducted under a combination of constant vertical load and quasi static, cyclically imposed horizontal load. The behaviour of tested specimens was of typical shear type. Compared with the behaviour of plain masonry walls, the presence of tie-columns resulted into higher resistance and displacement capacity, as well as smaller lateral resistance degradation. The response of the model was determined by storey mechanism with predominant shear behaviour of the walls and failure mechanism of the same type as in the case of individual confined masonry walls. Adequate seismic behaviour of this particular masonry structural type can be expected under the condition that the buildings are built as confined masonry system with limited number of stories.

Seismic Response of URM Walls Strengthened with FRP Reinforced Coating

A set of individual URM walls as well as an assemblage of a three-storey URM hollow clay block masonry structure composed of two shear- and two cross-walls have been tested in original and strengthened state. As a method of strengthening, the coating of the walls, consisting of glass fiber reinforced polymer (GFRP) grid laid in fiber reinforced cementitious mortar matrix (sometimes called textile reinforced mortar), anchored to the walls with glass fiber anchors, has been used. All specimens were subjected to constant vertical load simulating the effect of gravity loads and cyclic horizontal displacements with step-wise increased amplitudes, induced either at the top of the walls or at the floor levels of the assemblage, simulating the effect of seismic loads.The observed behaviour and failure mechanisms were of the shear type. The results show that by the application of FRP reinforced coatings, the seismic performance of URM structures can be significantly improved. As the results of experiments indicate, the energy dissipation, displacement capacity and shear resistance of URM increase substantially. In this regard, adequate anchoring of coating to the masonry and into the r.c. floor structures is essential.

Preliminarno istraživanje utjecaja orijentacije vlakana u mikroarmiranim mortovima

The influence of steel fibres in fibre reinforced mortars is considered in the paper. Fresh mortar samples with randomly distributed fibres are placed in a spiral coil and exposed to electromagnetic filed so as to achieve orientation of fibres. The location and orientation of fibres is defined by x-ray images. The bending strength testing with deflection checking using the ICS system (Digital Image Correlation System) is conducted. Considering the fibre orientation and load applied, the results exhibit better energy dissipation and greater energy at fracture in case of samples with oriented fibres.