Evaluation of a new proposed seismic isolator for masonry walls

Low rise masonry structures are relatively inexpensive and easier to construct compared to other types of structures such as steel and reinforced concrete buildings. However, masonry structures are relatively heavier and less ductile and more vulnerable to damages in earthquakes. In this research, a new innovative low-cost seismic isolator using steel rings (SISR) is employed to reduce the seismic vulnerability of masonry structures. FEA of a masonry structure, made of concrete blocks is used to evaluate the effect of the proposed SISR on the seismic response of the structure. Two systems, fixed base and isolated from the base with the proposed SISRs, are considered. Micro-element approach and ABAQUS software are used for structural modeling. The nonlinear structural parameters of the SISRs, extracted from a recent experimental study by the authors, are used in numerical modeling. The masonry structure is studied in two separate modes, fixed base and isolated base with the proposed SISRs, under Erzincan and Imperial Valley-06 earthquakes. The accelerated response at the roof level, as well as the deformation in the masonry walls, are the parameters to assess the effect of the proposed SISRs. The results show a highly improved performance of the masonry structure with the SISRs.

Being the first railway station as bridge form above the train track, constructed in Istanbul in 1915, Göztepe Train Station is one of the most special structures conserved in terms of both structural and architectural features till today. In the scope of Marmaray CR3 project, this historical landmark has been renovated and actively used as a train station. The original structural system was composite masonry, including brick masonry walls, steel beams to support timber roof, stone masonry walls and a volta slab to elevate the station. Since the region is seismically active, requirement for seismic strengthening was mandatory in order to maintain the station. There were two main goals during this project: Modifying the main train station building with minimum intervention while achieving target seismic performance level and satisfying the increased demand requirements. Structural system of the historical structure underneath the main station required in order to increase the number of train tracks from two to three. Masonry walls on the sides of the rail tracks have been removed and replaced with reinforced concrete shear walls. While working underneath, the existing station building was suspended until the new structural system below the superstructure is constructed. A special methodology has been developed for this purpose. This method allowed keeping the entire station building intact and preventing any risk of damage to the adjacent structures. Since masonry structures are primarily vulnerable to lateral forces, the masonry structural system is converted to reinforced concrete without modifying the exterior shell of the station. This conversion is carried out by employing in-situ concrete members where special care has been taken to maintain the original facades. Additionally, a seismic isolation system composed of nine curved surface sliding devices has been installed in order to reduce the seismic actions transmitted to the upper structure. It should be noted that seismic isolation also facilitates reduction for modifications at the upper structure. Structural models have been developed based on the characteristics of the base isolation devices, and by considering the modifications on the substructure and the superstructure. As a consequence of the implemented retrofit methodology, the historical structure has been modified at the minimum level, earthquake performance is brought to the target seismic performance level, and the structure was made suitable for functioning of the increased number of tracks.

Experimental investigation and numerical simulation of masonry walls designed in different versions of Chinese codes

Understanding the development of cracks in masonry walls can provide insight into their capability for earthquake resistance. The crack development is characterized by the displacement difference of the adjacent positions on masonry walls. In seismic oscillation, the instantaneous dynamic displacements of multiple positions on masonry walls can warn of crack development and reflect the propagation of the seismic waves. For this reason, we proposed a monocular digital photography technique based on the PST-TBP (photographing scale transformation-time baseline parallax) method to monitor the instantaneous dynamic displacements of a masonry wall in seismic oscillation outdoors. The seismic oscillation was simulated by impacting a suspended steel plate with a hammer and by simulation software ANSYS (analysis system), for comparative analysis. The results show that it is feasible to use a hammer to impact a suspended steel plate to simulate the seismic oscillation as the stress concentration zones of the masonry wall model in ANSYS are consistent with the positions of destruction on the masonry wall, and that the crack development of the masonry wall in the X-direction could be characterized by a sinusoid-like curve, which is consistent with previous studies. The PST-TBP method can improve the measurement accuracy as it corrects the parallax errors caused by the change of intrinsic and extrinsic parameters of a digital camera. South of the test masonry wall, the measurement errors of the PST-TBP method were shown to be 0.83mm and 0.84mm in the X- and Z-directions, respectively, and in the west, the measurement errors in the X- and Z-directions were 0.49mm and 0.44mm, respectively. This study provides a technical basis for monitoring the crack development of the real masonry structures in seismic oscillation outdoors to assess their safety and has significant implications for improving the construction of masonry structures in earthquake-prone areas.

Empirical drift capacity models for in-plane loaded unreinforced masonry (URM) walls are derived from results of quasi-static cyclic shear-compression tests. The experimentally determined drift capacities are, however, dependent on the applied demand, i.e., on the loading protocol that is used in the test. These loading protocols differ between test campaigns. The loading protocols applied in tests are also different from the displacement histories to which URM walls are subjected in real earthquakes. In the absence of experimental studies on the effect of loading histories on the wall response, this article presents numerical simulations of modern unreinforced clay block masonry walls that are subjected to different loading protocols. The study shows that the force capacity is not very sensitive to the loading protocol. The drift capacity of walls failing in shear is, however, rather sensitive to the loading history while the drift capacity of walls failing in flexure is not. The largest difference in drift capacity of up to 100% is observed between monotonic and cyclic loading for shear controlled walls under double-fixed boundary conditions and low axial load ratios.

Experimental behaviour of unreinforced and reinforced concrete block masonry walls under uniaxial compression

Given that a significant fraction of buildings and architectural heritage in Europe's historical centers are masonry structures, the selection of proper diagnosis, technological surveys, non-destructive testing, and interpretations of crack and decay patterns is paramount for a risk assessment of possible damage. Identifying the possible crack patterns, discontinuities, and associated brittle failure mechanisms within unreinforced masonry under seismic and gravity actions allows for reliable retrofitting interventions. Traditional and modern materials and strengthening techniques create a wide range of compatible, removable, and sustainable conservation strategies. Steel/timber tie-rods are mainly used to support the horizontal thrust of arches, vaults, and roofs and are particularly suitable for better connecting structural elements, e.g., masonry walls and floors. Composite reinforcing systems using carbon, glass fibers, and thin mortar layers can improve tensile resistance, ultimate strength, and displacement capacity to avoid brittle shear failures. This study overviews masonry structural diagnostics and compares traditional and advanced strengthening techniques of masonry walls, arches, vaults, and columns. Several research results in automatic surface crack detection for unreinforced masonry (URM) walls are presented considering crack detection based on machine learning and deep learning algorithms. In addition, the kinematic and static principles of Limit Analysis within the rigid no-tension model framework are presented. The manuscript sets a practical perspective, providing an inclusive list of papers describing the essential latest research in this field; thus, this paper is useful for researchers and practitioners in masonry structures.

Carbon fibre-reinforced polymer (CFRP) emerges as a viable solution for reinforcing unreinforced masonry (URM) walls subjected to shear loads. While masonry structures are straightforward to construct, the complexity of the construction materials, especially in terms of their mechanical properties, poses challenges for numerical studies of their structural behaviour. Walls, being fundamental components in masonry construction, play a crucial role in transferring both horizontal and vertical lateral forces. This study investigates the enhancement of masonry wall behaviour through the reinforcement of CFRP. CFRP reinforcement increases ductility and strength, reducing the risk of failure under shear conditions. Additionally, CFRP composites present a practical solution to strengthening masonry structures compared to traditional reinforcement. However, brick, mortar, and CFRP have not been thoroughly investigated. Experimental tests on the bond behaviour of different configurations of CFRP-retrofitted masonry triplets have not been performed before and are therefore presented in this paper. Triplet specimens, comprising three bricks and two mortar joints, both with and without CFRP strengthening, were subjected to bond testing. The study affirms that masonry triplets strengthened with CFRP under shear loads exhibit strength levels at least four to six times greater than those without CFRP. The experimental work was carried out with eight different CFRP configurations on triplet masonry, and each test was repeated four times. Further, the bond stress-slip relationship in the case of masonry triplets with and without CFRP was predicted with new mathematical equations based on the conducted test results. These equations were included in the commercial finite element software ANSYS and used to conduct simulations of CFRP-reinforced masonry triplets. The numerical results indicate good agreement between the finite element model and the test results. The outcome of this research improves the current knowledge on the use of CFRP to reinforce masonry walls with brick and mortar, which will contribute to the understanding of the effect of CFRP on masonry structures.

Seismic behavior of autoclaved aerated concrete masonry walls reinforced with glass-fiber geogrid

Masonry structures have demonstrated their seismic vulnerability during recent world seismic events. This paper investigates in-plane seismic performance of unreinforced masonry (URM) walls before and after they are retrofit using fiber-reinforced polymer (FRP) materials. An assessment of available design formulas for evaluating both the in-plane performance of URM walls and the contribution of FRP strengthening systems was performed. Walls with two configurations of the FRP reinforcement have been analyzed: one based on FRP strips installed parallel to the mortar joints, the other characterized by FRP strips arranged along the diagonals of the wall. Based on shear–compression tests carried out on FRP-strengthened masonry walls available in the literature, a comparison between theoretical and experimental data is performed. A discussion about the FRP strains at failure of the walls is provided and values of effective FRP strains to be used for design purposes are proposed.

In Mexico, and in other Latin-American countries, masonry walls are the main structural components in housing construction, about 90% are self constructed. This kind of masonry structures are prone to damage during earthquakes because of its high stiffness in relation with its relative low strength. Thus it is necessary to investigate repair methods to recover the original strength of the damaged masonry structures. On the other hand, since vulnerable structures exist in seismic regions, it is necessary to investigate strengthening methods to increase the strength of the masonry so damage is prevented. Methods for repair and strengthening masonry walls had been studied in Mexico as well as other countries, however, most of the techniques involved are expensive. In this paper ten different techniques for rehabilitation and strengthening of concrete masonry walls were investigated using as principal elements steel and plastic straps. The experimental program including specimens with and without previous damage, was divided in three stages: (1) Two prismatic specimens for each technique were tested in diagonal compression (2) Additional tests were performed on prismatic specimens representing the best techniques (3) Four models of masonry walls were tested under reversing cyclic loads. Two walls with previous damage were tested to study the repair method and two walls in the original state for the strengthening method. The experimental results are presented in terms of the hysteretic behaviour observed. The increment in strength, deformation capacity and energy dissipation is evaluated and compared with other studies related with different repair techniques. Design criteria are proposed from the analysis of the test results. In this work it is demonstrated that with the application of tighten steel and plastic straps, according to the techniques proposed, a confinement action is attained which allows a better structural behaviour in terms of strength and deformation capacity. It is concluded that the techniques here introduced and investigated have potentiality to decrease the vulnerability of low cost housing.

Experimental study on seismic performance of damaged masonry walls reinforced with high-polymer cementitious composite material

This paper deals with delamination buckling of fibre-reinforced polymer (FRP) strips glued to reinforced concrete (RC) beams or to heterogeneous material as masonry. In the field of rehabilitation of existing civil structures, the strengthening using composite materials is becoming a frequent technique although many points have not yet been clarified. The delamination of FRP strips' layer can be often the cause of loss of the strength capacity in strengthened elements. In general, the delamination is due to loss of adhesion of FRP on the adherent material under tensile loading. This type of delamination foresees a slip of FRP strip and development of fracture energy until the detachment. Delamination buckling of FRP strips is instead due to compression loading. Although the FRP is usually adopted to improve the tensile capacity, in civil structural elements subjected to cycle loading, as RC frames in seismic areas or masonry cross walls, the loading is cyclic and the strengthening of FRP strips may be subjected to compressive stresses with separation of the layer from the adherent element. This type of delamination may significantly influence the strength, stiffness and stability. In this paper experiments on the strengthening of RC beams and masonry walls with GlassFRP strips are shown further, analytical and numerical analysis have been developed to study this mechanism of delamination which too often has been missed in the design of strengthening with FRP strips.

The strength of hollow concrete block walls, reinforced hollow concrete block beams, and columns

Recently the Armenian Missionary Association of America (AMAA) has approached the author of this paper with the request to carry out base isolation retrofitting design for the existing 2-story building with stone bearing walls and to simultaneously convert it into a 3-story kindergarten. In Armenia seismic isolation of existing buildings is becoming a more common method of providing protection from earthquake damage. Thanks to the author’s works in nowadays Armenia is well known as a country where seismic (base and roof) isolation systems are widely implemented in construction of new and retrofitting of existing buildings. The number of seismically isolated buildings per capita in Armenia is one of the highest in the world – second after Japan. The paper given below emphasizes that Armenia achieved significant results also in local manufacturing/testing of seismic isolation laminated rubber-steel bearings (SILRSBs). Several remarkable projects on retrofitting by base isolation of the existing buildings like apartment, school, hotel and hospital buildings are briefly mentioned in the paper to demonstrate the retrofitting experience accumulated in Armenia. Based on the gained experience further developments take place and unique base isolation structural concepts and technologies created by the author are applied more and more to the existing buildings. In this paper base isolation retrofitting design and analysis by the Armenian Seismic Code for the 2-story building with stone bearing walls is described. This will be a first application of base isolation retrofitting technology to an existing stone building with simultaneous increase of the number of its floors by one. The other important factor is that applied structural concept allows retrofitting by base isolation when reconstruction works in superstructure and construction of the additional 3-rd floor were going on in the same time.