Static Cyclic Shear Research Articles

Dynamic characteristics of coral silt with consideration of static-cyclic loading coupling

Coral silt, a type of coral soil with more than 50% silt content, is formed during the process of land reclamation. Given the frequent action of waves, wind, earthquakes and other dynamic loads, the cyclic dynamic shear characteristics of coral silt are important for determining the seismic safety of reef infrastructures. A series of symmetrical and asymmetrical cyclic simple shear tests were performed to characterize the cyclic behavior of coral silt with particular consideration given to the static-cyclic shear stress coupling. Two empirical formulas for the undrained peak shear strength and critical state strength in monotonic simple shear tests are proposed. For both symmetrical and asymmetrical-loading cyclic simple shear tests, a CSR threshold value lying between 0.05 and 0.075 controls the final failure. The cyclic shear stress significantly influences the cyclic deformation, cyclic pore water pressure, cyclic strength, and cyclic shear modulus of coral silt.

I-Shaped Unreinforced Masonry Wallettes with a Soft-Layer Bed Joint: Behavior under Static-Cyclic Shear

AbstractIn order to extend the latest findings on the in-plane shear behavior of rectangular unreinforced masonry (URM) wallettes with soft-layer bed joints and gain insight into the possible influ...

Masonry walls with a multi-layer bed joint subjected to in-plane cyclic loading: An experimental investigation

A series of static-cyclic shear tests on full-scale unreinforced masonry (URM) walls with multi-layer bed joints have been performed within a research project on the seismic behaviour of unreinforced masonry walls with soft layer membrane placed in the bed joint to induce sliding. Walls were made using typical perforated Swiss clay blocks and standard cement mortar and the so-called multi-layer bottom bed joints, which comprise a core soft layer protected by two layers of extruded elastomer and placed in the middle of mortar joint. The preliminary testing phase was aimed at choosing the most suitable core soft layer type among the four types considered (rubber granulate, cork, cork-rubber granulate and bitumen). The main testing phase comprised five tests on storey-high URM specimens with rubber granulate core soft layers performed to investigate the influence of the size, the pre‐compression level and the aspect ratio on the seismic behaviour of URM walls with a multi‐layer bed joint. Sliding occurred in all tested specimens. However, the final failure mode as well as the displacement capacity of test specimens were governed by the extent of shear and tensile (vertical) cracks that developed from the bottom brick course. The response of specimens can be interpreted using a multilinear horizontal force-displacement response idealization, whose parameters can be estimated using the proposed equations.

Masonry elements with multi-layer bed joints: Behaviour under monotonic and static-cyclic shear

The goal of the research project presented here is to investigate the effect of multi-layer bed joints on the shear behaviour of unreinforced masonry elements subjected to cyclic actions, and to assess the shear mechanical characteristics of multi-layer bed joints. Such joints consist of a core soft layer protected with two thin extruded elastomer membranes, which in turn are placed in a bed mortar joint. The extruded elastomer membranes are employed to prevent and/or limit the deterioration of the core soft layer during the cycling action, which has been observed in previous investigations. Five different core soft layer materials, namely rubber granulate, cork-rubber granulate, cork, bitumen and polyvinylchloride were employed. A total of 57 clay block masonry triplets were subjected to both monotonic and static-cyclic loading under varying levels of pre-compression.The shear behaviour of the specimens was greatly influenced by the applied pre-compression level and by the loading speed. Increasing the level of pre-compression leads to the higher values of shear strength. The same is true for increasing loading speed. Further, for the prediction of the failure shear force a Mohr–Coulomb failure criterion with zero cohesion can be applied. Finally, experimental findings showed that extruded elastomer layers largely fulfilled the intended protective role.The results indicate that multi-layer bed joints with adequate material properties have the potential to change the typical brittle shear response of unreinforced masonry walls to a more desirable quasi-ductile behaviour. Moreover, based on the observed hysteretic behaviour, considerable energy dissipation could be expected in masonry structures with multi-layer bed joints. Such behaviour would be desirable for enhanced seismic performance.

Displacement capacity of contemporary unreinforced masonry walls: An experimental study

A research project on the displacement capacity of contemporary unreinforced masonry (URM) walls is underway at the Institute of Structural Engineering of ETH Zurich. The development of the basis for the displacement-based design of URM structures is the prime objective of the present project. In the experimental phase of the project, a total of 10 static-cyclic shear tests on full-scale URM walls made of clay and calcium-silicate blocks were performed to investigate the effects of various factors, i.e. unit type, vertical pre-compression level, aspect ratio, size, and boundary conditions, on the displacement capacity of URM walls. This paper presents and discusses the obtained test results. All the walls (regardless of their failure mode) exhibited limited displacement capacity. The test results show that as the vertical pre-compression level increases, the displacement capacity decreases. Furthermore, they indicate a possible reduction in the displacement capacity of URM walls in the case of an increase in the height or a decrease in the aspect ratio, i.e. the height divided by the length. It is also shown that the values recommended by the current codes of practice for the displacement capacity of URM walls cannot be considered as reliable. Finally, a simple empirical model for the displacement capacity of contemporary URM walls is proposed, based on the results obtained from the tests.

Masonry wallettes with a soft layer bed joint: Behaviour under static-cyclic loading

The main goal of the research project presented herein is to investigate the effect of damp proof courses and soft layer wall bearings on the seismic shear behaviour of unreinforced masonry walls subjected to cyclic actions, in particular how the lateral load resisting mechanism of the wall is influenced thereby. Unreinforced clay block masonry wallettes with soft layers of three different thicknesses (3, 5 and 10mm), and two different materials (rubber granulate and extruded elastomer) were subjected to static-cyclic shear under varying levels of pre-compression. The soft layer was placed either in the first bed joint of the wallette or in the interface joint between the wallette and the underlying concrete slab.Soft layers were beneficial when the tested wallettes failed in sliding. Such sliding failure was observed for wallettes with rubber granulate soft layers placed in the first bed joint. This resulted in quasi-ductile behaviour of the wallettes, with a displacement and energy dissipation capacities significantly larger than those of the conventional unreinforced masonry control specimens. Furthermore, wallettes failing by sliding along the joint containing the soft-layer showed considerably less damage compared to wallettes that exhibited other failure modes at the same displacements levels. The progressive deterioration of the rubber granulate layers lead to a decreasing shear strength at larger horizontal displacements. Wallettes with extruded elastomer layers and wallettes with layers placed in the interface joint did not fail in sliding. Apart from slightly increased energy dissipation, no beneficial effect on the shear force–deformation behaviour of the wallettes could be observed in these tests.The results indicate that soft-layers with adequate material properties placed in the first bed joint have the potential to change the typical brittle shear response of unreinforced masonry walls to a more desirable quasi-ductile behaviour.

On the Use of CFRP Sheets for the Seismic Retrofitting of Masonry Walls and the Influence of Mechanical Anchorage

This work reports the outcomes of an extensive experimental campaign on the retrofitting of masonry walls by means of carbon fiber reinforced polymer (CFRP) sheets, carried out at University of Applied Sciences (UAS) Fribourg. In the first stage, static-cyclic shear tests were conducted on the masonry walls, followed by a second stage of tensile tests on alternative configurations of mechanical anchorage so as to assess the effects on the structural response and to identify the associated limits. In the static-cyclic shear tests, it was found that the resistance of masonry walls retrofitted with CFRP sheets was improved by up to 70%, and the deformability was improved by up to 10% in comparison to the un-retrofitted specimens. The experimental tests conducted on alternate configurations of mechanical anchorages indicate that the tested materials and configurations rely heavily on details. The sensitivity of CFRP sheets to edges, non-uniformities on any adherend, and bonding defects can cause premature CFRP failure and, hence, pose problems for the efficient design of a retrofitting scheme. As indicated by the results of this investigation, effective anchorage can be achieved when eccentric loading of the mechanical anchorage is avoided and a smooth bonding surface is guaranteed.

Retrofitting Masonry Walls with Carbon Mesh

Static-cyclic shear load tests and tensile tests on retrofitted masonry walls were conducted at UAS Fribourg for an evaluation of the newly developed retrofitting system, the S&P ARMO-System. This retrofitting system consists of a composite of carbon mesh embedded in a specially adapted high quality spray mortar. It can be applied with established construction techniques using traditional construction materials. The experimental study has shown that masonry walls reinforced by this retrofitting system reach a similar strength and a higher ductility than retrofits by means of bonded carbon fiber reinforced polymer sheets. Hence, the retrofitting system using carbon fiber meshes embedded in a high quality mortar constitutes a good option for static or seismic retrofits or reinforcements for masonry walls. However, the experimental studies also revealed that the mechanical anchorage of carbon mesh may be delicate depending on its design.

Seismic effects in secondary containments: Research needs

The purpose of this paper is to discuss the status of current and projected research on the behavior of nonprestressed secondary containment structures carrying combined pressurization and seismic shear. Ongoing experimental research at Cornell University on specimens carrying combined biaxial tension and static cyclic shear is described. The remainder of the paper treats research needed to better predict the response of containments to seismic effects and to serve as the basis for improved design methods for reinforced concrete containments.