Cyclic Responses of Two-Side-Connected Precast-Reinforced Concrete Infill Panels with Different Slit Types

This study aimed to study the cyclic behavior of two-side-connected precast-reinforced concrete infill panel (RCIP). A total of four RCIP specimens with different slit types and height-to-span ratios modeled at a one-third scale were tested subjected to cyclic lateral loads. The failure mode, hysteretic behavior, lateral strength, stiffness degradation, ductility, and energy dissipation capacity of each RCIP specimen were determined and analyzed. The specimens experienced a similar damage process, which involved concrete cracking, steel rebar yielding, concrete crushing, and plastic hinge formation. All the specimens showed pinched hysteretic curves, resulting in a small energy dissipation capacity and a maximum equivalent viscous damping ratio lower than 0.2. The specimens with penetrated slits experienced ductile failure, in which flexural hinges developed at both slit wall ends. The application of penetrated slits decreased the initial stiffness and lateral load-bearing capacity of the RC panel but increased the deformation capacity, the average ultimate drift ratios ranged from 1.41% to 1.99%, and the lowest average ductility ratio reached 2.48. The specimens with high-strength concrete resulted in a small slip no more than 1 mm between the RC panel and steel beam, and the channel shear connectors ensured that the RC infill panel developed a reliable assembly with the surrounding steel components. However, specimens with concealed vertical slits (CVSs) and concealed hollow slits (CHSs) achieved significantly higher lateral stiffness and lateral strength values. Generally, the specimens exhibited two-stage mechanical features. The concrete in the CVSs and CHSs was crushed, and flexural plastic hinges developed at both ends of the slit walls during the second stage. With increasing concrete strength, the initial lateral stiffness and lateral strength values of the RCIP specimens increased. With an increasing height-to-span ratio, the lateral stiffness and strength of the RC panels with slits decreased, but the failure mode remained unchanged.

Geogrid Reinforced Brick Buildings for Earthquake Disaster Mitigations

In the event of a severe earthquake, the walls of brick buildings experience in-plane shear and out-of-plane bending, leading to diagonal crack and corner failure respectively. In this study, an experimental investigation was carried to observe the above damages on brick masonry buildings reinforced with geogrid embedded in bed joint mortar of the walls. It was observed that the geogrid reinforced brick panels showed better shear strength, lateral strength, ductility, etc. A qualitative comparison was made using a sinusoidal shake table test on a one-fourth single-room building model consisting of two sets of corner walls with and without geogrid reinforcement. It was observed that the corner wall without reinforcement showed crack initiation at 0.45g and complete collapse with over toppling of the transverse wall at 0.90g, while no sign of damages for the corner walls strengthened with geogrid reinforcement for any level of shaking.

Damped outrigger semi-active control for seismic vibration mitigation

In earlier days, the only way to resist the lateral loads was to increase the lateral strength of the structure obtained by making larger cross sections and massive buildings. Structural control is one of the solutions and important topics in both points of view of security and comfort in recent years. To reduce the effect of seismic energy, one of the structural forms used is the outrigger. In recent years, supplementary devices are installed into the outrigger structure so that damping of the structure increases and helps in mitigating the vibration, this concept is called damped outrigger. In this study, a damped outrigger structure replicating St. Francis Shangri-La Place skyscraper is excited for the El-Centro earthquake, and the Kobe earthquake is numerically modeled with viscous dampers and Magneto-Rheological damper to compare its effectiveness. The finite element approach is used for the analysis of the structure using Bernoulli’s Euler beam theory in modeling the core of the structure as a beam element. The state-space approach is used in modeling the structure, dampers, and controller interface in MATLAB and Simulink, then results are obtained for the peak value of displacement, acceleration, and mean values of the response of the structure. The results are discussed, which shows the significant distinction between uncontrolled and controlled responses.

In-Plane Seismic Response of Unreinforced and Jacketed Masonry Walls

Low-rise residential and public masonry structures constitute a large portion of the building patrimony, yet they were erected during the massive reconstruction of Southeast Europe after World War II before any design rules existed in the engineering praxis. Unreinforced unconfined masonry buildings (URM) were proven rather vulnerable during stronger earthquake motions in the recent past. To determine lateral strength, stiffness, and capacity of energy dissipation of the URM walls, in-plane tests were performed at the University of Sarajevo. Two full-scale plain walls (233 × 241 × 25 cm) built with solid clay brick and lime-cement mortar and two walls strengthened with RC jacketing on both sides were subjected to cyclic lateral loading under constant vertical precompression. Plain walls failed in shear with a typical cross-diagonal crack pattern. Jacketed walls exhibited rocking with characteristic S-shaped hysteretic curves and significantly larger ductility compared with plain walls. Wallets were tested for modulus of elasticity and compressive strength of masonry and the results showed considerable variations.

A Fibre-Based Modelling Technique for the Seismic Analysis of Steel-Concrete Composite Shear Walls

Steel-concrete composite shear wall offers a favourable lateral strength and deformation ductility for seismic applications while significantly shortening the project schedule through eliminating the use of formworks and taking advantage of modular construction methodology. This paper presents a fibre-based modelling technique for simulation of the cyclic nonlinear response of composite walls by taking advantage of existing reinforced concrete and steel plate shear wall models. The improved modelling technique for cyclic analysis of composite walls that benefits from the macro models available for steel and concrete shear walls is introduced. The model is validated using experimental test data from 20 wall specimens. A sensitivity analysis is performed to examine the influence of various geometrical and material properties using the proposed modelling technique. A step-by-step modelling recommendation is finally proposed. The results show that the proposed modelling technique can efficiently be used to reproduce the nonlinear cyclic response of composite walls.

Seismic and Energy Integrated Retrofitting of Existing Buildings with an Innovative ICF-Based System: Design Principles and Case Studies

This work proposes an innovative integrated retrofitting system aiming to improve both the seismic and energy performance of existing reinforced concrete and masonry buildings. The system is based on engineered insulating concrete form panels, installed on the outside of existing buildings as a shell exoskeleton. A key major advantage of the proposed system is that it addresses the contemporary improvement of seismic and energy performances of existing buildings in a single installation stage, operating exclusively from outside of the building. The insulating formworks are ad hoc prefabricated in a factory on the base of the specific geometry of the existing buildings so as to greatly maximize the ratio between overall retrofitting benefits and costs and at the same time to simplify the installation procedures. The objectives of the presented research are, on one hand, to highlight the major structural issues that the system aims to address, and on the other hand to illustrate the main characteristics and combined benefits of the proposed retrofitting system. From a structural point of view, the proposed system is conceived to behave as a non-dissipative structure with regard to seismic actions, and the lateral strength and stiffness of the structural elements are designed accordingly. An analytical design approach is proposed and validated using the available data from an experimental test performed on a full-scale simple building. Moreover, numerical modeling strategies for the proposed system are illustrated for two complex case study buildings. The results of the analyses show a considerable increase in lateral stiffness of the retrofitted buildings that, considering the non-dissipative behavior of the elements, leads to a relevant reduction of seismic deformation demand on existing structural elements.

In-plane retrofitting of masonry structures by using GFRP strips in the Bedjoints

Many unreinforced masonry structures were vulnerable in the past earthquakes and required retrofitting. However, the vulnerability of masonry structures could solve by providing numerous retrofitting approaches, scarcity of appropriate methods that may provide a solution for the historical masonry structures with lesser effects on their façade is vehemently sensible. In this study, two one-third scale masonry wall specimens made by clay bricks were tested under constant vertical and cyclic lateral loading. The specimens consist of an unreinforced wall and a wall retrofitted by GFRP strips. This study investigates the seismic behavior of unreinforced masonry walls before and after using GFRP strips on their bedjoints. To this purpose, various patterns of using GFRP strips have been studied by simplified micro-modeling. The consequence indicates that the proposed retrofitting technique could improve the lateral strength and stiffness of the unreinforced masonry wall along with a considerable increase in the energy dissipation and ductility content, which leads to making a change in the behavior of the wall from brittle to ductile failure. The proposed method could apply to the modern historical structures in which cement mortar has been used as an adhesive between the masonry layers.

Development of disc spring stack containment methods for vibration isolation

Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations. However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement. A method to contain the isolator stack then becomes critical for practical uses. Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance. In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design. Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks. Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve. However, significant differences in isolation performance are observed in vibration testing and found to depend on characteristics such as lateral stability, lateral strength, and degrees of freedom. Lastly, advantages, disadvantages, and appropriate applications for each containment method are summarized. The conclusions of this work are that containment method is an important variable in the application of disc spring isolators and robust, versatile containment designs have been demonstrated.

Lateral Strength Evaluation of Ferrocement Strengthened Masonry Infilled RC frame Based on Experimentally Observed Failure Mechanisms

In developing countries, lateral strengthening of seismically vulnerable masonry infilled RC buildings is one of the major concern. In this context, ferrocement can be used as a low cost and less labor-intensive strengthening scheme for those buildings. This study aims to experimentally identify major failure mechanisms, and to develop a lateral strength evaluation procedure of ferrocement strengthened masonry infilled RC frame. Subsequently, ductility of all of the identified major failure mechanisms is compared. Mainly four major failure mechanisms (i.e. overall flexural, column punching-joint sliding, diagonal compression, and diagonal cracking-sliding) are identified from the current experimental work and past experimental studies. The strength evaluation procedure, based on the identified failure mechanisms, is proposed and verified with an average calculated to experimental lateral strength ratio of 0.8. Among the identified failure mechanisms, overall flexural, and diagonal cracking-sliding mechanisms showed relatively ductile behavior when compared to the ductility of column punching-joint sliding, and diagonal compression failure mechanism.