Cyclic behavior of a two-span RC beam built with plain reinforcing bars

Reinforced concrete structural elements lacking appropriate seismic detailing and built with plain reinforcing bars, and subjected to cyclic loads like the ones induced by earthquakes, are particularly sensitive to the bond-slip mechanism. Though, existing studies on the cyclic behavior of RC structures generally refer to elements with deformed bars. As a result, the behavior of elements with plain bars is not yet fully understood. In this framework, the cyclic behavior of a two-span RC beam built with plain reinforcing bars, collected from an ancient building structure, was investigated. The support and loading conditions observed in-situ were simulated in the test setup. The beam displayed a flexural failure and the damage was concentrated in three short plastic hinges. The poor damage distribution evidences the effects of the bar slippage mechanism on the beam behaviorFCT - SFRH/BD/27406/2006FCT - SFRH/BD/62110/200

Structural Assessment and Seismic Retrofitting of Existing Adobe Constructions

Earth is one of the oldest building materials, having been used throughout the world since ancient times until the present day (Houben and Guillaud 1994). Nowadays, a significant percentage of the world population still lives in earthen buildings (Minke 2012). There is also a vast earthen built heritage, with many examples inscribed in UNESCO's World Heritage List (Gandreau and Delboy 2012). In Portugal, adobe, which is one of the most common earthen building techniques, was very used until the mid-twentieth century. At present, there are still many adobe buildings in use, some of which with great cultural and architectural value (Silveira et al. 2013, Oliveira et al. 2013). Earthen constructions have many advantages, such as low cost and reduced environmental impact (Morton et al. 2005, Shukla et al. 2009). However, these constructions, if not effectively designed and strengthened, may perform very poorly when subjected to seismic loads, as has been observed in recent earthquakes (Blondet 2008, Elnashai et al. 2010, Gautam et al. 2016). Knowledge on the mechanical properties and structural behaviour of these constructions is thus fundamental to support their adequate rehabilitation and strengthening. In order to contribute to this knowledge, research on the existing adobe constructions in Aveiro district, Portugal, has been developed in the last decade. A brief overview of some of the studies carried out is presented in the following sections

Experimental assessment of the monotonic and cyclic behaviour of exterior RC beam-column joints built with plain bars and non-seismically designed

The seismic behaviour of reinforced concrete structures built with plain reinforcing bars is sometimes conditioned by the slippage between the reinforcing bars and the surrounding concrete in the elements as exterior beam-column joints. The anchorage of the beam reinforcing bars in the core joint with weak concrete confinement, inappropriate reinforcement detailing for seismic loads and poor bond properties are the common reasons for collapse of many structures. This paper presents the results of four unidirectional cyclic tests and two unidirectional monotonic tests carried out on full-scale exterior beam-column joints built with plain and deformed reinforcing bars. These specimens are representative of reinforced concrete structures built without adequate reinforcement detailing for seismic loads. The influence of bond properties, lapping of the longitudinal bars, anchorage of the beam reinforcing bars and loading on the beam-column joints response are investigated

Simplified guidelines for retrofitting scenarios in the european countries

A large part of the European building stock was built before implementing the recent energy and structural codes, resulting in buildings characterized by deficiencies in terms of comfort, energy savings and structural safety. The retrofitting and rehabilitation of the existing building stock need to be adequately performed, aiming to improve the seismic and energy performance simultaneously. The work summarized here is dedicated to defining priority scenarios for buildings’ retrofitting to improve the seismic safety and energy efficiency of the European Union (EU) building stock. First, the state of the EU building stock is analysed in terms of buildings’ age, types of structures, energy efficiency, energy consumption and energy poverty. Then, the EU climate demands are presented, namely the regions with higher temperature variations, i.e., heating or cooling degree days. The EU seismic risk is also presented and discussed in terms of average annual losses, average annual economic losses and average annual life losses. Based on these input parameters, nine seismic–climate regions in the EU are proposed using a simplified approach. Finally, retrofitting scenarios are proposed for two types of buildings (i.e., masonry and reinforced concrete) based on their seismic–climate region.publishe

BENEFIT FROM CHAINED MASONRY WALLS TO IMPROVE THE SEISMIC RESPONSE OF REINFORCED CONCRETE BUILDINGS

     The multiple earthquakes have proved the effect of chained masonry walls on the seismic behavior of multistoried reinforced concrete buildings. The chained masonry walls have been considered one of the types of masonry infill walls but without gaps. This participation came intending to study this effect through the modeling of several two-dimensional frames for a multistoried reinforced concrete building, taking into account the hollow brick walls, which represent the most common type in Algeria. We analyzed the proposed models using ETABS finite element software, relying on the response spectrum method and respecting the most important requirements according to the applicable Algerian Seismic Code. After analysis of the different models, the results have been compared according to the parameters of the period, base shear, lateral displacement, and stiffness. Through a critical synthesis of the results, we concluded that these walls could significantly affect the seismic behavior of this type of buildings. Moreover, the neglect of these walls in the modeling process can lead designers to have a false perception of the behavior of these buildings towards seismic loadings.   &nbsp

Optical FBG sensors for static structural health monitoring

In this paper, the monitoring of an adobe structure with optical fiber sensors is reported. Static measurements were made during a destructive test on a full-scale wall, in which an in-plane cyclic force was imposed by a hydraulic jack until its collapse. The recorded data with these sensors and the force applied evolution allows to identify the two instants when the major diagonal cracks occur in the wall. Initially, before the cracking, a linear elastic response was observed, corresponding to a deformation at each monitoring point proportional to the applied lateral force, being quantified the relation between the external force and the deformation at each point. This structural test allows demonstrating the feasibility of applying static optical FBG sensors to study the behavior and performance of civil engineering infrastructures even for extreme loading events

Comparative seismic fragility of torsionally irregular RC buildings designed using Indian and European codes

Presence of irregularities in building tends to increase its seismic vulnerability. To improve their performance, many current seismic design codes specify larger demand and more stringent design requirements for torsionally irregular buildings, as compared to regular buildings. The current Indian seismic design code (IS 1893 Part 1), however, provides design guidelines that are essentially applicable to only regular buildings. With this view, the objective of the present study is to evaluate the behaviour and capacity at collapse of mid-rise RC frame-shear wall buildings, with and without torsional irregularity, designed according to current IS 1893 (Part 1) and BS EN 1998-1 codes. For this purpose, three-dimensional building models are subjected to bi-directional incremental dynamic analyses (BIDA), using a set of far-field ground motion records. To account for the cyclic deterioration of stiffness and strength, the non-linear behaviour of beams is modelled using an experimentally calibrated lumped plasticity model, while the columns and shear-walls are modelled using fibre-hinge models (ETABS-CSI, 2016) duly calibrated with the experimental results available in literature. Results of the BIDA are used to assess the collapse capacity, and for developing seismic fragility curves according to the FEMA P695 methodology. The results are compared and discussed, with particular emphasis on the adequacy and limitations of the design provisions and recommendations in the two codes, in context of torsionally irregular buildings

Characterization of the earth-based construction techniques used in the 18th and 19th centuries in the historical centre of São Luís (MA, Brazil)

The architectural heritage of the historical city centre of Sao Luis of Maranhao, located in the northeast region of Brazil, has approximately 5,600 registered buildings, out of which 1,400 were included in the UNESCO World-Heritage List in December 1997. The architectural heritage of 18(th) and 19(th) centuries is made up of sobrados (ground storey for commercial and upper storeys for residential use), solares (constructions with distinguished finishing, exclusively for residential use by privileged families) and single-storey constructions where poorer families used to live. Different construction systems can be found in the same building of the historical city centre. It is common to have structural walls made of stone masonry with lime mortar (in rare cases made of adobe) and interior partition walls made of pau-a-pique (also called taipa de mao), cruz de Santo Andre (resembling the gaiola pombalina style) and tabique. Therefore, in the majority of the internal partition walls earth-based masonry is found, which, in many interventions, was replaced by contemporary techniques. This article discusses the earth based masonry typologies found in the buildings from the 18(th) and 19(th) centuries in the historical centre of Sao Luis belonging to the registered areas at federal and state level. It characterizes the different typologies of the earth-based masonries, analysing the historical, cultural and socio-economic period when they were used in the region. It is designed to contribute to the scientific and technological knowledge of the earth-based masonry systems used in Sao Luis in the 18(th) and 19(th) centuries and thus to the preservation and rehabilitation of its heritage

Seismic assessment of low ductile RC structures: Buildings from before the modern seismic codes

Purpose - When a numerous amount of buildings was built in reinforced concrete, in a period whenthe regulations did not have the design philosophy for the occurrence of earthquakes, it is of extremeimportance to carry out full and effective structural assessments, specially considering and comparingbare frame and infilled structure. The paper aims to discuss these issues.Design/methodology/approach - Among several possibilities to make the evaluation as, simplified,linear analysis and static non-linear analysis, the non-linear dynamic can provide the most accuratenumerical behaviour compared to the real one. The time-history non-linear analyses are developed onthe software SeismoStruct for different levels of intensity. Local verifications are then appliedseparately from both Eurocode and Italian Code.Findings - The application of validated models for the analysis of real buildings allows a completeseismic assessment. The level of uncertainty increases integrating particularities regarding the infillmasonry walls. The paper shows important global and local seismic safety for these complex typologyof buildings.Originality/value - A representative common concrete structure without seismic provisions is firstanalysed and discussed in terms of global behaviour, deformations and progression of forces. The casestudy structure is considered both as bare structure and with integrated infill panels. It is alsodiscussed in a local level, about brittle and ductile mechanisms, and extra comparisons betweendifferent interpretations of different standards. The case study structure is considered both as barestructure and with integrated infill panels.Keywords 3D modelling, Dynamic and non-linear analysis, Infill masonry, RC building,Seismic assessmentPaper type Case stud

Seismic assessment of rc structures with infill masonry panels in Nepal: sensitivity analysis

Reinforced concrete (RC) buildings in Nepal are constructed as RC frames with masonry infill panels. These structures exhibit a highly non-linear inelastic behaviour resulting from the interaction between the masonry infill panels and the surrounding frames. In this context, the paper presents an extensive case study of existing RC-framed buildings in a high seismic risk area in Nepal. A sensitivity analysis of the structures with masonry infill is performed. For this, the influence of different material properties is studied, namely diagonal compressive stress, modulus of elasticity and tensile stress of masonry infill panels. Result shows the influence on the structural behaviour particularly by variation of the diagonal compressive strength of infill masonry panels