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A non-linear masonry infill macro-model to represent the global behaviour of buildings under cyclic loading

Rodrigues, H.; Varum, H.; Costa, A.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.67%
The presence of masonry infill walls in RC buildings is very common. However, and even today, in the design of new buildings and in the assessment of existing ones, these infill walls are usually considered as non-structural elements and their influence in the structural response is generally ignored. For horizontal loading, infill panels can drastically modify the response, attracting forces to parts of the structure that have not been designed to resist them. This paper presents an improved non-linear numerical simulation model for the influence of the masonry infill walls in the seismic behavior of structure. The model is implemented in the PORANL program. After the implementation and calibration of the proposed masonry model, a series of non-linear dynamic analyses of a building representative of Modern Architecture in Europe were carried out. The main objective was to investigate the behavior of this type of building, and any weakness under seismic loading. The building geometry and the dimensions of the RC elements and infill walls were set in the original project, and confirmed in the technical visits. The building under study has nine storeys and the structure is mainly composed of 12 plane frames oriented in the transversal direction. The building was analyzed with a simplified plane model...

Seismic behaviour characterization of reinforced concrete buildings

Varum, H.; Rodrigues, H.; Fernandes, C.; Costa, A.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.52%
The seismic vulnerability assessment associated to existing reinforced concrete buildings, constructed until the late 70’s in many European countries with moderate to high seismic hazard, designed and constructed without considering adequately earthquake provisions, is of extreme importance. They constitute a significant source of risk for our cities. In this paper are presented the main results of research developed in the field of seismic assessment and retrofitting of existing RC buildings.; Stanovení seismické zranitelnosti železobetonových budov postavených do konce sedmdesátých let v mnoha evropských zemích s mírným až vysokým seismickým nebezpečím, projektovaných a postavených bez přiměřených protiseismických opatření, má extrémní význam. Tyto budovy představují významný zdroj rizika pro naše města. V článku se uvádějí hlavní výsledky výzkumu na úseku stanovení seismické zranitelnosti a modernizace existujících železobetonových budov.

Vulnerability assessment and strengthening of R.C. buildings non-seismically designed

Varum, H.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.41%
The seismic vulnerability associated with existing buildings, constructed until the late 1970’s, in urban areas in most southern European countries, with moderate to high seismic risk, is of extreme importance. In that period, reinforced concrete buildings were designed and constructed without considering earthquake provisions, constituting a significant risk. Recent major earthquakes around the world have evidenced that this type of existing buildings lacking appropriate seismic resisting characteristics are very vulnerable. Their retrofit should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. Despite the evident advantages of a refined non-linear dynamic structural fibre modelling, it must be admitted that this approach can frequently become elaborated and costly. Simplified non-linear static models considering just one DOF (such the Capacity Spectrum Method) are frequently not able to assess accurately irregular structural systems. These facts sustain the development of less complicated structural models without debasing the essential features of dynamic response. It is demonstrated a recently proposed simplified methodology for nonlinear dynamic analysis of buildings based on the multi-modal spectral seismic response...

Numerical models for simulation of the seismic behaviour of RC structures: a case study

Varum, H.; Costa, A.; Rodrigues, H.
Fonte: UMSNH, aSMMNI, CIMNE Publicador: UMSNH, aSMMNI, CIMNE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.59%
Seismic analysis of RC structures requires realistic but simple analytical models. In this paper are presented two models proposed and implemented in the program PORANL, to represent the RC buildings behaviour under earthquake loading. The first model represents the bending behaviour of slender RC elements, and the second model represents the influence of infill walls in the global building response. The models are calibrated with test results on full-scale specimens. It is studied the vulnerability of one building, representative of the Modern Architecture, in Lisbon. Non-destructive tests on materials and natural frequencies measurement were performed to calibrate the model. The building was studied, with the proposed non-linear models, and the seismic safety was evaluated according to recently proposed assessment procedures. Additionally, it is proposed and studied a retrofitting solution, to improve the seismic performance of the building, based on a bracing system with a damping device associated.

A Model to predict the non-linear shear and flexural behaviour of RC elements subjected to cyclic loading

Rodrigues, H.; Costa, A.; Varum, H.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.73%
The development and implementation of an integrated numerical model to predict the nonlinear response of RC structural elements, including nonlinear flexural and shear behaviour, is proposed and discussed. The presence of RC elements with dominant behaviour in shear is quite common in a significant number of existing and new buildings. Severe damages and/or collapse of buildings have been observed in recent earthquakes due to disregarding of the shear behaviour of these stocky elements. The main objective of the work proposed is the development of a numerical model able to simulate the cyclic behaviour of RC elements subjected to cyclic loads, as the induced by earthquakes. The proposed model would allow to better estimate the nonlinear response of RC buildings under severe ground motions, combining the nonlinear flexural behaviour with the nonlinear shear behaviour. The proposed model for nonlinear shear behaviour has been implemented in the computer program VisualANL and was calibrated with experimental results on full-scale tests on RC columns.

Numerical model to account for the influence of infill masonry on the RC structures behaviour

Varum, H.; Rodrigues, H.; Costa, A.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.57%
It is a common misconception considers that masonry infill walls in structural RC buildings can only increase the overall lateral load capacity, and, therefore, must always be considered beneficial to seismic performance. Recent earthquakes have showed numerous examples of severe damages or collapses of buildings caused by structural response modification induced by the non-structural masonry partitions. From a state-of-the-art review of the available numerical models for the representation of the infill masonry behaviour in structural response, it was proposed an upgraded model. The proposed model is inspired on the equivalent bi-diagonal compression strut model, and considers the non-linear behaviour of the infill masonry subjected to cyclic loads. The model was implemented and calibrated in a non-linear dynamic computer code, VISUALANL. In this paper, it is presented the proposed model and the results of the calibration analyses are briefly introduced and discussed.

Seismic response of current RC buildings in Nepal: A comparative analysis of different design/construction

Chaulagain, H.; Rodrigues, H.; Jara, J.; Spacone, E.; Varum, H.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.57%
This paper presents the seismic response of the current reinforced concrete (RC) buildings in Nepal. It was achieved by non-linear static and dynamic analyses of four structures corresponding to four scenarios of design/construction, namely a building: (i) representing the Current Construction Practice (CCP) (ii) the Nepal Building Code (NBC), (iii) the Modified Nepal Building Code (NBC+) and (iv) a Well Designed Structure (WDS). The seismic demands are analyzed and discussed in terms of base shear, maximum roof displacement, capacity curve and inter-storey drift. The results indicate a good correlation between the static and dynamic methods. The Current Construction Practice (CCP) structure and Nepal Building Code (NBC) structures experience inter-storey drift demands higher than the other models and they also present some irregularities in the drift profile. The modified Nepal Building Code (NBC+) and Well Designed Structure (WDS) have presented a better performance with low inter-storey drifts. Finally, the safety assessment is performed based on drift limit proposed by ATC-40 and FEMA-356, showing that CCP and NBC building are highly vulnerable to earthquakes.

Cyclic response of RC beam-column joints reinforced with plain bars: an experimental testing campaign

Melo, J.; Varum, H.; Rossetto, T.; Costa, A.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.37%
Existing reinforced concrete (RC) buildings constructed until the mid-70’s, with plain reinforcing bars, are expected to behave poorly when subjected to earthquake actions. This paper describes an experimental program designed to investigate the influence of poor detailing on the cyclic behaviour of RC beam-column joint elements. Cyclic tests were performed on five interior and five exterior full-scale beam-column joints with different detailing characteristics and reinforced with plain bars. An additional joint of each type was built with deformed bars for an evaluation of the influence of bond properties on the cyclic response of the structural element. The force-displacement global response, energy dissipation, equivalent damping and damage behaviour of the joints was investigated and the main results are presented and discussed. The experimental results indicate that the bond-slip mechanism has significantly influenced the cyclic response of the beam-column joints. The specimens built with plain bars showed lower energy dissipation, stiffness and equivalent damping.

Reflection on the seismic vulnerability associated to common RC buildings in Nepal

Chaulagain, H.; Rodrigues, H.; Spacone, E.; Varum, H.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
66.63%
The present paper studies the evolution of the Nepal Building Code recommendations and its possible influence on the real construction and safety of RC buildings in Nepal. To this, it was designed a representative reinforced concrete building structure (WDS)) following the seismic ductile detailing principles and the results were compared with similar buildings detailed with: i) Current Construction Practices (CCP) and ii) Nepal Building Code (NBBC) recommendations. The results obtained for the three structures are analyzed and discussed in terms of beam and column cross sections and reinforcement. From the global comparison of thee structures under study it was observed for the CCP structure a low amount of reinforcement in beam and column sections when compared with the WWDS structure. For the structure designed according with the NNBC recommendations, improvements are clear relatively too the CCP structure, but it may be not sufficient for the demands in regions with medium/high seismic hazard. The comparisons performed also show that the structures designed for high and medium seismic hazard demands (WDS) presents approximately double reinforcement in beams when compared to the structures in low seismic zones.

Performance evaluation of retrofitting strategies for non-seismically designed RC buildings using steel braces

Varum, H.; Teixeira-Dias, F.; Marques, P.; Pinto, A.; Bhatti, A.
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.48%
Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions...

Seismic assessment and retrofitting of existing RC buildings in Kathmandu

Varum, H.; Chaulagain, H.; Rodrigues, H.; Spacone, E.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.59%
The effectiveness of reinforced concrete (RC) column jacketing for improving the seismic performance of existing RC building structures were studied. Four three storey buildings with different structural configuration and detailing were selected for seismic assessment and retrofitting purpose. The response of structures (original and retrofitted) was evaluated in terms of capacity curve and inter-storey drift. The case studies also intend to verify the effect of P-delta effects and bi-axial response of columns under non-linear time history analysis. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. Finally, a seismic safety assessment is performed based on the drift limit proposed by FEMA-356. The assessment of original building structures indicates that they may exhibit inadequate seismic performance. However, RC column jacketing highly improves seismic performance of all the structures and results maximum drift demand within the drift limit proposed by FEMA-356.

Seismic assessment of three-storey residential buildings in Nepal

Chaulagain, H.; Rodrigues, H.; Spacone, E.; Varum, H.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.63%
This paper evaluates the seismic performance of existing three-storey residential reinforced concrete (RC) buildings in Nepal. For this, it was designed a representative RC building structure (WDS) and the results were compared with similar buildings detailed with: i) Current Construction Practices (CCP); ii) Nepal Building Code (NBC) and iii) Modified Nepal Building Code (NBC+) recommendations. The results were analyzed and compared in terms of capacity curve, inter-storey drift and detailing of structures. The overall comparison indicates that CCP structure has a low amount of reinforcement both in beam and column sections when compared with the WDS structure. For the structure designed according with the NBC and NBC+ recommendations, improvements are clear relatively to the CCP structure, but it may be not sufficient for the demands in regions with high seismic hazard. Non-linear analysis shows that CCP and NBC structures experiences lower base shear capacity with higher inter-storey drift demand than other structures. Finally, the influence of seismic zone factor on reinforcement demand of the structure is analysed by designing the same WDS structure for a low, medium and high seismic hazard zone.

Design procedures of reinforced concrete framed buildings in Nepal and its impact on seismic safety

Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Varum, Humberto
Fonte: Multi-Science Publishing Publicador: Multi-Science Publishing
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.47%
The present paper analyses the design procedure and its impact on seismic safety of the structures. For this, a representative reinforced concrete frame building (WDS) is designed and the results are compared with similar buildings detailed with: i) Current Construction Practices (CCP); ii) the Nepal Building Code (NBC) and iii) the Modified Nepal Building Code (NBC+) recommendations. The seismic performance evaluation is done with global strength, inter-storey drift and displacement of the structures. Likewise, the sensitivity of the structural and geometrical parameters of the RC frame building is studied through nonlinear analysis. The study parameters considered for parametric analysis are column size, beam size, inter-storey height, bay length, bay width, and compressive strength of concrete. The results show that the influence on the structural behaviour, particularly by variation in column size and inter-storey height. Additionally, the influence of the seismic zone factor on reinforcement demand of the structure is studied. The result shows that structures designed for high to medium seismic hazard demands double the reinforcement in beams compared to structures in low seismic zone.

Response reduction factor of irregular RC buildings in Kathmandu valley

Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Guragain, Ramesh; Mallik, Radhakrishna; Varum, Humberto
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.78%
Most current seismic design includes the nonlinear response of a structure through a response reduction factor (R). This allows the designer to use a linear elastic force-based approach while accounting for nonlinear behavior and deformation limits. In fact, the response reduction factor is used in modern seismic codes to scale down the elastic response of a structure. This study focuses on estimating the actual ‘R’ value for engineered design/construction of reinforced concrete (RC) buildings in Kathmandu valley. The ductility and overstrength of representative RC buildings in Kathmandu are investigated. Nonlinear pushover analysis was performed on structural models in order to evaluate the seismic performance of buildings. Twelve representative engineered irregular buildings with a variety of characteristics located in the Kathmandu valley were selected and studied. Furthermore, the effects of overstrength on the ductility factor, beam column capacity ratio on the building ductility, and load path on the response reduction factor, are examined. Finally, the results are further analyzed and compared with different structural parameters of the buildings.

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

Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Varum, Humberto
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.68%
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.

Assessment of response reduction factor of RC buildings in Kathmandu Valley using non-linear pushover analysis

Chaulagain, Hemchandra
Fonte: Purbanchal University Publicador: Purbanchal University
Tipo: Dissertação de Mestrado
ENG
Relevância na Pesquisa
66.83%
This study addresses the issue of response reduction factor which is used in modern codes to scale down the elastic response of the structure. The level of ductility and overstrength of RC buildings in Kathmandu valley are investigated. The ductility and overstrength factors are estimated by analyzing the buildings using non-linear pushover analysis for 12 engineered designed RC buildings of various characteristics representing a wide range of RC buildings in Kathmandu valley. Finally, the response reduction factor of RC building in Kathmandu valley is evaluated by using the relation of ductility and overstrength factor.; Master of Engineering in Earthquake

Performance evaluation of retrofitting strategies for non-seismically designed RC buildings using steel braces

VARUM Humberto; TEIXEIRA-DIAS Filipe; MARQUES Paulo; PINTO VIEIRA Artur; QADIR-BHATTI Abdul
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Articles in Journals Formato: Online
ENG
Relevância na Pesquisa
46.48%
Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions...

Improved Seismic Risk Assessment of Non-ductile Reinforced Concrete Buildings

Fuselier, Blaine
Fonte: Universidade Rice Publicador: Universidade Rice
Relevância na Pesquisa
46.78%
Existing reinforced concrete (RC) buildings built to non-ductile specifications are highly susceptible to damage given lateral loads induced from earthquake ground motions. To explore the effects of these ground motions, non-linear finite element analyses are being used in research and practice to model representations of non-ductile RC buildings as well as conduct probabilistic analyses of their seismic fragility in as-built and retrofitted conditions. This study examines the influence of modeling fidelity on the response and fragility of non-ductile RC buildings, testing the role of explicitly capturing local failure in the finite element model as well as providing new insight into the probability of component damage levels given system level failure. Also, a survey is presented to assess the tagging decisions made during post-earthquake rapid evaluations of reinforced concrete buildings and compare these results to empirical data from past earthquake reconnaissance reports. The results of this study will provide insight into several key issues in seismic performance assessment for RC buildings.

Assessment of seismic strengthening solutions for existing low-rise RC buildings in Nepal

Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Varum, Humberto
Fonte: Techno-Press Publicador: Techno-Press
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.86%
The main objective of this study is to analytically investigate the effectiveness of different strengthening solutions in upgrading the seismic performance of existing reinforced concrete (RC) buildings in Nepal. For this, four building models with different structural configurations and detailing were considered. Three possible rehabilitation solutions were studied, namely: (a) RC shear wall, (b) steel bracing, and (c) RC jacketing for all of the studied buildings. A numerical analysis was conducted with adaptive pushover and dynamic time history analysis. Seismic performance enhancement of the studied buildings was evaluated in terms of demand capacity ratio of the RC elements, capacity curve, inter-storey drift, energy dissipation capacity and moment curvature demand of the structures. Finally, the seismic safety assessment was performed based on standard drift limits, showing that retrofitting solutions significantly improved the seismic performance of existing buildings in Nepal.

Seismic response of current RC buildings in Kathmandu Valley

Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Varum, Humberto
Fonte: Techno-Press Publicador: Techno-Press
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.72%
RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric non-linearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover...