Pushover Curves Research Articles

Traditional High-rise Unreinforced Masonry Buildings: Modeling and Influence of Floor System Stiffening on Their Overall Seismic Response

ABSTRACT This paper summarizes a study whose primary objectives were to develop a model for nonlinear static analysis of unreinforced masonry (URM) buildings, considering the flexibility of the floor system and analyzing the influence of stiffening the floor system on the overall seismic response of such buildings. With this aim, a six-story building typical of the Eixample-Barcelona district was used as a case study. All the macro-elements, those that constitute the walls and the floor system, were developed with one-dimensional spring elements. The influence of stiffening the floor system was analyzed by applying conventional stiffening interventions to the two-floor systems common in the Eixample-Barcelona district. The overall seismic response was evaluated in terms of modal parameters, the characteristics of the pushover curves and the deformed shape of the floors. The outcomes are discussed in relation to recent studies and explained in the context of previous studies. Finally, in the two unstiffened cases of the prototype building, the stiffening of the floor system slightly increases in fundamental periods, slightly to moderately increases in base shear capacities, and significantly decreases in displacement capacities.

Refined Rigid Block Model for In‐Plane Loaded Masonry

In this work, a refined rigid block model is proposed for studying the in‐plane behavior of regular masonry. The rigid block model is based on an existing discrete/rigid model with rigid blocks and elastoplastic interfaces that already proven its effectiveness in representing masonry behavior in linear and nonlinear fields. In this case, the proposed model is improved by assuming rigid quadrilateral elements connected by one‐dimensional nonlinear interfaces, which are adopted both to represent mortar (or dry) joints between the blocks and also to represent inner potential cracks into the blocks. Furthermore, the softening behavior of interfaces in tension and shear is taken into account. Several numerical tests are performed by considering masonry panels with regular texture subjected to compression and shear. Particular attention is given to the collapse mechanisms and the pushover curves obtained numerically and compared with existing numerical and laboratory results. Furthermore, the numerical tests aim to evaluate the applicability limits of the proposed model with respect to existing results.

Application of the resettable semi-active damper device for macro modelling of confined semi-interlocking masonry walls

In previous research by the authors, the semi-interlocking masonry (SIM) was investigated as infill panels for framed structures and its favourable seismic performance was established through laboratory tests. Confined semi-interlocking masonry (CSIM) is a new application of SIM that aims to enhance earthquake performance of confined masonry buildings. Numerical simulations are performed to estimate the structural capacity of CSIM buildings. Micro and macro-modelling strategies are two major approaches for numerical simulation of masonry buildings. This paper proposes a macro-model for CSIM buildings by using a resettable semi-active damper model to simulate the behaviour of the SIM panel. The hysteretic performance of CSIM walls using the proposed macro-model was compared with the load-displacement pushover curve resulting from the FEA micro-modelling approach. The acceptable match between the responses of CSIM walls obtained from the micro and the macro-model confirmed the capability of the proposed model to capture the capacity of CSIM walls.

Pushover analysis of soft brick unreinforced masonry walls using analytical and numerical approaches

The seismic behaviour of low strength unreinforced masonry (URM) structures comprising soft bricks is still not clearly understood. This challenge can be addressed by numerically modelling soft brick URM wall panels using the simplified micro modelling technique. Alternatively, an analytical approach can be adopted to derive the load-deformation curves for soft brick URM walls. This paper presents results from pushover analysis on URM walls and compares the results obtained from the analytical and numerical techniques. The pushover curves and failure modes obtained from the finite element analyses are in good agreement with the results obtained using the analytical approach. It is concluded that the analytical and numerical techniques account for the various possible damage mechanisms associated with soft brick masonry and can be adopted for large scale analyses of soft brick URM structures.

Performance of Outrigger System by Non-Linear Static Method

High rise building structures are highly affected by lateral loads and wind forces. To enhance lateral force outrigger systems are developed, which are one of the most popular and efficient, because they are easier to build and they provides good lateral stiffness. With the rise of building height, deep beam become concrete walls at least of one story height. Axial shortening effect between core and perimeter structure has to be considered.In the present work 20 story reinforced concrete structure has taken with outrigger walls attached from core to the outer perimeter column. By changing the different position of outrigger level are kept for analysis.The building without and with outrigger are compared with bareframe. These are different building models analysed (a) Bare frame of twenty story building (b) Bare frame with core shear wall building (c) Outrigger system at top of building (d) Outrigger system at top & 0.75 Height of building (e) Outrigger system at top & 0.50 Height of building (f) Outrigger system at top & 0.25 Height of building. Non-linear static analysis results were compared. The analytical methods used in the work are pushover method. In this work, various parameters like pushover curve, displacement vs base force, story displacement, hinges formation are obtained for all the models.Outrigger at optimum level at 0.5 Height gives better results in both displacements and base force. To sustain peak lateral loads these systems are provided half of the height. These study gives has inelastic behaviour of structure.

Nonlinear Behavior of Building with Varying Percentages of Slab Opening

The work describes about irregular plan geometric forms that are more in metro cities. Irregularities are not avoidable in construction of buildings. In present scenario many buildings have irregular configurations both in elevation and plan. Now a day’s openings in the floors are common for many reasons like stair cases, lighting architectural etc. The present study focuses on the behavior of 10 storey reinforced concrete buildings under seismic zone-v, the plan dimensions is taken as 28 m x 28 m. The plan irregularities such as openings in slab with varying percentages is taken in this study. Study is done on various plan configuration buildings and the action of structural diaphragm on its performance during earthquake is studied. Pushover analysis is performed by using ETABS software, for present work five models are studied 1) building without opening in slab 2) plan irregular building with 10% opening in slab 3) plan irregular building with 20% opening in slab 4) plan irregular building with 30% opening in slab 5) plan irregular building with 40% opening in slab. Output from software consisting of Pushover curve and hinge formation results of all five models which are presented. Plan irregularity find better structural system solution such as in 20% opening shows better base shear.

Earthquakes Effect on the Behavior of Multi-Story RC Building Using Non-Linear Dynamic Analysis

One of the buildings that were designed depending on the old Syrian Code is selected and modeled using SAP2000 by taking its non-linear properties to be checked under dynamical loading. Three earthquake records are taken and applied to the model as Time History loading cases. The dynamical displacement of the top roof of the building and the hysterical diagrams of the relation between base shear and roof displacement is compared and discussed. Asymmetry of shear walls and cores is responsible of the differences in responses of building elements, and insufficient nonlinear modeling of shear walls prevents from finding the real capacity of the system, although comparing pushover curves with hysteric loops from the applied ground motion excitations shows that the building is capable, depending on its old design, to withstand various types of extreme ground motions and earthquakes.

A simplified retrofitting method based on seismic damage of a SDOF system equivalent to a damped braced building

A new Displacement-Based Design (DBD) procedure to proportion hysteretic damped braces (HYDBs) is proposed in order to take into account the effects of the seismic degradation of a structure that needs to be retrofitted. To this end, a hysteretic model based on plastic and damage mechanisms is adopted to describe the inelastic response of reinforced concrete (r.c.) frame members. Then, nonlinear seismic analysis of a single-degree-of-freedom system, equivalent to a multi-degree-of-freedom model of the structure, is used to generate the capacity boundary curve by means of the hysteretic model defined starting from the initial backbone curve. Two-, four- and eight-storey r.c. framed structures are designed for a medium-risk seismic zone of a former Italian code. These are then to be retrofitted by inserting HYDBs to attain performance levels imposed by current Italian code in a high-risk seismic zone. Different retrofitting solutions are compared, considering for each retrofitted structure: (i) variable damper ductility coupled with constant frame ductility; (ii) variable frame ductility coupled with constant damper ductility. The effects of different damage levels and different damage evolution laws are also investigated. Finally, pushover curves of the unbraced and damped braced structures are carried out, with and without considering degradation of the hysteretic response of r.c. frame members on the DBD procedure of the HYDBs.

Effects of Soil-Structure Interaction on the Inelastic Seismic Response of Continuous Bridges on Piled Foundation

Effect of soil-structure interaction (SSI) on seismic response of bridges is not clearly understood, and in general practice, bridge design is carried out ignoring its effect. This is due to the general consensus that fixed base leads to a more conservative design despite the fact that many researchers indicate that ignoring soil-structure interaction may lead to underestimation of seismic response. The current paper aims to investigate the effect of SSI on the nonlinear seismic behavior of 9-span continuous bridge supported on pile foundation penetrating sandy soils. Three types of soils were investigated representing medium to stiff sandy soil. Both pushover analysis and nonlinear time history incremental dynamic analysis are carried out using Opensees to investigate the effect of SSI on the seismic response parameters (namely, fundamental period, pushover curves, foundation rigid body motions, global ductility capacity and demand, and maximum drift ratio) of the bridge and to compare it to fixed base assumption (i.e., SSI ignored). The results indicate that although SSI increases the flexibility of the structure (accordingly increasing fundamental period), the seismic demand of the bridge increases. This increase is more pronounced as the soil becomes softer.

A Nonlinear Static Research on A G+5 Storey Existing RC Structure Under Seismic Loading

A six-story reinforced concrete structure area to a seismic hazard can be analyzed; as soon as the member has yielded, the plastic hinge will likely be used to symbolize the mode of failure in the beams and columns. The pushover analysis is carried out on constructing utilizing an identical static process from ETABS-2016 and IS 1893-2016. The analysis is regulated through efficiency-situated warmness engineering legal guidelines, even as an inelastic structural evaluation is combined with seismic hazard to calculate the expected seismic performance of the structure. The building's basis shear v / s roof strain curve referred to as the pushover curve is an enormous consequence of pushover evaluation; nonlinear dynamic evaluation is carried out in both respects (X & Y). Default hinge facets to be had in precise packages are built-in for every member in step with FEMA-440(Federal Emergency management agency) and ATC-40(applied technology Council) for every member.

Reduced-order modeling with multiple scales of electromechanical systems for energy harvesting

New technologies that aim at powering wireless nodes by scavenging the energy from ambient vibrations can be a practical solution for some structural monitoring applications in the near future. In view of possible large-scale applications of piezoelectric energy harvesters, an accurate modeling of the interfaces in these devices is needed for more advanced and reliable simulations, since they might have large influence on functionality and performance of smart monitoring infrastructures. In this perspective, a novel multiscale and multiphysics hybrid approach is proposed to assess the dynamic response of piezoelectric energy harvesting devices. Within the framework of the presented approach, the FE2 method is employed to compute stress and strain levels at the microscale in the most critical interfaces. The displacement-load curve of the whole device (so-called capacity curve or pushover curve) is then obtained by means of the application of a suitable pattern of static forces. Finally, the parameters of a reduced-order model are calibrated on the basis of the nonlinear static analysis. This reduced-order model, in turn, is employed for the efficient dynamic analysis of the energy harvesting device.

A study on the accuracy of force analogy method in nonlinear static analysis

SummaryIn this paper, the accuracy of the force analogy method (FAM) for nonlinear static (pushover) analysis is investigated. Hence, after explanation of the concept of FAM by a new approach, 12 2D steel special moment resisting frames with different configurations were derived from two different 3D archetypes and modeled using four various methods of capturing nonlinearity including SAP2000 super elements, OpenSees force‐based and displacement‐based fiber method, and FAM. In addition, a MATLAB code was developed for modeling and analyzing the frames by FAM. The accuracy of FAM in predictions of pushover curves, base shear forces, and plastic rotation of the critical hinges was investigated. The results indicated that in general, the predictions obtained using the FAM had a good agreement and compatibility with those from other methods of analysis currently used in practice for seismic performance assessment of structures.

Simplified and Refined Analyses for Seismic Investigation of Historical Masonry Clusters: Comparison of Results and Influence of the Structural Units Position

The goal of this work is the seismic vulnerability assessment of building aggregates within the historical centre of Arsita (Teramo, Italy), damaged by the 2009 L’Aquila earthquake, by comparing two different analysis procedures applied to a construction compound case study. First, the seismic vulnerability of structural units of the building compound, has been appraised by using a vulnerability evaluation quick form appropriately conceived for masonry aggregates. In particular, heading and intermediate structural units, having different geometrical configuration and seismic behaviour, have been inspected by using the before mentioned form, which allowed to calculate for them a synthetic vulnerability index. Starting from these indexes, the probable damages suffered by the examined structural units under different grade earthquakes have been estimated. Later on, both the single structural units and the whole construction compound have been modelled by using the macro-element refined method foreseen by the 3Muri non-linear analysis software. Static non-linear analyses performed on the above-mentioned structures have provided the related pushover curves, used to estimate, through the N2 method, the damages suffered under seismic actions expected in that site. Therefore, damages of single structural units have been compared to those experienced by the same structures within the building aggregate. Finally, the results deriving from the two analysis methodologies considered have been compared to each other, allowing to confirm the effectiveness of the simplest technique to predict the seismic damage and vulnerability of investigated structures.

Seismic performance of special concentric steel braced frames

Special concentric braced frames are provided in buildings located in severe seismic zones to resist earthquake loads. The seismic performance of these frames is mainly depend on the capacity of bracing in tension. However, the detailed studies are not available to find the optimal tensile capacity of such bracing to give the acceptable performance under severe earthquake. This paper presents the seismic performance of regular 6, 9, 12 and 15 storey special concentric X-braced frames in which tension bracings are designed for the lateral load of 100%, 70% and 60% of base shear. Demand to Capacity Ratio (DCR) is varied in beam and columns (0.4–0.7) and bracing (0.6–0.9) under design lateral loads. Pushover curves are developed to determine the strength and ductility of the frame for all the DCRs considered in the study. Column DCR of 0.4 and 0.5 is proven to be more effective with bracing DCR of 0.8 and 0.9 in terms of strength and ductility. It is also found that the displacement demand for the frames designed for 60% of the total base shear under maximum considered earthquake is within acceptable limit.

Verification of pushover analysis for a long-span steel truss structure

Pushover analysis has become an effective tool for seismic design of high-rise buildings under severe earthquakes. However, the applicability of traditional pushover analysis is often questioned for long-span structures due to their complex dynamic characteristics. In this paper, pushover analysis was adopted to determine the seismic behavior of a long-span steel truss structure under severe earthquakes. Load distributions were determined based on the fundamental modes for vertical and horizontal earthquakes respectively. Pushover curves were obtained by nonlinear static analysis. Target displacements were determined with capacity spectrum method. The maximum displacements and plastic hinge distributions determined by traditional pushover analysis agreed well with those by nonlinear time history analysis for both horizontal and vertical earthquake actions. It was then concluded that the seismic behavior of this kind of long-span steel truss structures can be evaluated by traditional pushover analysis accurately enough for practical design purpose.

Displacement-Based Design of RC Frames Using Design Spectra of Indian Code and Its Seismic Performance Evaluation

A set of 4-, 8-, 12-, and 15-storied reinforced concrete moment resisting frames were analysed and designed by direct displacement-based design method and performance-based plastic design method. The design spectra of Indian Standard IS 1893:2016 have been used for the calculation of base shear after its proper synchronization with respect to both the methods. The seismic performance evaluation was done by nonlinear static pushover analysis, and the parameters of comparison were (a) pushover curves, (b) storey drifts and (c) response reduction factor. Results show satisfactory performance of both the methods in terms of capacity and deformation. The response reduction factor values obtained for both approaches are greater than the IS 1893:2016-specified value which indicate the enhanced ductility for both methods.

Collapse Assessment for a RC Frame Structure in Bucharest (Romania)

The focus of this paper is to evaluate the collapse probability of a planar RC frame structure designed for the seismic conditions of Bucharest (Romania). The assessment is performed using both static and dynamic nonlinear analyses. 1000 pushover curves are sampled for the analysed structure taking into account the uncertainty due to the materials’ strengths and due to the gravitational loading. The nonlinear time–history analyses are conducted on equivalent SDOF structures derived from each sample of pushover curves. Finally, the collapse assessment is assessed through multiple stripe analyses performed using a ground motion dataset of 20 representative horizontal components recorded in Bucharest area during three past major intermediate-depth Vrancea earthquakes. The results show an annual collapse probability of the order 3.0 × 10−3 to 6.0 × 10−5, which represents a value similar with those obtained in order studies in the literature. The nonlinear analyses also show that the epistemic uncertainty due to the modelling uncertainties has a much smaller contribution to the total uncertainty as compared to the record-to-record variability. The most important parameters affecting the collapse fragility appear to be the concrete compressive strength and the Young’s modulus for concrete.

Seismic assessment of interacting structural units in complex historic masonry constructions by nonlinear static analyses

The damage occurred due to past earthquakes highlighted that the seismic behavior of historic masonry structures characterized by an aggregation of units with an own seismic behavior (e.g. palaces, fortresses, castles, etc.) is strongly affected by their dynamic interaction. At present, no codified and operational tools are available to perform the seismic assessment of such mutually interacting structures. This paper introduces a numerical procedure based on the use of nonlinear static analyses to fill this gap. The proposed procedure firstly requires the execution of a modal analysis on the 3D finite element model of the whole structure to define the modes which involve the dynamic response of each unit and their modal shapes. The latter are then fitted to define the load patterns to be applied on each unit through pushover analyses. The pushover curves obtained for each unit are then converted into capacity curves to finalize the seismic assessment. The effectiveness of the proposed procedure is shown through an application to a medieval fortress significantly damaged by the 2012 Emilia earthquake (Italy). The results achieved are promising and support the possible extension of the procedure to other typologies of complex historic structures composed by various interacting units.

Probabilistic models of abutment backfills for regional seismic assessment of highway bridges in California

Seismic responses of ordinary highway bridges that feature stiff superstructures have been shown to be strongly affected by abutment-backfill interactions. Seismic risk assessment of these bridges at the regional scale faces the added challenge of having to deal with the large uncertainty in backfill properties. In this regard, the study develops probabilistic backfill models to better quantify the uncertainties in modeling the abutment. First, efforts to establish the validity of the numerical method in predicting the pushover response of backfills are described. Advanced plasticity materials are used in finite element models (FEMs) to simulate sandy and clayey soils that yield consistent backfill force-displacement relationships against full-scale test results. Second, a probabilistic analysis framework is constructed to incorporate soil uncertainties that are identified from field investigations. Statistical moments are extracted from the resultant pushover curves to fully define the probabilistic backfill models, which are verified to bear appropriate uncertainty treatment and reasonable height adjustment factors. Further, statistical analysis tools are used to investigate the influences of different backfill models on the bridge demand estimates of two common bridge classes. The study reveals that backfill models will affect the response estimates of different bridge components in both diaphragm and seat-type abutment bridges. However, probabilistic models shall be especially considered on backfills for the bridge components that are expected to have dominant responses in the longitudinal direction. The proposed backfill models appear to outperform previous deterministic models in predicting realistic bridge responses. The models can be employed in the task of regional seismic assessment of various bridge classes.

Comparative study on the seismic performance assessment of existing buildings with and without retrofit strategies

A large number of infilled RC frame buildings have undergone moderate to extensive structural damages and even collapsed after the 2015 Gorkha earthquake. The repair and maintenance works are still being carried out in the existing RC buildings, many of them without any consultation with design engineers. Such practices are likely to create a benefit of doubt on the efficiency of the retrofitting works and repair/maintenance works. Therefore, the present study aims to evaluate the seismic performance of the existing non- and pre-engineered buildings, and later employed retrofit measures that are commonly practised in the region. The analytical results revealed that the selected buildings were seismically deficient and are most likely to undergo extensive damage to collapse states, at 0.3 g PGA. It was found that the retrofit measure significantly enhances the stiffness, maximum strength and ductility in the existing buildings. The pushover curves indicated that the steel bracing highly increased the stiffness, strength and ductility capacity in all case study buildings. The steel-braced building was recorded to have increased the maximum base shear capacity by almost ten times for the soft-storey MRT1 building. Similarly, the retrofit measures also eliminated the potential single storey drift concentration recorded in the original building, such that a uniform inter-storey drift profile can be attained throughout. The conditional probability of collapse for the case study buildings, at 0.3 g PGA, ranges from 13.5 to 42% and could be minimized below 4% in the worst case scenario for the shear wall. All the numerical results demonstrated that steel bracing was much more effective in enhancing the seismic performance of the existing buildings.