Nonlinear Static Analysis Research Articles

Optimization of Intervention Strategies for Masonry Buildings Based on CLT Components

Unreinforced masonry has been for centuries one of the most widespread constructive techniques for both massive structures and civil buildings (e.g., palaces, hospitals, houses), for the most still standing nowadays. Their future conservation relies on (i) their protection from main natural threats (e.g., earthquakes) and (ii) updating to current functionality and hygrothermal standards. In the former framework, existing masonry buildings proved to have some intrinsic vulnerabilities, depending on composition (units and binder) and structural typologies. Based on experience gathered from seismic events, various retrofitting techniques have been proposed. In such a context, the use of cross-laminated timber (CLT) components is a very promising solution, in terms of compatibility with built heritage and integration of seismic and hygrothermal performances. This paper aims at improving the knowledge of the structural performances of compound timber–masonry interventions by numerical simulations carried out at (i) pier scale and (ii) building full scale via finite element modeling and nonlinear static analyses (pushover). First, a coupled timber–masonry wall was simulated and underwent sensitivity analyses with the properties of both components varying; then, the optimized solution was applied to a case study to assess the intervention benefits, and the results were also cross-checked with those of more traditional interventions (e.g., grout injections).

Non Linear Analysis on CFDST columns with and without GFRP Wrapping

Abstract: Concrete Filled Double Skin Steel Tube (CFDST) columns are modified form of Concrete Filled Steel Tubular (CFST) columns, developed by several researchers. CFDST column composed of two concentric steel tubes in which concrete is packed in between them. It is available in various geometrical shapes. CFDST have many advantages such as high strength, high bending stiffness, good seismic and fire performance. But it is found that CFDST columns have some disadvantages including ageing of structures, corrosion of steel tubes etc. which reduces the strength of the column. So, to prevent these drawbacks and to strengthen the structure, Glass Fiber Reinforced Polymer (GFRP) can be used as an external cover. The present study aims to do nonlinear static analysis of CFDST columns having different hollow ratio wrapped with and without GFRP under axial compression using ANSYS finite element analysis software.

Non-Linear Static Analysis of Hollow and Solid SIFCON column under Axial Loading

Abstract: Concrete is a crucial material for creating various structures. The use of steel fiber reinforcement in concrete improves the ability of structural elements to withstand high stresses. SIFCON (Slurry Infiltrated Fiber Concrete) is a relatively new composite material using steel fibers in a cement-based matrix.SIFCON column is an innovation in the field of civil engineering that enhances the constructability.This paper aims to the Non-linear static analysis of hollow and solid SIFCON hexagonal columns under axial loading. For this study, three finite element models of Hexagonal SIFCON column with Hooked end steel fibers were analyzed using Ansys 2016 R1. Different hollow ratios is evaluated under axial loading to understand the total deformation and equivalent stress.The Study shows that hexagonal solid column shows maximum load carrying capacity than hexagonal hollow columns.

Fragility of single-span masonry arch bridges accounting for deterioration and damage effects

Masonry arch bridges, despite their age, are still fundamental structures in transport networks throughout Europe, especially for railways. Furthermore, these bridges are often found in seismic-prone areas, such as Italy. Developing of specific fragility models is of fundamental importance for large-scale seismic risk assessments of these structures and related transport networks. Unlike other types of bridges, for which significant progress has been made in assessing their seismic vulnerability and fragility, comparable results for masonry arch bridges are not fully available. Moreover, a realistic risk assessment of masonry bridges should account for deterioration and damage, which most of these bridges have developed being more than 100 years old and often in a poor state of maintenance. Therefore, this work intends to provide seismic fragility models for two generalised classes of single-span masonry arch bridges, i.e. segmental and semi-circular, taking into account their potential degradation through 2 D finite-element modelling and parametric nonlinear static analyses. Material loss from the intrados of the arch, material degradation, and longitudinal cracks on the arch barrel vault are investigated as typical defects. Overall, the seismic fragility of masonry bridges increases appreciably when the effects of degradation are considered, the loss of material being the most influential defect.

Evaluation of the Progressive Collapse of the Reinforced Concrete Frames Considering the Soil–Structure Interaction: Parametric Study Based on the Sensitivity Index

In this essay, to investigate the progressive collapse of the reinforced concrete (RC) frames, a nonlinear static pushdown analysis was performed with column removal scenarios from the first story. At first, a numerical model was simulated and verified with the experimental model in SeismoStruct software without soil–structure interaction (SSI). Afterward, the foundation, soil, and the RC frame were modeled simultaneously in FLAC software and verified with the numerical model of the SeismoStruct software. Furthermore, the effect of SSI was studied on the progressive collapse of RC frames based on the sensitivity index (SI). The sensitivity index is defined as the ratio of the residual capacity under gravity loading of the structure by removing the column to the value of the undamaged structure. The results showed that by considering SSI, the sensitivity index decreases. Then, a parametric study of the framed structures (thickness of the foundation) and substructures (soil density, soil types, soil layers, and the soil saturation conditions) was performed to evaluate the progressive collapse-resisting capacity based on the sensitivity index. The results showed that by considering SSI, with an increase in the soil density and decrease in the groundwater level, the conditions would be better for preventing progressive collapse. It was also shown that rock and silty sands (SM), compared to other studied soil types, and SM and silty sands—silty clay with low plasticity—silty sands (SM-CL/ML-SM), compared to other studied soil layers, are better for preventing progressive collapse.

A hybrid approach for the seismic vulnerability assessment of the modern residential masonry buildings

In this paper a hybrid approach for the seismic vulnerability assessment of the existing modern masonry buildings is developed. The procedure takes advantage of the standardized designs and technological features of the XX century masonry structures to define a hybrid framework constituted by two different phases: an urban scale one and one at the building level. The methodology is applied at the external outskirt of the city of Florence, where the residential stock is characterized by a significant number of masonry constructions. At the urban level a cognitive research based on archive research and data collection allowed the identification of the architectural and structural features of modern masonry buildings. Then, a selected case study representative of a wider class is chosen for a probabilistic procedure based on nonlinear static analysis and targeted at the derivation of fragility curves. The analytical results have been assumed to calibrate a simplified procedure available in literature and targeted at the definition of bilinear capacity curves. The calibration of the different coefficients was conducted in terms of generic outcomes, defining correlations within architectural elements and their seismic behavior (facades, side walls). The rapid methodology has been finally implemented at the urban scale, and the results of the work exhibit a relevant vulnerability of existing buildings. The simplified methodology overcomes the limits of the empirical methodologies at the urban scale constituting a valid tool for the rapid seismic vulnerability assessment at urban scales of the modern masonry structures of different contexts.

Effect of the capacity ratio developed at column-beam nodes and evaluation of its random degradation impact on the formation of global ruin mechanisms

PurposeThe purpose of this study, is to deals with capacity design (strong column – weak beam) in reinforced concrete frames, slightly slender, which depends on the determination of a capacity ratio necessary to reach a structural plastic mechanism. To find the capacity ratio allowing to achieve a fairly ductile behavior in reinforced concrete frames, it is necessary to validate this concept by a non-linear static analysis (push-over). However, this analysis is carried out by the use of the ETABS software, and by the introduction into the beams and columns of plastic hinges according to FEMA-356 code.Design/methodology/approachThis approach makes it possible to assess seismic performance, which facilitates the establishment of a system for detecting the plasticization mechanisms of structures. It is also necessary to use a probabilistic method allowing to treat the dimensioning by the identification of the most probable mechanisms and to take only those that contribute the most to the probability of global failure of the structural system.FindingsIn this study, three reinforced concrete frame buildings with different numbers of floors were analyzed by varying the capacity ratio of the elements. The results obtained indicate that it is strongly recommended to increase the ratio of the resistant moments of the columns on those of the beams for the Algerian seismic regulation (RPA code), knowing that the frameworks in reinforced concrete are widespread in the country.Originality/valueThe main interest of this paper is to criticize the resistance condition required by RPA code, which must be the subject of particular attention to reach a mechanism of favorable collapse. This study recommends, on the basis of a reliability analysis, the use of a capacity dimensioning ratio greater than or equal to two, making it possible to have a sufficiently low probability of failure to ensure a level of security for users.

Seismic behavior of linked column system as a steel lateral force resisting system

In previous research, the seismic behavior of linked column frame (LCF) system as a dual structural steel frame system that Consists of the primary linked column (LC) and the secondary moment frame (MF) systems has been evaluated. In this research, based on the high capacity of the linked column system in lateral load resisting, this system has been used as the only lateral load resisting system in the building frame. Studies have shown that this approach not only eliminates the main disadvantages of the LCF system, but also preserves the ability to repair structures after an earthquake. Therefore, the designed models of the linked column system have been evaluated using nonlinear static pushover analysis, nonlinear dynamic time history analysis, incremental dynamic analysis and endurance time method analysis. In the evaluation of the seismic behavior of the linked column system, design approach, structural stability and collapse mechanism, ductility, the seismic performance factors of response modification coefficient (R), overstrength factor (Ω0) and deflection amplification factor (Cd), the values of interstory drift ratio at the DBE and MCE seismic hazard levels, maximum seismic capacity and fragility curves, permanent displacement after the earthquake and the weight of steel used in the structure have been investigated. Each of the analysis results shows that the linked column system has a suitable seismic behavior against earthquakes. Therefore, in a preliminary evaluation, the linked column system is introduced as a steel lateral load resisting system that provides the ability to repair structures after an earthquake.

A novel meshfree radial point interpolation method with discrete shear gap for nonlinear static analysis of functionally graded plates

A novel meshfree radial point interpolation method with discrete shear gap for nonlinear static analysis of functionally graded plates

Interface modeling in load transfer mechanisms of multi-leaf masonry panels

Masonry heterogeneity and manufacturing imperfections affect structural behaviour of constructions; these unpredictable aspects are amplified in multi-leaf masonry walls by interfaces which play a main role on load transfer mechanisms and on global behaviour. In this paper, the performances of multi-leaf masonry walls subjected to compressive loads are investigated using experimental and numerical approaches. 9 experimental tests were performed on three-leaf specimens constituted by external leaves made of a regular pattern of brick elements and mortar joints, and a disaggregate internal core made of brick potsherds and mortar. FE models were developed to assess the interface interaction among layers through model updating procedure based on dynamic parameters experimentally identified at incremental load conditions, keeping fixed the mechanical parameters of external layers. FE models were updated by 13 parameters: i) unidirectional stiffnesses of 12 springs located between external layers and core; ii) elastic modulus of core. Updated models were tested through non-linear static analysis and results were compared with structural performances of multi-leaf masonry panels. Interface effectiveness regulated by different stiffness hierarchies among layers and between bricks and mortar joints handles the load transfer mechanisms and failure scenario. Compressive load is transferred through out-of-plane mechanisms triggered by maximum tensile stresses by 20% of failure load. In the plane the load is transferred with maximum compressive stresses at the ends (30% of failure load) decreasing centrally. Tangential stresses among layers are maximum near to load application and are linearly distributed in the plane of panels.

Performance‐based plastic design and seismic performance evaluation of twisted diagrids with shear links

SummaryTwisted diagrid tube structures have become popular due to their significant lateral resistance and esthetic potential. However, the ductility and energy dissipation capacity of twisted diagrid structures are poor. This paper presents a seismic resilient fused structural system named the twisted diagrids with shear links (TDSL), and the performance‐based plastic design (PBPD) method is introduced for designing a 24‐story prototype structure. The numerical model of the TDSL prototype is established, then nonlinear static and dynamic analyses are conducted to evaluate the seismic behavior of the prototype. The results reveal that the TDSL system can significantly improve the post‐yield performance compared to the conventional twisted diagrid structure, and the performance objectives are achieved properly. Subsequently, incremental dynamic analyses are carried out to investigate the collapse fragility of the TDSL prototype, and the collapse risk of the prototype is assessed by FEMA P695. The results indicate that the TDSL prototype has satisfactory collapse‐resisting capacity under earthquakes. It is also found that corner columns can improve the seismic safety of the prototype against collapse. In general, the TDSL system is an appealing choice for twisted buildings in seismic regions.

Comparative Assessment of Shear Demand for RC Beam-Column Joints under Earthquake Loading

This paper focuses on the evaluation of bi-axial shear demand for reinforced concrete (RC) beam–column joints assuming: (i) the SPEAR frame as a benchmark; and (ii) different structural analysis methods which share the same seismic input. A numerical model was implemented using lumped plasticity. The joints were modeled as rigid offsets of beams and columns. The shear demand at a joint is evaluated as a post-process of the beam’s nodal moment. The discussion focuses on the differences between the estimated shear demand considering modal-response-spectrum analysis (MRSA), non-linear static analysis (NLSA) and non-linear time history (NLTH). Strength assessment of joints is discussed as well. Significant strength differences were recognized by using different building codes targeted to existing structures which, in general, behaved on the safe side. The elliptical shear strength domain resulted in being conservative when compared to NLTH shear demand orbits. NLSA, using modal combination, proved to estimate the larger shear demand with respect to MRSA and NLTH.

A fundamental-period-preserving seismic retrofit methodology for low-rise buildings with supplemental inerters

Stiffness retrofit is a very effective technique to increase the seismic capacity of low-rise buildings. However, the shift of the fundamental period might lead to potential adverse effects when considering the spectral content of the ground motions. To address this issue, this paper proposed a fundamental-period-preserving (FPP) retrofit methodology. By augmenting traditional stiffness retrofit techniques with inerters, the fundamental period can be preserved. In addition, the normalized seismic input force and higher mode effects can be reduced. Different retrofit examples were evaluated through a series of nonlinear static and nonlinear dynamic analyses. Different performance objectives, including roof drift, story drift, story acceleration, base shear, and the force generated by inerters were used to demonstrate the effectiveness and the applicability of FPP approach in structure retrofit. The results showed that the FPP approach is an attractive alternative to the seismic retrofit of low-rise buildings.

Experimental and numerical study on the mechanical properties of honeycomb plate box-type hollow roof structure

In this paper, a new honeycomb plate box-type hollow roof structure is prepared. The failure mode and mechanical properties of the box-type hollow roof structure were analyzed by bearing capacity test and numerical analysis. The validity of the numerical analysis model is verified by comparing the results of bearing capacity test with the results of the complete coordinated model and the coupled model analysis. The results show that the failure mode of the specimen is tensile failure of the surface plate of the honeycomb plate with strengthened frame and buckling instability of the plate near the joint. The box-type hollow roof structure has good ductility. The results of static analysis and nonlinear buckling analysis of the honeycomb plate box-type hollow roof structure are carried out by coupling model are more consistent with the results of bearing capacity test.

Numerical Analysis of the Seismic Performance of Light-Frame Timber Buildings Using a Detailed Model

Timber structures have gained interest for the construction of mid-rise buildings, but their seismic performance is still a matter under development. In this study, a numerical analysis of the seismic performance of light-frame timber buildings is developed through a highly detailed model using parallel computing tools. All of the lateral-load-resisting system components and connections are modeled. Combinations of lateral load capacity distributions in structures of one, three, and five stories are studied in order to assess the effects on the global performance of different triggered failure modes through nonlinear static and dynamic analyses. The results suggest that shear bracket connections and sheathing-to-framing connections control the buildings’ responses, as well as the failure mode. For a ductile response, the lateral displacement must be dominated by the in-plane wall distortion (racking); therefore, the system must be provided with a story shear sliding stiffness and load capacity at least twice that of the walls. Furthermore, based on the pushover capacity curves, the performance limits are proposed by evaluating the stiffness degradation. Finally, the effect of the mobilized failure mode on the structural fragility is analyzed. Even though standard desktop PCs are used in this research, significant reductions in the computation effort are achieved.

Eurocode 8 revision – Implications on the design and performance of steel moment-resisting frames: Case study

Since the 2004 release of the European seismic code – Eurocode 8, various improvements have been proposed to its rules. The standard is being revised and, in its current revised state, it has been restructured and expanded in content. The revisions related to steel structures and especially to the design of steel moment-resisting frames (SMRFs) are notable. Modifications in the definition of the ductility classes, grade-dependent material randomness factors, behaviour factors, inter-storey drift sensitivity index (θ), the local hierarchy criteria, and the design rules for the dissipative ductility classes (DC2 & DC3) are a few of the notable proposed changes. This paper aims to study and compare seismic designs and performances of SMRFs using the revised specific rules for steel design. To this end, a parametric case study, consisting of 96 frames, is devised by varying the key parameters such that the effects of the recent changes can be highlighted. The parameters varied are the design code, ductility classes, number of storeys, span length, and material strength. The case study frames are analysed and designed to both versions of the EC8. Later, the seismic performance of the case study SMRFs designed to the current and revised EC8 provisions are investigated through non-linear static and dynamic analyses using OpenSees. Additionally, the significance of two distinct joint modelling techniques is explored.The results show that stability is not the governing requirement with the revised code. Lighter solutions in terms of steel mass were possible for the regularly spaced frames using the revised code. It was noted, however, that contrary to the design intent and despite the higher behaviour factor used in DC3 & DCH frames, their solutions were not found to be lighter than those designed to DC2 & DCM in both code versions. The actual behaviour factors estimated from non-linear analyses were also found to be different from those used in design by a considerable margin. The over-strength component of the behaviour factor varied significantly between frames of different steel grades and ductility classes. It was observed that the component plays such a significant role in the overall behaviour factor that assigning a constant value may result in misleading estimates. The dynamic analyses results showed that the frames designed to both versions of EC8 demonstrated acceptable performance even at the near collapse limit state.

Comparative study and performance evaluation of steel moment resisting frames design with: Force-based design and performance-based plastic design

Incremental Dynamic Analysis (IDA), Nonlinear Response History Analysis (NLRHA) and Nonlinear Static Pushover Analysis (NSPA) has been carried out to evaluate seismic performance of Steel Moment Resisting Frames (SMRF). SMRF’s are used as the lateral resisting systems which consist of columns and beams joined by welding or using high strength bolts or combination of both. The resistance offered to the lateral forces is due to rigid frame action which develops bending moment and shear force in the frame members and joints. The 9-storey SMRF is been evaluated for two frames designed by Force Based Design (FBD) method and Performance Based Plastic Design (PBPD) method. The FBD frame is designed by using codal provision of ASCE 7 (American Based Seismic Code) and AISC (American Institute of Steel Construction) whereas PBPD frame is designed as per proposed work of Lee and Goel (2001) in which energy balance equation and pre-selected yield mechanism is considered. The evaluation study showed that the PBPD method for steel moment resisting frame is significantly more efficient in achieving a certain inelastic displacement/ductility for given seismic hazards compared to the existing design standards/specification for this system. By Nonlinear Static Pushover Analysis (NSPA) the PBPD method has achieved the target yield drift of 1.11% and FBD method has achieved 1.22% where the assumed yield drift was 1%. From NLRHA the percentage difference in achieved ductility factor for frame design by FBD method is 46.28% whereas for PBPD method it is 16.81%. From IDA inter storey drift is observed maximum in AISC design frame compared to PBPD design frame. Therefore, PBPD method frames responded as intended in design with much improved performances over those of the corresponding FBD method.

STATIC BENDING ANALYSIS OF VARIABLE THICKNESS MICROPLATES USING THE FINITE ELEMENT METHOD AND MODIFIED COUPLE STRESS THEORY

This paper presents the nonlinear static bending analysis of variable thickness microplates by using the finite element method and modified couple stress. The present theory and mathematical model are confirmed by comparing the numerical data with those of open literatures. A parameter study is carried out to investigate the mechanical behavior of the structure, especially, the effect of nonlinearlity. The computed data can be used as a good reference in the use and design of these types of structures in engineering practice.

Engineering demand parameters for the definition of the collapse limit state for code-conforming reinforced concrete buildings

This article discusses the main Engineering Demand Parameters (EDPs) found in the literature to define collapse of newly constructed reinforced concrete buildings. Currently, the definition of building collapse is still under debate, as different building codes and authors define them with different EDPs and even different values of the same EDPs.The EDPs can be defined locally (chord rotation, Local Damage Index, etc.) or globally (Inter-Story Drift Ratio, Roof Drift Ratio, Global Damage Index, etc.). A modified Global Damage Index that considers damage in both structural and non-structural elements is proposed in this paper The study compares the outcomes of some of these EDPs when applied to two case study moment-resisting reinforced concrete frames designed and analyzed in the framework of the RINTC — Reluis Project funded by the Italian Civil Protection Department (Ricci et al., 2018). One is a 6-story buildings (in Naples) the other a 9-story building (in L’Aquila). Nonlinear static and multiple-stripe dynamic analyses were carried out on 3D models with concentrated hinges. In addition to the above mentioned EDPs this study proposes and tests a new economic EDP that assumes that collapse is reached when the repair costs become larger than the reconstruction costs. Complete validation of the proposed economic EDP requires additional testing on code-conforming and, most importantly, on non-conforming older buildings, where brittle failures become an important issue.

Modelling and Seismic Response Analysis of Existing URM Structures. Part 1: Archetypes of Italian Modern Buildings

ABSTRACT Five existing unreinforced masonry buildings, built in different Italian cities in a relatively recent time frame, were selected to study the seismic behaviour of modern existing structures, not designed to withstand seismic actions. The buildings were modelled using an equivalent-frame approach, adopting, and comparing two nonlinear constitutive laws and introducing specific modelling strategies to represent the distinctive features of modern existing URM structures. Nonlinear static analyses were performed to determine capacity and multi-stripe time history analyses to evaluate displacement demand at increasing return periods. Although non-exhaustive, the results show a trend of generally decreasing seismic vulnerability for more recent buildings.