Nonlinear Static Analysis Research Articles

Seismic Assessment of Combined Effects of Knee Bracing and Dog-bone Connections in Dual Moment Frame Systems for Tall Steel Structures

The growing population and urbanization have led to an increasing interest in constructing tall buildings, particularly in large cities. However, the frequent occurrence of earthquakes worldwide has necessitated the development of systems with high ductility and sufficient lateral stiffness. The special dual system of moment frame with bone connections and knee bracing systems are two examples of such systems. In this study, the seismic behavior of these two systems in combination with tall structures was investigated. Ten, thirteen, and sixteen-story frames with four different combinations of bone joints and knee bracing were analyzed using ETABS software. Linear and nonlinear static (pushover) analyses, as well as linear and nonlinear dynamic (time history) analyses, were conducted. Seismic parameters were then calculated for each case and compared. The results emphasized the importance of considering multiple factors and coefficients when evaluating the seismic performance of structures.

Evaluation of modelling uncertainties impact in older infilled frame RC structures

The seismic response of infilled frame reinforced concrete structures is affected by different sources of aleatory and epistemic uncertainties and is particularly sensitive to the modeling parameters evidenced by reported numerical and analytical studies. In the current study, a probabilistic sensitivity analysis is performed by nonlinear static (PNSA) and nonlinear dynamic analyses (PNDA) on a base-case infilled frame structure incorporating structural (beam, column) and non-structural (masonry infill) components behavior. Therefore, the state-of-the-art models of the most effective sources of nonlinear response employed herein as fiber section to depict the axial-moment interaction in frame components, bi-diagonal eccentric strut to capture the cracking and crushing of masonry infill, and the shear failure in columns caused by infill-frame interaction. Finally, results are illustrated by tornado plots incorporating probabilistic sensitivity to material and component parameters for operational (O), damage (D), life safety (L), and collapse (C) limit states. Results state that the building response is significantly affected by the modeling parameters of infill characteristics, mass source, and the damping of the structure.

Analysis of steel–concrete composite beam using Ansys 18.1 Workbench

Composite beams made from more than one material can cover large column-free spaces. Composite construction is faster than cast in-situ concrete as rolled steel and prefabricated components are used. Steel concrete composite beam consists of a steel beam above which a concrete slab with reinforcement is casted using shear connectors. In recent years, steel–concrete composite beams have been employed extensively in structures and on bridges. The concrete act together with steel to create a stiffer, lighter, less expensive structure. The analysis using ANSYS 18.1 Workbench is significant as it provides more accuracy compared to experimental analysis along with being cost efficient and time saving and it uses the principle of finite element analysis. An experimental study was done to study the behavior of composite beam under monotonic load by Bing Wang, Qiao Huang, Xiao ling Liu and Wenxian Li. The study was conducted on eight composite beams with various arrangement of shear connectors to assess their performance under monotonic load and fatigue load. This paper studies the structural behavior of steel concrete composite beam under monotonic load and also compares the experimental results obtained from above mentioned paper with the results obtained for four steel–concrete composite beams analyzed using Ansys 18.1 Workbench. Non-linear static analysis was done on four sets of beams based on the variation in number of studs and stud spacing. SOLID 65 element was used for concrete and LINK180 element for modelling reinforcement. The analysis as per the report generated by the ANSYS software, seems to stop on 156th iteration and the results were then obtained. Load-deformation and ductility index of the beams were obtained from software and were compared with experimental values. Crack pattern was also obtained using linear analysis. The percentage error occurred in terms of ultimate load, total deformation and ductility index is less than 10%. It was found that as the number of shear connector provided was beyond the permissible number there can be crowding which could result in more cracks. Hence, it is advisable to not to use increased number of studs, as that may result in harming the serviceability conditions of structure.

Parametric study of wood sheathed cold formed steel shear wall panels using OPENSEES

CFS members are widely used in transmission towers, bridges, and building structures. They are lightweight, stiff, and robust materials suitable for low-rise constructions. However, their lateral load capacity is limited, and to overcome this challenge, SWPs are employed in CFS structures to resist lateral forces. SWPs consist of CFS studs and tracks attached to sheathings, which can be made of metal or wood. This study aims to evaluate the lateral strength of wood sheathed SWPs. These panels can effectively dissipate energy under lateral loading due to the combined inelastic behaviour of their components: Frames, Sheathing, and screw connections. A precise material model is required to simulate this inelastic behaviour accurately under quasi-static or dynamic loading. Therefore, this study develops an algorithm to accurately model the linear behaviour of wood-sheathed SWPs. OPENSEES software is used for nonlinear behaviour, employing zero-length elements, the pinching4 material model, and the EEEP rule. The proposed analytical method is applied to analyse the lateral strength of wood-sheathed SWPs. Nonlinear static analysis, including cyclic and monotonic push tests, is performed using the proposed method for OPENSEES. Moreover, the study investigates various physical parameters that affect the nonlinear behaviour of wood-sheathed SWPs, such as screw spacing, sheathing thickness, screw diameter, and aspect ratio. Finally, a sensitivity study is conducted to evaluate the cyclic response of wood-sheathed SWPs by analysing the key physical parameters.

Design of a typical aerospace interstage structure using orthogrid/waffle configuration

The term interstage refers to a primary structure housed between two stages of a launch vehicle. It is configured to withstand the varying magnitudes of loads during the flight. In this study, an interstage cylindrical shell structure of a Launch Vehicle is designed with isogrid and orthogrid configurations, which are integral-rib-stiffened-skin configurations to have mass-optimised aerospace structures. Design based on closed form solutions, parametric optimisation and numerical analyses to validate the design are carried out for both the configurations and results are compared. Static - linear, static - nonlinear, linear eigen value buckling analysis and non-linear static riks analysis are the different kinds of numerical analyses carried out for estimating the load carrying capacity of the structural configuration under study. The objectives of this work include understanding different aerospace structural configurations, studying grided structures in depth, and using these two to model Orthogrid structures mathematically and design a typical launch vehicle interstage structure using this Orthogrid configuration. Abaqus, a general-purpose Finite Element software is used for the numerical validation. Study compares the results of both the configurations and concludes that orthogrid configuration can be designed with lesser mass for the interstage configuration, loads and kinematic conditions considered for the design problem. The least mass configurations corresponding to each configuration are obtained through parametric design iterations. Various numerical calculations are used to validate these results. The study's findings show that for the geometry, loads, and boundary conditions taken into account, orthogrid design provided superior mass optimisation than isogrid configuration.

Assessment of the Seismic Vulnerability of a Multi-storey RC Structure with Plan Irregularity: A Case Study

A nine-story reinforced concrete dual system (wall-frame) building located in Bucharest, categorized as plan-asymmetric and designed according to the provisions of Romanian and European codes was studied. The criteria for regularity in plan were verified comparatively according to three codes (Eurocode 8, ASCE 7-16 and the Romanian seismic design code P100-1-2013). The seismic behaviour of the studied building was further investigated by detailed nonlinear static analyses (pushover) and nonlinear dynamic analyses performed on the 3-D building model, for various load patterns and spectrum-compatible ground motion records, respectively. The seismic vulnerability of the building was estimated based on the structural vulnerability index, determined from the nonlinear analyses. The study highlighted the significant effects of the overall torsion on the investigated parameters, in particular on interstory drifts and roof displacements, but also on the seismic vulnerability index.

EVALUASI KINERJA STRUKTUR RANGKA BETON BERTULANG BALOK LEBAR DENGAN DISTRIBUSI BEBAN PELAT SATU DAN DUA ARAH

A reinforced concrete frame building system using wide beams is a solution for buildings with limited heights to get a larger number of stories, a higher distance between stories, and flexibility in installing architectural elements and MEP. This analytical study was conducted to evaluate the behavior and performance of open-frame structures with wide beams for one-way and two-way slab system conditions. This study was carried out using a structural analysis program by applying linear and nonlinear analyzes to four models of a five-story structure with square columns, which varied in beam dimensions and slab systems. The variations considered are normal beam with one-way slab system (1wSN), normal beam with two-way slab system (2wSN), wide beam with one-way slab system (1wSW), and wide beam with two-way slab system (2wSW). All structural elements are designed to follow and meet the criteria of the Indonesian Building Codes, which are then followed by a non-linear static pushover analysis to obtain the performance of each structural model. The results of the analysis show that a structure with wide beams has greater deformation than a structure with normal beams with a faster achievement of collapse conditions so that the ductility of the structure also becomes lower. This is caused by the stiffness of the wide beam-column joints is lower than that of the normal beam-column joints. The use of one-way or two-way slab systems on structures with wide beams does not have a significant effect

Influence of Masonry Infill Walls on the Seismic Assessment of Non-Seismically Designed RC Framed Structures

This paper examines how the decision to include (or exclude) masonry infill walls in the modelling of non-seismically designed RC framed structures can affect the results of the EC8-3 seismic assessment process. A frequently used macro-modelling technique for the simulation of infill panels within bounding RC members is first reviewed. A case-study application follows in which the seismic assessment of a sample structure is carried out, with and without considering the effect of its infill walls, using nonlinear static and dynamic analysis models. The obtained results are then discussed according to the applicable limit states’ performance requirements, and conclusions are drawn regarding the overall outcome. The study indicates that, when low and medium seismic input motions constitute the base demand for the assessment of older-type RC framed buildings, the protection provided to the RC members by the confined masonry infill panels should not be neglected. Moreover, it shows that the identification of the most likely collapse mechanism might also be significantly influenced by the modelling decision in question. As such, the default recommendation is to include masonry infill walls in the modelling of such structures.

Stability of the RC Column under Horizontal Impacts

Approaches to assessment of stability of reinforced concrete columns in case of horizontal emergency impact have been investigated. For this purpose, finite-element modeling of the system in spatial formulation, calculation according to the deformed scheme in the scope of nonlinear static analysis and dynamic transient process have been implemented. When constructing the model, the hexahedral elements were used, working in accordance with the Drucker-Prager model for concrete, and the rebars deformed according to the Prandtl model were used to modelling the reinforcement.The impact action was considered as a short-term pulse of constant intensity. Dependence diagrams for critical force on various scenarios of emergency impacts on the column have been obtained. Results of researches can be used for an estimation of resistance to the progressive collapse of reinforced concrete structures at their variants design and optimization.

Seismic Damage “Semaphore” Based on the Fundamental Period Variation: A Probabilistic Seismic Demand Assessment of Steel Moment-Resisting Frames

During strong earthquakes, structural damage usually occurs, resulting in a degradation of the overall stiffness of the affected structures. This degradation produces a modification in the dynamic properties of the structures, for instance, in the fundamental period of vibration (T1). Hence, the variation of T1 could be used as an indicator of seismic structural damage. In this article, a seismic damage assessment in four generic typologies of steel buildings was carried focused on verifying the variation of T1. To do so, several seismic damage states were calculated using the maximum inter-story drift ratio, MIDR, and following the Risk-UE guidelines. Then, a series of probabilistic nonlinear static analyses was implemented using Monte Carlo simulations. The probabilistic approach allows one to vary the main mechanical properties of the buildings, thus analyzing in this research 4000 buildings (1000 building samples for each of the four generic typologies). The variation of T1 was estimated using the capacity spectrum, and it was related to the MIDR for each damage state. As a main result of this study, the expected variation of T1 for several damage states is provided. Finally, a proposal for a seismic damage preventive “semaphore” and fragility curves are presented. These results may be useful as parameters or criteria in the evaluation of on-site structural monitoring for steel buildings.

Design Recommendations for Columns Made of Ultra-High-Performance Concrete and NiTi SMA Bars

The use of new materials in construction endows structures with better mechanical characteristics. The combination of ultra-high-performance concrete (UHPC) and nickel and titanium (NiTi) shape memory alloy (SMA) improves the behavior of building structures by increasing both their ductility and dissipation energy due to the low-damage and self-centering properties of NiTi SMA. Since UHPC and NiTi SMA are expensive materials and still scarce in distribution channels, this article tries to offer design recommendations to reduce the length of the column-beam connection in which these new materials should be introduced, leaving the rest of the column with conventional materials. To achieve this, a nonlinear static pushover analysis of columns using finite element software, SeismoStruct, was performed. This model was calibrated using experimental results. Next, a parametric analysis was carried out to propose the design recommendations. Results indicated that an adequate design for the column–beam connection, considering both economy and performance, should include a main zone with UHPC and SMA reinforcements, a transition zone with UHPC and steel reinforcements, and another zone with conventional reinforced concrete. The transition zone improved the hybrid column’s performance without excessively raising the cost. The main zone length, the transition zone length, and the strength of the concrete in the rest of the column must be determined to ensure that the critical section of the column was in the main zone to develop the maximum strength and ductility. The length of the main zone depended on the compressive strength of the conventional concrete, the relative axial load of the column, and the required ductility.

Influence and effectiveness of horizontal diaphragms and cladding wall panels on the seismic behaviour of precast RC industrial buildings

The seismic behaviour of precast reinforced concrete industrial structures has been extensively investigated in recent decades, especially after the damage caused by recent earthquakes. The interaction of the roof's horizontal diaphragm with the structural and non-structural elements can influence the seismic behaviour of these buildings. Thus, the present study aims to investigate this interaction, through nonlinear static and dynamic analyses using a simplified macro element to simulate the behaviour of cladding panels and an equivalent truss approach to simulate the roof in-plane stiffness. The analyses were performed on several structural models considering the current European single-storey precast reinforce concrete industrial building stock, with or without cladding wall panels, and with rigid or flexible diaphragm roof. Despite the uncertainties associated with the ability of common roof systems to ensure a rigid diaphragm, the analyses allowed the establishment of a correlation between the buildings generic properties and the roof horizontal stiffness required to approach a rigid diaphragm effect. In general, the results show that the consideration of a rigid diaphragm in numerical models may tend to produce a more realistic seismic behaviour of the overall structure. Furthermore, the contribution of facade cladding wall panels significantly influences the seismic behaviour of the building, especially for high-rise buildings.

Effect of lightweight steel partitions on seismic behaviour of moment resisting frames

For several years the partition walls were considered as architectural elements and were not accounted for in the structural design, despite they could significantly influence the overall performance of the structure. The principal aims of the present work is to investigate the influence of lightweight (LWS) steel partitions on the seismic performance of perimeter steel moment resisting frames (MRFs) and monitor the development of the damage within them. The behaviour of the partition walls was modelled through a non-linear spring properly calibrated on a set of five experimental tests. Static and dynamic non-linear analyses were conducted on a total of 24 MRFs, varying the design acceleration (i.e., 0.25 g and 0.35 g) and the beam span (i.e, 6 m and 8 m). Moreover, for each geometry, three sets of MRFs were alternatively designed according to the rules provided by: the current version of the EN1998–1, the North American codes, and the last draft of the next Eurocode 8. The results show that the presence of partition walls implies an increase in structural lateral stiffness and maximum resistance. The influence of the partition walls is a function of both the initial stiffness of the investigated MRF, thus more deformable is the system, larger will be the influence of the partition walls, and the rotational demand; indeed, increasing the lateral displacement will imply a gradual damage within the partition walls that for high value of interstorey drift will not provide significant contribution to the structural behaviour.

Degradation of the first frequency of an RC frame with damage levels

Damage in RC structures causes the degradation of stiffness and frequency parameters. In this study, the relationship between the two coefficients and damage severities is numerically investigated considering a three-dimensional (3D) reinforced concrete (RC) frame in which the concrete damage plasticity model (CDPM) and the elastoplastic model are selected to define concrete and reinforcement materials, respectively. Crack propagation of the frame is obtained utilizing a nonlinear static pushover analysis (NSPA). After the pushing procedure, according to the base shear force versus top displacement curve, the bending stiffness of the RC structure is determined rapidly. Thereafter, the degradation of the first frequency is obtained based directly on the nonlinear curve of stiffness. As a result, it is observed that the degradation of the first frequency of the RC frame is proportional to the severity of damage but not linearly. More significant damage, a more profound decrease in the modal characteristic. Particularly, the fundamental frequency of the RC frame reduces gradually until the base shear force reaches 70% of the ultimate value at which the parameter is about 60% of the counterpart at the intact stage. After that, the reduction gets more significant when the bending capacity approaches the ultimate value.

Beam-Truss Models to Simulate the Axial-Flexural-Torsional Performance of RC U-Shaped Wall Buildings

Reinforced concrete (RC) core walls are commonly used to provide buildings with lateral and torsional resistance against the actions of wind and earthquakes. In low-to-moderate seismic regions, it is not unusual to find a single peripheral core wall that alone should resist these actions, where the torsional (rotational) twist cannot be neglected. It has previously been difficult to have confidence in simulating the axial-flexure-torsion behavior of these RC core walls, primarily due to: (i) some types of modelling approaches being unable to appropriately account for the shear-flexural action, as well as torsional response; and (ii) the scarcity of experimental data, particularly for walls under torsional loads, which would be required to validate such models. In this research, beam-truss models (BTMs), which correspond to an interesting compromise between detailed modelling and practical applications, were used to simulate the in-plane and diagonal flexural response of RC U-shaped walls. Furthermore, the global torque-rotation results from a recent experimental wall test provided the evidence to further validate this powerful modelling technique. A case study building, comprising an RC U-shaped core wall structure with varying eccentricity values, was evaluated for an earthquake event with a 2475-year return period in the city of Melbourne, Australia, using the capacity spectrum method. Nonlinear static pushover analyses showed that, depending on the magnitude of torsion, the in-plane flexural strength and displacement capacity can be significantly reduced. The results from this research emphasize the importance of including torsional actions in the design and assessment of reinforced concrete buildings.

Seismic design and performance study of self‐centering moment‐resisting frames with sliding rocking beams and preloaded disc springs

AbstractThis paper focuses on the seismic analysis and performance assessment of the self‐centering moment‐resisting frames with sliding rocking beams (SCMRF‐SRB) through a nonlinear numerical simulation study. In the SCMRF‐SRB systems, the beam is comprised of three segments with the rocking beam placed in the middle segment. The beam growth (expansion) problem due to the gap‐opening in the rocking joint is counteracted by the sliding movement of the rocking beam inside the beam brackets. The restoring force of such SCMRF‐SRBs is generated by two sets of preloaded disc springs mounted on each side of the web of the beam and the energy dissipation is provided by replaceable hysteretic dampers (RHD). The relative movement of the rocking beam inside the brackets generates a friction force that contributes to the energy dissipation capacity and strength of the system based on prior experimental observations. Load vs. displacement relationships of an SCMRF‐SRB modular structure were formulated and verified with nonlinear finite element analysis results. A three‐story building located in downtown Seattle was designed and its seismic performance was studied through nonlinear static and dynamic analyses. According to the results of the nonlinear dynamic analyses, the prototype structure met the expected performance criteria in terms of inter‐story drift ratio (IDR), re‐centering behavior, and responses of the frame member at design basis earthquake (DBE). In different parametric studies, the effect of the length and location of the rocking beam on the seismic performance of the prototype structure was investigated. Moreover, the effects of the energy dissipation capacity and post‐yielding stiffness on the structural responses of the prototype buildings were studied. It was also shown that an SCMRF‐SRB structure with a large energy dissipation ratio of up to 90% can be utilized without adversely affecting the self‐centering performance of the system.

Modelling of the seismic behaviour of wall-to-horizontal diaphragm connections in historical constructions: Application to a case study

Out of plane mechanisms in historical earthquake-prone buildings are frequently due to weak wall-to-wall and wall-to-horizontal diaphragm connections solely designed for gravitational loads and generally neglected in the seismic analysis of unreinforced masonry buildings. Accurate modeling of structural connections is generally hard and nonlinear behavior can only be estimated when experimental data are available.This paper studies the influence of plain and strengthened wall-to-horizontal diaphragm connections on global and local analysis by developing and using simplified and advanced connections models calibrated upon experimental cyclic curves. The beneficial effects of the strengthened solution under study are demonstrated by means of global nonlinear static and incremental dynamic analysis, as well as local analysis based on the virtual work principle, but also advanced stability of rigid blocks. Hysteretic numerical models, accounting for strength degradation and energy dissipation capacity, are developed on the basis of available experimental results seeking to simulate the nonlinear behaviour of wall-to-horizontal diaphragm connections. This study aims at providing an innovative procedure at the forefront of the global and local analysis of structural connections in historical constructions.The behaviour of the building modelled with nonlinear connections is in between that of the building modelled with (i) poor and (ii) perfect connections commonly adopted in favor of simplified analysis. Results reveal that simplifications may imply errors up to 70% of the overall capacity of the building.

Influence of Single External Store on Geometrical Nonlinear Flutter of High-aspect-ratio Wings

High-altitude and long-endurance UAVs, distributed electric propulsion aircraft and large passenger aircraft often use high-aspect-ratio wings, which have obvious geometric nonlinear large deformation effect, and are usually arranged with a certain number of external stores, which have an impact on their geometric nonlinear aeroelastic characteristics. Based on the “quasi-linear” hypothesis, the updated Lagrange incremental finite element method and doublet-lattice method are used to perform the geometrically nonlinear static aeroelastic analysis, and the mass, stiffness and aerodynamic matrices of large deformation are updated, and the geometrically nonlinear flutter characteristics of high-aspect-ratio wings are calculated. The influence of the position and mass of the external store on geometrical nonlinear flutter characteristics of high-aspect-ratio wing structure is investigated. Results show that the change of the position and mass of the external store causes the relative position between the elastic axis and the center of gravity of the wing, and the wing’s large deformation equilibrium state to change, resulting in differences in the stiffness characteristics of the wing and the natural vibration frequency of the equilibrium state, thus affecting the wing flutter characteristics. When a single external store is installed near the wing root, changing the mass and direction of the store has no significant effect on the geometric nonlinear flutter characteristics of the wing. The improvement of wing flutter speed is most obvious when the hanging point is moved to the leading edge of the wing near 0.65 times the wingspan.

Seismic Behaviour of the Low-Rise RC Buildings in Nonlinear Static and Dynamic Analysis

This paper presents the behavior of three different types of irregular low-rise buildings, subjected to earthquake load. The study is performed by numerically modelling the buildings for the linear static analysis. Structural parameters displacements, drift, and storey shear are checked for various time periods of the building. The same models are also analyzed using nonlinear pushover analysis. The model is made nonlinear by introducing the hinges in the beam and column. The execution of nonlinear analysis is done by applying push in X and push in Y directions in controlled displacement mode. After the execution of nonlinear pushover analysis, different colours of hinges were formed, which were used as a basis for the study. The parameters like maximum displacement, max storey drift, and storey shear were computed in both in X and Y directions. Peak ground acceleration of Gorkha earthquake, EI Centro earthquake, and Kobe earthquakes was used for time history analysis. The results for max displacement, base shear, and max storey drift are presented and the comparison is made for the different building models. The study showed that a building behaves well in seismic loading even though they have an irregular plan with a larger structure size, compared to a building that has a regular plan and a smaller structural member size.

Combined use of deformation and structural analysis for the structural damage assessment of heritage buildings: A case study in the Liguria region (Italy)

Cultural heritage buildings as they appear today are the result of continuous transformations occurred over the centuries. For this reason, their structural assessment should integrate structural analysis with a deep knowledge of the building history, actual geometry, damage, past alterations, and actions undergone over time. This paper presents the structural damage assessment of San Carlo Borromeo church, a historic masonry building located in the Liguria region (Italy) in a slow-moving landslide-affected area. To assess the effect of the landslide and identify the causes of the damage and deformations observed in the building, structural analysis was combined with historical research, on-site inspections, laser scanner survey and deformation analysis. A finite element model of the entire church in its geometric undeformed configuration was prepared by removing all the deformations identified through the deformation analysis from the actual deformed geometry obtained from the laser scanner survey. Nonlinear static analyses were then performed by applying at the base of the model a set of displacement fields obtained from the deformation analysis and representing the displacements experienced by the building due to the landslide and further phenomena that were found to have occurred. The damage and deformations predicted numerically were compared with those detected in the church. The good agreement proved that the deformation analysis is an effective tool to support structural analysis and assess the actual deformations and displacements experienced by historic masonry constructions.