Results Of Nonlinear Analysis Research Articles

Triggering Rainfall of Large-Scale Landslides in Taiwan: Statistical Analysis of Satellite Imagery for Early Warning Systems

Typhoon Morakot had a serious impact on Taiwan, especially the uncommon type of landslide called large-scale landslide (LSL), not many in number but serious in effect, the origin of which the study induced. To establish a specific relationship between LSL and triggering rainfall for future applications of LSL early warning predictions, relevant cases from satellite imagery, along with field investigation data, major event reports, and seismic data from 2004 to 2016, were collected. All collected cases are distributed around the mountainous area in Taiwan, and a total of 107 cases which were mainly distributed in the southern part of the mountainous area were finally selected, including 28 occurrence-time-known cases and 79 occurrence-time-unknown cases. In addition, 149 potential areas identified by the Soil and Water Conservation Bureau (SWCB) were used for improving bounding estimates. Based on the concept of safety factor, two dimensionless quantities, rainfall/landslide depth (R/D) and friction angle/slope (ϕ/θ), were analyzed by linear regression. In addition, D was assumed to be nonlinearly dependent on R, θ, and ϕ, and the parameter uncertainties were evaluated by the resampling with bootstrap method. Based on the currently obtained data, there were 8% Type-I errors in the results of the linear regression analysis, and 1% Type-II errors in the results of the nonlinear regression analysis. Through the comparison of statistical indicators, the results of nonlinear regression analysis have a better correlation trend. Based on the needs of early warning operations, more conservative indicators can reduce the risks faced by management operations. Therefore, according to the results of this study, the lower boundary values from nonlinear analysis could be used as the LSL early warning management settings. Incorporated with real-time rainfall forecasts, the variation of statistical indicators will provide the trend information dynamically, and will help to increase the response time for relevant evacuation operations, that will be welcome for the further extended applications to guide the evacuation operations of early warning systems.

Generalized response spectrum analysis based computational morphogenesis for metal gridshells with buckling-restrained braces subjected to seismic loading

Structural morphogenesis is widely used as a parametric tool to find an optimal structural shape of shell structures for a prescribed objective function and a given design load. However, the current optimization methods are limited to finding a geometry under only a specific static load like the dead load or an equivalent static seismic load for predefined geometrical shapes, and so can not be applied to free-form gridshells. This poses a challenge to achieving an efficient free-form shell structure in high seismic hazard areas. This paper aims to resolve this by presenting a computational morphogenesis method to obtain form-found shell structures by considering the dynamic seismic loads and the response reduction effects of seismic energy-dissipating devices using generalized response spectrum analysis. The method was applied to optimize the buckling-restrained brace layouts on target spherical metal gridshell structures with different diameter-to-height ratios. The resulting form-found structures had an efficient roof geometry, along with an efficient damper layout (to prevent member buckling and the dropout of finishing materials). Dampers were found to be more efficient if placed in the (relatively heavy) supporting structure instead of the roof, and a flattened but locally bulged roof shape proved to be the most efficient in mitigating the seismic response. The generalized response spectrum analysis significantly reduced the computation time while evaluating the displacement response with sufficient practical accuracy, although it slightly underestimates the acceleration response if compared to the conventional nonlinear response history analysis results.

Isogeometric Level Set-Based Topology Optimization for Geometrically Nonlinear Plane Stress Problems

This paper addresses geometrically nonlinear topology optimization using IsoGeometric Analysis (IGA) and Level Set Method (LSM) under plane stress assumptions. The IGA is employed to solve governing equations and accurately describe geometric modeling. The pointwise gradient-based sensitivity analysis is applied to derive the normal velocity of the Reaction–Diffusion Equation (RDE) to update the control net of the Level Set Function (LSF). The Generalized Displacement Control Method (GDCM) is used to obtain the equilibrium path based on the Total Lagrange (TL) formulation. A pointwise energy interpolation strategy is employed to avoid low-density instabilities. The exact Heaviside function is also applied to obtain a 0/1 manufacturable design. The objective is to maximize the total strain energy of structure, which is defined as the total external work within a specified displacement, while a certain volume of the design domain is considered. To demonstrate the ability and efficiency of the proposed method, several numerical examples are presented. By making comparisons, the results of both optimization algorithm and nonlinear analysis are shown to be in good agreement with the literature. Also, it is shown that obtained layouts are different from those in the linear behavior modeling due to considering buckling effects. In addition, linear and nonlinear final layouts are analyzed under large deformation assumption and the load–displacement curves are compared to illustrate the improvement of the objective function and final load. • Optimized topologies are parameterized using NURBS. • A pointwise energy interpolation strategy is employed to avoid low-density instabilities. • The control net of the design domain is updated by the reaction–diffusion equation. • Pointwise sensitivity analysis of the optimization problem is analytically derived. • 0/1 manufacturable design was performed using an exact (binary) Heaviside step function.

Evaluation of seismic performance factors for dual steel SMF-SCBF systems using FEMA P695 methodology

The present study evaluates the seismic performance factors of typical buildings with dual lateral force resisting system (LFRS) consisting of special moment frames (SMFs) combined with special concentrically braced frames (SCBFs) using FEMA P695 methodology. For this purpose, six building archetypes with 2-, 4-, 8-, 12-, 16- and 20-stories, in two short- and long-period performance groups were analyzed by the response spectrum method and designed based on the requirements of ASCE 7–16 and AISC 341–16. Validated nonlinear models were developed for each building in the OpenSees software platform. Then, the static and dynamic behavior of each building was investigated up to the collapse stage by nonlinear static analyses and nonlinear time history analyses under 44 far-field ground motions of FEMA P695. In this investigation, the peak and residual drift ratios, hysteresis behavior of the stories during the earthquake, collapse fragility curves, and seismic performance parameters (R, Ω, and Cd) were obtained and discussed. The results of nonlinear analyses demonstrated that code-compliant long period dual SMF-SCBFs (16 stories or higher) performed poorly and can be severely damaged in strong earthquakes.

Machine Learning for Enhanced Regional Seismic Risk Assessments

The ability to conduct accurate regional seismic risk assessments is key to informing a risk-reduction policy and fostering community resilience. This paper presents a machine learning-based framework to predict a building’s postearthquake damage state using structural properties and ground motion intensity measures as model inputs. The machine learning techniques assessed, namely, logistic regression, k-nearest neighbors, decision tree, random forest, AdaBoost, and gradient boosting, are trained using a dataset of nonlinear response history analysis results from 36 detailed structural models of modern reinforced concrete shear wall buildings ranging from four to 24 stories and subjected to approximately 500 ground motion records with a range of shaking intensities. The results indicate that the gradient boosting classifier is the most efficient algorithm by achieving a prediction success (F1-score) of 87%. The proposed framework also leverages synthetic data samples to support the prediction of severe damage state instances, that is, collapse. The percentage of observed collapse cases correctly classified by the gradient boosting algorithm is increased from 76% to 93% when synthetic data are also used for training. The framework is implemented in a portfolio of reinforced concrete shear wall buildings across the Metro Seattle region to quantify earthquake-induced damage and collapse risk. The framework shows great potential for enhancing regional seismic risk assessments by leveraging datasets of detailed nonlinear response history analysis results.

Nonlinear surface EMG analysis to detect the neuroprotective effect of citicoline in rat sciatic nerve crush injury.

Surface electromyography (sEMG) is a method involving physiological signals with a complex behavior. The aim is to analyze the sEMG signals by nonlinear techniques for investigating the possible neuroprotective effect of citicoline for early period of administration in rat sciatic nerve crush injury. Thirty-two Wistar rats were randomized into four groups: the sham-operated group with the intact sciatic nerve and the sciatic nerve crush groups, which received crush on the left sciatic nerve and administrated i.p. citicoline (50 and 250mg/kg/day, 7day) or saline (control group). Function assessment analysis was performed and sEMG signals were recorded and analyzed with nonlinear methods. Citicoline administration improved functional recovery in comparison with control group. Largest Lyapunov exponent and correlation dimension parameters were decreased due to the crush injury and increased related with the healing of sciatic nerve. Results of nonlinear analysis of sEMG are in line with the results of functional recovery and electrophysiological assessments. These results suggest that administration of citicoline protects the sciatic nerve from the crush injury which may be attributed to its antioxidative properties. Nonlinear analysis of sEMG is a promising supporting method for determining the nerve regeneration process during the treatment of peripheral nerve injuries.

Gediminas Hill Slopes Behavior in 3D Finite Element Model

In this manuscript, we present the results of three-dimensional finite element analyses performed in the cloud of a large-scale model of the Gediminas Hill buildings and the construction remains of the Upper and Lower castles in Vilnius city. The greatest challenge associated with the simulated numerical model is the difficult geological layer surface inclinations and soil–structure interaction behavior prognosis, which require significant computational resources. The purpose of this research work is to present current and possible worst-case scenarios for Gediminas Hill, considering its buildings and construction remains, regarding the stability of its slopes through a safety analysis. The construction of a numerical three-dimensional model of Gediminas Hill allows for us to assess the soil–structure interaction behavior. The results of non-linear analysis on the created model are in agreement with the tendencies observed in direct geodetic measurements and the relevant landslide history.

Performance-based seismic design of full and partial self-centering steel braced frames using modified lateral force distribution

Design base shear and lateral force distribution are two important aspects of the seismic design process. Different design methods have been proposed to obtain the design base shear of different types of structures. However, the study related to the lateral force distribution is limited, especially for self-centering (SC) structures. The primary objective of this research is to develop a performance-based seismic design (PBSD) procedure for steel braced frames considering the modified lateral force distribution. Six-story steel braced steel frames are designed to explore the influence of the energy dissipation factor on the lateral force distribution of the frames. Results of nonlinear time-history analyses indicated that the lateral force acting on the roof increases with the decrease in energy dissipation factor. Following the parametric analyses of single-degree-of-freedom (SDOF) systems, the energy factor design spectra are established and the corresponding PBSD procedure for the steel braced frames is proposed. Finally, the four six-story braced steel frames are redesigned using the PBSD procedure with the modified lateral force distribution to illustrate the efficiency of the proposed design method. Analyses results indicate that the steel braced frames designed by the proposed design can satisfy the expected inter-story drift limit with a reasonably uniform distribution of peak inter-story drifts. Furthermore, the ‘partial’ SC system appears to be a desirable option that effectively controls the residual displacement and peak acceleration responses at the same time, and could achieve a manageable cost control compared to the full SC systems.

Experimental validation of a model for a self-adaptive beam–slider system

A system consisting of a doubly clamped beam with an attached body (slider) free to move along the beam has been studied recently by multiple research groups. Under harmonic base excitation, the system has the capacity to passively adapt itself (by slowly changing the slider position) to yield either high or low vibrations. The central contributions of this work are the refinement of the recently developed system model with regard to the finite stiffness of the beam’s clamping, followed by a thorough validation of this model against experimental results. With the intent to achieve repeatable and robust self-adaption, a new prototype of the system was designed, featuring, in particular, a continuously adjustable gap size and a concave inner contact geometry. The initial beam model is updated based on the results of an Experimental Nonlinear Modal Analysis of the system (without slider). By varying the excitation level and frequency in a wide range, all known types of behavior were reproduced in the experiment. The simulation results of the updated model with slider are in excellent agreement with the measurements, both qualitatively (type of behavior) and quantitatively. Minor deviations are attributed to the system’s sensitivity to inevitable uncertainties, in particular with regard to the friction coefficient and the linear natural frequency. It is thus concluded that the proposed model is well-suited for further analysis of the system’s intriguing dynamics and for model-based optimization for technical applications such as energy harvesting.

Investigation of Fire Effects on Reinforced Concrete Members via Finite Element Analysis.

Structural deterioration during fire leads to significant economic losses, severe injuries, and deaths. Research to accurately estimate the impact of fire on structural security and performance, and to identify ways to reduce it, has been increasing recently with capital investments in the building and infrastructure sectors. This research aims to establish a reliable algorithm for simulating the behavior of reinforced concrete (RC) beams under thermal and structural loads. The proposed algorithm is based on the combination of thermal and structural analyses using the sequential link technique. These analyses use material characteristics such as conductivity, specific heat, stress–strain relationship, and thermal expansion to capture thermal and structural responses during the heating phases according to Eurocode 1 and Eurocode 2 using the finite element method. Beam models in the study, which have been exposed to the ISO-834 fire curve, were designed to exhibit flexural failure. Nonlinear numerical analysis results have mostly coincided with the previous studies regarding the residual load-bearing capacity. Depending on the outcomes of the previous experimental studies, an RC member’s structural strength increases when the internal temperature is between 150 and 250 °C and degradation starts after 300 °C. This outcome has been supported by the previous numerical and experimental studies, propounding the accuracy of preferred modeling and analysis approaches. As the essential distinctness of the research, the effects of elevated temperatures on the bonding behavior between concrete and rebar were considered for numerical analyses.

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.

Parametric Analysis of the Performance of Steel-Concrete Composite Structures Designed with TBDY 2018

In this study, the seismic behavior of steel-concrete composite buildings designed using ÇYTHYE 2016 and TBDY 2018 was investigated. For this purpose, composite moment resisting frame buildings with concrete filled steel tube columns and composite beams with 5, 10, 15 and 20 stories are modeled. Buildings are designed at high ductility (DCH) levels. During the design of the DCH class structures, the design was carried out for the ZA soil class for 0.79 g PGA in the region selected from the earthquake map given in the regulations. Within the scope of the study, SeismoStruct software was used during the design and performance evaluation of the structures. Incremental dynamic analyzes were used along with nonlinear static pushover analyses. In the static pushover analysis, uniform and triangular load distributions of the lateral load are adopted. In the dynamic analysis, 16 earthquake ground motions were obtained from AFAD earthquake acceleration databases according to the relevant design area and used. The variation of the seismic behavior of CMRFs depending on the variation of the floor number was investigated using nonlinear analysis results. Accordingly, the variation in lateral response, overstrength factors and ductility factors for CMRF structures are presented comparatively. In addition, the section deformation capacities were investigated during the IDR changes during dynamic and static nonlinear analyses. The behavior factor of all CMRFs, especially the CMRFs studied in the case study, demonstrated above-expected performance according to the design assumptions.

Experimental validation and numerical simulation of a dual-self-centering variable friction braced frame under strong ground motions

The dual self-centering variable friction brace (DSC-VFB) is a novel resilient system with a loading stiffness higher than the unloading stiffness and an enhanced energy dissipation capability. This study presents experimental and numerical analyses of a 1/3-scaled dual-self-centering variable friction braced frame (DVBF). The pinned beam–column, column–base connections in the DVBF ensured that the DSC-VFBs were a standalone lateral seismic resisting system. Three ground motions scaled to six shaking intensities were conducted to evaluate the seismic responses of the DVBF. The ground motions were subjected to far- and near-field earthquakes. Owing to the high seismic resistance of the DVBF, the stiffness degradation could be omitted after several strong earthquakes. The frame returned to its initial position with nearly zero residual drift, although the maximum drift exceeded 2.5%. The grooved friction plates and self-centering system, which could be disassembled and replaced conveniently, had no observable damage after the tests. A 3D simulation model was developed based on practical constructions. The nonlinear analysis results were compared with the experimental results. The two exhibited good agreement. The results showed that the DVBF under near-field pulse earthquakes resulted in larger displacement and acceleration responses than those under far-field and near-field no-pulse earthquakes. The present study verified the effective working mechanism and good resilience of the DSC-VFB and DVBF even under strong seismic shaking intensities.

The Normative Effect of Harmonic Loads on Pile Group Depends on the Characteristics of Dynamic Response

Pile-supported machine foundations are examined in this work to identify the dynamic features of linear and nonlinear theories. A three-pile group with a 3 m pile length and an outer diameter of 0.114 m is given axial harmonic loading before field-based forcing vibration testing. For four distinct eccentric moments, tests are carried out at a static load of 12 kN. Each eccentric instant's reaction in terms of frequency and amplitude is examined. The continuum approach technique is also used for theoretical analysis, which employs both linear and nonlinear solutions. All of the eccentric moments' dynamic field test findings are compared to theoretically expected frequency-amplitude responses. In comparison to the actual test findings, the linear solution's anticipated responses show lower resonant amplitudes and substantially higher resonant frequencies. The dynamic response curves predicted by the nonlinear solution fit the test findings rather well in this situation. To achieve this degree of agreement with nonlinear analysis results, precision in border zone parameters and soil-pile separation lengths was necessary.

Analytical determination of the influence of geometric and material design parameters on the stress and strain fields in non-prismatic components of wind turbines

Non-prismatic beamlike elements have long been used in engineering applications to optimize the performance of structures such as wind turbines, aircraft, and civil bridges, just to mention some examples. Unfortunately, engineering methods and formulas commonly used to analytically evaluate stresses and strains in prismatic beams do not hold and provide incorrect results for non-prismatic geometries. Large displacements and non-uniform material properties further complicate the analytical prediction. In order to determine the state of stress and strain in non-prismatic beamlike elements and its dependence on important design factors (such as taper parameters), a suitable mapping of the shape of such elements and a variational approach are used. The resulting field equations are exploited to derive application-oriented stress-strain formulas. Examples and comparisons with results of non-linear 3D-FEM analyses confirm the effectiveness of the modelling approach and of the new formulas proposed in this work.

Nonlinear Analysis of Reinforced Geopolymer Concrete Beams

To decarbonise the current construction sector and meet the global net-zero target, there is a pressing need to develop an environmentally friendly alternative to Portland cement concrete. Alkali activated and geopolymer concrete have much to offer in this regard. At present, however, there is limited study on the behaviours of alkali activated structural members, particularly on flexural members, which encompass most practical design situations. This paper presents a database of 37 tests on slender alkali activated and geopolymer concrete beams available in the literature, with the aim to investigate the flexural strengths of this alternative concrete when used as a structural member. In addition, the results of nonlinear finite element analyses on fourteen reinforced geopolymer concrete beams are presented to highlight key influencing factors governing the behaviour and failure of flexural members. Of particular interest is to study the influence of reinforcement ratio, compressive strength, and material brittleness on the overall strength and ductility. Overall, it is shown that the flexural response of geopolymer concrete beams under short-term loading is comparable to that of ordinary reinforced concrete beams.

Hysteretic behavior of a new type of outsourcing hybrid joint

The joints of the upper and lower structures are the key to ensure the overall cooperative capacity of reinforced concrete frame-added layer hybrid structure. A new type of outsourcing joint and a new type of outsourcing reinforced joint for the hybrid structure were proposed in this study, which were used to effectively alleviate the stiffness mutation and enhance the column foot constraints on the upper structure. The quasi-static experimental and finite element nonlinear numerical analysis results of new joints and exposed rigid joint were carried out. The anti-seismic performance of its hysteretic curves, skeleton curves, strength degradation, stiffness degradation and energy dissipation capacity were compared and analyzed. Results indicate that the three specimens are all beam hinge failures. The hysteretic curve of new type outsourcing reinforced joint is plump, and the plastic hinge is moved outwards, which protect the core area of the joint effectively. Its stiffness degradation, equivalent viscous damping coefficient, energy dissipation capacity and other indicators are improved to different degrees compared with the new type of outsourcing joint and exposed rigid joint. Thus, the new type of outsourcing reinforced joint has a higher load-bearing capacity and stiffness, and better seismic performance. This study can provide scientific basis and technical support for the popularization and application of steel structure-added layer hybrid structure.

Reliability of fully assembled precast concrete frame structures against progressive collapse

Although fully assembled precast concrete (PC) frame structures using dry connections have been widely promoted, limited studies have been carried out on anti-progressive collapse performance. This study presented a methodology to analyze and compare the reliabilities of entire structural systems between RC and fully assembled PC frame structures, which evaluates the risk and vulnerability of a structure when column failure occurs under accidental loads. First, based on the existing test results of three half-scale moment sub-structures, nonlinear finite element (FE) macro-models were established in OpenSEES software. The verified FE models were applied to three seven-story frame structures (one RC frame and two PC frames). To evaluate the progressive collapse resistance, nonlinear pushdown analysis was conducted on the frame structures using the alternate load path (ALP) approach. Combining the Nataf transformation-based point estimate method (i.e. the improved point estimate method (IPEM)) with the nonlinear analysis results, various load amplification factors (αmax) were estimated. Finally, the reliability indices of the intact and damaged frame structures were calculated using the Zhao-Ono high-order moment method (HOMM). The results revealed that the fully assembled PC frames had higher failure probability (2.1–6.6%) than the RC frame (0.2%) in a catastrophic event.

The effect of tension stiffening in moment-curvature responses of prestressed concrete members

Although tensile resistance of concrete is often neglected in calculating the nominal flexural capacity of a concrete member, it needs to be taken into account to accurately trace the deformation response of concrete members as it affects pre- and post-cracking behavior. To adequately address tensile resistance contributed by concrete in moment–curvature analysis, it is necessary to exploit a proper concrete tensile stress–strain model. While constitutive stress–strain models of reinforced concrete in tension have been studied by many researchers and well documented, those of prestressed concrete have gained relatively less attention. There are also conflicting results on how prestressing force affects concrete tension stiffening. This study fills the gap in existing studies and suggests an appropriate and simple model capturing the concrete tensile stress–strain relationship of prestressed concrete in a moment–curvature analysis. Based on an inverse-engineering approach using experimental test data and nonlinear analysis results, the effect of concrete tension stiffening varied by the level of prestressing force is investigated. The results show that concrete tensile properties hardly affect the force–deformation response of beams with high-level prestressing. Additionally, several parameters related to concrete tension stiffening are examined in the parameter study. By comparing predicted moment–curvature responses with test data, ideal values for considered parameters are obtained. Based on the parameter study, simple equations are proposed that are expressed in concrete compressive strength to simulate the concrete tensile stress–strain responses of partially prestressed members. The proposed equations are demonstrated using several prestressed beam tests found in previous studies.

Probabilistic evaluation of post-earthquake functional recovery for a tall RC core wall building using F-Rec framework

This paper presents a detailed evaluation of the functional recovery of a 42-story reinforced concrete core wall building located at a site of high seismicity using a newly developed, fully probabilistic, and comprehensive analytical framework for the assessment of post-earthquake functional recovery of buildings. This innovative framework allows complete and detailed evaluation of the seismic performance of tall buildings considering all structural and nonstructural building components/systems, and the calculation of performance metrics relevant for the assessment of functional recovery, including building’s post-earthquake functionality along with the duration and path of functional recovery. A nonlinear model of the building is created in OpenSees using a recently developed three-dimensional macro model for RC walls. Building seismic response is obtained for three seismic hazard levels corresponding to Service-Level Earthquake (SLE), Design-Based Earthquake (DBE), and Maximum Considered Earthquake (MCE). Based on the results of nonlinear analyses, damage-impaired losses are calculated using FEMA P-58 tools, while the building recovery process is evaluated using a novel framework for functional recovery (F-Rec framework). Building seismic performance obtained using new, advanced structural and recovery models suggest that the post-earthquake functionality of the tall building is primarily governed by the structural subsystem. In particular, for SLE, the functionality of the building is compromised mostly due to the damage to shear walls resulting in 3 to 6 months of functional recovery time (FRT); for DBE, the building’s functionality is fully impaired due to significant damage to slab-column connections and shear walls (FRT = 8 to 13 months); and for MCE, the building’s functionality is fully impaired due to significant damage to slab-column connections, shear walls, coupling beams, and partition walls (FRT = 12 to 16 months). Given the great contribution of tall buildings to community resilience, this study reveals a need for the development of design requirements for improving the post-earthquake functionality of tall buildings.