Results Of Nonlinear Analysis Research Articles

Urban Morphology Influencing the Urban Heat Island in the High-Density City of Xi’an Based on the Local Climate Zone

Urban form plays a critical role in enhancing urban climate resilience amidst the challenges of escalating global climate change and recurrent high-temperature heatwaves. Therefore, it is crucial to study the correlation between urban spatial form factors and land surface temperature (LST). This study utilized Landsat 8 remote sensing data to estimate LST. Random forest nonlinear analysis was employed to investigate the interaction between the urban heat island (UHI) and six urban morphological factors: building density (BD), floor area ratio (FAR), building height (BH), fractional vegetation coverage (FVC), sky view factor (SVF), and impervious surface fraction (ISF), within the framework of local climate zones (LCZs). Key findings revealed that Xi’an exhibited a significant urban heat island effect, with over 10% of the study area experiencing temperatures exceeding 40 °C. Notably, the average LST of building-class LCZs (1-6) was 3.5 °C higher than that of land cover-class LCZs (A-C). Specifically, compact LCZs (1-3) had an average LST 3.02 °C higher than open LCZs (4-6). FVC contributed the most to the variation in LST, while FAR contributed the least. ISF and BD were found to have a positive impact on LST, while FVC and BH had a negative influence. Moreover, SVF was observed to positively influence LST in the compact classes (LCZ2-3) and open low-rise class (LCZ6). In the open mid-rise class (LCZ5), SVF and LST showed a U-shaped relationship. There is an inverted U-shaped relationship between FAR and LST, with the inflection point occurring at 1.5. The results of nonlinear analysis were beneficial in illustrating the complex relationships between LST and its driving factors. The study’s results highlight the effectiveness of utilizing LCZ as a detailed approach to explore the relationship between urban morphology and urban heat islands. Recommendations for enhancing urban climate resilience include strategies such as increasing vegetation coverage, regulating building heights, organizing buildings in compact LCZs in an “L” or “I” shape, and adopting an “O” or “C” configuration for buildings in open LCZs to aid planners in developing sustainable urban environments.

The Influence of Soil Deformability on the Seismic Response of 3D Mixed R/C–Steel Buildings

Following effective seismic codes, common buildings are considered to be made of the same material throughout the story distribution and based on an ideal rigid soil. However, in daily construction practice, there are often cases of buildings formed by a bottom part constructed with reinforced concrete (r/c) and a higher steel part, despite this construction type not being recognized by code assumptions. In addition, soil deformability, commonly referred to as the Soil–Structure Interaction (SSI), is widely found to affect the earthquake response of typical residence structures, apart from special structures, though it is not included in the normative design procedure. This work studies the seismic response of in-height mixed 3D models, considering the effect of sustaining deformable ground compared to the common rigid soil hypothesis, which has not been clarified so far in the literature. Two types of soft soil, as well as the rigid soil assumption, acting as a reference point, are considered, while two limit interconnections between the steel part on the concrete part are included in the group analysis. The possible influence of the seismic orientation angle is explored in the analysis set. Selected numerical results of the dynamic nonlinear analyses under strong near-fault ground excitations were plotted through dimensionless parameters to facilitate an objective comparative discussion. The effect of SSI on the nonlinear performance of three-dimensional mixed models is identified, which serves as the primary contribution of this work, making it unique among the numerous research works available globally and pointing to findings that are useful for the enhancement of the seismic rules regarding the design and analysis of code-neglected mixed buildings.

Dynamics of a thin film of viscoelastic fluid flowing down an inclined or vertical plane

The stability characteristics of a thin film of viscoelastic (Walters’ B′ model) fluid flowing down an inclined or vertical plane are analyzed under the combined influence of gravity and surface tension. A nonlinear free surface evolution equation is obtained by using the momentum-integral method. Normal mode technique and multiple scales method are used to obtain the results of linear and nonlinear stability analysis of this problem. The linear stability analysis gives the critical condition and critical wave number kc which include the viscoelastic parameter Γ, angle of inclination of the plane θ, Reynolds number Re and Weber number We. The weakly nonlinear stability analysis that is based on the second Landau constant J2, reveals the condition for the existence of explosive unstable and supercritical stable zone along with the other two (unconditional stable and subcritical unstable) flow zones of this problem which is 3(1+3Γ)Re−3cotθ−4ReWek2 = 0. It is found that all the four distinct flow zones of this problem exist in Re-k-, θ-k- and Γ-k-plane after the critical value of Rec,θc and Γc, respectively. A novel result of this analysis is that the film flow is stable (unstable) for a negative (positive) value of Γ irrespective of the values of Re and θ, as for example, a solution of polyisobutylene in cetane, compared with the viscous (Γ=0) film flow case. Finally, we scrutinize the effect of Γ on the threshold amplitude and nonlinear wave speed by depicting some numerical examples in supercritical stable as well as subcritical unstable zone of this problem.

Temperature change-induced linear and nonlinear axial responses of internal replacement pipe (IRP) systems for pipeline rehabilitation incorporating the effects of soil friction

The internal replacement pipe (IRP) is a developing trenchless system utilised for restoring buried steel and cast-iron legacy pipelines. It is crucial to ensure that this advanced system is appropriately designed to reinstate the functionality of damaged pipelines effectively and safely. The present paper investigates the structural response of IRP systems used in repairing pipelines with circumferential discontinuities subjected to seasonal temperature changes. Analytical and numerical approaches verified via experimental data and available closed-form solutions were implemented to analyse a total of 180 linear and nonlinear finite element (FE) simulations. A set of analytical expressions was developed to describe the loading and induced responses of the system. Based on an extensive FE parametric study, five modification factors were derived and applied to developed analytical expressions to characterise the structural response incorporating the effects of soil friction. Results showed that there is a major difference between the results of linear and nonlinear analyses highlighting the importance of including the material nonlinearities in the FE analysis. A significant difference was observed between the discontinuity openings with and without the consideration of soil friction implying that appropriate inclusion of soil friction in the FE model is crucial to get realistic system responses subjected to temperature change. Although the application of IRP holds immense promise as a trenchless solution for rehabilitating legacy pipelines, the lack of established design procedures and standards for these technologies has restricted their application in gas pipelines. Results obtained from numerical and analytical models developed in the present research will provide valuable insights for the design and development of safe and efficient IRP systems urgently needed in the pipeline industry.

Seismic Performance Evaluation of Multi-Storey Residential Building with Friction Pendulum Bearings: Indonesia case study

The methodology for seismic performance evaluation of a residential building in Indonesia with the use of seismic isolation is considered. An 8-storey reinforced concrete frame residential building with shear wall structural system was selected as a case study. Nonlinear methods of seismic response analysis were used to calculate the response of the structure: nonlinear static (Pushover) and Nonlinear-Time History Analysis, NLTHA. The analysis is performed in STERA 3D freeware. The nonlinear time history analysis was performed for seven pairs of horizontal components of earthquake ground motions, selected according to the parameters of possible earthquakes for the considered site (Bandung city). The selected earthquake records were modified using the spectral matching procedure for design spectrum. Friction-pendulum bearings developed by Nippon Steel Corporation of Japan were used as seismic isolation. The results of nonlinear time history analysis show that shallow earthquakes result in greater damage compared to megathrust earthquakes, with both scenarios providing a life safety (LS) performance level. The use of seismic isolation can reduce seismic loads, as evidenced by the reduction in top-level accelerations and shear forces at the base.

A new performance‐based seismic design method using endurance time analysis for linked column frame system and a comparison of structural systems and seismic analysis methods

SummaryThis paper presents a new performance‐based seismic design method for the design of repairable linked column frame (LCF) and linked column system (LCS). Currently, the biggest problem of these systems is the lack of a simple and practical design method that leads to the design of optimal models with sufficient seismic capacity. The interaction of the primary and secondary systems, changing the lateral load pattern during an earthquake, and the implementation of the target performance objectives have complicated the design of these systems. The evaluations carried out in this research show that the rotation of link beams must be controlled in the design. Therefore, the ultimate plastic rotation of links is determined to be 0.01 rad for the seismic intensity of design base earthquake and 0.015 rad for maximum considered earthquake. The results show that the models designed using the presented method are optimal, have sufficient seismic capacity, and achieve the target performance objectives. In addition, although previous researches have shown that these systems have a suitable seismic behavior, their seismic behavior have not been compared with other structural systems. Comparing can show the behavioral characteristics of a new structural system; hence, the elastic and plastic behavior of the LCF and LCS models have been compared with other common steel structural systems using all analysis methods. Moreover, in the presented method for the design of LCF and LCS systems, nonlinear time history analysis using the endurance time method (ETM) is used, and due to the newness of the endurance time method, its results are compared with the median results of nonlinear time history analysis at different seismic hazard levels and incremental dynamic analysis (IDA), in 45 samples. The results show that the endurance time analysis is a reasonable and efficient method, and in this comparison, the difference between the results of ETM and IDA methods is 6% on average.

Long short-term memory based modeling of heat treatment and trigger mechanism effect on thin-walled aluminum 6063 T5 for crashworthiness

ABSTRACT Vehicle safety relies on the capacity of vehicle systems to decrease the likelihood of biomechanical injuries to both vehicle occupants and pedestrians. This can take the form of active or passive measures applied to the materials and their geometry in the event of an impact. Nevertheless, due to the nonlinear behaviour of materials and deformation, a distinct collapse process emerges that requires analysis; this analysis can be virtual or through experimental tests. While observed performance can be ascertained through experimental designs, executing such a design for every parameter combination can be time-consuming and costly. This study employs a Long Short-Term Memory (LSTM) to predict the energy absorbed and crushing force of thin-walled aluminium 6063 T5 tubes subject to different collapse triggers and heat treatments. The LSTM model is constructed using experimental data derived from experiments that consider trigger shape, area, trigger position, furnace duration, cooling temperature, and heat treatment soaking method. The LSTM model achieved a Root Mean Square Error (RSME) of 0.56 and 0.0025 for crushing force and energy absorption, respectively. LSTM proves to be a valuable tool for predicting results in nonlinear analysis, particularly in the context of crush behaviour. Also, a comparison of the LSTM and finite element analysis (FEA) predictive performance is presented.

Seismic strengthening of isolated RC framed structures through orthogonal steel exoskeleton: Bidirectional non-linear analyses

The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings; in Europe, most of the existing buildings were built after World War II and since they have largely exceeded their useful life, are characterized by a high vulnerability linked both to the durability of the materials and to the lack of seismic provisions in design. The current trend in constructional field is to design interventions aimed at the seismic and energy improvement of these structures jointly, in order to achieve a sustainable and integrated retrofit intervention. To this aim, the use of 2D orthogonal steel exoskeletons for the seismic strengthening represents a suitable solution, providing at the same time an enhancement in thermal insulation, through a ‘double-skin’ solution. Due to the growing interest in the design of steel exoskeleton interventions, a detailed dynamic characterization of this external strengthening solution is needed. In this framework, the present work, aims to investigate the effectiveness of the investigated strengthening solution by means of bi-directional non-linear dynamic analyses. Extensive numerical analysis was carried out. The selected case-study is an Italian existing pre-1980 s RC frame building located in Mugnano di Napoli (NA, Italy), which is a medium-high seismic hazard site in Italy (peak ground acceleration equal to 0.156 g). Two alternative strengthening solutions were numerically investigated by means of non-linear time-history and incremental dynamic analyses performed applying fifteen bidirectional ground motions on three-dimensional numerical models. The results of the dynamic non-linear analyses allow to quantify more appropriate performance indicators, both in terms of expected demand and overall collapse capacity, useful for the development of optimization strategy and design of exoskeleton system. The results highlighted that both the investigated strengthening scenarios allow to increase the stiffness of the existing building and allow it to meet the current code safety requirements reducing also the residual inter-storey drift. The obtained results are not strictly related to the investigated case study, but can be extended to all the structures retrofitted that follows the presented design procedure.

A diagram‐based design procedure for Intermediate Isolation System in existing buildings with inelastic behavior

AbstractVertical extensions of existing buildings can be realized through Intermediate Isolation System (IIS): the extension, equipped with a base isolation system on the rooftop of the existing building, can work as a mass damper, thus reducing the seismic demand on the old structure. The idea proposed in this paper is to predict the elastic or inelastic response of the existing structure in the IIS configuration by means of the results of simple linear analyses. Parametric response spectrum analyses are performed on simplified two degree‐of‐freedom models by varying the mass ratio and the periods of both the existing building and the new isolated vertical extension. So‐called IIS design spectra are derived, and the results are provided as design charts. Given the period of the existing building and the mass ratio, the period of the new isolated vertical extension is selected to obtain the required/desired response of the existing building. For existing buildings working in the elastic field, the designer can derive the response of the existing building by utilizing the IIS design spectra as design charts. For existing building working in the inelastic field, the design charts can still be adopted, though within a more complex procedure, which accounts for two limit behaviors that the extended building exhibits in the inelastic field. The outlined design procedure is applied to some case studies and validated through the comparison with the results of nonlinear time history analyses.

One Dimensional Ground Response analysis in Patan: Implications to Damage Pattern due to the 2015 Mw 7.8 Gorkha Earthquake

The 2015 Mw 7.8 Gorkha earthquake caused extensive damages in Kathmandu Valley located about 78 km SE from the epicenter. The damage patterns in the city clearly indicated the subsurface geology of the city had strongly modified the ground motion causing typical damages to tall structures. In this contribution, following one-dimensional approach, a ground response analysis is performed in Patan utilizing the deep borehole, shear wave profile and dynamic soil properties adopting both equivalent linear and non-linear approaches. The results of both equivalent linear and non-linear analyses were compared with the measured ground motions at soil site. It is found that the non-linear analysis better simulates the deamplification of the peak ground acceleration and strong shaking at longer period than the equivalent linear analysis. The obtained results confirm that the deamplification of PGA was due to the strong non-linear behavior of the fluvio-lacustrine deposits.

Seismic Vulnerability of Segmental Bridges with Drop-In Span by Pushover Analysis

Insight into the application of pushover analysis to prestressed concrete segmental bridges built in the 1950s–1970s by cantilevering with medium-large span length is provided. Seismic assessment must be carried out considering the whole structural response and, in particular, the task of tall piers, bearings, and drop-in spans with Gerber saddles, which are likely to be subjected to girder pounding and/or unseating. In this paper, the assessment of seismic vulnerability is initially performed by linear modal dynamic analysis; then, the efficiency in assessing the seismic response of different methods of pushover analyses is compared, assuming as a benchmark the results of non-linear time history analysis. The outcomes show that, for the bridge with the drop-in span, criteria for selecting the load pattern considered in pushover analysis, the reliable modeling of the bearings, and tall piers play a dominant role in the assessment of the seismic vulnerability, particularly in longitudinal motion.

Not all are alike: Assessing the effect of geopolitical risk on regional renewable energy development in China

Frequent recent episodes of geopolitical risk have spurred scholarly interest in its economic and environmental implications. Compared with previous research, this study constructed a panel data set of China's 30 provinces/municipalities to assess how geopolitical risk affects the development of renewable energy. The results of both linear and nonlinear analysis reveal that the effect of geopolitical uncertainty is not alike and is region- and state-dependent. Compared to its effect in China's eastern and central regions, geopolitical risk exerts a negative effect on renewable energy development in the western region. This negative effect tends to be more pronounced in areas characterized by relatively weak economic and social conditions. We also observe a threshold effect between them, as geopolitical risk typically weakens (enhances) renewable energy development when the economic condition is at a lower (higher) level. Finally, a sound financial system oriented toward “going green” and a stronger environment of technological innovation lessen the harmful effect of geopolitical risk. These findings provide targeted insights for policymakers seeking to improve local economic conditions, promote energy transition, balance regional energy inequality, and realize sustainable development.

Enhancement of Starch Gel Properties Using Ionic Synergistic Multiple Crosslinking Extrusion Modification.

Crosslinking is a promising method to modulate the gel properties of food-grade starch gels. Still, the poor crosslinking effect of a single type of crosslinker limits the application of this method in starch gel modification. In this study, an Ca2+ synergistic multiple crosslinking modification method was proposed to prepare crosslinked starches with good gel properties and setting. The rheological properties of the samples were tested. The modified sample (SC-Ca-N3, G' = 1347 ± 27) showed a 79% improvement compared to the starch without synergistic crosslinking modification (SC-N, G' = 752 ± 6). The elastic modulus of starch gels can be adjusted by changing the degree of the crosslinking reaction. The results of nonlinear rheological Lissajous curve analysis showed that the synergistically crosslinked gel system strongly resisted deformation. In addition, the microstructure of the modified samples was characterized using scanning electron microscopy. The XPS, FTIR, and XRD results indicated that multiple molecular forces participate in the synergistic crosslinking reaction.

Choice of the shape imperfections model in dynamics problems of a long flexible cylindrical shell subjected to force couples

The issue of modeling geometrical imperfections in the dynamics problems of thin-walled shells was little researched. In cases when the natural modes of shell coincided with its buckling modes, the issue of choosing a dangerous imperfection model did not arise. When these shell modes did not coincide, it was important to investigate and compare the effect of different imperfections models on the static and dynamic characteristics of such shells. The choosing the shape imperfections model of a long flexible cylindrical shell subjected to force couples, the natural and buckling modes of which did not coincide, was studied using procedures of the finite element analysis software NASTRAN. The shell wall as a set of plat rectangular elements with six degrees of freedom at the node in the cylindrical coordinate system was modeled. The action of force couples as the concentrated forces were distributed at the nodes of the shell edges in accordance to the presentation of A.S. Volmir. The linear buckling problem and the geometrical nonlinear static analysis of the perfect shell by the Lanzosh method and the Newton-Raphson one were performed, respectively. The long half-waves buckling mode was taken as the first shell imperfections model. The modeling of the second shape imperfections as the first natural mode of the perfect shell using the natural vibration analysis by the Lanzosh method was performed. The different amplitudes of geometrical imperfections in proportion to the shell thickness using a program adapted to this software were set. The results of the geometrical nonlinear static analysis of the imperfect shell by the Newton-Raphson method showed that the shape imperfection model in the form of long half-waves more reduced the values of critical buckling loads. Investigations of natural shell vibrations by the Lanzosh method revealed the same influence of different imperfections models on the natural frequencies and natural forms. We think that the shape imperfections model in the form of long half-waves in studies of forced vibrations and dynamic stability of a long flexible cylindrical shell subjected to force couples will be more effective.

Evaluation of ultimate bearing capacity of large-scale perforated beams with variable cross-section: Experimental verification and numerical simulation

In order to meet the requirements of outfitting layout and light weight, circular or elliptical holes need to be opened on the web of the hull beam. Excessive opening will lead to stress concentration and reduce the bearing capacity of the beam. For the super-standard openings, the general strengthening method cannot guarantee the ultimate bearing capacity of the beam, and locally increasing the web to form a variable cross-section beam can compensate for the lost bearing capacity. In the present paper, the three-point bending load tests of variable cross-section opening beams and equal cross-section beams are carried out. Combined with the results of nonlinear finite element analysis, the ultimate bearing capacity and failure mode of transverse bending are compared, and it is verified that the ultimate bearing capacity of beams with variable cross-section openings is better than that of beams with equal cross-section. By changing the cross-section size and optimizing the transition form, the variable cross-section perforated beam is further improved and optimized to enhance the ultimate strength.

System redundancy of steel I‐girder bridges and proposal of a system factor for load rating

Abstract3D nonlinear FE analyses of existing plate‐girder bridges were carried out to investigate system redundancy. A comparison of the ultimate live load factors between a whole bridge system (WBS) model and a single girder (SG) model shows that WBS's ultimate live load factor is larger than SG's factor. This difference in the ultimate load factors is interpreted as the system redundancy effect. A system factor to quantify the system redundancy has been proposed based on the nonlinear FE analysis results. The proposed system factor is defined as a factor to convert the ultimate live load factor and rating factor for load rating based on linear analysis into those based on nonlinear analysis. A case study to calculate the system factor for three existing bridges shows dependency of the system factor on the number of girders, composite/non‐composite girders, simple span/continuous span.

Nonlinear buckling analysis of cat-head transmission tower under strong wind load

Based on ANSYS APDL finite element analysis software and B-R criterion combined with displacement equality criterion, the dynamic stability of the cat-head transmission tower is analyzed. In this paper, the static characteristics of the cat-head transmission tower are analyzed first, and the wind load is gradually increased according to the wind speed gradient of 5 m/s. The results show that the cat-head transmission tower cannot be normally served under the wind speed of 45 m/s. In order to analyze the specific instability wind speed of the transmission tower in detail, the nonlinear buckling analysis is used to analyze the cat-head transmission tower. The nonlinear buckling analysis results of the cat-head transmission tower are as follows: the wind speed of instability is V10=43.65 m/s. Therefore, the influence of wind load fluctuation on the dynamic stability of the transmission tower should not be ignored, and the influence of fluctuating wind should be considered in the design of the transmission tower.

Nonlinear analysis on mechanical behaviour of high strength steel extended endplate connections and equivalent T-stubs in fire considering axial force

In fire, ignoring the axial force acting on the high strength steel (HSS) beam-column endplate connections when considering catenary action may lead to a safety risk for the whole steel structure. Hence, a nonlinear analysis is conducted to reveal the actual performance of HSS T-stubs and HSS extended endplate connections in fire using the software ABAQUS. The ultimate displacement, failure mode and bearing capacity of HSS T-stubs under tension-shear combined action are investigated. The failure modes and moment–rotation curves of HSS endplate connections obtained by the numerical study are verified with test results in fire. Furthermore, the effects of bolt diameter, endplate thickness, endplate strength, the combination of endplate thickness and endplate strength, as well as temperature on the mechanical behaviour of HSS endplate connections considering axial force are studied. The results of nonlinear analysis are verified against Eurocode 3 Part 1–8 in various situations. The results indicate that when the shear-to-tension ratio is 2.0, the tensile bearing capacity and ultimate displacement of HSS T-stubs at 600 °C decreased to 38% and 31% of the pure tension, respectively. The parametric analysis shows that when the temperature is 600 °C, the initial stiffness and ultimate flexural capacity of connections are only about 40% and 31% of that at 20 °C.

Experimental and modeling investigation of freezing behavior for frozen sand molds

The essence of the freezing process in frozen sand molds is the heat transfer issue within the water-containing porous medium. In this paper, the evolutionary mechanism of the water-ice phase interface in frozen sand molds was studied through simulations and experiments at the mesoscale. Firstly, the evolutions of the phase field and temperature field during the unidirectional freezing process of frozen sand molds with different pore structures were investigated through numerical simulations. Then, utilizing the low-temperature freezing in-situ characterization platform, the nucleation mechanism of ice crystal bonding bridges between sand particles of varying materials was explored. The influence of sand mold characteristics on the freezing behavior of frozen sand molds was evaluated by the unique variable principle. Additionally, power function relationships for freezing time of frozen sand molds with different scales and materials were established, enabling the prediction of the time required for complete freezing of frozen sand molds. According to the results of multiple nonlinear regression analysis, the model showed reliable accuracy in predicting the time for fully frozen. This work will provide a valuable reference for further research on the engineering application of frozen sand molds.

Behavior of RC Buildings under Blast Loading: Case Study

In recent years, civil wars and terror activities have caused blast-loading effects on reinforced concrete buildings, resulting in catastrophic human and material damage. When a building is exposed to a blast load, a very high air pressure affects the building within a very short duration. To decide on the reconstruction or retrofit of a building exposed to blast loading, the behavior of the building under blast loading should be investigated. In this paper a case study of a RC building exposed to blast loading during the Libyan war in the last years was investigated. Nonlinear analysis results indicate that the failure mode is localized and that most structural elements remain elastic after explosions. The paper presents, building description details, material tests, finite element model and nonlinear analysis results.