Design and Nonlinear Dynamic Response of a Steel Stack

This paper evaluates the seismic behavior of four methods for retrofitting typical reinforced concrete school building. The original school (SO) suffers from limited ductility and lateral resistance. The four seismic upgrading methods are using carbon fiber reinforced polymers (SUFRP), steel jacket (SUSJ), bracing (SUBR), or concrete jacket (SUCJ). Nonlinear pushover and time history analyses are made for the five schools. Three code-scaled natural earthquakes are utilized for the inelastic response history analysis. The pushover analysis revealed that providing the school with bracing (SUBR) results in reducing the lateral displacements. However, the three other types of seismic retrofit (SUFRP, SUSJ, and SUCJ) develop larger lateral displacements when compared to the original school (SO). The translation ductility and energy dissipation for school SUBR is poor while they are good for schools SUFRP, SUSJ, and SUCJ. The base shear is increased for the four upgrading methods (SUFRP, SUSJ, SUBR, and SUCJ) compared to school SO. From the nonlinear time-history analysis, the maximum interstorey drift was approximately similar for schools SO, SUFRP, and SUCJ. Lesser values for the maximum interstorey drift are obtained for schools SUSJ and SUBR. The nonlinear time-history analysis also gives similar base shear for all the upgrading methods compared to school SO with the exception of school SUCJ which showed increase in the base shear.

Evaluation of Load Distributions in Pushover Analysis Nonlinear pushover and time history analyses are common used methods to determine the nonlinear behavior of structures under earthquake loading. The aim of the present study is to evaluate the push over analysis, which is commonly used to determine the performance of R/C structures, comparing with time history analysis. For this purpose, 3, 5, 8 and 15-story R/C frame structures with various natural periods are analyzed by performing nonlinear pushover and dynamic time history analyses. The load distributions for pushover analyses are chosen as rectangular, triangular (IBC, k=1) and parabolic (IBC, k=2). To evaluate the results from the pushover analysis, nonlinear dynamic time history analysis is performed for 50 different stations’ data during various earthquakes. Finally, the best load distribution is determined for pushover analysis and the results are evaluated regarding with story height of the selected structures.

Nowadays, seismic isolation system has been widely applied in the world to mitigate damage risk of structures. Although maximum displacement demand can be obtained through nonlinear time history (NLTH) analysis, many approximate methods are frequently recommended in structural specifications to reduce the required computational time. One of the best-known methods is the equivalent linear (EL) method, in which the nonlinear response of isolator can be adequately modeled using a fictitious viscously damped elastic structure. In this paper, a comparison between existing expressions supplying the state of research is carried out and then, an improved expression is presented for equivalent linearization of structures supported on lead rubber bearings (LRB). Based on the concept of secant stiffness, the optimal damping ratios, which minimize the errors of maximum displacement between EL analysis and NLTH analysis, are calculated and averaged over 12 ground motions. Then, a rational model to estimate equivalent damping ratio is derived through statistic analysis of the optimal damping ratios. To examine the prediction accuracy of the proposed model, mean ratios of approximate to exact maximum displacement and root mean square error for different isolated period are calculated as evaluation indicator. Compared with other EL models, the newly proposed model predicts a displacement that is in better agreement with the one obtained through NLTH analysis.

Three different buildings built according to the same design have experienced three different near-field strong ground motions over a period of 11 years in three different cities in Turkey. The input motion was known for each because strong-motion sensors were located adjacent or close to the buildings. We examine the performance of the five-story, reinforced concrete-frame buildings. Bidirectional nonlinear time history and nonlinear static analyses on 3-D analytical models are performed. The principal focus is to assess whether the analytical model of the buildings could indicate column-beam damage consistent with that observed at the sites after the earthquakes. Results illustrate that nonlinear time history analyses are capable of indicating the occurrence of shear failure in captive columns; however, they overestimate the global damage. The overestimation is greater where the building sustained a pulse-type motion without significant distress. It appears that difference between visual observations and analytical results persists.

The seismic behavior of the steel connection equipped with the lead extrusion damper (LED) is examined through the experimental and analytical studies. The LED implemented has spherical type bulge and does not consist any lubricant layer. The experimental study is performed in Structural and Earthquake Engineering Laboratory of Istanbul Technical University (STEELAB). In the experimental part, force-displacement relations of the connections with and without LED are achieved for the reversal displacement cycles. The measures of the dissipated energy, the equivalent damping ratio and the effective stiffness are obtained from the experimental study and compared for the connections. The total energy dissipated by the connection with the LED is approximately 175% greater than the total energy dissipated by the bare connection. In the analytical part of the study, nonlinear dynamic time history analyses are performed for the selected earthquakes and mass condition using the analytical models for the connections with and without LED. The maximum top displacement decreases approximately 50% for the connection equipped with the LED respect to the bare connection for the considered earthquakes. The maximum value of restoring force for the connection equipped with LED is approximately 25% greater than the bare connection for the accomplished analyses. Finally, the LED responses obtained in the nonlinear time history analyses are compared with the isolated LED test results.

Evaluating seismic performance is essential for structures in earthquake-prone regions, particularly reinforced concrete (RC) frames commonly used in countries like Indonesia. This study compares two prominent assessment methods: nonlinear time history analysis (THA), known for its high accuracy but computational demand, and the capacity spectrum method (CSM), which offers greater efficiency through pushover analysis but requires validation. A six-story RC frame with vertical irregularities, such as setbacks at intermediate levels, was modeled and analyzed under seismic loading based on the 1940 El Centro ground motion. Numerical results from both THA and CSM were benchmarked against experimental data from a previously conducted shake table test documented in the literature. The comparison focused on inter-story drift responses, which serve as key indicators of seismic performance. The results show that both methods produced slightly higher drift values compared to the experimental data, though the differences remained within acceptable engineering tolerances. The findings demonstrate that while THA remains a benchmark for detailed analysis, CSM provides a viable and faster alternative for the seismic assessment of irregular RC structures, especially during preliminary design or evaluation stages. This reinforces the potential of CSM to support performance-based seismic design in a more efficient manner without significant loss of accuracy.

Masonry infills are usually treated as nonstructural elements in buildings, and their interaction with the bounding frame is often ignored in analysis and design of reinforced concrete structures. The main aim of this study is to develop a seismic fragility curves showing the probability of exceeding a damage limit state for a given structure type subjected to a seismic excitation. For the purpose of this study, three distinct buildings namely, seven-story, eleven-story and sixteen-story, with typical floor plan were proposed as the case study. Each building cases are explicitly modeled as a bare frame and HCB infilled model with varying percentage of infill configurations. All building models under the case study were analyzed using Seismo-Struct software to assess seismic vulnerabilities. Non-linear dynamic time history and pushover analysis were employed to generate fragility curves. 30 generated artificial accelerograms were employed in the nonlinear dynamic time history analysis. Accordingly, for developing a fragility curve, nonlinear dynamic analyses of 30 building models for each case are conducted and the maximum roof displacement (ID) for each ground motion is recorded. Results of the study showed that bare frame has a highest probability of failure and building models with a larger percentage of infill configurations have lesser failure probability than slightly infilled building models. Basically these infills have significant contribution in arresting large lateral deflections and results in lower and most tolerable story displacements under excited earthquake motion and eventually reducing the structure’s probability of failure at life safety and collapse prevention limit states

This paper investigates the soil effect on seismic behaviour of reinforced concrete (RC) buildings by using the spread plastic hinge model which includes material and geometric nonlinearity of the structural members. Therefore, typical reinforced concrete frame buildings are selected and nonlinear dynamic time history analyses and pushover analyses are performed. Three earthquake acceleration records are selected for nonlinear dynamic time history analyses. These records are adjusted to be compatible with the design spectrum defined in Turkish Seismic Code. Interstory drifts and damages of selected buildings are compared according to local soil classes. Also, capacity curves of these buildings are compared with maximum responses obtained from nonlinear dynamic time history analyses. The results show that, soil class influences the seismic behaviour of reinforced concrete buildings, significantly.

در طراحی بر اساس عملکرد، تعیین نیازهای لرزه‌ای یک گام مهم و اساسی در روند طراحی می‌باشد. نیازها را می‌توان به‌کمک روش‌های خطی یا غیرخطی تعیین نمود. دستورالعمل به‌سازی لرزه‌ای ساختمان‌های موجود، روش‌های تحلیلی مختلفی را به‌منظور ارزیابی و تعیین نیازها معرفی می‌نماید. از آن‌جایی که انتظار می‌رود اعضای سازه‌ای تحت اثر نیروی لرزه‌ای رفتار غیرخطی از خود بروز دهند، لذا منطقی است که در تعیین نیازهای اعضا، روش‌های غیرخطی مورد استفاده قرار گیرند. از بین دو روش غیرخطی، روندهای استاتیکی شامل تحلیل‌های بارافزون نسبت به روندهای تاریخچه زمانی مقبولیت بیش‌تری دارند. لذا در این مقاله به بررسی روش‌های غیرخطی و تفاوت‌های موجود بین روش‌های استاتیکی و دینامیکی غیرخطی برای تخمین نیازهای لرزه‌ای ‌پرداخته می‌شود و نتایج و آثار استفاده از روش‌های بارافزون در تخمین نیاز لرزه‌ای اعضا تحت اثر زمین‌لرزه‌های حوزه‌ی دور و نزدیک مورد بحث و بررسی قرار می‌گیرد.مقایسه‌ی نتایج حاصل از روش بارافزون با نتایج تحلیل تاریخچه‌ی زمانی غیرخطی نشان می‌دهد که روش‌های بارافزون در سطوح فوقانی سازه نیازهای لرزه‌ای را در حد پایین‌تری تخمین می‌زنند. این امر اهمیت ارتباط مشارکت مدهای بالاتر را در سازه‌های میان‌مرتبه و بلندمرتبه مشخص می‌نماید.

Improved seismic performance objectives (Immediate Occupancy and Continued Operation) set by owners of high-tech manufacturing facilities have resulted in increased use of supplemental damping and base isolation designs. This article reviews the design and construction process of industrial base isolated buildings with focus on code requirements, design and analytical methodologies, and constructability challenges. Due to velocity/displacement dependent behavior of base isolation systems, the building code (IBC/ASCE-7) requires performing a Non-Linear Time History (NLTH) analysis to determine the seismic loading on the base isolated structure. However, due to the complexity of NLTH and because the superstructure must be essentially elastic, the code also permits performing a staged analysis. The staged analysis consists of: 1) performing a linear (modal) analysis of the superstructure to determine the lumped-mass dynamic characteristics of the building, 2) performing a NLTH analysis of the isolation system and superstructure to determine system forces, displacements, and base shears, 3) performing superstructure design using a linear (modal) analysis with scaled base shear forces, and 4) designing the base isolator footings and support framing to resist the system design displacements and resulting forces. The required series of time history analyses are performed for a suite of time history records, each scaled to the Design Earthquake (DE) and the Maximum Considered Earthquake (MCE), variations of upper bound and lower bound isolator properties, and position of center of mass at each floor. A case study of a multi-stage analysis, design, and construction of three concrete industrial buildings built on a single base isolation slab is presented to discuss details and challenges related to design and construction of isolator selection, mounting, and support, as well as the design criteria for utility displacement compatibility at the isolator moat, and reduced equipment and contents anchorage requirements.

This paper presents a special type of bracing element termed self-centering friction damping brace (SFDB) for use in seismic-resistant concentrically braced frame (CBF) systems. The SFDB is a passive energy dissipation device with its core recentering component made of stranded superelastic Nitinol wires while enhanced energy dissipation mechanism of the SFDB is achieved through friction. Compared with conventional braces for steel frame buildings, SFDB has a few desirable performance characteristics such as minimized residual drifts of the CBF system and its ability to withstand several design level earthquakes without the need for replacement. The mechanical configuration of the SFDB is first described. A comparative study of SFDB frame and buckling restrained braced (BRB) frame was carried out, which is based on nonlinear dynamic analysis of two prototype CBF buildings—a three- and a six-story steel frame. Two suites of earthquake ground motions, which represent the frequent and design basis earthquakes for Los Angeles, were considered in the nonlinear time-history analysis. The results of the nonlinear time-history and pushover analysis show that the SFDB frame can achieve a seismic response level comparable to that of the BRB frame while having significantly reduced residual drifts. The SFDB thus has a potential to establish a new type of CBF system with self-centering capability.

An improved multi-objective optimization approach for performance-based design of structures using nonlinear time-history analyses

An accurate optimal pushover analysis is developed to predict the higher-mode influence in multi degree of freedom (DOF) buildings. Performance levels are determined and seismic demands are calculated using two different ground acceleration records. The methodology is based on elastic structural dynamics theory and retains the simplicity of standard pushover procedures that rigorous time history analyses do not provide. A variant inertial load pattern is determined by updating the building’s vibration properties at each stage of yielding. Each load pattern is derived using one mode shape at every yielding stage thereby capturing the higher-mode effects (HME). Using the energy under the building’s capacity curve then enables a single optimal mode shape to be determined; this defines a representative single-DOF system (R-SDOF). Towards this end, an optimization algorithm is written to minimize the target displacement error between the pushover and nonlinear time-history analyses of a few buildings for a certain ground record. Optimal capacity and demand parameters are then determined and used to combine the individual mode shapes from each stage of yielding into the single optimal mode shape. This approach enables HME and phenomena such as HME and P-∆ effects to be captured through the optimal parameter identification. These same parameters are then applied in a pushover analysis of other buildings. The results are shown to compare favorably to a separate nonlinear time-history analysis.

Partial Capacity Design (PCD) has been developed by using magnification factor to keep some columns undamaged during major earthquake. By doing so, the structures will experience the partial side sway mechanism which is also stable, instead of the beam sidesway mechanism. However, in some cases, structures designed by PCD method failed to show the partial side sway mechanism since unexpected damages were still occurred at some columns. In this research, modification of PCD method is proposed by using two structural models in the design process. The first model is used to design beams and columns which are allowed to experience plastic damages, while the second model is used to design columns which are intended to remain elastic when the structure is subjected to a target earthquake. Two nominal earthquakes corresponding to Elastic Design Response Spectrum (EDRS) level with seismic modification factors (R) of 8.0 and 1.6 are used in the first and second structural models, respectively. It should be noted that the second model is identical to the first model except that the stiffnesses are reduced for elements to simulate potential plastic damages. This proposed method is applied to symmetrical 6 and 10 storey buildings with seismic load according SNI 1726:2012 and with soil classification of SE in Surabaya city. A Non-linear Static Procedure (NSP) or pushover analysis and Non-linear Dynamic Procedure (NDP) or time history analysis are employed to evaluate the performance of the structure. The evaluation is conducted at three earthquake levels which are nominal earthquake that is used in second model, earthquake corresponding to EDRS level, and maximum considered earthquake (MCER) specified by the code (50% higher than EDRS level). The building performances satisfy the drift criteria in accordance with FEMA 273. However, the partial side sway mechanism was not achieved at NDP analysis at maximum seismic load, MCER.

Pushover analysis was the recommended method of seismic analysis before this generation. Even though Non-Linear Time History analysis is a recommended method of practice for the current generation due to its accuracy, Pushover analysis has the capability which gives much more flexibility and information on its final results. The well-known concept of ‘Performance criteria’, which is the specification of an acceptable level of damage to a building, can be found using this method. Using pushover analysis, it’s possible to study the parent factor, which is responsible for the behaviour of buildings during seismic events. In this review, we discussed the possible lateral load combinations that can be applied during the analysis procedure and how the results can be analysed. From previous studies, it is concluded that the pushover analysis can be influenced by the geometry of the building, lateral load pattern, and the method of result evaluation.