Journal of Numerical Methods in Civil Engineering
Volume:5 Issue: 2, Dec 2020

Nonlinear Time History (NTH) analysis is currently the most reliable method for estimating structural behavior. Considerable computational demand and complexity of this method may cause difficulty for its routine practical application. Based on the Methodology of Endurance Time (ET) method, it can estimate the nonlinear response of structures with a much lower computational cost. In this research, the reliability of the ET method in the analysis of concrete moment frames will be discussed. The results of the ET method are compared with those acquired from the NTH method by considering some energy Engineering demand parameters(EDP) like base shear roof displacement. Furthermore, the  accuracy of this method for estimating damage in structures was evaluated by considering inter story Drift, Park-Ang, and Bozorgnia-Bertero models as samples of damage indices. It is observed that the nonlinear dynamic response of structures and damage indices can be estimated by the ET method with reasonable accuracy.

Various methods have been presented to improve the performance of buildings against earthquakes. Friction damper device is one of the energy dissipation devices that appropriately absorbs and dissipates the input energy and decreases displacements. In this paper, the possibility of using endurance time method to determine the efficiency index and optimum slip load for these dampers was investigated by comparing the results of endurance time and nonlinear time history analyses. The efficiency indexes acquired from the average of results for nonlinear time history and endurance time analyses were close to each other. In this research, by ‎assuming identical ‎optimum slip ‎load ‎for the dampers in all ‎stories, the ‎normalized damper ‎strength was ‎increased in a number of equal ‎steps ranging from ‎zero to one to ‎determine the efficiency index of ‎dampers in each step. ‎Then, the optimum ‎slip ‎load ‎of dampers in ‎the steel frames was ‎calculated according ‎to ‎the minimum ‎efficiency index ‎of dampers.‎ As a result, employing the endurance time method instead of a high number of nonlinear time history analyses is also possible, and using the endurance time method diminishes 57% of computational endeavors.  Lastly, a relation for acquiring the optimum slip load of the friction damper devices in steel structures was proposed in terms of the weight of the structures. After adding optimal FDDs to the structures and investigating the effectiveness of the dampers, it was concluded that by using endurance time excitation function with ‎better ‎energy consistency, the endurance time results ‎could be improved.‎

This study aims at determining the critical seismic intensity at which cracks are expected to develop in a concrete arch dam. This intensity is referred to as crack initiation intensity. The crack initiation intensity measure implies that earthquakes with the intensity measure higher than this value are expected to induce cracks in the arch dam. This quantity is an indicator for seismic evaluation of arch dams. Determining this parameter using conventional time history analyses requires multiple trials and errors applying several up and down scaling of a suite of ground motions which can be very time consuming. As an alternative method, endurance time method is well suited for this kind of study. In the endurance time method, structures are subjected to predefined intensifying acceleration time histories and all intensity measures are continuously covered in a single time history analysis. The continuous coverage of intensity measures in the endurance time method provides a tool to conveniently determine the transition points such as crack initiation in a single time history analysis. In this regard, a framework is proposed and then applied to Morrow point dam, a doubly curved arch dam, as a case study. Results are obtained by using three different endurance time excitation series; ‘kn’, ‘kd’, and ‘lc’. The aim of using three endurance time series was to compare their differences in dynamic analysis of arch dams. Observations indicate the acceptable compatibility of different series of endurance time excitation. In order to investigate the accuracy of the results obtained by the endurance time method, the dynamic analysis of the arch dam subjected to ten ground motions scaled by the calculated crack initiation intensity measure is performed. It is shown that the proposed method can be conveniently applied for determining the crack initiation intensity.

The optimum seismic design of structures is one of the biggest issues for engineers to build resistant and economic structures. In this research, the application of the endurance time method in optimum performance design of steel moment-resisting frames using the uniform deformation method is evaluated. First, three steel moment-resisting frames with 3, 7 and 12 stories are considered. After that, the structures are optimized by endurance time method analysis and the uniform deformation theory, under a series of acceleration functions. Also, results are compared with the results of time history analysis based on earthquakes. The results revealed that endurance time method and time history analysis of earthquakes at low and moderate seismic hazard levels are well matched, while this adjustment does not exist for high seismic hazard level. In addition, the optimum structure at one hazard level does not lead to optimum structure in other hazard levels. To have the best performance at different hazard levels, the frames should be optimized at the moderate seismic hazard level. In order to optimize the structure at all seismic hazard levels, the GAP dampers can be used. These dampers should be effective after a specified drift at the lower seismic hazard level. In addition, the best values for convergence power of the uniform deformation method are between 0.05 to 0.15 for this purpose. By using such dampers, it is possible to have uniform drift distribution at different seismic hazard levels.

This study deals with the seismic performance evaluation of a typical five-story sandwich panel building with load-bearing wall as the only lateral force-resisting structural elements. For this purpose, incremental dynamic analyses (IDA) were performed on the model making use of seven selected ground motions. As a substitute to IDA, the response of the model in terms of maximum plastic strain, base shear and the inter-story drift ratio of the first story were compared with those from Endurance Time (ET) analysis. The results show that ET can simulate the seismic response of the studies model with an acceptable accuracy. However, the discrepancy between the ET results and those of the real ground motions increases with by increasing the excitation intensity. In general, ET underpredicts the drift ratios in very intense excitations, whereas the error of base shear with respect to the real ground motions remains almost constant regardless of the ground motion intensity.

In this paper, the performance of a super-tall tower is evaluated through Milad Tower in Tehran, Iran, as a case study. The structure is a 435 meters tall telecommunication tower and is structurally studied in this paper. For this purpose, linear endurance time (ET) method and time history (TH) analysis are used to compare the results and focus on the structurechr('39')s dynamic properties and behavior. The analyses are performed on a finite element model with SAP2000 and Abaqus software. Assumptions in linear modeling are investigated, including shell or solid element type and mesh sizing. Furthermore, the model is verified with experimental modal data. Performance-based analysis is performed according to ASCE41; the tower’s behavior and strength capacity is evaluated for different tower elevations. The scaling method effect on the response of the structure is demonstrated to have a major role. The Endurance Time method as a simplified and alternative analysis tool is exerted to estimate the structurechr('39')s significant responses and compared to ground motions with different spectrums. Results show that the ET method can adequately estimate the results in comparison with the TH method.