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CONTENTS
Volume 21, Number 1, July 2021
 


Abstract
Buildings with fundamental vibration mode dominated by torsion are characterized in the literature as "torsionally flexible" or "torsionally sensitive". Given that the seismic behavior of such buildings may be governed by torsion, modern seismic codes prescribe simplified criteria in order to identify them. The objective of the present paper is to evaluate the relevant criteria adopted by four seismic codes. For this purpose, the accuracy of the aforementioned criteria is theoretically investigated with the aid of a well-established analytical criterion based on single-storey one-way asymmetric models. In addition, in order to quantify the shortcomings of some criteria, three illustrative examples are presented. The whole study leads to useful conclusions which contribute to the clarification of some crucial aspects of the torsional seismic response of buildings.

Key Words
irregularity in-plan; radius of gyration; seismic codes; torsional flexibility; torsional radius; torsional sensitivity

Address
Asimina M. Athanatopoulou: Department of Civil Engineering, Aristotle University of Thessaloniki, University Campus, 54124, Greece

Grigorios E. Manoukas: Department of Civil Engineering, Aristotle University of Thessaloniki, University Campus, 54124, Greece

Abstract
The fire which occurs after an earthquake causes great problems for buildings situated in moderate to high seismic regions. In this article in order to have an understanding regarding the impacts of post-earthquake fire on the structures, implementing the finite element method, the behaviour of tall steel concentrically braced frames when subjected to this type of loading was investigated. The simulation under seismic loading was done using the nonlinear time history analysis. Assuming the post-earthquake situation of the structure as the initial condition, the mechanical-thermal analysis was applied using the temperature-time diagram on the exposed elements. The analysis results showed that regardless of the earthquake record and fire scenarios for the tall steel concentrically braced frames, the fire resistance duration was short and the impacts of the previous earthquake on the structure fire resistance were not considerable.

Key Words
concentrically braced frames; fire following earthquake; fire resistance; multi-stage analysis; overall behaviour

Address
Rasul Kaffasha:Department of Civil Engineering, Ferdowsi University of Mashhad, Iran

Abbas Karamodin: Department of Civil Engineering, Ferdowsi University of Mashhad, Iran

Abstract
This research aims to address the problem of frequency sensitivity of traditional tuned mass damper (TMD) and the difficulty in connecting the rocking wall by combining the construction technology of rocking wall with the vibration-control mechanism of TMD. The two 1/10 scaled six-story RC frame structures with and without rocking wall TMDs were precast and tested on a shaking table based on the principle of "consistent similarity law" to assess the seismic performance of the innovative system of vibration control, namely rocking wall TMDs. The results show that under three ground motions namely EL Centro, Taft and Artificial waves with peak accelerations of 0.2 g and 0.4 g, the rocking wall TMDs effectively controlled the primary structure response and the vibration-control effect of rocking wall TMDs was more significant with increased seismic intensity. Due to weaken the connections between the rocking wall and the primary structure, the out-of-phase vibration were more obvious, contributing to momentum exchange and tuning primary structure frequency. Consequently, the maximum acceleration, displacement, inter-story drift angle and Fourier spectrum decreased significantly under different seismic excitations, improving the frequency sensitivity of the traditional TMD. In addition, the rocking wall TMDs set along the height of the structure effectively enhanced the momentum exchange of each floor, which in return reduced the dynamic response amplification, controlled the structural deformation mode, and achieved overall vibration control effect. Therefore, the rocking wall TMDs have good seismic performance and robustness.

Key Words
out-of-phase vibration; rocking wall TMDs; seismic performance; shaking table test; vibration-reduction effect; vibration control

Address
Wei Nie: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Shuxian Liu: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Shasha Lu: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Shaodong Liu: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Chun Bai: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Hang Yin: Department of Civil Engineering, Liaoning Technical University, Fuxin 123000, China

Abstract
This paper proposes an energy-based approach for estimating the yield force coefficient of reinforced concrete (RC) frame structures. The procedure is mainly based on the energy balance concept and it considers the nonlinear behavior of structures. First, an energy modification factor is defined to consistently obtain the total energy of the equivalent elastic-plastic single-degree-of-freedom (SDOF) system. Then, plastic energy is formulated as functions of the several structural parameters such as the natural frequency, the strength reduction factor and the yield displacement. Consequently, the plastic energy formulation is derived for multi-degree-of-freedom (MDOF) systems and the yield force coefficient is determined by equating the plastic energy relation to the work needed to push the structure from the yield displacement up to the maximum displacement monotonically. The validity of the energy-based approach is assessed on several RC frame structures by means of nonlinear static pushover analysis considering both material and geometrical nonlinearity. A modification factor is proposed for the yield force coefficient to consider the strain-hardening effects in lateral forces. Moreover, the modified energy-based yield force coefficients are correlated to practical design by using the ductility ratios imposed by Turky Building Earthquake Code and a quite good agreement is observed.

Key Words
energy modification factor; nonlinear static pushover analysis; plastic energy; RC frame structures; yield force coefficient

Address
Onur Merter: Department of Civil Engineering, Izmir University of Economics, 35330, Balcova, Izmir, Turkey

Taner Ucar: Department of Architecture, Dokuz Eylul University, 35390, Buca, Izmir, Turkey

Abstract
In order to evaluate the seismic response characteristics of full light-weight concrete prefabricated utility tunnels, four prefabricated utility tunnels were conducted for test with different variables. Under unidirectional seismic excitation, the seismic response characteristics were analyzed by shaking table tests. And the corresponding numerical analysis models were proposed with ABAQUS. Based on the comparison between the simulation results and the experimental data, the influences of the parameters that full light-weight concrete, haunch heights, and reinforcement ratio on seismic response of prefabricated utility tunnels were systematically studied. The results indicated that the value of the peak acceleration, acceleration amplification factor, and peak displacement were reduced significantly with full light-weight concrete, which could decrease the seismic response of prefabricated utility tunnels. When the haunch heights and reinforcement ratio were properly increased, the seismic performance of prefabricated utility tunnels could be improved slightly. In addition, the peak displacement of full light-weight concrete prefabricated utility tunnels could meet the requirements, and there was no obvious damage until the end of test. The simulation results were in good agreement with the experimental data, and the seismic response characteristics were consistent. The results of this paper could provide a technical basis for the promotion and application for full light-weight concrete prefabricated utility tunnels.

Key Words
full light-weight concrete; numerical simulation; prefabricated utility tunnel; seismic response characteristics; shaking table test

Address
Yanmin Yang: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China

Ran Xu: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China

Yongqing Li: Institute of Water Conservancy and Planning Research, Changchun City, Changchun 130000, China

Zigen Li: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China

Abstract
In this paper, a detailed probabilistic seismic damage analysis of RC high-rise buildings was performed and as a result, the damage states (DSs) and appropriate performance levels (PLs) were defined in a quantitative manner. DSs were quantified using inter-story drift, where the drifts were determined at the onset of each DS. The analysis was performed on three RC high-rise buildings: 20-story, 30-story and 40-story with core wall structural system. Probabilistic seismic damage analysis was performed for 60 earthquake records, recorded on rock and stiff soil, and scaled to two intensity levels associated with probability of exceedance, 10 % in 50 years - 475-year return period (10%/50) and probability of exceedance, 2 % in 50 years - 2475-year return period (2%/50). In addition to these analyses for estimation the damage index, nonlinear static pushover analyses (NSPAs) were performed using different modal combination patterns. Large deviations among the pushover curves for individual considered modal combination patterns were observed. In order to adequately select the parameters for calculating damage index, an analysis of drifts and shear forces for individual modal combination patterns was performed. The functional dependencies between inter-story drifts and damage index were derived using the regression analysis. Based on the derived dependencies, the values of inter-story drifts at the onset of considered DSs for high-rise buildings were proposed.

Key Words
damage state; inter-story drift; Nonlinear Time-History Analysis (NTHA); Nonlinear Static Pushover Analysis (NSPA); RC high-rise buildings; regression analysis

Address
Jelena R. Pejovic: Faculty of Civil Engineering, University of Montenegro, Podgorica, Montenegro

Nina N. Serdar: Faculty of Civil Engineering, University of Montenegro, Podgorica, Montenegro

Abstract
The performances of repaired RC exterior beam-column joints were reported in this paper. The aim of the study was to restore back the lost capacity of the beam-column joint to the original state or more. Five type of exterior beam-column joint with different position of cold joint in the column were casted and subjected to reversed cyclic loading. The damage zones were confined with welded wire mesh (WWM) of 20 mm grid size and jacketed with polymer modified mortar (PMM). Damaged specimens after repairing were also subjected to similar cyclic displacement as those of control specimens. Seismic parameters such as load carrying capacity, energy dissipation, ductility, stiffness degradation, equivalent viscous damping, damage indices and nominal principal tensile stresses were analyzed. Results show that repaired specimens exhibited better seismic performance and hence the adopted repairing strategies could be considered as appropriate. These findings would be helpful to the field engineers to adopt a suitable rapid and cost-efficient repairing technique for restoring the damaged frame structural joints for post-earthquake usage. Further, the study revealed that there is an improvement in seismic capacity of the specimens as the location of cold joint is placed away from the soffit of the beam for lower story column.

Key Words
beam-column joint; cold joint; polymer modified mortar; reversed cyclic loading; satisfactory; seismic capacity

Address
Comingstarful Marthong: Department of Civil Engineering, National Institute of Technology Meghalaya, Shillong 793003, India

Jonathan Vanlalruata: Department of Civil Engineering, National Institute of Technology Meghalaya, Shillong 793003, India

Abstract
Base isolation system is originally known as one of the most efficient earthquake-resistance control systems. Isolated strategic structures may also experience terrorist attacks during their lifetime. In this paper, a design method is proposed for lead rubber bearing (LRB) isolation system under multi-hazard of explosion and seismic. This method is based on transforming the design problem into an optimization problem. The seismic response of structure has been defined as objective function while the constraints have been applied on its blast response. To validate the effectiveness of the proposed design method, LRB is designed for controlling a four-story steel moment-resisting building. For comparison objectives, this control system has been also designed under seismic hazard without paying attention to its blast performance. The results show that the earthquake-based optimally designed LRB has effective performance under seismic hazard whereas its blast performance is not as good as its seismic performance. Therefore, this control system cannot be considered as a well-designed control system for multi-hazard. The multi-hazard-based optimally designed LRB shows excellent performance under both blast and seismic loadings, so the proposed design method can be introduced as an effective design approach for LRB under multi-hazard of explosion and seismic.

Key Words
base isolation system; explosion hazard; lead rubber bearing; multi-hazard-based optimal design; seismic hazard

Address
Hamed Dadkhaha: Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Mohtasham Mohebbi: Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran


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