Special Moment Resistant Steel Buildings

The seismic response of special moment-resisting frames (SMRF), buckling restrained braced (BRB) frames and self-centering energy dissipating (SCED) braced frames is compared when used in building structures many stories in height. The study involves pushover analysis as well as 2D and 3D nonlinear time history analysis for two ground motion hazard levels. The SCED and BRB braced frames generally experienced similar peak interstory drifts. The SMRF system had larger interstory drifts than both braced frames, especially for the shortest structures. The SCED system exhibited a more uniform distribution of the drift demand along the building height and was less prone to the biasing of the response in one direction due to P-Delta effects. The SCED frames also had significantly smaller residual lateral deformations. The two braced frame systems experienced similar interstory drift demand when used in torsional irregular structures.

Earthquake Analysis of a High-Rise Building Retrofitted with Support Braced Systems

The use of support braced systems represents one of the best solutions for retrofitting or upgrading the tall reinforced concrete buildings in areas with a high earthquake hazard. In this study, the behavior of a reinforced concrete tall structure under seismic loads is examined based on the Turkish Building Earthquake Code 2019 (TBEC-2019). Support braced systems were added to the 25-story structure on 0.4H and 0.8H levels (H is height of structure). For two different models, firstly, the Mode-Superposition Method for linear computational methods used within the scope of strength-based design is performed. In order to determinate more accurately the behavior of tall buildings, as in the earthquake regulations of other developed countries, the TBEC-2019 advises a nonlinear deformation-based design approach. In addition, the nonlinear time history analyses of these buildings were performed. As a result of these analyzes, it was determined whether the two models examined were within the targeted performance effects or not. In the model having support braced system, stiffness and shear forces in shear walls were increased. Thus, displacements, relative story drift, plastic rotations and bending moments of shear walls were decreased.

Influence of Optimal Intensity Measures Selection in Engineering Demand Parameter of Fixed Jacket Offshore Platform

This research identifies the significant optimal intensity measures (IM) for seismic performance assessments of the fixed offshore jacket platforms. A four-legged jacket platform for the oil and gas operation is deployed to investigate the seismic performance. The jacket platform is applied with nonlinearly modeled using finite element (FE) software OpenSees. A total of 80 ground motions and 21 different IMs are incorporated for numerical analyses. Nonlinear time-history analyses are performed to obtain the jacket structure’s engineering demand parameters (EDP): peak acceleration and displacement at the top of the structure. Four important statistical parameters: practicality, efficiency, proficiency, and coefficient of determination, are then calculated to find the significant IMs for seismic performance of the jacket structure. The results show that acceleration-related IMs: effective design acceleration (EDA), A95 parameter, and peak ground acceleration (PGA) are optimal IMs, and the acceleration-related IMs have good agreements with the acceleration-related EDP.

Effect of bidirectional excitation on seismic performance of regular RC frame buildings designed for modern codes

The existing practice to estimate seismic performance of a regular building is to carry out nonlinear time history analysis using two-dimensional models subjected to unidirectional excitations, even though the multiple components of ground motion can affect the seismic response, significantly. During seismic shaking, columns are invariably subjected to bending in two orthogonal vertical planes, which leads to a complex interaction of axial force with the biaxial bending moments. This article compares the seismic performance of regular and symmetric RC moment frame buildings for unidirectional and bidirectional ground motions. The buildings are designed and detailed according to the Indian codes, which are at par with the other modern seismic codes. A fiber-hinge model, duly calibrated with the biaxial experimental results, is utilized to simulate the inelastic behavior of columns under bidirectional bending. A comparison of the estimated seismic collapse capacity is presented, illustrating the importance of considering the bidirectional effects. The results from fragility analysis indicate that the failure probabilities of buildings under the bidirectional excitation are significantly higher as compared to those obtained under the unidirectional excitation.

Assessment on the deflection amplification factor of steel buckling-restrained bracing frames

Researchers in the field of earthquake engineering are always looking for new ways to improve the seismic behavior of structures. The buckling-restrained brace (BRB) is one of these exciting innovations that are employed to increase the ductility capacity of traditional steel braced frames. Understanding the nonlinear response of these novel systems in estimating maximum displacements due to an earthquake has been of significant importance for structural designers. Accordingly, this research is carried out to study of deflection amplification factor ( C d) in BRBs, which have recently been presented in seismic design provisions as one of the seismic lateral-resisting systems. To this end, five 3-, 5-, 7-, 10-, and 15-story BRBs are modeled in the software framework of OpenSees. Ground motion simulation is performed by selecting several scaled earthquake records, and the values of elastic and ultimate displacements of structural systems are computed through pushover and nonlinear time-history analyses. The results showed that the deflection amplification factor suggested within famous building codes (such as ASCE-7-16) compared to the obtained values is, in some cases, for certainty; conversely, it is underestimated under some conditions. In fact, the findings indicate that the magnitude of C d in these systems is strongly related to the height of the building.

Quasi-static tests on RC building columns strengthened with CFRP

To explore the possibilities and benefits of using CFRP (Carbon Fibre Reinforced Polymers) in strengthening RC building columns, quasi-static tests (compression and bending) were carried out at the Institute of Earthquake Engineering and Engineering Seismology - IZIIS, Skopje by variation of concrete class, reinforcement percentage and by using various strengthening technologies. Some recommendations and outcomes regarding the approach, technology and conclusions drawn from practical application of these materials, are given. Based on the analysis of values obtained from nonlinear static and nonlinear time history analyses, it can be concluded that the ductility capacity for displacement of model strengthened with CFRP is greater by 60 %, while its strength capacity is greater by 7.7 % when compared to the values obtained for the model without CFRP. It can generally be concluded that CFRP systems are a very practical tool for strengthening and retrofitting concrete structures, as they can extensively improve flexural strengthening, shear strengthening, column confinement, and ductility.

Seismic Evaluation of Self-Centering Bi-Rocking Walls via Micro Modeling of Rocking Joints: Locating the Rocking Section

The rocking concrete shear wall is one of the new self-centering seismic systems applied in high-rise buildings. To reduce the effects of higher modes on base-rocking walls, the idea of using multiple rocking walls has been evolved. This paper presents a comparative investigation on the seismic performance of base-rocking and bi-rocking wall systems. To this aim, structures of 4-, 8-, 12-, 16-, and 20- stories have been evaluated subjected to three sets of seismic earthquake records including 22 Far Field (FF), 14 Near Field (NF) with pulse, and 14 Near Field (NF) no-pulse ground motions. The nonlinear time-history analyses were conducted in two directions using OpenSEES software. To determine the appropriate location of rocking section in bi-rocking walls, one-quarter (R2-M1), one-half (R2-M2), and three-quarter (R2-M3) models were examined. The obtained results revealed that R2-M3 model is not efficient in reducing the effects of higher modes. However, R2-M2 model in high-rise buildings under FF and NF-no-pulse records could be effective in decreasing the moment by a maximum of nearly 41% and the shears by a maximum of 25% and 18%, respectively. Furthermore, the results showed that bi-rocking walls could not be effective in reducing the influence of higher modes under NF-pulse ground motions. Generally, the residual drifts were negligible in all the rocking systems under study.