Next generation seismic resistant structural elements using high-performance materials


2018-12-11In the recent past, earthquakes have proven that reinforced concrete (RC) structures remain highly vulnerable to lateral loads. The yielding of longitudinal reinforcement as the main source of energy absorption, in conjunction with the cracking and spalling of the concrete, leads to severe damage and permanent deformations, which jeopardizes the post-earthquake functionality of these structures. A swift response and recovery in the aftermath of a major disaster strongly relies on the serviceability of key infrastructure, including bridges and other vital service structures such as hospitals and government buildings. Recently, the use of high-performance materials such as Engineered Cementitious Composites (ECC) and Superelastic Alloys (SEA) have been considered as alternative materials for conventional concrete and steel reinforcing bars (rebar), attracting heightened attention to improve the seismic performance of RC structures. ECC refers to a special class of high-performance fiber-reinforced cementitious composites (HPFRCC) that exhibit superior tensile ductility, energy absorption, bond characteristics and shear resistance. SEAs are innately capable of recovering large inelastic deformations upon stress removal. ❧ The primary endeavor of this study is to improve the performance of bridge columns and beam-column joints of special moment frames (SMF) using high-performance materials, particularly, ECC and Cu-Al-Mn SEA bars. To this end, an innovative bridge column design is first introduced and examined through an experimental framework. The column design comprises of a prefabricated reinforced ECC (RECC) hollow section that is embedded in a RC foundation and filled with conventional concrete. Additionally, the longitudinal reinforcement at the potential plastic hinge region is totally or partially replaced using the recently developed Cu-Al-Mn SEA bars. The proposed approach utilizes the deformability of the ECC in order to enhance damage tolerance of the bridge columns and large strains recovery capability of Cu-Al-Mn SEA to reduce permanent deformations. Following the completion of experimental work, a finite element approach is developed to numerically investigate the performance of the bridge columns designed on the basis of this proposed approach. The developed finite element approach is verified using the results ascertained from the tested columns and used to carry out a parametric study to obtain an optimal design strategy for the proposed design concept. Furthermore, in an attempt to improve the performance of corner and exterior beam-column joints in SMFs, conventional RC in 3D beam-column subassemblies is substituted with reinforced ECC (RECC) that extends from the panel zone area into the adjacent beams and columns in order to cover the potential plastic hinge regions. The 3D RECC beam-column subassemblies are then subjected to complex loading scenarios, including torsion, to investigate their performance due to more realistic seismic loads in 3D structures. ❧ The results from the experimental works indicated that ECC can significantly improve damage tolerance of bridge columns and beam-column joints subjected to extensive seismic loads and shift the damage mode from concrete spalling to fine distributed cracks. Incorporating ECC in panel zone of corner and exterior beam-column subassemblies sufficiently tolerated complex loading combinations even in absence of panel zone transverse reinforcement, due to superior shear strength of ECC compared to conventional concrete. Additionally, replacing longitudinal reinforcement with Cu-Al-Mn SEA bars in plastic hinge region of bridge columns, considerably decreases the permanent deformations of RECC bridge columns compared to the conventional RC ones. Furthermore, conducting the numerical and parametric studies revealed that: (i) mechanical properties of ECC can be successfully simulated by introducing fibers as smeared reinforcement in concrete; (ii) cyclic behavior of bridge columns incorporating ECC and Cu-Al-Mn SEA bars can be accurately captured using numerical models; (iii) hollow RECC sections with maximum hollow ratio of 35% have comparable performance as solid RECC bridge column; (iv) ultimate strain hardening capacity of ECC has limited effect on performance of bridge columns; (v) design of the bridge columns can be optimized by implementing hollow sections and partial replacement of the longitudinal reinforcement with Cu-Al-Mn SEA bars

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This paper was published in USC Digital Library.

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