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1

Novel non-invasive seismic upgradation strategies for gravity load designed exterior beam-column joints

100%

Kanchana Devi A. K. , Karusala R. , Tripathi M. , Sasmal S.

Archives of Civil and Mechanical Engineering

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2018

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tom Vol. 18, no. 2

479--489

EN

Existing gravity load designed (GLD) structures are vulnerable to seismic event due to their inherent weaknesses. The present study, focuses on the development of non-invasive and feasible strategies for seismic upgradation of these non-seismically designed structures. Three novel schemes, namely (i) single haunch upgradation scheme (U1), (ii) straight bar upgradation scheme (U2) and (iii) simple angle upgradation scheme (U3) are proposed for seismic upgradation of GLD specimens. The efficacy and effectiveness of these upgradation schemes are evaluated by conducting the reverse cyclic load tests on control and upgraded GLD exterior beam-column sub-assemblages. The performance of the upgraded specimens is compared with that of the control GLD beam-column sub-assemblage, in terms of load–displacement hystereses, energy dissipation capacities and global strength degradation behaviour. Tremendous improvement in the energy dissipation capacity to the tune of 2.63, 2.83 and 1.54 times the energy dissipated by the control GLD specimen is observed in single haunch upgraded specimens, straight bar upgraded specimen and simple angle upgraded specimen respectively. The specimen with single haunch upgradation performed much better compared to the GLD specimens upgraded with the other two schemes, by preventing the brittle anchorage failure, delaying the joint shear damage and redirecting the damage partially towards the beam.

2

Structural performance of reinforced concrete interior beam-column joints with high-strength bars

84%

Kim S.-W. , Chang H.-J.

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tom Vol. 21, no. 3

200--213

EN

This study evaluates the structural performance of reinforced concrete interior beam–column joints having high-strength screw-type steel bars mechanically connected with couplers. A total of six full-scale specimens were cast and subjected to repeated cyclic lateral loads. High-strength screw-type reinforcing bars, with a yield strength of 690 MPa, were used as longitudinal reinforcement of the specimens. The main test variables were designed with and without couplers and the longitudinal reinforcement ratio of the beam. The couplers were applied to the plastic hinge zones of columns and beams to maximize their impact. The experiment confirmed that the flexural cracks generated near the couplers slightly influenced the initial stiffness, the yielding point of the longitudinal reinforcement of the beams, and the displacement at peak load of the specimens. However, the load versus story drift relationship, the peak load, and the ductility capacity of the specimens were not significantly affected. In addition, the analytical results obtained using the current structural design codes and finite element analysis were similar to the experimental results.

3

Seismic behavior and damage assessment of mid-rise cold-formed steel-framed buildings with normal and reinforced beam-column joints

84%

Jiang L. , Zhang X. , Ye J. , Jiang L. , Zhou L.

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tom Vol. 21, no. 3

675--690

EN

This paper investigated the effects of normal and reinforced beam–column joints on seismic behavior and damages of mid-rise cold-formed steel (CFS) framed buildings, where the reinforced beam–column joint is strengthened by a pair of steel blocks and a gusset plate. Shaking table tests were conducted on a 5-story CFS frame building with normal beam-column joint (CFSM-NJ) and a 5-story CFS frame building with same configurations but with reinforced beam–column joint (CFSM-RJ). Formulae fitted from four damage models were used to assess the seismic damage indexes of these test buildings, and the assessed results were validated by the damage indexes observed from tests. The results show the following: (1) the CFSM-NJ failed due to plastic hinges formed at the column bases and large separate deformation at the beam-column joints; however, the weaken-story failure mode was appeared on the CFSM-RJ; (2) the peak inter-story displacement of the building was reduced about 10–30% due to the reinforced beam-column joints; (3) the Park-Ang model is more appropriate for seismic damage assessment of column bases, but all the damage models overestimates the seismic damages of CFS beams. Finally, the authors comment on the difference between the assessed seismic damage indexes and the observed results, and the maximum damage indexes obtained from the simplified formulae are recommended as the preliminary assessed damages for mid-rise CFS buildings.

4

Seismic evaluation of deficient reinforced concrete weak beam-column joint frames

67%

Rizwan M. , Ahmad N. , Khan A. N. , Fahad M.

Archives of Civil Engineering

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2020

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tom Vol. 66, nr 4

429--451

EN

The use of old building design codes and improper execution of recent seismic design practices have caused large amount of substandard and vulnerable reinforced concrete RC building stock majority of which are built with weak beam-column joint connections defect (i.e. joint panel having no transverse reinforcement and built in low strength concrete). In order to understand the seismic response and damage behaviour of recent special moment resisting frame SMRF structures with the defect of weak beam-column joints, shake table tests have been performed on two 1:3 reduced scaled, two story RC frame models. The representative reference code design and weak beam-column joint frame models were subjected to uni-directional dynamic excitations of increasing intensities using the natural record of 1994 Northridge Earthquake. The input scaled excitations were applied from 5% to 130% of the maximum input peak ground acceleration record, to deformed the test models from elastic to inelastic stage and then to fully plastic incipient collapse stage. The weak beam-column frame experienced column flexure cracking, longitudinal bar-slip in beam members and observed with cover concrete spalling and severe damageability of the joint panels upon subjected to multiple dynamic excitations. The deficient frame was only able to resist 40% of the maximum acceleration input as compared to the code design frame which was able to resist about 130%. The seismic performance of considered RC frames was evaluated in terms of seismic response parameters (seismic response modification, overstrength and displacement ductility factors), for critical comparison.