https://orcid.org/0000-0002-6037-9775
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ABSTRACT
Strength hierarchy assessment method is a capacity analysis procedure that can be used to identify the sequence of failures likely to occur within reinforced concrete (RC) frame buildings under lateral actions such as earthquakes or wind loads. Previous publication on this method mainly focused on the application of this method to (a) the vulnerable RC beam-column joints without any joint shear reinforcement where principal tensile stresses were considered critical, (b) modern RC beam-column joints with joint shear reinforcement where extreme principal compression stresses were considered critical. In this paper, joint shear capacity representation for modern RC beam-column joints (with transverse reinforcements in the joint) is generalized to include both critical components: principal tensile and principal compression stresses. Using strength hierarchy assessment, the investigation showed that it is possible to express the joint shear capacity as an N-M interaction envelope analogous to the N-M interaction of columns. The resulting joint shear capacity N-M interaction concept is validated using a database of 22 external and 22 internal RC beam-column joint tests with joint shear reinforcement at their joint core which resulted in joint shear failure in their tests. Considering the importance of axial load levels on the expected performance of RC beam-column joints, the proposed concept can be used for the general assessment of the joint shear capacity or for beam-column joint modeling purposes, which can be practically used by the design engineers.
11. Notation
| A0, Al | = | The cross sectional area of a single leg of the transverse reinforcement and longitudinal column intermediate reinforcement |
| Ast | = | Total column longitudinal steel area passing through the joint |
| α | = | The angular orientation of additional ties/transverse reinforcement with respect to shear direction |
| bc, hc | = | Cross sectional width and height of the column |
| bw, hb | = | Cross sectional width and height of the beam |
| C, T | = | Concrete compression and steel tension forces |
| d, jd | = | Effective depth of the beam reinforcement and the lever arm of the beam reinforcement |
| fc’ | = | Compressive strength of concrete |
| fy, fyw | = | Yield strength of the longitudinal reinforcement and yield strength of the transverse reinforcement |
| Fi | = | Floor equivalent static force at ith floor |
| Fjt | = | Part of the floor equivalent static force acting on a single beam column joint (in strength hierarchy assessment) |
| Fjts | = | Equivalent diagonal tension force capacity description given by transverse and intermediate longitudinal reinforcements within the joint |
| lb | = | Effective span length of a beam (general description) |
| lc | = | Column height between the inflection points above and below the considered joint |
| Mci | = | Joint shear capacity represented as column moment below the joint at ith storey (Considered storey) |
| µ | = | Displacement ductility |
| NG | = | Gravity load on the column before any seismic action |
| N, V, M | = | Axial force, shear force and bending moment |
| Pt,, Pts, Ptt | = | Principal tension capacity of an unreinforced beam-column joint, principal tension capacity given by the available joint shear reinforcement and the total principal tension capacity (Ptt=Pt+Pts) |
| Pc | = | Principal compression capacity |
| ϕ1, ϕ2 | = | Geometric coefficients for the moment representation of beam column joint shear strength |
| ΣFwx, ΣFwy | = | Total horizontal and total vertical capacity contribution by transverse and intermediate column reinforcements within the beam-column joint |
| Tswx, Tswy | = | Tension in transverse and column intermediate reinforcements within the joint |
| θ | = | Approximate diagonal cracking angle at the beam-column joint |
| νjt | = | Average joint shear stress (=Vjt/(bc∙hc)) |
Acknowledgments
The author would like to express his deepest gratitude and love for his father Ibrahim Tasligedik who passed away on 25th of March 2020. He has not only been a role model, but the most perfect father one could wish for and has been his main teacher/mentor in this life. He will be deeply remembered.
The author would also like to express his gratitude to Greg Preston (UC Quake Centre, Christchurch, New Zealand), the University of Canterbury Engineering Library (Christchurch, New Zealand) and Middle East Technical University Library (Ankara, Turkey) for helping with the access to some of the old reports and photos needed in this article. The author would also like to thank the late professors Thomas Paulay and Robert Park for their timeless contributions and insight into the understanding of reinforced concrete structures, which still carries a significant insight aiding our research efforts in modern times.