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Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which is directed at satisfying the capacity design requirements without excessively large sections, consists of proportioning the column so that the seismic action effects shall be resisted by the maximum of the bending moment–axial force interaction curve. That design condition is defined by two equations whose solution provides the optimal aspect ratio (or, alternatively, the optimal section side length) and the maximum feasible reinforcement ratio. The method can be used directly to determine the optimal column for given beam spans and vertical loads, or indirectly to determine the optimal beam spans and vertical loads for given cross-sectional dimensions. The paper presents the method, including its proof, and some applications together with the analysis on the optimality of the obtained solutions. The method is intended especially for the practicing structural engineer, though it may also be useful for educators, students, and building officials.

Numerous seismic damage investigations have demonstrated that reinforced concrete (RC) frame structures tend to exhibit a Strong-beam Weak-column failure mechanism, which contradicts the intended Strong-column Weak-beam design philosophy. To explore the underlying causes of this discrepancy and identify effective strategies to enhance the realization of the Strong-column Weak-beam behavior, the mechanical performance of RC frames with varying axial compression ratios and beam-end reinforcement ratios was analyzed using the finite element analysis software ABAQUS. Key structural characteristics of failure modes, such as deformation patterns, concrete tensile damage distribution, stress distribution in slab reinforcement, concrete compressive strain in columns, plastic hinge distribution, and structural displacement ductility were examined. The results indicate that merely reducing the amount of reinforcement at beam ends has limited effectiveness in altering the failure mode and improving displacement ductility, even reduce the amount of top reinforcement at beam end to 33 % of designed quantity which is below the minimum value specified in structural design codes, the failure mode and ductility of the RC frame still cannot be substantially improved. Whereas lowering the axial compression ratio significantly enhances structural performance, when the high axial compression ratio is adjusted to a low one, for instance, from 0.9 to 0.3, the ductility of the frame structure is significantly improved, and the plastic hinge at the column end of the upper floor is successfully shifted to that beam end. Furthermore, the influence of the monolithic slab on the failure behavior of RC frames is twofold: it not only involves the contribution of slab reinforcement parallel to the beam ribs, but also stems from the presence of the monolithically cast slab-beam-column system, which improves the overall structural integrity performance. Moreover, to better measure the participation effect of the cast-in-place floor slab and reflect the potential participation capacity of the monolithic slab, the calculation formulas for the bending resistance reserve of the exterior and interior the middle frame were respectively proposed. This formula breaks through the rigid limitation of the 6 times of the slab thickness (6 ) as the width of the beam end flange suggested by the code, and better estimates the participation effect of the cast-in-place floor slab.

The fishbone model is a simplified numerical model for moment-resisting frames that is capable of modelling the effects of column-beam strength and stiffness ratios. The applicability of the fishbone model in simulating the seismic responses of reinforced concrete moment-resisting frames of different sets of column-beam strength and stiffness ratios are evaluated through nonlinear static, dynamic and incremental dynamic analysis on six prototype buildings of 4-, 8- and 12-stories. The results show that the fishbone model is practically accurate enough for reinforced concrete frames, although the assumption of equal joint rotation does not hold in all cases. In addition to the ground motion characteristics and the number of stories in the structures, the accuracy of the model also varies with the column-beam stiffness and strength ratios. The model performs better for strong column-weak beam frames, in which the lateral drift patterns are better controlled by the continuous stiffness provided by the strong columns. When the inelastic deformation is large, the accuracy of the model may be subjected to large record-to-record variability. This is especially the case for frames of weak columns.

The strong-column weak-beam (SCWB) design concept for RC frames has been adopted in many seismic design codes. However, seismic investigations show that the minimum column-to-beam flexural strength ratio (CBFSR) required in seismic codes usually cannot guarantee the SCWB failure mode of RC frames during strong earthquakes. This paper investigates the seismic performance of RC frames designed according to Chinese seismic codes with different CBFSRs by numerical simulations. The RC frames are subjected to near-field pulse-like and far-field non-pulse-like ground motions. The displacement responses and failure modes are analyzed. The results show that (1) larger CBFSR values are required to achieve the SCWB failure mode under the excitation of pulse-like ground motions than those under the excitation of non-pulse-like ground motions. (2) The uncertainties of the displacements decrease with increasing CBFSR and increase with increasing seismic intensity. The uncertainties of the displacements under the excitation of pulse-like ground motions are larger than those under the excitation of non-pulse-like ground motions. (3) With increasing CBFSR, the maximum interstory drift ratio (IDR) in the lower stories decreases, while the maximum IDR in the upper stories increases. Finally, recommended CBFSRs are proposed for achieving the SCWB failure mode with an 80% guarantee rate for different seismic hazard levels and ground motion characteristics.

In order to ensure the structural safety and serviceability of existing reinforced concrete (RC) structures, there is a compelling need to develop efficient techniques for the rapid replacement of damaged RC beams within strong-column–weak-beam structural systems. This study introduces a novel prefabricated RC beam with welded cover-plate steel sleeve and bolted splice designed to facilitate accelerated replacement and enhance construction efficiency. The proposed beam is connected to cast-in-place RC columns, forming a prefabricated novel prefabricated RC joint with a welded cover-plate steel sleeve and a bolted splice; this configuration contrasts with conventional monolithic RC joints, which are formed by integrally casting beams and columns. The assembly speed of the prefabricated system markedly surpasses that of its cast-in-place counterpart, and the resulting beam–column system is fully demountable. Finite element simulations of the novel prefabricated RC joint with welded cover-plate steel sleeve and bolted splice, performed using ABAQUS, identified the thickness of the welded end-plate as a pivotal parameter influencing the joint’s mechanical behavior. Accordingly, quasi-static tests were carried out on three novel prefabricated RC joints with welded cover-plate steel sleeves and bolted splices and one cast-in-place RC joint, with the welded end-plate thickness serving as the primary test variable. The failure patterns, hysteretic responses, energy dissipation capacity, ductility, and stiffness degradation were systematically analyzed. Experimental findings indicate that increasing the end-plate thickness effectively improves both the peak load-bearing capacity and the ductility of the joint. All prefabricated specimens exhibited fully developed spindle-shaped hysteresis loops, with ductility coefficients ranging from 3.47 to 3.64 and equivalent viscous damping ratios exceeding 0.13. All critical seismic performance metrics either met or exceeded those of the reference cast-in-place RC joint, affirming the reliability and superior behavior of the proposed novel prefabricated RC joints with welded cover-plate steel sleeves.

Performance-based seismic codes ensure proper inelastic behaviour of reinforced concrete frames through capacity design, among others. This strategy relies not only on avoiding brittle failures and providing ductility to plastic hinges but also in their distribution within the frame aimed at a greater number of storeys involved in the eventual collapse mechanism. Although codes are generally in agreement to some basic principles in order to ensure capacity design, they show some discrepancies regarding the specific strategies. In this paper, capacity design provisions proposed by some European current codes—Eurocode 8, Italian NTC, and Spanish NCSE-02—are compared, and their effectiveness is discussed. The alternative formulation proposed by Italian code for “strong column–weak beam” turns out to be not suitable under specific circumstances, such as with large gravity loads or significant cantilever deformation in lower storeys. Regarding the value of axial load in columns to be considered for the calculation of shear and moment capacities, provisions in the three codes could eventually cause unconservative design for perimeter columns. The Spanish whole set of provisions is proved to not be effective due to their different fundamentals—they are based on overstrength instead of capacity. For all the three cases, some alternative procedures are suggested in this work.

The main objective of this study is to employ a probabilistic approach to determine the appropriate value of the strong column-weak beam ratio (SCWBR) for three mid- to high-rise moment frames. These buildings are subjected to pulse-type ground motions. The nonlinear soil-structure interaction (SSI) is also involved as another seismic energy dissipation mechanism. A set of incremental nonlinear dynamic analyses are performed for 91 pulse-like ground motions. The proposed approach includes global and local performance criteria. Park-Ang damage index is utilized as the damage measure for columns. In this regard, simple mathematical equations are also derived to quantify the impact of the SCWBR. This framework introduces an upper bound on the SCWBR beyond which further increase of this parameter would not be required to limit the damage of columns. The results indicate that for the 4-story building, the applicability of the SCWBR extends to values as large as 2.4, while for the 8 and 12-story buildings, this is restricted to 1.8 and 1.6, respectively. However, these values substantially depend on the pulse period in such a way that the SCWBR of 1.2 would be sufficient when the pulse period is approaching the fundamental period of structures. The SSI may improve the collapse probability of high-rise structures to a larger extent compared to SCWBR. Nevertheless, its effect can be diminished by more damage of columns at the lower portion of buildings.

Reinforced concrete (RC) frames are designed based on the strong column-weak beam (SCWB) philosophy to reduce structural damage and collapse during earthquakes. The SCWB design philosophy is ensured by the required minimum flexural strength ratio of columns to beams (FSRCB) in the seismic code. Quantifying the relationship between the FSRCB and the collapse capacity of the frames may facilitate the efficient assessment of the seismic performance of the existing or newly designed RC frames. This paper investigates the influence of different FSRCBs on the collapse capacity of three- and nine-story RC frames designed according to Chinese seismic codes. The results show that the collapse capacities of the RC frames can be efficiently improved by increasing the FSRCB, and the collapse capacities of frames with FSRCB = 2.0 are improved by approximately 1.6–2.0 times compared with those of the frames with FSRCB = 1.2. Compared with the middle- or high-rise (nine-story) frames, it is more efficient to improve the collapse capacity for low-rise (three-story) frames by increasing the value of CBFSR. The logarithmic standard deviation of the collapse capacity of the RC frames designed according to the Chinese seismic codes ranges from 0.5–0.9, which is larger than the proposed maximum logarithmic standard deviation (0.4) in FEMA P695.

Incremental dynamic analyses are conducted for a suite of low- and mid-rise reinforced-concrete special moment-resisting frame buildings. Buildings non-conforming and conforming to the strong-column weak-beam (SCWB) design criterion are considered. These buildings are designed for the two most severe seismic zones in India (i.e., zone IV and zone V) following the provisions of Indian Standards. It is observed that buildings non-conforming to the SCWB design criterion lead to an undesirable column failure collapse mechanism. Although yielding of columns cannot be avoided, even for buildings conforming to a SCWB ratio of 1.4, the observed collapse mechanism changes to a beam failure mechanism. This change in collapse mechanism leads to a significant increase in the building’s global ductility capacity, and thereby in collapse capacity. The fragility analysis study of the considered buildings suggests that considering the SCWB design criterion leads to a significant reduction in collapse probability, particularly in the case of mid-rise buildings.

Based on the design concept of a strong column and weak beam, a new type of reinforced concrete frame structure beam–column joint is proposed. Considering different column end amplification factors (beam–column bending moment ratio), the finite element method (FEA) is used to analyze the parameters that affect the seismic performance of RC frame structure beam–column joints. The reliability verification error is within 4.8% to 11.7%, meeting the requirements of engineering accuracy. Then, through parameter analysis, the effects of different concrete strengths, stirrup diameters, and axial pressures on the seismic performance of the joint are studied. The study results show that enhancing concrete strength has a significant effect on the seismic performance of the structure, especially when the amplification factor is 2.0. Compared with the C20 specimen, the bearing capacity of the C40 specimen increased by 26.88%. However, the increase in stirrup diameter did not significantly improve the performance of the specimen. In addition, a high axial pressure ratio may affect the bearing capacity of the structure. This study provides a new type of beam–column joint that conforms to the design concept of a strong column and weak beam and provides a theoretical basis for its application in engineering.