Seismic Rehabilitation of Existing Buildings

It is not correct to state that the collapse of the Wilkins Air Force Base depot building occurred without warning. The structure was known to be extensively cracked in shear well before the collapse, and it is the discusser’s understanding that some beams in the building were already being braced with shoring consisting of various wooden poles. The observer was in fact looking for additional trouble at the time of the collapse, although it must be argued that the fact that the failure occurred while he was present was coincidence. The record of cracking for the particular design at Wilkins was so bad that a revised design had already been prepared and was used in some similar buildings. The January 1957 issue of the ACI Journal had several articles dealing with the failure and with the repairs to other structures of the same group that had not failed but that were showing significant shear cracking.

Discussion of "Recent Approaches to Shear Design of Structural Concrete"

Abstract Material nonlinear analyses of reinforced concrete (RC) beams considering the tension softening branch and bond slip have been conducted. Instead of adopting the sophisticated layer approach which has some limitations in application to large structures with many degrees of freedom, we have used the moment–curvature relationships of RC sections previously constructed through section analysis. To reduce numerical instability according to the finite element mesh size used, a relation simulating the tension softening branch has been taken into consideration. For the purpose of removing the imprecision in calculation of ultimate resisting capacity, we have included the plastic hinge length in finite element modeling. In addition, governing equations describing the bond-slip behavior in beams have been derived. Unlike the conventional bond elements using double nodes, the proposed model has used beam elements representing the structural response by two nodes at both ends, and has simplified the finite elements modeling and analytical process, besides effectively describing the bond-slip behavior. Moreover, the developed algorithm has been reflected in the moment–curvature relationship of RC section. Finally, correlation studies between analytical and experimental results have been conducted with the objective to establish the validity of the proposed algorithms.

모멘트-곡률 관계에 기초한 철근콘크리트 보의 비선형 해석 = Nonlinear analysis of RC beams based on moment-curvature relations

In this paper, three one-third scale reinforced concrete (RC) beam-column-slab structure specimen tests were conducted to investigate the collapse mechanisms under a loss of the corner column, including a frame with slab (S-COR), a frame with slab and secondary beams (SS-COR), and a frame without slab (NS-COR). The slab and secondary beam’s contributions were investigated by comparing the SS-COR and NS-COR, SS-COR, and S-COR specimens. The results show that the RC slab significantly enhanced the load resistance. Only a slight increase in peak resistance capacity of the SS-COR specimen was observed, while the ductility improved obviously due to the existence of secondary beams. The failure mode of the SS-COR frame is different from that of the S-COR frame: No concrete failure line occurs on the slab bottom, and the cracks develop entirely on the slab top. Moreover, based on the test results, finite element models (FE) were updated by adapting the OpenSeespy, which shows a good fit between the test curves and simulation results. Finally, 1,000 samples considering the uncertainty parameters were generated using Monte Carlo sampling to better understand the effect of uncertainty on the structure response. Data-driven models based on machine learning were used to predict the peak resistance capacity of the RC structures with slab and secondary beams. 

Assessment of RC Frame Capacity Subjected to a Loss of Corner Column

In the present study, an attempt has been made to experimentally investigate the flexural performance of ten simply supported reinforced concrete gable roof beams, including solid control specimen (i.e., without openings) and nine beams with web openings of different dimensions and configurations. The nine beams with openings have identical reinforcement details. All beams were monotonically loaded to failure under mid-span loading. The main variables were the number of the created openings, the total area of the created openings, and the inclination angle of the posts between openings. Of interest is the load-carrying capacity, cracking resistance and propagation, deformability, failure mode, and strain development that represent the behavior of reinforced concrete gable beams. Test results showed that the total concrete weight consumed for the tested gable beams with openings was lower than the solid gable beam by (14.9–26%). This reduction in weight led to a reduction in the flexural stiffness and, in turn. in the load-carrying capacity by (6.2–17.9%). The percentage of the decrease in the concrete consumption to the reduction in the load-carrying capacity for the tested beams with openings attained (140–240%). It was recorded that the maximum crack width depended on the total area of the created openings rather than the number of these openings.

Structural Performance Under Monotonic Static Loading of Reinforced Concrete Gable Roof Beams with Multiple Web Openings

Collapse Load Estimation of Rectangular Reinforced Concrete Beam-Slab Systems—New Insights

A simple algorithm is proposed to develop a nonlinear moment-curvature relation for Reinforced Concrete (RC) T-beam sections using nonlinear material models. The flange in the beam adds to the complexity of analysis compared to rectangular beam sections. This algorithm has been validated by laboratory testing of simply supported flanged beam specimens, subjected to two-point loading. The load- deflection data obtained from the experiments is converted to a moment-curvature relation for the section applying simple bending theory. The results predicted numerically by the proposed algorithm are found to be in good agreement with the experimental data. The algorithm developed can be used to generate the load-deflection curve of an RC T-beam subject to any given loading. A portion of continuous slab integrally connected to the beam serves as flange and the supporting beam as web. The flexural capacity of such sections can be enhanced when the flanges are in compression. The web helps in resisting shear stresses. The moment-curvature relation is obtained by carrying out sectional analysis of RC T-beam section. In this analysis, different cases are considered depending on the position of the neutral axis (6). Testing of three T-beams has been carried out in the laboratory. These beams are loaded symmetrically at two points to simulate pure flexure. Load- deflection data obtained from these tests is used to generate moment-curvature relation using theory of simple bending. The results generated by numerical algorithm are validated with these experimental results. The behavior of the beams is studied for variation in depth of flange and tensile reinforcement. The nonlinear sectional analysis for these RC T-beams is explained in the next section.

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Moment-curvature relation of Reinforced Concrete T-beam sections - Numerical and Experimental studies

Yield line analysis and testing of reinforced concrete rectangular slabs with primary and secondary beams

Assessment of Shear Strength of Circular Reinforced Concrete Beams

The earthquake resistant design code in India, IS: 1893, has been revised in 2002 to include provisions for torsional irregularity in asymmetric buildings. In line with other international code, IS 1893: 2002 requires estimating the design eccentricity from static and accidental eccentricity. The present study attempts to evaluate the effectiveness of the design code requirements for designing torsionally irregular asymmetric buildings. Two similar asymmetric buildings designed considering and ignoring code requirement has been considered for this study. Nonlinear static and dynamic analyses are performed on these buildings to realize the difference in their behaviour and it is found that the plan asymmetry in the building makes it non-ductile even after design with code provisions. Code criterion for plan asymmetry tends to improve the strength of members but this study indicates that changing the stiffness distribution to reduce eccentricity may lead to a preferred mode of failure.

Bijily Balakrishnan

Papers

Collapse Load Estimation of Rectangular Reinforced Concrete Beam-Slab Systems—New Insights

Moment-curvature relation of Reinforced Concrete T-beam sections - Numerical and Experimental studies

Yield line analysis and testing of reinforced concrete rectangular slabs with primary and secondary beams

Assessment of Shear Strength of Circular Reinforced Concrete Beams

Efficacy of Code Provisions for Seismic Design of Asymmetric RC Building