Response Of Reinforced Concrete Frames Research Articles

Numerical Assessment of URM Infilled RC Frames Retrofitted With Near-Surface Mounted Reinforcing Steel Bars

This paper presents a study on a retrofit technique for masonry infilled reinforced concrete (RC) frames. The proposed retrofit technique involves the addition of reinforcing steel bars into epoxy-filled pre-cut grooves on the surface of infill walls. The feasibility of the developed technique is initially investigated experimentally through pull-out tests conducted on near-surface mounted (NSM) reinforcing steel bars. The experimental results are used to augment an existing nonlinear finite element modeling approach used to simulate the response of RC frames with the retrofitted infill panels and to calibrate the numerical models developed. The nonlinear finite element models employ smeared-crack and zero-thickness cohesive-crack interface elements to model the RC members and masonry infills, while nonlinear truss elements are used to model the reinforcing steel bars. The modeling scheme is used to numerically simulate the performance of one- and two-bay infilled RC frames with a variety of reinforcing steel retrofit configurations under lateral loads. The results indicate that the retrofit solution can improve the deformation capacity of existing infilled frames, and its effectiveness depends on the orientation and the distribution of the NSM reinforcement steel bars that are added to the infill panels.

Impact Analysis of Thermally Pre-Damaged Reinforced Concrete Frames.

In the present study, the influence of thermally induced damage of reinforced concrete (RC) frames on their static and dynamic response is experimentally and numerically investigated. In the experimental test, the RC frame is first pre-damaged through fire exposure and then loaded from the side with the impact of a steel pendulum. To verify the recently developed coupled thermo-mechanical model for concrete, transient 3D FE simulation is carried out. The rate and temperature-dependent microplane model is used as a constitutive law for concrete. It is first shown that the simulation is able to realistically replicate the experimental test. Subsequently, the numerical parametric study is performed where the dynamic and static response of RC frame is simulated for both hot and cold states. It is shown that the pre-damage of RC frame through fire exposure significantly reduces the resistance and changes the response. Finally, it is demonstrated that for the impact load the rate sensitive constitutive law of concrete significantly contributes to the response of RC frame.

Seismic response of RC frames under far-field mainshock and near-fault aftershock sequences

Engineered structures built in seismic-prone areas are affected by aftershocks in addition to mainshocks. Although aftershocks generally are lower in magnitude than that of the mainshocks, some aftershocks may have higher intensities; thus, structures should be able to withstand the effect of strong aftershocks as well. This seismic scenario arises for far-field mainshock along with near-field aftershocks. In this study, four 2D reinforced concrete (RC) frames with different numbers of stories were designed in accordance with the current Iranian seismic design code. As a way to evaluate the seismic response of the case-study RC frames, the inter-story drift ratio (IDR) demand, the residual inter-story drift ratio (RIDR) demand, the Park-Ang damage index, and the period elongation ratio can be useful engineering demand parameters for evaluating their seismic performance under mainshock-aftershock sequences. The frame models were analyzed under a set of far-field mainshock, near-fault aftershocks seismic sequences using nonlinear dynamic time-history analysis to investigate the relationship among IDR, RIDR, Park-Ang damage index and period ratio experienced by the frames. The results indicate that the growth of IDR, RIDR, Park-Ang damage index, and period ratio in high-rise and short structures under near-fault aftershocks were significant. It is evident that engineers should consider the effects of near-fault aftershocks on damaged frames that experience far-field mainshocks as well.

Simplified macro-modelling strategies for the seismic assessment of non-ductile infilled frames: a critical appraisal

Reinforced concrete frames (RCFs) represent the most widespread structural typology in several high-seismic regions worldwide. Two categories of buildings can be distinguished: modern buildings designed following a specific seismic code and existing buildings designed only to resist to gravity loads. In both cases, the structural response of RCF may be positively or negatively conditioned by the non-structural masonry infills. Neglecting the infills in the analyses can produce an unsafe prediction of the seismic performance of a structure. In contrast, simplified modelling approaches are needed in current engineering practice, since rigorous modelling strategies, namely non-linear finite-element models, are generally incompatible with the standard hardware/software adopted by practitioners. In this paper two macro-modelling approaches, namely the equivalent diagonal strut model and a recently introduced 2D discrete macro-model, which are currently employed by engineers for predicting the seismic behaviour of infilled frames, are compared. The aim of this investigation is to highlight the influence of the modelling approach and calibration procedures on the seismic performance assessment of infilled frame structures. A recent experimental study on a 1-bay infill frame prototype and a multi-storey frame are considered as benchmark cases. The results obtained highlight the differences between the two approaches in terms of capacity curves and collapse mechanisms.

Response of low-quality solid concrete block infilled frames

The characteristics of low-quality solid concrete block infills and their influence on the response of reinforced-concrete (RC) frames under lateral loading were investigated. To this end, the constituents of the masonry infill were investigated separately under compressive load as well as in the form of assemblages in order to evaluate the compressive strength, bond strength and coefficient of friction of the prisms. The diagonal tensile strength and shear strength of the masonry walls were then evaluated using masonry wallets. To investigate the influence of the infill on the lateral response of RC frames, quasi-static tests on three full-scale single-bay frames (one bare frame and two infilled frames with centre-to-centre dimensions of 2·480 m × 2·310 m) were performed. The obtained experimental data in the form of load–deformation curves clearly indicate that, even with the presence of low-quality infill panels, both the strength and stiffness of the RC frames were greatly enhanced. In addition, the presence of infill was found to significantly alter the deflected shape and internal forces in various elements of the infilled frames in comparison with bare counterparts.

Effects of vertical irregularity and thickness of unreinforced masonry infill on the robustness of RC framed buildings

SUMMARYPresence of irregularities in reinforced concrete (RC) buildings increases seismic vulnerability. During severe seismic shaking, such buildings may suffer disproportionate damage or even collapse that can be minimized by increasing robustness. Robustness is a desirable property of structural systems that can mitigate susceptible buildings to disproportionate collapse. In this paper, the effects of vertical irregularity and thickness of unreinforced masonry infill on the robustness of a six‐story three‐bay RC frame are quantified. Nonlinear static analysis of the frame is performed, and parametric study is undertaken by considering two parameters: absence of masonry infill at different floors (i.e., vertical irregularities) and infill thickness. Robustness has been quantified in terms of stiffness, base shear, ductility, and energy dissipation capacity of the frame. It was observed that the infill thickness and vertical irregularity have significant influence on the response of RC frame. The response surface method is used to develop a predictive equation for robustness as a function of the two parameters. The predictive equation is validated further using 12 randomly selected computer simulations. Copyright © 2013 John Wiley & Sons, Ltd.

Response of RC Frame under Lateral Loads

The experimental response of a single‐story, indeterminate reinforced concrete (RC) frame with floor slabs is investigated in this paper. The frame was quarter‐scale and tested under static lateral‐load reversals simulating earthquake load. The internal force redistribution occurring within the inelastic range of response and the beam flexural overstrength resulting from slab contribution are evaluated. It is shown that the pattern of lateral‐load distribution in indeterminate structures is severely affected by the partial restraint that continuity imposes on the inelastic member expansion, particularly at large levels of lateral displacement. Specimen behavior is characterized in terms of strength, stiffness, lateral drift ratio, and plastic hinge‐formation. The mechanism by which shear is introduced to beam‐column joints of connections with floor slabs is examined. The performance of the current code recommendations for design of beam‐column joints is investigated in view of the combined effects of continuity and contribution of floor‐slabs to the flexural resistance of the beams.