Performance Of Reinforced Concrete Frame Structures Research Articles

On the progressive collapse performance of RC frame structures under impact column removal

Currently, progressive collapse studies are mostly conducted based on an event-independent assumption. With studies employing an event-dependent premise mainly concerning explosion or fire events, the aftermath of impact loading is seldom reported. Meanwhile, interactions between reinforced concrete (RC) members and superstructures under impact loading need further evaluation. In this paper, finite element models of RC structures subjected to impact loading and progressive collapse are established and validated utilizing LS-DYNA. A valuing methodology of erosion parameters for the continuous surface cap model (CSCM) considering element size is proposed in this process. The influence of impact column removal (ICR) on the progressive collapse performance of RC frame structures is studied at sub-assemblage and structure levels. The parametric study indicates that the ICR process can be described by an impact loading stage and a gravity load stage. It is also found that structures experiencing ICR are exposed to a higher risk of progressive collapse, with the downward force exerted by the impacted columns being a significant contributing factor. Dynamic analyses demonstrate that the acceleration of the column removal point (CRP) can be used to validate and quantify the downward force. The hybrid force-displacement boundary conditions of frame columns give rise to the development of downward force. Recommendations for resisting progressive collapse considering ICR are proposed based on the analytical results of the paper.

Influence of mechanical properties of modified mortar on In-plane and Out-of-plane seismic performance of RC frame structure with infill walls

The reinforced concrete (RC) frame structures with infill walls are severely damaged under earthquakes. Therefore, enhancing the seismic performance of infill walls is essential to improve a building’s seismic resistance. Experimental investigations were carried out in this paper to enhance the mechanical properties of modified mortar using liquid nano-SiO2, polyethene acrylic acid (SA) emulsion, and polypropylene (PP) fibers as an additive. The results show that the flexural strength, compressive strength, tensile bond strength and shear strength of mortar along through joint were increased by 8.3%, 4.5%, 60.3%, and 60.8%, respectively, when adding 1% liquid nano-SiO2. The addition of SA emulsion improved the tensile bond strength but reduced the compressive strength and shear strength of the masonry along through joint. Adding PP fibers to mortar can improve the flexural and compressive strength but reduce masonry’s tensile bond strength and shear strength of the masonry along through joint. A finite element model of the infill wall-RC frame structure was established in ABAQUS, and the influences of modified mortar’s mechanical properties on in-plane (IP) and out-of-plane (OOP) seismic performance were analysed. The optimum percentage of liquid nano-SiO2 based on the simulation results was 1%. Compared with ordinary mortar, the initial stiffness of IP and OOP were increased by 8.45% and 13.3%, respectively, and the ultimate bearing capacity of IP and OOP were increased by 9.4% and 5%, respectively, when the containing of liquid nano-SiO2 was 1%. The IP and OOP initial stiffness and ultimate bearing capacity of the infill wall-RC frame structure with the SA emulsion mortar were lower than ordinary mortar. The IP and OOP seismic performances of the infill wall-RC frame structure with the PP fibers mortar were similar to ordinary mortar. The addition of nano-SiO2 emulsion improved the cement’s hydration performance and significantly enhanced the IP and OOP seismic performance of the infill wall-RC frame structure.

Experimental study on a novel method to improve progressive collapse resistance of RC frames using locally debonded rebars

The alternate path (AP) method is widely used to evaluate the capability of reinforced concrete (RC) frame structures to resist progressive collapse. Previous studies have found that the double-span beam, caused by an internal column removal, fails to sufficiently develop catenary action due to strain concentration and premature fractures of longitudinal reinforcements near beam ends. To enhance catenary action, a novel method is proposed in this study by embedding locally debonded rebars at the half-height of beams near beam ends. For verification, five RC beam-column substructures were quasi-statically loaded representing an internal column removal scenario. Two test parameters were considered, i.e., the amount of additional rebars and whether they were debonded from the surrounding concrete. Test results found that the vertical resistance of the RC substructures using the proposed method increased by 66%–159% compared to that of conventionally designed substructure. The resistance of RC substructures using locally debonded rebars increased by 13%–21% compared to the substructures using an identical amount of bonded rebars. The reason for this resistance improvement is that the locally debonded rebars can improve both the ultimate rotation capacities of beam ends and axial tension forces in beams, resulting in sufficiently developing catenary action. In addition, the resistance contribution at the catenary action stage was identified and the lesser impact on the seismic performance of RC frame structures was discussed when using the proposed rebars. Finally, an analytical model was proposed to predict the ultimate rotation of beam ends and the ultimate resistance of RC substructures with locally debonded and bonded rebars.

Design parameters and material‐scale damage evolution of seismic upgraded RC frames by viscoelastic haunch bracing‐dampers

AbstractTo improve the seismic design of reinforced concrete (RC) frame structures and upgrade existing RC frame structures that have insufficient seismic design, a new suitable seismic upgraded solution, the installation of viscoelastic haunch bracing‐dampers (VHBD) to increase the seismic performance of RC frames, is proposed in this paper. For a comprehensive and systematical research about this new upgraded frames system, a comparative study on the seismic performance between 15 RC frame structure specimens by adding the VHBD with different design parameters and one common RC frame structure specimen is performed under sinusoidal dynamic loading. The specific items of seismic performance mainly include hysteresis performance, load‐bearing capacity, stiffness degradation, energy dissipation capacity, and additional damping ratio, and so on. First, on the basic of this, the material‐scale damage evolution of structure specimens at each stage is qualitatively analyzed. Then, six reasonable material‐scale damage indexes that can describe the damage evolution of the structures precisely are proposed. Finally, a quantitative comparative analysis on the material‐scale damage evolution of structure specimens in the whole process is carried out under different design parameters. The research results indicate that the upgraded scheme (reasonable design parameters of and ) proposed in this study can improve the seismic performance of RC frame structures to the appropriate level required for the design, in terms of load‐bearing capacity, stiffness, energy dissipation capacity, and damping ratio. At the same time, the failure mode of the structures can be well controlled. The occurred damage at beam‐column joints is reasonably transferred to the beam area, which can guarantee the seismic design requirements of “strong joints and weak components.”

Experimental and modeling study on the progressive collapse resistance of a reinforced concrete frame structure under a middle column removal scenario

SummaryA reinforced concrete (RC) frame structure is one of the widely used structural system. A localized damage caused by extreme events may lead to progressive collapse of entire structures. In this paper, progressive collapse test of three 1/3‐scaled reinforced concrete frame, including a single‐story without a slab, single‐story with a slab, and double‐story with slabs, are reported. Experimental results show that the progressive collapse process of RC frame consisted of five stages: an elastic stage, yield stage, beam mechanism stage, transient stage and catenary stage. The reinforced concrete slabs contribute to large progressive collapse resistance force compared with the specimen without slab. Furthermore, validation of the test results by using a refined solid finite element model was established. The effect of extensive parameters, including slab thickness, beam section height, seismic design intensity, and so forth, on the progressive collapse performance of RC frame structures was simulated as well. The simulation results indicated that the collapse resistance of RC structures was substantially improved with the increased of the slab thickness and seismic design intensity. Finally, a simplified model is proposed in accordance with experimental and numerical results to calculate the collapse resistance of RC frame structures.

Research on Improved Equivalent Diagonal Strut Model for Masonry-Infilled RC Frame with Flexible Connection

The reinforced concrete (RC) frame with masonry infill wall is one of the most common structural systems in many countries. It has been widely recognized that the infill wall has significant effects on the seismic performance of RC frame structure. During the Wenchuan earthquake (China 2008), a lot of infilled RC frame structures suffered serious damages due to the detrimental effects brought about by the infill wall rigidly connected to the surrounding frame. In order to solve this problem, flexible connection, introduced by Chinese designers, is recommended by the updated Chinese seismic design code, because of its effect to reduce the unfavorable interaction between infill wall and frame. Although infilled RC frame structure with flexible connection has a lot of advantages, but because of the lack of research, this structure type is seldom used in practical engineering. Therefore, it is of great significance to scientifically investigate and analyze the effects of flexible connection on structure behaviors of infilled RC frame. In this study, a macrofinite element numerical simulation method for infilled RC frame with flexible connection was investigated. Firstly, the effects of connection between infill wall and surrounding frame on in-plane behaviors of infilled RC frame were discussed. Secondly, based on deeply studying the equivalent diagonal strut models for infilled RC frame with rigid connection, an improved equivalent diagonal strut model for infilled RC frame with flexible connection was proposed. Employed with inversion analysis theory, the parameter in the proposed model was estimated through artificial fish swarm algorithm. Finally, applied with the existing experiment results, a case study was conducted to verify the effectiveness and feasibility of the proposed model.

Performance of RC frame structure with various beam to column flexural capacity ratio – a case study

The effectiveness of various Strong Column Weak Beam (SCWB) factors to enhance seismic performance is assessed for Reinforced Concrete (RC) frame building structures. In this study five RC frame buildings of different storey numbers have been analysed using different column overdesign factors. The results are compared as the influence of various SCWB factor over the expected performance of selected RC frame buildings in terms of enhancement in capacity and failure mechanism. With the lower value of SCWB factor insignificant change in capacity curve is observed while gradual improvement is observed with the higher factors. In terms of failure mechanism gradual change from column failure mechanism to beam failure is observed but the hinge formation at the base of bottom storey column is seen even with the higher value of SCWB factor. The effectiveness of alternative method of column flexural capacity enhancement by proposed modified SCWB (MSCWB) was also studied. MSCWB is found to be more effective in terms of enhancement in capacity curve and failure mechanism.

Evaluation of Strong Column Factors for RC Frames Based on Seismic Vulnerability Analysis

Augmenting the flexural strength of columns in the seismic design of reinforced concrete (RC) moment resisting frames is a key measure among all the detailing procedures of seismic capacity design, which induces the desirable beam side-sway mechanism for the structure to dissipate energy during a strong earthquake. The objective of this paper is to assess the influence of various strong column factors which is employed to perform seismic vulnerability analysis to the seismic performance of a six-story deterministic RC frame structure. Seismic vulnerability analyses indicate that augmenting the flexural strength of columns is an effective measure to improve seismic performance of RC frame structures. Increasing strong column factor improves the displacement capacity of structure and induces the biggish grads between the different damage limit states, which provide caution to prevent the abrupt collapse of structure during a strong earthquake. Seismic vulnerability curves provide the quantitative criterion for evaluating the seismic performance of structure and choosing appropriate target strong column factor.

Probabilistic Evaluation of Effects of Column Moment Magnification Factor on Seismic Performance of Reinforced Concrete Frames

Enhancing column flexural capacity is the key measure in seismic capacity design to achieve strong column-weak beam failure mode and determinate the probabilistic relation between column moment magnification factor (CMMF). In the paper the effects of column moment magnification factor on seismic performance of reinforced concrete (RC) frames are evaluated to limit the occurrence probability of column-hinging failure modes within an acceptable tolerance. Monte Carlo simulation methodology is used to calculate the probability of drift demand exceeding drift capacity of two typical frame structures with consideration of major uncertainties. And fragility curves are constructed to obtain the relationship between CMMF and probability of structural damages and assess the seismic vulnerability of RC frame structures. Results show that the seismic performance of RC frame structures can be significantly enhanced by improving CMMF. The CMMF is required to be equal to or greater than 2.0 to achieve acceptable probability of exceedance of column-hinging failure mode.