Recycled Aggregate Concrete Frame Research Articles

Seismic damage and evaluation analysis of joints in enhanced-performance recycled aggregate concrete frame

Through the low cycle loading test of three full-scale enhanced- performance recycled aggregate concrete frame joints, the damage evolution and accumulation are analyzed according to the traditional ductile damage model (single parameter) and the improved Park-Ang damage model (double parameters): when the characteristic displacement of each specimen equals 20 mm, the specimen has been damaged, but the calculated results are negative according to ductile damage model; when the characteristic displacement exceeds 100 mm, the calculated results of the improved Park-Ang damage model show that all the specimens have been completely destroyed and cannot continue to bear load, but the actual results of the specimens still show certain bearing capacity and energy dissipation capacity. Therefore, it is necessary to modify the aforementioned damage model to make it suitable for enhanced-performance recycled aggregate concrete structures. Based on the foregoing test results, the fiber coefficient a, displacement coefficient α, and correction coefficient of energy coefficient k were proposed and fitted for the improved Park-Ang damage model. In addition, a corresponding modified Park-Ang damage model was established. Finally, using the proposed damage model, the error analysis of damage index was carried out with the example of HF-RAC2. The results show that the average error is within 6%, so the proposed two-parameter damage model can be applied to the analysis of seismic damage assessment of EC-RAC frame joints.

Rate sensitivity analysis of structural behaviors of recycled aggregate concrete frame

Based on the dynamic constitutive model of recycled aggregate concrete (RAC), the structural restoring force behaviors affected by the strain rate and replacement ratio (R) of recycled coarse aggregate (RCA) were simulated and analyzed, and the rate-dependent damage model of the RAC frame structures was proposed and experimentally verified by shake table tests. Based on the quantitative comparisons and analysis of characteristic parameters, the calculation models of characteristic parameters for restoring force coupling strain rate and replacement ratio (R) of RCA was proposed, and the strain rate influence factor models of cracking load and deformation, yielding load and deformation, peak load and deformation, and ultimate load and deformation, were given respectively considering different replacement ratios of RCA. The research work of this paper provides an experimental and theoretical basis for solving the rate sensitivity of the structural behaviors of RAC frame structures.

Nonlinear damping and nonlinear responses of recycled aggregate concrete frames under earthquake loading

The recorded data of a shaking table test on a recycled aggregate concrete (RAC) frame model conducted by the authors is used to analyze the nonlinear behaviors of the RAC structure under earthquake loadings and white noise excitations. Firstly, the nonlinear damping behavior of the RAC model with damage accumulation is studied. A damping model that combines a viscous damping and a quadratic damping mechanism is extended to consider ambient vibrations and to describe the nonlinearity of the damping properties as well as to detect the damage of the RAC frame model under white noise excitations. The quadratic damping factor δ introduced is a reliable damage indicator with a promising damage-sensitive feature in the health monitoring for RAC structures. The percentage of the energy dissipated by the quadratic damping mechanism to total energy dissipation increases from 5.7% to 98.4% with damage accumulation, indicating that the energy dissipation mechanism changes from a viscous damping mechanism to a nonlinear damping mechanism. Secondly, a data-driven parameter identification method based on Hilbert-Huang transform (HHT) is proposed and conducted to analyze the nonlinear behaviors of the RAC model under strong ground excitations from the point view of the distribution of nonlinear story forces, natural frequency, and damping ratio. The equivalent damping ratio of the RAC frame increases up to 45.06% with the damage accumulation and demonstrating a significant percentage of the nonlinear energy dissipation. Finally, a quantitative damage classification method for RAC frames is proposed by using the quadratic damping factor δ as a damage indicator.

A comparative study on nonlinear damping behaviors of precast and cast-in-situ recycled aggregate concrete frames

It has been well accepted that applying recycled aggregate concrete (RAC) into structural engineering is a sustainable method to solve the problem of construction and building waste (CDW) accumulation meanwhile to save natural resources exploitation. Precast RAC members in factories is beneficial to improve their qualities and will extend the RAC application. This study presents nonlinear damping behaviors of precast and cast-in-situ RAC frames after simulated earthquakes, as a reference of quality control of precast RAC members, and of damage detection under ambient vibration. The nonlinear damping of precast RAC slabs with different damage degrees was studied to validate the feasibility of applying the quadratic damping coefficient as a sensitive damage factor without any requirement of undamaged baseline. Meanwhile a comparative study on nonlinear damping behaviors of a precast and a cast-in-situ RAC frames was conducted. Results highlight a change of nonlinear damping mechanism for both precast and cast-in-situ RAC frames from a viscous damping into a nonlinear damping. The precast RAC frame had a comparatively larger quadratic damping coefficient before and after earthquake hitting, indicating it had more severe initial damage and damage developed more significantly compared with the cast-in-situ frame. A unified damage classification was proposed for both precast and cast-in-situ RAC frames based on quadratic damping coefficient and observation.

Seismic Testing and Numerical Analysis of Beam-Column Knee Joints in Recycled-Aggregate Concrete Frames

Seismic Testing and Numerical Analysis of Beam-Column Knee Joints in Recycled-Aggregate Concrete Frames

Seismic Performance of Interior and Exterior Beam–Column Joints in Recycled Aggregate Concrete Frames

AbstractThe failure of beam–column joints in RC frame buildings induced by a strong earthquake can lead to the collapse of buildings. Therefore, numerous experimental studies have been carried out ...

Micro-concrete composites for strengthening of RC framemade of recycled aggregate concrete

In this paper, to access the suitability of recycled aggregate for structural applications, concrete strength i.e., compressive, tensile and flexural strength were evaluated and compared with those specimens made of natural aggregates. Test results indicated that 30 to 42% of the mentioned strength decreases. To study the performance of frame structures made of recycled aggregate concrete (RAC) two reinforced RAC frames were prepared and tested under monotonic loading. The joint regions of one of the RAC frame were casted with micro-concrete. A reference specimen was also prepared using natural aggregate concrete (NAC) and subjected to a similar loading condition. The RAC frame resulted in a brittle mode of failure as compared to NAC frame. However, the presence of a micro-concrete at the joint region of an RAC frame improved the damage tolerance and load resisting capacity. Seismic parameter such as energy dissipation, ductility and stiffness also improves. Conclusively, strengthening of joint region using micro-concrete is found to have a significant contribution in improving the seismic performance of an RAC frame.

Compressive stress-strain relation of recycled aggregate concrete under cyclic loading

This paper has focused on the structural performance of recycled aggregate concrete (RAC) under both cyclic and monotonic loading. RAC specimens with different recycled coarse aggregate (RCA) replacement percentages of 0%, 25%, 50%, 75% and 100% were cast and tested. The compressive stress-strain relationship and the failure mode were investigated for each RCA replacement ratio. The effects of the RCA replacement percentage on the compressive mechanical properties of the RAC specimens including the strength, elastic modulus, peak strain, ultimate strain and Poisson's ratio were also studied. The RAC specimens have shown similar failure characteristics regardless of monotonic or cyclic loading. In addition, the compression skeleton curves of the RAC specimens under cyclic loading agree well with those under monotonic loading. Based on the experimental results, the characteristic points pertaining to the hysteresis loop were defined and their relations were established. Furthermore, the constitutive equations of the RAC as well as its simplified form were proposed and applied in numerical simulations of RAC columns and frames under cyclic loading. The proposed constitutive equations have shown promising accuracy in predicting the hysteresis performance of RAC on both component and structural levels.

Investigation on the Seismic Damage of Recycled Aggregate Concrete Frame Structure

The current research trends focus on the popularization and application of recycled aggregate concrete (RAC) structures in civil engineering. So far, the damage evolution mechanism of RAC structures has been investigated and reviewed by few engineering researchers and practitioners. In this study, a classification criterion for earthquake damage for the RAC frame structure is put forward. The damage index-based limit state criterion is proposed, and the corresponding seismic performance level is established. The refined models based on the stiffness degradation and the cumulative dissipated energy, and the modified Park and Ang model are developed and compared with the experimental results.

Experimental study on frame structures with recycled aggregate concrete under lateral cyclic loads

This paper presents an experimental study on the seismic behavior of frame structures made with recycled aggregate concrete (RAC). Three 1:2 scaled frame specimens were tested under lateral cyclic loads and constant vertical load. One of these frames was conventional concrete frame, while the remaining two frames were RAC frames with a recycled coarse aggregate (RCA) replacement percentage of 25 and 50%, respectively. The structural performances, in terms of the failure pattern and mechanism, ultimate lateral load capacity, hysteretic response, backbone curve, ductility capacity, energy dissipation capacity and stiffness degradation were analyzed in detail. The effect of RCA replacement percentage on the seismic performance of RAC frames was investigated carefully. The experimental results indicate that the seismic performance of RAC frame is similar to that of conventional concrete frame and not significantly affected by the incorporation of RCA. All of the tested frames behaved with the same failure pattern, which is a ductile failure mechanism. The average value of the ductility coefficient and the equivalent viscous damping ratio of the RAC frame are 3.55 and 0.089, respectively. The RAC frame structure with an RCA replacement percentage of 50% still has adequate capabilities of ultimate strength, deformation and energy dissipation and is able to withstand an earthquake attack.

Analysis and Evaluation of the Stochastic Damage for Recycled Aggregate Concrete Frames Under Seismic Action

In this paper, the seismic response of recycled aggregate concrete (RAC) frames was investigated through the bidirectional shaking table test for a three-storey RAC frame model with 1:4 reduced scale. According to test results, the variation regularity of the structural frequency, damping, and the inter-storey displacement angle was analyzed, which illustrated a good seismic behavior of this RAC framework. Furthermore, a damage model of the corresponding RAC integral structure was proposed with a comprehensive consideration of the different frequencies in X and Y directions, damping ratio, stiffness, vibration mode of the structure, variety of structure forms, and test methods for natural frequency. Based on the damage model for the RAC structure, the damage grade was analyzed. Meanwhile, combined with the classification of earthquake damage to buildings and special structures, code for seismic design of buildings (GB50011-2010), and other literature, a standard with five damage grades of the RAC structure was established. At last, to apply for practical engineering, a quick computational formula for RAC structure damage index was fitted. The results obtained from the previous studies indicate that the damage model is basically consistent with the experimental results and is capable of applying into seismic damage quantitative evaluations and analyses for actual RAC structures.

Seismic Analysis on Recycled Aggregate Concrete Frame Considering Strain Rate Effect

The nonlinear behaviors of recycled aggregate concrete (RAC) frame structure are investigated by numerical simulation method with 3-D finite fiber elements. The dynamic characteristics and the seismic performance of the RAC frame structure are analyzed and validated with the shaking table test results. Specifically, the natural frequency and the typical responses (e.g., storey deformation, capacity curve, etc.) from Model 1 (exclusion of strain rate effect) and Model 2 (inclusion of strain rate effect) are analyzed and compared. It is revealed that Model 2 is more likely to provide a better match between the numerical simulation and the shaking table test as key attributes of seismic behaviors of the frame structure are captured by this model. For the purpose to examine how seismic behaviors of the RAC frame structure vary under different strain rates in a real seismic situation, a numerical simulation is performed by varying the strain rate. The storey displacement response and the base shear for the RAC frame structure under different strain rates are investigated and analyzed. It is implied that the structural behavior of the RAC frame structure is significantly influenced by the strain rate effect. On one hand, the storey displacements vary slightly in the trend of decreasing with the increasing strain rate. On the other hand, the base shear of the RAC frame structure under dynamic loading conditions increases with gradually increasing amplitude of the strain rate.

Simulation study on dynamic response of precast frames made of recycled aggregate concrete

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of Recycled Coarse Aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. As a result, the comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

Polygonal loop model for hysteretic behaviour of frame structures with recycled aggregate concrete

On the basis of shaking table tests on the recycled aggregate concrete (RAC) precast frame structure subjected to excitations of Wenchuan wave (WCW, 2008, N-S), El Centro wave (ELW, 1940, N-S) and Shanghai artificial wave (SHW), this study employed a new polygonal loop model (PLM) with its two core characteristics, that is, stiffness and strength degradation to describe the hysteretic behaviour of RAC frames. The implementation of the PLM model underwent different stages such as backbone curve, pivot points and unloading/reloading rules. The validation by shaking table tests on the precast RAC frame and application of the PLM to one cast-in-place RAC frame structure revealed that the hysteresis loops generated by the proposed PLM model not only traced the hysteretic trend but also fitted well with the tested hysteretic curves. Given these findings, it may be concluded that the new PLM model can be used to predict the seismic behaviour of RAC frame structures.

Shake Table Test on Seismic Response of a Precast Frame with Recycled Aggregate Concrete

A precast frame model made of Recycled Aggregate Concrete (RAC) was constructed with precast beams, columns and Cast-In-Place (CIP) joints. Then a shaking table test was carried out with three types of earthquake ground motions, namely Wenchuan, El Centro and artificial Shanghai waves. Based on the shaking test, structural responses such as dynamic characteristics, cracking and failure pattern, seismic responses as well as the overall seismic performance of the model were analyzed and evaluated. The results indicate that the precast RAC frame structure has an adequate load bearing potential as well as ductility against moderate and severe seismic excitations. Therefore, the perfect combination of RAC and precast structures is feasible to apply and popularize precast RAC frame structures with mid-rise buildings in the seismic regions.

Seismic Behavior of Cast-in-Place and Precast Recycled Aggregate Concrete Frames: A Comparative Study

Shaking table tests were carried out on two recycled aggregate concrete (RAC) frames, one of which was cast-in-place (CIP) and the other was precast. The dimensions and reinforcements of the two structures were designed similarly for the purpose of comparing seismic performance. The comparative analysis of the structural behavior indicated that both the models performed favorably with respect to their capacity for seismic resistance and presented similar dynamic response tendencies in the elastic and early nonlinear stage. In the later elastoplastic stage, for the precast RAC frame, the deformation was relatively larger, the overall seismic capacity was lower and the stiffness degradation was faster compared to the CIP frame. A further analysis of the frame joints of the two frames was undertaken and it demonstrated that serious damage to the post-cast joints in the precast frame was the main reason for the inferior structural seismic behavior during earthquakes of high-level intensity.

Restoring Force Model of a Cast-In-Situ Recycled Aggregate Concrete Frame

The hysteresis behavior of a cast-in-situ recycled aggregate concrete (RAC) frame was analyzed based on shaking table tests on a one-fourth scaled model of a two-bay, two-span and 6-storey RAC frame. Then feature points and the stiffness degradation were defined and the deteriorating four-line-typed restoring force model was put forward. In the hysteresis model, the monotonic behavior is described by a four-line-typed skeleton curve which accounts for concrete cracking, yielding of reinforcing bars, maximum and ultimate point of the RAC frame model. The hysteresis behavior is described through a number of rules for unloading and reloading. Therefore, the restoring force model proposed in this study can capture the hysteresis response of the frame under seismic actions. Moreover, the displacement ductility of the RAC frame structure is evaluated based on the proposed restoring force model. It can be concluded from this investigation that the RAC frame structure with proper design and construction has favorable load-carrying capacity, deformation capacity, energy dissipation ability and seismic performance, and can be applied and popularized in the area with the requirement of aseismic fortification intensity.

Nonlinear analysis and test validation on seismic performance of a recycled aggregate concrete space frame

SUMMARYThree‐dimensional recycled aggregate concrete (RAC) nonlinear finite element models are developed by OpenSees software to investigate the seismic responses of a 1/4‐scaled six‐story, two‐bay and two‐span RAC space frame, which has been tested on a shaking table subjected to various earthquake scenarios. The simulated natural frequencies and vibration modal shapes, the acceleration amplification factors, the maximum story displacements and the inter‐story drifts are carefully validated by and compared with the test data with overall good agreement. The simulated seismic responses of the RAC frame and the natural aggregate concrete (NAC) frame are also compared. The aseismic capacity of the NAC frame structure is better than that of the RAC frame structure in the early stage, and they behave almost the same in the severe stage under strong earthquake excitations. Both tested and simulated results indicate that not only the peak ground acceleration and duration and frequency of ground motion but also concrete material properties play a prominent role in the overall seismic performances of frame structures. Copyright © 2014 John Wiley & Sons, Ltd.

Study of the seismic response of a recycled aggregate concrete frame structure

Based on six-degree-of-freedom three-dimensional shaking table tests, the seismic response of a recycled aggregate concrete (RAC) frame was obtained. The analysis results indicate that the maximum story shear force and overturning moment reduce proportionally along the height of the model under the same earthquake wave. The story shear force, base shear coefficient and overturning moment of the structure increase progressively as the acceleration amplitude increases. The base shear coefficient is primarily controlled by the peak ground acceleration (PGA). The relationships between the PGA and the shear coefficient as well as between the PGA and the dynamic amplification factor are obtained by mathematical fitting. The dynamic amplification factor decreases rapidly at the elastic-plastic stage, but decreases slowly with the development of the elastic-plasticity stage. The results show that the RAC frame structure has reasonable deformability when compared with natural aggregate concrete frame structures. The maximum inter-story drift ratios of the RAC frame model under frequent and rare intensity 8 test phases are 1/266 and 1/29, respectively, which are larger than the allowable value of 1/500 and 1/50 according to Chinese seismic design requirements. Nevertheless, the RAC frame structure does not collapse under base excitations with PGAs from 0.066 g up to 1.170 g.

Investigation on Seismic Behavior of Recycled Aggregate Concrete Structures under Dynamic Loadings

Based on the ever finished investigations of physical and mechanical properties of recycled aggregate concrete (RAC), and a series of experimental studies on the durability, the fatigue behavior, mechanical behavior and the seismic behavior of RAC components. A full scale model of a one-storey block masonry structure with tie column + ring beam + cast-in-place slab system and a one fourth scaled model of a 6-storey frame structure, which are made of reinforced recycled aggregate concrete, are tested on a shaking table by subjecting it to a series of simulated seismic ground motions, and the seismic behaviors of the RAC structures were experimentally investigated. The dynamic characteristics and the seismic response were analyzed and discussed. The overall seismic performance of RCA structures are evaluated, the analysis results show that the recycled aggregate concrete structures with proper design exhibits good seismic behavior and can resist the earthquake attacks under different earthquake levels in this study. It is feasible to apply and popularize the RAC block masonry buildings less than 2 stories and the RAC frame buildings less than 6 stories in the region where the seismic fortification intensity is 8.