Seismic performance of frame structures with recycled aggregate concrete

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Abstract

This paper deals with an experimental study on the seismic performance of frame structures with recycled aggregate concrete (RAC). Based on the seismic tests of four 1:2-scaled frame specimens under low-frequency cyclic lateral load with constant vertical actions, the failure pattern, the hysteresis curves, the skeleton curves, the energy dissipation capacity, and the stiffness degradation laws of frame structures with recycled coarse aggregate (RCA) are investigated. The effects of different RCA replacement percentages (i.e., 0, 30%, 50% and 100%) on the seismic performance of the reinforced recycled aggregate concrete frames are emphasized and analyzed in detail. It is concluded that the general seismic behaviour of a frame structure with recycled aggregate concrete declines with an increase of the RCA replacement percentage. Nevertheless, a frame structure with a higher content of RCA still behaves well enough to resist an earthquake attack.

Introduction

Recycling of waste concrete is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. For the effective utilization of waste concrete, it is necessary to use waste concrete as recycled aggregates for new concrete. To make this technology feasible, a significant amount of experimental works have been carried out worldwide. Previous investigations were mainly engaged in the processing of demolished concrete, the mixture design, and the physical and mechanical properties as well as the durability improvements. Most of the achievements have been extensively reviewed and summarized by Nixon [1], Hansen [2], [3] and the ACI 555 Report [4]. It is shown that some mechanical properties of recycled aggregate concrete (RAC) may be generally lower than those of normal concrete (NC), but they are still sufficient for some practical applications in civil engineering.

With regard to popularizing recycled aggregate concrete, the structural behaviour of recycled concrete ought to be investigated. In fact some studies concerning the performance of beams [5], [6], [7], [8], [9], slabs [10], columns [11], [12], and beam–column joints [13], [14] made from recycled aggregate concrete are reported in the literature. Except for too much effective stress loss of prestressed tensions in prestressed concrete beams, the major research conclusions by most previous investigators are positive; that is, the cracking patterns and failure modes of reinforced recycled concrete (RRC) elements are similar to those of the ordinary reinforced concrete (RC) elements, but the load capacity of RRC elements is somewhat reduced, however to an allowable extent. It has been reported that an office building using concrete made from recycled demolition material was built in Darmstadt, Germany in 1998 [15]. However, to the best knowledge of the authors, there are few investigations engaged in research on the seismic behaviour of frame structures with recycled aggregate concrete.

In this study, experiments were designed to provide a comprehensive understanding of the structural behaviour of recycled aggregate concrete, particularly focused on the seismic performance of frames under a low-frequency cyclic lateral load with constant vertical actions. The influences of the RCA replacement percentage on the failure pattern, the hysteresis curves, the skeleton curves, the energy dissipation capacity, and the stiffness degradation laws of frame structures with recycled aggregate concrete were examined. The results presented in this paper should be useful to efficiently apply RAC in practical projects.

Section snippets

Materials

Ordinary Portland cement (OPC) with a 28 d nominal compressive strength class of 32.5 MPa was used in this investigation. The fine aggregate used was river sand (S). The applied coarse aggregates were natural coarse aggregate (NCA) and recycled coarse aggregate (RCA) (5–15 mm accounting for 60%, and 15–31.5 mm accounting for 40% in weight) obtained from the waste concrete brought from the runway of an airport in Shanghai, PR China. The physical properties of the natural coarse aggregates and

General observations and failure patterns

After the application of all vertical loads both on the column and the beam, no obvious changes were observed in the frame specimens. In the stage of load control, when the lateral load reached ±20 kN, cracks were found in the end and mid-span of the beams in FRAC-0, FRAC-30 and FRAC-50 while for FRAC-100 only hair-like cracks appeared in the beam end. Therefore, it could be concluded that all frames behave linearly. With the increase of the lateral load up to 40 kN, more and more cracks

Hysteresis curves

Fig. 5 shows the hysteresis curves, which trace the development of lateral displacement on the top of all frames under the cyclic loading. Clearly, the four hysteresis curves show no obvious difference and have a fine shape from the seismic behaviour point of view. When the lateral load is less than 30% of the maximum load, i.e., at the stage of no cracking or just before cracking, these curves are approximately straight lines. Within each cycle, the decrease of the secant stiffness caused by

Conclusions

This paper discusses the experimental results of the seismic response of reinforced concrete frames with recycled aggregate concrete. The results show that

  • (1)

    All the investigated frames behave similarly in the aspects of the failure pattern under low-frequency lateral loading regardless of the recycled coarse aggregate replacement percentage. That is, the frames failed at the end of beams then at the bottom of columns, which is characterized in a manner of “strongest joints, stronger columns and

Acknowledgements

The authors wish to express their sincere appreciation to Shanghai Science and Technique Committee in China for funding this research project (No. 04DZ05044). Special thanks are also extended to the Alexander von Humboldt Foundation in Germany, who sponsored Jianzhuang Xiao’s research at TU Braunschweig for more than one year.

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