Behavior of low-rise, steel fiber-reinforced concrete thin walls under shake table excitations

Significance Statement

Low-rise reinforced concrete walls have become a popular form of residential construction in several countries. Reference to the large wall-to-floor area ratio used in these systems, concrete placement and setup of typical reinforcement in these thin walls, normally 100 mm, can be time consuming as well as labor intensive, which in turn can be too costly for low income regions. In quest of more affordable solutions, some researchers have concluded that owing to large wall-to-floor area ratio as well as the high redundancy offered by this form of construction, the web reinforcement could be reduced in low seismic regions with respect to that required  if the shear strength is less than one-half the concrete contribution to shear strength.

However, past  studies have shown that steel fiber-reinforced concrete (SFRC) may be helpful in increasing the deformation capacity and shear strength of reinforced concrete members. Searching for options to applying deformed bars or welded wire reinforcement, the implementation of SFRC in walls with thin webs have been evaluated in experimental and numerical studies. Steel fibers are generally more costly. Fortunately, their ease of fabrication as well as installation costs are expected to offset higher material costs, consequently leading to net savings.

Julian Carrillo at Universidad Militar Nueva Granada in Colombia, José A. Pincheira at University of Wisconsin-Madison and, Sergio M. Alcocer at Universidad Nacional Autónoma de México presented the response of six steel fiber reinforced concrete walls exposed to shake table excitations. Each wall was made of a different type of steel fiber and fiber volume content. The researchers studied three fiber contents, 45, 60 and 75 kg/m3, and two aspect ratios of 64 and 80. Their work is published in the peer-reviewed journal, Engineering Structures.

The authors assessed experimentally the implementation of SFRC for low-rise walls in low seismicity locations. They conducted shake-table tests of both steel fiber-reinforced concrete and conventionally reinforced concrete walls under a number of ground motions to failure. The authors also studied variables such as aspect ratio. They analyzed wall performance in terms of failure modes, hysteretic response, crack patterns, and lateral resistance.

The authors also observed that the onset of inclined cracking occurred at a shear stress in the range 0.17f´c MPa-0.22f´c MPa; drift to inclined cracking was observed to vary from 0.15%-0.26%. Walls with welded wire reinforcement or deformed bars in the web exhibited a large number of cracks as well as more uniform distribution of cracks as compared to steel fiber reinforced concrete walls.

The researchers also found that the failure modes observed in steel fiber reinforced walls was controlled by diagonal tension, which encompassed fiber bond failure as well as strengthening of end hooks. This was, however, independent of fiber type and fiber volume content. For the selected type of fiber and volume contents, steel fibers were found to contribute about 50% to peak shear strength.

Steel fiber reinforced walls with 0.75% and 1% fiber volume content indicated stable hysteretic response for lateral drifts as well as larger strengths as opposed to those of walls set up with welded reinforcement or even deformed bars in the web.

Steel fiber reinforced concrete walls with 0.75% or more fiber content offered a viable alternative and exhibited better performance as compared to that of conventionally reinforced walls of low rise, residential construction.

Reference

Julian Carrillo, José A. Pincheira, and Sergio M. Alcocer. Behavior of low-rise, steel fiber-reinforced concrete thin walls under shake table excitations. Engineering Structures, volume 138 (2017), pages 146–158.

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