Title: Experimental Investigation of Hybrid Concrete Elements with Varying Fiber Reinforcement under Concentrated Load

Author(s): Plückelmann, S.; Breitenbücher, R.

Publication: Symposium Paper

Volume: 343

Issue:

Appears on pages(s): 422-431

Keywords: Steel fiber reinforcement, hybrid reinforcement, splitting stresses, bearing behavior

DOI:

Date: 10/1/2020

Abstract:
In special cases, concrete members are exposed to high locally concentrated loadings. Such concentrated loadings lead to a multi-dimensional stress state beneath the loaded area. Due to the load diffusion, large splitting tensile stresses are generated in the upper regions of the concrete member (i.e. St. Venant disturbance zone) and spread along directions perpendicular to the load. In order to resist these splitting tensile stresses, the state of the art is to reinforce concrete members with transverse steel reinforcement. An alternative approach is to add steel fibers to the concrete matrix. However, regarding economic concerns it may not appropriate to reinforce the entire concrete member with an adequate high amount of steel fibers, rather only those zones where high splitting stresses are expected. The main objective of the presented experimental study was to investigate the load-bearing and fracture behavior of hybrid concrete elements with splitting fiber reinforcement under concentrated load. For this purpose, in a first step, hybrid specimens were produced containing both plain and fiber concretes. The reference specimens consisted exclusively of plain concrete, while the hybrid specimens were partially strengthened with various types of steel fibers only in the St. Venant disturbance zone, instead of a full range fiber reinforcement. The thickness of the reinforcement layer was varied in order to determine the optimal configuration of fiber reinforcement. Taking into account the influence of the casting direction on the fiber orientation and consequently on the bearing and fracture behavior, the hybrid specimens were cast either in standing or in lying molds by means of a “wet-on-wet” casting technique. These hybrid elements were then tested under concentrated load. The test results showed that under concentric loads the maximum bearing capacity of the hybrid specimens increased progressively with growing thickness of the fiber reinforced concrete layer. In contrast to the plain concrete specimens, the fiber reinforcement led to a remarkable improvement in the post-cracking ductility. Compared to the fully reinforced specimens, the hybrid specimens that were only reinforced in the St. Venant disturbance zone exhibited - besides an almost identical bearing capacity - a similar local behavior in the postcracking zone. Furthermore, a significant impact of the casting direction on the bearing as well as fracture behavior could be proved.