Bond of Ribbed Steel Bar in High-Performance Steel Fiber Reinforced Expanded-Shale Lightweight Concrete

Mingshuang Zhao,Shunbo Zhao,Lingli Liu,Yanyan Zhang,Guirong Liu,Kang Shi

doi:10.3390/buildings11120582

Mingshuang Zhao, Shunbo Zhao + Show 4 more

Open Access

https://doi.org/10.3390/buildings11120582

Copy DOI

Abstract

For the structural application of high-performance Steel Fiber Reinforced Expanded-shale Lightweight Concrete (SFRELC), a reliable bond of ribbed steel bar should be ensured. In this paper, an experimental study was carried out on the bond properties of ribbed steel bar embedded in SFRELC by the direct pull-out test. The SFRELC was produced with a strength grade of 35 MPa and a volume fraction of steel fiber as 0%, 0.8%, 1.2%, 1.6% and 2.0%, respectively. Fifteen groups of specimens were made with a central placed steel bar with diameter of 14 mm, 20 mm and 28 mm, respectively. Complete bond stress-slip curves were determined for each group of specimens, and the characteristic values of bond-stress and slip at key points of the curves were ascertained. Results show that the bond strength, peak-slip and residual bond strength increased with the increase of the volume fraction of steel fiber. With the increase of steel bar diameter, bond strength decreased while the peak-slip increased, and the descending curves became sharp with a decreased residual bond strength. Formulas for calculating the bond strength and peak-slip were proposed. The relationships were determined for the splitting bond strength, residual bond strength with the bond strength, the splitting bond slip and residual bond slip with the peak-slip. Combined with rational fitting analyses of bond strength and slip, a constitutive model was selected for predicting the bond stress-slip of ribbed steel bar in SFRELC.

Highlights

Bond performance of ribbed steel bar embedded in concrete is a foundation ensuring the joint work of these two kinds of materials
Zhang et al [2] reported that the bond strength and the peak-slip respectively increased by 58.4% and 78.2% when the lightweight aggregate concrete (LAC) strength increased from 21.2 MPa to 42.3 MPa; the bond strength increased by 9.2% and the peak-slip decreased by 19.3% when the diameter of steel bar varied from mm to 25 mm; and the bond strength and the peak-slip respectively increased by 28.2% and 61.7% when the thickness of LAC cover increased from 32 mm to 67 mm
Lachemi et al [3] reported that the bond strength increased by 65.7% and 9.2% for steel bar in LAC with strength grade of 30 MPa and 40 MPa when the thickness of LAC cover increased from 20 mm to 42 mm, while the bond strength decreased by 16–58% when the bond length increased from 60 mm to 320 mm, and decreased by 54–68% when the diameter of steel bar increased from 8 mm to 28 mm

Summary

Introduction

Bond performance of ribbed steel bar embedded in concrete is a foundation ensuring the joint work of these two kinds of materials. In case of pull-out failure of test specimens, the bond strength presented a better relationship to the tensile strength than the compressive strength of LAC [4,5,6,7], and the peak-slip corresponding to the bond strength increased with the diameter of steel bar and mainly influenced by the ratio c/d of concrete cover to diameter of steel bar [2,8,9]. As the specimens remained intact or even did not crack, the steel bar was pulled out of the LAC with the increasing content of steel fibers, and a complete bond stress-slip curve was obtained [7,20].

Pull-Out Test Method

Test Results and Analysis

Failure Mode

12. Bond stress-slip curve of Model The shape coefficient αw can be