Title:
Acceptable Elongations and Low-Cycle Fatigue Performance for High-Strength Reinforcing Bars
Author(s):
Drit Sokoli;Graham Hogsett; Albert A. Limantono;Ariel Suselo;Dhiaa Al-Tarafany;Wassim M. Ghannoum
Publication:
CRC
Volume:
Issue:
Appears on pages(s):
Keywords:
high-strength, reinforcing, low-cycle, constructability, concrete, fatigue,
DOI:
Date:
8/26/2019
Abstract:
High-strength reinforcing bars (HSRB) with varying mechanical properties and
performance under low-cycle fatigue are being introduced to the U.S. market driven by
constructability and economic incentives. The project described in this report is part of a
larger national effort aimed at quantifying changes in the seismic collapse risk of concrete
structures associated with switching from conventional grade 60 reinforcing bars to HSRB.
Correlations between seismic collapse risk and bar properties are crucial for code bodies
to set acceptable properties for HSRB, especially fracture elongations and low-cycle
fatigue performance. However, in order to objectively and reliably evaluate the seismic
collapse risk of concrete buildings, the effects of the varying mechanical properties of
HSRB on the deformation capacity of seismically detailed concrete members must be
quantified. The objective of this project in particular is to provide the necessary
experimental data and behavioral models to identify when longitudinal bars in seismically
detailed frame members reach fracture during seismic events across all types of bars and
grades in production or under development in the U.S. Three tasks were undertaken to
achieve project objectives: 1) a low-cycle fatigue-capacity model was calibrated to cyclic
tests conducted on bars of different grades and mechanical properties; 2) a mechanicsbased model was developed and calibrated to experimental data from the literature to
correlate member global deformations with strain demands that govern the fatigue behavior
of longitudinal bars in concrete members; and 3) based outcomes from tasks 1) and 2), a
methodology was proposed to estimate the point during a seismic loading history at which
longitudinal bars fracture in seismically detailed concrete frame members. Cyclic tests
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were performed on reinforcing bars to bolster available fatigue data. Additional tests
included bars of varying grades of steel, manufacturing techniques, clear lateral bracing
spans, and strain amplitudes.