Title: Effect of Service Load Levels on Long-Term Deflection Multiplier

Author(s): Stephanie Walkup, Eric Musselman, and Shawn Gross

Publication: Structural Journal

Volume: 116

Issue: 2

Appears on pages(s): 89-100

Keywords: deflection; deflection multiplier; glass fiber-reinforced polymer (GFRP)-reinforced concrete beams; GFRP reinforcement; long-term deflection; service load levels; sustained loads

DOI: 10.14359/51711137

Date: 3/1/2019

Abstract:
ACI 318 and ACI 440.1R amplify initial sustained load deflections by a long-term deflection multiplier λΔ to calculate long-term sustained load deflections. Calculation of this multiplier λΔ is a function of only the duration of sustained loading and the compression reinforcement ratio. This research study examines three steel-reinforced and nine glass fiber-reinforced polymer (GFRP)-reinforced concrete beams subjected to varying Ma/Mcr and Msus/Mcr ratios to determine their effect on λΔ. Due to the constant beam cross section and various reinforcement ratios, the Ig/Icr ratio also varied between specimen subsets. Experimental results demonstrate that as Ig/Icr and Ma/Mcr increase, λΔ decreases. Higher Msus/Mcr ratios increased long-term deflections, but this ratio has no effect on the multiplier λΔ. Analysis using Yu and Winter’s effective modulus of elasticity method combined with Bischoff’s equation for effective moment of inertia that incorporates the Ig/Icr and Ma/Mcr ratios is used for verification to analytically bound the experimental long-term deflection multipliers.