# Frontiers of Structural and Civil Engineering

 Front. Struct. Civ. Eng.    2018, Vol. 12 Issue (1) : 148-162     https://doi.org/10.1007/s11709-016-0375-5
 RESEARCH ARTICLE |
Intermediate HSS bracing members during seismic excitations: modeling, design, and behavior
Department of Architectural Engineering, United Arab Emirates University, P. O. Box 15551, Al Ain, UAE
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 Abstract Concentric hollow structural section (HSS) bracing members are used frequently in steel framed structural systems to resist seismic excitations. Finite element modeling of the HSS braces that utilizes the true stress-strain curves produces hysteresis responses that are reasonable matches to the experimental response. True stress-strain curves are obtained from coupon tests or stub-column tests while utilizing an exponential function or strain hardening rule with a trial and error procedure to obtain the hysteresis behavior. In the current study, the true stress-strain curves are directly obtained from tests on stub-columns extracted from the full scale HSS bracing members away from the mid-length plastic hinge after cyclic testing. Two experimental tests (Shaback 2001 and Haddad 2004) were used to validate the model. Results indicate that the stress-strain curves for these braces are not unique. A refined damage accumulation model for ultra-low-cycle fatigue is implemented to predict fracture of the brace tests. The refined damage model is then used in the finite element modeling to predict fracture of braces in a chevron braced frame of an eight-storey building subjected to selected ground motions analyzed using OpenSees program. Results indicate that all braces could sustain the selected earthquake records without fracture. Corresponding Authors: Madhar HADDAD Online First Date: 06 April 2017    Issue Date: 08 March 2018
 Tab.1  Geometric properties of the HSS specimens with initial imperfection values Tab.2  Material properties of the HSS specimens Fig.1  Engineering and true stress-strain curves with the elastic offsets Fig.2  Specimen 4B with end connection Fig.3  Effect of mesh density at mid-length plastic hinge on the significant cumulative plastic strain Fig.4  Axial-hysteresis stress-strain loops: (a) experimental; (b) finite element analysis Tab.3  Geometric measurements of HSS specimens Tab.4  Experimental versus numerical peak points Fig.5  Axial and lateral hysteresis loops Fig.6  (a) Local buckling with small size bent; (b) fracture of specimen 4B Fig.7  (a) Axial strain hysteresis loops; (b) axial displacement versus axial strain hysteresis loops Fig.8  (a) Axial strain hysteresis loops; (b) critical plastic strain Fig.9  Prototype building studied Tab.5  Characteristics of ground motion earthquake records Fig.10  Axial hysteresis loops Fig.11  Axial deformation time histories for the left (a) and right (b) braces under stepwise incremented ground motion record No. 767 Fig.12  Significant plastic strain for the left (L) and right (R) braces under magnified displacement histories of SF = 2.0, record No. 767