Access Type

Open Access Dissertation

Date of Award

January 2023

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Fatmir Menkulasi

Abstract

The inelastic behavior of a dual performance high-capacity hybrid frame-wall system intended for cold formed steel construction is presented. The investigated frame-wall system features cold formed steel studs to support gravitational loads and a combination of cold formed steel straps and nonprestressed strands to provide braced frame action for lateral loads. In addition, hollow structural steel chords are used to resist overturning moments. The chords can be either hollow structural steel sections or steel tubes filled with ultra-high performance concrete. System behavior when subject to lateral loads or lateral displacements is characterized in terms of failure mode, ultimate strength, initial stiffness, and ductility. This behavior is then compared to that exhibited by traditional strapped wall systems that features tension only braces. The contribution of moment frame action provided by the slab and chords, as well as braced frame action provided by the straps and braces is quantified. In addition, the influence of multiple strand bracing layers on failure mode is investigated. Numerical modeling guidance is provided to facilitate analysis and design and allow the examination of alternative configurations. It is found that the failure mode is characterized by the yielding of the straps, and subsequent yielding and rupture of prestressing strands. The inclusion of multiple strand layers significantly enhances capacity although it comes at the cost of reduced system ductility. The contribution of slab chord action is found to be significant and responsible for providing 40% of lateral load capacity when a single layer of strands is considered. The inclusion of slab reinforcement sized to resist gravitational loads has negligible effect on the lateral load behavior of the system. The increase in cold-formed steel strap yield stress causes a nonproportional increase in lateral load capacity due to the participation of strands and the provision of slab-chord action and results in a slight reduction in system ductility. The influence of increasing the chord wall thickness is nonlinear with some changes causing a significant increase in lateral load capacity and other causing a minimal change. The prestressing of the strands does not improve behavior under monotonic lateral loads. The behavior of cold-formed steel studs that are part of the hybrid frame wall and which feature irregular hole spacings under gravity loading is presented including methodologies appropriate for predicting axial capacity. Since the strand bracing is connected eccentrically to the chords, the moment curvature relationship of composite tubes chords filled with ultra high performance concrete is characterized for capturing potential yielding in the chords.

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