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Author ORCID Identifier

https://orcid.org/0000-0002-0528-7413

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil Engineering

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Sergio F. Breña

Second Advisor

Simos Gerasimidis

Third Advisor

Peggi L. Clouston

Subject Categories

Civil Engineering | Structural Engineering

Abstract

The American Concrete Institute (ACI) Building Code Requirements for Structural Concrete and Commentary (ACI 318-14) indirectly accounts for resistance to progressive collapse by providing requirements for structural integrity in concrete structures. ACI 318-14 structural integrity requirements are intended to provide alternate load paths so that progressive collapse is avoided in the event of the unintended loss of an interior support.

ACI 318-14 §9.7.7.5 requires that splices of structural integrity reinforcement be designed as Class B splices near mid-span for top reinforcement and near the support for bottom reinforcement. However, ACI 318-14 does not provide a clear definition for the support region where bottom reinforcement splices should be located. In addition, bottom reinforcing bar splices at the face of the support or inside the beam-column joint have the potential for generating congestion and introducing difficulties during construction. Therefore, relocating the splice location outside the joint may improve constructability but it is not clear if this practice will affect the behavior and the load redistribution capacity of the system.

The research presented in this dissertation is intended to evaluate the effect of splice location of structural integrity reinforcement on the performance of beams in perimeter frames after loss of an interior or an exterior column in a hypothetical reinforced concrete frame building. The ten-story reinforced concrete building prototype was designed for a low seismic design category following the requirements of the ACI 318-14 Code, excepting Chapter 18. The study includes laboratory testing of three full-scale sub-assemblages of a ten-story reinforced concrete building prototype that simulate the loss of an interior column for the purpose of investigating the effect of bottom lap splice location. The two-span laboratory specimen contains a center column stub where the existing building column was removed to simulate loss of an interior support from an extreme event. The test specimens achieved similar maximum applied force values in the three experiments. After reaching the maximum force, a sudden decrease in the applied force occurred because of shear failure at the exterior end of one of the beams. This failure was generated by loss of aggregate interlock in the concrete after development of the critical diagonal crack. Premature failure of the beam limited the development of catenary action that has been reported to develop at large displacements by other researchers in laboratory experiments of similar specimens, but where seismic design details have been employed. Rotations just prior to the shear failure were similar for the north and south beams in the exterior plastic hinge regions for all specimens.

Three-dimensional structural models were built and analyzed using a commercially available structural analysis program (SAP 2000) to investigate the progressive collapse behavior of the ten story prototype concrete building after non-simultaneous removal of an interior and a corner column. The plastic collapse mechanism was captured by assigning nonlinear hinges at critical moment sections of beams and columns using a lumped plasticity approach. Hinges were also assigned at different locations along elements to capture the possibility of hinge formation away from ends of elements after moment redistribution occurred. The moment–curvature relationship of a beam plastic hinge was constructed analytically and subsequently calibrated using the experimental results of Specimen 3. Based on the GSA 2016 Guidelines and the performance on the plastic hinges, the interior perimeter column removal condition met the requirements of prevention for progressive collapse. In contrast, a corner perimeter column removal did not meet the requirements to prevent generating progressive collapse according to the GSA 2016 Guidelines. The research highlights the importance of proper reinforcing detailing of reinforced concrete frames to provide progressive collapse resistance, and the importance of three-dimensional modeling to evaluate moment redistribution of reinforced concrete perimeter frames after loss of supports.

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