Award Date

5-1-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Ying Tian

Second Committee Member

Nader Ghafoori

Third Committee Member

Ryan Sherman

Fourth Committee Member

Samaan Ladkany

Fifth Committee Member

Brendan O'Toole

Number of Pages

179

Abstract

Following column failure in a reinforced concrete (RC) frame structure, a progressive collapse may result if the beams supported by the failed column cannot generate an alternate path to carry the redistributed gravity loads. Past studies of the collapse resistance of RC frame beams were limited to their short-time load-carrying capacity. Axially restrained frame beams experience a compressive arch action as a beneficial load-resisting mechanism not considered in a conventional structural design. Due to the compressive arch action, the column failure may not cause an immediate collapse; however, gravity loads still act on the damaged structure, inducing high sustained stresses in the beams initially supported by the failed column. It is unknown how the sustained gravity loads would impact the collapse resistance of RC frame beams. This research aimed to experimentally characterize the time-dependent response of compressive arch action in axially restrained RC beams subjected to high sustained loads. To achieve the research goal, six specimens were constructed at a 1/3 scale for cross section and tested after 267 to 480 days of concrete casting. Detailed test data of five specimens subjected to sustained loading are presented. Each specimen consisted of two beams and one central column representing the failed column. Major test variables were sustained load level and beam span-to-depth ratio. Two specimens had a span-to-depth ratio of 10.6 and the remaining three had 7.5. The sustained loads were applied at four levels: 80%, 90%, 95%, and 100% of the predicted short-time loading capacity under compressive arch action. To explore the effects of previous sustained loading on the structural behavior of frame beams during the subsequent sustained loading, two specimens were tested with two levels of sustained load. A test setup was designed and fabricated to apply both axial and rotational restraints to beam ends and enable the test specimens to be statically determinate. Depending on deflection increase rate, the sustained loading lasted for 10 to 50 days in specimens that did not fail during the sustained loading. Measurements included applied load, beam deflections at selected locations, passively developed compressive axial force, and concrete and rebar strains at the critical sections. Two specimens failed after carrying the sustained loads for 3 and 65 minutes. The tests suggested that the sustained loading capacity of RC frame beams with a span-to-depth ratio of 10.6 and 7.5 can be taken as 90% and 95% of the short-time loading capacity under compressive arch action, respectively. Regardless of span-to-depth ratio, compressive arch action enhanced beam flexural capacity by at least 161% at the center with a reinforcement ratio of 0.63% and 56% at the support with a reinforcement ratio of 1.14%. The evolution of Poisson’s ratio of concrete cover indicated whether the sustained loads were close to the failure loads. Neither the level nor the duration of sustained loading affected beam residual loading capacity. The research provided experimental data crucially needed for calibrating mechanical models for system-scale numerical simulations.

Controlled Subject

Concrete beams;Structural failures

Disciplines

Civil Engineering | Engineering

File Format

pdf

File Size

17600 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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