Abstract
Abstract Prestressed composite steel-concrete structures are scarcely used due to a lack of clear standardized design guidelines and formulations on the subject. The present research aims to present design methodologies for steel-concrete composite beams with external pretension applied via straight tendons. A computer program to perform structural analysis of such beams was developed based on two different methodologies: the first one is presented in ABNT NBR 8800:2008, in which the guidelines for the design of composite beams with compact webs are adjusted to include the effects of the pretension force. The second methodology is extracted from international literature and presents a structural design process based on stress distribution on the beam. Ninety prestressed and thirty non-prestressed beams were analyzed and designed with the aforementioned computer program to evaluate the influence of beam length, degree of symmetry of the steel profile and eccentricity of the pretension force on the mechanical resistance of the beams. It was observed that, although the prestressing force considerably improved resistance to bending, it introduced high compression stresses on the steel profile; hence, the pre-stressing of composite beams is proved efficient only for steel profiles with symmetrical cross-sections.
Highlights
External prestressing applied to steel-concrete composite beams results in elements of great structural efficiency, able to cover large spans and resist high loads with reduced structural weight
Ultimate limit state verifications related to bending moment and shear force were performed along with checks of the serviceability limit state of excessive deformation
For the L⁄d ratio equal to 27, Figure 13, the ultimate bending moment is reducing on average 0.62% when the eccentricity increases by 100 mm and 3.07% when the eccentricity increases by 150 mm
Summary
External prestressing applied to steel-concrete composite beams results in elements of great structural efficiency, able to cover large spans and resist high loads with reduced structural weight. This technique is of interest for structural recovery and / or reinforcement of existing structures presenting severe pathologies caused by deterioration due to environmental agents or increases in service loads such as, for example, a bridge that experiences an increase in traffic or other loads throughout its lifespan. In 1966, Regan [6] analyzed the effects of variations in slab thickness, prestressing forces and load types on the behavior of supported composite steel-concrete beams
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