DBPapers
DOI: 10.5593/sgem2017H/63/S26.080

RESILIENT STEEL-CONCRETE SEISMIC RESISTANT FRAME ASSEMBLED BY POST-TENSIONING

M. Pastrav
Thursday 23 November 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgemviennagreen.org, SGEM2017 Vienna GREEN Conference Proceedings, ISBN 978-619-7408-29-4 / ISSN 1314-2704, 27 - 29 November, 2017, Vol. 17, Issue 63, 635-642 pp; DOI: 10.5593/sgem2017H/63/S26.080

ABSTRACT

The building sector is interested in developing new types of structures capable to resist seismic loading.
There is introduced a new structural detailing of mix steel-concrete structures. The innovative design consists in use of the precast concrete slabs and steel frames, assembled by post-tensioning, of the prestressing procedure for the steel members and also a different column-beam connections having resilient characteristics.
Each of the listed features is also special. The prestressing reinforcement is located in the centroid horizontal plane of the beams and is non-adherent with respect to the structural members except for fixing ends and connections. For the post-tensioning of the tendons only a limited value of the prestressing capacity is used. The column-beam connections are designed as dual type ones due to the fact that beside the prestressed tendons, screws and nuts are used for the stress transfer between joint members and the precast concrete slabs are supporting exclusive gravity loads. This last issue is conceived for two reasons, the former to avoid damages in horizontal members and the latter to direct seismic caused damages in pre-established locations, where they are easy to asses and simply to repair, after a seismic event. The precast concrete slabs are supporting only gravity loadings.
This experimental research aims to determine the behavior of a model representative for the innovative design of mix steel-concrete structure composed of precast concrete slabs and steel frames, assembled by post-tensioning, under seismic type loading. The mentioned new designed characteristics of the mix structure have to be proved by experimental tests and also its resilient joints assumed characteristics. In consequence, a half scale structural plane is tested under lateral seismic type forces, up to a 0.035 storey drift ratio, 40% over the upper limit given by the Romanian seismic code. The model consists of a two storey column and two beams connected at the column mid span with dual connections.
The principal test results expressed in overall and local behavior observations, resistance capacity and structural response are presented. The force transfer mechanism in the dual connections is also deducted from the actual behavior of the model.
The overall behavior of the tested model subjected to cyclic seismic type loading is different from the in use concrete-steel structures. The beams have mainly rigid body displacements while the deformations of the horizontal members are concentrated at the beam column dual joints. In those locations the post elastic deformations develop and also the majority of energy is dissipated through this manner. Thus, the control of the hard column - soft beam structural behavior can be done by calibration of the dual joints resistance and plastic characteristics, as precast concrete slabs are designed to support only gravity loadings. The paper concludes with a sketch of further development of the research in order to establish reliable design equations and acceptance criteria for test-based design of this innovative structures.

Keywords: prestressed steel beams, dual type connection, non-adherent post-tensioning, seismic response