No abstract

No abstract

No abstract

The most of the reinforced concrete frame structures of the European building stock have been built without attention to the seismic action or according to obsolete code. Before the 1970's, in all the Mediterranean area, plain rebars were employed for the longitudinal reinforcement of structural members. Due to their smooth surface, they are characterized by poor bond capacity; this results in a significant slip of the loaded bar from the surrounding concrete, which strongly increases the structural deformation capacity compared to modern ribbed rebars. Whereas the cyclic response of non-conforming reinforced concrete members and structural sub-assemblies is deeply investigated in literature, a scarce knowledge about anchored plain bar cyclic behaviour is noticed. In the recent years, detailed non-linear modelling of gravity load designed structures is widely used for the seismic vulnerability assessment; a deep investigation on full scale anchorage detailing is then fundamental for the correct modelling of such structures.. In the present paper an experimental investigation on different anchorage solution of plain rebar embedded in concrete is presented; straight, hook-ended and 45° bent rebar were analysed, monitoring their axial stress versus slip behaviour. A non-linear stress-slip behaviour was observed for all the anchorage solutions since the lower loading level. Stiffness degradation due to cyclic loading was observed; on the other hand, strength decay was visible only for straight anchorage length. Hook-end device and bar bent resulted effective in providing a good anchorage performance, on the other hand their response showed a progressive plasticization.

No abstract

No abstract

The innovative infill construction technique for seismic resistance, implementing horizontal sliding joints to partition the wall into subpanels, it is here tested in presence of a full height opening. With the double aim of protecting the opening fixtures (window or door) from the infill sub-panels' relative sliding and offer out of plane support to the infill, a post is placed at the opening side spanning between the top and bottom beam of the frame. The post stiffness and strength design is the object of the study. The role of the post deformability was studied by modifying the post's stiffness with additional steel profiles coupled to the initial wooden post configuration, in different test phases. The shear action at the post ends was measured with specific load cells, to provide information for the proportioning of the post and its connection to the beams. The results showed the efficiency of the post in governing the sliding mechanism between the infill sub-portions and the role of the post's stiffness in modifying the in-plane response of the infill. Thanks to the post's deformability, the overall infill-frame interaction was reduced with respect to previously tested similar infills without openings.

The resource of shear resistance provided by the dowel mechanism of rebar in reinforced concrete (RC) structures can significantly affected by the simultaneous presence of axial loading. This occurs for example of plastic hinges of seismic resistant structures. In fact, at load reversals in cycles of large deformation demand, rebars are subjected to combined axial and shear loading, particularly in those section where the shear transfer via aggregate interlocking is jeopardized by the opening of the crack throughout the entire section depth. Thus, a reliable assessment of the shear capacity of dowels under combined shear and axial load is required to check the element shear resistance. The paper describes the results of a specific experimental campaign on rebar dowels subjected to shear loading in presence of different levels of axial load. Both smooth and ribbed rebar dowels were investigated. A marked reduction of the dowel shear strength and stiffness in presence of increasing axial loading was experimentally observed, only partially compensated by the kinking effect. The latter was found to characterize the entire resource of dowel capacity when the axial load was close to the rebar yielding strength. The paper proposes an analytical model, adapted from others available in the literature, to predict the dowel shear-displacement response accounting for the applied axial load. The model helps the understanding of the dowel response, is suitable for hand calculation and can easily assist the dowel design. The experimental response was quite well captured for smooth dowels, while the prediction was less accurate for ribbed ones. Future refinements may address the local damage induce by the rebar pull-out, typical of ribbed rebars, which is neglected in present form of the model.