Souzana P. Tastani

State of Bond along Lap Splices

AbstractDesign requirements for development length of lap-spliced reinforcing bars in concrete refer to the associated rules for anchorage, practically treating the two problems as one. This was based on the empirical observation that development capacity of reinforcement obtained from both lap-splice and anchorage tests converge to the same experimental values. Nevertheless, from a theoretical viewpoint the similarity between the states of stress of these two problems is not well addressed. In order to trace the underlying relationship between these two bond conditions, the field equations governing lap-splice behavior are established and solved from first principles using simplified constitutive relationships for steel and bond between reinforcement and concrete; the state of stress thus estimated is subsequently compared with the state of stress that occurs along an anchorage of the same length. Because lap splices occur in the clear span of members in the presence of flexural moment, an essential poin...

Strain Resilient Cementitious Composites of Unclassified Calcareous Fly Ash and PP Fibers: Performance by also Considering Durability Effects

Strain Resilient Cementitious Composites (SRCC) is a class of ECCs, following the design philosophy in terms of grain fineness of mixing materials and the high dosage of plastic fibers, but differentiating in the tensile response: after first cracking they develop a wide parabolic response sustaining adequate tensile strength up to high levels of strain. The material’s deformation is concentrated near a limited number of cracks emanating from the anchorage conditions of the embedded fibers. In the case of SRCC made by the less studied calcareous fly ash (of low pozzolanic ingredients and high lime) and polypropylene (PP) hydrophobic fibers, early studies have shown that strong chemical bond links are developed in the fiber-binder interface as the material hardens with time. This time-dependent effect alters the mechanical behavior of fibers from partial pullout at early age to elongation at advance time; the latter mechanism promotes the occurrence of early crack stabilization with the development of few cracks which sustain the tensile resistance due to the sufficient anchorage length of the fibers. This paper presents experimental results for the mechanical characterization of four SRCCs with parameters the Greek calcareous fly ash and the PP fiber contents at advanced age. In total 120 specimens were tested in compression (cubes) and tension (3-point bending prisms and 4-point bending beams for definition of material’s tensile strength/fracture energy and deformation capacity respectively) by also considering assessment of materials’ durability in regards to the impact of hearing and freeze-thaw cycling.

Testing Procedure for Determining the Bond-Slip Law of Steel Bars in Strain Hardening Cementitious Composites

In order to advance the use of Strain Hardening Cementitious Composites (SHCC) in structural applications it is essential to understand the mechanics of bond of reinforcement anchored in this type of material. The strength of the cover against splitting as well as the strain development capacity of bars anchored in SHCC are studied in the present experimental study through tests conducted on specially designed tension pullout specimens. Parameter of study was the steel bar diameter and the anchorage length as well as the bar cover. The experimental results obtained from a series of 24 specimens were used to calibrate a mechanistic frictional model for bond along reinforcement anchorages embedded in SHCC. It was shown that the sustained tensile resistance of the SHCC up to large levels of tensile strain was engaged confining the bar-cover interface, thereby preventing through-splitting of the cover as would normally occur in plain concrete matrices. This enabled the contribution of a frictional component to the anchorage strain development capacity that is directly traceable to the deformation capacity of the SHCC matrix. This modelling approach was motivated by the experimental evidence where splitting failures may be mitigated even with short anchorage lengths and relatively small covers (cover thickness = bar diameter) up to large levels of pullout slip of reinforcement.

A MECHANISTIC APPROACH IN DEFINING INELASTIC ROTATION CAPACITY OF RC COLUMNS

When a reinforced concrete (RC) column is subjected to lateral sway as a result of earthquake action, the large strain demand in the end sections is supported by development of strains in the anchorage. This causes the bars to displace (or slip) relative to the anchoring concrete at the column fixed end(s). The lumped slip causes rigid-body rotation of the column, thereby alleviating partially the column deformation. This reinforcement slip is assumed to occur in the tension bars only and cause the rotation about the neutral axis. Development of flexural yielding and large rotation ductilities in the plastic hinge zones of frame members is synonymous with the spread of bar reinforcement yielding. Yield penetration in the anchored reinforcing bar inside the shear span of the column where it occurs, destroys interfacial bond between bar and concrete and reduces the strain development capacity of the reinforcement. This affects the plastic rotation of the member by increasing the contribution of bar slippage. In order to establish the plastic rotation in a manner consistent with the above definition, this paper uses the explicit solution of the field equations of bond over the shear span of a column. Through this approach, the bar strain distributions and the extent of yield penetration from the yielding cross section towards the shear span are resolved and calculated analytically. By obtaining this solution the aim is to illustrate the true parametric sensitivities of plastic hinge length as a design variable for practical use in seismic assessment of existing structures. Results obtained from the analytical procedures are compared with experimental evidence from tests conducted on reinforced concrete columns under seismic loading reported in the literature. 2739 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2739-2752

Confinement of RC Elements by Means of EBR FRP Systems

This chapter reviews the issues of confinement in plain and reinforced concrete under concentric compression and summarizes the state of the art regarding the available confinement models for strength and stress-strain behaviour of encased confined concrete, and the corresponding magnitude of dependable strain capacity. The mechanisms of confinement failure, the evolution of Poissons’ effects under low and high confinement, and the ensuing material compaction at high confining pressures (plastification) are discussed. The effects of stress concentrations near corners, the effectiveness of layers and influence of adhesive, other scale effects and the influence of specimen morphology on mechanical behaviour are also outlined. Next, the chapter concentrates on the effects of embedded reinforcement both longitudinal and transverse. Confinement effectiveness in the presence of combined flexure and shear (in plastic hinge regions), local effects due to rotation capacity increase, and effects of FRP confinement on overall member behaviour are discussed. Shape effects that occur in hollow or oblong sections are also considered. Furthermore, the chapter gives an outline regarding the characteristics of the international database of tests for confinement, and its calibration with the database of the available confinement models including those included in the design standards (ACI, CNR and EC8-III).