Juan Murcia-Delso

Bond strength and cyclic bond deterioration of large-diameter bars

A study on the bond strength and cyclic bond deterioration of large diameter reinforcing bars embedded in well-confined concrete is presented. The study included monotonic pullout tests and cyclic pull-pull tests conducted on No. 11, No. 14, and No. 18 (36, 43, and 57 mm) reinforcing bars. The bond stress-slip relations obtained from the tests are presented, and the effects of the compressive strength of concrete, bar size, pull direction (for a vertically cast bar), and slip history on the bond strength are examined. Moreover, a phenomenological bond stress-slip law for monotonic and cyclic loading is proposed for bars embedded in well-confined concrete. This law has been validated with experimental results obtained in this study and in previous research.

Bond-Slip Model for Detailed Finite-Element Analysis of Reinforced Concrete Structures

A new interface model to simulate the bond-slip behavior of reinforcing bars is presented. The model adopts a semiempirical law to predict the bond stress-versus-slip relations of bars, accounting for the bond deterioration caused by cyclic slip reversals, the tensile yielding of the bars, and the splitting of concrete. The wedging action of the ribs is represented by assuming that the normal stress of the interface is proportional to the bond stress. The model has been implemented in a finite-element analysis program and has been validated with laboratory experiments that include monotonic and cyclic bond-slip and anchorage tests of bars with different embedment lengths and a test on an RC column subjected to cyclic lateral loading. The model is easy to calibrate and computationally efficient, and it accurately predicts the bond-slip behavior of bars embedded in well-confined concrete. It also simulates bond failure attributable to the splitting of concrete in an approximate manner.

Fragility Analysis of Reinforced Masonry Shear Walls

Fragility functions have been developed to evaluate the damageability of fully grouted and partially grouted reinforced masonry shear walls subjected to in-plane seismic loading. Six damage states are considered, representing different levels of flexure, diagonal shear, and sliding shear damage. For each damage state, two classes of fragility functions have been developed. One has the story-drift ratio as the demand parameter. The other uses normalized demand parameters that account for the specific loading condition and design details of a wall component. All the fragility functions are derived from experimental data except for those developed for partially grouted walls and the sliding shear damage state. With both classes of fragility functions, the seismic damageability of flexure-dominated cantilever reinforced masonry shear walls in a four-story building has been assessed. It has been shown that the normalized flexural demand parameter provides a better correlation to the degree of damage developed in a wall than the story-drift ratio.

Tension development length of large-diameter bars for severe cyclic loading

This paper presents a study on the tension development length of large-diameter reinforcing bars embedded in well-confined concrete. Pull-push tests were conducted on No. 14 and 18 (43 and 57 mm) bars to evaluate whether the development length requirements in the AASHTO LRFD (American Association of State Highway and Transportation Officials Load and Resistance Factor Design) Specifications are adequate for large-diameter bars subjected to severe cyclic loading. The data have been used to validate finite element models, which have been subsequently employed in a parametric study to establish a formula to determine the tensile capacity of a bar as a function of the embedment length, and the concrete and steel strengths. Monte Carlo simulations conducted with this formula have shown that the AASHTO requirements are adequate to develop the yield strength of a bar in tension, but they do not have the desired reliability to develop its ultimate tensile strength when uncertainties are considered. Hence, an improved development length requirement is proposed.