Ahmed Atta

Improving the Failure Mode of Over-Reinforced Concrete Beams Using Strain-Hardening Cementitious Composites

AbstractOver-reinforced sections fail suddenly by compression concrete crushing when their ultimate compressive strain has been exceeded but the longitudinal reinforcement strain has not yielded. This study investigates the use of cementitious repair materials for the compression side of over-reinforced concrete beams to change their failure mode to ductile failure. In this study, 11 over-reinforced concrete beams were cast (1 as a control specimen and 10 as strengthened beams). The study’s strengthening material was an ultra-high-performance strain-hardening cementitious composite (UHP-SHCC). The effect of shear connectors with the strengthening material was investigated. Meanwhile, replacement of the concrete cover, use of a welded wire mesh inside the additional layer, and concrete strength were tested. Crack pattern and failure modes were noted, and deflection behavior, failure loads, steel strains, and crack width were measured. The tests results showed that using strengthening UHP-SHCC material is a...

Finite Element Analysis of External Prestressing Beams Made of Strain Hardening Material

The use of finite element analysis has been widely used as a means to analyze individual elements and the effects of concrete strength under loading. This paper is a study of prestressed concrete beams made of strain hardening material called UHP-SHCC (Ultra High Performance Strain Hardening Cementitious Composite) using finite element analysis to understand their response. A finite element model is studied and compared to experimental data. The basic parameters included second order effect of prestressed beam, and prestressing tendon depths have been considered in the analysis. The present study indicated the following conclusions: the number of deviators significantly influences the ultimate capacity and the strains values of UHP-SHCC beams, the change of external prestressing tendon depth has a significant effect on the cracking load, failure load, deflection values, and ultimate stress in the tendon in case of using UHP-SHCC beams but keep the final mode of failure without change.

Damage mechanics based model for low-rise infilled RC frames incorporating neural networks

Purpose – Separately, nonlinear finite element analysis, artificial neural networks (ANNs) and continuous damage mechanics (CDM) attracted many investigators to model masonry infilled frames. The purpose of this paper is to pursue four phases to develop a versatile model for partially and fully low-rise infilled RC frames using these tools. Design/methodology/approach – The first phase included the study of the behavior of 1,620 low-rise infilled reinforced concrete frames using macro-scale nonlinear pushover finite element analysis. The approach helped to explore the effects of imposing different masonry infill distributions for one of the typical models of school buildings in Egypt. The outputs of this phase were used in the second phase for the development of an ANN model where input neurons included number of stories, continuity conditions, frame geometry, infill distribution and properties of RC sections. The third phase included the employment of the notions of CDM on the structural scale. Monitorin...

Improvement the structural behavior of recycled RC elements using CdO nanoparticles

Purpose This study aims to investigate the use of CdO nanoparticles with recycled aggregates (RAs) and its effect on the structural behavior of reinforced concrete (RC) slab elements. Design/methodology/approach The study has been conducted through three phases: in the first phase, the structure of lab-synthesized CdO nanoparticles was investigated and then cement was partially replaced by CdO nanoparticles to estimate the optimum dose. The second phase focused on the properties of the RA collected from demolition wastes. In the third phase, RC slabs with different concrete mixes using RA and CdO nanoparticles were experimentally tested. Findings The results indicated good effect of using CdO nanoparticles with RA to improve the RC slab specimens’ behavior compared with the control specimen. Originality/value In present times, nanoparticles have a promising importance in the construction field. The influence of nanoparticles on the compressive strength of the concrete has been investigated by many researchers, but using it with RA is considered a new topic.

Structural performance of reinforced concrete exterior beam–column joint subjected to combined shear and torsion

This article presents the results of an experimental study conducted in order to investigate the behavior of Type-I beam–column joints, where the beam was subjected to shear stresses due to combined effect of shear force and torsional moment (beam eccentric loading). Eight beam–column joint specimens were constructed and tested up to failure in order to better understand the complicated behavior due to combined loading transmitted from the beam to the column. The studied parameters were the eccentricity of beam load (torsional-moment-to-shear-force ratio Mt/Q), the configuration of beam side and compression reinforcing steel, the existence of the joint reinforcing stirrups, and the beam rigidity. Generally, the shear failure at the beam zone or at the joint panel was noticed to be the governing mode of failure for all tested specimens. The test results highlighted the importance of the configuration of both longitudinal side and compression reinforcing steel of the beam, where the inadequate embedded length of both of them into the joint panel including stirrups decreased the beam ultimate capacity but it kept the failure zone away from the joint panel. Finally, a three-dimensional truss model was presented and analyzed. The results of the three-dimensional model showed good agreement with the experimental findings.