Mohamed Ahmed Ali

AUTOMATIC GENERATION OF TRUSS MODEL FOR OPTIMAL DESIGN OF REINFORCED CONCRETE STRUCTURES

This paper presents a new approach to the computer-aided design of distributed regions of concrete structures. An optimization approach is used to define the topology of the equivalent truss structure needed to provide a specified load capacity while requiring an absolute minimum volume of reinforcement. The algorithms include 2 new features: 1) a practicality factor to avoid the generation of impractical reinforcement layout; and 2) a stress redistribution factor related to the total plastic energy required in developing the capacity of a given truss. Comparisons between alternate optimal solutions and between theory and experiment are also provided.

ENHANCED CONTACT MODEL FOR SHEAR FRICTION OF NORMAL AND HIGH-STRENGTH CONCRETE

Shear friction is the term used to describe the mechanism of shear transfer along a concrete-to-concrete interface subjected to simultaneous shear and normal compression. The aim of this paper is to suggest a rational, yet simple, methodology for obtaining shear friction capacity of both normal and high-strength concrete. The approach considers the following factors: interface morphology (roughness), concrete strength, amount of reinforcement crossing the interface, and normal stress applied to the interface. The interface roughness is probabilistically idealized according to the contact density model developed by Li and Maekawa. The relation between interface roughness and concrete strength is established based on a fracture energy approach. Finally, the suggested methodology is compared with American Concrete Institute (ACI) 318-95, Mau and Hsu, and the Canadian Code.

Consideration of compression stress bulging and strut degradation in truss modeling of ductile and brittle corbels

The paper presents a newly introduced modification of the strut-and-tie model that takes into account compression stress bulging of the strut with proper attention to its degradation as tensile strains increase. The method is capable of discriminating between brittle and ductile modes of failure, thus eliminating the gross underestimation of capacity often observed in applying the truss model to brittle corbels. The proposed method provides improved corbel-capacity prediction in comparison to the provision of three design codes.