الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 205 |  |  |
| | | from | 205 | | |
Abstract
Prestressed concrete is a form of reinforced concrete that gather the advantage of the strengths of steel and concrete that has many usages such as high rising buildings, power station and numerous types of bridge systems, but high self weight and low ductility of prestressed concrete members are the most problems that face its application. Lightweight concrete has many advantages such as thermal and acoustic insulation and low self-weight. The most common way to produce it is by using lightweight aggregate. Disadvantages are weakness and brittleness of lightweight aggregate. Adding short discrete steel fibers plays an important role in improving mechanical properties of concrete. The main objective of this investigation is to study the effectiveness of a volume fraction of discrete steel fibers and a partial prestressing ratio on the behavior of post-tension prestressed lightweight aggregate concrete beams, in addition to validating the experimental results with a finite element analysis using ANSYS program. The experimental program was divided into two phases. The first phase (Phase I); is the study of the effect of the volume fraction of discrete steel fibers on structural lightweight aggregate concrete by studying of mechanical properties and physical properties. The second phase (Phase II); is the study of the effect of the volume fraction of discrete steel fibers and the partial prestressing ratio on post-tension prestressed structural lightweight aggregate concrete beams. The volume fractions of discrete steel fibers were 0%, 0.5%, 1.0% and 1.5%, and the partial prestressing ratio were 60%, 80%, 85% and 90%. Nine post-tensioned lightweight aggregate concrete beams categorized into four groups according to the partial prestressing ratio and the volume fraction of discrete steel fibers designed to fail under static bending load. The beams have dimensions of 200x350x2500 mmiii and a clear span of 2250 mm. All beams have 75% pumice lightweight coarse aggregate instead of natural aggregate by volume. Experimental results show the crack distribution, spacing between cracks were improved by using discrete steel fiber. Moreover, fibrous lightweight concrete beams exhibited more ductility and energy absorption. By increasing partial prestressing ratio controls crack initiation and decreased ductility, energy absorption and ultimate deflection. On the other hand, by comparison experimental results with finite element analysis for all tested beams. The results referred to an agreement the constitutive models used for concrete and reinforcement that could capture the fracture behavior for an adequate certain level.