8321

8321

بررسي خواص رئولوژي ---- بتن هاي تراكم و رفتار آن در اعضا خمشي تحت اثر بارهاي رفت و برگشتي

دكتري

عمران - سازه

89

89

قدوسي - احمدي

Abstractَ Concrete and its application in civil engineering is the most common and interesting material in the construction. Convectional concrete is brittle in nature and posses difficulties in executions. Today the large and infra structures are constructed with high performance concrete. "High Strength Self Compacting Fiber Reinforced Concrete" is categorized as this material. The goal of this dissertation is to study about the rheolgy and the cyclic behavior of self compact reinforced concrete in flexural elements. The scope of this research includes the technology and structural engineering. In order to perform this study, compressive strength of 60 Mpa is selected for self compact concrete according to the current conditions of construction in country. First an applicable mix proportioned is prepared according to existing method and recommendations. Then a mathematical model is developed to estimate the coarse aggregate content in fiber reinforced concrete by using the "covering mortar thickness" theory to keep proper workability. After that, some mix proportioned of self compact fiber reinforced concrete with one type hooked-end steel fiber and two type propylene fibers are produced. Toughness test are carried out in order to choose the optimum mix for structural element testing. The result shows that the hooked-end steel fiber increases the toughness and energy absorption in compare to propylene fibers. In order to meet the self consolidation requirement, fiber content of 0.75% is selected for structural specimen. In continue fiber pullout test is conducted to interpret and evaluate the result of toughness test which are presented the similar result in high and moderate strength specimens. New equipment is designed and made to perform fiber pullout test. Fiber pullout test shows that the strength of concrete doesn’t affect mainly the pullout response of hooked-end steel fiber behavior and the hooks play considerable roles. Also the self compact concrete which utilize the viscosity modify agenda (VMA) has lower level of fiber pullout response due more created pores in compare to those utilize mineral additives. In the next stage a complete analytical model is developed to predict the fiber pullout response. This model is stress-controlled model. The concept of bond shear stress versus slip relation between fiber and matrix has been used to develop fiber force and bond stress. In this model the effect of curvatures on the forces and stresses distribution along the hook ended fiber length have been analyzed at the. Then the theoretical relations for hook ended fiber have been developed with using the force and stress distribution at the curvatures of anchorages. Finally the model has been validated with the existing experimental report on the hook-end steel fiber. The result shows that the model is capable to estimate the main pullout mechanism due to mechanical anchorage of hooks. Another simple analytical model is extended for predicting the pullout response of hooked-end steel fiber. Two different assumptions are used in this model which is a new simple concept of