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Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

The primary objective of the dissertation work is to examine the capacity of precast concrete diaphragms. This work is part of a multi-university research effort to develop a new seismic design methodology for precast/prestressed concrete floor diaphragms. To accomplish this, two-dimensional finite element (FE) models of precast floor diaphragms are created, including new elements to match the response of reinforcing details under combined forces. Using these models, nonlinear static "pushover" analyses are performed by applying body forces in the plane of the floor.The analyses are composed of three major parts:(1) Parametric studies to determine the required diaphragm shear strength relative to design (flexural) strength, termed "shear reinforcement overstrength", to promote a ductile mechanism in precast diaphragms. The performance of precast diaphragms with different shear reinforcement overstrength is examined. Appropriate shear reinforcement overstrength design factors are proposed to produce certain performance targets, in terms of a number of key parameters related to diaphragm geometry and the properties of the diaphragm reinforcing details.(2) Parametric studies to examine the effects of "secondary" diaphragm elements (spandrels, internal beams) on precast diaphragm behavior. Though not directly counted in design to participate diaphragm action, the secondary elements and their connections to the main diaphragm may modify the strength, stiffness and deformation capacity of the diaphragm. Analytical studies are performed to examine their effect on the global characteristics and local demands of precast floor diaphragms. The parameters evaluated include the characteristics of the connection details, the seismic hazard level used in design, diaphragm geometry, and layouts of spandrels and internal beams.(3) Development of a rational method for calculating the service stiffness and yield strength of precast concrete diaphragms. The method involves input of diaphragm geometry and reinforcing details. The method is verified analytically through comparisons to a set of FE analyses for an idealized diaphragm representation (regular single span diaphragm idealized with simple end supports). The method verified for a single set of diaphragm reinforcement details is used to estimate the properties over a range of untopped and topped diaphragm systems. Consideration of spandrel and internal beams in the method is discussed.

The purpose of work was to show properties of concrete modified with wooden fibres and to compare whem with unmodified concrete in order to show influence of these wooden fibres on chosen properties and to check if using of these types of admixtures is benificial in economical and technical point of view.

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