Load Bearing Capacity Prediction of Steel Fiber Reinforced Concrete Elements Subjected to Bending Loads
Andrejs Pupurs

09.12.2011. 14:30, BF sēžu zāle

Andrejs Krasņikovs

Jānis Brāuns, Jānis Andersons, Ralejs Tepfers

At present concrete researchers and engineers in European and world-wide level are focusing their efforts towards developing generally accepted international design regulations for steel fiber reinforced concrete (FRC). It is realised that the lack of generally accepted design regulations has been too long in terms of time and despite the clear advantages of FRC in many applications the use of it has often been limited due to inconsistency of the existing design recommendations. It is therefore important to contribute to FRC research community with original results and concepts of models for predicting the behaviour of FRC structural elements. While in order to determine the properties of FRC most of the currently available design recommendations use inverse approach (approximation of experimentally obtained relations), the direct approach, on the other hand, can provide more economical and realistic structural design of FRC by evaluating the actual type, amount and orientation of fibers. The present Thesis therefore is aimed towards elaborating a constitutive model for prediction of load bearing capacity and post-cracking behaviour of FRC structural elements using the direct modeling approach. The model is elaborated in a simple form so that it could be applicable for integration within a structural design document in the future. The modelling procedure described in this Thesis is applicable to FRC structural elements subjected to bending loads, and the main principle of the model is based on the observation that performance of a FRC element strictly depends on the pull-out resistance of fibers. The same principle could be also used in the future for prediction of behaviour of FRC structural elements subjected to tensile loads. The present Thesis consists of three major parts: in Chapter 3 extensive experimental study of fiber pull-out resistance of three types of commercially available steel fibers is performed. The effect of fiber embedded length and inclination angle is experimentally determined and the average pull-out laws for different configurations are presented. In Chapter 4 numerical modelling of the fiber pull-out process is performed using finite element method. Using fracture mechanics principles, steel fiber/concrete matrix interface debond crack growth is parametrically analyzed. Numerical modelling of the whole pull-out process of straight fibers is also performed in Chapter 4. From comparison and best fit with the experimental results different important parameters are determined that are difficult to measure experimentally. Finally, in Chapter 5 a model for predicting the load bearing capacity and post-cracking behaviour of FRC beams is elaborated by using the previously obtained fiber pull-out laws. Unlike most of the existing models available in the literature and design recommendations, the model proposed in this Thesis takes into account the actual amount and type of fibers in the FRC mix. FRC beams subjected to 4 point bending were tested experimentally to validate the modelling results and the obtained agreement was very good despite the simplicity of the model. This Thesis demonstrates the potential and advantages of applying direct approach of modelling to FRC alternatively to inverse methods suggested in most of the available design recommendations since the load bearing capacity and post-cracking behaviour of FRC beams was accurately predicted. The present work is also one of the few studies in literature so far that has been focusing on FRC with high fiber fractions (100−300kg/m3), which is essential for structural applications.

Fiber reinforced concrete, micromechanical analysis, fiber pull-out, experimental, FEM modeling, structural elements, load bearing capacity

Pupurs, Andrejs. Load Bearing Capacity Prediction of Steel Fiber Reinforced Concrete Elements Subjected to Bending Loads. PhD Thesis. Rīga: [RTU], 2011. 157 p.

Publication language
English (en)
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