The fib International PhD Symposium in Civil Engineering is an established event in the academic calendar of doctoral students. It is held under the patronage of the International Federation for Structural Concrete (fib), one of the main international associations that disseminates knowledge about concrete and concrete structures. The 9th fib International PhD Symposium was held at the Karlsruhe Institute of Technology (KIT), Germany, from July 22 to 25, 2012.

Selected chapters from the German concrete yearbook are now being published in the new English "Beton-Kalender Series" for the benefit of an international audience. Since it was founded in 1906, the Ernst & Sohn "Beton-Kalender" has been supporting developments in reinforced and prestressed concrete. The aim was to publish a yearbook to reflect progress in "ferro-concrete" structures until - as the book's first editor, Fritz von Emperger (1862-1942), expressed it - the "tempestuous development" in this form of construction came to an end. However, the "Beton-Kalender" quickly became the chosen work of reference for civil and structural engineers, and apart from the years 1945-1950 has been published annually ever since. Ultra high performance concrete (UHPC) is a milestone in concrete technology and application. It permits the construction of both more slender and more durable concrete structures with a prolonged service life and thus improved sustainability. This book is a comprehensive overview of UHPC - from the principles behind its production and its mechanical properties to design and detailing aspects. The focus is on the material behaviour of steel fibre-reinforced UHPC. Numerical modelling and detailing of the connections with reinforced concrete elements are featured as well. Numerous examples worldwide - bridges, columns, facades and roofs - are the basis for additional explanations about the benefits of UHPC and how it helps to realise several architectural requirements. The authors are extensively involved in the testing, design, construction and monitoring of UHPC structures. What they provide here is therefore a unique synopsis of the state of the art with a view to practical applications.

Sustainable construction, with the overarching goal of reducing the environmental footprint of everything we build is becoming increasingly important and urgent in the light of the climate change the world is facing. The use of innovative and sustainable building materials, especially concrete as the worldwide most commonly used building material, offers a great opportunity to significantly reduce climate-relevant emissions in the construction sector. Due to their performance and reliable durability, the use of innovative high-performance concretes will help to reduce the need for new constructions and to sustainably repair existing infrastructure. In new buildings in particular, the use of high-performance materials can help to save energy and natural resources, which reduces climate-relevant emissions and thus global warming. With the current HiPerMat 6, we are responding to the growing understanding of the impact of our construction activities on the environment by placing greater emphasis on sustainability issues.

fib Model Code 2010 represents the state-of-the-art of code-type models for structural behaviour of concrete. It comprises constitutive relations and material models together with the most important explanatory notes. However the underlying normative work, i.e. the fundamental data as well as the considerations and discussions behind the formulas could not be given within the Model Code text. Based on various experiences gained after the publication of Model Code 1990 this lacking background information will lead in the following to numerous questions arising from Model Code users. Consequently the present bulletin claims to conquer this general weakness of codes in a way to guard against any future misunderstandings of the Model Code 2010 related to its chapter 5.1 (Concrete). It discusses the given formulas in connection with experimental data and the most important international literature. The constitutive relations or material models, being included in MC1990 and forming the basis and point of origin of the Task Group’s work, were critically evaluated, if necessary and possible adjusted, or replaced by completely new approaches. Major criteria have been the physical and thermodynamical soundness as well as practical considerations like simplicity and operationality. This state-of-the-art report is intended for practicizing engineers as well as for researchers and represents a comprehensible summary of the relevant knowledge available to the members of the fib Task Group 8.7 at the time of its drafting. Besides the fact that the bulletin is a background document for Chapter 5.1 of MC2010, it will provide an important foundation for the development of future generations of code-type models related to the characteristics and the behaviour of structural concrete. Further it will offer insights into the complexity of the normative work related to concrete modelling, leading to a better understanding and adequate appreciation of MC2010.

Within this work a material law was developed which correctly describes the creep and relaxation characteristics of young and mature normal strength and high-strength concretes. It is based on an aging thermodynamically sound rheological model and considers the complex nonlinear creep behavior under constant and variable stresses. In case of relaxation the corresponding integral relation is solved by means of a numerical algorithm.