Manuel Alvarez

Tension chord model for structural concrete

Based on a simple tension chord model, problems of cracking, minimum reinforcement, tension stiffening and deformation capacity of structural concrete members are treated in a unified manner. Key f...

Rotation Capacity of Reinforced Concrete Slabs

Results of bending tests on three continuous reinforced concrete slab strips are compared with calculations according to linear, nonlinear, and limit analysis approaches, as well as with code provisions. It is demonstrated that the reduced ductility properties of cold-deformed and coiled small-diameter reinforcing bars and wires may result in dangerous strain localizations, impairing rotation capacity, permissible moment redistribution, and ultimate strength. A nonlinear analysis method for refined deformation investigations is presented, and minimum ductility requirements for reinforcing steel are suggested.

Swiss Federal Roads Office Guidelines for Integral Bridges

Abstract Integral concrete bridges have a long-lasting tradition in Switzerland. In particular, during the main construction period of the national motorway network (1960–1985), numerous jointless reinforced and prestressed concrete bridges were built. Based on this experience, and because of the often unsatisfactory long-term behaviour of expansion joints, the Guidelines of the Swiss Federal Roads Office (FEDRO), edition 1990, established as a general rule that expansion joints be avoided for bridges with lengths up to a range of 30 … 60 m. As a consequence, integral and semi-integral concrete bridges have become well established construction types in Switzerland. In effect, today more than 40% of the existing bridges on the FEDRO network are (semi-)integral structures, a considerable amount of them even exceeding the stipulated maximum bridge length. The Swiss experience with integral bridges is mainly positive, both in terms of construction and maintenance. Thus, it seems appropriate to potentiate their construction and extend their range of application. Following this aim, in the current revision of the FEDRO Guidelines, the design provisions for integral bridges have been substantially refined and extended to allow for wider applications, including specific guidance for semi-integral bridge ends.

A Numerical Investigation for Optimization of the Load Carrying Capacity of a Swiss Rockfall Protection Gallery

A variety of natural hazards can endanger the built environment and the lifeline in the Alpine areas of Switzerland. Due to climate changes, rockfall events are among the increasing hazards over the last decades. Rockfall protection galleries are one of the few adequate structural measures, which provide the required safety against falling rocks. They are typically composed of reinforced or posttensioned concrete slabs covered by a soil cushion layer. Many of the existing galleries in Switzerland were built in the 1970s and 1980s. An accurate evaluation of their load carrying capacity is important for the decision-making on their strengthening and possible further use. Recent developments allow improving the energy absorption and thus the performance of these structures through the use of alternative cushion materials. The present paper covers a numerical investigation of the impact load carrying capacity of an existing rockfall protection gallery, which is situated below the Lopper cliff at the shore of Lake Lucerne in Switzerland. The numerical results obtained from explicit finite element analyses indicate that the gallery may not be able to perform satisfactorily if it is subjected to the maximum impact energy resulting from an extreme rockfall event with a return period of 100 years. In addition, the possibility of improving the performance of the gallery is examined through a comparison of the slab responses when covered by three different cushion materials, namely gravel, sand, or a so-called Three-Layered Absorbing System (TLAS). The comparison confirms that the performance of the gallery can be optimized by using a cushion material with a better energy absorption capacity than the original gravelly soil, which is currently in place covering the gallery.