Optimizing precast structural elements

Options provided by a service-life design

Fig.1 Example of a tunnel built of tubbing segments (left), position of the splash fill in a cooling tower (center) and the example of a precast concrete beams of a hall construction(right).

Fig.1b

Fig.1c

Fig. 2 Open storage building used as an example (left) and the selected requirements for the parameter configuration of the service-life design (right).

Fig.2b

Fig. 3 Reliability of the component related to the limit state (left) and the probability of failure subject to the service life for the parameter study „Var. I“.

Fig.3b

Fig. 4 Limit-state related reliability of the component depending on the service life for the parameter configuration “concrete technology”.

Fig. 5 Limit-state related reliability of the component
depending on the service life for the parameter configuration
“concrete cover“.

Fig. 6 Example of a precast concrete bridge: pedestrian and bicycle overpass near Möhrendorf (Germany), pre-stressed precast structural elements with a single span of 30 m and a clamped mid-span column.

Fig. 7 Cross section of a bridge built of structural elements topped with in-situ concrete used as an example (left) and the selected requirements for the parameter configuration of the service-life design (right).

Fig.7b

Fig. 8 Limit-state related reliability of the structural element depending on the service life for the parameter configuration for optimizing a bridge superstructure.

Fig. 9 Comparison of the distribution functions of the chloride migration coefficient for a cast-in-situ concrete structural element and for a precast component.

In Germany, it is so far common to dimension and manufacture precast structural elements of reinforced concrete or pre-stressed concrete in respect of the structural behavior, the serviceability as well as the durability according to approaches of German standard DIN 1045-1 [1]. Another possibility for optimizing precast structural elements is provided by probalistic design approaches allowing to determine a technical lifespan or a certain resistance to the existing environmental conditions by defining a relevant limit state or by a defined reliability level.

Introduction

For planning and design of precast structural elements of reinforced concrete or pre-stressed concrete being optimized in terms of the cross section several design and pre-dimensioning facilities are available considering above all structural issues having regard to the verification of the limit state in respect of the structural behavior and serviceability as well as fire protection requirements. With growing environmental awareness and the request for “sustainable construction”, the demands on durability gain in importance too as well as the question about an examination of...