RC frame structure strengthening by reason of insufficient concrete strength

Abstract

During the reconstruction of a university in Olomouc (Czech Republic) it was discovered that the concrete used in one load-bearing structure was of insufficient strength. The university building complex was constructed in the years [1955][1956][1957][1958][1959][1960]. It is built from a reinforced concrete skeleton. The four-storey building is founded on RC footings and continuous footing. A detailed structural investigation of the structure of the first floor determined that the strength of the used concrete varied, ranging from concrete class C3/3.5 to C12/15. The original designed concrete class was C10/13.5, while the plain reinforcement utilised according to the original design was steel with a design strength of 180 MPa. Three structural repair variants were designed based on construction surveys:• steel bandages for the columns and girders, and strengthening/supporting of the girders via steel cross-beams fitted to the bandages;• steel bandages for the columns and girders, and strengthening of the girders via prestressing tendons;• additional non-prestressed reinforcement of the structure by covering it with sprayed concrete.Based on the economic (cost), structural and technical aspects (minimising of additional load), the variant using bandages with additional external prestressing of the majority of the girders via tendons was preferred.

The Strengthening of Reinforced Concrete Structures

“…Prestressing force depends on losses due to friction (besides other things) along the trajectory. It is necessary in some cases to design a tendon with a length of about 30 m or more and a total angle of about 10 rad (radius of curvature = 0.4 m, in the case of low level of tendon stress); see [2] and Fig. 6.…”

“…It is usually necessary to develop a special solution for structural details during every extensive reconstruction, for example: the anchorage of a strand close to a construction joint -Fig. 7, [2].…”

Reconstruction of the Municipal Bath House

“…5. The corrosive harmful fumes swelled and increased their volume which caused the concrete layers to peel off [8].…”

“…More and more attention has been paid to improvements of the reinforced concrete structures because more and more structures have becoming degraded both in the Czech Republic [2], [3], [5], [9], [10] and abroad, see, for instance, [1], [4]. Various issues should be addressed when assessing, diagnosing and designing technologies and materials for redevelopment, see [6], [8]. In many cases it would be easier to demolish the degraded load-carrying structures completely and build them, using the advanced technologies and materials.…”