Jämförelsestudie för tre olika metoder att beräkna genomstansning i betong
Skillnader i genomstansningskapacitet för metoderna i BBK04, EK2 och BHB
Before the European construction standards were introduced in January 2011, it was mainly themethod in BBK04 that was used for calculating punching capacity in concrete structures, and in lesscommon cases the method in BHB. The method of BBK04 is easy to use and have had the samestructure since the first was published in 1979. The Concrete handbook method (BHB) where usuallyonly used when a higher punching capacity was needed and the cross-sectional height where fixed,calculations using this method entails more work, but will in return usually give a higher capacity. Italso allows the use of shear reinforcement to increase the cross-section capacity. The method ofcalculating punching shear in EC2 differs largely from the methods of BBK04 and BHB. The methodis similar to a large extent of the so called ?alternative model? to calculate the shear capacity inBBK04.The purpose of this study is to make a comparison between the different methods, mentioned above.The study aims to find out which one of these models/methods that will provide the maximumpunching capacity and utilization. The results of the study can then be used to make a quick and fairlyassessment if a construction can withstand the same load situation that it was originally analyzed forwhen using the European construction standards.In the comparison, three different kinds of concrete qualities was used C25/35-C45/55, and fourdifferent kinds of reinforcement contents ? = 0.02 ? 0.1%, and a span of effective cross section heightsin the range d = 0.1 - 2m.The study shows that for an older concrete structure dimensioned in accordance with BKR andBBK04 it?s very likely that the utilization when recalculating it with the Eurocode will not be aproblem. This seems to apply to all concrete qualities, reinforcing contents and cross-sectional heightsused in this study. The method in EC2 provides between 20-130 % higher punching capacities. Thedifference between the two methods increases with the cross-sectional height. For effective heightsover 0.2 m the punching capacity is at least 36 % greater than what is obtained with method inBBK04. The load in EC2 is in this case 16-27 % greater than the load obtained when using BKR.Even a quite significant increase of the loads could in most cases be done.When then concrete manual method (BHB) is used and the reinforcement content of the structure isabove 0.5 % that method generally achieves better capacities or at least equal capacities compared tothe method in EC2. For low cross-sectional heights, the method in EC2 sometimes gives better valuesof capacity. It is unlikely that a structure that has been optimized with the help of BHB couldwithstand the greater loads that are achieved when using the Euro codes. This also applies to crosssections that needs shear reinforcement.