Structural evaluation of concrete buildings considering bearing capacity, load combinations, and safety regulations : Analyzing the difference design methods used in old Swedish Norms “Statliga betongbestämmelser 1949, BBK79, Eurocode”
Abstract: Design regulations for concrete structures differ through time and place. Throughout the years design regulations have been changed and adjusted for improvement and to ensure safe and secured structures. In Sweden, several design codes and regulations were published from time to time, regulations that needed to be followed when designing structures for different purposes. Some of the design codes that were used during the 20th century were BABS (Byggnadsstyrelsens anvisningar till byggnadsstagdan, 1947-1968), SBN (Svensk Byggnom, 1968-1989), NR (Nybyggnadsregler, 1989-1994), and BKR (Boverkets Konstruktionsregler, 1994-2010) used for the consideration of load combinations on different structures. For design methods and theories “Statliga betongbestämmelser of year 1949” and “BBK 79, Nya betongbestämmelser” were published and used at that time. With development in the construction industry, new laws and regulations were issued to bear with today’s high standards and safety regulation. The Eurocodes were released to consider all new improvements and adjustments as well as facilitate trade between the European countries participating in the European standardization work, CEN. The Eurocodes were set as a base reference for several design purposes among the Europe area. The thesis was performed at the engineering consultancy company WSP to collect and assemble knowledge about the old norms and calculation methods and compare them with Eurocode and identify similarities and differences. The knowledge on the old and new codes was used to study two case studies. Case studies 1 and 2 are both office building structures where high and varying loads occur. Case study 1, built in 1954, consists of a 6-floor story building with the upper floors used as offices and the ground floor as commercial shops. Case study 2, built in 1961, consists of an 8-floor story building with 6 upper floors for office use and ground floors for commercial shops. From each case study one upper floor was chosen for the design and a continuous beam was designed for bending and shear. The design of columns was done on the last column which lays on the foundation of each building. The design calculations are made for beams and columns starting with “Statliga Betongsbestämmelser” as a reference code and the area of steel obtained from the dimensioning are kept the same in the design using “BBK79” and “Eurocode”. The variable difference are the load combinations that differ among the three codes BABS, SBN80 and Eurocode and the change in the design method which resulted in the change in the utilization ratio. The results were similar for both case studies which shows the consistency in the calculations. The total load q increased by 10% in SBN and 41% increase in Eurocode compared to BABS. This showed the change in safety standards by raising the total load on a structure by the use of partial coefficients. For beams in case 1, the utilization for bending was 98% of its capacity when designing using BABS with Statliga Betongsbestämmelser. This value decreased to 64% while using SBN80 with BBK79. In Eurocode the ratio of utilization increased to a value of 75%. Moreover, the utilization of columns in bending using BABS with Statliga betongbestämmelser showed a ratio of 84% and then decreased to 47% in SBN80 with BBK79 and increased somewhat to 51% in Eurocode. Regarding shear design all three norms were critical and strict in the method of design. It showed the importance and sensitivity of beams against shear. For BABS 67% of shear utilization was obtained and this value decreased to 54% in SBN and 52% in Eurocode. This shows the change in the method of designing using consecutive codes at three different times. The change concerns new concepts in the safety regulations from applying the safety on the material in the old norms to increasing the load and allow more usage of the material in the more recent codes. BBK79 and Eurocode share similarities in the design procedures and the use of the partial coefficient method. The increase of utilization in the Eurocode is due to the higher partial coefficient values and the modified load combination equations that resulted in a higher possible load than that from BBK79 but with almost the same load-bearing capacity in both BBK79 and Eurocode.
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