Euro-SiBRAM’2002 Prague, June 24 to 26, 2002, Czech Republic
Session 8 - Comment
Serviceability Assessment – From LRFD to SBRA
In 1986 the ASCE Ad Hoc Committee on Serviceability Research (Committee on Research of the Structural Division) published a paper “Structural Serviceability: A Critical Appraisal and Research Needs” [1]. This paper summarized the results of evaluation of the serviceability assessment according to the LRFD method and corresponding codes. It was stated that “Serviceability limit states in building structures are conditions in which the functions of the building are disrupted during normal use by excessive deformation, motion, or deterioration. As standards evolve toward probability-based limit states design methods, serviceability issues are expected to become an increasingly important design consideration”.
The resulting recommendations presented in the mentioned paper are (quotation):
“Design Loads and Load Combinations: Consistent probability-based loads and load combinations should be developed for checking applicable serviceability limit states.
Structural Load Modeling: Simple load models that can be used for analyzing creep, deferential settlement, and cracking should be developed”.
Responding to these recommendations, the authors of the SBRA method (documented in the textbook [2]) gave a special attention to the development of a qualitatively new probabilistic concept applicable for safety, as well as for serviceability and durability assessment of structures. The SBRA method is based on expressing all input variables by non-parametric distributions (e.g., bounded histograms), load effects are expressed by “Load Effects Duration Curves”, the limiting values are expressed by Reference Values, RV, the reliability function is analyzed using Monte Carlo simulation in order to calculate the probability of failure, and the reliability is expressed by comparing the obtained probability of failure Pf and target probability Pd. (contained already in codes, see e.g. Czech Code CSN 73 1401-1998, allowing for application the probabilistic simulation-based SBRA method [2]). Using SBRA, same approach is applied in case of safety, serviceability and durability assessment as recommended in paper [1]. Same loading effects, however different target probabilities are applied in case of safety and serviceability assessment.
Numerous serviceability assessment examples, using probabilistic SBRA method and corresponding computer programs M-Star and AntHill, are contained in three textbooks and in papers all listed on the SBRA web site www.itam,.cas.cz/SBRA.
Referring to the more than ten years long existence of the SBRA method, the probabilistic serviceability assessment according to the SBRA method [2] indicates that this approach can be considered as one of the alternatives meeting the suggestions and recommendations outlined in the paper published by the Ad Hoc ASCE Committee in 1986 [1].
[1] Journal. of Str. Div. ASCE, Vol. 112, No.12, December, 1986, Paper No. 21106,
[2] Simulation-based Reliability Assessment for Str. Eng. (1995), CRC Press, Inc., Florida