Euro-SiBRAM’2002 Prague, June 24 to 26, 2002, Czech Republic
Session 8
Reliability assessment of a steel column according to SBRA method and ÈSN 73 1401
The subject of the paper is the application of the SBRA method [0] in case of the design and reliability assessment of steal industrial building. Special attention is given to the assessment of a steel column exposed to several mutually uncorrelated loadings such wind, snow, crane and dead load.
The difference in the results and the
procedures obtained by the design according to the method SBRA (see
ÈSN 73 1401 1998 – Appendix A) and according to the code
ÈSN
73 1401-1998 is evaluated and discussed.
Fig.1: Scheme of the steel hall
Input variables
The webs are made from welded section with constant height, steel S235 is used, elastic modulus E = 210000 MPa.
The construction is exposed to the dead load, snow load, wind loads, where we consider the wind direction from the left as well as from the right side of the building. The crane loads are considered by horizontal and vertical acting. The horizontal crane force occures only in case, when the vertical crane force is not equal zero.
Assessment
The statically indeterminate construction is solved with the statical method, when we look for statically indeterminate force Xi ( for every single state of loading ) corresponding to the horizontal force acting at the bearing point of the roof girder. The resultant force X is calculated as sum of the individual forces Xi determined for the single states of loading.
The internal forces are calculated for the released left column at the characteristic sections. The buckling of the latticed column is upright to the substantial as well as upright to the intangible axis considered.
Fig. 2: Charactesistic sections
Fig. 3: Buckling of the column
Results
Using the Partial Factors method, the reliability assessment can be written in the form:
NSd is less than Nb,Rd , where NSd is the axial force in the internal shaft of the latticed column and Nb,Rd is the resistance of the compressed bar.
The required cross-sectional area of the internal shaft is 12 000 mm2.
Using SBRA method, the reliability assessment is determined by comparing the probability of failure of the bar and the assignet target probability.
The required cross-sectional area of the internal shaft is 10 800 mm2.
Observations:
( a ) By comparing both applied methods, it can be concludet that SBRA method leads in investigated situations to non negligable material savings mainly due to more consistent load effects combination analysis.
( b ) The resulting response of the structure to the loadings and the resistance considered in the SBRA approach allow for better understanding of the actual behavior and reliability of the structure.
( c ) The SBRA method makes the load effects combination analysis simple, does not require determination of extreme „design“ values of internal forces ( as it is the case in Partial Factors design ) and allows for direct calculation of the probability of failure.
References
[0] Marek p., Gustar M., and Anagnos T. (1995). Simulation based reliability assessment for structural engineers. CRC Press, Inc, Boca Raton, Florida.
[1] Gere, J.M., Timoshenko, s.p. Mechanics of Materials, 3rd Ed., solutions manual. PWS-KENT Publishing Company, Boston, 1990.
[2] Marek, P., Guštar, M. a Bathon, L.: Tragwerksbemessung. Von deterministischen zu probabilistischen Verfahren. Academia, Praha 1998.
[3] Marek, P., Brozzetti, J., Guštar, M.: Probabilistic Assessment of Structures using Monte Carlo Simulation. Background, Exercises and Software. Institut of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Praha, 2001.