Stability of Concrete Moment Resisting Frames in View of Current Codes Requirements

In this study, the different approaches currently followed by design codes to assess the stability of buildings utilizing concrete moment resisting frames structural system are evaluated. For such purpose, a parametric study was performed. It involved analyzing group of concrete moment resisting frames having different slenderness ratios (height/width ratios), designed for different lateral loads to vertical loads ratios and constructed using ordinary reinforced concrete and high strength concrete for stability check and overall buckling using code approaches and computer buckling analysis. The objectives were to examine the influence of such parameters that directly linked to frames’ lateral stiffness on the buildings’ stability and evaluates the code approach in view of buckling analysis results. Based on this study, it was concluded that, the most susceptible buildings to instability and magnification of second order effects are buildings having high aspect ratios (height/width ratio), having low lateral to vertical loads ratio and utilizing construction materials of high strength. In addition, the study showed that the instability limits imposed by codes are mainly mathematical to ensure reliable analysis not a physical ones and that they are in general conservative. Also, it has been shown that the upper limit set by one of the codes that second order moment for structural elements should be limited to 1.4 the first order moment is not justified, instead, the overall story check is more reliable.

• Mahmoud A. Mahmoud
• Ashraf Osman

• Buckling
• lateral stability
• p-delta
• second order.

[1] MacGregor, J. G.; and Hage, S. E., “Stability Analysis and Design of Concrete Frames,” Proceedings, ASCE, V. 103, No. ST 10, Oct. 1977.
[2] Ford, J. S.; Chang, D. C.; and Breen, J. E., “Design Indications from Tests od Unbraced Multipanel Concrete Frames,” Concrete International, V. 3, No. 3, Mare. 1981, pp. 37-47.
[3] MacGregor, J. G.; Breen, J. E.; and Pfrang, E. O., “Design of Slender Concrete Columns,” ACI Journal, Proceedings V.67, No. 1, Jan. 1970, pp. 6-28.
[4] Grossman, J. S., “Slender Concrete Structures—The New Edge,” ACI Structural Journal, V. 87, No. 1, Jan. – Feb. 1990, pp. 39-52.
[5] Hoenderkamp, J. C. D., “Critical Loads of Lateral Load Resisting Structures for Tall Buildings,” The structural design of tall buildings, Struc. Design Tall Build. 11, pp. 221-232, 2002.
[6] ACI 318 (2005), “Building Code Requirements for Structural Concrete (ACI 318M-05) and Commentary,” American Concrete Institute, Farmington Hills, MI.
[7] ACI 318 (2008), “Building Code Requirements for Structural Concrete (ACI 318M-08) and Commentary,” American Concrete Institute, Farmington Hills, MI.
[8] ASCE 7 (2005), “Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-05),” American Society of Civil Engineers, Reston, VA.
[9] ASCE 7 (2010), “Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10),” American Society of Civil Engineers, Reston, VA.
[10] Eurocode 8 (2004), “Design of structures for earthquake resistance-part1: General rules, seismic actions and rules for buildings, EN 1998-1: 2004,” European Committee for Standardization, Brussels, Belgium.
[11] Computers and Structures (2015), “ETABS: Integrated analysis, design and drafting of building systems.” Berkeley, CA.