Portland State University. Department of Engineering and Applied Science
Franz N. Rad
Date of Publication
Master of Science (M.S.) in Applied Science
Reinforced concrete construction, Structural frames
1 online resource, digitized manuscript. Color/BW photographs
The main objective of this study was to determine whether Limit Design could be applied to low-rise unbraced concrete frames. The investigation was carried out both analytically and experimentally.
In the analytical part, two mathematical models were used to determine the behavior of unbraced frames. The first method used a nonlinear computer program, which takes into account the material and geometric nonlinearities of concrete frames. Several cases of frames with different reinforcement ratios and under different beam to column load ratios were investigated. For each frame the gravity loads were increased proportionately to 3/4 of the ultimate frame capacity. Then, lateral load was applied to failure while keeping the beam and column loads constant.
The second mathematical model solved for the frame stability equation by assuming elasto-plastic moment curvature relationships for members. Also, the stability solution was carried out by reducing the frame to a column attached to a linear spring.
In the experimental part, two frames were designed for the same loading conditions but by two different methods; and were tested to failure. Frame USD-1 was designed by the Ultimate Strength Design, while Frame LD-1 by a Limit Design method. The columns were 21-in high while the beam was 84-in long. The loading procedure consisted of proportionately loading the beam and columns up to the design load, and then applying the lateral load to failure.
The computer study and the stability model solution showed that frames subjected to low column thrusts remained in stable equilibrium until two plastic hinges form, thus constituting a mechanism. The two experimental frames remained in stable equilibrium until two plastic hinges formed in the beams. The ultimate lateral loads of Frames USD-1 and LD-1 exceeded the design lateral load by 66% and 33%, respectively.
Based on this investigation, it appears that Limit Design may be used for low-rise unbraced reinforced concrete structures.
Gavin, Thomas Joseph, "Limit Design of Unbraced Reinforced Concrete Frames" (1977). Dissertations and Theses. Paper 2562.