Geometric Parameters and Behavior Factor of Knee-Braced Steel Frames Using Nonlinear Static Pushover (NSP) Analyses

During the recent years, the new knee-braced frame (KBF) system has been interested to achieve a proper seismic behavior. Briefly introducing KBF, the present study evaluates the geometric parameters and behavior factor of multi-story knee-braced steel frames. The studied models include three-, five- and eight-story steel CBFs, EBFs and KBFs. Using linear static analyses, the present study evaluates lateral stiffness of knee-braced frames and plots their co-stiffness curves. Using co-stiffness curves, then, the best range is determined for geometric parameters of KBFs to achieve the proper stiffness. In addition, ductility-related seismic force reduction factor (Rμ), incremental resistance coefficient (RS), and behavior factor (R) are calculated for the frames using incremental nonlinear static analyses, and compared with the corresponding concentric and eccentric frames.

Analytical Analysis of Seismic Behavior of Cold-Formed Steel Frames with Strap Brace and Sheathings Plates

Cold-formed steel frames (CFS) are popular all over the world. In this study, we have investigated 112 frames with different bracing arrangements and different dimensional ratios with different thicknesses of sheathing plates under cyclic and monotonic loading using Finite Element Nonlinear Analysis. We also evaluated seismic parameters including resistance reduction factor, ductility, and force reduction factor due to ductility for all specimens. On the other hand, we calculated the seismic response modification factor for these systems. The maximum modification factor among shear wall panels with sheathing plates related to GWB (gypsum wall board) specimen with thickness of 15 mm was 5.14; among bracing specimens in bilateral bracing mode related to B sample was 3.14. The maximum amount of resistance among the specimens with bilateral (2-side) bracing systems belongs to the specimen C (2-side double X-bracing) with the dimension ratio of 2 (4.8 m × 2.4 m) and resistance of 305.60 kN and also among the shear wall panels with sheathing plates, it belongs to DFP (douglas fir plywood) with a thickness of 20 mm and resistance of 371.34 kN.

Development of Seismic Force Reduction and Displacement Amplification Factors for Autoclaved Aerated Concrete Structures

This paper addresses the development and application of a rational procedure to select the seismic force reduction factor ( R) and the displacement amplification factor ( Cd) for the design of autoclaved aerated concrete (AAC) structures. The values of R and Cd are proposed based on a combination of laboratory test results and numerical simulation. The test results are obtained from 14 AAC shear-wall specimens tested under simulated gravity and quasi-static reversed cyclic lateral loads. Analytical responses are predicted using nonlinear analysis models whose hysteretic characteristics are based on the experimentally observed responses. Using an iterative procedure, typical AAC structures are designed using successively larger trial values of the factor, R, until the structure's response (either ductility or drift) exceeds the experimentally determined capacity. A lower fractile of those critical values, modified for probable structural overstrength, is taken as a reasonable value of 3 for R. Using an analogous procedure, a reasonable value of Cd is determined as 3. These values will undoubtedly be refined based on field experience, just as they have been for other structural systems.

Probabilistic Study on Accidental Torsion of Low-Rise Buildings

A probabilistic study on accidental torsion is presented. Multistory shear systems, representative of low-rise buildings and subjected to bidirectional earthquake ground motions are considered. Ductility demands of lateral resisting elements (LREs) due to uncertainties on (1) center-of-mass locations, (2) LRE stiffness, and (3) LRE yield forces were studied. Building code recommendations on accidental torsion as well as the effects of both eccentricity and lateral-force reduction factor are assessed. Results indicate that considering one random variable in the accidental torsion problem can lead to larger ductility-demand probabilities of exceedance than using two or more variables. Individual effects of each one of the variables considered are not superimposed when all variables take place at the same time. For systems designed for torsion, ductility demands of LREs decreases for increasing eccentricities. Increments of yield forces and decrements of probabilities of exceedance due to the use of increasing values of factor β associated with the accidental eccentricity are presented.