Editor’s Note

Doerich and Rotter present the geometrically nonlinear and bifurcation “Behavior of Cylindrical Steel Shells Supported on Local Brackets,” each bracket rigidly connected to a stiff column or floor. The different failure responses of a shell of the same geometry under different analyses are investigated. In materially nonlinear analysis, plastic collapse was achieved with membrane yielding all around the bracket. By contrast, geometrically and materially nonlinear analysis showed yielding below and beside the bracket but compressive stresses above the bracket, causing buckling. The high shear stresses on the side of the bracket did not produce buckling despite attaining the yield stress, due to their rapid decay horizontally.

“Extension of the Gravity Method for 3D Cracking Analysis of Spillway Piers Including Uplift Pressures” is developed by Stefan and Léger for arbitrary sections, such as those of spillway piers. Robust algorithms using strength of materials are developed to compute the kernel of arbitrary sections, locate the neutral axis (NA), and compute the normal stress distribution considering a coupled biaxial hydromechanical interaction problem. A case study is presented on an actual spillway to illustrate the convergence of the proposed algorithms. In certain cases, a nonconverging oscillatory response for the location of the NA may result, and a heuristic approach is proposed to obtain a conservative equilibrium solution.

A study in which finite-element (FE) simulations were used is described by Kim and Vecchio in “Modeling of Shear-Critical Reinforced Concrete Structures Repaired with Fiber-Reinforced Polymer Composites.” Details are presented of the numerical techniques used to represent the RC frame, the FRP, and the bond between FRP and concrete. The FE analysis is performed by using a 2D nonlinear FE analysis program based on the disturbed stress field model. Validation studies are carried out by using data from lateral load tests of a two-story, single-span large-scale RC frame. The frame was first heavily damaged in shear and retested after repairing it with FRP wrapping. A detailed comparison is carried out between analytical and experimental results for the hysteretic response, damage mode, crack pattern, and deformation of the frame. It is concluded that reasonably accurate simulations of the behavior of FRP-repaired shear-critical structures can be achieved through FE modeling.

The effect of global second-order effects are discussed by Hellesland in “Mechanics and Slenderness Limits of Sway-Restricted Reinforced Concrete Columns.” The analysis indicates that the end moment ratios of approximate moment magnifier expressions and slenderness limits should be expressed in terms of sway-modified end moments. The author questions the rationale of providing separate slenderness limits for columns of nonsway and sway frames in the American Concrete Institute (ACI) building code requirements. Several inconsistencies in the ACI limits are highlighted with respect to their differences and the different basis on which they were derived. A new, more comprehensive limit is proposed to replace the two separate ACI expressions.

A mix design method is proposed by Pereira et al. in “Steel Fiber-Reinforced Self-Compacting Concrete: Experimental Research and Numerical Simulation” to develop cost-effective and high-performance steel fiber-reinforced self-compacting concrete (SFRSCC). The material properties, as well as the potential of SFRSCC as a structural material, are assessed through punching and flexural tests on panel prototypes. To assess the contribution of steel fibers in punching resistance, a material nonlinear analysis is carried out and the fracture parameters of the constitutive model are obtained from inverse analysis, using force-deflection relationships obtained from beam bending tests.

Findings from an “Experimental Study of Complex High-Strength Cold-Formed Cross-Shaped Steel Section” are reported by Yap and Hancock. The shape is chosen so that it has a local buckling mode, two distinct distortional buckling modes, and a flexural-torsional mode. The first distortional buckling mode has a shorter buckle half-wavelength than the other distortional mode. When compared with the existing methods, the test results indicate that at intermediate and longer specimen lengths, the interaction of local and distortional buckling modes have a significant effect on the strength of the section.

Results from testing nine full-scale W14 column specimens representing a practical range of flange and web width-to-thickness ratios is presented by Newell and Uang in “Cyclic Behavior of Steel Wide-Flange Columns Subjected to Large Drift.” The specimens were subjected to different levels of axial force demand (35, 55, and 75% of nominal axial yield strength) with lateral loading producing up to 10% story drift. No global buckling was observed in any of the test specimens. Flange local buckling was the dominant buckling mode. Specimens achieved interstory drift capacities of 0.07 to $0.09\mathrm{rad}$ due to the delay in flange local buckling resulting from the stabilizing effect provided by the stocky column web of the W14 section specimens. These findings indicate that the ASCE 41-predicted plastic rotation capacities are very conservative. The ASCE 41 criteria do not specify plastic rotation capacity at axial load ratios greater than 0.5; however, the tested specimens exhibited significant plastic rotation capacities of approximately 15 to 25 times the member yield rotation.

Wood frame structures typically rely on wood shear walls to resist seismic loads. The walls are known to exhibit highly nonlinear behavior at relatively low levels of seismic excitation, resulting in structural and nonstructural damage. Shape memory alloys (SMAs) have never been applied for use in seismic protection of wood shear walls. Findings from “Shake Table Testing of a Superelastic Shape Memory Alloy Response Modification Device in a Wood Shearwall” are reported by van de Lindt and Potts. The results from the testing were compared with those for a regular wood shear wall subjected to the same suite of ground motions. The superelastic SMA-based device is shown to significantly reduce wall displacements that in turn effectively eliminate damage to the wall.

“Performance of Light-Frame Wood Residential Construction Subjected to Earthquakes in Regions of Moderate Seismicity” is examined by Ellingwood et al. using stochastic methods to model the uncertainties in ground motion intensity and structural response. Fragility curves defining damage state probabilities as a function of ground motion intensity are developed for typical lateral force-resisting shear wall systems subjected to increasing levels of ground motion. A comparison of these fragilities with those embedded in HAZUS provides additional perspective on the damage potential for residential construction in regions of low-to-moderate seismicity.

“Dependence of Damping Correction Factors for Response Spectra on Duration and Numbers of Cycles” is investigated by Stafford et al. Generic equations are derived that may be used to estimate the spectral response over a wide range of damping ratios as a function of significant duration, both $D5–75\%$ and $D5–95\%$ , and number of cycles. Although the dependence upon these predictor variables is clear, the derived relationships cannot be directly incorporated into design codes since strong ground motion duration and number of equivalent cycles are generally not specified as part of seismic design actions.

“Seismic Response of Tall Guyed Masts to Asynchronous Multiple-Support and Vertical Ground Motions” is investigated by Faridafshin and McClure. Three existing masts with varying heights were studied numerically under the effects of three earthquake records with all three translational ground motion components. The earthquake excitation was prescribed as a displacement-controlled motion, providing the opportunity to consider the asynchronous shaking of the cable ground anchors and mast base. This effect was studied by varying the shear-wave velocity of the traveling wave corresponding to different degrees of soil stiffness and observing the general trends of selected response indicators. More severe structural response was obtained for softer soil conditions, and the tallest $\left(607\mathrm{m}\right)$ mast showed sensitivity even for relatively stiff soils. Structural damping and the vertical component of ground motion were also found to significantly affect the response.

ASCE 7–05 states that “it is not likely that the 500-year event is the actual speed at which engineered structures are expected to fail” due to resistance factors in materials, conservative design procedures that do not always analyze all load capacities, and lack of a precise definition of “failure.” In “Low-Rise Steel Structures under Directional Winds: Mean Recurrence Interval of Failure,” Duthinh et al. propose a working definition of failure for steel structures using nonlinear FE analysis. A methodology is proposed for estimating the MRI of failure under wind loads that accounts in a detailed and rigorous manner for nonlinear structural behavior and for the directionality of the wind speeds and the aerodynamic effects.

In “Experimental and Numerical Analysis of a Glass-to-Steel Joint,” Amadio et al. investigate the tensile strength of a glass pane with holes. Fifty experimental tests were conducted on a series of glass panes made of heat-strengthened and tempered glass with different positions of the holes. Interpolation curves are proposed to predict the average failure load based on the distance between the hole and the pane edge. Experimental results are compared with FE-based simulations, and a simple design procedure for glass-to-steel joints is proposed based on the evaluation of the stress intensity factor.

The issue concludes with two discussions on the paper “Inelastic Buckling of Reinforced Bars” by Bae et al., which was published in February 2005. In the first discussion, Gil-Martín et al. seek clarification of the details on how the initial eccentricity was imposed and on the actual boundary conditions at the gripping ends of the bars. They contend that initial imperfection does not influence buckling behavior for fixed-fixed end conditions. Also raised are issues related to approximations introduced by the writers in estimating axial strains and in ignoring the differences in compression and tension when resorting to engineering stress and strain. In the second discussion, Rodriguez seeks clarification on the definition of the onset of bar buckling used by the authors. The discusser also questions the validity of applying monotonic test data to compare the response of reinforcing bars in a reinforced concrete column subjected to cyclic lateral loads.

In their closure, Bae et al. disagree with the contention that initial eccentricity does not affect buckling response and present additional results to demonstrate their experimental findings. In response to some of the modeling issues, the authors state that simplifying assumptions in the development of their model are justified and valid in the context of engineering design. They also indicate that the use of natural coordinates in specifying uniaxial stress-strain behavior may be unnecessary for large $L∕d$ ratios where buckling and transverse displacement will dominate the response.