Editor’s Note

The leadoff paper in this issue, which was written by Kalkan and Graizer, examines “Coupled Tilt and Translational Ground Motion Response Spectra” for seismic analysis of structures. A complete equation of motion for a single degree-of-freedom oscillator that incorporates tilt as a secondary $P\text{-}\Delta$ effect is developed. The consequences of neglecting the effects of the tilt component of the ground motion on both elastic and inelastic spectral estimates are then investigated. The study finds that the imposed demands can be greatly underestimated if tilt motions are ignored and that structures subjected to combined translational and tilt motions exhibit asymmetric yielding and softening behavior because of amplified $P\text{-}\Delta$ effects. A frequency-domain method is developed by Takewaki to evaluate the “Earthquake Input Energy to Two Buildings Connected by Viscous Dampers.” The authors show that the input energy to the buildings and added viscous dampers can be defined as the work done by the boundary forces between the subsystems on their corresponding displacements. Additionally, the total input energy is approximately constant regardless of the quantity and location of the connecting viscous dampers. Hence, increasing the energy consumption in the dampers can lead to reducing input energy to the building structure.

A new type of mechanical damper is proposed by Cai et al. in “Cable Vibration Control with TMD-MR Damper System: Experimental Exploration.” The main feature of the new damper is the combination of the position flexibility of TMDs and the adjustability of the MR dampers. Experimental tests to examine the effectiveness of the proposed damper indicate that the addition of the damper reduces vibration by 20–30%, although tuning to achieve optimal performance is not straightforward because of cable-damper interaction. Obata and Goto present the “Development of Multidirectional Structural Testing System Applicable to Pseudodynamic Test.” The system consists of a unique three-dimensional hinge and a spatial truss-type displacement transducer. To demonstrate the ability of the system, a cyclic bidirectional load test and a corresponding pseudodynamic test are carried out on hollow circular steel cantilever columns. The tests further point to the importance of multidirectional loading in evaluating the seismic response of steel structures.

The effect on connection performance of potentially large catenary forces is examined by Khandelwal and El-Tawil in “Collapse Behavior of Steel Special Moment Resisting Frame Connections.” A calibrated micromechanical fracture model that has been validated with available test data is used in the analytical simulation study. The simulation results indicate that connection ductility and strength are adversely influenced by an increase in beam depth and an increase in the yield to ultimate strength ratio and that the beam web-to-column detail plays an important role in the connection response.

Kanvinde and Deierlein present “Finite-Element Simulation of Ductile Fracture in Reduced Section Pull-Plates Using Micromechanics-Based Fracture Models.” The void growth (VG) and stress modified critical strain (SMCS) models are applied to a series of twelve pull-plate tests that represent net or reduced section conditions in bolted and reduced beam section connections. The models are observed to predict ductile fracture initiation more accurately than basic longitudinal strain criteria. Discrepancies in fracture prediction were found to be larger for HPS70W than A572 steel, and the SMCS model was found to be generally more accurate than the VG model.

Critical web limit states in unstiffened, unbraced steel beams used in bridge falsework construction are the subject of the paper “Web Yielding, Crippling, and Lateral Buckling under Post Loading” by Carden et al. Current AISC guidelines were found to be adequate for predicting web yielding and crippling capacity, although a 1:1 stress gradient through the flange and fillet of the web is determined to be more appropriate and conservative for web yielding than the 2.5:1 assumed in the AISC provisions. The effect of accidental eccentricity between the flange and post is not significant if limited to three times the web thickness. In “Flexural Strength for General Lateral–Torsional Buckling,” Xian-Xing Li investigates the buckling behavior of general prismatic and tapered steel members with doubly and singly symmetric sections. A taper coefficient is introduced that synthetically reflects the effect of member taper on later-torsional behavior. Formulas for calculating lateral-torsional buckling moments of prismatic and tapered members under general moment diagrams are developed by introducing modification factors similar to AISC methodology. Finally, the inelastic buckling capacity equations are developed by using a straight-line transition from the elastic buckling curve to the section strength.

Results from a combined experimental-analytical study on steel beams with adhesively bonded FRP strips are used by Sebastian and Luke to deduce the “Interface Failure Mechanics of Elastically (Advanced Composite) Reinforced Steel Members.” The elastic nature of the strips leads to high interface stresses. For elastic strips bonded in tension, failure occurred by buckling of the steel member and brittle separation of the strip; the zone of highest shear bond stress was either an elastic region near strip curtailment or an elastic-plastic zone of varying moment; and for strips used in compression, failure was caused initially by buckling of the deliberately unbonded length of the strip and subsequently by brittle separation.

The transfer of forces across the interface between steel bars and concrete is investigated by Harajli in “Numerical Bond Analysis Using Experimentally Derived Local Bond Laws: A Powerful Method for Evaluating the Bond Strength of Steel Bars.” The bond characteristics of fully developed or spliced bars in tension under different design and strength variables are presented. Experimentally based local bond laws are integrated into a numerical analysis technique to develop relationships that are applicable to normal strength, high strength, fiber-reinforced concrete, and concrete confined with fiber-reinforced polymer laminates. The accuracy of the numerical methodology is validated with experimental data. Voon and Ingham develop a “Design Expression for the In-Plane Shear Strength of Reinforced Concrete Masonry,” with particular emphasis on the interaction between flexural ductility and masonry shear strength. It is found that the current NEHRP shear equation does not address masonry shear strength within plastic hinge regions, hence limiting its use in seismic regions. Further, it is established that the current New Zealand Standard 4230:2004, which essentially adopted a conservative version of the formulation proposed by the writers, provides a significantly improved prediction of shear strength.

Bäckström and Kliger investigate the behavior of “Partition Walls and Their Restraining Effect on Warp in Built-In Wall Studs” by focusing on the propensity of studs to warp at different moisture content. Full-scale walls comprising Norway spruce studs and gypsum wallboard cladding were tested under in-service conditions. It is concluded that erecting a wall with double-sided gypsum wallboard cladding reduces the difference in twist in timber studs significantly compared with unrestrained studs, whereas single-sided cladding is very sensitive to differences in moisture content when it comes to crook, and the restraining effect is only marginally beneficial.

“Load Carrying Capacity of Timber–Concrete Joints with Dowel-Type Fasteners” is analyzed by Dias et al. Shear tests on various timber species, concrete mixtures, and fasteners were performed; and the observed response was compared with predictions obtained from three different analytical models. The model that is based on the assumption of elastic perfectly plastic behavior of concrete provides the closest comparison with load-carrying capacity, whereas the best statistical correlations were obtained with the model that assumed linear elastic behavior with crushing.

A series of analyses are presented by Palermo and Vecchio in “Simulation of Cyclically Loaded Concrete Structures Based on the Finite-Element Method” to demonstrate that quick and reliable simulation of nonlinear behavior is possible by employing simple modeling techniques. The simplification included the use of low-powered rectangular membrane elements and smeared material properties. Comparison of simulated responses with observed behaviors such as peak strength, ductility, energy dissipation, and failure mechanism validate the proposed methodology.

“Rotational Spring Analogy for Buckling Analysis,” as outlined by Izzuddin, permits geometric stiffness for a large class of structural problems to be formulated by using common notions from linear structural analysis. The analogy is initially formulated to deal with the deflecting trajectory of the axial force in axially loaded members and is then generalized to deal with varying axial force, distributed radial load, and axial members that bend. Application of the proposed analogy to single degree-of-freedom, multi degree-of-freedom and continuous systems is demonstrated with examples.

Concluding this issue is a discussion item by Scarino on “Nonconstrained Flagpole Design Formula.” The discusser raises concern about the proposed formula, since most existing methods—including the proposed one—ignore factors such as three-dimensional effects, shape of posts, and friction. Moreover, different assumed distributions of soil resistance give widely varying results. Hence, the value of a new approach that does not necessarily overcome some deficiencies of previous methods is debatable. In providing closure to the subject, the original writer acknowledges the issues raised by the discusser indicating that the intent of the technical note was to provide an alternative or complementary procedure to the existing ICBO formula.