Editor’s Note

A “Simple Rational Model for Reinforced Concrete Subjected to Seismic Shear” to predict the load-deformation response of reinforced concrete subjected to reversed cyclic shear is proposed by Gérin and Adebar. Average strains due to crack displacements are separated from concrete strains using simplified assumptions resulting in a model that can account for two sets of cracks that are open when the applied shear reverses direction. With the separation of strains due to crack displacements, simple material stress-strain relationships for concrete and reinforcement are sufficient to capture the complexities of cyclic response. The model accurately predicts underlying mechanisms such as accumulation of plastic strain in reinforcement, which defines the degree of pinching in the hysteretic response of reinforced concrete subjected to cyclic shear.

In “Reconsideration of Seismic Performance and Design of Beam-Column Joints of Earthquake-Resistant Reinforced Concrete Frames.” Zhou reevaluates observations from past experimental data of RC joints subjected to cyclic loading. It is observed that joint shear failure under cyclic loading is characterized by significant inelastic joint shear deformation. Further, joint transverse reinforcement does not have a significant influence on joint shear deformation and bond deterioration in the joints but may have significant influence on joint axial capacity under cyclic loading. Hence, the requirement for joint transverse reinforcement may be formulated by keeping the joint axial capacity larger than the column axial capacity under seismic action. It is proposed that joint shear strength be controlled by two requirements: that joint shear deformation remains elastic prior to story drift yield and that the contribution of joint shear deformation to the story drift remains constant during the inelastic seismic response of the RC frame. Results of six full-scale tests are described by Li et al. in “Effects of Axial Compression Load and Eccentricity on Seismic Behavior of Nonseismically Detailed Interior Beam-Wide Column Joints.” Varying axial compression loads as well as quasistatic cyclic loading simulating earthquake actions is applied and the overall performance of each test assembly is examined in terms of lateral load capacity, drift, stiffness, energy dissipation capacity, and joint shear strength. All the specimens failed at the joint panel with gradual strength deterioration. It is concluded that special reinforced-concrete interior beam-wide column joints with nonseismic detailing possesses inherent ductility for adequate response to unexpected moderate earthquakes.

An experimental study to investigate the performance of “Steel Plate Shear Walls with Various Infill Plate Designs” is carried out by Choi and Park. The test parameters were the connection method between the boundary frame and the infill plate (welded connection versus bolted connection), length of the welded connection (full connection versus partial connection), and opening in the infill plate (solid wall versus coupled wall). Regardless of the infill plate design, the steel plate wall specimens exhibited excellent strength, deformation capacity, and energy dissipation capacity, although the walls with bolt-connected infill plates exhibited a slightly lower deformation capacity. This result indicates that for architectural reasons and enhancement of constructability, various infill plate designs can be used in practice without a significant reduction in the structural capacity of the steel plate walls.

Martinez-Saucedo and Packer propose “Static Design Recommendations for Slotted End HSS Connections in Tension” based on a comprehensive review and analysis of published data. A new procedure for determining the capacity of such connections in tension is presented, and it is shown to be a significant improvement over current international design provisions. Moreover, it is also applicable to elliptical, square, and rectangular hollow sections. A model to account for shear lag is also presented and good correlation is obtained with existing experimental data. In “Tests and Design of Aluminum Tubular Sections Subjected to Concentrated Bearing Load” Zhou et al. present results from a series of web bearing tests on specimens fabricated by extrusion using 6061-T6 heat-treated aluminum alloy. The tests were carried out under end and interior loading conditions and closely simulated the support condition of the floor joist members seated on solid foundation. It is shown that the design strengths predicted by the American Aluminum Design Manual and European Code are either quite conservative or nonconservative. Current design rules are modified to predict the web-bearing strength and it is shown that the design strengths calculated using the modified web-bearing design rules are generally conservative and agree well with the experimental results.

Duarte and Ji investigate the “Action of Individual Bouncing on Structures” including the load generated and its effect on the dynamic response the structure. A simply supported beam is used as a supporting structure and 433 tests were conducted by varying the bouncing frequency from $0.4\text{to}3.2\mathrm{Hz}$ to determine the load factors of individual bouncing loads. Dynamic load factors are determined based on the measurements and the assumption that the dynamic responses induced by the sum of harmonic functions are at discrete loading frequencies. The proposed load model is validated by comparing the predicted responses and measurements on another beam. Human-structure interaction tests for an individual bouncing are also conducted and it is found that a bouncing person interacts with the test rig, but the degree of the human structure interaction is less significant than that between a standing person and the rig.

A study of “Low-Frequency Variations of Force Coefficients on Square Cylinders with Sharp and Rounded Corners” is carried out by Mola et al. to explore and quantify low-frequency variations of the aerodynamic forces on lighting poles. The results show that low-frequency components are a basic aspect of the flow over finite length cylinders and are associated with the three-dimensional flow characteristics near the free end of the cylinder. This is related to the loss of synchronization of the vortex shedding which, in turn, results in variations of the mean drag coefficient along the cylinder. These variations are more significant in the case of cylinders with sharp corners than rounded corners. Such variations should be carefully considered in the design for both static and dynamic wind loading on lighting poles.

The evaluation of the mean annual frequency of exceeding a limit state is presented by Rizzano and Tolone in “Seismic Assessment of Existing RC Frames: Probabilistic Approach.” Using the approach developed by Jalayer and Cornell for the SAC/FEMA project, the methodology accounts for the uncertainties involved in the seismic response evaluation of structures. The procedure is validated using experimental data from three full-scale frames (bare frame, frame with brick infilled walls, and a frame with infilled walls reinforced with shotcrete) tested pseudodynamically at the ELSA Laboratory in Ispra, Italy.

The “Integrated Design of Controlled Linear Structural Systems” based on simultaneous optimization of controlled structures is presented by Cimellaro et al. A procedure is developed using a two-stage approach, beginning with the design of an optimal control system using a linear quadratic regulator (LQR) algorithm followed by redesign using an optimization procedure to match the performance of the controlled system obtained in the initial design. A linear single-degree-of-freedom (DOF) steel portal frame and a linear 9-DOF shear-type structure are used as examples to illustrate the feasibility of the proposed approach that reduces the structural weight of buildings by incorporating active or passive control elements while preserving the performance objectives.

Pakzad and Fenves present findings from data collected from 64 sensor nodes on the main-span and south tower of the Golden Gate Bridge in “Statistical Analysis of Vibration Modes of a Suspension Bridge Using Spatially Dense Wireless Sensor Network.” Analysis of the vibration data using power spectral densities and peak picking provide approximate estimates of vibration modes with minimal computation. Statistical analyses of the multiple realizations provide distributions of the vibration frequencies, damping ratios, and mode shapes, with 95% confidence intervals. Analysis of the ambient vibration data and system identification results demonstrate that high spatial and temporal sensing using the wireless sensor network give a high resolution and confidence in the identified vibration modes.

The “Dynamics of a Class of Horizontal Setback Buildings with Flexible Floor Diaphragm” is evaluated by Basu with the objective of providing a convenient modeling/design procedure to minimize the adverse effect of in-plane floor flexibility. The existence of such a class requires proportional eigenvalue problems of all the constituting frames regardless of the floor properties. A step-by-step proportioning procedure, in the presence of nonrectangular joint region, is outlined such that “nearly” rigid floor modes exist and the participation of the flexible floor modes under spatially uniform ground motion is close to zero.

The issue concludes with a discussion by Harris on the paper “Conceptual Seismic Design of Regular Frames Based on the Concept of Uniform Damage” by Park and Medina. The discusser seeks to clarify the design lateral load distribution used to determine the initial elastic member strengths. The question being raised is whether the method requires two independent distributions: one for stiffness (to maintain the same mode shape used by authors) and another for story strength. In providing closure to the discussion, the original writers indicate that the basic premise of the paper is that a lateral stiffness distribution is given. The single-bay generic frame models used in the paper were meant to represent the global stiffness and strength characteristics of multibay moment-resisting frames. The discussers further clarify the iterative procedure to achieve the target story ductility levels.