Editor’s Note

A two-part paper by Nie, Bai, and Csai examining the response of a “New Connection System for Confined Concrete Columns and Beams” opens this issue of the Journal. In the proposed connection system for a concrete-filled steel tube composite column and reinforced concrete beams, the steel tube is interrupted while the reinforced concrete beams are continuous in the joint zone. Multiple lateral hoops that constitute the stiffening ring are provided to confine the core concrete in the connection zone. In the first part of the paper, the authors report findings from axial compression experiments on six specimens and reversed cyclic loading tests on three interior column specimens and three corner column specimens. The experiments confirm that effective confinement can be achieved by the stiffening ring and adequate axial bearing capacity can be obtained, as well as a superior ductility and energy dissipation capacity.

In the companion paper, the bearing strength of composite columns and the joint in axial compression is obtained based on the stress-and-strain analyses. The critical volume fraction of transverse stirrups of the composite column and the effective confining radius in the stiffening ring are proposed, based on the thick cylinder model with the assumption of a plane stress state. Reasonable estimates of the stress distribution in confining concrete and the bearing strength of the confined concrete are obtained. The nondegrading Clough hysteresis model is used to simulate the hysteresis loops of the specimens under cyclic loading. The results of the theoretical modeling are shown to be in good agreement with experimental observations.

Full-scale laboratory tests were carried out by Das et al. to investigate the “Effect of Monotonic and Cyclic Bending Deformations on NPS12 Wrinkled Steel Pipeline.” Under monotonically increasing bending loads and deformations, the test specimens exhibited ability to undergo significant plastic deformation and did not fail in fracture (leak or rupture in the pipe wall). However, when subjected to elastic-plastic strain reversals due to cyclic bending deformations, fracture developed at the wrinkle. The study concludes that the current pipeline design method using wrinkle limit strain is conservative, and presents test procedures and fracture limit strain values obtained from the full-scale tests.

A comprehensive study is carried out by Yakut and Yilmaz to investigate the correlation between the maximum interstory drift demand of low- to mid-rise concrete frame structures and a number of widely used ground motion intensity parameters in “Correlation of Deformation Demands with Ground Motion Intensity.” The ground motion database was compiled from recorded accelerograms to represent a wide range of seismic forces that impose varying degrees of elastic as well as inelastic response of the frames. Results indicate that spectrum intensity parameters, having the strongest correlation, are superior to other parameters, such as peak ground velocity (PGV), peak ground acceleration (PGA), and spectral acceleration.

In “Hybrid Simulation with Improved Operator-Splitting Integration Using Experimental Tangent Stiffness Matrix Estimation,” Ahmadizadeh and Mosqueda develop a new method for online estimation of the tangent stiffness that only utilizes readily available force and displacement measurements. The proposed scheme is shown to improve the accuracy of a hybrid simulation with a highly nonlinear experimental substructure, and its application and effectiveness are demonstrated through hybrid simulations of multi-degree-of-freedom experimental substructures.

The “Behavior of RC Beams Subjected to High Rates of Concentrated Loading” is investigated by Cotsovos et al. using commercial finite-element software. The effects of the applied loading rate on the exhibited structural response are primarily attributed to the inertia forces that develop within the beam, and not to the rate sensitivity of the mechanical characteristics of the materials. The results obtained from numerical simulations are shown to correlate closely with the experimental observation. A simple design model is proposed that is able to quantify the observed increase in load-carrying capacity exhibited by RC beams with increasing rates of applied loading.

A “Statistical Model of Crowd Jumping Loads” is developed by Sim et al. that realistically captures the randomness in the jumping process. The model is based on a large database of experimentally measured individual jumping loads. Key parameters are introduced to characterize the timing and shape of the jumping impulses, and probability distribution functions are fitted to these parameters. A realistic ensemble of individual jumping loads is generated through repeated sampling that can be used to assess the dynamic response of assembly structures excited by rhythmic motion of large crowds moving in time to a musical beat. The model is suitable for use in Monte Carlo simulations based on the fitted probability distribution functions, in which the load model is applied to simple structural models, and representative structural responses are deduced.

A flexible layering scheme incorporating the transverse shear deformation is presented by Wang and Teng in “Finite-Element Analysis of Reinforced Concrete Flat Plate Structures by Layered Shell Element.” A 3D hypoelastic material model is implemented to model reinforced concrete, and important effects such as tension softening and stiffening, aggregate interlock, and compression softening in multidirectionally cracked reinforced concrete are considered. The influence of the distribution of transverse shear strain on the punching shear failure mode of flat plate structures is identified.

Dharma and Tan present findings from “Experimental and Numerical Investigation on Ductility of Composite Beams in Hogging Moment Regions under Fire Conditions.” Four composite beams with deck slabs representing the internal joint of a continuous beam were first heated to a certain temperature and then tested to failure under a static point load. The test results provided a basis to calibrate and validate a finite-element model, which was then used in numerical parametric studies to examine the influence of several parameters on the moment-rotation response and rotational capacity of the beams at elevated temperatures.

The variability of wind effects estimates based on tests conducted at six wind tunnel laboratories is presented by Fritz et al. in “International Comparison of Wind Tunnel Estimates of Wind Effects on Low-Rise Buildings: Test-Related Uncertainties.” Based on pressure tap measurements made on wind tunnel models of four buildings, comparisons were made between estimated 50th percentiles of the peak positive moments in a frame section near the knee joint and peak pressure coefficients of a roof tap nearest a building corner. Modeling of suburban terrain is stated to contribute significantly to the variability. Other factors include eave height, wind direction, and frame location within the building. The coefficients of variation were about 10 to 40%.