Eric M. Hines

FORCE-DISPLACEMENT CHARACTERIZATION OF WELL-CONFINED BRIDGE PIERS

This paper outlines an approach to estimating the horizontal force-displacement response of well-confined reinforced concrete bridge piers. Special attention is paid to the hollow rectangular piers designed to support 3 new toll bridges in the San Francisco Bay Area. This approach accurately assesses a piers elastic displacement, its spread of plasticity and plastic displacement, and its shear displacement for most ductility levels. The shear transfer mechanism inside a piers plastic hinge region is key to this assessment. This mechanism appears as a fanning crack pattern and results in concentrated compression strains at the base of a pier. These concentrated strains oppose the traditional notion of curvature that assumes plane sections remain plane. The assumption that there is a linear distribution of plastic curvatures inside the plastic hinge region, however, largely overcomes the problem of relating plastic curvatures to plastic rotations, both experimentally and analytically. At most levels of ductility, the mean difference between analytical assessments of the spread of plasticity and results from 12 large-scale structural tests is 16% with a 12% coefficient of variation.

PREDICTION AND MITIGATION OF BUILDING FLOOR VIBRATIONS USING A BLOCKING FLOOR

AbstractBuildings that are located near transportation corridors often experience floor vibrations induced by passing trains or traffic, which causes building owners some concern. In this paper, a mathematical, impedance-based (wave propagation) model is presented for predicting train-induced floor vibrations in buildings. The model analytically predicts velocities, velocity ratios, and impedances. The analytical predictions of the model were compared and validated with the measured floor vibrations in a 4-story scale model building constructed by the writers. These predictions closely mimicked the measured responses. Using the results from the method presented indicate that the vibrations on the upper floors can be mitigated by increasing the thickness of a floor at a lower level in the building. This lower-level floor with the increased thickness is called a blocking floor. The scale model building was tested with and without a blocking floor. The predicted and measured responses of the scale model buil...

Cyclic experimental behavior of angles and applications for connection design and modeling

Recent work on the seismic behavior of low-ductility steel braced frames has suggested that adding top and seat angles to gravity framing connections can increase a building’s reserve capacity and hence its collapse performance. To this end a comprehensive suite of 133 tests has been developed and is currently in progress to establish a baseline of ultimate capacities under monotonic and cyclic loading. Angles range in size from L4x4x5/16 to L8x6x3/4, and will be fastened using 3/4” A325, 1” A325, and 1” A490 bolts. The distance from the heel of the angle to the bolt centerline in the vertical leg, referred to as the gage, has previously been shown to be an important parameter, particularly in relation to the thickness of the angle. Low gage-to-thickness ratios indicate stocky configurations, while high ratios indicate slender, flexure-controlled configurations. The ratios within this study range from 1.25 to 8.00. Based on the test results, this study aims to develop simple analytical models that can reasonably predict ultimate moment capacities and rotations of beamto-column connections reinforced with top and seat angles.

Ground-Motion Suite Selection for Eastern North America

Ground-motion suite selection for Eastern North America (ENA) is distinguished from suite selection for high seismic regions by uncertainty related to earthquake intensity, spectral shape, and the wide range of relevant periods experienced by low-ductility structures. Whereas trends in high seismic regions point toward developing smaller, more efficient suites for use in practice based on reliable intensity parameters, current research on moderate seismic regions requires the development of ground-motion suites capable of exciting the widest range of structural periods while accounting for uncertainty related to ground-motion intensity. This paper discusses uncertainty related to ENA ground motions in terms of the logic tree in the probabilistic seismic hazard analysis (epistemic uncertainty) and the deaggregation of hazard into magnitude and distance bins (aleatory uncertainty), recommends a suite selection process for addressing this uncertainty without amplitude scaling, and evaluates the effectiveness of a specific suite in the context of reliability-based performance assessment procedures. DOI: 10.1061/(ASCE)ST.1943-541X.0000258.

Predicting Train-Induced Vibrations in Multi-Story Buildings

Urban societies face the challenge of working and living in environments filled with noise and vibration caused by construction, manufacturing, and transportation systems. Due to soaring prices of real estate in modern cities, air-rights developments are becoming more widespread. As residential towers and hotels are built over or adjacent to train stations, subways, and highways, traffic noise and vibration play an ever increasing role in causing discomfort to the occupants. Research laboratories conducting highly sensitive measurements and manufacturing plants for nanotechnology are also prone to disruption by feelable and audible vibrations. In this research, a wave propagation model is developed to predict train-induced vibrations in buildings. The analytical predictions are compared to experimental data obtained using an electrodynamic shaker in a full-scale building. The floor responses to controlled shaking are used to calibrate the wave propagation model by estimating model parameters using optimization techniques. Traininduced vibrations, introduced at the building foundation, are also measured and compared to analytical predictions.

Full-Scale Cyclic Testing of Low-Ductility Concentrically Braced Frames

AbstractTwo full-scale, two-story, low-ductility steel concentrically braced frame (CBF) systems were tested to evaluate failure mechanisms, postelastic frame behavior, reserve capacity, and overal...

Experimental Behavior of Low-Ductility Brace Connection Limit States

In low-ductility concentrically braced steel frames (CBFs) with traditional fillet welds between the gusset plates and slotted HSS braces, fracture of the fillet welds or net section rupture of the tube are viewed as the most likely connection failure modes. After such failure, the braces lose all their tensile strength but may still re-engage in compression to provide some degree of reserve strength to the structure. A test program was recently completed to verify the behavioral limit states and probable reengagement strength of brace connections. Six specimens with slotted-HSS weldedgusset plate connections were examined in this research. The connection specimens were part of a 9-story prototype building with chevron CBFs located in eastern North America and designed with an R factor of 3.0. The connection specimens were proportioned to exhibit weld or net section rupture failure modes. The tests showed that connections can re-engage in compression after weld or net section rupture, when the edge of the HSS slot comes into contact with the edge of the gusset plate. For slender gusset plates, connection buckling occurred due to the eccentricity resulting from unsymmetrical damage modes, such as coupled weld and net section ruptures, before substantial connection re-engagement can develop in bearing.

Large-Scale Testing of Low-Ductility, Concentrically-Braced Frames

In regions of moderate seismic hazard, the costly structural detailing necessary to ensure adequate ductile performance of a braced frame during an earthquake event can be difficult to justify economically. Structural engineers, however, are permitted to design low-ductility systems if larger demands are assumed. In regions of moderate seismic hazard, this philosophy has proved to be economical and has resulted in widespread use of such low-ductility braced frame systems. Despite this popularity, the inelastic behavior and collapse performance of these systems are not currently understood at a fundamental level. A broadened understanding of the inelastic behavior of low-ductility braced frames can lead to an improved seismic design philosophy and provide practicing structural engineers with a coherent, rational, and transparent design approach applicable to moderate seismic regions. This research aims to identify low-ductility braced frame failure mechanisms and the sequence in which they occur, as well as to draw conclusions on the implications of the observed behavior contextually in building collapse performance.

Seismic behavior of low-ductility concentrically-braced frames

Current codes allow engineers in moderate seismic regions to ignore seismic detailing as long as they design the structure using R = 3. However, recent research has raised questions regarding the reliability of such systems. When subjected to the maximum considered earthquake seismic hazard, the collapse of these systems becomes inherently dependent on their reserve lateral load-resisting capacity. Several sources of reserve capacity in these structures have been identified: connections in the gravity framing system, connections in the braced frame system, column continuity, base fixity, and brace re-engagement. In this paper, the results of several parametric OpenSees studies are presented in order to evaluate the effect of these sources of reserve capacity in traditional R = 3 systems, with focus on a three-story prototype chevron concentrically-braced frame. Nonlinear inelastic static analysis as well as nonlinear inelastic incremental dynamic analysis for a suite of earthquake ground motions were performed. Various limit states for these structures were identified, and failure of the welded connection between the brace and gusset plate was identified as the prominent event affecting collapse performance.

Web crushing capacity of high-strength concrete structural walls: Experimental study

This paper discusses the relationship between concrete strength and web crushing capacity based on results from large-scale tests of thin-webbed structural walls with confined boundary elements. Eight walls with concrete strengths ranging from 39 to 138 MPa (5.6 to 20 ksi) were tested to web crushing failure under cyclic and monotonic loading. These tests clearly demonstrated differences between elastic and inelastic web crushing behavior and their dependence on concrete strength. Walls with higher concrete strengths reached higher levels of displacement ductility due to an increase in web crushing capacity. Evidence with respect to monotonic tests showed that degradation of the diagonal compression struts from cyclic loading increases with concrete strength, thus limiting the inelastic deformation capacity gains. Thus, concrete compressive strength does not linearly increase web crushing strength as implied by rational web crushing models; rather, the relationship is nonlinear, with a decreasing limit as concrete strength increases. The ACI (American Concrete Institute) shear stress limit considerably underestimated the web crushing capacity of the walls. Test results and observations are reported with the intent of providing physical insight into the web crushing failure mechanism and the inherent limits of thin-webbed concrete members in shear.