Journal of Structural Engineering

This paper discusses the progressive collapse resistance of steel-concrete composite floors in which steel beams are attached to columns through shear tabs. This is a common type of system used for the gravity bay portions of steel buildings. The study is conducted using computational simulation models validated through extensive comparisons to disparate test data. The models are used to investigate key parameters influencing the robustness of generic composite floors subjected to the removal of a center column. In particular, the effects of deck thickness, steel reinforcement, and the numbers of bolts in the shear tab connection on the behavior of the system are studied as a function of the loading scheme. The simulation results show that the majority of collapse resistance comes from the steel deck and that, for the system considered, increasing connection strength by adding more bolts might not be that beneficial in increasing overall collapse strength. The dynamic impact factor, which is widely used to account for dynamic effects within a static design framework, is also computed and the DIF value recommended in existing design guidelines is evaluated.

This paper presents an experimental study of six steel shear tab connections to hollow structural section columns. This study focuses on the plastic behavior of shear tabs and their supporting column walls. The column walls had width-to-thickness ratios ranging from 21 to 34. Large bending deformations were observed on both the column walls and the shear tabs. All six specimens failed owing to an excessive vertical deflection followed by a punching fracture of the tube wall around the perimeter of weld at the top of tab. The test results were found to agree well with two plastic mechanisms proposed for analysis. This study demonstrates that the shear strength of the tabs welded to a flexible wall support should be reduced when compared with that of the tabs welded to a rigid support. This paper also finds that the width-to-thickness ratio criterion for a rigid wall support is a function of the ratio of the length of tab to the width of the supporting wall and the relative bending strength between the tab and the wall.

Based on in-service inspection of poles with traditional designs, the inventory of Wyoming Department of Transportation (WYDOT) exhibited approximately a one-third cracking rate. A ring-stiffened connection is presently used. Sixteen fatigue tests were performed on 12 ring-stiffened cantilevered traffic signal pole connections to quantify the fatigue resistance. Two pole sizes were tested in three loading configurations: in plane, out of plane, and diagonal. Cyclic loading was applied to produce stress ranges (SRs) at several levels up to 16 ksi in the main member, more than six times the SR observed during monitoring an in-service pole. The WYDOT stiffened connection appears to be adequate to resist Wyoming’s sustained winds that average approximately 12 mph in many locations. The possibility of using this connection with longer mast arms exists. Connection bolt fatigue failures were observed and may be the limiting fatigue design feature and important for inspection.

An analysis method for predicting the shear strength and behavior of structural shear walls under both monotonic and cyclic loading is presented in this paper. The proposed analysis method is based on the softened truss model theory and utilizes a newly proposed cracking angle of the concrete strut. The cracking angle is developed using a regression analysis of the reported shear capacity values of 100 experimental shear walls. The analysis pays particular attention to parameters expected to influence the walls’ shear capacity including the geometric properties, reinforcement ratios, internal stresses, and concrete strength. The proposed method has been used to predict the shear capacity of the tested walls, and their deformation behavior both pre- and postcracking, and the results compared well with the experimental data. The proposed strut cracking angle also matched well the cracking patterns obtained experimentally.

This paper presents tests that were performed on square large-scale steel-fiber-reinforced high-strength concrete (HSC) columns under concentric compression loading. The experimental program was mainly designed to examine the effect of the volumetric steel-fiber ratio on the behavior of reinforced HSC large-scale elements subjected to axial compression loading. The test program was also designed to examine the combined confinement effect of steel fibers and transverse steel reinforcement. Thus, the test variables studied herein are the steel-fiber volumetric ratio and the volumetric ratio, yield strength, and spacing of the transverse steel ties. The results show that adding discrete fibers to HSC mixtures in reinforced concrete columns not only prevents the premature spalling of the concrete cover but also increases the strength and ductility of the axially loaded reinforced member. This behavior was predicted by the proposed fiber-reinforced concrete stress-strain model, which takes into account most of the parameters that influence confinement effectiveness: the concrete strength; the spacing, yield strength, volumetric ratio, and configuration of the transverse reinforcement; the distribution of the longitudinal reinforcement; and the diameter, length, shape, volumetric ratio, and frictional bond strength of the fibers. Predictions were found to be in good agreement with experimental results.

The composite interaction in timber-concrete beams is usually achieved with mechanical devices, such as shear connectors or plates driven into the materials. However, this connecting system shows some inherent inconveniences, such as the need for drillings and the limited mechanical improvement owing to interface slip. Using adhesives instead of mechanical connectors might attenuate these drawbacks. However, engineers are hesitant to apply adhesives for structural purposes, mostly because of the different thermohygrometric behavior of the adhesive and the connected material(s). This is particularly concerning timber because its hysteretic response to moisture may cause interface delamination. Therefore, as a preliminary stage for the test of composite beams, an extensive experimental campaign on small-size specimens was performed. The study focused on the shear strength at the interface and the role of some factors. Several series were considered by changing those parameters, and the results were compared. Both prefabricated and cast-on-site concrete specimens were considered. The results show that this system looks suitable for structural application, at least under steady dry conditions.

This paper reports an experimental program on composite timber-concrete beams with glued interface. The test results are compared to those provided by an analytical model based on the assumption of a fully composite behavior. Both cast-on-site and prefabricated composite timber-concrete beams were produced, aimed at simulating rehabilitation situations or the possibility of a partial or of a full prefabrication of the composite element. Timber-concrete beams with dowel-type shear connectors were also produced and tested for comparison. The results show that the strength is similar, but the glued beams displayed a larger stiffness and, consequently, smaller deflections, which may be of relevance in design. The results also show that, at least under stabilized and dry room conditions, the prevailing mode of failure is tension in timber and, when shear failure occurs, it is mostly conditioned by the shear strength of the concrete or the timber, not by that of the adhesive. As the system depends on the shear strength of the interface, a preceding program consisting in tests on small-size composite specimens was undertaken and is reported in a companion paper.

The current National Design Specification (NDS) for Wood Construction design methods for dowel-type connectors are based on four-yield modes for connections in double shear. These yield modes were formulated for use with steel dowels as fasteners. Hence design with nonferrous fasteners, such as wood pegs, common in timber frame joinery, is not addressed. Wood pegs, while large in diameter, are considerably more flexible than steel dowels of the same size. A fifth failure mode is proposed for use with wood pegs. This new failure mode, called Mode V yielding, which is an effective cross-grain dowel failure, has been observed in physical testing as well as numerical modeling. The objective of this paper is to establish a design procedure for the Mode V yielding of pegs. The procedure is calibrated to the level of performance (reliability) expected from the other yield modes. A regression equation to relate the effective cross-grain yield capacity of pegs to specific gravity is also developed for use with the Mode V design equation. A reliability analysis indicates that the proposed Mode V design equation can be used in conjunction with existing NDS yield equations for design of wood doweled connections.

In July 2009, a full-scale midrise light-frame wood apartment building was subjected to a series of earthquakes at the world’s largest shake table in Miki, Japan. This article focuses on the test results of that full-scale six-story light-frame wood building. The objectives of the testing program were to (1) demonstrate that the performance-based seismic design procedure developed as part of the NEESWood project worked on the full-scale building, i.e., validate the design philosophy to the extent one test can and (2) gain a better understanding of how midrise light-frame wood buildings respond, in general, to a major earthquake while providing a landmark data set to the seismic engineering research community. The building consisted of $1,350{\text{m}}^2$ $\left(14,000{\text{ft}}^2\right)$ of living space and had 23 apartment units; approximately one-half one-bedroom units and one-half two-bedroom units. The building was subjected to three earthquakes ranging from seismic intensities corresponding to the 72-year event to the 2,500-year event for Los Angeles. In this paper, the construction of the NEESWood Capstone Building is explained and the resulting seismic response in terms of base shears, selected wall drifts, global interstory drifts, accelerations, hold-down forces, and roof drifts are presented. Detailed damage inspection was performed following each test and those results are summarized also. The building performed excellently with little damage even following the 2,500-year earthquake. The global drift at roof level was approximately 0.25 m and maximum interstory drifts were approximately 2% for the floor average with individual wall drifts reaching just over 3% in one corner of the building at the fifth story.

One of the greatest challenges in the United States today is overcoming the deterioration of an aging infrastructure system. In particular, the highway/bridge infrastructure system has traditionally been neglected of maintenance and repair. One of the most concerning degrading mechanisms in the bridge infrastructure is corrosion, and it is compounded by the fact that much of the older infrastructure is not consistent with current seismic code requirements. The research presented here determines the effects of corrosion on the seismic response of a typical reinforced concrete bridge designed according to recent standards, predominantly governed by flexural deformations, and based on realistic lifetime deteriorations in strength due to the reduction in cross-sectional area of the reinforcement and in stiffness due to concrete cover spalling. The findings of the research, given the noted modeling assumptions, are that the losses in strength and stiffness only marginally influence the seismic fragility of the selected bridge.

This paper presents an effective numerical reliability-based optimization technique for the design of base-isolated concrete building structures under spectrum loading. Attempts have been made to automate the integrated spectrum analysis, reliability analysis, and design optimization procedure and to minimize the total cost of the base-isolated building subjected to multiple design performance criteria in terms of the story drift of the superstructure and lateral displacement of the isolation system or corresponding reliability constraints. In the optimal design formulation, the cost of the superstructure can be expressed in terms of concrete member sizes while assuming all these members to be linear elastic under a specified design earthquake. However, the base isolation is assumed to behave nonlinearly and its cost can be related to the effective horizontal stiffness of each isolator. Based on the principle of virtual work, the drift responses and corresponding reliability indexes can be explicitly formulated and the integrated optimization problem can be solved by an optimality criteria method. The technique is capable of achieving the optimal balance between the costs of the superstructure and isolation systems while the seismic drift performance or corresponding reliability of a building can be simultaneously considered. An illustrative example shows that conventional deterministic design optimization cannot ensure designs with satisfactory reliability levels, whereas the reliability-based design optimization can achieve the objective when uncertainties are considered. It is believed that such an optimization technique provides an effective tool for seismic design of building structures.

The research into modeling walking-induced dynamic loading and its effects on footbridge structures and people using them has been intensified in the past decade after some high profile vibration serviceability failures. In particular, the crowd induced loading, characterized by spatially restricted movement of pedestrians, has kept attracting attention of researchers. However, it is the normal spatially unrestricted pedestrian traffic, and its vertical dynamic loading component, that is the most relevant for vibration serviceability checks for most footbridges. Despite the existence of numerous design procedures concerned with this loading, the current confidence in its modeling is low due to lack of verification of the models on as-built structures. This is the motivation behind reviewing the existing design procedures for modeling normal pedestrian traffic in this paper and evaluating their performance against the experimental data acquired on two as-built footbridges. Additionally, the use of Monte Carlo simulations is also investigated. Possible factors that cause discrepancies between measured and calculated vibration responses, including possibility of existence of pedestrian-structure dynamic interaction, are discussed.

Measurements from load tests may lead to numerical models that better reflect structural behavior. This kind of system identification is not straightforward due to important uncertainties in measurement and models. Moreover, since system identification is an inverse engineering task, many models may fit measured behavior. Traditional model updating methods may not provide the correct behavioral model due to uncertainty and parameter compensation. In this paper, a multimodel approach that explicitly incorporates uncertainties and modeling assumptions is described. The approach samples thousands of models starting from a general parametrized finite-element model. The population of selected candidate models may be used to understand and predict behavior, thereby improving structural management decision making. This approach is applied to measurements from structural performance monitoring of the Langensand Bridge in Lucerne, Switzerland. Predictions from the set of candidate models are homogenous and show an average discrepancy of 4–7% from the displacement measurements. The tests demonstrate the applicability of the multimodel approach for the structural identification and performance monitoring of real structures. The multimodel approach reveals that the Langensand Bridge has a reserve capacity of 30% with respect to serviceability requirements.

A dominant opening in a windward wall will generate large positive internal pressures during windstorms, which, in combination with large suction pressures on the roof, commonly causes building failures and is hence a governing design criterion. The fluctuating (and peak) internal pressures are dependent on the external pressure and the size of the opening and the size of the building volume. This study presents ratios of internal pressure to external pressure standard deviations and peaks in terms of the nondimensional opening size to volume parameter, $S^{\ast }$ , and the size of the dominant opening and discharge coefficient. The study also analyzes equations that have been proposed as design formulas for inclusion in codes and standards.