Journal of Structural Engineering

A methodology is introduced to estimate the strength of suspension bridge cables using results of tensile strength tests performed on wire samples extracted from the bridge’s main cables. The innovation of the proposed methodology is to consider the spatial correlation of the wire strength over the wire’s length, a real and experimentally measured property of ductile steel wires that is disregarded in the current standard approach. The wire strength is modeled as a nonGaussian random field along its length. The number of parallel wires in the cable’s cross section is then considered to estimate the strength of the entire cable. The capabilities of the proposed methodology are demonstrated through an application involving an experimental data set of wire segments extracted from the Williamsburg Bridge. Results of the proposed methodology are compared to corresponding results of the current standard approach. It is explained why the former results are relatively more accurate than the latter. A procedure for estimating the tensile strength of a cable composed of parallel wires at different corrosion stages is also presented.

This paper presents a new approach for the treatment of parameter uncertainty for linear static structural mechanics problems. Parameter uncertainties are introduced as interval numbers. Interval arithmetic is applied to finite-element method to analyze the structural responses due to uncertain loading, axial and bending stiffness. However, a naïve use of interval arithmetic in the formulation of finite-element method, i.e., replacing the deterministic parameters with corresponding interval ones, will result in meaningless wide results due to the so-called dependency problem. In the present approach, an element-by-element technique is used to reduce the overestimation and compatibility conditions are ensured by a penalty method. With the newly developed overestimation control, most sources of overestimation are eliminated and a very sharp enclosure for the system response is obtained. A number of numerical examples are introduced.

As the use for regional seismic risk assessment increases, the need for reliable fragility curves for portfolios (or classes) of structures becomes more important. Fragility curves for portfolios of structures have the added complexity of having to deal with the uncertainty in geometric properties, along with the typical uncertainties such as material or component response parameters. Analysts are challenged with selecting a prudent level of uncertainty treatment while balancing the simulation and computational effort. In order to address this question, this study first evaluates the modeling parameters which significantly affect the seismic response of an example class of retrofitted bridges. Further, the relative importance of the uncertainty in these modeling parameters, gross geometries, and ground motions is assessed. The study reveals that savings in simulation and computational effort in fragility estimation may be achieved through a preliminary screening of modeling parameters. However, the propagation of these potentially variable parameters tends to be overshadowed by the uncertainty in the ground motion and base geometry of the structural class.

This paper reports on an investigation of the effects of fire on long span truss floor systems in a tall building environment. The effects of fire spread over multiple floors of a building are the focus of this research, especially where this may lead to progressive collapse. The results from an investigation of a two-dimensional model of a multistory office building analysis are presented. The model is representative of the type of construction used in the World Trade Center Towers 1 and 2. The local and global response of the model is described over the course of a concurrent fire on three floors reaching a peak compartment temperature of $800°\mathrm{C}$ . The results of the analysis show that large displacements may occur in long span structural floor systems without failure, however, the interaction of the highly deflected floors with the exterior or perimeter columns can lead to structural collapse. Additional structural members, such as hat trusses, that allow redistribution of loads away from the exterior columns to the core columns have a significant beneficial impact on the robustness of the structure.

The dynamic behavior of an eccentrically prestressed simply supported beam under a moving harmonic force is studied by using the higher order shear deformation theory in this paper. The prestressed tendon is assumed straight and unbonded with the concrete. The Lagrange’s equations are used to examine the dynamic response of the beam. Trial functions denoting the deflection of the beam and the rotation of the cross sections are expressed in polynomial forms. The Kelvin-Voigt model for the material of the beam is used. By using Lagrange’s equations, the problem is reduced to a system of differential equations and they are solved by using the direct time integration. Convergence study is performed. The effects of an eccentric and an axial prestress force, velocity of a moving harmonic force, excitation frequency, shear deformation, and the viscous damping of the material on the deflection of the beam are examined.

This paper reports on the effect of temperature on the modal properties for a curved posttensioned bridge. The goal has been to explore how ambient vibrations based on routine traffic excitation can be used as part of a long-term bridge monitoring approach. This requires the establishment of a baseline that incorporates the sensitivity of the measured modal properties. The ambient vibration characteristics are based on both the health of the structure and the environmental and operational conditions which may mask normal changes due to structural changes. The primary environmental influence on the structural modal properties is temperature. A database developed over a $5\text{year}$ period to explore bridge monitoring techniques has been used to evaluate how temperature variations influence the modal properties. The results show that the variability of measured modal parameters due to temperature should be well understood and quantified prior to the establishment of a baseline for use in damage assessment algorithms.

This paper focuses on the study of tensegrity active control in situations of partially defined loading and damage events. Self-diagnosis and self-repair methodologies are proposed and validated experimentally on a full-scale active tensegrity structure. Self-diagnosis involves load identification and damage location. The response of the structure to a load and damage is measured and compared with the response of the structure to candidate solutions for load and damage. Self-diagnosis solutions result in sets of candidate solutions for loads and damage. These solutions are employed to compute control commands of shape control and self-repair for the structure. Self-repairing control commands increase stiffness and decrease stresses with respect to the damaged state. Self-repairing control commands are computed using a multiobjective approach. The application of a control command results in self-stress modifications by changing the length of active struts. The proposed methodologies are attractive for tensegrity active control in situations of partially defined loading and damage events.

For a rigid element equilibrated by a set of initial forces, the geometric stiffness matrix derived is the same, whether it is straight or curved, as long as it has identical nodal degrees at the two ends. Thus, one can first derive the geometric stiffness matrix for a rigid straight beam that has the same ending points as those of the curved beam using a rigid displacement field, and then transform this matrix from the Cartesian coordinates to the cylindrical coordinates to obtain the one for the rigid curved beam. The geometric stiffness matrix so derived (for treating the rigid displacements) can be used along with the elastic stiffness matrix (for treating the natural deformations) in the buckling analysis of curved beams. The present approach is featured by the fact that no assumptions are made for the kinematic behavior of curved beams, while the procedure of derivation is simple, explicit, and physically meaningful. Good characteristics of convergence are achieved as the finite-element mesh is refined. The robustness of the proposed approach is demonstrated in the solution of some benchmark problems.

This paper presents a stochastic dynamic programming (DP) procedure for multiobjective optimization of bridge network maintenance planning that involves a group of existing highway bridges with various remaining service lifetimes and different reliability importance factors to the bridge network. The complex multiobjective optimization problem is solved by using a two-phase DP approach. The Phase I problem consists of identifying the optimal maintenance plans for individual bridges that have minimum life-cycle maintenance costs, while satisfying both condition and safety requirements for a targeted service lifetime period. This problem is solved by using a specific DP optimization algorithm along with Monte Carlo simulation. The Phase II problem is to rationally allocate the limited annual maintenance budgets in such a way that the identified optimal maintenance plans for individual bridges can be satisfied for as many bridges as possible. A single-objective formulation derived from multiple attribute utility theory with weight assignment from reliability importance factors is developed. This is solved by a binary integer programming algorithm. The ultimate goal of this study is achieved in terms of finding the most efficient combinations of available maintenance actions applied to all bridges in a highway network.

Fatigue cracks were found on a series of end-coped crane runway girders after 14 years of service in a steel mill building in China. Two typical crane runway girders with different spans were studied in this paper. Finite element analyses were conducted to investigate the stress concentration at the coped ends. Analytical results showed the stress concentration effect was highly localized and the stress concentration factor decreased with increasing cope radius and decreasing total depth. The analytical results agreed well with the field measured data. Fatigue tests were conducted to determine the fatigue strength using eight 1/5-scaled end-coped girder specimens. Based on the analytical results and limited test data, the fatigue strength for a maximum principal stress range of $103\mathrm{MPa}$ at 2 million cycles may serve as a possible design guideline for end-coped crane runway girders using the conventional S-N curves. Procedures for design and evaluation of the fatigue life of end-coped crane runway girders are suggested.

In an experimental study, a series of tests was performed on seam-welded structural stainless steel circular hollow sections (CHS) subjected to bending. The test program included various cross section geometries of CHS that covered a range of structural responses. Three-dimensional nonlinear finite-element (FE) models (ABAQUS) were established and verified with the experimental results accounting for material nonlinearity and manufacturing distortions. Close agreement was achieved between the test and finite-element analysis results in terms of load-deformation response and ultimate strength. The test and finite-element strength results with additional FE results generated for CHS models not considered in the test are compared with the strengths predicted using the American, Australian, and European specifications for cold-formed stainless steel structures. In light of the experimental/numerical results and code recommendations, strength and cross section classification criteria for stainless steel circular hollow section members in bending were examined. The results showed that significant improvements are possible for cross section slenderness limits provided by the current specifications.

When coupled core wall (CCW) systems are built in regions of high seismicity, the ductility demands on the coupling beams can be of critical concern. Steel coupling beams, whether encased in concrete or not, offer a very high degree of ductility relative to common concrete coupling beams. Hybrid core wall systems, that is CCW systems with steel or steel/concrete composite coupling beams, provide excellent lateral stiffness from the walls and coupling action, while providing excellent energy dissipation and ductility characteristics of steel coupling beams. Previous research pertaining to steel coupling beams has made great strides in furthering the understanding of the behavior of steel coupling beams, and recommendations regarding design methodologies have been established. However, as steel coupling beam ends are embedded in the wall piers, postdamage repair can be costly. This paper presents the results of large-scale cyclic tests of a steel coupling beam designed and detailed based on the writers’ previous recommendations and an innovative “fuse” steel coupling beam which provides an added feature to the steel coupling beam in that postdamage repair/replacement difficulties and expenses are minimized.

The wind moment frame (WMF) method has been and continues to be widely utilized in the central and eastern United States, resulting in a very large population of structures having been designed without a rigorous analysis with respect to lateral loads. The primary objectives of this paper are to determine whether moment-resisting frames designed by the WMF method are adequate to handle the increased demand on lateral resistance made by modern seismic codes, and to evaluate and compare the seismic performance of existing and new moment-resisting steel frames with partially restrained (PR) connections. Three prototype frames were designed and analyzed utilizing synthetic ground motions for the Mid-America region. The seismic performance of these PR frames was evaluated in accordance with FEMA 273/356 criteria. In addition, studies were conducted on the confidence level of the performance results to take into account the uncertainties and randomness inevitably involved. This analysis and evaluation found that all PR frames designed in this study satisfied the selected performance objective with 99% confidence level for the global performance limit. Thus, the seismic performance of the PR frames in the Mid-America region will be satisfactory even under large ground motions.

This paper presents relatively simple, analytically derived curves to model the axial and the lateral stress-strain relations of circular concrete columns. The analytical curves describe the full elastoplastic behavior of the confined concrete column. The solution to the partially confined reinforced concrete column in the elastoplastic range is derived by replacing the discrete lateral reinforcement with an equivalent tube and the Drucker–Prager (DP) yield criterion is applied to represent the concrete behavior in the plastic range. Application of the DP model does not require an iterative procedure in order to solve the problem and thus an explicit solution is obtained. It is shown that the proposed model properly simulates the behavior of reinforced concrete columns partially confined by steel ties and of columns that are fully confined by fiber-reinforced polymer sheets.

Tests were carried out on shear walls with diagonal or transverse (horizontal) lumber sheathing. A total of 16 full-scale shear walls were tested to investigate the effects of hold-downs, vertical load, and width of lumber sheathing on in-plane shear capacity. Test results were also used to examine whether the shear resistance is cumulative when diagonal or transverse lumber sheathing is used on one side and gypsum wallboard panels on the other side. Monotonic and reversed cyclic displacement schedules were used as loading protocols. The load-displacement response of each test specimen was recorded, from which the initial stiffness, ultimate load and displacement, and energy dissipation were calculated. The results show that for shear walls with single diagonal lumber sheathing, the load-displacement responses under tensile and compressive loads are asymmetric if hold-downs are installed only at the bottom of the end studs. Use of steel rods in lieu of hold-down connections only at the bottom of the walls improves the ductility of walls, but still results in asymmetric behavior. With proper hold-down connections, the design values in the United States and Canadian codes are appropriate for shear walls with single diagonal lumber sheathing. For shear walls with double diagonal lumber sheathing, the in-plane shear capacities are approximately 2–3 times that of shear walls with single diagonal lumber sheathing.

The benefits of using “puddled” fiber-reinforced high-strength concrete for the transmission of loads from high-strength columns through slabs is demonstrated. Compression tests were performed on two slab-column specimens and four isolated column specimens (without the surrounding slab). For the tests on the slab-column specimens, vertical slab loading was applied to simulate realistic conditions at the slab-column joint. Predictions using current North American code approaches are compared to the experimental results.

A closed-form solution for the optimum tuning ratio of a liquid column damper (LCD) that is valid for damped structures subjected to generalized seismic loading is presented. The closed-form expression is based on the extension of the theory of “fixed-point” frequencies for a classical undamped structure-mass damper system to damped structure-nonlinear LCD system. For the specific case of white noise input, the values of optimum tuning ratio have been compared with those obtained from a standard expression.