Journal of Structural Engineering

Concrete-filled steel tubular (CFT) columns have been used increasingly in building structures because of their construction efficiency and provision of high stiffness and strength. A relatively new configuration design with inserted inner steel tubes, so-called concrete-filled double-skin steel tubes (CFDSTs), has been developed in the field. To promote the seismic capability of the CFT/CFDST columns further, the authors present results from an experimental investigation of CFT and CFDST columns using ultrahigh-strength steel. Eight scaled column specimens were examined by subjecting them to combined axial and flexural cyclic loadings. The performance of the CFT and CFDST design configurations using high-strength steel was comparable and both provide large moment capacities and elastic deformation capacities. The ultimate member moment capacity could be predicted accurately using a proposed simple formulation based on the concept of the superposed strength method. Various performance parameters are evaluated and discussed, and the influence of compressive strength of the concrete core, applied axial loads, and inserted inner steel tubes on the seismic behavior of the column members is clarified by the experimental results.

This paper presents a technique for computing the time-dependent behavior of reinforced and prestressed concrete as a composite material. This technique, when implemented in a finite-element model and assuming that the concrete and steel reinforcement act as a composite material, is computationally advantageous compared with explicitly modeling the concrete and steel materials separately. The method is developed assuming linear viscoelasticity and uncracked sections. The approach starts by first approximating the creep compliance functions for the viscoelastic concrete as a Kelvin chain model. This approximation allows the viscoelastic behavior to be framed as a rate-type creep law, which converts the analysis to an equivalent elastic problem, simplifying the computations. This approach, originally developed for plain concrete, is extended in this paper to account for the effects of linear elastic reinforcement. Several implementation examples are provided documenting the viability of the method for problems of uniaxial, multiaxial, and bending behaviors. For the presented cases, the composite method is shown to provide similar results compared with models containing explicitly modeled reinforcement. The paper concludes with a discussion regarding how to extend the methodology to the general case with linear viscoelastic reinforcement and matrix materials.

A novel system decoupling approach (SDA) that enables three degree-of-freedom (3-DOF) bridge flutter analysis is proposed in this study to simultaneously investigate the relationships between modal parameters and 18 flutter derivatives. Based on the incentive-feedback mechanisms, the aerodynamic coupled system is conveniently decoupled in an iterative solution. Based on the SDA, it is unnecessary to simultaneously calculate all multiple frequencies for determining modal parameters and eventually quantifying critical flutter wind velocity. The efficacy and accuracy of the SDA is verified using a numerical example of thin flat plate. The coupling effects among three DOFs and influence of 18 flutter derivatives on flutter performance are quantified using the newly proposed method. The flutter mechanisms of thin flat plate and bluff deck section of the Akashi Kaikyo Suspension Bridge are numerically examined, and both difference and common grounds for two typical flutter phenomena are summarized. The results by the SDA show good agreement with those by the commonly used complex eigen-value analysis (CEVA). For the Akashi Kaikyo Bridge with bluff deck section, the analytical results of 2-DOF coupled flutter are coincident with the 3-DOF case and the experimental observations. This study provides significant insights into the flutter characteristics of 3-DOF bridges and explores the roles played by various parameters in modifying bridge deck aerodynamics and the evolution of modal coupling with increasing wind velocity. The simplified formulation that only concerns $A_1^{*},A_2^{*},A_3^{*},H_3^{*}$ is presented, by which acceptable accuracy of flutter parameters can also be achieved for torsional modal branch. It is validated using a thin flat plate and the Akashi Kaikyo Bridge with bluff deck.

In this paper, an analytical model is developed and used to predict the horizontal behavior of unbonded fiber-reinforced elastomeric isolators (FREIs). An advantageous feature of unbonded FREIs is the ability to undergo rollover due to the lack of flexural rigidity of the reinforcement and the unbonded support conditions of the isolator. The rollover causes a characteristic softening, followed by stiffening, as the initially vertical faces of the isolator come into contact with the upper and lower supports—defined as full rollover. The force-displacement relationship is modeled by dividing the isolator into three sections: a central section, which experiences pure shear, and two rollover sections, which experiences combined shear and bending. The displacements of the rollover section are used to establish the curved deformed profile and predict full rollover. The model is evaluated with experimental data from four unbonded FREI designs. A parametric study is conducted to determine the influence of the aspect ratio and bending stiffness of the composite fiber reinforcement matrix on the horizontal force-displacement relationship.

This paper presents an experimental program to investigate the progressive collapse resistance of reinforced-concrete (RC) building structures subjected to a loss of a penultimate-external (PE) column that is the exterior one nearest to the building corner. Under this accidental scenario, any mobilization of catenary action in beams and slabs bridging over the column, as an alternative load path, should rely solely on the strength of a half perimeter compressive ring forming within the deflected slab area. Three one-third scaled beam-slab substructures were designed, built, and tested by a static loading scheme to examine the overall load capacity and displacement ductility that are two aspects of the progressive collapse resistance of RC building structures. The test variables are (1) additional amounts of beam stirrups, (2) additional beam longitudinal reinforcement, and (3) the aspect ratio of the slab panel. The boundary condition of the specimens is rotationally and vertically restrained, but laterally unrestrained. A 12-point loading system is used to simulate uniformly distributed loads. Based on the test results, a simple but conservative approach to quantify the progressive collapse resistance of RC building structure under a PE column loss scenario is proposed.

The seismic response of exposed hollow steel section columns to base plate connections is examined through a series of eight experiments. The prototype-scale tests investigate a range of variables including base plate size and thickness, column size, and anchor rod layout (four rods in two rows, and eight rods in three rows). The specimens were subjected to cyclic flexural loading and instrumented to provide direct (rather than inferred) measurement of tension forces in the anchor rods. All the specimens showed excellent deformation capacity, with a stable hysteretic response for base rotations as large as 0.057–0.13 rad. Three specimens failed by fracture of the weld between the column and the plate, whereas five did not fracture. Evaluation of the test data against the current design approach prevalent in the United States suggests that (1) the design approach is reasonably conservative but (2) does not address the effect of the third (i.e., central) row of anchor rods; as a result, it cannot be used to design them. A new design method is presented that explicitly incorporates the third row of rods. The new approach is evaluated against the test data and it is determined that the new approach reflects the internal mechanics of the connections in an improved way while providing more accurate estimates of forces in the rods. Recommendations for the design of the connections are outlined, along with ongoing work that leverages the deformation capacity of these connections for displacement-based design. The limitations of the study are summarized, especially in terms of challenges to the generalization of its findings.

The article presents a three-dimensional nonlinear finite-element model that was developed for the study of a top and seat angle bolted steel connection with double web angles. Unilateral contact and friction laws were used to simulate the interaction among the connected parts. Large displacements as well as the von Mises failure criterion were also considered for the steel parts and bolts. Numerical results were compared with the experimental research conducted on the same steel joint. This study finds yielding of the top angle as well as shear failure of the bolts connecting the beam bottom flange with the seat angle to be very important for the overall response of the structure. For this reason, a parametric investigation of the influence of the top angle on the behavior of the structure and the study of the prying forces developed at the top angle were conducted.

Cyclic loading tests were performed on framed stud walls with strap brace and steel sheathing. Each stud panel was strengthened with either the conventional straps or steel sheathing. The framed stud wall specimens were prepared by framing four stud panels with a lightweight steel frame (or boundary frame). To mitigate damage to the corner joint and to improve the energy dissipation capacity, new detailing methods for the framed stud walls were proposed. Test results showed that the framed stud wall specimens exhibited high deformation capacity ($>5.37\%$) and ductility ($>5.76$). However, because of premature buckling of the tension-only straps and steel sheathing, significant pinching was observed in the cyclic behaviors. The energy dissipation capacity was enhanced in the specimen where the beam-column joints of the boundary frame were strengthened by reducing the column section (RCS). Based on the plastic mechanisms such as strap yielding and column yielding, the load-carrying capacity, stiffness, and yield displacement of the framed stud walls were predicted. In addition, based on the tests, recommendations for the design and detailing of the framed stud walls were given.

Building envelope is a critical line of defense against external explosions, and laminated glass can greatly reduce the hazard of flying shards. Blast-resistant glazing research exists, but few areas remain unexplored related to resistance and blast response of the window system, the effect of the negative phase of the blast wave, and the dynamic reactions transmitted to the window frame and supporting structure. Therefore, dynamic numerical simulations and shock tube testing are presented in this paper. The dynamic response, in terms of center deflection and dynamic reactions, is measured and compared with the numerical results using the blast positive and negative phases. The measured dynamic material response of the interlayers was used for the model. The numerical model deflections and dynamic reactions correlated well within the first few peaks of the measured response of the glazing systems. The results of this study can be used to improve existing methods for predicting the response and dynamic reactions of structural glazing under blast, and to provide affordable design recommendations.

The postbuckling behavior of seismic-resistant braces in steel frames under a cyclic axial force is often evaluated by time–history analyses; however, brace fracture is seldom considered. The authors previously proposed a physical model for predicting the moment of fracture of circular-tube braces after buckling using phenomenological hysteresis. However, the accuracy of that model was confirmed only against the test results of the gradually increasing amplitude loading protocol, and its applicability under other loading histories has not yet been verified. In this study, cyclic loading tests were carried out until fracture on circular-tube and H-section braces under various loading histories, followed by FEM analyses. The validity of the proposed formulas for evaluating the strain-concentration index under various loading histories was examined. The proposed method was used for predicting the moment of fracture and the cumulative deformation capacity until fracture, and the predictions agreed well with the test results.

An experimental study investigated the behavior of large-scale steel-plate composite (SC) walls subjected to cyclic lateral loading. The testing program involved four rectangular SC wall specimens with an aspect ratio (height-to-length) of 1.0. The specimens were anchored to a concrete basemat with a pretensioned bolted connection that was designed to be stronger than the walls. The design parameters considered in the investigation were wall thickness, reinforcement ratio, stud spacing, and tie bar spacing. The pretest analyses, global force-displacement responses, contributions of the steel faceplates and infill concrete to the lateral resistance, load transfer between the faceplates and infill concrete, and damage to the face plates and infill, are documented. The four SC walls failed in a flexural mode characterized by tensile cracking of the concrete, tensile yielding of the steel plates, crushing of concrete at the toes of the wall, outward local buckling of the steel faceplates, and fracture of the steel faceplates. The walls achieved the peak shearing strengths estimated using simplified procedures and ABAQUS. Pinching of the force-displacement response was observed at displacements greater than those associated with peak load. The distance between the baseplate and the first row of connectors affected the postpeak shear strength behavior and the fracture of the faceplates. The connection of the SC wall to the foundation block had a significant influence on the initial stiffness of the walls.

Two geotechnical centrifuge tests were designed to elicit the influence of soil–foundation–structure interaction (SFSI) and structure–soil–structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structure are tracked for the SSSI cases. For these tests, SSSI consistently results in increased peak foundation moment and foundation base shear demands, regardless of the geometric layout of the structures. These increases propagate throughout the superstructure, resulting in increases in moment, shear and curvature ductility demands in the structural components. SSSI effects are observed to be most significant for low–to–moderate intensity earthquake motions, suggesting that particular consideration should be given to the likelihood of SSSI for highly probable earthquakes.

This paper presents detailed analyses of experimental results pertaining to the cyclic behavior of a reduced-scale reinforced masonry (RM) asymmetric building with walls aligned in two orthogonal directions. The current study focuses on analyzing the influence of twist, as a system-level effect, on the displacement and strength demands of the building’s individual seismic force resisting system (SFRS) wall components. The study evaluates the individual wall contributions to the overall building response characteristics within both the elastic and the inelastic response phases. Documentation of the compressive strains at the wall toes is also presented and correlated to the damage levels anticipated for each wall. In addition, the building center of rotation and center of strength are determined and the corresponding twist angles and moments and building torsional stiffness values are evaluated throughout the loading history. Moreover, the trends of stiffness degradation for the walls and for the building are presented, and the relationship between the individual walls’ and building’s stiffness is discussed. Finally, the trends of energy dissipation increase with increased building displacement ductility are established for different system-level ductility levels. The information presented in this paper is expected to provide useful benchmarking data that can contribute to the understanding of RM system-level response and how it compares to the behavior of individual RM SFRS components.

Although concrete in compression and wood in flexural tension are both intrinsically brittle, composite beams made of these two materials can develop a reliable measure of softening before failure when ductile shear connectors are used to link concrete and wood, provided the connectors are dimensioned to yield before failure of wood or concrete. This article describes an analytical method for predicting the complete load-deflection response of timber/concrete composite beams with ductile shear connectors. The approach involves the superposition of results obtained from a series of linear models, each of which has a progressively smaller number of connectors corresponding to the order in which they yield. The nonlinear behavior of the system can thus be determined without iteration using only linear computations. The analytical method is validated against experimental data.

The component method is widely recognized as a suitable tool for the prediction of the mechanical response of beam-to-column steel joints. Recently, this method has been extended also to aluminum structures. For some joint components, i.e., the ones based on equivalent T-stubs, the formulations traditionally given for steel have been properly adapted to aluminum by using some corrective factors which have been calibrated on the basis of experimental and numerical analyses. On the contrary, due to the lack of exhaustive studies in literature, other joint components have been preliminarily extended to aluminum by simply proposing the same expressions used for steel. Nevertheless, this type of assumption may lead to an inappropriate evaluation of the actual strength. Therefore, the current paper aims at developing suitable formulations for predicting the strength of an aluminum column web in tension, on the basis of calibrated FE numerical models. The results of a parametric analysis, implemented by varying the mechanical features of the base material, are presented, including also the influence of the heat-affected zones. Finally, the results of a sensitivity analysis on the column axial load are shown. Therefore, based on the obtained outcomes some refined formulations are suggested and proposed for possible implementation in existing codes.

The quantification of damping in a structure is of significant interest in structural dynamics. At present, there is still no clear consensus on how damping issues are resolved. Although the Rayleigh damping model, which combines mass-proportional and stiffness-proportional parts, leads to reasonable engineering demand parameters of a structure within its elastic range, it does not include nonlinear response history analysis. On the other hand, a great deal of material tests demonstrate that most metallic materials under cyclic loading exhibit a stress-strain relationship that is not elastic even at stresses well below the yield point, however, the material damping effect is seldom taken into account in dynamic analysis. The present study proposes an approach that explicitly considers the additional material damping effect based on Goodman’s theory on energy dissipation of materials. The approach is applied to the nonlinear dynamic analyses of single-layer latticed domes subjected to earthquake ground motions. Parametric studies are carried out to evaluate the structural material loss factors under different seismic hazard levels. Finally, a comparative study of the effect of material damping on dynamic responses is discussed. The objective of this study is to quantify the structural material loss factors and to obtain reasonable dynamic seismic demands by means of the easy-to-apply numerical procedure proposed in this paper.

Large deployable high-frequency mesh antennas are being envisioned for future space missions. The static determinacy is required to ensure the long-term dimensional stability of cable net reflectors of mesh antennas under extreme space environments. In this paper, the design methodologies for creating statically determinate cable net topology configurations of AstroMesh and umbrella-type antennas are proposed on the basis of the generalized Maxwell’s rule, respectively. To generate these configurations, the number of subdivisions of mesh reflectors is first determined by the allowable surface accuracy. Then, by introducing the concept of nodal connectivity, the cable net topology configurations of AstroMesh antennas are deduced from a general analytical solution of linear algebraic theory. The desired topology configurations of umbrella-type antennas are obtained by adjusting the number of nodes, cables, and kinematic constraints under uncertain supporting boundary conditions. Some novel cable net topology configurations with static determinacy are created for AstroMesh and umbrella-type antennas. These design results will provide valuable topology configurations for the structural design of deployable mesh antennas.

Wind turbines are typically designed for a target service life of 20 years because of fatigue-related failures of the moving components such as the rotors and blades. Designing the tower to have the same lifetime as other components is clearly desirable for optimization of the wind turbine system. This study focuses on the fatigue life of the tower base connection subjected to wind loading. A simplified finite-element model for wind turbines subjected to nonlinear wind loading in time domain was developed specifically for application in this study. The relative motion between the wind speed and moving blades in the flapwise direction only creates force nonlinearity for the applied wind load and hence, necessitates application of a simple fluid/structure interaction model. Then, a model for fatigue assessment (Mode I), including crack propagation, was developed for the tower base connection. The inclusion of crack propagation is expected to extend the service life of the tower compared with conventional fatigue life analysis using the characteristic S-N approach. By varying the tower thickness, diameter, and considering predefined levels of crack propagation, fragility curves based on a fatigue life limit state are developed for application of performance-based design. The desired fatigue life of a wind turbine tower for different wind sites can be obtained based on the fragilities. Finally, performance-based design for a typical 5 MW wind turbine is used as an illustrative example in this study.

In the present study, the maximum shear strength of simply supported reinforced concrete beams with rectangular cross section was investigated. In beams with heavy shear reinforcement exceeding a certain limit, concrete crushing failure of the compression zone occurs before the yielding of the shear reinforcement. Thus, the maximum shear strength of such members is limited by the concrete crushing failure. In the present study, considering the shear-compression failure mechanism of the compression zone, the maximum shear strength was defined by material failure criteria of the concrete subjected to the combined compressive and shear stresses. The proposed model was applied to specimens tested in the previous studies. The results showed that the proposed method predicted the maximum shear strengths of the specimens with a reasonable precision. Furthermore, a design equation for the maximum shear strength was proposed to secure the ductile flexural behavior of beams without early shear failure.

A simplified anisotropic constitutive model for orthotropic metal sheets is developed herein to analyze the off-axial stress-strain response of cold-formed metal sheets, where the material plastic anisotropy is induced by work hardening during the forming process. Hill’s 1948 anisotropic yield criterion is used to determine the material initial yielding, and the strain hardening is modeled using a mixed kinematic-isotropic hardening law along with constantly changing material principal directions as a result of the off-axial plastic loading. The isotropic hardening parameters were expressed using Fourier series and are functions of the loading directions. The expression of hardening parameters using Fourier series allows the model to be adaptively calibrated to the current state of stress using as few as three sets of off-axial stress-strain data. The proposed model is able to predict the direction-dependent strain hardening behavior of orthotropic metal sheets, as well as account for the progressive changing in material principal directions as a result of the off-axial plastic loading. The predicted results were validated using published experimental data of AA7018-T1 aluminum alloy. Finally, as an illustrative example, the anisotropic plasticity model was implemented, along with the simplified analytical approach, to analyze the push-over responses of a sheet-metal shear wall structure with a cold-rolled infill plate. The results predicted by the simplified model match closely with those of finite element analysis and indicate that the performance of the shear wall system depends on the installation direction of the infill metal sheet with respect to its rolling direction.