Journal of Structural Engineering

Slender open-section cold-formed steel members that contain flanges with edge stiffeners may buckle in different modes and with mode interactions. The element design approach (effective width method) has been shown to produce unconservative capacity predictions for a particular class of such members. This paper presents a modification to the effective width method derived from an investigation of the fundamental behavior of edge stiffened flange elements and sections that contain them. The modified element design approach is validated against the results of 913 compression and bending members collected from the literature, where all section and member buckling modes and interactions were evident. A section design approach is also presented which is directly in line with the element approach. The unified element and section approach is shown to provide accurate and reliable design solutions for cold-formed steel compression and flexural members. Proposals for the North American specification for cold-formed steel structures are presented.

This paper presents a series of 48 full-scale tests on press-braked stainless steel lipped channel section columns subjected to concentric compression. The tests were carried out between fixed ends in the Structures Laboratory of the University of Liège and the test specimens were designed such that distortional buckling developed in the section prior to overall flexural-torsional buckling. The stainless steel alloy was 1.4003 chromium weldable steel, popularly known as 3Cr12. Three different geometries were tested using the same experimental setup. A critical summary of the standards and methods for calculating the carrying capacity of cold-formed stainless steel compression members is presented in a companion paper by the same writers.

This paper provides a critical summary of the European standards and design methods available for calculating the strength of cold-formed stainless steel compression members. The standards considered (so far mainly applied to columns failing by flexural buckling) are applied to the case of lipped channel section columns failing by combined distortional and overall flexural-torsional buckling. As observed during the tests presented in a companion paper, distortional buckling is found to have a considerable effect on the cross section resistance and is prone to interact with the global flexural-torsional mode. It is investigated how the different formulations account for the two buckling modes and their interaction and how accurate strength predictions they provide. A new direct strength method taking into account these failure modes is then presented and compared to the test results.

Plate steel shear links offer enhanced design freedom, including the ability to use steel grades that are not available in rolled shapes. This paper discusses the cyclic response of five types of shear links designed using steel grades that ranged from 485 to 100 MPa yield strength. The design and subsequent performance was categorized into two groups; conventional design and those designed without stiffeners using low yield point steels. Ductile failure modes and desirable hysteretic behavior that resulted in efficient cyclic energy dissipation were observed for all specimens. The links designed without stiffeners using low yield point steel reached shear deformations exceeding 0.20 rad, outperforming the conventional designs that exhibited approximately 0.12 rad capacity. The enhanced performance was the result of shifting the failure mode by excluding intermediate stiffeners and providing low web compactness. This combination eliminated welding and decreased measured plastic strain demands on the face of the inelastically deforming webs.

Hybrid fiber-reinforced polymer (FRP) concrete-steel double-skin tubular columns are a new form of hybrid columns recently proposed by the second writer. The new column consists of an inner steel tube and an outer FRP tube, with the space between them filled with concrete. The new column possesses several advantages over existing columns including excellent ductility and corrosion resistance. This paper first examines the behavior of the confined concrete between the two tubes using a finite-element model to understand the effects of the key parameters including the stiffness of the FRP tube, the stiffness of the steel tube, and the size of the inner void. Based on the available experimental observations and the results from the finite-element model, a simple stress-strain model for the confined concrete is proposed for use in practical design. Comparisons with test results show that the proposed model provides reasonably accurate and conservative predictions.

A simple physical model, for prediction of ultimate shear strength of steel fiber-reinforced concrete (SFRC) beams is developed on the basis of a plastic approach originally proposed for reinforced concrete beams without stirrups. It is founded on the hypothesis that cracks can be transformed into yield lines, and thus is know as crack sliding model (CSM). First, the CSM is improved to take into account the shear strength increase for deep beams, due to the arch effect. Then, the effectiveness factors for fibrous concrete under biaxial stresses are evaluated, taking into account the postcracking tensile strength of SFRC and its ability to control slippage along shear cracks. With the aim of providing a handy and fast tool for design of SFRC beams without stirrups, a simplified design model is also derived. Finally, the proposed models are validated by the results of a large set of experimental tests taken from literature.

This paper presents a nonlinear model for pretensioned prestressed concrete girders. The model consists of three main components: a beam-column element that describes the behavior of concrete, a truss element that describes the behavior of prestressing tendons, and a bond element that describes the transfer of stresses between the prestressing tendons and the concrete. The model is based on a two-field mixed formulation, where forces and deformations are both approximated within the element. The nonlinear response of the concrete and tendon components is based on the section discretization into fibers with uniaxial hysteretic material models. The stress transfer mechanism is modeled with a distributed interface element with special bond stress-slip relation. A method for accurately simulating the prestressing operation is presented. Accordingly, a complete nonlinear analysis is performed at the different stages of prestressing. Correlation studies of the proposed model with experimental results of pretensioned specimens are conducted. These studies confirmed the accuracy and efficiency of the model.

Tensairity is a lightweight structural concept comprising struts and cables stabilized by a textile membrane which is inflated by low pressurized air. This paper addresses the effect of fabric webs inside the membrane hull on the static response of spindle-shaped Tensairity columns to axial compression. Two full-scale spindle-shaped columns, one without and one with webs, were fabricated and tested. The columns were subjected to axial compressive loading for various levels of internal air pressure to quantify its effect on the global structural response. It was found that the stiffness and the load bearing capacity for both columns increased with increasing air pressure. The experimental results also revealed the benefits of including fabric webs in the spindle configuration in terms of axial stiffness and buckling load. Comparisons with an analytical solution and finite-element predictions showed good correlation for the axial stiffness in the case without webs. For the case with web deviations between predicted and experimental results indicated that structural detailing and imperfections in the manufacturing process strongly influence the performance of Tensairity columns with internal webs.

This paper presents an adaptive harmony search algorithm for solving structural optimization problems. The harmony memory considering rate and pitch adjusting rate are conceived as the two main parameters of the technique for generating new solution vectors. In the standard implementation of the technique appropriate constant values are assigned to these parameters following a sensitivity analysis for each problem considered. The success of the optimization process is directly related on a chosen parameter value set. The adaptive harmony search algorithm proposed here incorporates a new approach for adjusting these parameters automatically during the search for the most efficient optimization process. The efficiency of the proposed algorithm is numerically investigated using two large-scale steel frameworks that are designed for minimum weight according to the provisions of ASD-AISC specification. The solutions obtained are compared with those of the standard algorithm as well as of the other metaheuristic search techniques. It is shown that the proposed algorithm improves performance of the technique and it renders unnecessary the initial selection of the harmony search parameters.

Real-time hybrid simulation combines experimental testing and numerical simulation by dividing a structural system into experimental and analytical substructures. Servohydraulic actuators are typically used in a real-time hybrid simulation to apply command displacements to the experimental substructure(s). Servohydraulic actuators may develop a time delay due to inherent actuator dynamics that results in a desynchronization between the measured restoring force(s) and the integration algorithm in a real-time hybrid simulation. Inaccuracy or even instability will occur in a hybrid simulation if actuator delay is not compensated properly. This paper presents an adaptive compensation method for actuator delay. An adaptive control law is developed using an error tracking indicator to adapt a compensation parameter used in the proposed compensation method. Laboratory tests involving large-scale real-time hybrid simulations of a single degree of freedom moment resisting frame with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the proposed adaptive compensation method. The actuator tracking capability is shown to be greatly improved and exceptional experimental results are still achieved when a good estimate of actuator delay is not available.

In this study, the finite-element method is used to investigate the seismic behavior of rectangular liquid tanks in two-dimensional space. This method is capable of considering both impulsive and convective responses of liquid-tank system. Two different finite-element models corresponding with shallow and tall tank configurations are studied under the effects of both horizontal and vertical ground motions using the scaled earthquake components of the 1940 El-Centro earthquake record. The containers are assumed fixed to the rigid ground. Fluid-structure interaction effects on the dynamic response of fluid containers are taken into account incorporating wall flexibility. The results show that the wall flexibility and fluid damping properties have a major effect on seismic behavior of liquid tanks and should be considered in design criteria of tanks. The effect of vertical acceleration on the dynamic response of the liquid tanks is found to be less significant when horizontal and vertical ground motions are considered together. The results in this study are verified and compared with those obtained by numerical methods and other available methods in the literature.

An innovative system for reinforced concrete masonry walls based on the combination of vertical and horizontal trussed reinforcement is proposed. The mechanical characterization of the seismic behavior of such reinforced masonry walls is based on static cyclic tests carried out on panels with appropriate geometry. The influence of the factors influencing the in-plane cyclic behavior of concrete masonry walls, such as the horizontal reinforcement, precompression, and masonry bond pattern, is discussed. The results are analyzed in terms of failure modes and force versus displacement diagrams, from which the seismic performance is assessed based on the ductility and energy capacity dissipation. The results stressed that the increase on the precompression level leads to a stiffer and more brittle lateral behavior of the masonry walls. The presence of horizontal reinforcement ensures better control and better distribution of cracking, even if only a marginal increase of lateral strength was found in the particular testing program.

The Philippines has good potential for wind energy utilization. However, it is also prone to strong typhoons. Thus, wind turbines that will be erected in these areas maybe categorized into a special safety class and the reference wind speed is left to the discretion of the designer. Due to this scenario, the writers proposed a new reference wind speed applicable to Philippine climate which take typhoons into account. Annual extreme wind speeds gathered from fifty weather stations around the country were fitted to a generalized extreme value distribution. For each station, buckling failure of a wind turbine was analyzed using reliability theory. Based on these results a new 50-year mean wind speed and a new reference wind speed for a wind turbine in typhoon-prone areas in the Philippines are proposed.