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A series of experiments and analyses have been conducted to assess the vulnerability of hollow circular web members in welded aluminum sign truss structures to wind-induced resonant vibrations. Results from nondestructive field testing were used to develop and verify a reliable method for determining the fundamental natural frequency of vibration for various categories of truss web members (incorporating end connection fixity effects). These natural frequencies for different types, sizes, and lengths of web members were then related to their computed vortex-shedding frequencies, toward estimating the critical wind speeds for web member resonant vibration. Outcomes were correlated with wind-related fatigue damage observed in the field; simple design recommendations for preventing this sort of damage by limiting the maximum web member slenderness ratio have been developed. CE Database subject headings: Vortex shedding; Welds; Aluminum; Trusses; Tubes; Joints; Fatigue; Nondestructive tests; Sign supports.

Predicting the fatigue life of solder interconnections is a challenge due to the complex nonlinear behavior of solder alloys and the importance of the load history. Long experience with Sn-Pb solder alloys together with empirical fatigue life models such as the Coffin-Manson rule have helped us identify reliable choices among package design alternatives. However, for the currently popular Pb-free choice of SnAgCu solder joints, designing accelerated thermal cycling tests and estimating the fatigue life are challenged by the significantly different creep behavior relative to Sn-Pb alloys. In this paper, a hybrid fatigue modeling approach inspired by nonlinear fracture mechanics is developed to predict the crack trajectory, and fatigue life of a solder interconnection. The model is shown to be similar to well accepted cohesive zone models in its theoretical development and application and is anticipated to be computationally more efficient compared to cohesive zone models in a finite element setting. The approach goes beyond empirical modeling in accurately predicting crack trajectories and is validated against experiments performed on lead-free as well as Sn-Pb solder joint containing microelectronic packages. Material parameters relevant to the model are estimated via a coupled experimental and numerical technique. [DOI: 10.1115/l.2840057] Keywords: lead-free solder, acceleration factors, cohesive zone modeling

This study investigates the effect of base plate flexibility on the behavior and fatigue performance of welded socket connections commonly used in sign support structures. The results of a three specimen static load testing program, extensive finite-element analysis, and parametric study are discussed. Results clearly show that base plate flexibility, primarily base plate thickness, has a major influence on the stress distribution in the tube wall adjacent to the welded socket connection. Currently, AASHTO gives no specific guidance on the design of the base plates for sign support structures that explicitly address flexibility. Increasing base plate thickness is shown to be a very effective method to improve the fatigue resistance of this detail. Based on this trend, a simple procedure that incorporates the influence of base plate flexibility into the infinite life, nominal stress approach to fatigue design is proposed. CE Database subject headings: Plates; Connections, welded; Fatigue; Sign supports.

The paper presents the cost optimization of the composite I beam floor system. The composite I beam floor system is designed to be constructed up of a reinforced concrete slab and doubly-symmetrical welded steel I beams. The optimization was performed by the nonlinear programming approach, NLP. An accurate objective function of the manufacturing material, power and labour costs was developed and applied for the optimization. The composite I beam floor system was optimized according to Eurocode 4 for the conditions of both the ultimate and the serviceability limit states. A numerical example of the cost optimization of a composite I beam floor system is presented at the end of the paper to expose the advantages of the proposed approach. Keywords: Structural optimization, nonlinear programming, composite structures, welded structures, manufacturing costs, INTRODUCTION Cost effective design of building structures is commonly obtained after the time-consuming trial-anderror analysis of various structural alternatives. In the conceptual design level, the costs related with a change [...]

This paper presents a discrete formulation of the nonlinear minimum weight design of welded connections, in which global throat stresses along every fillet are approximated by piecewise linear shape functions. With this formulation it is possible to find the set of throat thicknesses of a welded connection that gives the minimum amount of weld metal necessary to support an arbitrary set of external actions and a stress field in equilibrium with these actions and satisfying a strength criterion. The formulation adopted involves a linear form of objective function and equilibrium equations, which, together with the convex character of the nonlinear constraints, gives a full convex set of constraints and consequently a global optimum of the objective function. Moreover, the structure of the set of constraints makes it possible to demonstrate that stress and throat thickness values are unique at the optimum, which allows the optimum stress distributions to be simplified, to establish practical design recommendations. Realistic conditions can be imposed on the stress field. The problem is solved with a very accessible and well-known scientific library, which allows this method to be implemented by anyone involved in welding practice. The method proposed is developed for the case of a planar connection. Two practical applications using the strength criterion of Eurocode 3 are included, discussing the results obtained for two types of common arrangements and showing that numerical results are consistent and CPU times reasonably low.

Welding in space will be an important process for the permanent repair of both low- and high-pressure fluid line assemblies used on large spacecraft. Space station fluid systems are candidates for in-space repair. They provide a variety of tubing materials, sizes, pressures, and working fluids as well as including ancillary systems that demonstrate typical constraints to the repair process for a more realistic overall scenario. Damage to on-board fluid systems could occur as a product of faulty or fatigued joints, micrometeoroid impacts, collision with other objects, and over-pressure strain or burst. Incorporating terrestrial experience with automatic pipe-welding tools and that of both the U.S. and former Soviet space programs in space welding, hypothetical repair scenarios were analyzed using Space Station Freedom as a representative baseline. Weld joint design criteria are then derived. A new weld joint for in-space repair, which meets these system-derived criteria, is presented and a stress analysis is performed.