Journal of Structural Engineering

The goal of this research is to evaluate different structural control methods in enhancing the overall structural performance under seismic excitations. This study focuses on steel moment resisting frames and several types of possible controllers: (1) friction pendulum base isolation system; (2) linear viscous dampers; and (3) active tendon brace system. Two structures are selected from the SAC Phase II project, the three story system, and the nine story system. Simulations of these systems, both controlled and uncontrolled, are prepared using the three suites of earthquake records, also from the SAC Phase II project, that represent three different return periods. Several controllers are developed for each structure, and their performance is judged based on both roof and interstory drift and normalized dissipated hysteretic energy. Results indicate that structural control systems are effective solutions that can improve structural performance. All three control strategies investigated can significantly reduce the seismic demands on a structure, thereby reducing the expected damage to the structure.

In box girders with wide flanges, an uneven flange stress distribution (the flexural normal stress is greater at the edges than that at the center of the flange), so-called shear lag (or positive shear lag), may occur following the characteristics of stress concentration problems. However, Foutch and Chang in 1982 discovered the shear lag anomaly called negative shear lag in which the stress distribution is opposite from that in positive shear lag. Several attempts have been made to explain it. However, existing studies lack a more general and physical explanation on the origin of negative shear lag. In this paper the origin of the anomalous phenomenon is explained from the physical point of view. It is shown that, at any given location, negative shear lag can take place whenever the portion of the shear flow acting along the flange edges, which produces the shear lag-aftereffect, is larger than the remaining portion of shear flow caused by positive shear lag.

Steel angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion. However, the recommendations of many design codes are unnecessarily conservative when applied to the bending of angle section beams, or are of limited application, or fail to consider some effects which are thought to be important. In this paper, consideration is given to the first-order elastic analysis of the biaxial bending of angle section beams including the effects of elastic restraints, and proposals are developed for the section moment capacities of angle sections under biaxial bending which approximate the effects of full plasticity in compact sections, first yield in semicompact sections, and local buckling in slender sections. Proposals are developed for the bearing, shear, and uniform torsion capacities of angle section beams in a companion paper. The proposals in this and the companion paper can be used to design steel angle section beams which are laterally restrained so that lateral buckling or second-order effects are unimportant.

Steel angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion. However, many design codes do not have any design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important. In this paper, proposals are developed for the section capacities of angle sections under bearing, shear, and uniform torsion. In a companion paper, consideration is given to the first-order elastic analysis of the biaxial bending of angle section beams, including the effects of restraints, and proposals are developed for the section moment capacities of angle sections under biaxial bending. The proposals in this and the companion paper can be used to design steel angle section beams which are laterally restrained so that lateral buckling and second-order effects are unimportant.

The aim of this paper is to study the stress concentration factors of doubler plate reinforced tubular T joints subjected to various types of basic loading such as axial tension, axial compression, and in-plane and out-of-plane bending. The finite-element method is adopted in the numerical parametric studies to evaluate the stress distribution. To verify the numerical results, a typical full-scale doubler plate reinforced tubular T joint was fabricated and tested. The strain distributions at the intersection region subjected to various combinations of loading were measured. The results from the experiment compared well with the numerical results. The finite-element modeling techniques were then verified to be accurate and reliable. After the verification, a database was generated from a parametric study by varying some geometrical parameters, such as the wall thickness ratio, diameter ratio, etc. A set of parametric equations with the nondimensional parameters as variables was then established for the evaluation of the stress concentration factors of the doubler plate reinforced tubular T joints. The stress concentration factors on the doubler plate reinforced joints were found lower than the unreinforced joints.

There is an increased use of thin-walled $\left(t<4\mathrm{mm}\right)$ hollow sections in the manufacture of lighting poles, traffic sign supports, swing ploughs, linkage graders, trailers, and haymakers. These structures are subjected to fatigue loading. A review of current fatigue design guidelines showed that there is a lack of design rules for nodal joints made up of thin-walled $\left(t<4\mathrm{mm}\right)$ hollow sections. This paper describes the tests carried out on welded thin-walled $\left(t<4\mathrm{mm}\right)$ tube-to-tube T connections made up of square hollow sections under cyclic in-plane bending. Different failure modes were obtained during fatigue testing. The experimental stress concentration factors determined in this investigation were found to be significantly lower than the stress concentration factors from the existing parametric equations from the International Institute of Welding. The design $S_{r\text{.}\mathrm{hs}}-N$ curves have been determined for the hot spot stress method from $S_{r\text{.}\mathrm{hs}}-N$ data based on both experimental and parametric equation stress concentration factors. Design $S_{r\text{.}\mathrm{hs}}-N$ curves have been derived from the fatigue data using the least-squares method. The design $S_{r\text{.}\mathrm{hs}}-N$ curves derived from the experimental fatigue data are lower than the expected design curve resulting from the current trend for design $S_{r\text{.}\mathrm{hs}}-N$ curves for different thicknesses from the International Institute of Welding and the International Committee for the Development and Study of Tubular Construction. Three design approaches are proposed for welded T connections in thin cold-formed square hollow sections under cyclic in-plane bending.

Stiffened Z-section beam purlins were tested to evaluate the deflection behavior of lap joints under combined bending and shear. The tested beams had a span length of 243.84 cm (8 ft), nominal web depths of 20.32 cm (8 in.) and 24.13 cm (9.5 in.), and a metal thickness ranging from 1.542 mm (0.060 in.) to 2.565 mm (0.101 in.). The corresponding web depth-to-thickness ratio $(h/t)$ ranged from 79 to 131. The experimental program included testing a single section beam of each Z section and lapped beams with lap-to-span ratio $(l/L)$ ranging from 0.25 to 1.0. The test results indicated that the lapping process enhanced the ultimate load capacity and stiffness of the beams. This enhancement was more pronounced for beams with lap-to-span ratios less than or equal to 0.5. For higher $l/L$ ratios, little or no change in the results was noted. The failure mechanism was governed by bending stresses and was caused by buckling of the compression flanges at stress levels close to the yield stress of the parent steel. A relative stiffness behavior approach was used to analyze the results. This approach compares the deflection behavior of lapped beams with that of a single section beam having the same span length and the same Z section. Based on this analysis, semiempirical equations were obtained to predict the deflection of lapped beams. Theoretical deflection equations were also derived and the results based on these equations were compared with the experimental results. It was concluded based on this comparison that the proposed correlation was adequate for predicting the deflection in the lap joint zone of nested Z beams.

Structural condition assessment can be made with probabilistic based methods. The structural system is analyzed using a reliability model, based on the different possible failure modes. This paper presents a procedure developed to conduct a systems reliability analysis for highway truss sign supports subject to random wind loading and corrosion. The procedure provides a method for updating the resistance strength as the structure deteriorates. The study has demonstrated that the most effective way to improve the system reliability is to increase the restraint of the connection at the top of the truss where it supports the sign and to increase the column stiffnesses.

This paper reports on work, conducted under Task 1.5.3 (Reliability Studies) of the CUREE-Caltech Woodframe Project, with the objective of developing a risk-based methodology for seismic design of shear walls. Along with diaphragms, shear walls are primary lateral force resisting components in woodframe structures. The methodology developed herein is based on reliability principles as well as emerging performance-based concepts for seismic design. The specific subobjectives of Task 1.5.3 were: (1) to conduct a sequence of sensitivity studies to evaluate the contributions of various sources of uncertainty to shear wall performance as predicted using the CASHEW program (developed in another task of the project); (2) to evaluate the variabilities in, and thereby statistically characterize, the peak response obtained using a suite of ordinary ground motion records taken to characterize the seismic hazard in southern California; and (3) to develop a risk-based procedure for performance-based design of wood shear walls. Design charts developed using this procedure could be used to determine limits on the seismic weight to ensure target nonexceedence probabilities for the different performance (drift) levels.

The shrink–swell action of expansive soils is one source of structure foundation movement responsible for widespread problems with respect to the serviceability performance of lightweight masonry structures. The most obvious problem is that of cracking in masonry walls. Numerical models for soil movement and structural response have been combined to develop a probabilistic model for crack prediction. The model is capable of predicting the likelihood of cracking and the expected crack widths based on variability in both external effects and structural response. The ultimate aim is to develop rational design criteria for the serviceability design for masonry structures.

Dynamic properties of a prototype soundwall composed of recycled plastic members are determined by experimental testing on a full-scale field structure. An impact hammer is used to impart transient excitation to individual columns, isolated wall panels, and the entire soundwall, and response of structural members is recorded at different locations with accelerometers. System identification and a peak-amplitude method are utilized in complementary analyses to determine essential dynamic properties such as natural frequencies and damping. A frequency spectrum associated with a design wind event is developed and compared with natural frequencies of the prototype soundwall. Then, a finite element model of the soundwall is used to simulate deterministic and probabilistic effects of strong winds. Estimates of maximum deflection and acceleration at the top of the wall are obtained by numerical simulation. Behavior is determined to be quasi-static.

The objective of this study is to describe a problem formulation and an optimization procedure for the design of elevated reinforced concrete foundations for vibrating machines. Special emphasis is placed on structures composed of footings, beams, and columns. The dimensions of the structure and its reinforcement are the design variables for the optimization problem. The objective function consists of costs of the concrete, the steel, the form, and the propping form. Constraints related to material and soil failure, as well as geometrical limits and human comfort are imposed. A new failure surface for columns and beams subjected to biaxial bending and axial loads is defined and used in the formulation. The main motivation of using the new failure surface is to save a large amount of computational effort in the solution of this dynamic response optimization problem. The problem of minimizing the structural cost while satisfying the operating and safety requirements is solved using an augmented Lagrangian method. A large number of constraints (time dependent and time independent) is treated without any difficulty in the method. The numerical methods used in the solution process are described. Optimal solutions for an example problem are obtained and discussed.

Use of the reciprocal load method for evaluating the capacity of reinforced concrete (RC) columns under axial load and biaxial bending is suggested in concrete design handbooks and in commentaries to the design codes. The reciprocal load method interpolates such a capacity from the interaction diagrams obtained for the uniaxial bending cases. The adequacy of the reciprocal load method for short reinforced concrete columns of normal strength concrete has been verified in the literature. It is noted that the validity of this method for reinforced concrete columns of high strength concrete is rarely discussed, and that the characteristic of the stress–strain relation of normal strength concrete differs from that of high strength concrete. A numerical assessment of the adequacy of the reciprocal load method for short RC columns of normal and high strength concrete was presented in this study. Also, the possibility of using the reciprocal load method for slender reinforced concrete columns was investigated. The assessment was carried out by comparing the predicted capacities obtained using the reciprocal load method and those obtained by solving several nonlinear coupled governing equations that are established based on statics and considering the nonlinear stress–strain relations of concrete and steel.