Journal of Structural Engineering

When subjected to strong sustained fluctuating wind uplift, screw-fastened light-gauge-steel profiled roofing sheets may fail locally in the vicinity of fasteners by cracking due to fatigue, resulting in the sheeting being pulled free of the fastener. A series of fatigue tests was performed on three types of commonly used profiled roofing sheets to investigate their fatigue performance and profile effects under both constant-amplitude repeated loads and simulated uplifting wind loads. The sheeting profiles considered were arctangent, trapezoidal, and ribbed, and an alternate (or equivalent alternate) sheeting crest-fastening system was adopted. It was found that the fatigue performance of roofing sheets greatly depends on their profiles. The fatigue resistance of the arctangent type of sheeting to low-amplitude repeated loads was found to be higher than those of the other two types of roofing sheets. However, the situation is reversed under high-amplitude repeated loads. The linear and bilinear S - N curves on a log-log plot were used, respectively, to fit the experimental data, and the Goodman method was employed to approximately account for the effect of mean load. Load-sequence effects and the application of Miner's rule to the fatigue-life prediction of screw-fastened profiled roofing sheets under simulated wind loads were also investigated.

This paper presents a new rational approach for the evaluation of the effects of creep on reinforced-concrete axially loaded columns at sustained service stresses. The analysis involves a straightforward computation based on a closed form procedure and the assumption of linear elastic materials for both concrete and steel. The analysis may be easily extended to cover the case of reinforcement at yield. The results of the proposed approach may be superposed with those from a shrinkage model presented by Park and Paulay in 1975, and the overall behavior of column axial shortening and stress transfer from concrete to steel may be described using the combined approach. The process involved is very convenient to use from an engineering viewpoint since it requires few input parameters, which are easy to estimate or measure experimentally, such as the modulus of elasticity of concrete and the creep coefficient. The results of the theoretical approach correlate well with experimental tests conducted on specimens in the laboratory, and with deformations of columns measured in the Water Tower Place and Lake Point Tower, in Chicago.

Full-scale exterior beam-column-slab subassemblages were tested under reversed cyclic loading to investigate the role of the spandrel beam in the overall response. Results from specimens having different spandrel beam sizes and different amounts of torsional reinforcement in the spandrel beams provided a better understanding of their behavior. Detailed strain measurements together with the crack patterns indicate that the effective width of the slab contributing to the negative bending of the main beam is affected by the torsional yielding of the spandrel beam. However, after this yielding, a different force mechanism, involving concrete compressive struts and tension ties in the slab and spandrel beam bars, provides means of transferring additional forces from the slab bars to the joint region. It is important to consider the effect of these forces, since they increase the negative moment capacity of the beams, and, hence, they may affect the hierarchy of yielding between the columns and the beams. Design proposals, accounting for the flow of forces through the spandrel beam, are presented and illustrated by a number of examples.

The objective of this study is to present the derivations in closed-form series for moments and deflections of thin orthotropic plates with general edge beams (boundaries) under arbitrary out-of-plane loading. The displacement solutions for the major components of the system (plate and beam) or macroelements are obtained by first solving for the unknown interactive forces and moments at the beam or nodal line locations after satisfying displacement compatibility along nodal lines. Such an approach is referred to herein as the macroapproach. The displacement functions for the macroelements are proposed in Fourier cum polynomial series after making sure that the series satisfies the boundary conditions. Using known solution forms of summation equations, solutions of systems of equations in open form has been avoided. The proposed series solution can be applied to all types of orthotropic decks with bridge boundaries. Numerical examples involving orthotropic plates with various aspect ratios, loading cases, and bridge-type boundary conditions are presented to demonstrate the accuracy of the approach for predicting deflections and moments. The major advantage of this technique is the development of a solution algorithm in the form of summation equations, leading to fast converging closed-form series solutions.

The theoretical relations between the tension and compression stress-strain curves of ductile metals in the natural coordinate system are presented. In addition, a macroscopic model is formulated to predict the cyclic stress-strain behavior of reinforcing steel. The model is based on the natural coordinate system and represents the Bauschinger effect by a simple expression. It also considers the reduction of the unloading modulus with the plastic strain. Furthermore, the reduction of the ultimate tensile strain is taken solely as a function of the maximum compressive strain when the number of cycles is small enough to ignore the effects of low-cycle fatigue. Data collected from tests on New Zealand manufactured steel grades 300 and 430 were used in the calibration of the model. It is shown that the shape of the Bauschinger effect is dependent on the chemical composition of the steel. It is proposed that a generalization of the calibrated model for use in other reinforcing steel types may be possible by considering the carbon content as a variable.

Predicting stress levels caused by thermal effects is a main factor in the correct design of structures; both relate to aspects of the maximum stress limitation and the durability of constructions. A numerical procedure based on the finite-element method for the stress-strain analysis of concrete structures exposed to time- and space-variable thermal loads is presented in this paper. Different environmental conditions can be simulated by means of suitable boundary conditions imposed on the differential equations governing the phenomenon. In particular, the seasonal and daily variation of external temperature is considered. The presented procedure can also consider the heat generation phenomenon, due to the hydration reaction of the cement, which can cause considerable temperature gradient and related mechanical stresses, especially for thick concrete casting. The stress-strain-thermal analyses of a concrete dam (Sa Stria dam, Sardegna, Italy) and a typical bridge section (i.e., box-girder cross section) are carried out to prove the effectiveness and reliability of this numerical method in practical structural design.

A novel method of reinforcement for welded-truss connections between hollow structural sections (HSS), in which the chord member is filled with concrete, is described. The behavior of concrete-filled T-, X-, and gapped K-connections is examined by means of tests on 31 filled and unfilled connections, and the effects of concrete filling on structural performance are established. It is shown that there is a significant improvement in strength for connections that have a branch member, or members, loaded in compression. Moreover, the strength of concrete-filled HSS connections can be adequately predicted by considering the bearing capacity of the confined concrete (under compression loading) or a subset of existing design expressions for unfilled HSS connections (under tension loading).

A stress-strain model for confined high-strength concrete has been developed and calibrated against the test results from 50 large-scale high-strength concrete tied columns tested under concentric loading. The effects of the concrete compressive strength, tie yield strength, tie configuration, transverse reinforcement ratio, tie spacing, and longitudinal reinforcement ratio are accounted for in the proposed stress-strain model. The determination of the strength and ductility of confined concrete is based on the computation of the effective confinement pressure, which depends on the stress in the transverse reinforcement at maximum strength of confined concrete, and on the effectively confined concrete area. A method is proposed to compute the stress in the transverse reinforcement at maximum strength of confined concrete.

A one-fifth model reinforced-concrete beam-slab bridge deck was tested to destruction, and the vibrational response to ambient excitation was measured at different stages of cracking and spalling. Observations showed that the neutral axis remained close to the lower flange of the T-beam throughout the loading range. A method capable of assessing the load-carrying capacity as well as the structural condition of a T-beam slab bridge deck has been developed. This requires prior information on the geometric dimensions and fundamental modal frequency of the structure, and two methods are discussed and proposed for assessment. The results of a parametric study of the effect of different boundary conditions on the fundamental modal frequency are presented in this paper. Different potential sources of error in this process are discussed and the manner of implementing the method is presented.

Laboratory tests on a model reinforced-concrete beam-slab bridge deck were briefly described in the first part of this two-part paper. These results and some theoretical studies were used to support the possibility that the measurement of the fundamental modal frequency might be used to assess both the structural condition and load-carrying capacity of a bridge. Two factors were proposed in the original paper to measure these structural qualities. This second part of the paper details the results obtained from measurements of 13 full-scale bridge decks. The two proposed factors are calculated for this group of bridges, and the preliminary results suggest this approach could hold some promise as a means of assessing the structural condition of bridges.

The results of a study of 12 tubular joint models with varying branch to chord diameter ratios β and branch inclination angles θ, subjected to axial tension, axial compression, and in-plane bending moment, are presented. The analyses were performed using finite-element software that is capable of modeling elasto-plastic material behavior and geometric nonlinearities as well as ductile and brittle fracture. The results showed that the current use of sin(θ) in design equations for inclined branches is reasonable, but somewhat conservative. When compared with the current experimental database, a close correlation of results was obtained for all axial tension cases, and for axial compression and in-plane bending moment cases for low to moderate β values. For a β value of 1 and compression and bending loads, the enhanced strength that was observed was attributed to uncertainty in the definition of failure, and the effects of various support conditions and chord lengths in the experimental studies. It is recommended that these properties be standardized for the definition of the database.

Design equations for tubular joints are based on simplified analytical models that are modified by empirical constants to match test data. Their accuracy depends on the quality and number of test results that are available, and the range of their applicability depends on the assumptions used to derive their basic form. In a companion paper, finite-element modeling was used to perform a parametric study on the static strength of T-, DT-, Y- and X-joints when subjected to axial compression, axial tension, and in-plane bending moment. On the basis of the results, a new form for ultimate strength equations for tubular joints is derived using a modified version of the ring model. The new form is capable of modeling the increase in joint strength for joints with large branch to chord diameter ratios. The data from the numerical study is then used to develop specific design equations for joints under axial tension, axial compression, and in-plane bending moment.

Computer simulation and an approximate method were used to study the lifetime behavior of wood floor and roof systems. A simplified beam-spring model was used to model the systems. In this study, two-way action of the sheathing; partially composite action between the sheathing, connectors, and lumber members; the random mechanical properties of the lumber members; the random postyield properties of the partially composite members; and the cumulative damage of wood were included. The approximate method was the first-order reliability method incorporated with the distributions of order statistics. System reliability analysis, including system effects and load duration effects, is presented in this paper. System factors for load and resistance factor design (LRFD) as they are related to component properties, mostly the postyield properties of partially composite members and variability of lumber modulus of rupture (MOR), are determined. The results herein apply only to uniformly loaded systems simply supported at two edges.

An efficient method for elastoplastic large-deflection analysis of steel frames using an element with plastic hinges at midspan and two ends is proposed. The need in conventional methods to divide a member into two or more elements to model the distributed loads, and the need to allow for a plastic hinge at its span is eliminated. The formation of plastic hinges is simulated as gradually softening springs. This approach prevents the overestimation of the capacity of a steel frame and also reduces the complexity in data handling. Because the element stiffness matrix is explicitly derived, the additional computational effort for forming the element matrix only involves a few algebraic calculations and is therefore minimal. The saving in the overall computer time and data input and output efforts is considerable since a single element can be used to model one beam member in the ultimate analysis of most practical structures. Most importantly, the linear structural model can be directly used for a second-order inelastic analysis, leading to a convenience and consistency in extending a linear analysis to a nonlinear analysis.

Proof-load testing is considered a reliable approach to evaluation of an existing structure's load-carrying capacity. It can be effectively used for highway bridge evaluation, to either enhance an existing rating obtained by an analytical method or establish a rating for bridges unsuitable for analytical rating. Proof-load factors in design and evaluation codes vary, and their basis has not been well documented. For highway bridge evaluation in the United States this paper proposes proof-load requirements in the format of load and resistance factors, to determine target proof loads and resulting load ratings. They are derived to reach target structural reliability levels consistent with current practice by analytical methods, and to ensure relatively uniform safety of bridges. These requirements may be included in specifications for highway bridge evaluation by proof-load testing in the United States, and their application requires little knowledge of structural reliability theory.

A practical approach to the distortional analysis of steel box girders is presented herein. The EBEF (equivalent beam on elastic foundation) method is an enhancement of the BEF (beam on elastic foundation) method, which has been widely used in design practice. Using the EBEF method on closed (or quasi-closed) box girder analysis provides a simplified procedure to account for the deformation of the cross section for the effect of rigid or flexible interior diaphragms and continuity over the supports. The methodology, numerical examples, and stiffness matrix are also presented in this paper.

Advanced cladding connections take advantage of the interaction between architectural cladding panels and the building structure to dissipate energy. At the same time, like other passive dissipators, they provide additional lateral stiffness to the structure. A design criterion formulated in terms of energy provides the optimal balance of stiffness and energy dissipation to be added to the structure by the connections. Nonlinear models of advanced connections were incorporated into a two-dimensional structural model of a building with two cladding panels per bay. The response of the structure to a variety of seismic motions is presented. Time histories of the energy demand and supply to the building, both with and without cladding, trace the response of the structure to earthquake excitations. Results show that, when designed according to the proposed criterion, energy dissipative elements can be responsible for the total hysteretic energy dissipated in the structural system. The reduction in displacements (e.g., interstory drift) will depend on the position of the modified fundamental frequency of the structural system with respect to the critical frequency of excitation.

Seismic overstrength of multistory reinforced concrete frames has been assessed by means of nonlinear pseudostatic analysis on four-bay, three-, six-, and nine-story frames designed for seismic zones I to V as per Indian codes. In pseudostatic analysis, the lateral force profile corresponding to the first mode of elastic vibration is applied monotonically. It is seen that the overstrength varies with seismic zone, number of stories, and with design gravity load. The dependence on seismic zone is the strongest. The average overstrength of these frames in zones V and I is 2.84 and 12.7, respectively. The overstrength increases as the number of stories decreases; overstrength of the three-story frame is higher than the nine-story frame by 36% in zone V and 49% in zone I. Further, interior frames have 17% (zone V) to 47% (zone I) higher overstrength as compared to the exterior frames of the same building. These observations are significant for seismic design codes which, at present, do not take into account the variation in overstrength.