Influence Of Prestress Research Articles

Prestress Influence on Shear‐Lag Effect in Continuous Box‐Girder Bridge

The shear-lag effect in a thin-walled box girder has been recognized and introduced in the technical literature. In contrast however, a discussion of shear-lag effect caused by the combination of prestress force and self-weight of a box girder is limited. In this paper, the shear-lag effect is treated by the principle of superposition by considering that the configuration of a prestressed tendon takes the form of a broken straight line. Two equal spans of a continuous box girder of constant depth with a shear-lag effect are used as an illustrative example. If λ\N denotes actual stress due to bending under symmetrical loading over the stress computed by elementary beam theory, a compound parameter \IN\N\I\dy\Nθ\N/ω\N\IL\N is a measure of the shear-lag effect in this particular example, where \IN\N\I\dy\N is effective prestress force, θ\N is the inclined angle of tendon at support, ω\N is the intensity of uniformly distributed load, and \IL\N is the span length of bridge. On the \IN\N\I\dy\Nθ\N/ω\N\IL\N and λ\N diagram, an asymptote exists. Usually in engineering practice \IN\N\I\dy\Nθ\N/ω\N\IL\N is equal to or greater than unity. Based on this approach, some preliminary conclusions are presented for this study.

Transient Response of Beam Under Initial Stress

The effect of initial stress on the transient response of a beam subjected to impulsive end loading is investigated. This loading can be prescribed in the form of stress, strain, velocity or acceleration boundary conditions. The Timoshenko equations, modified to include the presence of initial stress, are used to model the beam. The analysis is based on the concept of a wave as a carrier of discontinuities in the field variable and its derivatives. These discontinuities are determined from a set of recurrence relations that are, in turn, generated by using time‐harmonic asymptotic series solutions to the equations of motion. The numerical results obtained confirm the influence of prestress on the transient velocity, bending moment, and shear force distributions in the beam. The results for zero initial stress compare favorably with those from a closed form solution, while the other results follow a particular trend. Solutions to problems with other boundary conditions can be obtained by using the present results.

Analytical Study of a Braced Excavation in Weak Clay

Analysis of the problem of braced excavations is complicated by the large number of variables involved and by the complex interaction and behavior of the soil and the supporting materials. For this reason a parametric study was made using the finite-element method of analysis to evaluate the influences of the variables. A rather unique computer modelling technique has been used to accommodate both the large number of variables and the problem of interaction and dissimilar behavior. An example of a computer simulation of a well-instrumented braced cut in Norway is given in sufficient detail to illustrate the applicability of the program.For the parametric study a typical excavation with fully penetrating sheet-pile walls was chosen. Of the parameters concerning soil conditions, the soil deformation modulus was found to have the greatest influence. The relative influence of shear strength, of initial in situ stress, of direction of mobilization of shear stress, and of soil-to-pile adhesion is also shown. All of the parameters concerning support conditions are important but pile stiffness and effective strut stiffness are the most important. The influence of prestressing and strut spacing is also shown.

Influence of Prestressing and Cyclic Stressing on Stress-Strain Characteristics of Magnesium Alloys

Influence of Prestressing and Cyclic Stressing on Stress-Strain Characteristics of Magnesium Alloys