Theoretical Study on the Flexural Behavior of Structural Elements Strengthened with External Pre-Stressing Methods

This study aims to strengthen the flexural behavior of structural elements with external pre-stressing tendons, thereby improving their load-carrying capacity and increasing their resistance against the external load. Different techniques were used to apply external pre-stressed strengthening to RC beams and RC frames. Seven identical RC frames were analyzed: an original sample without an external tendon, two strengthened samples with external tendons at the positive bending zone, two strengthened samples with external tendons at the beam–column connection zone, a strengthened sample with external straight line tendons along the beam and, finally, a strengthened sample with external U-shape tendons along the beam of the frame. The analysis and the results were obtained using ANSYS WORKBENCH finite element (FE) program. Comparisons were performed between these techniques to determine which technique is better for strengthening. The failure mode, vertical deflection, column stress, load-carrying capacity, and ductility of the samples were listed and analyzed under four-point vertical loading. The results show that using external tendons significantly increases the load capacity and the stiffness of structural frames. Moreover, the tendon in the beam zone is more effective than the tendon in the column zone.

Nonlinear Finite Element Modelling and Parametric Study of Prestressed Steel Box Girder

The prestressing technique is easy to apply and is generally used to strengthen steel bridges and controls their gross deflection. ANSYS has been used to establish a numerical model for the mechanical behavior of a steel box girder and prestressed by external tendons. In this paper, steel plate girders with and without strengthening technique was tested to assess the effectiveness of this technology. The results showed that prestressing improves the mechanical behavior of a girder and that its effect is proportional to magnitude of the applied external load. The results of the numerical model showed good agreement with the experimental data. A full-course simulation was conducted with ANSYS for a parametric study to analyze the influence of prestressing force magnitude, span-height ratio, and tendon configurations in increasing the effectiveness of prestressed technique.

Strengthening of Burri box Girder Bridge by using External post Tensioning Technology (Sudan)

Ageing, and increasing traffic loads, has become a major problem into today bridge industry. These bridges go deficiency in its Load Carrying Capacity from ageing, exhibited in excessive deformation which renders the bridge usage to an unacceptable level. These will either, impose traffic restriction, or upgrading the existing bridges to defy these adverse conditions. At Burri Bridge, after 33 years on operation, signs of ageing showed in the excessive deformation and the departure of the deformed shape of the super structure from the design profile, and travelling along the bridge was un-comfortable and difficult trip riding. The Objective was to explore the strengthening of the Burri Bridge by using external post tensioned tendons to mitigate the ageing effects and to elevate the capacity of the bridge. It was requisite to examine the bridge before the application of external tendons to insure the stresses in its past status will qualify it for repair. Hence, the present study contains the analysis of the Bridge superstructure in two stages. The first is done in its Past status, and the second when external tendons are added to boost its capacity and defy the effect of past load level, and a new standard load tested. The model was analyzed using Midas Civil software. The study includes the design of the anchor beams where the fresh external tendons are terminated. The study proved that, the capacity of the Bridge is increased by 4.6 %, and this is interpreted in the increase of the Ultimate Flexural Strength and the decrease of the deformation after adding these external tendons. Some of the Techniques implemented are presented.

Strengthening strategies of highway viaducts in Germany

<p>An entire generation of reinforced concrete highway bridges built in the post-war period in Germany meanwhile is approaching the end of their service life. The federal government and regional highway administrations have realized the need to repair, strengthen or to replace these structures and engage in extensive infrastructural investments to meet this challenge. It is not possible to replace those bridges in a short period, so that a guideline for reassessment of bridges has been developed to enable to prioritize the structures. Besides the replacement of the bridges, measures need to be taken in order to extend the lifespan of the decaying bridges until such replacement becomes available. Using the examples of four major highway viaducts near Frankfurt/Main and Hamburg efficient strategies to strengthen existing structures will be presented.</p><p>In the first example the efficient usage of external tendons to reduce the danger of a fatigue induced failure of a 50 years old prestressed concrete bridge will be presented.</p><p>A bridge of five spans with a total length of approximately 300 m showing inadequate shear resistance has been enhanced by installing inclined steel struts at the pillars. The struts are activated with a predefined force by built-in hydraulic jacks, while special spring elements used as supports reduce the effect of imposed deformations. Furthermore in critical areas of the webs additional shear reinforcement is mounted and subsequently covered by a concrete layer.</p><p>Another large viaduct was showing signs of fatigue at the coupling joints. A detailed analysis of the structure revealed, that the lifespan could be sufficiently prolonged by supporting the critical coupling joints with a predetermined force. The magnitude of the force is maintained constant by a balanced beam resembling a seesaw, which is mounted on a steel tower and fitted at its opposite end with counterweights.</p><p>The final example shows how to apply controlled uplift forces using an elastic bedded supporting beam construction.</p><p>These realized examples demonstrate, how with smart and intelligent measures critical bridges can be strengthened and an essential increase in lifespan can be achieved.</p>